21 replies to this topic

[therealdmt]

This thread is a spin-off from my previous thread where I was looking for a 50mm telescope/finder: https://www.cloudyni...are-my-options/

 

I ended up getting the 52mm f/4.8 Askar, and then things started getting into details on the somewhat quirky Askar rather than just being a general finder/mini-telescope discussion, so I’ll post my findings on the Askar here in this seperate thread and hopefully others may join in.

So, it’s an approximately 50mm guidescope that can take (come to focus with) a diagonal and so act as a small refractor telescope or as a RACI finder (depending on the diagonal and mounting used). Of course it could act as a straight-through finder too, but my neck has no interest in that…

 

And, it’s a guidescope (the manufacturer’s main intended purpose, it would seem).

 

Anywho, so here it is with a dielectric mirror diagonal and some eyepieces I might typically use in it (the black eyepiece next to the 25mm NPL Plossl is a 24mm 50 degree afov reticle eyepiece that was sold by Sky Rover at some point):

 

And then here it is mounted as a finder with a prism diagonal in it:

It works well with a Svbony 3-8mm zoom through the prism diagonal. The 20mm ES 68° doesn’t quite come to focus though through the prism diagonal unless I lift the eyepiece out a few millimeters and then screw it tight there, a situation which makes changing eyepieces a non-smooth experience. Accordingly, I’ve ordered a set of 42mm spacers to try to get an appropriate backfocus for use with the prism

[therealdmt]

I’m currently using an unbranded 1.25" prism diagonal. At first I was using an "E. Frantis" dielectric mirror star diagonal (it seems that brand no longer sells such a product, and I don’t know who the OEM was, but anyway it’s just a basic dielectric mirror star diagonal that I saw in a shop once and picked up on a whim, not a planned purchase of a particular make and model. Same goes for the no-brand 90° prism one and also my no-brand 45° prism one, too).

 

(not a great arrangement for me as, when viewing in the main eyepiece, I bump my head on the finder’s diagonal unless I switch to my left eye [which isn’t my regular observing eye])

[therealdmt]

Somewhat reposting from the previous thread, just to get things up to speed here:

 

First, I’m not in love with it, but it does work.

 

There is slight vignetting with my 68° eyepieces. However, the 68s are still quite useable and I’ve mainly been using an ES68 20mm the last few times out. My 50°s (Plossls) and my 7-21 zoom were pretty much free of vignetting as tested against both a clear blue sky and at night. 82° eyepieces (most of my eyepieces are 82s) show quite noticeable vignetting though, so 82s are out. This could be a good excuse to get started on a 60° eyepiece set

The Moon really looks great through the 52. I also got nice views of the thin crescent Venus while it was still around (meanwhile, by accident while looking for Venus handheld, I came across Mercury for the first time in a few years!). With a 30mm Plossl, it easily takes in all of the Beehive, the M41 open cluster or the Orion sword area, etc. At relatively high mag (zoomed in with the 7-21 zoom), Sirius did showed a faint blue-ish haze around it, but there were a lot of scattered clouds so that might have been atmospheric, I don’t know yet (havent re-tested that).

 

It’s not great on double stars at low mag, though that might be due to the Plossl eyepiece I was using in it a lot at first, I’m not sure yet. But some doubles that I could [if only barely] distinguish as doubles in my 9x50 SkyWalker RACI weren’t clearly double in this Askar. Of course, the big difference is that with the Askar 52SD, one can use higher mag eyepieces, too. The Winter Albireo (h3945), for example, showed quite nicely through the Askar using a 3-8mm zoom.

 

Regarding field curvature, there is some. It wasn’t noticeable at first, but for example, when focusing on the almost full Moon at a mag where the Moon’s disk filled a good portion of the field of view, in trying to get perfect focus, I noticed that perfect focus wasn’t happening everywhere at once. Interesting, as it’s pretty subtle. The field curvature is barely noticeable when starhopping. The problem is, though, focusing in general. It’s a chore. The focusing ring is a bit stiff and, turning it maybe 20 or 30 degrees at a time, I found it took approximately 100 turns(!) to go from one end of the focusing range to the other. This became much less of an issue once I finally figured out approximately where in the focusing range my eyepieces would focus with my two diagonals (different ends of the focusing range for with my mirror and for with my prism), but at first it was quite a chore. Meanwhile, while the rough focus takes forever (if you aren’t in the right neighborhood), for fine focus it somehow seems too sensitive, I guess due to that subtle field curvature. Due to that and having to have the 20mm eyepiece pulled out a bit in the prism diagonal’s eyepiece holder, I just stuck with that one 20mm eyepiece the last three times out (instead of freely switching between eyepieces per my original intentions for this scope).

