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7.5" diameter f3.7 LENS - what to do

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#1 scout72

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Posted 13 February 2019 - 11:31 PM

I have no idea what the original use was- it is an air spaced doublet in a very nice machined cell...I am thinking ---wide field sweeper, but wondering if it is worth it to mount given the coma this is going to have- anyone used a similar lens? 

 

Thanks

 

 



#2 Sean Cunneen

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Posted 13 February 2019 - 11:38 PM

I don't know about your lens specifically, but most show bad correction as they were for photographic use and corrected in yellow light. At f 3.7, there will be lots of crazy color and only the very center will be in focus. Usually, anyways...
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#3 starcanoe

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Posted 13 February 2019 - 11:49 PM

Rig up a temp tube/board. Mount the lens on one end....focuser on the other.

 

Probably horrible at f3.7. But stop it down so that it more like a 4 inch f8, use a 50 mm plossl, and might make a darn nice wide field scope. Might not even be too bad at medium powers.


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#4 Ian Robinson

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Posted 14 February 2019 - 04:07 AM

Some of these are military surplus (ex WW1 , WW2, and more recent wars).

 

If it's from an old aircraft mounted aerial camera , it's going to be a very good astrocamera with a very flat focal plane that's huge.

http://alag3.mfa.kfk...enses/200mm.htm

 

Is it a The Perkin-Elmer Type I Aerial Camera Lens, for 9x18 in plates/film

 

Photos of it will help people ID it for you.


Edited by Ian Robinson, 14 February 2019 - 05:21 AM.

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#5 Jeff Morgan

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Posted 14 February 2019 - 10:02 AM

That would make a very interesting scope for a NV eyepiece. With a H-alpha filter, color correction is not a factor (you're only letting in 656nm.) And it could be very good with a 640nm long pass filter for clusters and galaxies.

 

If you don't have a NV eyepiece, I suppose you could apply the same principles and build a scope dedicated for O-III use. Unfortunately, list of large O-III targets (the scope would not have much focal length) is pretty small.


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#6 dddileo

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Posted 16 February 2019 - 07:28 PM

I wonder if a negative doublet near inside or outside of the primary focus may make it a practical system?

 

 

 

 

Dominic Di Leo



#7 MitchAlsup

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Posted 16 February 2019 - 07:36 PM

I have no idea what the original use was- it is an air spaced doublet in a very nice machined cell...I am thinking ---wide field sweeper, but wondering if it is worth it to mount given the coma this is going to have- anyone used a similar lens? 

It is not difficult to completely correct coma in a 2 lens refractor. Coma is the least of your worries.

 

Coma is only inherent in Newtonians, most other optical systems can eliminate or ameliorate coma.



#8 Jeff Morgan

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Posted 17 February 2019 - 12:17 AM

Coma is only inherent in Newtonians, most other optical systems can eliminate or ameliorate coma.

Refractors can have coma too.

 

Not likely ... but possible when you come across an objective of unknown pedigree:

 

http://bobmay.astron...ign.htm#Littrow




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