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Ceph and Cass

A different slant on a stage 2 PST-mod.


Merlin
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The bane of stage 2 modders is the dreaded LOCTITE, but it occured to me that we can do a stage 2 mod without removing the black box in its entirety.

We can saw/mill off about two-thirds of the box and cover the remainder with an aluminium plate with a hole to take a focuser. But could the vibrations from sawing decontact the etalon? Any ideas?

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No Merlin, bad idea. The locktite is a PITA, but its not impossible to dissmantle the pst. just harder than it needed to be. Once you cut your black box you can never ever put the pst back together again. I can assemble my pst back to its original configuration in less than 5 mins, and convert it to a stage 2 in the same amount of time. Keep your options open. You may want to sell the pst someday and get something better.

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I haven't found a PST yet in which the etalon could not be separated from the black box....the box held in a padded vice and the HD Boa to remove the etalon. It's more difficult (sometimes) to remove the etalon from the gold tube.

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Thanks chaps. I have two PSTs, one double-stacked with a LS50F and the other a stage 1 mod. Regarding the latter, Ken( Merlin66 ) has often stressed that we should get away from the pentaprism, a point most of us would wholeheartedly agree with!

It doesn't really matter to me how I do this, including leaving part of the blackbox attached to the etalon, thus avoiding strap-wrenching the etalon and having to acquire a brace of adaptors.

Done properly, it would be a neat job and I could retain the internal finder arrangement, albeit with some modification. I don't intend to sell either of the PSTs, so I would only be adapting them for my own use. I might just give it a go on the stage 1 PST.

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If you feel that you want to try this, then by all means go ahead. Post some pics of the mod when its finished.

I don't think there is any risk of decontacting the etalon providing you do it carefully. You might want to cover the etalon lens to avoid any risk of damage from metal filings etc.

I was just doing that but you beat me to it. :laugh:

Edited by allcart
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Merlin,

I think the lack of answers/ comments reflects the lack of first hand knowledge....I've never heard of anyone trying this type of mod..

The etalon is sensitive to shock and can certainly be de-contacted following a drop...If you take your time and apply some caution it should go OK..

Double check the amount of back focus you will need for the focuser, BF and camera etc.

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Have you seen my stage 0.5 mod, Merlin?

You might find a focuser a little shorter than the one I have, but not by much I'd imagine, and there's not a huge amount of backfocus left to play with after that even though the focuser goes straight on the back of the etalon, especially with a diagonal in for visual use. Without the diagonal there's a little more room to play with, but only 30mm or so.

James

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In fact, I've just measured the adaptor I made to take the PST eyepiece holder (the entire thing) and fit it into the 1.25" focuser. It adds exactly 30mm to the optical path and in fact I need to take it down a bit as I've discovered I can't reach focus with all the kit I'd like to use. 20mm might be a better length, though I'll probably take it down to 25mm first and see how things go.

My focuser only adds around 90mm to the optical path from the end of the etalon itself, so unless you can find a very short focuser you're not going to end up with very little of the black box left.

James

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I sense that you really want to try this out, so do let us know how it goes. You may need to choose your focuser very carefully to allow it to work out. You may also need to cut down the actual drawtube at the inner end. My adaptor is 9mm thick from memory, some of which is obviously needed to allow the etalon to screw into it, but on the other side it is hollowed because at full inwards travel the focus tube extends beyond the end of the focuser body. If you're using the PST black box there may well be no clearance for that.

I honestly think you're going to make life far harder for yourself than it need be, but human endeavour should not be confined to what other people think is possible :D

James

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I sense that you really want to try this out, so do let us know how it goes.

I honestly think you're going to make life far harder for yourself than it need be, but human endeavour should not be confined to what other people think is possible :D

James

Couldn't agree more.

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If it completely goes pear shaped, I have a spare black box which will get you back to original spec.

As do I, so if it doesn't work out you won't end up with a useless scope. Not unless you damage the etalon, at least :)

James

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