PST Black Box Mods

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AndiesHandyHandies
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PST Black Box Mods

Post by AndiesHandyHandies »

Hi

As part of doing a set up for various Stage 1 Mods I have done a few things to the black box.

I managed to get the side panel off. Just had to drill of one head so a new set of screws.
Some of the grease on the slide had migrated to the prism faces, or careless handling.

Using it on the Sun with the side off I could see several bright red spots on the inside of the box.

The prism is not silvered relying on total internal reflection so light leaks out on each reflection.
So I flocked the back and bottom of the box and painted the rest with Black2.

The prism is not square to the output side of the box.
Round the web its always reported as being like that.
I found an Edmund Scientific paper on pentaprisms which said they should be square to the light.
But one assumes like filters and so on it has to be offset to reduce reflections.

Looking down on the blocking filter with no eyepiece there seemed to be some reflections off the prism top and bottom faces.

So I had a stop fitted in the front opening to the black box to make sure the input beam was inside the prism face and supress scatter.

This week we had a go at taking of the eyepiece end. Just the top blocking filter part came off.
Despite a blowtorch applied the bottom part stayed put.
So my desire for another stop in the entrance there had to be a bit of a bodge.
Rod found a bit of scrap tube which was a good push fit in the ribbed barrel so a ring was turned off and pushed down.
A repair washer with 6mm hole was turned down to fit and a rubber ring found to hold it in.
I cuntersunk the hole to make a reasonable knife edge and Black2ed it.

With the blocking filter off its easier to see what is happening in the prism.
The input stop clearly keeps the input beam within the prism face.
The top and bottom faces of the prism have a lot of reflection as the beam bounces around the prism from scatter.
So the new stop should stop that getting into the comb blocking filter.

Trying the new set up on the 127mm refractor resulted in a dim off axis refection showing I cannot recall seeing before.
Perhaps some reduction in masking glare?

Remiving the front UV-IR and back Beloptic KG3 did not take it away. So I assume it was from the Bobs ERF in the collimator lens holder, a loose fit as thinner.

The next day I Started with the 110mm Vixen. The reflection was there.
Removed the Bobs ERF from the PST.
Put a Baader 35nm in the front adapter.
A brighter ghost in a different place.

So I put three little slivers of flocking on the edge of Bobs ERF, one on one side and two seperated on the other side across from the first one to make a triangle. To angle it.

Dropped it carefully into the PST Collimator lens space and carefully screwed the holder on.

On the Vixen the ghost dissapeared and the background is inky black, to the eye.

Went back to the 127mm Meade.
Looking down the eyepiece holder lining up there was a bright ghost just overlapping the main image.
With the eyepiece in a fair amount of glare. Not any formal baffling work done yet.

I had to stop at that point.

These solar scopes seem tricky to set up.

Andrew


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Re: PST Black Box Mods

Post by marktownley »

Yup, mods are never straight forward!


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Re: PST Black Box Mods

Post by AndiesHandyHandies »

Hi

The problem with the 127mm was contrail sourced clouds causing veiling glare.

With a clear sky between clouds the view is fairly black. Just a bit of glare opposite the Sun out of field.

Andrew.


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Re: PST Black Box Mods

Post by AndiesHandyHandies »

Hi

I put an Omega Bobs 40nm ERF filter in the front of the PST Black Box in place of the Collimating lens. Same diameter as the lens. Convert to 'Combat'.

I put two bits of flock 12mm apart on the edge on one side and one piece opposite them on the other so its in a stable position.

I did not think about orientation when I put it in but then I thought it should point down the length of the penta prism because of the repeated reflections off either side.

So I moved it today before a review session of the stage 1 Mod.

Looking in with no blocking filter there is a bright reflection where I expect now from the tilted filter and its between the row of side reflections. And fortunately just outside the one visible stop edge.

The problem with Maksutovs and Cassegrains seems to be the inside of the mirror baffle tube.
I have Black2ed the inside of the sloping out bit at the top inside. And given a piece of 180 grit Wet and Dry paper another Black2 coat to finally mask the shiny reflections off the grit. Rolled up in the baffle after a step.

Looking from the back the inside of the baffle is the brighter bit. From the first of many sloping knife edge baffles the inside of rest of the moved forward Collimating lens fixture and the PST is pretty black now. Reflections off the side of the pentaprism seem impossible to stop.

Put baffles on the secondary, to mask the un-blackened correction lenses, and on the top of the mirror baffle, size of the Sun there and moved up a bit. Those and a 21mm baffle in front of the moved Collimator lens mask off the stray skylight almost completely. Just a faint arc, need to check allignments carefully.

Looking from the back with the blocking filter off the inside of the baffle does not seem to be in the optical path fortunately. But I cannot find my small sighting eyepiece barrel to check at the focus its true.

The incoming Sun does glance off the baffle because only a small part of the Sun is visible at f of 1035mm. And there is a violet/blue back reflection off the Bobs filter in the right place.

The Maksutov might be more sensitive to haze than my next PST Stage 1 and Double Stack with Omega Bobs 1.5A pair Stage 2 Mod on the 127mm Meade.

Andrew


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Re: PST Black Box Mods

Post by AndiesHandyHandies »

Hi

Found the old eyepiece barrel with stop in.

With the top blocker unit removed and holding the stop, 4.5mm, about where the focus will be you cannot see the inside of the mirror baffle tube. I assume its masked by the first stop in front of the moved forward Collimator lens.

So as much baffling done as practicable. Apart from a front baffle for better skylight control and limit beam into the scope to the Sun only. Which has to be filtered of course!

Re-fitted the Barlow unit holding the Collimator lens in the Vixen eyepiece T2 adapter tube. A bit better centred as the slight skylight getting past the added secondary and primary baffle stops is a bigger arc. Perhaps a bit of nudging needed, like secondaries in big Newtonians.

Done?

Andrew.


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Re: PST Black Box Mods

Post by daslolo »

AndiesHandyHandies wrote: Wed Jul 17, 2019 12:07 pm I put an Omega Bobs 40nm ERF filter in the front of the PST Black Box in place of the Collimating lens. Same diameter as the lens. Convert to 'Combat'.
What is 'combat' ?


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Quark + Orion 120mm + beloptik
LX65 8" ACF
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Re: PST Black Box Mods

Post by AndiesHandyHandies »

Hi

Its a play on 'Combo'.

Andrew


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Re: PST Black Box Mods

Post by daslolo »

and what does it combine?


PST on its way to modding heaven
Quark + Orion 120mm + beloptik
LX65 8" ACF
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