Thx heaps Cuiv, it's certainly a crucial topic. I believe the only aspect you may have added was 'adjustable flattener/ reducers' possibly a more tecent. I use Williams Optics Refractors, & Pegasus Astro gear - they offer a rotator, all work well with N.I.N.A. Thx again for your advice & passion

@CuivTheLazyGeek

4 жыл бұрын

That is an excellent point Geoff - thank you so much for that! Pinning the comment so others can see it.

@icanifuwill

4 жыл бұрын

@@CuivTheLazyGeek like to add. It only made sense once I wrote down every spec (mm width) of each item. Then purchased addition al 'fine' spacers such "Artesky m42 fine tuning ring kit". After success & failures, photographed the image train to record noting dims so if changes one has baseline.

@brentonrasheed384

2 жыл бұрын

@@icanifuwill thanks Geoff - likewise - callipers and the fine spaces made all the difference .

Another great informative Vid Cuiv, I gotta tell you, I'm still impressed by the shear rate at which you get these quality videos out. Trev, Chuck, Dylan and crew need to watch out, the Lazy Geek is coming for them! eheh. Seriously thou... as much as I love to watch those guys (and have watched them for years), more recent content sees them taking the shots etc.. and then the BIG reveal shot with the dramatic music/zoom at the end. This is all very impressive of course. But perhaps this is because they have already done most of the educational stuff in previous vids so... fair enough. Even so, it is still refreshing to me to have someone new explaining things, this is why I have been glued to your channel, purely because of the shear amount of useful information you give (and especially the way in which you deliver it) to help me and I'm sure a lot of others to ultimately achieve the kind of end result that those guys get. I thank you for taking the time and effort to do these videos, and I hope it will continue. Cheers Dave UK

@CuivTheLazyGeek

4 жыл бұрын

Thank you for that feedback Dave! I'm not out to get anyone of course, but it is flattering to be compared to the "big ones" out there :) I can't say how my channel will evolve going forward, but I think I like explaining stuff too much to ever go into a direction where I stop explaining ;) There is just too much to understand and explain in this hobby! Thanks for the feedback again, and clear skies!

By the way, I've now convinced myself mathematically of the 1/3rd of filter thickness backfocus rule, so I can confirm it is appropriate. My spreadsheet here if anyone is interested. Thanks all for watching! docs.google.com/spreadsheets/d/1RrgDAzVE-OK1BFK9CX_BVbTnl1mlLnCIPkE6D8Cs4H0

Great video Cuiv, thanks for sharing. This is a hobby that definitely keeps you learning and thinking!

Great explanation of how to achieve back focus, and more importantly why it's relevant. And yes, I had to wait until the end of the video. Worth it, though! Thank you Cuiv!

Another clear and helpful video! Thank you, this subject has never been really clear to me, but you have helped enormously.

this explains ALOT of issues I noticed with my imaging results. Thank you :D

Thanks! As someone new to the hobby, I've found your videos to be super helpful!

@CuivTheLazyGeek

4 ай бұрын

Thanks so much for the support, and glad I've been able to help!

M42mm x 1.0mm pitch is a popular camera lens fitting on early Pentax and other brands of SLR, Edina etc. When adapters started appearing for using accessories on telescopes, the T-Mount was introduced with a M42mm x0.75mm pitch thread. Another headache was born, we now needed adapters to go from M42mm x 1.0mm pitch to M42mm (usually written as M42) to the new T-Mount thread of M42 x 0.75mm pitch. And as we now see, we need adapter rings to go from M42-M48, which has become another standard in Astro camera’s and accessories fittings. Many folks are often thrown when trying to screw an M42 x1.0mm pitch into an adapter with the finer 0.75mm pitch, or vice versa, things screw together for maybe 2 or 3 threads then stop. I am lucky in having a workshop with lathes so I can make my own adapters and settle on either a 1mm pitch thread or the finer 0.75mm. Over 60 odd years I have stuck with 1.0mm pitch, which is more robust and one I can machine without too many gear wheel changes. Making my own gear has always been part of the fun for me. Greetings from Tasmania Australia 😁🇦🇺🦘’

Ah, the joys of backfocus! A dark art. Even though many reducers etc do state 55mm and even with the adjustment for filters in the light path, it may not be getting good star shapes at the edges. I’ve heard of some people needing to be quite a few mm off the set distance to get a good image. I think you are right to recommend the callipers as you need to be accurate and then it’s trial and error around the 55mm or other recommended distance. Great idea for using the little thin rings to adjust rotation in systems where there is some flexibility in backfocus distance. Love the videos you put up and always learn something new.

