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What Was The Maker Of This Thinking?

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#1 Tom Duncan

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Posted 17 July 2019 - 08:35 PM

I'm baffled by this home made piece. 

 

Unbranded mirror diagonal with a Nikon lens mount on one side, standard 1.25" EP/accessories tube on the other. 

 

Any ideas? Using Nikon lenses as eyepieces? 

 

Tom Duncan 

 

 

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#2 OldManSky

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Posted 17 July 2019 - 08:42 PM

I would guess using Nikon lenses as a finderscope...


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#3 Jon Isaacs

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Posted 17 July 2019 - 08:55 PM

I would guess using Nikon lenses as a finderscope...

:waytogo:

 

I think you are right.  The chrome tube on the left is an old style eyepiece holder, no set screws, just spring loaded steel to hold it in place. This same design is partially visible in this old Edmund diagonal.  

 

597503-1.jpg

 

Jon



#4 telesonic

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Posted 17 July 2019 - 09:13 PM

I'm not so sure this gizmo is for using lenses for finders......

Because I think the optical length would be too long, for lens use (@ infinity focus) but I've never tried something like this.

 

I'm of the opinion that this was probably a DIY focusing tool for a 35mm camera and astrophotography. And a rather clever one at that.

 

You see, if one sets this up with a specific f/l eyepiece.... and make this unit parfocal to the camera - 

Then you simply attach this device to your T-ring, focus your scope...lock the focuser, remove device. Then you put the camera back on, and you are ready to image.

 

Makes sense in my mind, and that would be my best guess as to what you have here Tom.

Do you know if the owner was an astrophotographer by any chance?

 

Best,

Temp


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#5 Kunama

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Posted 17 July 2019 - 09:41 PM

I have seen one like this used with a Nikon telephoto lens as the OTA and some plossls on the eyepiece side.... Made for a fine refractor of about 70mm aperture.....



#6 lphilpot

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Posted 17 July 2019 - 09:55 PM

Yeah, I had an old UO focuser that had a T-cut with spring loaded 'wings' to hold the eyepieces. Actually worked pretty well for my little 1.25" oculars.


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#7 Don Taylor

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Posted 17 July 2019 - 09:59 PM

The Nikon (F mount) flange to film (or focal plane) distance is 46.5mm which means for the device shown to reach infinity focus the eyepiece used must have it's focal plane near the end of the barrel - like an old Ramsden.

 

Or, maybe not intended to reach infinity focus?


Edited by Don Taylor, 17 July 2019 - 10:01 PM.

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#8 carolinaskies

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Posted 18 July 2019 - 06:49 PM

I'm baffled by this home made piece. 

 

Unbranded mirror diagonal with a Nikon lens mount on one side, standard 1.25" EP/accessories tube on the other. 

 

Any ideas? Using Nikon lenses as eyepieces? 

 

Tom Duncan 

Could have been used in a labratory setting.  I have several old bits and pieces from a local university c1950s/60s that would be put together for various purposes.  Some for photography with microscopes, etc.  



#9 Tom Duncan

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Posted 18 July 2019 - 08:15 PM

I tried to attach a Nikon lens onto this and it wouldn't go on because the depth beyond the mount is too shallow, the back of the lens hits it before the bayonet can be engaged. I then tried just holding up a lens to it and found that it would only focus at very close distances. The optical path is much too long to get anywhere near infinity focus. 

 

Looks like this is heading to the free bin at the next astro swap. 

 

Tom  



#10 Michael Covington

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Posted 18 July 2019 - 08:21 PM

It could be something where the builder assembled it (painstakingly) before checking out the basic optical and mechanical requirements!



#11 Eddgie

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Posted 18 July 2019 - 09:50 PM

My guess is that it is a home-made piece that allows the user to attach the diagonal to a T adapter on an SCT so that rather than having to remove the T adapter and Nikon to T mount, they could just simply remove the camera and mount the diagonal in its place.  

 

That is just a guess though, but using a T adapter on an SCT with a Nikon or Canon adapter used to be pretty common place in the 80s and early 90s, and it has that era look to it.  This was back when we were using film cameras with hyper-pan film.  

 

This would have been much easier than changing the visual back. 

 

Just a guess though. As pointed out, it does not look like it has a short enough light path to reach focus with a Nikon lens.  You can make a diagonal that will do that, but about the only way to do it is to use a lens cap with a thin wall, cut a hole in it, and bond it to the front of a diagonal with a very thin housing.

 

(it has a handcrafted look to it.. It looks as if the original brass 1.25" nose was cut off and smoothed and that a filled in flange was used to make the connection, plus there may be screws in the unfinished metal piece that holds it to the diagonal body, but it could simply be bonded.  Looks home made to me though, and knowing that it would make going back and forth between the T connector with the Nikon to T mount adapter to the diagonal makes me think that this is why it was made and the purpose it served. I am old, and I remember imaging with Tech Pan film 35mm camera, and I remember being quite awful at it. I also remember converting back and forth, and perhaps someone more clever than I am crafted this as a solution to make it dead easy.)


Edited by Eddgie, 18 July 2019 - 09:53 PM.

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#12 luxo II

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Posted 19 July 2019 - 02:53 AM

Using a camera lens as a finder - I’ve made similar before with a Pentax K mount. 

 

I used an old Unitron 20mm Erfle eyepiece with either a 200mm f/4 telephoto, or a compact 500mm f/8 mirror lens. Worked quite well.


Edited by luxo II, 19 July 2019 - 02:55 AM.



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