Quote:
Originally Posted by Xeteth
Cheers for the info Greg!
I have a flat panel box which I've currently been using for flats, but I've had some really weird results with them (usually over-correcting). I've tried various ADU's for them to no avail - I was wondering whether the issue was related to tilt and/or incorrect gain/offset. I'll see how I go with the 16200, I'm hoping the issue resolves itself (although my curious brain will still make me figure out what was going wrong with the QHY8-Pro  ).
The focuser on the OTA seems to be decent enough, but certainly not amazing - something that is on the long list of upgrades. I'm not entirely sure what you mean by "pack out the camera", but would love to learn about it (and see if it fixes my issue if needs be) - if you could share that write-up that'd be great! Cheers again! |
Flats.
I read one writeup of flats that worked out to be 30,000 ADU for the flats. I find that too much and you overcorrect. Also with my cameras which have shutters I need to take a flat that is at least 3 seconds long otherwise I see the shutter opening in the image.
I generally go for dusk flat with a white Tshirt over the end of the scope. I do Ha first whilst the light is still a bit bright.
I go for around 20,000 ADU. I usually only take 3-6 flats.
I take about 16 bias shots and usually reuse them for some time as bias does not seem to change over time that I have noticed. Same with darks. I try to get about 16 darks but often its only 6.
I make a master flat in CCDstack and do not bias subtract when they are made.
I use CCDstack to calibrate and I use the corresponding dark and bias, flat and bias. I use the adaptive subtraction option for darks which asks for a bias and then does a calculation based on your image and scales the dark.
For tilt. Pack out the camera refers to getting a very thin spacer between the camera and say the filter wheel or some other part of the imaging train before the camera.
I take an image about 10 seconds long and put a torch with a rag over it pointing at one corner of the scope. I then see where that light spot is in the displayed image. This orients me to which corners of the physical camera match the displayed image. I orient from standing behind the camera looking at it. In my scope set up left and right and up and down are both reversed. Don't miss this step or its easy to get confused later.
Now take an image of the stars at 2x2 binning and inspect the corners. Are all 4 corners showing sharp stars or are one or two corners showing bloated stars. Lets say the displayed image shows top right corner bloated stars but the other corners look tightly focused. Now you know from step 1 that top right of the image is bottom left of the physical camera looking at it from behind the camera. Loosen the connection and slide in a thin packer. I use spark plug gap spacers you get from auto shops or I got some thin brass sheet from a metal shop. Its usually very thin spacers like .08mm.
I am assuming here you have solid threaded adapters and solid spacers and have checked they are all snug or tightened up first.
Slip in the packer and retighten. Take another shot, inspect the corners - better or worse? Keep it up until all 4 corners are good.
Sometimes a side needs to be packed out, sometimes just one corner. It can't really be 3 corners only 1 or a side.
If you find you are packing it out too much then you are probably doing the wrong corner. Stop and start again. Unless you setup is poorly done then it should be a thin packer not a large one.
Once you get used to it you can do it in about half an hour. I think the fastest I have taken is 10 minutes. The slowest is 3 days! Its a bit like drift polar alignment. Make sure you do the orientation step or you can expect a 3 day job!
I hope this helps.
Greg.