@CuivTheLazyGeek

4 жыл бұрын

Exactly, backfocus is indeed a dark and mysterious art, for it is dark and full of terrors! And yeah, sometimes the 55mm quoted is not correct... Somehow I've seen that most often with SCT FRs, but not sure why (the good thing being that SCT FRs, with the exception of EdgeHD, seem to not care that much about backfocus). Always glad to be teaching people something new, and thanks for watching! :)

Love the Holy Grail quote

Great video! I knew to hit the like button as soon as I saw who the video was from and the title! Would love a video on setting up PHD2 guiding for the first time and how to choose the parameters in PHD2 and EQMOD for guiding?

@CuivTheLazyGeek

4 жыл бұрын

Thanks for the feedback! That's on the list - PHD2 setup, guiding parameters, and PPEC with EQMOD, etc. I'll get there, but I have to wait for some good weather!

@Daxcv2009

4 жыл бұрын

@@CuivTheLazyGeek thank you! Your videos are brilliant. You clarify things in such a simple, easy to understand way. I would 100% recommend anyone beginning astrophotography to subscribe and watch your videos. Keep up the great work!

Another great video Cuiv! One thing I stumbled across in my search for backfocus was a line of products called VariLock from Baader which are inserted into your image chain and allow for very precise adjustment of your backfocus using only one device. They aren't cheap, although they are compared to any camera, lol. But what is great is that you can get precise back focus down to tenths of mm with only 1 piece instead of having a stack of spanners. I have both the 29-49mm and the 20-29 mm versions which pretty much cover all of my bases.

@CuivTheLazyGeek

4 жыл бұрын

Wow, that looks great indeed, I am tempted now! I may buy the same that you have... So one end is male T2 and other is female T2? The pictures make it look like make M48 - male T2. And I assume that as you adjust it, it rotates, so that if you want to keep the same camera angle, you'd need to use a rotation mechanism somewhere right? Thank you!

@LampCord99

4 жыл бұрын

@@CuivTheLazyGeek Yes, it is male T2 to female T2 so it fits anywhere that is convenient in your T2 chain. It also has some adapters. I believe a T2 to M48. And it does require rotation, it has a locking mechanism. It also has one side held on by 6 Allen screws (wrench included) which means theoretically, you could get the exact proper length, loosen those screws, rotate the camera and tighten them back up although I'm not sure how practical it is in the field! I have a Celestron T-Adapter that uses a locking nut so I can rotate my camera that way so I've never tried the Allen screw idea.

A little info on the 42mm camera threads, commonly used back in the days before many camera manufacturers changed from 42mm screw mounts to bayonet, the ‘standard’ was 42mm diameter by 1.0mm thread pitch. So many lenses were interchangeable with different camera makes, PENTAX, PRACTICA ETC

Just when I thought "Oh I know this one!" I stand corrected after 5 Minutes... thanks again. That must be one of the advantages of the Celestron SCTs, the adapters that come from Celestron and ZWO are very well adopted for each other and the back focal distance is shown using those combinations....

@CuivTheLazyGeek

4 жыл бұрын

Yep, that is indeed very true - it makes it all a bit easier, but kind of forces you to stay within one ecosystem. SO pros and cons, as usual!

exactly what i wanted to know, cheers Cuiv hope you are well

I would love to see you make a video on camera sensor tilt and how to verify your backfocus is correct on top of just measurements.

What an incredible video! Thanks so much!!!

@CuivTheLazyGeek

2 жыл бұрын

Thank you! Glad it helped!

Ah, good information here. Yea, this is stuff I never really ran across in photo/video world, as lenses would be already designed for the camera. I actually just had a camera adapter recommended to me, which I noticed was very short compared to the one I have here for another camera, and I was curious about the difference. They are both mirrorless cameras, so the suggested T-ring probably wouldn't have worked, had I ordered it. Well, not without some extra steps, anyway. Great channel, thank you.

Great videos lots of important information here , thanks 👍

Thanks for sharing your knowledge on our complicated hobby (obsession)

Thanks for another useful video. Well, as a Celestron 8" Newtonian owner, I must say that the eyepiece holder is very useful for rotating camera, but it's a killer for cam+filter wheel combination. Celestron shoud produce that part 25mm shorter. I had to order a focuser, going to chance the Celestron one. I'll loose the advantage of cam rotation, on the other hand I'll have the chance to use my filter wheel. Keep doing great vids Cuiv.

@CuivTheLazyGeek

4 жыл бұрын

Often, it's all a matter of compromises... I hope you can get everything sorted out, even if you lose the ability to rotate the camera!

Great tutorial 💫

lucky me, lazy me with my refractor !!! and tbh on my RC I never had to look for back focus not even with the reducer... lucky me, lazy me again !!! Love your explanations again my friend !!! Salute and clear lazy nights !!! \m/

@CuivTheLazyGeek

4 жыл бұрын

Refractors are our friends :) Although even them will usually require a focal reducer or field flattener, and thus precise backfocus... unless you have one with Petzval design! Clear skies!

