Thanks! I'll probably also shoot until I get a high integration time like you do. A few questions: How did you modified your camera? And could you explain that part of your text that I highlighted in red?
I followed some (written) tutorials (for example, LifePixel's) and mainly a video tutorial by Digital Shaman dismantling a D5300 to replace the shutter ("How to replace shutter on the Nikon D5300. Lesson.") - it's not in English, but you really don't need the audio to understand what he's doing. I only watched it until he reached the sensor and its stock filter, which was what I was interested in.
Here are some tips that I came up while I astromodified mine:
- mark with a fine point permanent marker the three screws that hold the sensor down, before removing them and count how many turns it takes you to unscrew each one. You'll need to get them pretty much exact when you screw them back in, if you want to keep the sensor flat (otherwise you'll have tilting in your images)
- get yourself some kind of UV/IR cut filter. You do not want to leave the camera full-spectrum, otherwise you'll have bloated stars and possibly halos around them (like if you were taking photos with an achromatic refractor). I couldn't find any pre-cut, rectangular filter that would have the same dimensions of the stock Nikon filter that I replaced. I resorted in buying a 2" UV/IR cut filter and cutting it to size with a glass cutter. With my calculations, 4 full rectangular filter should fit easily in the 2" circle - so if you are careful, at least one attempt should succeed
- clean the replacement filter the best you can, on both surfaces, before mounting it. Or get ready to become the best you can at taking flats. Even if the filter looks clean, it won't be. You'll most likely have residual dust spots somewhere, so flats will become a necessity
- be careful with the ribbon cables and connectors, they are flimsy and delicate. Remove the battery quite sometime before opening the camera, so the capacitors can have time to fully discharge. You do not want to short anything (I also made a bracelet with some wire and attached the free end of the wire to my mount tripod - without the mount head - to ground myself)
- mark all the screws and their positions. They are all different sizes and lengths. What I did was I made a rough drawing of each layer of the camera I removed, I marked the holes on each drawing, and while I was taking the screws off, I taped them with clear tape next to the corresponding hole in the drawing. This way, it was very easy to remount everything, just following the drawings in the reverse layer order
- take pictures before and after, as you remove and disconnect cables and ribbons, so you can go back to the pictures to see how they were placed, if they were twisted in a certain way, ect.
It's pretty straight forward, but many things can go wrong. So be careful, clean the room well before you do it, keep order on the table, and be ready to dedicate it at least a few hours.
These are the dimensions of the stock filter:
34.5mm x 21.5mm
If you cut a UV/IR cut filter to size, I would suggest you to cut it a little smaller (for example 34mm x 21mm): if you cut it too big, it won't fit inside the rubber frame, so it's better to err on the smaller side, rather than the big one. Too small and it will fall in on top of the sensor and won't be held in place by the filter bracket, so be careful.
As far as ADUs go, this thread - warning: lots of math! - (Help Me Optimizing My D5300 Capturing and Calibrating Workflow) explains the process on how I came up with those numbers. You open an uncalibrated RAW light frame in PixInsight and run the Statistics process on it - this will tell you the mean ADU (and other useful things). To determine the read noise of your camera (which should be pretty similar to mine), instead, you need two bias frames, two flat frames and two dark frames (these taken at two different exposure times - I used 60s and 600s).
If you go through the thread, you will find a lot of different opinions on the "best" numbers to use. At the end, I settled for 800 ADUs or a little higher (sometime I go as high as 1200). If you go too low, you'll end up with many frames to stack. Too high, and you might saturate stars / lose dynamic range / have other problems (tracking, guiding, wind, vibrations, etc. - the longer the exposure, the more you have to lose if one of these things go wrong).
Edited by endlessky, 30 November 2020 - 03:01 PM.