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Image Quality Issues with Boller and Chivens 16"

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#1 smartin53

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Posted 05 January 2013 - 09:43 PM

Got a fun one for you. I'm presently working as a volunteer with the Smithsonian's Public Observatory Project. We have a Boller and Chivens 16" f/18 Scope on loan to us from Harvard.

Details http://bollerandchivens.com/?p=338

The problem is the images seem to be blurrier than they should be. Everything lacks sharpness even when perfectly centered, resulting in a loss of detail. I've used a focusing mask to verify that focus travel is fine, and the unit is collimated as far as I have been told and can see with standard tests. Also, while there is some light dust on the mirror, it is not significant enough to cause these kinds of issues. I can't get a good look at the secondary to see its status though.

Even though the scope is from the 60s I can't imagine that it was always this bad. My 5" Meade ETX puts out better images. At this point all I can imagine is that the articulating eyepiece holder is causing issues but thats just a guess. Removing it is a headache though so I have not tried to see how things look without it yet.

Figured I would put this out there to try and gather any other ideas to look at. Thanks.

#2 Spectral Joe

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Posted 05 January 2013 - 11:58 PM

I think you're right about that articulating eyepiece thing. I would pull that off and look at the cass focus before doing anything else. B&C made good stuff, and engineered it well. My only direct experience with them was the 36 inch at Princeton, which I used and did maintenance on in the 1980's. Check the focal plane directly and I think you'll find the problem is in the relay optics. If not, my second guess would be the primary cell. Check inside and outside of focus for astigmatism.

#3 Mirzam

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Posted 06 January 2013 - 05:43 AM

What magnification are you using? I imagine it may be quite high and that the blurryness is partially due to this.

Got any cooling fans on that thing?

JimC

#4 Darren Drake

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Posted 06 January 2013 - 11:01 AM

I've looked through a 24 inch B and C at Yerkes and the images were very good. I would not think that its in the optics themselves based on my experience with that scope. The bad images are most likely due to miscollimation, bad thermal issues, or something in the eyepiece or diagonal.

#5 DAVIDG

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Posted 06 January 2013 - 12:02 PM

I won't be surprised if it had bad optics. I refigured a 24" f/16 Tinsley Cass at Mt Cuba observatory back in 1985 that had a bad optics. When getting ready for Halley's Comet the mirror was removed to be recoated and I had a chance to test it. The figure was a deep hole with a badly turned edge. It had abaout 2 waves error in it. The Board of Directors at that time didn't believe me since this telescope cost $65,000 back in 1962, so they had someone from Questar come in to independently test the mirror. He said the same thing. I refigured it and the result were again independent varified.
Over the years I have tested hundreds of telescope optics and have seen many bad one from just about every company that has made them. If you never got a good image out of that scope it's time to test the optics and see exactly what the surfaces look like.

- Dave

#6 PeterKA

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Posted 11 February 2013 - 10:58 PM

Has there been any progress on this issue?
As noted, there is nothing much to say until the articulating eyepiece holder is removed and an eyepiece used directly.
If your group has a budget for an air ticket & hotel, one of the lead engineers at B&C, Don Winans, is still available for consultation.
Peter Abrahams

#7 x-ray

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Posted 17 February 2013 - 11:57 PM

I used that scope when it was still at Harvard, and it did show astigmatism, an elonfated star image that changed direction inside and outside of focus. My best guess is pinched optics, as B&C made good optics. It would take a little detective work to peek inside and see how the mirror supports are working today. Cheap USB "endoscope" cameras on a 2-5m cable are available now, and it might shed some light on the subject, literally.
Alan Sliski

#8 smartin53

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Posted 03 August 2013 - 06:29 PM

Its been a while but I figured I would finally update. They finally took off the articulating eyepiece extension and lo and behold the image instantly was fine. They've went ahead and sent in the eyepiece extension for repair. Not sure when we'll get to use it again though as they may start tearing down the observatory for a rebuild (eg. moving from a temp to permanent structure) about the same time we start night observing in the fall.

#9 Datapanic

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Posted 03 August 2013 - 08:43 PM

With 4 diagonals and whatever optics inside it, I would imagine the articulating eyepiece extension would degrade the image even if it didn't have any other issues. Glad you were able to get it off and test the scope without it!






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