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Pentax Telescopes & Mounts

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#101 RichA

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Posted 29 October 2020 - 12:17 AM

Oh, a Pentax telescope thread! Nice. I don’t have a Pentax telescope, but I do have a Pentax 1000mm f/8 camera lens refractor w/M42 screw mount & an integrated 60power(about) eyepiece & 90degree prism. Yes, it is a camera lens, even including a manual stop-down aperature from the said f/8 to f/45. At the given 60power, I have split double stars to 2.5arcseconds. With such good performance, does anybody have a clue where I could find an eyepiece giving about 150power(about 7mm eyepiece) with an integrated 90degree diagonal w/M42 lens mount attachment. Yeah, yeah, I know. I’m talking about something that hasn’t been made for 50-55 years?

You could pretty easily disassemble a T-adapter or dead M42 lens and mate the threaded part to a diagonal.  Though i doubt (depending on how the Pentax focuses, is it a rack and pinion like a big 1000mm Olympus Zuiko?) it will reach infinity focus.  Some people have used long camera lenses as scopes but usually with the tube assemblies and other internal lenses discarded.  Might want to do that to a valuable vintage lens.  I had a 100mm f/5.6 refractor made up of a Leitz 560mm telephoto lens, but only because the lens cell conveniently unscrewed from the lens body like a  telescope lens and cell.  Also, some lenses, even long ones with few elements may depend on some of the internal lenses for aberration correction.  I used a couple converted spotting scopes as astro scopes, a B&L ED unit worked beautifully, a Kowa Fluorite did not.



#102 litesong

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Posted 29 October 2020 - 01:38 AM

Did they make a M42 teleconverter?  That would double the focal length and magnification and still probably maintain focus distance?
 
Dave

Oh, thank you for that idea. I’ve never liked converters too much, but I’ve always had cheap ones that could only give fair performance by stopping-down lenses. Some manufacturers did make 3 element apo-chromatic converters in M42 screw mount, even with multi-coating. A 2x Tele-converter wouldn’t give the 150power I was looking for. But, too much power would be difficult to keep a target double star in the field, while I was screwing out the 60power eyepiece/diagonal & then screwing the Tele-converter to the diagonal AND FINALLY screwing the Tele-converter/diagonal/eyepiece back on the Pentax lens.
Forty years ago for terrestrial photography only, I even stacked 2x & 3x Tele-converters to get 6 times the focal length of the camera lens focal length.
Anyhow, thanks for the idea! It’ll be an option.

Edited by litesong, 29 October 2020 - 01:45 AM.


#103 litesong

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Posted 29 October 2020 - 02:10 AM

You could pretty easily disassemble a T-adapter or dead M42 lens and mate the threaded part to a diagonal.  Though i doubt (depending on how the Pentax focuses, is it a rack and pinion like a big 1000mm Olympus Zuiko?) it will reach infinity focus. Might want to do that to a valuable vintage lens.  I had a 100mm f/5.6 refractor made up of a Leitz 560mm telephoto lens, but only because the lens cell conveniently unscrewed from the lens body like a  telescope lens and cell.  Also, some lenses, even long ones with few elements may depend on some of the internal lenses for aberration correction.

Thank you for your thoughtful answer! The Pentax is rack&pinion. However, my integrated eyepiece/diagonal with M42 screw mount, ALSO FOCUSES. No, I would never jerry-rig or dis-assemble anything.
The Pentax is a 3 element design. I don’t know if the 3 elements are integrated together or spaced in the tube. I understand that at some point, Pentax improved the 3 element, 1000mm f/8 lens to a 5 element design. I suspect it was to improve images at f/8. Of course, that lens would have the Pentax bayonet mount.

Edited by litesong, 29 October 2020 - 02:18 AM.


#104 AnakChan

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Posted 29 October 2020 - 05:55 AM

Any of you folks with the Pentax 100SDUF, 125SDP, and alike have a motorised solution for the helical focuser? I'm hoping to see if anyone knows a maker with an off-the-shelf solution before I start seeking custom brackets for the ZWO EAF (or some other brand).



#105 Spyke

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Posted 08 November 2020 - 12:20 PM

I had a Pentax J60 complete with mount etc back in 2005. Despite knowing what I had, I somehow decided to part with it. I really miss that little mount. It would've been ideal for my Swift 839 that I have now ...

 

gallery_976_3555_1407436512_5370.jpg

 

Later on, I also had a J80 OTA which was a nice performer. I went through a lot of small to medium size refractors back then, looking for some kind of ethereal quality, so needless to say I don't have that one either, but would gladly welcome it back into the fold.

 

Ant


Edited by Spyke, 08 November 2020 - 01:18 PM.

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#106 Haukka

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Posted 05 December 2020 - 03:12 PM

Hello there,

 

I have a 75SDHF, using this little nice scope for deep-sky photography. As it seems impossible to find the original 0.72x focal reducer anymore, does anybody has any idea of what modern reducer could fit this scope, for reducing the focal length and maintaining the coma-free and flat field?

 

Marc



#107 Steve_M_M

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Posted 08 January 2021 - 10:16 PM

We got a 3D printer for Christmas.  My teenage boys are using it, but between uses, I am printing telescope parts.  Today I printed a 60.2mm to 1.25" adapter and a 60.2mm to 2" adapter for my 75EDHF.  I then tapped a 6mm hole for a set screw(which I also printed).  As those of you know who own the 75EDHF and 75SDHF and others in larger aperture, the big issue is in focus when using a 1.25" or 2" diagonal.  This adapter cuts the light path down significantly compared to using other types of over the counter 60mm to 1.25" adapters.

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Edited by Steve_M_M, 08 January 2021 - 10:17 PM.

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