love these videos. this is a really superb explanation of how it works

@Aero19612

4 жыл бұрын

Thanks, Philip!

Hi, Very interesting video! Thank’s a lot. Clear skies to you. JM

@Aero19612

4 жыл бұрын

Thanks for watching, Jean-Marc!

You can't simply apply an auto-stretch to a frame difference because you may be seeing insignificant data. The noise components in a flat of reasonable exposure are insignificant.

Professional explanation as always! Thank you . I have a question? What's your recommendation when taking the flat frames? Such as the recommended ADU, recommended exposure time ! How do I know I took a good flat frames ?

@Aero19612

3 жыл бұрын

Thank you, Kayed! I think if you stay between 35% and 65% max ADU you should be fine. You just want to make sure the histogram trails off to "zero" on the low side and the high side. Exposure time will vary. I take T-shirt flats in the mornings so my exposure times tend to be short. You just want uniform illumination (hence, why I use a T-shirt). You'll know if you have a bad flat because your vignetting, smudges, and OAG shadow will be under or over corrected (i.e., too dark or too bright). But, this isn't always something wrong with your flat (for example, see my video: kzread.info/dash/bejne/gml5xqidgZDgmLw.html). If you shoot too close to a bright star or bright moon, the illumination in your light frame won't be uniform like your flat so your flat won't correct those light frames but make work great with other light frames collected that same night away from that bright star/moon. Good Luck!

Very informative. I’ve always wondered the difference between the 2 flat frame calibration methods. Quick question. How often do you take flat frames? If the image train is sealed and the only possible change in dust would be on the corrector plate, is it feasible to use the same flats over and over? How visible is a dust mote on the end of a telescope compared to dust on the sensor or a filter? Thank you for all of this great information.

@Aero19612

4 жыл бұрын

Thanks, Jim, and thanks for watching! You can absolutely re-use your flats. The only reason to retake them is when you change the orientation of the imaging camera (or guide camera if using an OAG) and if you suspect the additional dust/dirt has settled on the exposed glass, or after you clean the exposed glass. I find I take flats more often with the SCT because if/when it dews over badly, I will get additional residue on the corrector plate.

@jimmydigital00

4 жыл бұрын

James Lamb thanks for the reply. I will probably continue to take them after each session to ensure they are optimized. I’ve read that bias frames are not recommended for the asi1600 and haven’t used them for calibration. Have you ever done a similar comparison, comparing a file calibrated with a dark, bias and flat compared to one taken with only a dark and flat? I’ve heard some people say that the bias is included in either the dark or flat so it was in essence subtracting twice. Thanks again!!

@Aero19612

4 жыл бұрын

Here's my understanding: Let's start with Dark-Flats. In this case you take darks with the same exposure as the flat frames and they are only used for flat frame calibration. In this case, do not delete the bias from these darks because they already have the bias built in as it were. So you calibrate the flats with these Dark-Flats and DO NOT click "optimize" and you don't use a Master Bias. In this case, when you calibrate the Light frames, you can skip the Master Bias as long as you use a Master Dark that does not have the Master Bias subtracted from it (the Master Dark will have the Bias included) and the Master Flat. Now, let's look at the other option. Use a Master Bias (same gain as flats and lights, but fastest exposure time the camera offers). Also, use a Master Dark, probably with the same exposure time as the lights, but that has the Master Bias subtracted (i.e., you have to calibrate the Dark frames by subtracting the Master Bias). When calibrating the Flats, specify the Master Bias and the Master Dark (with Master Bias deleted) and specify "optimize" with the Master Dark to convert it down to the exposure level of the Flats. When you calibrate the Lights, specify the Master Bias, the Master Darks (with Bias deleted), and the Master Flat. You can't go wrong taking flats at every outing...

Maybe this is a dumb question, not entirely related to the video. I'm doing EAA with a dew shield on my 9,25" but I shot my flats without the dew shield. During live stacking it looked like I had some vignetting that the flats were not calibrating out. should I re-shoot them with the dew shield in place?

@Aero19612

4 жыл бұрын

Yes. In my earlier "flats video", I saw a "bigger" issue when I calibrated Lights (taken with a dew shield) with flats taken without a dew shield.

@cmas-astronomy4715

4 жыл бұрын

@@Aero19612 Thank you, much appreciated advice.

Flats are only for the British.. Jk. good explanation as to why sometimes you should hit Optimize darks on either DSLR or CMOS otherwise not..( Adam Block)

@Aero19612

4 жыл бұрын

Haha. Thanks, Mitch! I may need to follow up your statement and see what Adam Block's reasoning is. I'm sure it's solid. Always room to learn in this hobby. Fortunately, no one is getting any sleep in this hobby either.

@BrokenPik

4 жыл бұрын

@@Aero19612 tell me about it.. last night i went in the field looking for Comet Swan ( hope i got it , once i check the data) and there was a gazillion Skeeters , so i packed it up and drove to another location under a turbine (way better) then re-setup and went at it again.... last week i stayed up till 5:14 am to catch the dawn Comet Swan... now at least its after sundown under Capella somewhat.

This is far too complex for me, I am only just starting in this :P

@Aero19612

4 жыл бұрын

HaHa. Get a couple of years in this hobby under your belt and your brain will double in size (your wallet will be half its current size). Thanks for watching, Lance!

@lancewilliams8732

4 жыл бұрын

@@Aero19612 I get so confused, I have spent weeks, and weeks, and weeks. I have a CPC800, and a GSTAR-EX3. For EEA, it seems ok, not brilliant, but ok. I was thinking a Hyperstar might bring down those exposure times ?