dark current noise

Astrotripper wrote:

alexisgreat wrote:

Astrotripper wrote:

I wonder what the minimum distance from filter to focal plane would be with your set up?

The distance from the base of the custom T-ring, to the end of the barlow lens tube (where you would screw the filter on) is 65mm. It's about 55mm alone, without a T-ring. So it's a pretty long thing, much longer than a dedicated threaded nosepiece that you linked to earlier.

Thanks, I'm trying to figure out if there is any way I can get the filter close enough to the sensor of the E-PL6 to avoid vignetting. At f/10 it needs to be 54mm from the sensor, at f/6.3, 35mm.

In that case, the filter threaded male/female T-adapter that you linked here before is your safest bet. If you can make a T-ring similar to mine, you should be able to sqeeze that filter below 40mm distance from the sensor (if my guesstimates are right).

Oh, and for a telescope like that Nexstar of yours, you don't have to worry much about the length of all the junk you put between the camera and the telescope. I'm pretty certain catadioptric telescopes like that have a much longer range of focus adjustments than the Newtonians. And there's no problem with the tube obstructing the primary mirror. I've used some crazy long solutions on my little Maksutov and was able to achieve focus without problems.

So yeah, just get the male/female T-adapter that takes your filter and put it between your T-ring and nosepiece (or whatever it's called). A standard Micro 4/3 T-ring will be a bit too long (it's 35mm long from base to end) to clear those 54mm, but that should be enough to get you going.

But I have to warn you, at f/10, even the Moon will require very high ISO to keep the shutter fast enough. As for imaging deep sky objects at long exposures, you definitely could use that focal reducer to get it down to f/6.3.

Thanks! So you have a MAK too? To complement my 8" SCT, I also have an ETX-90RA, 90mm MAK. I think the E-PL6 may be the only interchangeable lens camera still made that the tabletop equatorial mount of that telescope can handle!

I know you said I shouldn't worry about all the junk between the camera and telescope, but should I still definitely leave the correct image diagonal out?  The only reason I was thinking of using it is for imaging near the zenith it will rotate the camera 90 degrees so the camera isn't near the base of the mount.