Shooting the moon with prime focus - Help!

So, I have pretty good luck shooting the moon with my Canon 7D--1/100 SS, f/11, ISO 100. Since I just picked up a the Celestron edgeHD 800 (2032mm FL, f/10), I thought I would try some prime focus pics of the moon with the following setup:

Celestron > Celestron 93644 T-adaptor* > T-ring > 7D

* This T-adaptor provides the proper back focus for the edgeHD

The problem I ran into is when I tuned on Live View to focus and compose, the LCD screen was completely black. I made a couple of exposures anyway and they turned out under-exposed and out of focus, but at least they were framed OK and the moon did fill the frame

So I am a newbie at this, but I am guessing that because the telescope is slower than my usual camera lenses (f/10 vs f/4 on my 70-200mm), I am not getting enough light through.

Assuming this is right, is it simply a turning up the ISO and/or lowering the SS, or is there some better approach? Or did I miss the boat completely?

Thanks,

Omar

What mode are you using in live view?

When I use my manual focus lenses in M mode in live view, it doesn't show exposure correctly...I think it would be the same as using a telescope (no electronics in the adapters). I also have it set to exposure simulation (so I can get the histogram), but the histogram is completely different in M mode when I use manual lenses in live view, compared to the image taken. Works fine w/ my EF(s) lenses though. I assumed it's because it can't control/doesn't know the aperture.

If you're using live view, try starting off in Av, or Tv mode instead. It'll should show the exposure/histogram correctly. Adjust ISO to keep from using really low shutter speeds. Also, you can temporarily increase ISO and/or use a slower shutter speed just to increase visibility for focusing (I do that sometimes when focusing on stars).

I suspect that you have misunderstood this and that you are a mile out with your focus. The adapter puts the camera in the right position for the best image when focused, but it can't focus the telescope for you. You need to adjust the focus knob to bring the moon into focus. It may be quite some distance from where it was in focus with an eyepiece. I would suggest looking through the viewfinder for the initial rough focus as it's easier to see if it's getting better or worse. Once it looks like a moon, then switch to liveview x5 to nail the focus.

Prime focus on a f/10 telescope is exactly the same as f/10 on your lens so the same ISO & shutter settings will work. Even though it's a f/4 lens, you had it set to f/11 (which is close enough to f/10).

Steve.

Hmmm...so much to learn....thanks guys, you gave me some more stuff to try--I'll keep playing with it tonight until my fingers go numb again.

Regards,

Omar

Thanks guys--your help did the trick: https://photography-on-the.net …?p=13817258&pos​tcount=710

Omar

Well done. That's a really good result.

Omarsultan, do you have another Astros photos?

No so far--a few more pics of the moon, but the weather has not been cooperating so much. I tried playing around with stacking and some pics of the Orion nebula over the weekend, just to try and get the experience. So, I got a feel for the workflow but the subs sucked (didn't have the focus nailed), so not much to show for my efforts. Tomorrow is supposed to be pretty clear, so I'll be out there again.

Hopefully, I'll have some shots to brag about eventually--stay tuned.

Thanks for asking,

Omar

Get a Bahtinov (or other focusing) mask to help you focus. It's the 2nd most useful accessory I've ever bought (a Telrad was #1).

Thx Archer1960...I picked one up, but have been currently waiting for a) clear skies and b) to get healthy...sigh

Omar