The Holly Hand grenade, now that's funny. I noticed you where looking to your left a few times, was that the rabbit? Anyways, I just learned what the stars look like when backfocus to a flattener/reducer etc... looks like. Time to purchase some rings. Super video.

@CuivTheLazyGeek

4 жыл бұрын

I'm glad some picked up on the reference :D such an epic scene! It was not the rabbit, but almost as bad! I thought I could hear rain approaching, so I was visually checking. Good luck with the back focus!

I am going thru your very informative videos for a "lazy geek" (that's me). It would be nice to have the theory behind proper back-focus *before* going thru all the steps to calculate spacers, gears, distance to sensor (cameras). I got it at 22:49 in the video (but I should of course have "google'd it first" 😂). Edit: And you said that yourself some seconds later in the video, so I take it back 🤗

Oops, didn't wait till the end. You referred to plastic rings adding additional space. Washers/rings, got it.

If you put a filter on the telescope side of the flattener/reducer (they sometimes have M48 threads for 2in filters), then you don't need to worry about changes to backfocus to the camera sensor. Handy tip that saved me from backfocus issues and sourcing 1 mm and 0.5 mm shims to sort it out. I screwed the filter onto the reducer so light is filtered before it is corrected, and 55 mm works just fine. Maybe somebody mentioned this in the comments, just too many on your vids to read them all! Clear skies.

I'd be willing to bet that the diagram for the EdgeHD is slightly off and that the back focus is really to the flat part of the reducer. Great video!

Superb - again :)

Hey Cuiv - another great clip from you - always entertaining and informative. Just a question really to confirm understanding - if the telescope manfacturer's manual specifically tells us what backfocus we need betweeen the sensor and (say) the flange of the flattener (mine states 75mm) - I presume this value takes presidence over the camera backfocus default (of 55mm)? Cheers!!

@CuivTheLazyGeek

4 жыл бұрын

Thank you for the feedback! You are correct - the backfocus is dependent on the optical element in front of the camera, the flattener in your case. So for you, you want the camera sensor to be 75mm from the flange of the flattener. Cheers & clear skies!

Hi Cuiv, Excellent video by the way just what I was looking for, my focal reducer for my Saxon 127 arrived recently and I am in the process of getting it adapted to my camera and scope. I had to order an other adaptor so an other long wait for it to arrive. I measured the b/f for my canon dslr which is 55mm with the tee ring on, which is what I require, now my question is, is there any rule to say that you can't fit a filter draw on the other end of the f/r and still be focused? I have been through videos and surprisingly there is no mention of this been done. The other option is to take the camera out and fit the filter in the nose piece each time I want to use a different filter, then the hassle of refocusing, the filter draw in the train seems a better option to me. Robert Vic' Aust'

Great vid!

@CuivTheLazyGeek

4 жыл бұрын

Thank you!

So since buying my rig and dedicated astro camera (cheap astro camera) I did notice I couldn't achieve focus straight away without pulling the imaging sensor back within the eyepiece housing... Even more recently I found out this was due to back focus (although I did think that such an inaccurate method was probably not the best). So I have a Skywatcher Explorer 150p which I believe has a focal length of 750mm F/5, I'm using a Bresser full colour HD deep sky camera, I use no filters (although I have a Svbony IR/UV filter which does literally nothing probably because I never used back focus now I think about it). Given the complexity of this video for much more advanced setups what should my back focus be? I have nothing else in the imaging train at this point, but could do with some guidance as to being more precise, this will help when I eventually start considering a more advanced setup.

Put that cardboard on a telescope sales website and you can ask at least 20$ for it I think;) Was struggling with finding information about this for the 533 and my telescope. I put an UV/IR filter in the camera and wondered how to see if my backfocus was good. I reasoned having a reasonably flat field of stars should be a good measure. But this video clarifies some things!

@CuivTheLazyGeek

4 жыл бұрын

Hahaha yes the prices in the hobby are sometimes quite hilarious :D And it always is interesting that manufacturers seem to put backfocus diagrams that don't include a UV/IR filter (at least for OSC cameras). If you get reasonably flat fields then you're good, no need to be a pixel peeper! :)

Truly informative, thanks! I need to get those M42 extender tubes. I'm using a very controversial field flattener on my ED80 F6 at 55mm back focus, well, as specified by the manufacturer. However, the corners of the resulting image show coma, this time seemingly shooting away from the center - trails of stars pointing to the center. Wondering if the field flattener has overly corrected the coma. In that case, do you suspect I need to increase or decrease the back focus? I cannot decrease though.

@jekanyika

Жыл бұрын

I have a similar problem, did you manage to resolve it?

