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Question: Counterweight shaft thread size of the Pentax 100 (non ED) Green mount

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#1 vvalmiki

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Posted 16 February 2021 - 11:38 PM

The thread size that screws into the mount, obviously it is metric and I have random metric bolts I could use to figure out.

 

But asking is easier.

 

I thought I got one with my purchase....either I lost it or I never got one.

 

Regards, Vinay



#2 ccwemyss

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Posted 17 February 2021 - 12:18 AM

My calipers place the diameter at 13 mm or 0.7".

 

The 85 uses the same mount. (They have the same tube diameter.) But the 100 usually came with the drive.

 

Chip W. 



#3 vvalmiki

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Posted 17 February 2021 - 12:52 AM

so an M13 ??

 

regards, Vinay



#4 ccwemyss

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Posted 17 February 2021 - 10:25 PM

Sorry, I totally misread the dial. That's what I get for trying to measure something after midnight, and a long work day.

 

I should have said 18mm or 0.7".  M13 isn't even a normal size (and would be just over 0.5").

 

The pitch, however looks like 2mm, which isn't standard. From what I can find, M18 standard pitches are 2.5 for coarse and 1.5 for fine. 

 

Chip W. 



#5 vvalmiki

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Posted 18 February 2021 - 11:23 AM

Thanks Chip,

 

I wonder if anyone has one for sale.

 

Regards, Vinay



#6 ccwemyss

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Posted 18 February 2021 - 12:42 PM

Pentax parts are very hard to find. I've been looking for a motor drive for a long time, with no luck.

 

If you loosen the set-screw on the conical reducer at the end of the Dec axis, I think it unscrews. You could take it to a machinist and have a shaft cut with threads to match. The Pentax shaft uses the same threads, and threaded counterweights, which are also hard to find. The 85 uses two smaller weights, and the 100 had two longer ones, so they aren't interchangeable. If you have a shaft custom-made, you can get a smooth one in a diameter to take standard weights.

 

Chip W. 



#7 photoracer18

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Posted 22 February 2021 - 07:29 PM

A motor drive for that big hole in the center of the Pentax 85/100 mount tray is hard to find. Not sure how many ever made it to the US as they had to be redesigned for the US market from 100v 50Hz to 115v 60Hz. At the time I acquired my 85 it was during the period when they either quit the US market with scopes or when they lost their only major dealer, Abercrombie & Fitch. I know at the time that Pentax USA in Denver had a complete lens and cell for the 85ED in stock. but the cost of cutting down my tube and converting it was equal to what I paid for the scope ($900) originally used.



#8 ccwemyss

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Posted 22 February 2021 - 08:05 PM

The drives were standard with the 100, but an option for the 85. As far as I know, none of the buyers of the 85s we sold from the shop where I worked, while I worked there, took the option (but we only sold a few).

 

There wasn't any conversion required - the inverter took 12VDC and output 100VAC@ 50Hz. But you need their inverter - you can't just plug the motor into US AC power. 

 

Chip W. 




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