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Pentax Telescopes & Mounts

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#176 Nippon

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Posted 05 August 2022 - 11:10 PM

I will add anothers informations regarding the pentax 100mm series design for complet steveP post as i have the two versions of this series. SteveP has fully right, construction is completely different between the Pentax 100 and Pentax 100ED, no chrome on the ED series only; black anonized aluminium but it stays like this from the begining until the end the series as i have got a friends who has a late ( after 1984) version of the Pentax 100 Achro and it was also fully chrome

 

I do not have the official explanation but maybe there are two ways:

 

- First cost killing, pentax will make a compromise for winning money on this scope as producing ED glass at high level precision must cost more money especcially at begining ED period and if you look at the selling price, ED version difference cost was not so much than "normal" version.

 

- Second is regarding balancing scope and overall weight, ED glass is more heavy than normal glass so if you ad the chrome focuser from achromat who is really heavy you create an unbalancing and heavy scope and we do not forgot that's only 100mm scope.

 

Anyway this scope family was very good, regarding the 4" achromat version it is probably the best 4" that i have test.

 

Pictures of this two scope.

Are you talking about the chrome versus black drawtube? If so I may have a third theory. I had a Celestron Firstscope 80 back in the late 80s and a friend had a Celestron SPC80. The optical tubes were identical except the Firstscope had a brushed aluminum drawtube and the SPC 80 had a chrome drawtube. I reasoned at the time since the Alt/Az mounted Firstscope would be more likely to see some daytime use it had a dull brushed drawtube finish to keep glare out of the users' eyes.


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#177 Kitfox

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Posted 11 February 2023 - 09:18 PM

I’m sure this is the VCD’s grandfather. Have you ever done any photography with it?  The Vixen was notoriously and perpetually out of alignment. A real shame…
 

 

I've recently added a new Pentax to the collection:  

 

Pentax 100 EDUF

 

400mm focal length, 100mm aperture (f4), 4 optical elements in two groups in a Petzval-like configuration, with ED glass.  First manufactured in the 1980's, the EDUF and its more recent siblings are also known as Tsuchinoko, after the mythological Japanese snake known for its short, stout body.  Tsuchinoko...REAL!    

 

I'm determined to use this both visually and for imaging (4" of aperture with potentially a 6 degree fov, without the need of flatteners or additional reducers cannot be resisted.)  These earlier versions of the Pentax astrograph likely exhibit more chromatism than the newer Pentax 100 SDUF and modern f3.8 $6000USD Vixen VSD100 version, which I haven't tried yet.   I expect some of the differences between EDUF and SDUF to be similar to those of the Pentax 75 EDHF vs SDHF.   

 

For visual use, I ordered a Baader M84 (Zeiss format) to M68 adapter, which will work on both my 75 EDHF and this 100 EDUF and then I will use a low profile M68 format 2" visual back/eyepiece holder to get additional inward travel over the factory adapters.   Previously, I was using a machined 2" to 2.5" adapter to work with the Pentax accessories, but I think the M84 to M68 adapter will be a more elegant, low profile solution for using standard 1.25" and 2" eyepieces.  My adapter should arriving today and cut at least 30mm of light path length.

 

I knew this would fail, but just had to try:

 



#178 ccwemyss

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Posted 07 February 2024 - 09:56 PM

I've confirmed that the screw thread of the counterweight shaft for the mount used by the Pentax 100 and 85 achromats is a JIS M18X2.

 

The tap just came from McMaster, and it nicely chased the dirt out of one of my weights. Since I haven't seen this spec anywhere else, I thought I would document it here. 

 

I'll be using it to adapt some 3 lb iOptron weights, to augment the two that are on my 85 mount. 

 

Chip W. 


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#179 photoracer18

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Posted 08 February 2024 - 03:49 PM

I owned an 85 F12 and a 75EDHF at different times. I owned the 85 at the same time the late Bruce owned one while he worked for Marty at C7. I watched Shumaker/Levy hit Jupiter with my Pentax 85 and saw the flash of one explosion around the limb of the planet and the dark marks in the cloud layer where different pieces had hit. Now while I owned it I found out that PentaxUSA in Denver had a set of 85mm F9 ED optics that they were willing to remake my OTA for at a cost of $900. But frankly I did not think paying as much as I paid for the scope was going to get that much better performance. I bought it originally from Sanders Lewelan when he came to Wash DC to run FONZ (Friends Of the National Zoo). He ended up with a house in Chevy Chase  (too many trees) so sold the Pentax and his C8 in favor of a Questar and a small Tak if I remember so he could transport them easier to NOVA star parties. I sold the Pentax when Gary Hand came to me ( before I worked for him) and said he had a buyer in Japan that wanted one back. In return Gary found me my first Dob a Sky Designs 14.25". Always liked Pentax scopes and eyepieces. I was likely the only owner in NA that owned a Pentax 60XL eyepiece (along with all the other XL ones). While I did not own any of the big 150-250mm Pentax APOs that it fit I did have an adapter made for my rare Borg 150ED so I could use the eyepiece. Markus Ludes has a review of that somewhere in the archives here. I sold it a few years later to a lady in Italy who had a Pentax 200 APO if I remember correctly. List on that eyepiece was $3995. I won it off eBay for $400 from Henry's. It had gone back to Japan to be refurbished and they did not know what to do with it when it returned. When I got it I found it connected to a Pentax scopes with an 84mm thread. Just happened the original focuser on the Borg, the helical one, had an 86mm thread on it. 

