Baader 1.125x GPC correct orientation. F/8 to f/10 conversion PST Mod.

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Wednesday 9th Feb 42´3F, heavy overcast with rain.

As mentioned yesterday, I have removed the Baader 1.125x binoviewer GPC from just behind the PST etalon.  I had trapped the GPC flange using the PST etalon body after enlarging the AOK Swiss rear, etalon adapter's baffle. Now it seems I have been using the GPC reversed to its correct orientation. 

It had never occurred to me to check the GPC's orientation until I removed it. I have never owned the binoviewer. Which the GPC was designed for. So I never saw it installed in actual use.

Most users of the Baader 1.125x GPC in this context will be converting their f/8 to f/10 to match the PST etalon's needs.

While I was using the GPC to increase the image scale in my 150mm f/10 iStar H-alpha refractor. With the intention of spreading the PST etalon's sweet spot. All I was really doing was looking at a smaller area of the image at the image plane. 

Sadly, the greatly increased scale had found the limits of the presently poor, winter seeing conditions. Low sun with a much greater light path through the Earth's turbulent atmosphere. Made worse by the proximity of the heated, house roof to my south.

This image [left] was borrowed from Baader's website for educational purposes. It shows the "nose" of the GPC should really face the telescope objective. Not the camera or eyepiece!  I might have been introducing optical aberrations by reversing the GPC. Though it was being used in monochromatic light for solar work. Which would be unaffected by chromatic aberration. Other aberrations might still have been an issue. The entire H-alpha etalon-filter system is removed for lunar imaging.

I can, of course, reverse the GPC if it is worthwhile. This will need the GPC flange to be trapped behind the AOK Swiss baffle. Instead of in front of it. Unfortunately the weather has returned to normal. i.e. Overcast and wet! So I shall have to be patient before I can see the effects of GPC reversal.

I had a trial fitting of the GPC reversed in the baffle of the AOK Swiss, rear etalon barrel. The convex element of the GPC contacted the rear of the PST etalon body when it was screwed in. Grr! Being cautious, I had placed a pad of tissue to prevent glass to metal contact. Don't try this at home without at least a 4-5mm spacer to push the GPC away from the etalon housing! Consider yourself warned of the potential for serious damage to the GPC's front element if you ignore the problem!

Adding an extra, full disk baffle [to carry the GPC within the PST etalon housing] will prevent the following 2" push fit extension from seating fully. Best to make a baffle to fit inside the empty, tubular nose of the following 2" extension. With the baffle inset far enough for plenty of clearance for the GPC's nose. 

The inside of most 2" extensions has a standard 2" [M48 x 0.75mm] filter thread. Now I can't find an M48 male to T2 female without an outer flange. The M48 needs to be continuous to allow enough inset.

As I write this the sun is shining as the sky is becoming clear.  Worth a try at imaging? Sun soft and low. With continuous racing cloud from the west. Hopeless but still managed a couple of soft images. Just for the record.

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