Good info. I use Vixen AX103S with ASI294MM and ZWO Filterwheel and get weird star shape, somewhat like a comet. The stars are crisp on one side but un focussed on the other. It become worse when image is out of focus. It affects the images with H O and S filters more than LRGB and if I use no filter (empty slot in filterwheel) the stars look round. I use 3nm Astrodon (H and S) and 3nm Antlia O filters. So I am not sure if it is back focus issue or something else. Distance from back of my scope to the surface of camera is 98.6mm so the total back focus distance is 105.1mm. My Vixen dealer told me that backfocus distance for my scope is 103mm but i read online it is 150mm.

@CuivTheLazyGeek

2 жыл бұрын

That sounds like a weird problem. It could indeed by a backfocus distance issue, and not having any filter hides it due to star blooming on the camera. Really hard to tell - unfortunately I am unfamiliar with that scope so can't really help...

Very Informative video, Thanks for sharing. The M42mm adapter's are they the same thickness? I'm guessing you add a few of them together for what distance is required.

@CuivTheLazyGeek

3 жыл бұрын

My pleasure Jim! My M42 adapters are typically of different thicknesses, and you are right, I'll use several to get just the backfocus distance that I need!

Very much informative video. Thanks. I need a suggestion: For the f/9.8 (102/1000mm) refractor, which is the suitable 0.5x focal reducer (FR) for astrophotography using ASI294MC Pro camera? 1.25 or 2 inch FR?

Vid Cuiv, great videos and information you share with us. Two questions, first, I can not see the responses given to the questions or comments being published, the second part is regarding back focus, my ZWO camera requires 55mm for backfocus plus the filter correction I should be looking for 56mm for backfocus, but how critical is to have 56.5mm (is what I got), should I must get to the 56mm? or what is the tolerance acceptable for backfocus? as you show in the video what are the effects of being short or pass the backfocus, but how critical the distance is? ,. Recently I'm getting in to the dedicated CCD camera and this is recently being a topic I'm addressing. My best regards

That kit looks the business. I didn't realize they existed. I only have the rings and spacers that ZWO provided, and judging by results (slightly stars oval at the corners) the claimed correct length puts me about half a mm too far out. I guess that's production tolerances but I was wondering how to fix it. Thanks for ANOTHER tip Cuiv!

@CuivTheLazyGeek

2 жыл бұрын

My pleasure, glad this helped!

@amp2amp800

2 жыл бұрын

@@CuivTheLazyGeek Indeed it did thanks, and the vingetting story, and the effect of the filter. I feel really good about my light train now, and I'm just waiting for a clear sky to find out how big a liar you are 🤣(or how bad I am at math & measuring).

Happy New Year Cuiv! - gotta say, watching this again was so helpful. A question - what is the back focus of a guide camera (in my case the 290MM mini). I was going to look it up, but is there a formula for calculating back focus? Spec says 8.5mm. Don't know what to make of that. (?) Is it the same as the main camera in an OAG situation? 55mm?

@CuivTheLazyGeek

2 жыл бұрын

I have no idea! As long as the camera reaches focus, we're good!

Back focus is the bane of my existence. I can't use my super fast Sony E Mount glass with any of my QHY cameras. My QHY 16200A CFW7 has a back focus of "around" 54 to 55 mm (you can't physically measure it). I don't know if the filters in the device have been taken into account but with some luck, they will add another mm to my back focus. Lets hope the 16200A is 54 mm so I can get 55 mm with the filters. My telescope has a "deep" thread so when screwing the OAG part of the camera onto the reducer, I can't screw it all the way to the flange. So either I ditch the OAG or I hope and pray that the 55.8 mm back focus length I have won't screw up my images. Don't get me onto the incredibly poorly designed ZWO OAG (bought prior to the QHY stuff) or I will be booted off KZread for profanity. :o BTW, excellent information as always.

@CuivTheLazyGeek

4 жыл бұрын

Yeah backfocus is such an annoying part of the whole thing! Once it's dialed in there is no need to bother about it anymore, but it can be such a pain to get correctly. And then when you realize your camera eats up a lot of that backfocus, it can get extremely aggravating... The ZWO OAG by the way got a second version, which is actually decent. ZWO often has poor first release, and then they listen to feedback and start selling a decent v2. It has been the case for their OAG, whose v2 is much better than their v1. Thanks for the feedback and clear skies!

Yes Sir, Good evening to you today. I have been following your channel for quite sometime and really like your content and unique approach. That being said, I am inquiring as to how I may contact you regarding a business inquiry? And no worries, not sales but if anything the opposite. Thanks for your time and again, you have a great channel. Keep up the great work. Cheers, Chad

@CuivTheLazyGeek

6 ай бұрын

Go for cuivlazygeek at gmail com

“Back focus” is a way to mystify and intimidate newbs 😂. I was lucky that Takahashi shipped the right spacers already installed on the telescope. I was confused at the time because I couldn’t achieve focus with a diagonal when I first set it up. 😮

i'll be doing my backfocus tomorrow. Link didnt show at 11:45 in :) I don't like the plastic rings if you use more than 1 of them it can affect tilt. Elongated stars only on some corners. I prefer a variable extender which I just bought. Also I found if the stars are elongated from centre to corners then you are too short and vice versa. Thanks for a really great video!

