17 replies to this topic

[Photo-Dave]

I just picked up an original Edmund Scientific Astroscan, the ball type Newtonian. It came with both the Body Cap and eyepiece cap, the strap, base, and a peep sight finder.
It didn’t have the original RKE 28mm eyepiece.

My questions are: What eyepieces work best with these scopes?
I tried 3 Plossles that I had available a 20mm Meade, a 25mm Orion & a 40mm generic. The 20 & 40mm worked fine in testing with terrestrial & Astro subjects. I was impressed with the brightness & sharpness of the stars & Venus. Looking at Orion with the 40mm all 3 stars of the belt shown brightly across the field of view.

The 25mm Orion appeared to have the secondary mirror show up in the middle of the field of view. What about this lens caused that?

The sight/finder that came with the scope, was this an Edmund accessory or is this some adapted 3rd party piece. It attaches under one of the strap thumbscrews, and seems cut to fit. But hangs loosely on the far end. It consists of a bent, black metal bracket with two sight holes one small and the other about 3x larger.

A few other observations. At first I thought the focus mechanism was broken. But after I helped it rack out the first time, it got much better with repeated use.

Also the bolt that holds the base in place for transport seems to barely catch one full thread or so.

Thanks in advance for any feedback. Dave

[ShaulaB]

Very nice clean specimen. We own one, and when I pass, my ashes will be kept in the Astroscan.

 

Before the plague hit, I used the Astroscan with children at outreach events to safely let them handle a telescope.It has been to many scout camps as well, as it is so durable. Much delight has ensued over the years!

 

The finder is crap, it's not 3rd party. So I use a 40mm eyepiece instead of the yukky finder and it works out ok. I also use an 8-24mm zoom eyepieces with it, as changing eyepieces with its wonky focuser is kind of a pain.

 

If you plan to clean the primary, best of luck, it takes courage and considerable hand strength to release the front glass plate.

[halx]

Hey, Dave. Congrats on your acquisition! And great images of it!

 

I have one as well for many years (you can see some write ups on it in my blog filtered on it here: https://www.dobmod.c...label/AstroScan). Just love it!

 

It's a quite praised on this forum little fella. So just search Astroscan word here there are plenty of information. Here is my favorite "surgery report" out of most recent threads: https://www.cloudyni...-refurbrebuild/

To answer your questions:
- The pip sight looks authentic stock model. But surely there are some aftermarket and DIY options circulating around. Can't comment on it being flimsy I'm using a laser pointer instead.

- All regular 1.25" eyepieces work just fine with it as soon as you can focus them with its quite short focal plane distance. You will have issues with too-long-focused pieces though (like that secondary's shadow you see with your 25mm). The optimal magnifications range for its 105mm  aperture would be 15x ~ 250x, which makes the well overshooting EPs range from 30mm to 2mm. I'm surprised you haven't seen the central obstruction with your 40mm. While you can easily see it with 25mm having your eye pupil contracted in the bright daylight or looking at the Moon through it. The 30mm is for the 7mm pupil size of the fully darkness adapted and young adult eye.
- I have never used that "parking bolt" you have suspicions about, but if that's the same one holding the shoulder strap (and the pip) it might be too short for the reliable job indeed. Replace with any long enough 20 x 1/4".
- The focuser is indeed quite weak, especially for heavy eyepieces. Originals are very light plossls. You can disassemble it and inspect/clean/rejuvenate/reinforce/replace the rubber piece in the middle. It's definitely prone to aging.

Try it without the base, it's a fantastic replacement for handheld binoculars.

[halx]

Aww, ShaulaB, what a romantic idea for the ashes! Must steal it!
The 8-24 zoom was also my favorite with it before I've managed to mate it with the 9x101 !

 

What "wonky focuser"? There is none!

Edited by halx, 21 April 2020 - 12:57 AM.

[Photo-Dave]

Thank you All for the informative replies

I have wanted one since I first saw it in Edmund’s catalog way back when. When I saw this for sale on my local Facebook marketplace I jumped on it. The plastic body is in excellent condition. The front plate had mold outside & in. I already cleaned the outside but don’t have the tool to squeeze the snap ring to release the front plate to clean it.

I’m reluctant to because the alignment seems quite good and I don’t want to ruin it by removing the plate to clean it.

