Gave the 150mm f/4.25 achro a run. 10x8 min at 800 ISO, 16x16 min at 800 ISO. Canon 5DH with Astronomik 13nmHA filter. Used both stacked exposures to produce a HDR image. If the weather is kind will collect O3 and colour. If you look carefully you can see three outer loops. If you have imagination you can see the fourth. The vertical 'noise' bars or lines is the variation due to bias. Yes folks this shows the lot from noise to max signal!
I did all flat, dark and bias corrections in mono bayer filter array or 16 bit fits. That way all corrections are done at the individual pixel level not at the colour level where interpolation has already occurred. When you are trying to get very faint data this is the only way to go. I then converted to colour tiffs before stacking in RegiStar. I only stacked the red data as a tiff because any blue or green noise interferes or distorts the stacking.
Mike it is a 150mm aperture Skywatcher achro and it is well corrected for spherical aberration. I have been warned about spherochromaticity but have not found any great sign of it. It is a native F5 but with a Hutech FR/FF #7887 it is an f/4.25. The field as you can see is flat over a full frame (36x24mm ). I have figured out a way to focus for each narrow band filter in situ. I then collect full colour data with my 100ED and merge the data with IP. So then I end up with dim nebula data and all the stars have colour! Actually this is not as onerous as it seems as you can get NB data with the Moon around and get full colour when it is not around.
Of course this does not beat a 152mm AP or TMB etc. But at least I can get data that is close. My greatest enjoyment is cutting up OTA's and modifying them and hopefully make them perform better. The 150mm skywatcher has an Astro Physics 2.7" focuser to minimise vignetting for a full frame sensor. I will put up some images tomorrow.
Here are a few images of the setup Mike. The finder is a GstarEX behind a 16 to 180mm F1.8 c-mount Canon zoom. The first image is a hand held image taken by a 20D from the screen. This is what you see on the 7" screen in real time and yes it is the Helix Nebula. Since I put a piece of LPR filter in front of the sensor of the GstarEX I can see most nebula in real time.
Well done Bert. What was the temperature like? I find that doing longer than 15 minute subs on warmer nights brings on a fair bit of thermal noise. I like the dial to show your focus position accurately. The extra data you have sure shows more detail thats for sure.
Scott
Scott the camera was in the fridge at -10.0C! Without it at 800ISO and 16 minutes exposure, the noise would swamp the faint signal from the outer loops. How many can you see? The dial indicator is critical as you can swap filters and refocus without losing framing or the same guide star. The achro is a 640mm FL F4.25 with an aperture of 150mm. It is very well corrected for spherical aberration. You can see how flat the field is with the Hutech FR/FF #7887 even on a full frame camera.
I will get full colour data with the 100ED to get the star colours etc and merge it with this data. To get this NB data with the 100ED would take about 36 minute exposures for the same photon count per pixel.
wow now there is some serious stuff happening around that scope looks kinda scary 
