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Yesterday I was reading about dark frames vs in camera long exposure noise reduction, and something caught my attention. As far as my (so far little but growing) knowledge goes, the best you can do is to take the calibration frames right after the imaging session. This can be a pain in the A, and as I read yesterday, many takes these frames separately, when there is nothing better to do, like on a cloudy afternoon. This is allright, it's a good idea, you can create different master darks and other master calibration frames on different temperatures (room temp, cold, hot etc), and use these when stacking images from your light sessions according to the temperatures the lights frames were capured at.
But. As far as I know, my darks should have the exact same settings and focus that my lights have. If I know I use for an example a prime wide angle lens at F2.8 all the time, with ISO 1600 to capture the milky way, that's okay. But what if something changes? What if I use ISO 3200 for some reason? What about the focus (okay, inifinity, but not exactly the same all the time when manual focusing)? What if I use a zoom lens on different focal lenghts? What about the other calibration frames?
It's definitely not impossible to be prepared for every scenario, but when you use lenses instead of telescopes, there are more variations.
Extra info, if that matters: I'm using a Nikon D5500, which is "ISO invariant".
I'm really curious about your replies, as this could greatly improve my image's quality, if It's possible to take calibration frames this way.
Thanks in advance!
By Emmanuel Marchal
I'm looking for a flat field generator for my SCT 10". There seem to be plenty of options around £200 but wondering if anyone had a try at simple office flat panels like these: https://trade.ledhut.co.uk/commercial-led-lighting/led-panel-lights/20-watt-led-panel-light-295x295mm-ip40.html which come at a fraction of the cost. Thoughts?
It's been a while since I wrote here, also because this year I've been less active in the field, unfortunately...
Anyway, I've now started to do autoguiding, with mixed results. I bought myself a laptop and guidescope, with CCD.
I'm able to do 10 minute exposures that come out fairly well most of the time. Guiding is mostly good. I tried PHD as well as Maxim, but lately Maxim seems to be doing better, or I just found the sweet spot for my setup.
The last 2 or 3 times however, I'm having difficulty in obtaining decent images. Even with no moon, the images I get are quite bright, with stars barely visible, and the stack is terrible: it's a light shade of grey, hiding all stars (let alone a nebula), and the histogram shows the peaks (in DSS) far to the right, so adjusting that is a nightmare, so much so that the last two times the result was not worth showing to anyone....
The site I go to is always the same, and I already obtained quite nice images, also with 10 minute exposures and the same ISO...
Apart from this, I'm having a very hard time getting my flats right... I've got a "flatbox" (EL panel with two sheets of white paper, 8 sec exposures at 800 ISO, the same ISO I use for the Light exposures) that I tried at home in the dark with the scope and camera, to get the right histogram, as I gather looking online: the peak should be at about a third of the histogram.
Problem is, which I discovered only last week, the histogram changes with the same setup, for the various "receivers" of the flat image: the camera, Maxim, or DSS. As shown in the photos below (the camera is a RAW picture, taken with the same settings as the FIT picture I used for the DSS and Maxim screen caps):
Apart from the histograms, I also always get those very ugly red hue photos in Maxim.. Is this something of Maxim, or am I getting something wrong?? The image obviously is not red, but the grey shade of the DSS photo (the photo of the camera screen shows only white, but that's because of the phone cam)... This means I can never check in a decent way if the exposures are coming out right while I'm taking them with Maxim... So, recapping, problems getting the flats right, and headscratching about the bright exposures I'm getting lately from a setup that already proved it doesn't have to be that way... At the moment I don't have examples of the latter problem to attach (because I didn't finish any stack, seeing as they came out so horribly), but I can attach some, if needed. Any suggestions? Somebody had the same problems? I'm getting a bit frustrated, I must say... Clear skies!! Gerhard.
OK, I may just be losing the plot here, but help!
Just how does one create a master dark frame and master flat frame for each observing session? I used to be able to do this using Registax, but I now want to use new tools such as AS!2 and maybe even Pixinsight (possibly), but certainly i AS!2's case it needs a master dark/bias/flat frame - not the video sequences that I capture
OK, so on each observing session - and in my particular case - its planetary imaging:-
i) take lights of object - in this case jupiter - usually 1min video in SER format using Sharpcap
ii) Put lenscap on scope and take darks @ same exposure gain settings - again 1 min video in SER format
iii) replace cap with light panel and take flats with exposure set to fill ~30% of the histogram - 1 min video in SER format.
- I'll investigate bias frames later - just trying to build a workflow for AS!2 at the mo.
I'm hoping to build a library of darks at different temperatures for each of my cameras
So how do I best convert the SER video files into dark & flat frames for use in AS!2? What software to use and what settings
Thanks in advance