The main mirror seems to be in quite good shape. While I’d like it to be spotless, again I’m not sure I want to risk opening it.

The stars are much more pinpoint sharp and bright in the Astroscan than my Classic Celestron C8.

[Photo-Dave]

Forgot to mention while cleaning it, I also gave it a coat of cleaner - sealant. This made it swivel oh so easily in the base, but seems to have backfired. With an eyepiece attached it won’t stay in any position other than vertical. It just wants to slide to horizontal. I’ll need to remove the wax from the ball base.

[ANM]

Very nice clean specimen. We own one, and when I pass, my ashes will be kept in the Astroscan.
 
Before the plague hit, I used the Astroscan with children at outreach events to safely let them handle a telescope.It has been to many scout camps as well, as it is so durable. Much delight has ensued over the years!
 
The finder is crap, it's not 3rd party. So I use a 40mm eyepiece instead of the yukky finder and it works out ok. I also use an 8-24mm zoom eyepieces with it, as changing eyepieces with its wonky focuser is kind of a pain.
 
If you plan to clean the primary, best of luck, it takes courage and considerable hand strength to release the front glass plate.

Won't that scratch the mirrors?
Edmunds still sells RKE eyepieces.

Edited by ANM, 21 April 2020 - 08:28 AM.

[Photo-Dave]

Hey, Dave. Congrats on your acquisition! And great images of it!

 

- All regular 1.25" eyepieces work just fine with it as soon as you can focus them with its quite short focal plane distance. You will have issues with too-long-focused pieces though (like that secondary's shadow you see with your 25mm). The optimal magnifications range for its 105mm  aperture would be 15x ~ 250x, which makes the well overshooting EPs range from 30mm to 2mm. I'm surprised you haven't seen the central obstruction with your 40mm. While you can easily see it with 25mm having your eye pupil contracted in the bright daylight or looking at the Moon through it. The 30mm is for the 7mm pupil size of the fully darkness adapted and young adult eye.
 

I want to order an inexpensive eyepiece or 2 to use with the Astroscan.  Looking at New SVBony Plossl's or a Used Meade.  Since this originally came with an RKE Edmund 28mm eyepiece, (mine didn't come with it)  Should I be buying a Plossl or a Kellner?
What characteristic of the lens causes me to see the secondary mirror in the FOV?

I'm looking at: 1.25" SPL Super Plossl Eyepiece Lenses 26mm FMC 52°   or

Meade Super Plossl 26mm Multi Coated Telescope Eyepiece Japan          or
SVBONY 1.25" K25mm-FL Eyepieces 3Element Kellner Telescope Eyepiece

Do either of these throw up a red flag other than the (2) SVBONY's being dirt cheap?   Thanks again,  Dave

[DAVIDG]

  You want to use the lowest magnification that matches to the exit pupil of the telescope. The formula is to take the diameter of the telescope aperture in millimeters  and divide that by the magnification. For a young person a dark adapted eye will open to 7mm. So in theory you want a magnification that gives you that exit pupil. For example a typical 7x50mm binoculars has 7mm exit pupil ie 50/7 = 7 

So the Astroscan has a clear aperture of 4 1/8" or 105mm.  So divided 105 /7 gives us a magnification of 15x.  The Astronscan has focal length of 17 1/2" or 445mm . So 445/15x = 29.6mm eyepiece focal length. So Edmund went with a 28mm RKE because that is very close and gave a bit more magnification so a bit smaller exit pupil. Now if your over 50 years old your eyes may not open up to 7mm so a smaller exit pupil maybe be more appropriate. The reason is if your eye opens to 6mm and the exit pupil of the telescope is 7mm  your eye is not letting all the light in from the scope so your effectively looking thru a small aperture telescope.

   Getting back to your original question, a good quality Plossl eyepiece will work well in the Astroscan and I would recommend in the 20mm to 28mm focal length range. 

 

                   - Dave  

Edited by DAVIDG, 21 April 2020 - 02:22 PM.

[Photo-Dave]

Thank You very much. I’ll add that formula to my Astronomy Notebook . Dave

[DAVIDG]

Thank You very much. I’ll add that formula to my Astronomy Notebook . Dave

 BTW here is a link of  how I repaired a very old Astroscan , serial number #112 https://www.cloudyni...an#entry9756779

 

         - Dave 

Edited by DAVIDG, 21 April 2020 - 02:20 PM.

