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Old Camera Telephoto lenses Question

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#1 ASTERON

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Posted 31 July 2020 - 06:01 AM

Cruising on e-bay, I ran into some old Mamiya Sekor 300mm and 500 mm lenses for large format RB67 Mamiya cameras.

Some of these lenses ( mostly the non-APO ones) were reasonably priced ($ 300-400 range), the APO ones were about  1$K-1.5$

my questions are:

1) are these lenses any good as short focal length rich field telescopes?

2) How do the above prices compare with Modern APO triplets prices of similar optical parameters ?

3) has anybody ever used such old telephoto lenses as a scope ?

4) Would such lenses have excessive CA as compared to similar APO triplets available for similar prices ?

 

What is your opinion/experience with such lenses (for visual or AP use)

 

Thanks

 

Lihu



#2 TheMoonMan

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Posted 31 July 2020 - 07:19 AM

Dear Lihu,

 

In principle, these lenses could be used as a telescope, assuming you also purchase the correct adapters to accommodate an eyepiece.

Looking at the specs of the lenses, they are quite expensive for the benefit they provide. Their main price driver is the fact that the lenses have a large image circle illuminating the equivalent of the medium format negative of the Mamiya (60x45mm). This feature is useless for telescopes.

 

I would rather look at some manual focus 36x24mm lenses from Canon, Pentax, Nikon, Minolta and the like. Also, you may get a sweet deal on a autofocus lens with a broken AF motor or lenses with a defective aperture ring - you won't need either function in a telescope.

 

Good luck!

Hendric



#3 havasman

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Posted 31 July 2020 - 08:03 AM

I've got an old Zeiss 200mm f3.5 Tele-Tessar that I rigged up an ES82 18mm onto with an extension tube that made a pretty nice monocular "telescope" I played around with for a while. The double cluster was very sharp and pretty. But I never mounted it and it was heavy to hand hold. In the end it wasn't practical for me. I never used it on bright objects as that was not ever part of the equation so I can't add anything about CA.



#4 Don Taylor

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Posted 31 July 2020 - 09:10 AM

One of the problems with converting 35mm fornat lenses is the mount to focal plane distance is too small to accommodate a diagonal. You could adapt something for straight through viewing or plan on shortening the tube somehow.

A medium format lens for RB or other SLR would have greater mount to focal plane distance and might work with a diagonal without shortening the tube (i don't have the dimensions handy) but it is significantly greater to accommodate the larger reflex mirror required for medium format.

My opinion is that with low cost ED scopes like the AT80ED ($400) or AT102ED ($600) or current triplets like the AT80EDT ($800) or even the AT92 ($1800) the effort and expense to adapt one of the older photo lenses is not worth the trouble.

Edited by Don Taylor, 31 July 2020 - 09:21 AM.

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#5 ASTERON

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Posted 31 July 2020 - 10:35 AM

Hmmm.... so not such a great deal, these lenses, seems like with all the adapters and mods it may be better to just get a  proper small refractor, like Don said.

 

Thanks everybody for the good info and advice.bow.gif


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#6 daquad

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Posted 31 July 2020 - 10:39 AM

You can buy a dedicated RFT without the hassle of trying to convert a camera lens. 

 

I managed to convert an old Vivitar 35 mm 200 mm f/3.5 manual focus/f-stop with an adapter specifically designed for that purpose (to use a telephoto lens as a rich field telescope).  I also had to add an extension ring of the proper thread diameter (42 mm) that I had for macro photography.  With a 24.5 mm Meade SWA it makes a nice 8X scope with an 8 degree field of view.  Binoculars can do the same or better.  And to use either successfully, they would have to be mounted.

 

I think you would find adapters (if they exist) to use an eyepiece to be very expensive for a medium format lens.  

 

Dom Q.

Attached Thumbnails

  • Viv 200 f3.5.JPG

Edited by daquad, 31 July 2020 - 10:40 AM.

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#7 Jon Isaacs

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Posted 31 July 2020 - 11:11 AM

Hmmm.... so not such a great deal, these lenses, seems like with all the adapters and mods it may be better to just get a  proper small refractor, like Don said.

 

Thanks everybody for the good info and advice.bow.gif

 

Another factor is the high magnification performance. Camera lenses are designed to provide a uniform flat field. They're sharpest when stopped down. The planets and double stars would not be a strong point of a camera lens.

 

Telescopes are designed to provide on axis views very near the theoretical limit for their aperture, small ED/apo refractors provide views of the planets and double stars only limited by the diameter of the objective.

 

I've wonder if one could disassemble a ~200 mm F/4 camera lens and remount the optics and find enough room to use a diagonal. It would make a nice finder with a flat field.

 

Jon


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#8 Nippon

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Posted 31 July 2020 - 02:50 PM

True most camera lenses perform at their best stopped down about 2 stops except the big pro telephotos. They are tack sharp wide open but as an example a 300 f/2.8 Nikkor or Canon are about $7K


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#9 Don Taylor

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Posted 31 July 2020 - 04:04 PM

Paul. I was going to add the same. But i like Jon''s idea to convert a 200mm F4 which can be had cheap (used) - perhaps removing a section of barrel and attaching a diagonal. Goodbye field curvature - hello very wide flat field. But i'm not going to do that to my 180 f2.8Ed or 300 f2.8 or 500 f4 - i still use those!
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#10 Jon Isaacs

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Posted 31 July 2020 - 04:45 PM

Paul. I was going to add the same. But i like Jon''s idea to convert a 200mm F4 which can be had cheap (used) - perhaps removing a section of barrel and attaching a diagonal. Goodbye field curvature - hello very wide flat field. But i'm not going to do that to my 180 f2.8Ed or 300 f2.8 or 500 f4 - i still use those!