The 75EDHF became my travel scope for a while. I adapted a small camera tracking GEM once sold by Pocono Mountain Optics  (I think it was called a CameraTrak and made by Nihon Seiko) and with that I once used it to view Omega Centauri from the Bahamas. Now my travel rig is a WO FLT98 FPL-53 triplet on an iOptron HEM15. Times have changed.


Edited by photoracer18, 08 February 2024 - 03:53 PM.


#180 photoracer18

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Posted 08 February 2024 - 03:57 PM

I had two of the older 60 mm x 800 mm Asahi Pentax refractors and really enjoyed them. In part, this was because I had found two odd ball Burgess Optical diagonal eyepiece holders that fit the non standard visual back threading of the A-Ps visual back so I was able to use 1.25 inch eyepieces..

 

I briefly had a J60 but it had a 0.965" visual back and drawtube and I preferred the views of the older Asahi-Pentax..

 

What is the difference between Asahi-Pentax and Pentax, what the history there?

 

Hon

They changed from one name to the other in 1957 I think.



#181 ccwemyss

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Posted 08 February 2024 - 10:13 PM

My '76 and '79 refractors both say Pentax / Asahi Opt. Co. Japan.

 

Chip W. 



#182 SporadicGazer

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Posted 09 February 2024 - 12:06 AM

I don't know how the company and equipment were branded for astronomy, but in the photography world in the 70's the cameras were branded "Pentax" and were made by Asahi Pentax.



#183 RichA

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Posted 09 February 2024 - 12:09 AM

I owned an 85 F12 and a 75EDHF at different times. I owned the 85 at the same time the late Bruce owned one while he worked for Marty at C7. I watched Shumaker/Levy hit Jupiter with my Pentax 85 and saw the flash of one explosion around the limb of the planet and the dark marks in the cloud layer where different pieces had hit. Now while I owned it I found out that PentaxUSA in Denver had a set of 85mm F9 ED optics that they were willing to remake my OTA for at a cost of $900. But frankly I did not think paying as much as I paid for the scope was going to get that much better performance. I bought it originally from Sanders Lewelan when he came to Wash DC to run FONZ (Friends Of the National Zoo). He ended up with a house in Chevy Chase  (too many trees) so sold the Pentax and his C8 in favor of a Questar and a small Tak if I remember so he could transport them easier to NOVA star parties. I sold the Pentax when Gary Hand came to me ( before I worked for him) and said he had a buyer in Japan that wanted one back. In return Gary found me my first Dob a Sky Designs 14.25". Always liked Pentax scopes and eyepieces. I was likely the only owner in NA that owned a Pentax 60XL eyepiece (along with all the other XL ones). While I did not own any of the big 150-250mm Pentax APOs that it fit I did have an adapter made for my rare Borg 150ED so I could use the eyepiece. Markus Ludes has a review of that somewhere in the archives here. I sold it a few years later to a lady in Italy who had a Pentax 200 APO if I remember correctly. List on that eyepiece was $3995. I won it off eBay for $400 from Henry's. It had gone back to Japan to be refurbished and they did not know what to do with it when it returned. When I got it I found it connected to a Pentax scopes with an 84mm thread. Just happened the original focuser on the Borg, the helical one, had an 86mm thread on it. 

The 75EDHF became my travel scope for a while. I adapted a small camera tracking GEM once sold by Pocono Mountain Optics  (I think it was called a CameraTrak and made by Nihon Seiko) and with that I once used it to view Omega Centauri from the Bahamas. Now my travel rig is a WO FLT98 FPL-53 triplet on an iOptron HEM15. Times have changed.

Interesting, except the explosions on Jupiter were out of sight for people on Earth, I think an orbiter saw one though.



#184 ccwemyss

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Posted 18 February 2024 - 10:00 PM

It turns out that a 3lb iOptron counterweight (with a 20mm bore) is almost exactly the same size as the original Pentax 85 counterweights. I used an M18x2 JIS tap from McMaster to make an insert that is glued in with epoxy, and it fits just about perfectly. By a wonderful coincidence, when the two weights that came with the Pentax 85 are in their balance position, all that is needed to switch to the Pentax 100 is to spin this one on, right up to them. 

 

Counterweight - 1.jpeg

 

The only thing left is to sand it down and paint it with some Hammerite to make it blend in better with the others.

 

Chip W. 


Edited by ccwemyss, 18 February 2024 - 10:01 PM.

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#185 ccwemyss

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Posted 20 February 2024 - 05:29 PM

I can confirm that the selection on Precise Parts for the Pentax 85 focuser does fit perfectly (works for both the 85 and 100). I bought a thin lock ring from them, because I have a 2" diagonal that happens to have exactly the same thread. It normally spins on to where it snugs up pointing straight down. With the lock ring, I can get it to snug up at any angle now. The diagonal lets me use wider field 2" eyepieces for those very extended objects. 

 

They could also make an adapter to enable using a Baader 2" diagonal on the focuser, as they have all of those specifications in their list of outputs. 

 

Note that the path length for a 2" diagonal may be too long for some short fl eyepieces to reach focus.

 

Chip W. 


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#186 Dave Novoselsky

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Posted 20 February 2024 - 06:26 PM

Hi,

 

as I have posted in "A small beauty arrived" I have the 75 EDHF with the MS-3n now completed.

 

attachicon.gif P1030172.JPG

 

I am very happy with this.

 

best reagrds  Michael

Beautiful.  I’m envious.




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