@CuivTheLazyGeek

4 жыл бұрын

Good luck with you backfocus and that variable extender! Do you have a link to it? I'm interested. Weird about the link, I just checked and it's properly configured in the video... maybe some KZread bug! Hope you get perfect un-tilted backfocus!

@cryptoalchemist10minutes44

4 жыл бұрын

@@CuivTheLazyGeek www.365astronomy.com/search.php?mode=search&page=1&keep_https=yes

EdgeHD 800 back focus of 133.35 or 105mm (with reducer) are computed without considering the thickness of threads? SCT has 10mm but Reducer has 12.5mm - so be careful. Celestron diagrams are notorious for being wrong or inconsistent. ZWO cameras (usually) come with two spacers to make up the 55mm BF of a DSLR with T Mount - convenient and saves additional expense since many BF calculations assume a DSLR is being used. Celestron supply a 11.55mm spacer with their OAG to help get spacing exactly right (if not in their diagrams).

@CuivTheLazyGeek

4 жыл бұрын

Hey Simon! I don't know about without the reducer, but yes with the reducer, it is 105mm from the top of the threads rather than from the shoulder of the FR. It was wrong in an earlier Celestron diagram, and has been corrected since... Backfocus really is a dark art.

Hey just found your site on backfocus. Here is what I dont understand. I have an Explorer Scientific ED-80 . I us the ZWO294 MCpro. Now for my to focus I am using 2 35mm extensions then use the 21mm and 16.5 mm that came with the camera and the focuser has a scale on it that tell me I am 14mm back so that is 121.5 right there I have not accounted for the ring on camera or the filter screwed into the nose piece that is the 1 1/4 in. nose piece .. So where does 55MM come from ? Hope you can help.. Thanks for the video

Your filter drawer has a knob allowing easy insertion/removal of the filter and there is another knob that appears to be a locking kmob to keep the filter from falling out. I've read about that happening. I like the idea of a drawer with the lock. Can't find one. Who makes yours?

OK, one more. Adding an Optolong dual band filter, thickness is 1.85mm, 1/3 rule calculates out to .6mm additional backfocus. I haven't seen any spacers smaller than 1mm. Maybe a washer added to the chain? Any thoughts?

Thanks for that. You mentioned that it's particularly difficult to do Astrophotography with full frame. But iirc you never really touched on "why" that is. I currently use a full frame DSLR and I was looking into getting a Astro camera in full frame, but now I'm a bit scared. Could you tell me why it's so difficult, aside from the huge image circle needed. Also, Tokyo rocks! You're kind of living my dream rn :D

@CuivTheLazyGeek

4 жыл бұрын

Thanks for the feedback Princess Luna (and yeah, Tokyo is awesome :D) - so it's exactly what you mention: the optics. You want the huge image circle AND any defects in optics, or back focus will get immediately more visible on the edges of a FF sensor. Of course there is an easy solution: crop. The more difficult solution is to spend a couple of nights adjusting everything to get perfect backfocus and no tilt!

@prnzssLuna

4 жыл бұрын

@@CuivTheLazyGeek Id probably spend the time to get everything perfect because it would bug me the whole time that I'm paying FF just to crop stuff away afterwards xD. Thanks for answering, now I'm slightly less worried and confident enough that I can get it right, thanks :). And enjoy your time in Tokyo :3

Nice reference to Monty Python's Holy Grail killer rabbit scene.... Thanks for the video Cuiv....

@marvinwhisman3333

3 жыл бұрын

I wondered if anyone else would pick that up. What a great movie that was. The holy hand grenade of Antioch. "Three shall be the number thou shalt count, and the number of the counting shall be three." "Five is right out."

@mwales2112

3 жыл бұрын

@@marvinwhisman3333 My daughter gave me a Knights that say NE and Killer Rabbit shirt for X-Mas. Not one person has said anything while out wearing either of them.

Hello my Astro expert, when using the Askar 200 lens, do I have to bother with the exact back focus? Greetings from Tasmania 😁👍🇦🇺

Did you need any additional spacers to reach prime on your R200SS?

I know this is an old video and I'm a new follower. I have a Orion 8" RS (RICHIE-CRAITON) Sorry don't know spelling. 😅 I am installing a zwo asi294mc pro I think my back focus for this set up is 55mm? Could you check? My second problem is I need to us a focal reducer for the Orion 8"RA because my field of view on dso's is far to close. Maybe you can help. God bless. Keith...

