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Secondary size & CCD imaging
Considering all this, could one not
replace the 4" secondary currently installed with something much smaller, such as a 2.6" or 3"? Hi: You could. HOWEVER.... I doubt you'll notice any improvement in your images, and if you're not using the scope visually, anyway... Peace, Rod Mollise Author of _Choosing and Using a Schmidt Cassegrain Telescope_ Like SCTs and MCTs? Check-out sct-user, the mailing list for CAT fanciers! Goto http://members.aol.com/RMOLLISE/index.html |
#2
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Secondary size & CCD imaging
Considering all this, could one not
replace the 4" secondary currently installed with something much smaller, such as a 2.6" or 3"? I think this is an excellent idea. Depending upon how far outside the tube you need to bring the focal plane for the CCD, you could easily get by with a 2-2/3" minor axis diagonal. It would completely illuminate a 1/2" field with the CCD plane about 2" outside the light path and reduce your obstruction from 25% down to only 17%. I think that is significant for giving improved contrast to your CCD imagery. Clif |
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Secondary size & CCD imaging
"Chris L Peterson" wrote in message
... In fact, since CO is so unimportant for imaging, you might want to consider removing the secondary mirror altogether and putting your camera at the prime focus. This will give you a wonderfully balanced tube assembly. If you did this, woud you still need to have a focus mechanism of some kind? |
#5
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Secondary size & CCD imaging
On Mon, 28 Jul 2003 08:30:08 -0400, "Stephen Paul" wrote:
If you did this, woud you still need to have a focus mechanism of some kind? Unless your tube/struts have a zero coefficient of thermal expansion. I suppose that would be the trickiest thing about implementing a prime focus imager- coming up with a clean way to support a camera and focuser. That's quite a bit of weight for an ordinary spider. _________________________________________________ Chris L Peterson Cloudbait Observatory http://www.cloudbait.com |
#6
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Secondary size & CCD imaging
"Chris L Peterson" wrote in message
... On Mon, 28 Jul 2003 08:30:08 -0400, "Stephen Paul" wrote: If you did this, woud you still need to have a focus mechanism of some kind? Unless your tube/struts have a zero coefficient of thermal expansion. I suppose that would be the trickiest thing about implementing a prime focus imager- coming up with a clean way to support a camera and focuser. That's quite a bit of weight for an ordinary spider. I figure you have to remove the spider and bolt the camera closer to the open end of the tube in order to bring the camera far enough away from the primary to be at prime focus. But, I can't really see a reason to, as long as the photons will hit the detector I think I'll just keep it simple and stick with the 2" Focuser and the Starlight XPress MX series cameras. The MX bodies fit right down into the 2" focuser. I haven't tried it yet, but I'm guessing it will go in far enough to reach focus. Then, all I need is a dual axis EQ Platform with autoguider input, and to piggy back the ST80 as a finder scope. Does weighing the options never cease? -Stephen |
#7
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Secondary size & CCD imaging
Thanks to all for the replies. Good points were made in each and
every one of them, and I do appreciate the ideas and thoughts... I may experiment with both my 4" sec and a 2.6" (or 3.1")to see if there is any detectable difference in the images. I did forget to mention that I also do planetary imaging from time to time, and I suspect if there is any difference, this is where I will see it most. Thanks Again, Brian Sherrod |
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