Hey all again. I hope the general discussion forum will suffice for this topic.
So, I am new to measuring brightnesses, and I have recently learned a few IRIS commands. I understand how to use the software to measure magnitudes and export them into a spreadsheet, but I will still need lots more practice. That being said, I assumed like in most astrophotgraphy, that I would have to use darks, flats and maybe bias frames. How necessary is this? If I chose to make an uncorrected image that may look a bit bulgy in the middle with lower black to light contrast, would it provide the same magnitude data as a black flat image?
If it is the case that, in fact, the relative magnitude stayed constant between the stars within the field of view regardless of the use of darks and flats, would it not prove to be an unecessary step?
Has anyone tried both to see if the magnitudes matched between two photos: one using darks and flats, and the other not? If they do not match, then are we to assume that the data collected is done so in a fairly uniform manner?
Lastly, how important is this?
Thanks for entertaining my long windedness!
Kris
Darks and flats are essential for photometry. Without dark subtraction, you'll have hot pixels all over the place, potentially significantly affecting the sum of brightness detected within an aperture. In fact, the aperture photometry process might fail, depending on just what kind of thermal noise your camera has, and your software.
Without flatfielding, the relative magnitude of stars in various places on the frame will not be the true relative magnitude, so even differential photometry will be incorrect.
Flatfielding espeically, is not a trivial process, but doing dark subtraction and flatfielding is a basic part of CCD image processing before photometry.
Gary Billings
Thanks, Gary, for clearing that up! :-)
Kris,
I suggest you read the CCD Observing Manual.
https://www.aavso.org/ccd-photometry-guide
This should give you a lot of the basic information. You might also consider signing up for the AAVSO CCD Photometry-1 on-line course which will be given next March.
https://www.aavso.org/choice-course-descriptions
Phil
Hey, I guess I didn't clarify, but I plan on using a Nikon D300. I don't have a CCD cam. It should still work okay, right?
Yes, you can certainly do photometry with a DSLR. There's an AAVSO on-line course and a manual for for that as well.
Phil
Kristopher,
I was the instructor for the DSLR photometry course that finished a few weeks ago. Ditto Phil's recommendation: Download and read the DSLR photometry manual. You definitely need calibration frames for DSLR photometry. You can contact me if you have any other DSLR photometry questions.
Barbara
Thanks Phil and Barbara, I will get on top of that as soon as I can :-).
Kris