Hi Cuiv, can we put a tilt adapter between the telescope and field flattner. will this affect my back focus distance of 88mm after the field flattner and it's all used up ? Thanks

@CuivTheLazyGeek

4 жыл бұрын

Technically yes you can put a tilt adapter between the telescope and the field flattener - but not sure you want to tilt the incoming light rays ahead of that optical element (and also for SCTs, you want the FR/FF to be as close to the tube as possible). It would not affect the FF backfocus itself, but personally I would only put a tilt adapter in between the camera and the field flattener, and not ahead of the FF.

Sorry if I missed it in the video. I had thought this distance was just to get the image into the scopes focal area. Being that some scopes have a larger adjustment range that others.Could my SCT get correct focus with 45mm back focus or is it always doomed to not be sharp until the distance is correct? I'm currently doing manual focus on a 4" SCT so put the error down to the operator.

@CuivTheLazyGeek

4 жыл бұрын

That's a good question! Backfocus and focusing distance are slightly different. Backfocus is distance from sensor to a coma corrector, field flattener, focal reducer, or other corrective optic. You will typically still be able to get stars in focus, even with the wrong backfocus distance, but star shapes in the corner will be quite poor. So for your SCT, unless it is an EdgeHD (which has a corrective lens built in), the perfect backfocus is simply your point of best focus. But if you have a focal reducer, you will need to adjust the distance between it and the sensor to get good stars across the FOV. I hope this helps & good luck!

Complicated stuff. Good explanation though! By the way, the "g" in Vignetting is silent, so it's like "Veen-yetting".

@CuivTheLazyGeek

4 жыл бұрын

Thanks Itai! I will correct my pronunciation for the next videos :)

Need to check mine. The drawtube may be intruding into the optical path when using a Canon DSLR and Vixen t ring.

@CuivTheLazyGeek

4 жыл бұрын

I hope you can get it figured out... Good luck!

@Philip-KA4KOE

4 жыл бұрын

@@CuivTheLazyGeek Ah, I will. Never fear. But it can wait till the repairs/upgrades are done. This would explain the odd diffraction spikes. Does your ZWO imager screw directly into the R200SS drawtube assembly or do you use an adapt-TATER?

Hi, Cuiv! Very instructive video, but I have a problem, opposite of what you presented here and was wondering if you can help with some advice. Last night, for the first time, I tried connecting my OAG to my 8" f5 Newtonian, but couldn t reach focus. Not on my Oag cam (asi 290 mm mini), but on my main imaging cam (Panasonic gh4). I also have a Zenith Star 61 and haven t had any problems focusing both cams, but on the Newtonian the sensor of the dslr seems to be too far away if I add the OAG body. The telescope focuser was all the way in and I still couldn t get focus. It was closest to focus when all the way in... Should I unscrew the focuser and push it slightly more in the tube in order to reduce the distance or is there another way? I ran out of adaptors to remove in order to shorten the backfocus distance. I also removed the filter wheel, but I need it.. Would greatly appreciate some advice. Thanks!

@CuivTheLazyGeek

3 жыл бұрын

You want distance from OAG Prism to guiding cam to be equal to distance from OAG Prism plane to main imaging cam. That sets your distance from the OAG. Also, generally, you want the coma corrector flange to be 55mm from the camera sensor. So that sets pretty rigorous limitations... it may simply be that your camera + OAG are just too thick!

@alexandrumunteanu4076

3 жыл бұрын

@@CuivTheLazyGeek ok. Thanks. I think I will get a coma corrector. I need it anyway and maybe that will solve the focus problem by shifting the focus point/distance from main sensor...🤔?

This is so informative! What kind of Newtonian was that? looks big. Thx!

@CuivTheLazyGeek

11 ай бұрын

This was the R200SS from Vixen!

@lavers_1

11 ай бұрын

thx for the reply, that's a nice scope. Love the channel@@CuivTheLazyGeek

Hi Cuiv, don't you less 2 or 3 mm do the glass thickness of the filter ? or its not necessary?

@CuivTheLazyGeek

3 жыл бұрын

Yes, 1/3rd of the filter thickness needs to be added (so 56mm for me rather than 55mm, with my 3mm thick Astrodon filters). I actually have a video on that, as well as mathematics behind it :)

Given that you can sometimes get a fraction of a millimeter dimension in your stack up what is the allowable error from lets say the nominal 55mm dimension. Is there a rule of thumb for that? How close do you need to be?

@CuivTheLazyGeek

4 жыл бұрын

It really depends on the optical element, the size of the sensor (the larger the sensor the more obvious any issues will be in the corners) and how sensitive the end-user is to star shapes! And don't forget that it's 55mm (or whatever measurement) +- any manufacturing tolerances. The ultimate test is star shapes in the corner of the sensor. With a M4/3 sensor and my own equipment, I found being even 1.5mm out worked fine.

