OSC is hard! Widefield is hard!

[DEnc]

How do you folks do it?

The main image is a cropped view of the Veil Nebula complex from an unmodified Canon EOS T3 with an EF-S 18-55mm lens, set to 55mm; 50 subs x 2min at ISO 800. The smaller images are from a Stellarvue SV110ED achromat and an SBIG STT-8300M monochrome CCD, 5min R,G,B subs and 30min Ha,OIII subs.

The nebulae in the widefield are just a faint smudge, and probably they’ll be primarily OIII; there’s lots of noise too. This presents a new set of challenges and mysteries besides what I’m working through with the monochrome CCD. For example, today I characterized the DSLR with PixInsight’s BasicCCDParameters script, and saw that the maximum adu of saturated flats increased with increasing ISO—what’s up with that?

It never ends….

[yobbo89]

Shouldn't dynamic range drop with higher gain? Also don't you get dynamic range back from stacking?

[Star Dad]

I am surprised that at ISO 800 you have that much noise. Canons generally can do 1600 before noise becomes a problem. But in general as ISO goes higher so does noise. I've gotten stunning images of the Milky Way doing 60-60s exposures at 55mm using the Canon 70D at ISO 1600 with virtually no noise. Perhaps there is an issue with the sensor in your T3? Try ISO 400 (maybe even 200) and see if that makes a difference.

[DEnc]

Shouldn't dynamic range drop with higher gain?

It sure does. If I chase after this target I'll go with ISO 200 and plan on alot of stacking. Dynamic range:--

DR.jpg (7.53 KiB) Viewed 1944 times

[yobbo89]

looks like 800 iso is the sweet spot

[yobbo89]

this is a dificult target even for narrow ha / oiii mono imaging . i think even for total wide field most people still use mono cooled with narrowband on a fast lense . it is like imaging a faint galaxy in lp that produces only ha and oiii predominantly.

[OhNo]

I just transitioned over from a T3 Canon (un-modified). I have done a bit of nightscape imaging with the same setup as you described in your first post. IMO you are pushing the limits far beyond what the Camera/Lens is capable of. Any time you crop that much to get an image the results are ummmm, less that satisfactory. Our expectations of our equipment is always greater than it can produce, what is a good result is based on what we expected.

[DEnc]

I think I just found one factor that may improve my prospects--aperture control.

To image the Veil, I controlled the Canon T3 through SGP. As far as I can tell SGP does not offer control over aperture. I'm guessing the camera was set to the last aperture I used in the EOS Utility that I use for PC control of the camera in the daytime, and it was probably a small aperture.

So I ran a test where I set a small aperture in EOS, switched to SGP and shot an image; then back in EOS I opened up the aperture, switched to SGP, and shot a second image. Big difference!

Could any DSLR/SGP users confirm this? Thanks,

David

[JayTee]

You could switch from SGP over to APT. APT gives you the ability to control Canon lens aperture setting. APT is also significantly less expensive than SGP.

Cheers,
JT