Astrophotography Basics #3 | The Flat Frame
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- Опубликовано: 3 окт 2024
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A video by AstroFarsography about ADU and the flats aid:
• How To Take Flat Frame... (6:55)
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Thank you so much for stopping by, i wish you a wonderful day/night wherever you are, clear skies, and
May the night be with us!
I've been struggling with flats recently, and this video helped me get a better understanding. Thank you Tim!
Happy to help!
Seriously your calibration frames videos are the most clearly described and helpful I’ve found anywhere. Thanks.
Thanks a lot!
Best explanation of photographic issues related to astrophotography. Numerous other channels explain how to take calibration frames, but do not really explain/show what the actual problems are. Keep it going!
Thanks Tim, very well done
Great to see you back Tim ! 👍
I noticed you have Asiair - these have an auto exposure mode for flats that works really well
I know, it's really handy!
Thanks Tim. I have nothing but low budget equipment, so every bit of advantage I can gain from processing might help. I will try all calibration frames next imaging session.
Best of luck!
Thanks a very interesting video on an essential subject. I think this will be tricky to make sure a/ the lens focus does not move and also ensure a consistent level of light. As you said the histogram will definitely help.
Thanks Tim.
Any time
Very nice video Tim and very important! Thank you.
Welcome back tim. Your videos are extremely helpful to a newbie like me . Thanks 👍
One of the best explanations…thanx
One thing that I do find confusing… the t-shirt :)
I don’t like this because of risk of extra contamination on the surface of the lens…
T-shirt can be ‘fuzz’ generators lol
That's true, by now I am using sheets of paper
This series has been very informative, thanks for putting these together!
Glad you enjoyed it!
This is well explained in Adam Block’s video on WBPP. Nothing new here.
Like your other videos, this series of calibration frame videos is very well done Tim. Given the added depth of understanding you've provided, I do have a question regarding negative effects of changing focus. With auto focusers in play, I for one initiate a refocus after significant HFR changes are detected or after a meridian flip, or perhaps after some significant amount of drift has occurred.
Simply stated, how much change in focus are we talking about? Is it best not to refocus? I'm sure there is not a definitive answer here, but I would like your opinion/experience, or that of others'. Thank you and thanks again for your impactful contributions to our growing community of astrophotographers.
Comparing HFD numbers is not really possible, for they depend on the optical system. The best I can do is an HFD of 2.6, which can change visibly with temperature drops. But while stars change significantly with focus changes, the dust spots will stay about the same on a refocus. The flats don't care about those few micrometers. I hope this answers your question!
@@AstroAddict Yes Tim, this answers my question. Thank you for your quick response.
Hey, thanks for the video! However, I got a little confused at 9:53. Lowering the screen brightness (talking about PWM regulated displays) means the pixels or the backscreen stays on for a very short time in comparison to the duration they stay off. Thus we must increase the exposure length in order NOT to make their frequencies coincide with each other. If, however, brightness is on full, we can effectively lower the exposure length and make the process faster. Or did I misunderstand something..?
I always enjoy your videos. I've been doing astrophotography now since 2018. My flats have been a nightmare with this ASI294MC Pro I have. I use Pixinsight and APP sometimes still. I'm getting bright circles around my images equally spaced. never before seen this, and not sure what is causing it. I may go back to using Bias and keep the dark/flats as well, as you suggested and see if those bright rings disappear...Thanks again!
You should try NINA I've recently switched over to it and found it absolutely amazing for doing flats, if you connect your camera up to it it automatically reads the data from that if it can do that from there or do you have to do is plug in a little bit more information and then run a flat sequence and if then does all the work to produce a perfect flat for you
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But zwo and many other people suggest histogram between 1/3 to 1/2
Thank you for the video!
Question. I just did my imaging session. I took ~60 frames 30s each of Orion, stacked them, and got the result that I am proud of. However, then I decided to try adding flats to the stack. After I tried a new stack with flats, the resulting image is overcorrected for vignetting. The center of the image is overly dark, the corners are now bright, and almost all the colors are gone. What am I doing wrong?
I use Canon 2000D astromodified, Rokinon 14mm lens and Skyguider pro. I took flats using the ipad with white screen directly against the lens hood in the Av mode. I did not use white T-shirt because the image using a white T-shirt was "dirty" (many irregularities in the t-shirt weave structure is clearly visible in the resulting image). I then tried adding Dark Flats to the stack (lens lid on, exposure matching the Flats), and the resulting image is again overcorrected for vignetting and basically unusable.
If you use flats, you need dakrs and bias too. Otherwise the software can't normalize them properly
@@AstroAddict i am not sure i need all of them. Bias is allready removed with dslr software, and it is anyway included/substracted in Darks. It is different for dedicated astro cameras, but as I understand DSLR in-camera software deals with Bias.
My issue with flats was trivial - the viewing angles of ipad screen matrix. It becomes obvious on wide angle 14mm lens. Thus some sort of diffuser was needed. I dont understand why everyone keeps talking about white t-shirt. The irregularities in the t-shirt weave pattern is strongly present on the flat image, and the resulting "calibration" adds t-shirt patches and structure pattern, thus making the image unusable. I assume it works on longer focal lengths, as out-of-focus t-shirt is diffused enough to create a flat image.
My solution is 3% transparent white acrillic sheet placed in front of the ipad screen. Produces best results so far.
Hi there. Would have a "funny" question about the flats and the way to do them...
My little 72mm APO has a retractable dew shield, so, when imaging, the dew shield is extended, how about the flat frames? Does it matter (extended-retracted)?
Und sei noch weiter so cool und viel Erfolg und Clear skies 🤞
The dew shield position does not matter
Do you ever run into more dust / lint being introduced to the lens when you put the shirt on top?
Actually no. I shake the shirt pretty violently before putting it on, it does not add more dust. But you could use a sheet of paper as well.
Hello 👋🏻 thx for your video ! 👍🏻 To make flats calibration files, do I have to make them at the same temperature as the lights? (For example, if I took my lights at -10°, do I have to make the flats at -10° too) or does the temperature not matter for the flats?
If you keep the flats short, like below 1s (which I don't recommend), the temperature does not matter. But better safe than sorry