[halx]

I'd go for a cheap Zoom instead. That's already two of us here considering that an ultimate solution. E.g.: https://www.amazon.c...e/dp/B07MNYW9D8 (no affiliation or experience with that one, but I have no doubt it's the same thing Celestron is selling for $80, or at least should be on par with that SVBONY you are considering).

EDIT: Even for less: https://www.amazon.c...n/dp/B085L725TQ
I think, it worth a shot. Just ordered it myself so I could keep one inserted at all times...

Edited by halx, 21 April 2020 - 03:28 PM.

[clamchip]

There's something magical about the 28mm RKE and the Astroscan.

Better yet the Edmund 1-1/8" eyepiece, it's a Type 3 Kellner (Plossl in modern language) and very much

like the RKE but no field stop I like it better.

I don't think there is a modern equivalent to these extraordinary eyepieces.

Take a look here:

https://www.cloudyni...llection/page-2

 

Robert

Edited by clamchip, 21 April 2020 - 08:09 PM.

[halx]

Thank you for the link, Robert. Very fascinating.
I do like the stock 28mm very much. It seems like a very good bang for the buck. However, that's a rather ordinary plossl for the performance. I have a 27mm Russian plossl from NPZ(TAL), their oldest model from ~1981 (which I would never call a top in the line), which performs in Astroscan as good, even though there are no coatings on it at all YMMV

[Gil V]

It’s not difficult to remove the snap ring holding the front window in place. It can be done by hand, or if your model has holes in the ring, a cheap pair of snap ring pliers.

You have to reach into the focuser opening and push the glass from the inside to remove it after snap ring removal. It is surprisingly thick.

It’s usually a snug fit, and not difficult to reinstall in the correct position.

Removing the primary is an order of magnitude more difficult, especially the later Chinese made version. Either way, I wouldn’t mess with the primary unless it was significantly dirty, or well out of alignment due to deterioration of the foam behind the mirror. You can detect that by bouncing the scope on your knee - you can hear the mirror rattle if the foam is not doing it’s job holding the primary against the retaining ring.

Edited by Gil V, 24 April 2020 - 10:07 AM.

[Photo-Dave]

Is there any chance that in later builds they changed the type of foam used to hold the Primary mirror in place? My alignment seems very good. Stars are sharp and pinpoint. The number up under the focus assembly is 41937.

If I want to clean the inside of the front element and perhaps the Primary. What are the chances if I remove the front glass and put it back in the notch my alignment will hold?

Thanks, Dave

Edited by Photo-Dave, 24 April 2020 - 10:33 AM.

[Gil V]

I’ve done two of them. First was US model, front glass had alignment notch, replaced foam. Reassembled, perfect (and I mean perfect) alignment. Gave it to my BIL.

Second was chinese model with red dot finder. Front glass install same, but primary was encased in an adhesive glove of foam that reached to nearly the front surface. I actually pushed the primary out with a 1/4-20 screw from the back! After removing the retaining ring, of course.

It was impossible to get all the foam off, I was not prepared for a multi-day project, as the US model was a breeze. I was due to ship the scope to a friend.

I cleaned the glass as needed, reassembled and tested. The scope had the exact same astigmatism and slight miscollimation that it showed in pre-repair tests. I shipped the scope. My friend has severe vision issues, and wanted a wide field scope. The astigmatism at low power was tolerable under the circumstances.

Edited by Gil V, 24 April 2020 - 11:26 AM.

[halx]

Is there any chance that in later builds they changed the type of foam used to hold the Primary mirror in place? My alignment seems very good. Stars are sharp and pinpoint. The number up under the focus assembly is 41937.

If I want to clean the inside of the front element and perhaps the Primary. What are the chances if I remove the front glass and put it back in the notch my alignment will hold?

Thanks, Dave

You seem to have a pro-photography background, Dave. As soon as you are careful as you should with any optics - just go for it if you see it beneficial. The scope is tolerant to reassembling unless it has been in the tinkerer hands before already. E.g. I have two shims installed under the glass for the alignment correction which could shift if I forget to watch for them. And surely check mirrors' cleaning guides, as they are different from modern camera lens' (but similar to what you would do with a DSLR mirror without removing it).