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Old 03-07-2016, 11:31 AM
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codemonkey (Lee)
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Join Date: Jul 2013
Location: Kilcoy, QLD
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Thanks Bill, Colin and Rex. It's really my own fault for trying to cheap my way out of it in the first place. Changed my order at the last second and didn't put enough thought into it.

Quote:
Originally Posted by Shiraz View Post
is there any way to get a small positive lens inside the guide adapter to act as transfer lens. If you can do it, you could refocus the guider beam further out. I bluetacked in a positive correcting lens from an otherwise useless Barlow when I was messing around with an OAG, but I guess you could find something useful in any old eyepiece - you need a short focal length lens and will have to experiment with placement, but it does work.

the alternative would be to put a negative lens (essentially a Barlow) closer than the guider focal plane and throw the focal plane out further. The disadvantage of this is that the guide image will be larger and dimmer, which will make it more difficult to find a star - might be OK with binning though. Again, a suitable lens should be available in an old eyepiece or you could try an actual short 2x Barlow if you can get it down deep enough in the adapter

rough drawing attached
Ray, that's genius! The OAG has a helical focuser which leaves a bit of space, definitely enough for a small lens.

I dismantled the eyepiece (28mm) that came with the Esprit last night and tried to use the front element to do this.

I tried racking the focuser in and out but couldn't see any stars though I knew they were in the FOV. I didn't try very long as I just wanted to get some imaging done for once and decided to temporarily do away with the flattener.

I'll give this more of a trial though, might be that I just needed more distance between the lens and the guide cam.

Quote:
Originally Posted by glend View Post
Pointing out the obvious, with a separate guidescope you would not have this problem. At a focal length of just 840mm your not likely to have to worry about differential flex.
Cheers Glen. It's more about your imaging resolution than the focal length. I started with an OAG, went briefly to a guidescope, and even when sampling at lower resolution (higher "/px) I could see flex issues. I'm back to an OAG now (obviously) and I don't see myself ever looking at a guidescope again.
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