SW 50mm RACI Finder Scope for Imaging

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Harmonious
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SW 50mm RACI Finder Scope for Imaging

#1

Post by Harmonious »


I've converted a SW 50mm RACI finder to a guider by replacing the entire prism assembly with a
Hercules S8225 SCT Male Thread to M42/T2 Male Thread Adapter, and a 20 mm T-2 extension ring between the adapter and an ASI290 mono camera. Focusing as normal by loosening the knurled ring behind the objective and rotating the objective cell.

The result is a serviceable lightweight guide scope for refractors to f/7 and reaching its limits on a C-9.25 at f/10 or greater.

Looking at the image in PHD2 I wondered how it would fair the primary in my red zone area. It is mounted as finder on the C-9.25 and next to it is a piggybacked 85mm refractor all on a CEM60.

Unguided, 13 exposures at 15s stacked in SharpCap. No flats and no darks. Minimal processing in the Windows Photo app to reduce vignetting.
copyStack_13frames_195s.png
Makes one rethink small scopes or take another look at the SW Evoguide 50 APO (and the Starizona Evogiode field flattener
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Re: SW 50mm RACI Finder Scope for Imaging

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Post by Thefatkitty »


That is really good! I love the widefield, and I was thinking of getting a WO Redcat... you have me rethinking that! :D

Well done and thanks for sharing,
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Re: SW 50mm RACI Finder Scope for Imaging

#3

Post by Lady Fraktor »


I have seen a few people do this with good effect, have fun with it.
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Re: SW 50mm RACI Finder Scope for Imaging

#4

Post by Hankmeister3 »


Sweet, I have a spare Celestron RACI finderscope, so I might follow in your footprints. I have some of the adapter threadings, too. Interesting. Thanks for the heads up.
Telescopes: Meade LX90 10-inch f/10 UHC Coma-free SCT; Explore Scientific 127mm f/7.5 APO ED triplet refractor; Explore Scientific 102mm f/7 APO ED triplet refractor; Explore Scientific 80mm f/6 APO ED triplet refractor; Skywatcher 72mm f/6 ED Schott doublet refractor; Meade 70mm f/5 APO quadruplet astrograph refractor; Skywatcher Quattro 8-inch f/4 Newtonian astrograph; Orion 6-inch f/4 Newtonian astrograph; Skywatcher SkyMax 180mm f/15 Maksutov; iOptron 150mm f/12 Maksutov; Orion f/9 Ritchey-Chretien RC astrograph
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Re: SW 50mm RACI Finder Scope for Imaging

#5

Post by Harmonious »


It seems that straight through Celestron can be converted, depending upon the sensor recess of the the camera.

After my original post it dawned on me that the spacing from objective cell to sensor with the SW finder of 136mm (83mm tube+2mm adapter +40mm T ring + 12.5mm sensor recess)was just about the same as the Celestron straight through would be with just the adapter and no spacer. And with the 290 is does reach focus. An ASI224 cool, with a 17.5mm recess did not reach focus.
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Re: SW 50mm RACI Finder Scope for Imaging

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Post by pakarinen »


Geez, unguided and minimal processing? Impressive.
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Re: SW 50mm RACI Finder Scope for Imaging

#7

Post by Harmonious »


Thanks, it was an experiment that I thought others might want to try. I also had an SV-50 converted from RACI to straight through I was using as a guider. The SV-50 is more expensive, takes many but not all 1.25" EPs, but in RACI config it will not reach focus with cameras with a sensor recess of 17.5mm.

The finder scope's focal length and tube length are the critical factors. Unless you work out a way to recess the cam, which could be done, the objective's focal length must be outside the OTA.

The other drawback to many of these scopes is to focus you loosen a ring behind the objective cell and screw the cell in or out to attain focus. Not particularly easy with focusing mask and if the threads are sloppy final focus with zero tilt is not easy. But again this is a very casual imager.

I don't mean to discourage anyone from trying this. It was fun and started me thinking about the SW 50mm APO finder scope, or maybe a 60mm APO...maybe after I pay the endodontist and the dentist. In the mean time I have a combination guide scope and fun scope.
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Re: SW 50mm RACI Finder Scope for Imaging

#8

Post by pakarinen »


So... any new experiences / thoughts to share?

Somebody posted a pic of their set-up elsewhere: lawn chair, maybe a 50mm on a camera tripod with a camera, and a small laptop. Dunno, I still have some heartburn over the thought of needing a laptop with me while observing, but it did look intriguing.
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AT50, AT72EDII, ST80, ST102; Scopetech Zero, AZ-GTi, AZ Pronto; Innorel RT90C, Oberwerk 5000; Orion Giantview 15x70s, Vortex 8x42s, Navy surplus 7x50s, Nikon 10x50s
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Re: SW 50mm RACI Finder Scope for Imaging

#9

Post by Harmonious »


In fact I've been giving this some more thought, greatly influenced by seeing a Sharpstar 61EDPH in use. I was very impressed with it as a wide field scope. The newer and more expensive Sharpstar 61EDPHII 61mm f/5.5 ED Triplet includes a flattener.

Rebranded SharpStars are sold as Astro Tech and Williams Optics among others. The Radian Raptor for example.

The reason for looking at this scope is that it would be a much better match for cameras with a larger sensor. With the 290 however, one can have some fun with a 50mm without going for a RedCat 51.
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