 

I was freely switching between eyepieces when I used the mirror diagonal, but I want to use this with a prism, I think. Gotta wait for those spacer rings I ordered to get that all straightened out.

 

Also, I want to look into getting a secondary tuning helical of some sort, like maybe something on the eyepiece end. Finally, I’m going to look into other mounting strategies (I’m not thrilled with the 3 screw single clamshell-like holder). 
 

Will try it on my Dob at some point, too

[therealdmt]

Set photons to "Observe"!  

[nuffink]

Hi,

Can you tell me if the little Askar scope is splittable at the point I've indicated with the red arrow?..

ie. is the focuser and objective assembly screwed into the rest of the tube?

Edited by nuffink, 26 March 2025 - 07:54 AM.

[therealdmt]

Hi,

Can you tell me if the little Askar scope is splittable at the point I've indicated with the red arrow?..

raci.jpg

ie. is the focuser and objective assembly screwed into the rest of the tube?

As far as I can tell, it’s not splittable there (i just tried, using only hand strength). There are two included spacers/extension tubes for using it as a guidescope, as can be seen in the advert below, but they aren’t used if using this scope with a diagonal. The two spacers easily screw on and off, both from the scope and from each other (i.e., the scope assembly splits at the spacers).

https://www.sharpsta...GuideScope.html

 

But the focuser doesn’t seem to unscrew from the rest of the body where you indicated, nor does it otherwise seem to be splittable there (I could be wrong though — I certainly didn’t try to force anything).

 

Interestingly, in trying to confirm an answer to your question, I took the 42mm-to-1.25" adapter/diagonal-nosepiece-retainer at the back of the OTA off and then thought I would slip the scope entirely out of its holder, but… although the OTA got loose once I unscrewed the adjustment/retaining screws of the holder, the scope wouldn’t actually come out of the holder Remounting it in a different assembly such as two 50mm scope rings might not be as straightforward as I’d been thinking. Anyway…

[nuffink]

Oh dear, I hope I haven't caused you a problem. Thanks very much for trying.

Like you I was hoping to utilise the Askar (possibly the ED version) with a prism but I don't think it will have quite enough back-focus with, say, the Baader T42 amici. Hence my question. If it were splittable there, that would easily provide enough back-focus.

[therealdmt]

Oh dear, I hope I haven't caused you a problem. Thanks very much for trying.

Like you I was hoping to utilise the Askar (possibly the ED version) with a prism but I don't think it will have quite enough back-focus with, say, the Baader T42 amici. Hence my question. If it were splittable there, that would easily provide enough back-focus.

There was no new issue caused, no worries

 

Meanwhile, a prism diagonal can work — I’m using one now. But the scope is at the end of its focus range. My 3-8 zoom reaches focus, as does, iirc, my 30mm Plossl (? — not sure, actually, haven’t tried it in a week), but my 20mm ES68 needs to be lifted out of the diagonal a few millimeters. Accordingly, I’ve ordered a short spacer (actually 3 different ones to try) so as to get the focusing more in the middle of the focuser’s travel range when using the prism diagonal. That way, i should be able to get all my intended eyepieces to focus with plenty of focusing range to spare either side (well, that’s my theory anyway ).

 

About a T2 prism, if that has a 2" nosepiece, it wouldn’t fit as is (it might fit with some kind of adapter or replacement nosepiece though). The body of the Askar is 42mm, so less than 2" in diameter

[nuffink]

 

About a T2 prism, if that has a 2" nosepiece, it wouldn’t fit as is (it might fit with some kind of adapter or replacement nosepiece though). The body of the Askar is 42mm, so less than 2" in diameter

The T2 prism has a 42mm thread at both ends... https://www.baader-p...hs-coating.html and a path length of 47.5mm. I was hoping to use one with a Baader Click-lock clamp... https://www.baader-planetarium.com/en/1-25inch-clicklock-clamp-to-t-2a.html which has a minimum path length of 32mm. Assuming that the back focus length of the Askar is 80mm (2 x 40mm extension tubes) it just might work but it's a close run thing and an expensive mistake if it doesn't.

