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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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#108 coinboy1

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Posted 28 April 2021 - 09:32 PM

Got me a Pentax 75 SDHF and MS3n mount. 

 

What a wonderful combination. The quality is amazing, up there with Takahashi. Optics are very nice and focuser is silky smooth. Much better than Takahashi focuser (based on my experience).

 

 

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#109 ccwemyss

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Posted 28 April 2021 - 09:45 PM

Just yesterday I learned that preciseparts.com has pretty much all of the Pentax focuser thread sizes in their CAD database, and will make an adapter to convert to almost anything (including a generic 2" mount). They're not cheap. But it's an option I wasn't aware of when it was being discussed earlier. 

 

Chip W. 



#110 Volvonium

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Posted 28 April 2021 - 11:31 PM

Baader also has a direct thread-on 2" compression ring adapter for the scope, but it is special order.    I don't think I've ever seen the reducer in the wild; likely an item that pops up only once every few years.

 

Congrats on the scope!  I love my Pentax.  

 

t0HE7q9h.jpg


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#111 photoracer18

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Posted 30 April 2021 - 07:22 PM

When I got my first Pentax, the 85mm achromat I had this issue with the weird hybrid diagonal. But I found a solution using an old Meade eyepiece projection adapter in that a part slid in perfectly together and made the focuser tube 1.25". Later when I bought a Pentax 75 EDHF it came with American sized barrels.


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#112 Defenderslideguitar

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Posted 30 April 2021 - 08:27 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.

Steve   nice solution. This is a fortuitous thread for me to run into because I just got one of these Pentax EDHF III 75mm fl 500  today and I cannot do anything with it..      It did not come with any diagonal ..... I will need to fix the in focus issue apparently as others already knew. Not sure what to do or what to buy. I put a two inch diagonal on it with a 1.25 adapter   and it will not focus on a house 200 feet away.

 

I am okay addressing this issue but I do not want to buy stuff and do trial an error if other folks know what to do already A couple  of questions for everyone if I may.  What is the little green diagonal in Steve's pic? Is that the original? It sure looks original in lovely Pentax green It seems it is 1.25 but went into a a two inch focuser? Anyone have any idea why they might make a scope with obvious in focus issues and not provide a solution? How did these scope come for sale when new  and was this an issue then?Or is it that the original design of these scopes did this on purpose for a reason that eludes me? 

 

I would like to buy a correct diagonal and what ever else I will need if I am going to keep this Pentax.


Edited by Defenderslideguitar, 30 April 2021 - 08:36 PM.


#113 Defenderslideguitar

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Posted 30 April 2021 - 08:42 PM

Got me a Pentax 75 SDHF and MS3n mount. 

 

What a wonderful combination. The quality is amazing, up there with Takahashi. Optics are very nice and focuser is silky smooth. Much better than Takahashi focuser (based on my experience).

Nice scope   and it rides well on that mount

Is that an original diagonal? Is it 1.25 and does it go into a 2 inch focuser?  Thanks



#114 ccwemyss

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Posted 30 April 2021 - 09:03 PM

The original green diagonal is 0.965" and, at least on my Pentax 85, it has a 37mm barrel. The only place I found something compatible was a T-adapter for a Nikon microscope (which you can still find on eBay). From that I was able to attach a Baader T to 1.25" adapter. But , with a diagonal, it didn't have enough in-focus for every eyepiece. (I eventually found a Pentax 1.25" diagonal.) Pentax used different sizes of focuser (e.g., the 75 SDHF is 60.2 mm, while the 85 is more like 50) and then corresponding step-down rings to get to the 37mm opening.

 

What are the measurements of your focuser opening? Can you post a picture? Precise Parts does list the 75 SDHF 60.2mm in their CAD database. 

 

Chip W. 


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#115 Defenderslideguitar

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Posted 30 April 2021 - 09:09 PM

Thanks Chip    I will look into it. I saw the ad  and thought this will have great optics in a very portable package. The scope exudes quality   and it is cool 

I thought it will be  a wonderful wide field  sweeper.


Edited by Defenderslideguitar, 30 April 2021 - 09:48 PM.


#116 Steve_M_M

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Posted 01 May 2021 - 09:17 AM

Steve   nice solution. This is a fortuitous thread for me to run into because I just got one of these Pentax EDHF III 75mm fl 500  today and I cannot do anything with it..      It did not come with any diagonal ..... I will need to fix the in focus issue apparently as others already knew. Not sure what to do or what to buy. I put a two inch diagonal on it with a 1.25 adapter   and it will not focus on a house 200 feet away.

