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WO 71GT COLLIMATION

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#1 Chris Peace

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Posted 17 March 2020 - 06:35 AM

Here’s a Cheshire collimator image of my lens cell in a WO 71GT Triplet. It looks like my cell is not collimated but is that actually what this shows. I’d appreciate the forums experience on this.

 

Of course the lens cell on this scope cannot be collimated as it screws into the front of the tube with no adjustment available other than shimming or machining the end of the scope tube to be square with its axis. The individual lenses can be adjusted of course for alignment to each other as the second image shows. 

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#2 OldManSky

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Posted 18 March 2020 - 06:50 PM

I think I would look at the focuser being properly aligned (and the Cheshire IN the focuser attachment) as issues before the lens cell.  



#3 Chris Peace

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Posted 19 March 2020 - 01:59 PM

That’s a good suggestion but maybe I should have said the I have laser tested the focused and it’s centred to within 1mm of lens centre.

#4 turnerjs085

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Posted 19 March 2020 - 05:23 PM

Cell adjustments will affect centering of elements (and sometimes tilt depending on exactly how the spacers are done). Have you tried it on the sky to see what star images look like? Is there on axis coma and are the +/- x/y fields balanced?


It is very much worth confirming if and what sort of problem you have before messing with element alignment. I personally would not attempt those adjustments with a cheshire. Those almost need a collimator/point source or double pass point source as a minimum for feedback.

Jeremy
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#5 timmbottoni

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Posted 20 March 2020 - 09:17 AM

Here’s a Cheshire collimator image of my lens cell in a WO 71GT Triplet. It looks like my cell is not collimated but is that actually what this shows. I’d appreciate the forums experience on this.

 

Of course the lens cell on this scope cannot be collimated as it screws into the front of the tube with no adjustment available other than shimming or machining the end of the scope tube to be square with its axis. The individual lenses can be adjusted of course for alignment to each other as the second image shows. 

I don't recommend using a Cheshire collimator on a refractor like this.  If its even the slightest bit not square to the optics, you will make a mess of things.  I don't think its accurate enough, and I have never known anyone to align the elements of a refractor with this type of collimator.  It works well to align the mirrors of a reflector, but you are talking about an enormous distance between those surfaces, versus the incredibly small distance between lens elements.

 

The lens cell CAN be collimated, and the sets of screws is exactly how its done. In any refractor, you only want to adjust alignment of the elements to each other. You would never want to shim or machine anything in the scope on your own.

 

WO has a 2 year warranty, so I recommend trying it out and actually taking photos with it, or doing a high magnification star test before touching anything.  If you find it to be off, get a replacement scope or lens cell.  It unscrews off, as you know.

 

 


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