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風来坊@真幸福知

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GSO 0.5x reducer (for 2" eyepieces) modification for photography with GS-150CC (cassegrain CC6)

GSO 0.5x 2 inch reducer

My 6 inch Cassegrain GS-150CC has f=1830mm. It's too long for full Moon with APS-C, and too slow (F12) for DSOs. (also too long for guiding with old Vixen GPD mount)

Then I began to think about a focal reducer at a reasonable price.

AstroStreet, a shop in Japan, has a 0.5x reducer (produced by GSO, Taiwan) at ~5000JPY. It's originally for eyepieces and when I tried on my camera, I couldn't get focus. The focal position was too into the tube. I needed to shorten the back focus of the reducer so that the focal position moves back.

I made a short mount adapter from Kenko's product. It has a very short camera side ring and the back focus is adjusted by T2 rings in the front for various camera mouts. I picked up ones for Fuji-X and Nikon-F (my camera is Fuji) and combined Fuji-X body side ring and Nikon-F T2 ring, then it made this:

f:id:cheonghongsa:20210513155719j:plain

With this, I got the focus! and the image scale was 0.47x of the straight prime focus. Maybe this is too much reduction and the peripheral zone is much degraded.

f:id:cheonghongsa:20210513161142j:plain

I gave another try by putting the reducer's lens into the T2 ring for Fuji-X. It is much longer than that for Nikon, and the inner dia. just matches the reducer's lens dia.!

From the front:

f:id:cheonghongsa:20210513155522j:plain

and back:

f:id:cheonghongsa:20210513155545j:plain

Now the reducer lens is just in front of the camera's mount. The back focus to the sensor is only ~20mm.

It made this↓ The scale is 0.74x.

f:id:cheonghongsa:20210513161732j:plain

0.74x ... Humm. Maybe I will put a few millimeters of spacer at the back of the reducer, then it gives a bit more reduction, like ~0.6x.

Anyway, I tried this reducer on stars. An example is like this:

f:id:cheonghongsa:20210625082717j:plain

M57: GS-150CC, 0.74x DIY reducer, Sightron LPR-N filter, Fuji X-T20 ISO6400, 18x2min.

It seems working pretty well :-)

GS-150CC connection arrangements

Here's what the back end arrangements with GS-150CC are... Note that I usually use 50mm+25mm extension tubes that came with the scope. (It gives the focus with 1.25" diagonal mirror and eyepieces).

 

Straight prime focus

f:id:cheonghongsa:20210513163059j:plain

f:id:cheonghongsa:20210513163217j:plain

(2"-M42 AD/M42 ext. 15mm/mount AD)

 

With GSO 2" 2x ED Barlow (2" ext. tube added)(2.2x)

f:id:cheonghongsa:20210513163130j:plain

f:id:cheonghongsa:20210513163240j:plain

(2" ext./Barlow/2"-M42 AD/M42 ext. 15mm/mount AD)

 

The reducer (0.74x)

f:id:cheonghongsa:20210513163153j:plain

f:id:cheonghongsa:20210513163302j:plain

(2"-M42 AD/M42 ext. 15mm/reducer installed in Kenko mount AD)

END.