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Posts Made By: Thomas Bennett

January 5, 2020 11:00 AM Forum: Binoviewers

BV Eyepieces for C14

Posted By Thomas Bennett

I plan on using a BV on a C14 with 20mm Widescan III eyepieces that have maximum FOV for 1-1/4" format.

Is there any advantage in having a lower-power pair of eyepieces (24mm Panoptics for example) since they would not provide any wider FOV than the 20mm?

I'm thinking the Pans would have better edge correction than the Widescans on a fast scope but in a C14 (at about F/14 with binoviewer installed) there wouldn't be much difference.


January 6, 2020 10:01 AM Forum: Binoviewers

BV Eyepieces for C14

Posted By Thomas Bennett

Thanks Greg,

I tested the 20mm WSIII in a F/7.5 refractor with 2X Powermate (F/15 total) and they are sharp out to about 85% from the center and even the edge is not that bad. Not sure that a getting a more expensive eyepiece would benefit binoviewer performance in a C14.

I noticed the barrel on this eyepiece only has filter threads on the bottom 1/4-inch and the barrel widens-out above the threads (see image) maybe to allow for a wider field stop? Could this be how it achieves wider FOV than other 1-1/4” EPs that have threading further up the barrel like a 24mm Panoptic or 32mm Plossl?

November 13, 2021 01:12 AM Forum: Eyepieces

Identify this EY please

Posted By Thomas Bennett

Hi Felele,

Welcome to Astromart Forums.

Looks like a Q75 WA. Apparent field-of-view is about 70-degrees and eye-relief is about 10mm. It could be an Erfle variant.

Mine has labels on it that identify the model:

September 2, 2022 06:18 AM Forum: Telescope Making

Wooden Polishing Tool

Posted By Thomas Bennett

Has anyone used a wooden disk as a pitch lap base for polishing mirrors?

I've got two 10-inch F/4 mirrors and a 10-inch F/6.5 mirror that need refiguring and glued 3 baltic birch disks together for use as a pitch lap base shown in the attached images. After applying a belt-sander to make it a little convex and marine varnish to water proof it, I plan to pore a lap on this wooden base.

Is there some reason this won't work? Thanks!

September 5, 2022 03:59 AM Forum: Telescope Making

Wooden Polishing Tool

Posted By Thomas Bennett

I also remember buying a 6-inch ceramic tool mirror making kit from Telescopics in Los Angeles back in the 1970s as a kid. The Foucault shadows for that F/8 mirror were real subtle and didn't take much parabolizing.

One of the F/4 mirrors (from a TS Optic OTA) I plan on refiguring shows a smooth conic-section but over-corrected by about 2/3 waves. The other (from Chinese source) is showing so many zones - it's hard to get an SA reading. For these faster mirrors, I recall having to figure them slightly under-corrected to make up for the Foucault light-source and knife-edge being slightly separated. I have some left-over rouge but will have to order some fresh pitch to get started.