Finally! A decent video teaching on the question I get asked most often. Thanks Peter Food for thought. Agenis offers a great little packet of various sized spacers for very small adjustments like 0.5mm , 1mm etc to get you right on focus

Hey Peter, first off I would like to say that I love your videos. Very informative. I just wanted to clarify with everyone that the back focus distance that is shown on the SpaceCat/RedCat documentation is the MAX back focus. You do not want to go beyond that distance but can be anywhere before that max distance. I hope that makes sense.

@DeereX748

3 ай бұрын

Is this because there is no flattener/reducer in the imaging train? I'm still trying to learn this stuff, and have a short refractor that I want to use both with and without the flattener.

While ZWO provides all the spacers to create 56mm backfocus, this distance only has to be precise if you are going behind a refractor focal reducer. Most of these FRs use this same distance and you should measure precisely from the back lens to the camera sensor plane with a micrometer to be sure. If not using a FR behind refractor or camera lens, you only need enough spacers to get to a distance that is within the range of your focuser adjustment range, determined by just getting a sharp image, as in the video. Thanks for sharing, Peter!

@gothicm3rcy426

2 жыл бұрын

if you have a zwo focusser you can just adjust the distance it focusses by increasing the steps

Hi, Peter, back focus is more about illuminating the entire sensor evenly so you reduce vignetting and get as flat a field from edge to edge as possible. You will still be able to focus even if your back focus is off... the image will just not be evenly exposed from edge to edge.

@kiteriderz

3 жыл бұрын

Exactly what I found, the hard way. Was focused with a flattener but the image was not flat at all. My stars where elongated from the centre to the edge and I Realised that I needed more space to achieve the 55mm backfocus distance. Once I achieved the 55mm distance the field was perfectly flat and illuminated. Backfocus as nothing to do with focusing ;)

@OscarShu

Жыл бұрын

thanks for the explanation! I always wondered why I can focus even if my back focus is not right and thought focus can be achieved with the focuser of the OTA anyway

@fpanadero2626

Жыл бұрын

Proper backfocus Illuminates and keeps stars round across the whole sensor/image....?

Exactly what I was looking for!! Amazing how hard it is to find this kind of information. Much thanks.

Very nicely done,, Peter. Was at our local astronomy club's APSIG meeting yesterday, and a member was showing his 90mm Explore Scientific with auto-focuser, filter wheel, and camera train. The camera train was almost as long as the telescope. Because of that, he used three rings: 2 on the telescope body connected to one dovetail, one on the camera train connected to a second dovetail. Both dovetails were connected to one long dovetail providing a rigid platform for the rig. I suspect his rig would be a bit much for a StarWatcher Star Adventurer, weight wise.

Hi Peter.Thanks for the vid.Great info.I had an issue a while back I lost the 11mm ring.So I added in the 16mm ring on the redcat this wasn't a good idea as this caused vignetting and funny looking stars at the edges.I managed to find it the other day and the difference is amazing.Something to look out for as this makes a big difference to the images.Thanks to ZWO for making this easy.

Thanks, Peter for the demonstration-pictures are easier to explain how it’s done. ZWO also make life so easy by supplying all the correct items one needs. I really like their total integration systems at affordable prices. I have a lot of their cameras and accessories because quality is excellent and it’s a one stop shop. Regards from the Southern Cross Observatory-Tasmania 42 South.

I want to say thank you for this very helpful video, it’s so useful for beginners to watch your videos, very well done Peter!

Hey Peter Great video - love the way you simplify thngs

You have made another superb tutorial, thank you 😊🙏

Quite happy to know that we can attach the ZWO to a Nikon lens. I have an old 300mm f4 so I am very interested to find out how we can mount the lens on the ZWO while maitaining the aperture at its maximum. Great video as usual. Thank you.

Hi Peter, there should be a thin plastic which goes between the EFW and the ASI1600. This way the sensor ist not rotated with respect to the filter wheel. Cheers Stephan

Back focus is more about the correct distance to correctors like field flatteners or coma correctors. Those need a very specific distance to work (very often it is 56 mm). If you don't have the correct distance with those, they will not work properly but in these cases, you will also have to take any filter into account that is between the corrector and camera.

