I've used them "extensively" on my SCG without an eyepiece, but refractors may be different. ________________________________ From: Chuck Hards <chuck.hards@gmail.com> To: Utah Astronomy <utah-astronomy@mailman.xmission.com> Sent: Saturday, August 10, 2013 2:38 PM Subject: Re: [Utah-astronomy] Ring Nebula (M57) - Be prepared to squint An extension tube only works with eyepiece projection. It won't work for prime focus imaging. On Aug 10, 2013 2:32 PM, "Joe Bauman" <josephmbauman@yahoo.com> wrote:
Rather than a Barlow, I wonder if an extension tube would work -- I think it would tend to make the image larger, though I suspect a longer exposure would be required. But I haven't used refractors much so I may be blowing smoke. Instead of making exposures that are so long that they show the imperfections in alignment, I prefer to make a pile of shorter exposures and stack them. -- Joe
________________________________ From: Dave Gary <davegary@me.com> To: Utah Astronomy <utah-astronomy@mailman.xmission.com> Sent: Saturday, August 10, 2013 12:45 PM Subject: [Utah-astronomy] Ring Nebula (M57) - Be prepared to squint
Ring Nebula, M57. This has no more detail than viewing this feature visually through this scope. I couldn’t get any more detail because I wasn’t willing to invest the increased time on the exposures. These images are 4-minute exposures. You can see the mount was off a little. I kicked the mount by mistake while doing a fine focus. So much for good polar alignment. I don’t have an electric focuser for this little refractor. Wish I did. One question for anyone who knows or has experience with refractors: Does someone make a two-inch Barlow for a refractor that would allow the refractor to reach focus? I have a Zhummel 2-inch ED Barlow, but I do not have near the back-focus with this setup. Not even close. Is the solution, merely, to switch to the Schmidt-Cassegrain to use a Barlow? I don’t have enough experience with these things to know. I really like the little refractor for the tack-sharp focus (well, tack-sharp if you don’t trip over the tripod legs on a regular basis while acquiring an image). However, I’d like to have a slightly magnified image going to the CCD chip. What’s the solution? If this is a really stupid question try to suppress the laughter long enough to e-mail me back and tell me this is a really stupid question. Ask Patrick or Chris, it’s nearly impossible to hurt my feelings.
Thanks,
Dave
http://www.flickr.com/photos/78046474@N06/sets/72157635009053182/with/947806...
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