Edited by nuffink, 26 March 2025 - 09:07 AM.

[therealdmt]

The T2 prism has a 42mm thread at both ends... https://www.baader-p...hs-coating.html and a path length of 47.5mm. I was hoping to use one with a Baader Click-lock clamp... https://www.baader-planetarium.com/en/1-25inch-clicklock-clamp-to-t-2a.html which has a minimum path length of 32mm. Assuming that the back focus length of the Askar is 80mm (2 x 40mm extension tubes) it just might work but it's a close run thing and an expensive mistake if it doesn't.

Oh, okay. Best of luck if you try it. I’m just learning about this backfocus stuff myself (maybe I’ve been lucky, but this is my first time with any kind of backfocus issue to work through)

[The Cloud Gazer]

Thanks for the very interesting summary thread on your endeavour! 

 

I’m currently using an unbranded 1.25" prism diagonal. At first I was using an "E. Frantis" dielectric mirror star diagonal (it seems that brand no longer sells such a product, and I don’t know who the OEM was, but anyway it was just a basic dielectric mirror star diagonal that I saw in a shop once and picked up on a whim, not a planned purchase of a particular make and model. Same goes for the no-brand 90° prism one and also my no-brand 45° prism one, too).

 

IMG_2220.jpeg
(not a great arrangement for me as, when viewing in the main eyepiece, I bump my head on the finder’s diagonal unless I switch to my left eye [which is not my regular observing eye])

Concerning the arrangement problem, I also had that at some point and just rotated the tube in the rings. I guess you already thought of it but just to mention. The focuser knobs are not nicely arranged anymore like this but keeping my OCDs in check is fine (for this)  .

 

Love the picture with the refractor fleet  Great to compare sizes.

 

If field curvature bothers you too much, there is always the TSFlat that can help (I guess it won't eliminate it fully at this level but it should reduce it by a fair amount I think). But then again it costs as much as the finder 

[therealdmt]

Thanks for the very interesting summary thread on your endeavour! 

 

Concerning the arrangement problem, I also had that at some point and just rotated the tube in the rings. I guess you already thought of it but just to mention. The focuser knobs are not nicely arranged anymore like this but keeping my OCDs in check is fine (for this)  .

 

Love the picture with the refractor fleet  Great to compare sizes.

 

If field curvature bothers you too much, there is always the TSFlat that can help (I guess it won't eliminate it fully at this level but it should reduce it by a fair amount I think). But then again it costs as much as the finder 

Hi, yeah it was fun taking that picture

 

I’ll think more about what you said regarding rotating the tube in the rings. I’ll certainly experiment more. For now, I’ve put the li’l Askar on its own tripod and went back to my RACI on the refractor. The Askar’s diagonal should naturally be out of the way on my Dob I think, so I’m gonna try it there, too

[The Cloud Gazer]

Hi, yeah it was fun taking that picture

 

I’ll think more about what you said regarding rotating the tube in the rings. I’ll certainly experiment more. For now, I’ve put the li’l Askar on its own tripod and went back to my RACI on the refractor. The Askari’s diagonal should naturally be out of the way on my Dob I think, so I’m gonna try it there, too

I meant if you rotate the scope 90°, the finder will be to the right of your head, not the left anymore 

[Brain&Force]

Mine just came in today, and my first impression is that the build quality is fantastic, though getting the spacers unscrewed was surprisingly difficult the first time (I didn't even realize the M42/1.25" adapter was a separate piece from the extension). It's too cloudy (and I'm too busy) to observe until Thursday, but I will hopefully get a dielectric diagonal in by then.

[Brain&Force]

I've taken it out for observing (mostly as I've gone out for sidewalk astronomy) and so far it's done exactly what I need it to in conjunction with the 24 mm reticle eyepiece I just bought. It's quite a bit heavier than the 9x50 RACI finder I'm coming from, but it's so much more comfortable to use.

