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Request info on this B&L mak..

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#1 Darren Drake

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Posted 08 January 2020 - 07:41 AM

A friend recently acquired this 80mm mak.  There isnt much info online on this model.  Does anyone have any first hand knowledge or experience on this scope?  Looking for performance and history in particular.  Thanks..

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#2 Darren Drake

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Posted 08 January 2020 - 07:42 AM

Another pic of the focuser knob..

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#3 Eeqmcsq

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Posted 08 January 2020 - 04:46 PM

I did an image search and found this comment with pic. The box describes it as a "Lightweight Mirror Lens". More searching led to this page which says it was produced in 1992, and it's a combination camera lens and spotting scope.



#4 luxo II

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Posted 08 January 2020 - 07:08 PM

Interesting - it’s not a maksutov - the secondary spot (and the “corrector”) is dead flat. According to that second link it has 5 elements, 3 lenses and 2 mirrors. Mangin-Cassegrain with flat secondary mirror followed by a two-element correction group.



#5 saccuosti

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Posted 08 January 2020 - 07:47 PM

This is my scope.   The corrector lens on this scope is concave.  It has a primary and secondary mirror and no other elements.   It is a true Maksutov.   100_3569.JPG 100_3570.JPG 100_3571.JPG    

 

 


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#6 saccuosti

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Posted 08 January 2020 - 08:09 PM

100_3573.JPG 100_3574.JPG Two more pictures.....


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#7 luxo II

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Posted 08 January 2020 - 08:42 PM

Then your pics are a bit coy.  Let's see the corrector with some reflections of straight edges (eg your ceiling). My bet is the "corrector" is flat, with a secondary spot aluminised inside - but that a maksutov does not make.

 

Simple geometry says that OTA is way, way, too long to be a maksutov. Your pic with the ruler suggests the mirror spacing is more than 250mm, and the earlier pic at post #5 suggests it has a secondary obstruction around 50% and the reflections look dead straight - ie the secondary is flat. Two passes through that OTA give at least 500mm. This suggests to me the primary is probably is spherical at f/10 and the secondary is flat, or so close to flat it doesn't matter, to put the focal plane out the back for a 35mm camera or eyepiece.

 

Starting with a spherical primary (which for 80mm f/10 is diffraction limited), and putting a flat secondary in front of it with a 50% obstruction to fold the beam back will indeed give 800mm. That wouldn't even need any correcting lenses either, to give respectable image quality in the days of 35mm film.

 

If there's a lens or two in the backend barrel the main purpose is to seal the OTA to keep dust, humidity and fungus out rather than any optical function.

 

The earlier link is from someone who clearly disassembled one of these so I'm inclined to believe their account of what's inside.


Edited by luxo II, 09 January 2020 - 02:46 AM.


#8 saccuosti

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Posted 09 January 2020 - 05:30 AM

Although slight, the "corrector" lens is concave.   To double check and to make sure I was not imagining it,  I set the scope vertically  and used a syringe to apply 5mls of water near the edge of the lens at four points and sure enough, the water pooled in the middle.  I'm just stating the facts. It's only an 80mm lens to it is hard to take a picture and show the details.  The black tube has no glass in it at all.  It's really a fascinating scope.  The primary mirror has no slop unlike my 12" LX200.  I paid Meade $900 with shipping to correct everything on the LX200 and it still has mirror shift.  Short of me disassembling it and repairing it myself, I deal with it.    

 

lens.jpg


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#9 saccuosti

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Posted 09 January 2020 - 06:22 AM

PIcture of the corrector lens with a straight edge.   It is not dead flat.

 

Lens with straight edge .jpg


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#10 saccuosti

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Posted 09 January 2020 - 07:00 AM

The post by Eeqmcsq posted yesterday referencing a B&L "lens".... after looking at both pictures in the links of the post, although design is neat, they are not the same scope.   



#11 luxo II

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Posted 09 January 2020 - 03:41 PM

Ahah, ok !



#12 saccuosti

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Posted 09 January 2020 - 03:45 PM

Does anyone have any other thoughts about this scope....  someone offered to buy it if I was interested in selling it but they did not mention a price.....  Any ideas?




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