Skywatcher EvoGuide 50ED as a Luxury Finder

[Captain Scarlet]

Just under a year ago, I picked up an Evoguide 50ED, intending to use it as a super-luxury finder to go one better than the APM 50mm finder I already have, itself no slouch! It would mean that I could dedicate each to a scope and avoid too much re-alignment fiddling. Assigning the APM to my 200mm newt and the Evoguide to my 300mm newt. In theory, with my 24mm Panoptic, I'd get a 68-degree 10x50 finder.

Of course, I knew in advance that this scope is designed as a guidescope not a finder, and it comes with warnings that it will not reach focus with a diagonal attached. This didn't deter me. If necessary and in extremis I could perform some surgery on the main aluminium tube and shorten it, though that would be saved as a last resort.

Initially, I removed the green helical-focus unit and simply shoved a spare generic 2-inch SW star diagonal up the tube, taping it in place. I added my 24mm Panoptic. To my surprise, in daylight I did appear to be able to reach focus JUST ABOUT, but there were four problems:

1. it was UGLY, with a 2" lump jammed in to one end;

2. I had no convenient focus control, as I'd removed the helical unit;

3. Something I had not anticipated: severe, really severe, field curvature. A 16km-distant target (effectively infinity for a 242mm FL scope) at centre-field was lovely, easily the match of, say, my Leica 10x50 Ultravid binoculars. At the edge of the field, it was extremely blurry. If I re-focused to bring the edge into focus - crudely, by simply manually lifting the eyepiece out a bit - the edge became superb too, ruling out edge-aberration.

4. I only discovered this later using the Ugly Ducking on the night sky: it hadn't really come to focus during the day: my eye was highly stopped down, of course, being daylight, and I had obviously accommodated a bit - something I'm less able to do with my pupil fully dilated at night.

I'd been following @markse68's very similar project, and seen that two modifications could solve all the problems.

i. Baader T-2 prism diagonal, to screw directly onto the back of the OTA;

ii. Starizona Field Flattener, made specifically for this scope, which also increased total available back-focus to 55mm, AND of course does what it says: flattens the field.

 

The new diagonal and its low-profile eyepiece adapter arrived yesterday, I assembled it all and have just daylight-tested it. So far I couldn't be happier. I can achieve focus with an extra 5mm to spare. The field is now truly flat, an amazing difference, actually. Most importantly of course, it now looks the business. I can't wait to get it under the stars, and combine my 1830mm 300mm scope with a mega-wide-field well-corrected 242mm alongside.

Cheers, Magnus

 

 

Edited May 5, 2023 by Captain Scarlet

[JeremyS]

Yup, that looks the business Magnus. I like the blend of green and black of the TV EP and the OTA.

Should be a nice travel scope (with 4x the light gathering of my Pocket Borg).

Be interesting to see how it takes magnification.

[Mandy D]

@Captain Scarlet I, too, bought an Evoguide 50ED with the idea of using it as a finderscope, but never considered the possibility of using it with a diagonal, the I read that it was impossible without butchering the tube, so I've never really thought about it. I now have a Skytee 2 mount and use it in the top saddle with a straight through eyepiece, but you've got me thinking now and I'll have to keep a note of the parts to do this if I ever feel the need to. This scope does make a nice finder, though. Here is a photo of my setup with the 50ED riding on the Skytee.

[markse68]

Phew- that's a relief Magnus- I was a bit worried you'd be disappointed by the ff but it's great it worked out well for you. As I mentioned in pm I removed the ff in the end as although it was improving the edge of field in my setup, it was unfortunately vignetting the 16mm nagler fov and the field with that ep seems pretty flat anyhow

Mark

[Captain Scarlet]

2 hours ago, JeremyS said:

Be interesting to see how it takes magnification.

At the moment I’m unable to tell. Because of the very short eyepiece adapter, the eyepiece sits on the internal lip which prevents the nosepiece sitting atop the prism face. So it turns out that the critical dimension is the distance from the open end of the nosepiece to the eyepiece focal plane. As it happens, the Pan 24 has a very short nosepiece*. Those on all my other eyepieces, every one, are significantly longer. It’s lucky the one I really need to work, does so. But it does give me an excuse to take 10mm out of the middle of the tube at some stage.

M
 

* edit: the shortest of the whole TV range, it turns out, lucky coincidence for my 10x50.

Edited May 5, 2023 by Captain Scarlet

[Captain Scarlet]

Duplicate post

Edited May 5, 2023 by Captain Scarlet