First steps in a pst mod: installation and removal of ERF

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gabrieli
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First steps in a pst mod: installation and removal of ERF

Post by gabrieli »

I'll be picking up my Baader 135mm D ERF on Oct 3.

I wanted the ERF to do double duty - as a front mounted ERF for my 102 mm app refractor and an internal ERF fro my 150f12.
By a stroke of very good luck, I found that the 135 mm ERF would fit inside the filter cell I had used for the 102mm apo which housed Baader solar film.

Also by good luck, the cell would fit inside the OTA of the 150/f12 with a 3mm gap all around.

The final method of installing and removing the filter cell from the 150mm refractor took some time to figure out.
I wanted to fit the filter cell just outside the first baffle (about 16 inches from the objective). At first, I thought that a sure way of doing it was to remove the objective and install the filter cell through the front. This was possible but likely tedious, since I would likely have to collimate each time.

So, finally, I took a hint from the huge pst mod posted here a while ago showing an Istar refractor with a door in the side.
This would work except I didn't feel like cutting a door in the side of the tube to fit fit my hand into.

Then I thought: why not use a narrow slot?, long enough to fit the filter cell diameter and wide enough to accommodate its thickness. That's what I settled on.

The filter cell has upper and lower pins to secure the cell and allow rotation if reflections are a problem.
I quickly found that the cell rotates like a top. In the final version, I will use black weather stripping on the outside of the cell
to make a good fit with the inside of the OTA and to prevent unwanted rotation and act as a light seal.

Testing this large pst mod may take some time and certainly will not happen in cold weather.

I also have the 102mm mod to play with. This will be a single stack pst mod and a double stack when my 60mm etalon arrives sometime this month.

There is also a double stack LS80 on the horizon with the 60 mm etalon.

Here are the steps involved in cutting the slot:

a - masking tape guide for cutting slot
b - slot cut out with a Dremel + cutting wheel (used up 4 wheels)
c- bare slot
d- slot lined with edge liner
e-hole to secure lower pin on filter mount
f - filter mount showing upper and lower mounting pins (bolts)
g-cover plate when filter not in use
h - filter mount inserted into slot
i-after lower pin is secure in lower mounting hole, filter cell is rotated to face the light path
j- cover plate in place showing shorter outer pins (bolts) and upper filter pin
k- lower pin on filter mount (secured by wing nut when in use)
l-all pins secured

Flocking will be applied after any other issues have been dealt with.




RobBower

Re: First steps in a pst mod: installation and removal of ERF

Post by RobBower »

:rockon: gutsy and very impressive! I cant wait to see how it all turns out! :bow:


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Merlin66
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Re: First steps in a pst mod: installation and removal of ERF

Post by Merlin66 »

Whoooo
That's a neat solution!
Look forward to seeing first light results.


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Re: First steps in a pst mod: installation and removal of ERF

Post by marktownley »

Very nice idea indeed, and well documented!


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swisswalter
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Re: First steps in a pst mod: installation and removal of ERF

Post by swisswalter »

Hi Lou

congratulations, that's the solution, make the slot along the longside not square to the tube side :kiss:


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gabrieli
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Re: First steps in a pst mod: installation and removal of ERF

Post by gabrieli »

The ERF arrived and I almost had a heart attack when I got the impression through the wrapping paper that it was just clear glass. After unwrapping, I realized it had a mirrored surface and kind of bluish.

I may have to fine tune the placement of the ERF/mount in the OTA to maximize the area used. In the position shown in the image above, I slide the mount up towards the objective, and I lose about a cm all around the ERF due to the mount opening being that much narrower than the first baffle. I'm going to slide it to the far end of the cover plate half way to the second baffle to match the light cone diameter.

I just need to flip the cover plate around and drill a 1/4" hole in the bottom of the tube.


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