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  #41  
Old 09-06-2022, 06:36 AM
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Rerouter (Ryan)
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A way to mount a DSLR directly to a telescope dovetail mount, they kind of exist, but they all are rather crappy, assuming you need to source your own means of connecting it,
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  #42  
Old 09-06-2022, 04:46 PM
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This is beginning to sound like the tilt-shift mechanism used in special wideangle lenses for photographing architecture. Similar issue.
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  #43  
Old 09-06-2022, 06:41 PM
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Quote:
Originally Posted by Peter Ward View Post
My wish list would be a thin non-rotating focuser/spacer...AP (2.7") threaded..

Say 8mm-13mm thick (i.e 5mm of travel) . to allow for perfect backfocus adjustment.
Very cold in my workshop these days and I'd rather be spending time inside the house drawing lines on a computer screen, but 5mm of travel for an effective thickness of 8mm is a bit too much. Would 4mm of travel be acceptable? Also how much weight would you like it to carry?
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  #44  
Old 09-06-2022, 09:22 PM
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Pie in the sky idea: something to make the mount east heavy after a meridian flip. Wouldn't have a clue how to do this, mind
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  #45  
Old 10-06-2022, 12:15 AM
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Quote:
Originally Posted by AdamJL View Post
Pie in the sky idea: something to make the mount east heavy after a meridian flip. Wouldn't have a clue how to do this, mind
I saw a rather simple solution to this a while ago, and that was to place a rope over the RA axis somewhere and to have it hang down on the east side of the mount. this way, the the bias is always on the same side of the mount.
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  #46  
Old 10-06-2022, 12:57 AM
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Quote:
Originally Posted by Stefan Buda View Post
Very cold in my workshop these days and I'd rather be spending time inside the house drawing lines on a computer screen, but 5mm of travel for an effective thickness of 8mm is a bit too much. Would 4mm of travel be acceptable? Also how much weight would you like it to carry?
4mm would be fine. 3kg payload.
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  #47  
Old 10-06-2022, 07:55 AM
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4mm would be fine. 3kg payload.
Thanks Peter, I'll have a go at the "drawing board" and if it looks doable I'll post the drawing in this thread.
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  #48  
Old 10-06-2022, 04:57 PM
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Thanks Peter, I'll have a go at the "drawing board" and if it looks doable I'll post the drawing in this thread.
Excellent
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  #49  
Old 11-06-2022, 11:00 AM
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Ok, here's a preliminary design.
Josh, or anyone, please feel free to copy or improve.

I wanted to add compression springs for preloading the threads but the 8mm thickness is not quite enough for effective implementation. Instead, backlash elimination would have to rely on high viscosity dampening grease and that would make turning the outer ring a bit hard, so I added a lever for that purpose. The lever would also help with estimating the adjustment amount.
The red ring has 1mm pitch threads, left and right handed, so it would take two full turns for the full 4mm stroke.
The three custom SS screws act as guides and limit the stroke to 4mm.

The 6mm depth for the female 2.7" thread can be increased to 7mm.
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  #50  
Old 11-06-2022, 11:16 AM
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Hello Stefan.
Nice design, what locks the final spacing in its place?
Regards
Josh
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  #51  
Old 11-06-2022, 12:44 PM
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The three grey custom M3 screws.
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  #52  
Old 11-06-2022, 01:07 PM
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Sorry, I may be missing something. As far as I understand, those 3 SS screws are fixed in place in the blue adapter and the heads can slide inside the green adapter, and can not be turned, and they are to limit travel and to stop the 2 halves rotating with respect to each other. Is my understanding correct?
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  #53  
Old 11-06-2022, 02:36 PM
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That is correct. I should have pointed out that the three screws need to be locktited into the blue piece.
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  #54  
Old 11-06-2022, 02:39 PM
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Yes, I thought they would need something like that to keep them secure.
So once the desired length is acquired, how is it locked so the backspacing is maintained?
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  #55  
Old 11-06-2022, 02:51 PM
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No locking should be required. The large diameter threads combined with high viscosity grease should maintain the orientation of the lever. Of course this mechanism would have to be made to very tight tolerances. The threads may need a bit of diamond lapping after the anodising.
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  #56  
Old 11-06-2022, 03:08 PM
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It looks like a Good design, Stefan, and in theory with tight enough tolerances, it should work.
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  #57  
Old 11-06-2022, 08:46 PM
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Very clever Stefan

Josh...are small bills OK ?
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  #58  
Old 12-06-2022, 10:24 AM
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Hi Stefan.


I Think the design is probably the best way to do it given the constraints, however I'm going to try add a way of locking it in place while at the same time, removing any tolerance that may be present in the threads. I'll post my design here when I've come up with something.


Josh
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  #59  
Old 13-06-2022, 01:35 AM
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The kind of locking system I was trying to make had another threaded ring on top of the ring you turn to change the spacing. This outer ring, when turned, applied compression to the turning ring by way of a tapered fit. The inner ring you turn to change the spacing has a slit in it to allow it to close up. I realised its design has some manufacturing challenges so a simpler idea would be to machine the turning ring on Stefans design, to be an interference fit on the threads, then cut a slit in it axially, allowing it to open up just enough for a firm fit. The thickness of this ring could be adjusted if more resistance is needed. Some testing will be needed to see what mass can be held comfortably by the part without tilt caused by the outer ring opening up under the load. an alternative would be to have two tabs machined into the outer ring, with the slit in between them, and a screw through the two tabs to provide locking of the outer ring.

All things to work with
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  #60  
Old 13-06-2022, 07:02 AM
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Alternatively (if using the slit tube) you could lock the assembly using a separate split locking collar not unlike an OTA split tube ring.

Best
JA
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