 

The edges of the field are messy, but I've really only been using the 24 mm reticle eyepiece to observe, so I can't say if it's due to the eyepiece or if it's a problem with the optics. I don't really expect any of my eyepieces to do well at f/4.8, so that's not something I can really test rigorously anyway (though maybe my 32 mm Plossl is the best option). Either way, I think that's better done when I get back out to a dark site and look at a populated star field.

 

I'm thinking of picking up the SVBONY SA404 to replace the stock visual back. I was a bit surprised that it doesn't come with a compression ring visual back, and while I'm fine with having my cheap diagonal's nosepiece scratched, a compression ring provides way more security. Perhaps I'll also pick up an extra M48 extension: it would be nice if it came with a pair of 20 mm extension rings intstead of one of the 40 mm rings - similar to how my RC's focuser extension rings are provided (one 50 mm extension and two 25 mm extensions).

 

I'd also like to figure out a solution for storing it in a ready-to-go configuration for visual observing (diagonal and eyepiece attached) - a padded hard case is probably the best option, but something a little less bulky would be nice.

[Brain&Force]

Also, I want to look into getting a secondary tuning helical of some sort, like maybe something on the eyepiece end.

Starizona sells adjustable M48 adapters that seem to fit this need perfectly - providing some tuning without adding too much backfocal distance.

[therealdmt]

I've taken it out for observing (mostly as I've gone out for sidewalk astronomy) and so far it's done exactly what I need it to in conjunction with the 24 mm reticle eyepiece I just bought. It's quite a bit heavier than the 9x50 RACI finder I'm coming from, but it's so much more comfortable to use.

 

The edges of the field are messy, but I've really only been using the 24 mm reticle eyepiece to observe, so I can't say if it's due to the eyepiece or if it's a problem with the optics. I don't really expect any of my eyepieces to do well at f/4.8, so that's not something I can really test rigorously anyway (though maybe my 32 mm Plossl is the best option). Either way, I think that's better done when I get back out to a dark site and look at a populated star field.

 

I'm thinking of picking up the SVBONY SA404 to replace the stock visual back. I was a bit surprised that it doesn't come with a compression ring visual back, and while I'm fine with having my cheap diagonal's nosepiece scratched, a compression ring provides way more security. Perhaps I'll also pick up an extra M48 extension: it would be nice if it came with a pair of 20 mm extension rings intstead of one of the 40 mm rings - similar to how my RC's focuser extension rings are provided (one 50 mm extension and two 25 mm extensions).

 

I'd also like to figure out a solution for storing it in a ready-to-go configuration for visual observing (diagonal and eyepiece attached) - a padded hard case is probably the best option, but something a little less bulky would be nice.

I’ll be interested to read how it goes if you get that SA404 and/or a 20mm M48 extension.

 

i ordered a 20mm extension I thought should work, but it was the wrong size somehow and I’ve put that project aside for now.

 

Glad to hear you’re enjoying your Askar 52SD so far

[kwyjibo]

 

 

Also, I want to look into getting a secondary tuning helical of some sort, like maybe something on the eyepiece end. 

I use this with my mak for fine focusing to avoid the mirror flop and it I've been happy with it.

https://agenaastro.c...ep90-125ii.html

[therealdmt]

I use this with my mak for fine focusing to avoid the mirror flop and it I've been happy with it.

https://agenaastro.c...ep90-125ii.html

Oh man, I just made my big order for probably the year (at least until Christmas-y time) from Agena. Aughh, missed it by two days (already shipped). I think this would have been perfect. Still could be. It’s basically exactly what I was picturing. I’ll put it on my "wish list" for the future — thanks for pointing it out!

[kwyjibo]

Just saw this one as well.

https://www.stellarv...m-with-focuser/

[therealdmt]

Nice. And the price is even better. Thanks for posting the StellarVue one too, kwyjibo. It’s now also been added to my ever-growing astro wish list

[Brain&Force]

Actually, before I order the SA404, I'm interested if anyone knows of a twist-lock adapter that has M48 male threads and could suit this scope. I've been trying to move away from set screws due to an incident I had during an outreach event, and this scope is part of my sidewalk astronomy kit.

 

I could probably hack together a solution with an M48 male-to-male adapter and something like the William Optics rotolock adapter (which also has M48 threads), but that may introduce a bit too much of a path length to bring eyepieces into focus with a mirror diagonal.