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Evoguide 50 ED as an RA Finder


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I initially added this to another thread but on reflection the other (3-years-ago-last-post) thread was the wrong place to put it, so I’ve put it here instead…

I bought a one of these Evoguide 50 ED guide scopes on here a few weeks ago with the intention of turning it into a super-finder. The original plan was to do some surgery, i.e. to cut off some tube and use grubscrews to re-attach the focus unit and a diagonal.

But experimenting by simply slotting a generic SW 2” diagonal I had spare, I found that my Panoptic 24 sat in at exactly infinity focus. The problem to solve was that the female thread inside the 50 ED’s tube appears to be M53, and the small difference between a 2”/51mm nosepiece and a 53 thread does not allow for any adapter. Besides, none seem to exist. So I very carefully wrapped the 2” nosepiece in a few layers of plastic tape, screwed it in and it’s fine, pretty solid too. No actual surgery needed.

242mm FL and 24mm eyepiece gives me almost exact a 10x50 68-degree well-corrected finder. It certainly looks very nice at distant objects terrestrially. It’s not RACI, but I don’t mind that. But my neck does mind it not being RA. I can’t wait now to try it out on my 12” … I reckon I’ll get as much pleasure looking through the finder as I will through the 12” eyepiece. Well, nearly as much.

Cheers, Magnus

 

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Very nice Magnus! My own diy raci plans have fallen to back of the long queue so satisfactory is the humble SW 8x50 Raci I bought cheaply in the classifieds- not such a huge afov but very bright sharp and contrasty. What does it weigh? And how good is the edge of field? Looking forward to the report on night time use :)

Mark

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It weighs 1.29kg, so a fair bit heavier than the 0.80kg of the APM 8x50 finder it’ll be replacing  for my 12”. But the 12” comes in at 21kg so the odd extra 500g won’t matter much.

It’s forecast to be reasonably still with clear patches tonight so hopefully I’ll be able to give it its First Light, mounted on the Baader Stronghold you can see I’m the pic. I’ll compare it directly to the APM too…

M

 

Edited by Captain Scarlet
apostrophe!!!
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  • 3 weeks later...

Hello Magnus, 

I was wondering how you got on with the first light? I'm planning to potentially build a tiny scope using the method @DRT used, i.e. T2 prism diagonal with a low profile EP holder.

I was playing about with my TS-Optics 50mm RACI yesterday as a test to see if there's enough light gathering for my needs. It is nice as a finder but as a scope for actual observing, it suffers with off axis CA and field curvature, so I'm hoping that the Evoguide is better? Eager to hear your thoughts. 

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First night Light has yet to happen, it may well be tomorrow night though if the forecast holds. I have looked through it during daytime though, and while it’s a lovely wide-field view, very similar in quality to my Leica Ultravid 10x50 binoculars, the field curvature is severe. When focused for the centre, the edge is awful of course, but the edge is a lovely view when it itself is got into focus. I guess it’s a problem with very short focal length, the spherical nature of the field is that much more acute.

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Thanks! Yes, same issue with my finder, stars almost look like clusters or nebulae when at the edge. I wonder if the field flattener would help here for visual?

Looking forward to your first light report. What's the CA like in the daytime? Hoping it would be a lot better than my finder given that the Evoguide has FPL53. 

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43 minutes ago, Captain Scarlet said:

First night Light has yet to happen, it may well be tomorrow night though if the forecast holds. I have looked through it during daytime though, and while it’s a lovely wide-field view, very similar in quality to my Leica Ultravid 10x50 binoculars, the field curvature is severe. When focused for the centre, the edge is awful of course, but the edge is a lovely view when it itself is got into focus. I guess it’s a problem with very short focal length, the spherical nature of the field is that much more acute.

Are you going to try the field flattener for it then Magnus? Seems a shame to stop when you’ve got this far ;) 

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4 minutes ago, markse68 said:

Are you going to try the field flattener for it then Magnus? Seems a shame to stop when you’ve got this far ;) 

I just checked the spec and the Skywatcher FF has a backfocus distance of 17.5mm, so I don't think it would be possible to connect the diagonal as well. Starizona apparently do a field flattener with 55 mm backfocus however, and it's T-threaded so I reckon you could pop a Baader T2 prism on there at a push (I intend to do this although not with the FF). I'm not an image train expert so not sure if my assumptions are correct. 

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51 minutes ago, markse68 said:

Are you going to try the field flattener for it then Magnus? Seems a shame to stop when you’ve got this far ;) 

I think it has to be done.

I’ve just compared directly side by side the APM and the Evoguide, and the Evoguide is SO much more satisfying and contrasty to look through.

Starizona here I come…

Edited by Captain Scarlet
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35 minutes ago, Captain Scarlet said:

I think it has to be done.

I’ve just compared directly side by side the APM and the Evoguide, and the Evoguide is SO much more satisfying and contrasty to look through.

Starizona here I come…

Careful though Magnus- Looks like it’s designed to go into the green focussing bit that you removed- it might vignette if you use it in place of the diagonal nose like you have it now?

Edited by markse68
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The Starizona does indeed slide into the focuser body of the Evoguide, and looks like it has both a female T2 to screw on to the focuser, then a male T2 for the camera (or diagonal in our case). The clear aperture of the FF is 28mm apparently, so should be good for all 1.25" EPs I think? 

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26 minutes ago, markse68 said:

Careful though Magnus- Looks like it’s designed to go into the green focussing bit that you removed- it might vignette if you use it in place of the diagonal nose like you have it now?

Yes thanks. Although it’s usable the way I have it at the moment, when I go the FF route I’ll probably put the green focus unit back in but shorten the main tube by an appropriate distance.

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