psm40 optical path ds mod

[daveg]

q for the pst modders

I have a psm40 - are the pieces of glass at each end a lens system like the pst etalon. Im doing tests with this at mo and results are tantalisingly good. I have removed the tmax and front erf and taped whats left pf the psm40 to the end of the draw tube of the focuser on my pst-b120. while i get more detail (darker fils and much better ARs) theres something distorting the image badly. was thinking of taking rear lens off psm to get some sort of collimated beam heading towrd pst etalon, thats if it is a lens and not part of the etalon itself?

dg

[Merlin66]

Terminology...
I assume we're talking about a SM40 front mounted etalon filter??
There are no "additional" lenses on this etalon, just the bare optics. They are designed to work in a collimated beam so in your set up they will be "compromised" trying to work at f7 or what ever....
I did some trials a couple of years ago using a TV Big Boy barlow as a collimating lens infront of the SM40 with limited success.
There's a guy in mexico (!?) who has used a doublet as a collimator (increased physical length etc) and seems to get good results.
You need to rig up a collimated beam to get the benefits from the SM40...that then can be double stacked with the PST etalon.

[daveg]

OK that exlains it. So in fact another pst would be more useful for this than the front mounted psm40, if you got them as clsoe as possible together.

thanks as usual Ken for your vast knowledge on these matters

dg

[Merlin66]

Yes, a double stack using two PST etalons can and does work. I machined up a special adaptor to allow me to mount them very close together....I found matching the sweet spots and getting repeatable results very difficult... a combination of a SM60 and the PST was much easier!!
(There's a guy in HK who has fitted a second PST etalon onto a PST and got some good results)

ken