 

I am okay addressing this issue but I do not want to buy stuff and do trial an error if other folks know what to do already A couple  of questions for everyone if I may.  What is the little green diagonal in Steve's pic? Is that the original? It sure looks original in lovely Pentax green It seems it is 1.25 but went into a a two inch focuser? Anyone have any idea why they might make a scope with obvious in focus issues and not provide a solution? How did these scope come for sale when new  and was this an issue then?Or is it that the original design of these scopes did this on purpose for a reason that eludes me? 

 

I would like to buy a correct diagonal and what ever else I will need if I am going to keep this Pentax.

Barry, welcome to the club!  I find the 75EDHF equal to my FS78 with a bit more color if you look very closely.  I don't think Pentax thought there were in focus issues.  The OEM .965" Pentax diagonal that comes with the scope focuses with all their .965" eyepieces.  I think Pentax also made a 1.25" diagonal for this scope that also focuses with their older 1.25" eyepieces.  So, their repsonse would be something like, "well it works with our stuff  smile.gif "

 

I would be happy to make you an adapter as shown in my photo above.  I just checked and I have some black PLA filament which would look nicer than the gray I used above (or the red I used for my draft).  I could also make a 60.2mm to 2" adapter for you.  I have been using my Lumicon 1.25" diagonal, so let me check later to make sure my 1.25" AstroTech and 2" Televue come to focus with these.  I have never really checked once the Lumicon worked.


Edited by Steve_M_M, 01 May 2021 - 09:41 AM.

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#117 Steve_M_M

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Posted 01 May 2021 - 09:24 AM

Here’s my little Pentax collection of old and older eyepieces.  Also, the weird 37mm to .965” diagonal and it’s large long adapter are pictured. 

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#118 PawPaw

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Posted 01 May 2021 - 09:45 AM

Here’s my little Pentax collection of old and older eyepieces.  Also, the weird 37mm to .965” diagonal and it’s large long adapter are pictured. 

Steve.....That is a lovely set of Pentax eyepieces.......they look exactly like my GOTO eyepieces from the same era.  Makes me think they used the same source which could have been Pentax?

 

Cheers

 

Don


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#119 Defenderslideguitar

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Posted 01 May 2021 - 09:52 AM

Steve thanks so much. I would love to have some sort of adapter. Now the scope I just got has a 2.5 to 2.0 adapter right now. I would like to be able to use some kind of adapter from that to 1.25 and use a 1.25 prism diagonal. or use any adapter that gets me to 1.25 But this is all a work in progress.  While we  gravitate towards getting original parts for restoration and well originality    I just like the idea of using anything that works for this scope .  I love this overly cool and convenient small scope with the great lens  it is almost like with the dew shield moved in you could put this is your pocket...not really but you get the point. I would think it might be a good wide field sweeper but I just do not know yet..

 

 

 

I know these were pretty good for astrophotography  I guess there are ways to get some T adapter on a dslr like my cannon t2i


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#120 Steve_M_M

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Posted 01 May 2021 - 09:59 AM

Barry, can you post a picture of the 2.5 to 2 adapter you have?  Have yoiu tried just inserting a 2 to 1.25" adapter in there and see if it works?  My guess is not enough in-focus.



#121 coinboy1

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Posted 01 May 2021 - 10:30 AM

I have some original Pentax adapters and Pentax 0.965” diagonal I am willing to sell if anyone is interested. I have a Pentax 1.25” diagonal that I will keep with the 75SDHF.

#122 Defenderslideguitar

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Posted 01 May 2021 - 10:37 AM

In focus is a problem yes...  I have tried only the 2 inch diagonal into the 2 inch adapter that came with the Pentax   that brings it from 2.5 to 2.0  

 

some pics of what is here with it...

 

first the lovely Pentax

second the closed dew shield pic'

 

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#123 Defenderslideguitar

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Posted 01 May 2021 - 10:46 AM

adapter 2.5 to 2.0

 

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#124 Defenderslideguitar

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Posted 01 May 2021 - 10:50 AM

Yes  I would be happy just to get it working  with 1.25....some kind of 1.25 prism diagonal that works with the short in focus issue    will  need to get adapters that work    this is a work in progress  so  


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#125 ccwemyss

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Posted 01 May 2021 - 11:20 AM

Have you tried putting a low profile 2” to 1.25” adapter directly into the 2.5” to 2” adapter, and then use a 1.25” diagonal? The 2” diagonal adds a lot more length to the optical path. 
 

Chip W.


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