2800mm f/10 !!!! - DPChallenge Forums

05/13/2008 01:33:05 AM · #51

Originally posted by kirbic:

Originally posted by Venom:
#1: Did you find that having the camera body inline with the scope is better or have you tried using the angled eye piece? I was just wondering about either setup? It's just my opinion but I would imagine that I could get a sharper image with less corners/glass in the way?

The t-adapter screws directly into the back of the 'scope, so diagonal mirror use is not possible. In any case, you do want as few opportunities as possible for mechanical misalignment, and as few optical surfaces as possible. In addition, focus might be impossible to achieve with the distance of the diagonal considered.

Thanks, that's kind of what I had figured.

Originally posted by kirbic:

Originally posted by Venom:
#2: Is the "focal reducer/corrector" something additional to the T-Ring and the camera adapter?

Yes, it is. It's essentially a corrector lens. With SCTs (Schmidt Cassegrain Telescopes) it is normally necessary to use a field flattener for photographic use, especially with large-sensor cameras like DSLRs. They are not necessary for visual use, or for use with cameras with small sensors. Focal reducers usually incorporate the function of flattening the field.

Well, it looks like I'm going to have to spend $180 for more accessories. Is this what you're talking about? F/6.3 - Reducer / Corrector

A quote from their website. "It offers wide fields of view with any Schmidt-Cassegrain telescope. Used for astrophotography, it reduces exposure time by a factor of 3." That sounds alright with me. Thanks again -BB

05/13/2008 01:33:55 AM · #52

Originally posted by scalvert:

Don't forget the crop factor. I believe that telescope would be 4200mm f/10 on your Nikon D200.

AND with a 2x eyepiece, would that double? 8400mm f/20?

05/13/2008 01:44:11 AM · #53

Originally posted by Venom:

Well, it looks like I'm going to have to spend $180 for more accessories. Is this what you're talking about? F/6.3 - Reducer / Corrector

Shop around you can do better on the price. I got mine locally for $130 it is a Meade but as I understand it, made by the same manufacturer for both Celestron & Meade. Same thread as it is a standard SCT mount.

Message edited by author 2008-05-13 02:26:15.

05/13/2008 01:45:59 AM · #54

Originally posted by Venom:

Originally posted by scalvert:
Don't forget the crop factor. I believe that telescope would be 4200mm f/10 on your Nikon D200.

AND with a 2x eyepiece, would that double? 8400mm f/20?

No the eyepiece plays no part. It is replaced by the camera.

05/13/2008 06:29:55 PM · #55

Originally posted by thegrandwazoo:

Originally posted by Venom:
Well, it looks like I'm going to have to spend $180 for more accessories. Is this what you're talking about? F/6.3 - Reducer / Corrector

Shop around you can do better on the price. I got mine locally for $130 it is a Meade but as I understand it, made by the same manufacturer for both Celestron & Meade. Same thread as it is a standard SCT mount.

Ah, Here's a couple for a better price. f/6.3 reducer/corrector & Scopetronics

Is there any reason that I wouldn't want to consider getting an f/3.3 focal reducer?

-BB

Canon RF 24-70mm f/2.8 L IS

05/13/2008 06:40:50 PM · #56

Originally posted by thegrandwazoo:

Originally posted by Venom:
Originally posted by scalvert:
Don't forget the crop factor. I believe that telescope would be 4200mm f/10 on your Nikon D200.

AND with a 2x eyepiece, would that double? 8400mm f/20?

No the eyepiece plays no part. It is replaced by the camera.

Maybe that's another reason my focus field is so blurry around the edges. I'm going to try to see what in the world I was doing wrong!

PS. I was actually able to use the 2x eye-piece and get some really "in your face shots of the moon"; it's just that they were kind of dark! This was my only reason for mentioning this earlier. Like I said before Im still trying to figure this out.

kirbic

Canon EOS R5

05/13/2008 06:43:02 PM · #57

Originally posted by Venom:

Is there any reason that I wouldn't want to consider getting an f/3.3 focal reducer?

-BB

Your answer is in the graphic at the right side of your link. Your APS-C sensor is not that much smaller than 35mm film, when compared with the average astro-imaging CCD. So you will almost certainly see severe vignetting with an f/3.3 reducer/corrector with such a large sensor. Keep in mind the page you linked was written in 1999, when sensors of APS-C size (or 35mm film size, for that matter) were not something the average amateur would be using.

05/13/2008 06:48:57 PM · #58

Originally posted by kirbic:

Originally posted by Venom:

Is there any reason that I wouldn't want to consider getting an f/3.3 focal reducer?

-BB

Your answer is in the graphic at the right side of your link. Your APS-C sensor is not that much smaller than 35mm film, when compared with the average astro-imaging CCD. So you will almost certainly see severe vignetting with an f/3.3 reducer/corrector with such a large sensor. Keep in mind the page you linked was written in 1999, when sensors of APS-C size (or 35mm film size, for that matter) were not something the average amateur would be using.

That answers that! I didn't think about this being pre-digital. Thanks

kirbic, I'll have to get the 6.3 ordered so that I can start practicing with some constellations.

05/13/2008 06:55:03 PM · #59

The 3.3 and larger aperture focal reducers, as I understand it, work only with CCD imagers and not dSLR's. Starizona makes a focal reducer that makes your SCT a f/1.8 but can only be used with a CCD imager as well. Plus the one Starizona makes replaces the secondary mirror on the front of the telescope. The 6.3 is about the best we can get for a dSLR.

05/13/2008 07:08:42 PM · #60

Originally posted by Venom:

I guess I was doing something very wrong then because the only way I could get any focus or image (through the camera) AT ALL was to insert the eye-piece into the T-Ring!! I could actually then see something.

These shots were all shot WITH the eye-piece. (in the T-ring)

Maybe that's another reason my focus field is so blurry around the edges. I'm going to try to see what in the world I was doing wrong!

PS. I was actually able to use the 2x eye-piece and get some really "in your face shots of the moon"; it's just that they were kind of dark! This was my only reason for mentioning this earlier. Like I said before Im still trying to figure this out.

I can see through the camera when it is mounted and I just used the focuser on the N11 to get the moon in focus. I say keep trying as we have very similar gear so you should be able to see and focus through the camera without the angle prism/eye piece.