Binoviewers and pst mods

[Moonshane]

I have been happily using my pst stage two mod for a while now and fancied trying Binoviewers.

I am obviously aware of matching the position of the etalon at 200mm inside focus position. This ensures the etalon size makes most use of the aperture.  So far so good.  Here's my mod as used.

To use bvs I need to reduce the optical path (behind the etalon) and have successfully done so as below.

However it has occurred to me that the light cone will be wider, when it hits the blocking filter, in the second set up. If I use a gpc between the etalon and the bf this will presumably narrow the cone? But safely (from the perspective of the gpc - I don't think there's any residual heat post etalon)?

Worst case is that I lose effective aperture?

Has anyone done it this way?

Advice would be appreciated although I should be able to try it pretty soon.

Cheers

Shane

[Moonshane]

Anyone have any advice on this please?

[Merlin66]

The back focus on the PST mod is 200mm from the rear of the etalon assembly...

The size of the blocking filter (5mm) was designed to be as close as possible to the eyepiece/ camera to minimise vignetting.

If it's placed closer to the rear of the etalon then obviously you will get vignetting (this is why some mods go to the larger BF10/15 )

HTH

 

[Moonshane]

Cheers Ken

Just so I understand, this means I will lose field only not aperture,  resolution or brightness?

 

[Moonshane]

A good by product of this is that when using my 18mm BCOs or my 25mm plossl (I have borrowed one!) I get full disk with the 1.7x GPC. Never managed it with my 15mm plossl in cyclops mode!