FYI, the ZWO flow chart that shows how to reach optimal back focus has two starting points, one for a 42mm threaded telescope and one for a 48mm threaded telescope. The SpaceCat/RedCat has a 48mm thread, so you would start from the second starting point, which bypasses the M42-M48mm adapter.

Great info!!! Thank you!!!

Thank you! Thank you! Thank you! Thank you! Thank you! Thank you for this video!

Always great to go through your videos. I plan to buy the ASI 294 MC PRO, and the ZWO New Canon EF Lens to T2 Adapter. Now the Focus can be done by selecting MF on the lens, BUT how does one adjust the Aperture ?? OR will it just stay open at Full Aperture. However, if I use my Sigma 24mm f/1.4 then at 1.4 there is a lot of coma, and I need to stop down to close to 2.8, same problem with Samyang 14mm f2.8, have to stop down to almost 4 to get rid of Coma effect.

Regarding FR, you need to find out what the backfocus is on your FR FIRST. Once that number is given, you use that with your calculations. Example: The SW 0.77FR requires a specific backfocus (I forgot what that number is), but it also included adapters that when attached, it then only requires the standard 56mm that will need to be taken care of by user supplied adapters (which basically means you follow this video to make the connections to the FR). Hope this helps.

Great video Peter. I have the SpaceCat, just received the ZWO ASI294MC Pro but I don’t have the EFW. I’m gonna try this as soon as it’s clear, hopefully soon but do I use the 11mm, 16.5mm and the 21mm together with the camera?

TY for this tutorial. By the way, how much is this entire equipment? Do you plan to add something else?

Thank you Peter another great video/tutorial, so i have a regular filter wheel for 2" ,so i was following you until i had to screw the zwo to the FW but found out that one side of the fw has a bigger apperture(hole) and the spacers wouldn't fit , then all my measurements didn't add up, its not a zwo ,but i do have a zwo in 1.25",could this be the problem? thank you

good video , get same problem with asi071and the new 2zoll Filter wheel (m54 connector ) and the redcat51

Thanks for this really nice explanation. Any input on what adapter can be used to attach a 2” filter to a dslr (say a Nikon d7500 :))? Thanks!

I would like, if the camera chip was horisontally aligned with the filterwheel in the down position for good balance. Small faux pas from ZWO

Hi Peter, great video. One thing though not mentioned is reducer/field flattener. I'm told you need to work out the back focus length of this first. Any clue how I do this?

Your tutorials are the best, for noobies. Can I ask you how close the thru the window subject image for BF testing can be? I dont have the advantage of a long vista.

Great video! I will get the same camera and filters on friday! One thing, how do I know the backfocus if I have a field flattner?

@Chris_NGC6188Ara

4 жыл бұрын

Attach the FF to the back of the scope and measure from the back of it (camera side). The spacing remains the same.

Nice video!

Hi Peter I know this video is 3 years old but it was the closest thing I could find about connecting ZWO cameras to telescopes. I bought the Askar V and saw your imaging with it and loved it. I was all excited and ordered the 2” ZWO Filter Wheel and a 2600MC pro to pair with it. Surprise! The 2600 is a completely different connect method requiring a major disassembly of the wheel to mount with bolts and screws directly to the 2600…NOT like the simple thread on/off with the gear you have. Ugh! Guess I should have NOT assumed even staying within the ZWO ecosystem, the parts are not interchangeable. I realize the back focus at 55mm is about using adapters in the scope like a reducer or extender, to reach the focal plane of the camera sensor…but I wanted to shoot a bare bones rig with just an LP filter and not the big wheel. Looking for adapters to get me to the simplicity shown in your video. Otherwise it looks like they are going to be paired for life and a storage hassle at 9” deep to fit in a foam case. Oh well. Nice video. 👍🤩

Nice video Peter, but wait to test your rig on stars before being sure you achieved the right back focus.

Thank you!

Keep up to videos Peter, Thanks for all the info. Of course I shouldn't be thanking you for all the money you are making me spend!

@PeterZelinka

4 жыл бұрын

Hahaha I get blamed for that all the time!

Thanks for the great video 👍🏻 I have the redcat, and I bought my first dedicated astro camera, but it has been horribly clouded since I got it.... over a month now 😩 but can I test it during the day? I have been searching info about this but can’t find anything. Don’t want to ruin the camera.