Hi Cuiv, great series - learning a lot fast. I need a piece of advice please. I have a EvoStar 72ED with no flattener/corrector at the moment and I am using a Canon mirrorless camera (M50). Is it actually necessary for me to find a exact backfocus distance for my telescope? Because my focuser is changing that distance as I focus. I think I am a little confused here 😅

@CuivTheLazyGeek

2 жыл бұрын

I should have been clearer! Without a reducer/flattener (and I don't think the 72ED has one integrated into it), as long as you reach focus, you're fine! But on an APS-C you may find you need to crop a lot;

@SPACEJUNKastro

2 жыл бұрын

@@CuivTheLazyGeek Hi again Cuiv, thank you for your reply that got me on the right track! So I got myself a OVL field flattener for my 72ED combined with my Canon m50. For backfocus, I started with not overthinking it much and just used the EOS-M to EF adapter and a T-ring. This combo is getting 55mm from the top of T-ring to camera sensor. I screwed it directly to the OVL flattener. Good start I thought. On my first night out, I noticed 3 problems. I was shooting the eastern veil nebula and from Slovakia: 1. Top left and top right corners got extremely elongated stars - indicating need for longer backfocus distance 2. Bottom left and bottom right are much better, but it seems like the stars are misshapen to the other direction, indicating the need for shorter backfocus distance - I think 3. I have a lot of chromatic aberration, which was almost not present before the use of OVL FF. I am surprised (not very pleasantly) with what I got. I am clearly making a huge mistake that I am not seeing and I frankly do not know to what direction should I move. I have very few clear night these days, so I want to sort this with as little nights testing as possible. Please advise 🙏 P.S. I can upload pics of the image train, and a sub-exposure I was describing. Thank you ☺️

Hi Cuiv, I can see why getting back focus distance is important however on a refractor or Newtonian telescope like yours won’t the rack and pinion focuser not compensate for a couple of mm error in back focus? I can see why on a SCT such as my EdgeHD which has a 146mm back focus has no rack and pinion to move camera back and forth it’s important to be accurate.

@CuivTheLazyGeek

4 жыл бұрын

It's a good question! But in the end, the field flattener / focal reducer / coma corrector move together with the R&P focuser. So the distance from that corrective optics to the camera is not affected by the focuser! So you need to be just as accurate as with the EdgeHD. And actually this has been a point of discussion about using a Moonlite focuser with EdgeHD for example, as then focusing changes the backfocus compared to either the corrective lens in the EdgeHD, or the FR of the EdgeHD!

@grahamwhite75a

4 жыл бұрын

Hi Cuiv, yes I agree with you. It is all down to the relative position of the focuser and any correctors/flatners in the optical train. You video did indeed get me thinking about my moonlite focuser on my EdgeHD. I think the best compromise for this situation is to set the camera sensor at exactly 146mm from the back face of the focal reducer using the moonlite focuser to achieve that and then use the SCT mirror focuser to get a sharp image on the sensor. That will ensure SCT mirror is in correct position to allow moonlite to do very fine tuning using NiNA for example when a new filter is introduced into optical train. It’s funny I had not planned on looking at this video of yours, I was too lazy ;-) but I am glad I did it really got me thinking about my setup. Next job is to get some callipers!!! Incidentally one area that helps in this matter is the small but finite depth of focus range (as described by starizona.com/tutorial/focusing-2/) which gives a little wiggle room for imperfections in focal plain in particular on long focal length telescopes.

@CuivTheLazyGeek

4 жыл бұрын

Yep, I had an EdgeHD+FR+Moonlite a while back, and I did exactly what you described. The focuserneeds to move by a really small amount, so backfocus was ok in the end!

Ok....I have a 9.25. I'm getting a ASI533 and I'm using a 6.3 reducer. I know I need 105MM backspace from the reducer to the camera. With my T-adapter, the two spacers that come with the camera, I get my 105MM backspace from my reducer. Now....I want to add the Starizona filter slider. If I take off the ring that's on the front of the camera that comes with it, and THEN add the slider, I still have about 6MM too much backspace. Without looking at my numbers I did earlier....it might be 6.5MM. How can I get rid of that extra 6-6.5MM? Surely someone has had this exact same problem, and has an answer. Right? lol

Loved the monty python reference xD

well, this couldn't be anymore timely. I am in the middle of figuring out all the parts involved with a SCT/FR/OAG/FW/CMOS :( Been a long week) :)

@CuivTheLazyGeek

4 жыл бұрын

Wow, that does sound like a long week indeed!! Good luck getting all of that setup!! Is that an EdgeHD?

@yosmith1

4 жыл бұрын

@@CuivTheLazyGeek yes, the OTA is a 9.25 EdgeHD. all new stuff for me, so between hardware and the multitude of software options, it's been quite a learning curve. Still fascinating though.

