Slow progress on PST mod

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gabrieli
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Slow progress on PST mod

Post by gabrieli »

My two PST etalon adaptors arrived from aokswiss (about 7 business days to Ontario, Canada from
Switzerland) and , so far, I've easily separated the gold tube with etalon attached from the black body. I know that separating the etalon from the gold tube is more difficult.

**Is it possible to separate the etalon by holding the gold tube by hand and using a strap wrench
around the protruding part of the etalon or do I have to use clamps to secure the tube?


Also, I remember seeing a video a while ago about the PST etalon, by Mark Townley.
Mark, if you are reading this, I found your technique of achieving the special "-200mm"
condition without cutting the tube to be a huge help to some of us that might not want to do invasive surgery or that are new to doing mods.

That technique involved removing the collimating lens from the etalon, exposing complimentary 48mm (2 inch) threads on the etalon body and the etalon housing. Then, 48 mm threaded extensions can be used to easily extend the collimating lens' distance up into the tube until you reach the "-200mm" distance. So clever.

Unfortunately, the scope that this production is meant for (Istar 150/f12) has a defective lens.
I sent sample images to Istar and and was advised to send the lens back (happening Monday, May 13) for testing or replacement.

I'll say more as things happen.


colinsk

Re: Slow progress on PST mod

Post by colinsk »

I have found PSTs to be variable. Mine was able to be disassembled with no strap wrench. But others have a thread locker on them. The only thread lock on mine was the threads that heals in the collimating and re-imaging lenses.


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Re: Slow progress on PST mod

Post by marktownley »

I found that I needed two boa wrenches to separate mine one on the tube, one on the etalon housing. Make sure you remove the knurled rubber ring and the tuning ring that it sits on too, you'll find it easier to undo then, and there's no chance of damaging this ring (its only held on with one little screw).

Glad you found the extension trick useful btw :)


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Re: Slow progress on PST mod

Post by Allcart »

Just a word of warning about Mark's method. First let me say that there is nothing wrong with Mark's method of reaching the -200 by moving the etalon lens in its metal cell, but as explained in the video, the threads on the etalon lens cell are not a perfect match for the threads on the nosepiece. I tried attaching the etalon lens cell to the front of the nosepiece a few days ago and it worked fine.

Unfortunately when putting the scope away, I stood it upright on its dewshield. I was horrified to hear a loud clatter, then a chink, and sound I can only describe as like when a spinning coin comes to a slow stop on a table. It went on for quite a few seconds, but in that time I realised that the etalon lens cell had dropped down the tube of my 6" frac and had landed on the objective lens.

I removed the objective and examined it fearing the worst, but luckily there was no damage to the objective or the etalon lens.

Moral of the story is to always make sure everything is secure.


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Re: Slow progress on PST mod

Post by marktownley »

I always use a metal ruler to 'nip' it tight...


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Re: Slow progress on PST mod

Post by Allcart »

Definately a good idea Mark, Pity I didn't think of it at the time. I just used light finger pressure, but forgot to remove the pst assembly before I stood the scope on end. It was a scary experience and very nearly a costly mistake. Not one I will be making again any time soon.


Allan
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