I’m adding auto-guiding for the first time (OAG – ZWO) and have already had a couple optical train derailments and hoping for some help getting back on track. Right off the bat, I managed to bind a couple of the extension tubes and ruin both trying to separate them (it was the 5mm and variable, so next to nothing to grab on to). In the process, though, I also discovered a severe vignetting issue (see pics below) that I'm assuming? is because the ID of the new parts is a lot less than what I was using before (1.5” at the back of the scope vs 2.5” through to the camera connection). More than a little confused by the cacophony of thread sizes, types and configurations, since I had M48 connections I had ordered M48 parts….. I now believe I need M68 parts, or a custom part, but before I make another obvious blunder I wanted make sure….
Here’s my pre-OAG optical train:
SCT(C9.25 edge) > T-adapter(3.3in to M48 - ID 2.5in) > t-ring(M48 )> DSLR(Canon 5d IV, full frame)
OAG/M48 train:
SCT > Celestron adapter plate(3.3in to 2in - ID - 1.5in) > Adapter(2in to M48 – ID 1.61in) > Extender/spacers(M48 to M48 – ID 1.79in) > OAG(M48 to M48 ) > t-ring(M48 ) > DSLR
Proposed OAG/M68 train:
SCT > Adapter(3.3in to M68 – ID 2.6in) > Extender/spacers(M68 to M68 – ID 2.44in) > Adapter (M68 to M48 ) > OAG(M48 to M48 )> t-ring(M48 )> DSLR
Proposed OAG/custom part train:
SCT > Custom T-adapter(3.3in to M48 – ID 2.5in) > spacers (if necessary) > OAG(M48 to M48 ) > t-ring(M48 ) > DSLR
So, my questions are:
- Am I correct that it's the ID reduction causing the issue? I've already overlooked something obvious, so better than even odds I’m doing it again......
- Are M68 parts the way to go, reducing to M48 at the OAG connection (still closer to the scope than without the OAG, but as far as I can get)?
- My OAG is M48. There’s a ZWO M68 OAG, but is the OAG far enough away from the back of the scope that the ID reduction at that point doesn’t matter (it’ll reduce to M48 on the other side of the OAG to fit the camera t-ring anyhow)?
- Since the various M68 parts needed add up to more than a PreciseParts custom piece ($425 vs $339), any reason not to get a single part from PP?
- If I get a custom piece, should I have it made a couple mm short to give myself some leeway and dial it in with spacers?
On the plus side, I used what I have to try some actual guiding last night and I was able to find a star, successfully calibrate and start guiding! Stuff like this never works for me the first time!….or the second, or third…. Also learned a valuable lesson. I was so amazed that I was actually guiding that I just watched PHD2 do its thing on my laptop for a while, and then it started losing the star. At first briefly, and then for longer and longer periods. So, I started playing with the settings trying to figure what was going on and am embarrassed to say how long it took before I finally looked up to see an overcast sky….. So the lesson -- look up, dummy!
Thanks!
Scott
Without OAG and wider ID train (the images are of a slightly out of focus overcast sky)
With OAG and M48 parts
Here’s my pre-OAG optical train:
SCT(C9.25 edge) > T-adapter(3.3in to M48 - ID 2.5in) > t-ring(M48 )> DSLR(Canon 5d IV, full frame)
OAG/M48 train:
SCT > Celestron adapter plate(3.3in to 2in - ID - 1.5in) > Adapter(2in to M48 – ID 1.61in) > Extender/spacers(M48 to M48 – ID 1.79in) > OAG(M48 to M48 ) > t-ring(M48 ) > DSLR
Proposed OAG/M68 train:
SCT > Adapter(3.3in to M68 – ID 2.6in) > Extender/spacers(M68 to M68 – ID 2.44in) > Adapter (M68 to M48 ) > OAG(M48 to M48 )> t-ring(M48 )> DSLR
Proposed OAG/custom part train:
SCT > Custom T-adapter(3.3in to M48 – ID 2.5in) > spacers (if necessary) > OAG(M48 to M48 ) > t-ring(M48 ) > DSLR
So, my questions are:
- Am I correct that it's the ID reduction causing the issue? I've already overlooked something obvious, so better than even odds I’m doing it again......
- Are M68 parts the way to go, reducing to M48 at the OAG connection (still closer to the scope than without the OAG, but as far as I can get)?
- My OAG is M48. There’s a ZWO M68 OAG, but is the OAG far enough away from the back of the scope that the ID reduction at that point doesn’t matter (it’ll reduce to M48 on the other side of the OAG to fit the camera t-ring anyhow)?
- Since the various M68 parts needed add up to more than a PreciseParts custom piece ($425 vs $339), any reason not to get a single part from PP?
- If I get a custom piece, should I have it made a couple mm short to give myself some leeway and dial it in with spacers?
On the plus side, I used what I have to try some actual guiding last night and I was able to find a star, successfully calibrate and start guiding! Stuff like this never works for me the first time!….or the second, or third…. Also learned a valuable lesson. I was so amazed that I was actually guiding that I just watched PHD2 do its thing on my laptop for a while, and then it started losing the star. At first briefly, and then for longer and longer periods. So, I started playing with the settings trying to figure what was going on and am embarrassed to say how long it took before I finally looked up to see an overcast sky….. So the lesson -- look up, dummy!
Thanks!
Scott
Without OAG and wider ID train (the images are of a slightly out of focus overcast sky)
With OAG and M48 parts