 

I have an old Minolta 200 mm F/4 from the days I did some feeble film Astrophotography with a SRT-101. I suspect with multiple elements and old style coatings, it might be dim..

 

Jon


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#11 Don Taylor

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Posted 31 July 2020 - 10:11 PM

I have an old Minolta 200 mm F/4 from the days I did some feeble film Astrophotography with a SRT-101. I suspect with multiple elements and old style coatings, it might be dim..

 

Jon

I looked at a lens diagram of my (Nikkor Ai-S) 180 f2.8 ED and it's only 5 elements - essentially an ED triplet and a doublet field flattener.  All air-spaced & (supposedly) fully multi coated. Problem is the field flattener is about 1.5 inches in diameter and located just forward of the mount plane so there is not sufficient room for the optical path length of a diagonal and eyepiece holder between the last lens element and the eyepiece.  I wouldn't think it would be very practical to add a diagonal between the triplet objective and the field flattener. 

 

The lens diagram of the Ai-S Nikkor 200mm f4 is similar. The only Nikon telephotos without elements near the mount plane are the high speed 200mm F2.0, 300m f2.8 etc. but those are huge, heavy, and relatively expensive. [Data for late 1980's manual focus lenses].

 

Back to the OP's subject:  I can't find diagrams of the RB67 telephoto lenses but looking at photos of them online, it seems like the rear elements are (probably) well recessed (and the large mount to film plane dimension required for the reflex mirror) tells me one possibly could adapt one of these lenses to visual with a diagonal, unlike my Nikon example above. However the 350mm F5.6 or the 500mm F8 have effective apertures of only 62.5mm so after all the trouble you would end up with a 62.5mm scope. The AT60ED is only $369 and there is an optional field flattener for astrophotography for $100. Or for the $$$$ spent on acquiring and converting an RB lens you could get quite a bit more aperture with a conventional telescope.



#12 TONGKW

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Posted 01 August 2020 - 03:46 AM

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I have a few old camera lens lying around and I have converted them into spotting scope/telescope.
Adapters are available for fitting 1.25” eyepiece to Nikon/Canon/Sony camera lens.
One such adapter is available from Taobao website.
https://item.taobao....&id=14902366113

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SLR camera lens adapter 1.25 inch eyepiece interface.jpg

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#13 TONGKW

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Posted 01 August 2020 - 03:49 AM

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In converting a DSLR camera lens into a telescope, the biggest problem is infinity focus cannot be reached when a diagonal is added.
One way out is to add a Barlow lens in front of the diagonal.
I use the lens in cell of a Celestron 2x Barlow lens which can be screwed onto the front of the diagonal.

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1.25%22 diagonal_Barlow lens_adapter.jpg

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#14 TONGKW

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Posted 01 August 2020 - 03:51 AM

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Shown here is an old Tokina DSLR 100-300 mm f4 zoom lens (Nikon) converted into a telescope.
Due to the positioning of the Barlow lens in front of the diagonal, the effective focal lens of the lens may have been increased to around 1000 mm.
The view is reasonably sharp at up to 100x and there is very little chromatic aberration due to the use of SD elements in this zoom lens.

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  • Tokina 100-300 mm f4_telescope.jpg

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#15 Simon B

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Posted 01 August 2020 - 04:11 AM

The old Mamiya 645 / 67 lenses are commonly used in Japan for budget AP, since they can be picked up on the cheap

 

Some examples from Japanese APers - here's a Mamiya APO-SEKOR Z 250mm F4.5:

 

Mamiya APO-SEKOR Z 250mm F4.5.jpg

 

 

 

Mamiya 500mm F6 APO-L:

 

Mamiya 500mm F6 APO-L.jpg

 

 

 

The advantages of using these vs older Pentax Takumar and similar lenses is they are usually excellent wide open to the edge, even with a full-frame sensor, and are better corrected for CA. Test shot with Canon 6D / 500mm F6 APO-L (wide open):

 

20190108114750.jpg


Edited by Simon B, 01 August 2020 - 04:20 AM.

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#16 Jon Isaacs

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Posted 01 August 2020 - 05:54 AM

In converting a DSLR camera lens into a telescope, the biggest problem is infinity focus cannot be reached when a diagonal is added.
One way out is to add a Barlow lens in front of the diagonal.

I use the lens in cell of a Celestron 2x Barlow lens which can be screwed onto the front of the diagonal.

 

 

For use as a finder, a diagonal is necessary and a Barlow limits the field of view.  

 

I disassembled the rear end of my 200mm F/4 Minolta.  I think that with some custom machining and mounted RACI prism, it could come to focus with at least some 1.25 inch eyepieces.  

 

Jon



#17 Don Taylor

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Posted 01 August 2020 - 10:58 AM

The old Mamiya 645 / 67 lenses are commonly used in Japan for budget AP, since they can be picked up on the cheap

 

 

.............The advantages of using these vs older Pentax Takumar and similar lenses is they are usually excellent wide open to the edge, even with a full-frame sensor, and are better corrected for CA. Test shot with Canon 6D / 500mm F6 APO-L (wide open):

Very interesting. I was unaware of this. Thanks!


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