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Hi All, I am posting what I suspect is a newbie mistake question but hoping that someone can assist with the issue of flats.
Although I have been fumbling around the sky, taking snaps at leisure, recently I became serious. I have read up about the different calibration files (flats, darks, bias) and they seemed to make sense; different ways to capture the image defects and extract those from the image of the sky. After a few weeks (months) of further fumbling I went back to the very first target to receive my attention, M42 Orion Nebula.
In short, I took 20x 30s exposures in LRGB and ran these along with 20x LRGB each of darks, bias and flats. To obtain the flats I used a diffuse sheet of perspex (lightbox material) and an LED video lamp that has 180 white LEDs, turned to its lowest setting. Attached below is the stacked Luminance flat and the light image. In the lights I am getting very strong marks from dust and I had thought that the flats would subtract this but looking at the flats the marks are completely different shapes and do nothing to remove them from the lights.
The attached has been further stretched to show the issue. Now, I am obviously doing something wrong but I have no idea what, any pointers from the vast pool of knowledge will be much appreciated.
First post here, and I'm pretty new to AP, just picked up a Star Adventurer mount a couple months ago and have been happily playing around with it with DSLR and various lenses and a 72mm Sky-Watcher refractor. I'm new to the whole setup process, and I'm trying to do a decent job of leveling the tripod/mount, polar alignment, and I should probably think more about balancing the weight of things. I've gotten some decent shots, like 60-120 second subs with up to 300mm lens. My last time out I was getting star trails at 200mm and 15 second exposures, which could have been just a sloppy polar alignment, but today out of curiosity I looked through the polar scope and rotated the RA axis 360 degrees, and I saw that the target circle jumped a few times. I'm guessing that the target circle should appear not to move while the numbers 3, 6, 9, 12 would rotate around as I rotate the RA axis. So my guess is that the polar scope would need to be calibrated?
I have an unusual problem with my AZ-EQ6.
I decided that I wanted to try pulse guiding rather than ST4, to get rid of a cable.
I use MaxIm for all my controls, capture, guiding, pointing etc. and I use the EQMod ASCOM scope driver.
My initial pulse guiding efforts worked ok, the mount would move and guide etc, no worries. I was not pleased with the pulse guiding results after some fluffing around so I moved back to ST4 and this seems to be where my issues started.
Now, whether I choose ST4 or pulse guiding, my mount will no longer calibrate in the Y axis (Dec, I believe), or for that matter, guide. I have tried the move commands from inside MaxIm guide tab and X responds to a 10 pixel move but not Y.
I tested with both PHD 1 & 2 with the same results.
If it were a hardware issue, as in the mount has a Dec problem, would I be able unable to operate the mount with the hand controller or on screen motion buttons, both of which slew the mount fine? I could understand if the guide port were malfunctioning that ST4 would possibly have an issue but not when the mount slews as directed, so pulse guiding should work.
Could it simply be that my EQMod driver has got confused and needs to be re-set, or am I looking down the barrel of sending my mount back to the dealer?
Does any of this make sense?
Thoughts and feedback most welcome.
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!