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  #481  
Old 15-10-2021, 07:56 AM
Rod
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Quote:
Originally Posted by mura_gadi View Post
Rod, tyvm for the wire brush idea, I had been using the Stanley but that makes a lot of sense.
Hi Steve

The one I use is from bunnings and in this set:

https://www.bunnings.com.au/wire-bru...B&gclsrc=aw.ds

Only $3.50

Rod
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  #482  
Old 15-10-2021, 08:04 AM
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Sunfish (Ray)
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Thanks Rod , Steve and Werner. I have been using the Stellafane quarter circular stroke with a sub diameter but I will give the short straight a try . I have one of those wire brushes and it is true that the lap looks a bit shiny.

Last edited by Sunfish; 15-10-2021 at 08:38 AM.
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  #483  
Old 15-10-2021, 08:21 AM
Rod
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Meant to write short straight strokes mirror on top earlier. I’ve corrected my earlier post. TOT will probably work too but these days I’m finding MOT works best for me, probably because I use slightly oversized laps - usually about 6 mm larger.

Rod
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  #484  
Old 15-10-2021, 02:09 PM
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On another point , I have been wondering if the rib around the back edge of the cast Pyrex piece makes difference. The larger pieces I have a flat , but this Pyrex piece is cast in a tapered mould with a bottom with a ridge like a cup or bowl would.

Quote:
Originally Posted by Rod View Post
Meant to write short straight strokes mirror on top earlier. Iíve corrected my earlier post. TOT will probably work too but these days Iím finding MOT works best for me, probably because I use slightly oversized laps - usually about 6 mm larger.

Rod
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Last edited by Sunfish; 15-10-2021 at 02:27 PM.
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  #485  
Old 15-10-2021, 04:45 PM
Rod
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Blanks with a rim like that used to be common. It shouldnít pose any issues. By the look of it, itís a standard 1:6 thickness ratio so whatís on the back is not much of an issue.

Rod.
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  #486  
Old 15-10-2021, 05:44 PM
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Thanks Rod. Gave the extra cut and wired star sub diameter a go as I had the lap on hand . Did not seem to be any different so I will try the MOT oversize Bartel again which I also have from the initial polishing.
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  #487  
Old 17-10-2021, 05:08 AM
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Hello,

When using a Ronchi tester, is the diameter of the returned beam on the Ronchi screen related to the diameter of the illuminated field given in "Newt for the Web"?


Thanks
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  #488  
Old 17-10-2021, 08:32 AM
Rod
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Originally Posted by mura_gadi View Post
Hello,

When using a Ronchi tester, is the diameter of the returned beam on the Ronchi screen related to the diameter of the illuminated field given in "Newt for the Web"?


Thanks
Thereís no relationship that I can think of. The illuminated field given in newt is mainly determined by the diameter of the diagonal mirror and to a lesser extent if you have a narrow aperture stop in the system (eg. small diameter tube).

Rod.
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