Cuiv I wrote you about this in the past but you never answered me . I do not use anything in the imaging train except for a filter , so where do you measure for the back focus , and are extension tubes figured into the equation because with my ed80 I use like 3 to get focus

@CuivTheLazyGeek

2 жыл бұрын

Sorry, it is difficult to answer everyone about everything, especially about equipment I don't know. I am unfamiliar with the ED80, but if you're using it with a reducer or flattener, the backfocus that is specific to the reducer/flattener (typically 55mm for such scopes) is measured from the reducer/focuser shoulder (up to the sensor). If you don't have a reducer/flattener then whatever distance required to achieve focus is fine. Otherwise if you have a reducer/flattener, but you can't achieve focus with the correct back focus distance to the sensor... then I don't know...

@Steve_The_Ignorant_Astronomer

2 жыл бұрын

@@CuivTheLazyGeek Yea I use like 3 tube extensions so I dont know myself , but thx , hope your feeling better

Hey Lazy geek, have you down as a reference for most of the adjustments on my scope. But have a problem with this backfocus thingy... I've a Celestron 8SE and an ASI533MC pro... the focal reducer on the Celestron states 105mm optimum backfocus distance whereas the cameras states 55 mm ... what distance should I use?

@CuivTheLazyGeek

2 жыл бұрын

Trust the optics! The required backfocus is determined by the optics, and most reducers/correctors want 55mm, which is why cameras provide ways to achieve that distance. But in your case, you want 105mm between the reducer shoulder and the camera sensor!

@TanoMac73

2 жыл бұрын

@@CuivTheLazyGeek Thanks dude... that is most excellent!

Great video Just.. Please... LOCK FOCUS!!

@CuivTheLazyGeek

2 жыл бұрын

Better on the new videos!

Is the back focus dictated by the telescope or the camera? ZWO camera has a 55mm back focus but the TAK FSQ85EDX says that it can accommodate a long back focus of 200mm.

@CuivTheLazyGeek

2 жыл бұрын

Back focus is dictated by the optics. ZWO cameras provide ways to achieve 55mm of backfocus because many optical systems have that as their backfocus distance. However, the backfocus used by ZWO cameras (e.g. distance from camera shoulder to sensor) is important to take into account (6.5mm or 17.5mm for most ZWO cameras)

@nn1982in

2 жыл бұрын

@@CuivTheLazyGeek thanks !

Holly hand grenade reference. Lmao

@CuivTheLazyGeek

4 жыл бұрын

Glad you caught it :D

I think for me, backfocus is one of the most frustrating aspects of astrophotography. Especially when you want to buy near gear and have to recalculate all the distances and buy a bunch of adapters to get it just right.

@CuivTheLazyGeek

4 жыл бұрын

Yeah I fully agree. And once you've done everything right with backfocus you discover you have tilt. That kind of stuff :)

@AnakChan

4 жыл бұрын

It gets expensive too if you have custom adapters (e.g. from PreciseParts, etc.) and get the backfocus wrong. I've just made that mistake for new my newish ASI6200MM & the Takahashi µ250CRS, where I was short by 11.9mm!! The funny thing is that you still can achieve focus in the centre despite being that far off in the backfocus, however moving out 12mm from the centre, the stars get severely distorted.

@CuivTheLazyGeek

4 жыл бұрын

Oh no!! I hope you can get it corrected at some point!

Way to sneak in a Monty Python reference 😊

What is the consequence of being 2mm off with back focus? How do know when it is wrong.

@CuivTheLazyGeek

9 ай бұрын

Star shapes in the corner of large sensors become oblong!

Awesome Hocus pocus was back focus , but no longer.. get your variable adapter rings children.

@CuivTheLazyGeek

4 жыл бұрын

Hocus pocus back focus :D :D

I finally got my EdgeHD 8 and spent some time trying to attain the proper backfocus with the FR. I got it exact, however, the stars indicate that it should need a bit more (kzread.info/dash/bejne/qq6i0qlqed3Foqg.html) . If you take the distance from the edge of the threads like you mention, that should do it. Also, I do notice my stars appear bloated with the ASI294MC without a filter and when I use the IDAS NBZ filter they look great. I don't UV/IR filter yet but I do have a Baader Neodynium Skyglow filter. That should work until I get a UV/IR filter. Thanks as always Cuiv. Cheers Kurt

People always refer to lazy as a negative... I'm like don't diss it. Wasn't for being lazy we never invented the wheel.

@CuivTheLazyGeek

3 жыл бұрын

Being easy is the best. I remember the tale of a software developer reputed for clean code, who was later found to have outsourced his work to coders in China, paying them one third of his salary, while the guy could just do nothing all they. Mad respect!

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With all of these big words your using it doesn't seem like this tutorial is for "lazy people"!(smile) I love your telescope and thanks for the video but I was lost before you even really got started. I will watch again with my dictionary in front of me! ha! ha! ha!

lol Monty Python reference