@jacobgerritsenfilms3559

4 жыл бұрын

sure you can test it during the day, you have to turn the gain way down

Hi Peter, did you add the thickness of the filter glass to the value of the backfocus? That is important for the coma correctors for Newtons and other scopes.

@astroworks

3 жыл бұрын

Think its about 1mm - but it shouldn't matter for scopes of F7 ish and above - it matters with the fast f2's etc

Thank you so much. One question: when connecting a Full-frame lens to a camara with a smaller sensor, wouldn't it make sense to use a speed-booster to get all the light the lens collects on the sensor?

@daenu

4 жыл бұрын

Correction: in astrophotography, the converters are called "focal reducers", not "speed boosters". They should give a wider field of view and a lower f-stop number. I have no experience with them, but I suspect the image quality should be better. With a full frame lens and a 4/3 sensor, half of the light would be wasted. For deepsky objects, where we actually need the magnification, we can leave out the focal reducer. In that case, we would be better of with another lens, as the light is still "wasted" and the optics too large for the task.

@sandb1867

3 жыл бұрын

@@daenu "when connecting a Full-frame lens to a camara with a smaller sensor, wouldn't it make sense to use a speed-booster to get all the light the lens collects on the sensor?" As you mentioned, speedboosters are called focal reducers in astrophotography. However FRs should really be matched to the telescope otherwise one may introduce new optical aberrations. Also, the filters used in astrophotography often do not work well with "fast" short focal ratio scopes because of the steepness of the light cone.

Thank you

Very good and usefull video! I just have a question, would it be possible to photograph the millky way with the zwo 294mc pro and a 10mm samyang wide angle lens? I mean if i manage to get the right back focus it should work. I guess i could get better images than with a normal dslr. What do u think?

@PeterZelinka

4 жыл бұрын

I'm honestly not sure, but I'm planning to give it a try next month!

@blueastrophotography6131

4 жыл бұрын

Peter Zelinka that would be great, thanks ;)

Why does back focus come down to mm when you can move the camera back and forth with the focuser on the telescope? Alos why do people say to add very small spacers to fix odd shaped stats?

Hi Peter, very good video, but I still cannot find focus for my setup: Celetron 150/750 tube + ZWO 294MC COLOR PRO + a 2" filter (L-Pro, L-Enhance, etc)...based on your experience, what do I need to make this setup work? I'm a bit new in astrophotography so I'd really appreciate your help. Rgds

I am a bit confused. I assume this doesn’t matter if you are using a telescope where you can move the mirror or draw tube until you reach focus or is this different from just focusing the telescope. Thanks

Is 2inches filter wheel compatible to redcat 51 and asi533mm ?

Hi Peter, can I use explore scientific 80ed (400 mm) with skywatcher star adventurer 2I? I have star tracker, now i want some minis-telescope to attach with for deep sky astrophotography.

much needed

The plastic washers go between the EFW and camera to orient the camera

What if I have a image flattener ?

Proper backfocus Illuminates and keeps stars round across the whole sensor/image....?

Great info, thanks!

So if I'm using. .7 focal reducer that needs 105mm backfocus, do I need to add the 55mm to it?

@astroworks

3 жыл бұрын

Did you ever find out - I have the same question :)

@sketch6995

3 жыл бұрын

@@astroworks no. With the .7 reducer you need 105mm only. I found extension tubes on Amazon, sbvony and starboosa both have the 42s and 48s

Peter just a detail: you did not explain which filter side needs to be close to the camera. Good detailed video.

@Tommyr

4 жыл бұрын

He said the side with the "EFW" on it.

@olivierrethore9097

4 жыл бұрын

@@Tommyr I am talking about filters not the filter wheel. Narrow band filters do not have the same colour on each side.

@Tommyr

4 жыл бұрын

@@olivierrethore9097 Oh, my mistake. Sorry about that.

@gooe9561

3 жыл бұрын

The most reflective surface faces the objective, away from the camera.

This video is bit misleading. You don’t really need to care about the backfofus on petzval design lenses/telescope. Because by chainging the focus, the backfocus changes at the same time. Which means if you can achieve focus, the sensor is right where it should be. I presume the image you showed in the video is about max sensor distance in order to get a perfect flat field.