For any given scope, as the sensor size goes up, vignetting increases as the light cone illuminates the corners and edges of the sensor less and less.
In order of sensor size ... the Sony A7S (full frame sensor) is 35mm, the Canon DSLR is 26mm diagonal, ASI1600 is 21mm, Atik Infinity is 18mm or so, and ASI224 is barely 5mm.
Everyone gets around vignetting by either cropping out the corners, uses the AT Lens gradient tool or similar in post processing, or change scope. The high Mp cameras are able to cope much better than less Mp cameras as when cropped or zoomed they pixelate less/take the zoom better.
Chris, I haven't tried that but now you have me interested ... of course flats should work! Me a dummy. Here I have been fiddling like crazy with the AT lens gradient! LOL
I did use darks ages ago in AT and I know the same drag and drop technique should also work for flats because on dropping any frames into the AT filelist, it asks you if they are lights, darks, flats, darkflats or offset frames.
1. In EOS Utils or BYEOS change the folder to save the flats in to something other than AT monitor folder. 2. Take your flats so they go into that "flats" specific folder. 3. Drag and drop the flats from that folder into the AT filelist (IE in AT click the filelist 'button' and drag and drop the flats into the filelist) and it will ask you whether they are ... lights, darks, flats etc ... choose flats. 4. Make sure you go back into EOS Utils or BYEOS and change the folder back to the Monitor folder so when you start shooting lights again they save to where AT is monitoring.
If you try it and you get wierd results (as I occaisionally got with darks), you may have to open DSS and drop the flats into the DSS filelist. I think it also asks what they are so say they are flats, but also mark one as a light frame. I say that because for darks it needs at least one light for DSS to process it. So probably the same for flats. Dunno that totally for sure? Anyway, then on the left hand DSS menu there is a menu item Register Checked Pictures and when you click that it should create a Master flat. That is created in the original folder where you saved the flats. Once it creates that master flat, you then drag and drop that master flat into the AT filelist and check it as a flat.
So over to you to try as tonight its forecast 70% cloud and right now it is 100% cloud! LOL
ps havent ever googled and found out what darkflats do ... I can guess, but also interesting!
Last Edit: Oct 2, 2016 7:26:11 GMT by howie1: Added drag and drag the master flat text
Had a go at making flats. T-shirt and lights on a well lit white wall. They say you are supposed to do it at the same ISO and focus as your lights (and even camera position - but surely for us we near enough is good enough). Tried to make the master flat in DSS but it says you can't do it with jpegs. So re-took flats as raw files and made the master flat for different ISOs (also need raw lights).
I took some dummy shots in low light. Put in the master flat in AT, and then dragged my lights into the monitor folder. Hmmm. It doesn't seem to make a difference.
Back from the movies. Saw that film Sully - great. Clint Eastwood might have been a one dimensional actor, but he can make a great movie.
Didn't have time align or anything so just took some shots of anything. Took both jpegs and raw. Then put them in to astrotoaster with and without flats. AT did the flat subtraction with the raw files but not the jpegs.
I don't know why and I can't find anything about it. Rather not have to do raws as they take up a lot of space. But more importantly it really slows down the processing in AT. Any ideas ?
Bugger! I suppose its a choice ... if you want to do fast EAA/Outreach and still get pretty good shots then shoot in jpeg but have to muck around with the lens gradient tool in AT. If you want very close to AP quality then you have to shoot in RAW and suffer longer processing times. BTW googling I see ccd imaging also suffers the same issue. Its just physics of the light cone brightness falling off towards the edges thus the larger the sensor the more the light is falling off at the corners. Hence as mentioned before, a small sensor doesnt vignette as bad as a large sensor camera.
Had a go using raw files tonight. Had to stop after a while as its really windy. Two shots of Lagoon & Trifid 4x180s iso1600 using astrotoaster. Used similar settings (I think for contrast etc). Have not used lens gradient Just thought I'd do 3min subs as the polar alignment was good. I should try shorter next time.
Without flat & dark calibration files
With flat & dark
Damn. Forget about the dark in the second as I used a dark from last night and it is way warmer tonight So it does improve things. But might show up more on dimmer objects which you have to push harder. Also, the raw file images are very nice.
And the nebula is really nice with the dslr compared to the ZWO. The bigger well depth = little blowout of the core
Chris, Don on NSN has just started with his EOS ... and blow me down here's his most recent post ...
"As I wrote in my last post I needed to implement flats with the T3i. Yesterday I made two quick master flats. What I did was I took the scope with camera attached as it was from the night before and attached 6 white large coffee filters to the front of the scope and held it in place with a rubber band. I then set my MacBook Pro screen to white (I used an empty note pad page) and pointed the scope at the screen from 6" away. I then took a single 1 sec ISO100 images and lowered the screen brightness until I got a histogram level of just less than 1/3 from the left in BYEOS. I then took a series of 20 images. I set the ISO to 200 still at 1 sec and took another series of 20 images, which pushed the histogram graph to just beyond 1/3 from the left. I took each set of 20 flats and made a master from it in AstroToaster. The result was two Master Flats. Here are some of the image results from last night with the flats applied."
And also within his post is a great explanation of how to use AT to create the darks, flats etc (much better than my How To astrotoaster video explained it). Don is a great communicator in his broadcasts BTW .... have you ever watched his stuff. As well as being the Master of the atik 414, his shots using the EOS are already fantastic.
From Don ...
"Take your dark images and send to folder that AT will use as Monitor folder as you would do for regular images. Make sure only Monitor and Refresh tabs are on in AT. When AT is done loading all the frames press Stop. Then highlight all but the last one and right click on these highlighted ones and change them to Darks. So you will have all but the last frame marked as Darks. Make sure the Stop tab is pressed. Now press the Recalibrate Darks button and waiting til done processing. It will generate a Master Dark. Keep the Master Dark checked and remove all the other frames leaving only the checked Master Dark. Proceed as normal from this point on. Flats and bias offset Masters are done the same way using the same Recalibrate Darks button."
I don't remember where I read it but this is what I've done. Keep my scope focus from the night before. Put a white t-shirt over it. Point it at an evenly illuminated wall. Set on Av mode and shoot for each ISO I might use. I take a bunch of them and set a master flat in DSS.
Rubbish weather this week so won't do much for a week or two. Except make flats for the different focal reductions I'm using. I'll tell ya though. The flats really make a difference when stretching dim stuff (like me).
I can kind of see the advantage of your 8" F5 newt now. That must be a great combo for the dslr.