Sky-Watcher EvoGuide ED50

[DRT]

2 hours ago, nightfisher said:

Derek, if you wish to try a prism, i can loan you a circle T 1.25 prism, i would require it back at some stage

Thanks for the kind offer, Jules, but I have a Meade Prism on the way that I bought from another member yesterday.

[nicoscy]

Derek,

By any chance, do you have calipers at home? I'd be most interested in a measurement of the ID of the OTA once the entire back assembly is removed.

The OD is 56mm according to FLO so I suppose  the ID is probably M54 or so. In any case, it would be relatively easy to find an adapter from whatever thread to a T2 connection and then just shove a  T2 non rotating short helical focuser and then a Baader T2 to 1.25" short adapter and use any regular diagonal.

If the threading is "reasonable" here's what I am thinking (it's your fault for pursuing this and making this finderscope so interesting!):

Say it's M54: https://www.teleskop-express.de/shop/product_info.php/info/p203_TS-Optics-M54x1-to-T2-Adapter-fo-Skywatcher-Crayford-focusers.html (2.5mm)

Then this focuser: https://www.teleskop-express.de/shop/product_info.php/info/p4591_TS-Optics-short-T2-Helical-Focuser---Adapter---camera-does-not-twist.html (18mm)

Then this T2 to 1.25" adapter: https://www.teleskop-express.de/shop/product_info.php/info/p9743_Baader-2458121-Ultrashort-1-25----T2-Clamp.html (12mm)

I would really appreciate it if you could measure it and let me know.

As things stand, I have a wonderful Borg 55FL as a finderscope on my FS-128. I wouldn't mind selling the Borg and getting this one to use, and money to spare for further astronomical purchases

The quality of the optics is of interest of course and I really look forward to reading your detailed observations later on

 

EDIT: The pitch of the thread is also important

Edited May 21, 2018 by nicoscy

[DRT]

I'm sorry to say I haven't yet had an opportunity to really look through this little scope but here are a few more notes on things I have found:

1. The cheap Meade Prism reaches focus without the need for any modification and without the extension tube. There is enough travel to reach focus on terrestrial objects and infinity. I therefore have a working scope, but don't like the idea of a plastic diagonal with a screw fitting being my final solution.

2. The Baader T2 Prism reaches focus on near terrestrial objects but only when racked all the way in. There is no travel left to reach infinity. 

3. The focuser section does unscrew from the OTA. I have not measured any of the diameters or threads but it does open up the possibility of modification by adding an alternative focuser.

4. The objective cell and separate green retaining ring both unscrew from the OTA leaving a familiar male thread on the OTA. There seems to be 3-4mm of space available at that end to potentially shorten the OTA and create the equivalent amount of extra inward focus at the other end. Hmmm? Tempting, but a potential for disaster.

[DRT]

On 20/05/2018 at 19:29, happy-kat said:

I like that and will look into if I can shorten my already almost there star diagonal. (though an erect image diagonal would be better for day time)

 

On 20/05/2018 at 20:58, Rick_It said:

There is a single screw before the focuser, the first screw after the end of the white tube.

What's for? To remove the focuser section?

Because, if the focuser section can be removed, then someone with a machine shop can cut about 1cm of tube and solve once for all the diagonal problem. I'm also interested on that scope, but it needs to work with a diagonal.

PS: I really cannot understand why SW has not made the tube 1cm shorter and the extension tube 1cm longer.

 

On 20/05/2018 at 08:30, nicoscy said:

I wonder what the threading on the back of the OTA is.. if it’s something “sensible”, possibly a Borg helical focuser could go there and really reduce the length of the finderscope, permitting the use of a diagonal without a Barlow....

Ok, here is some more info that you guys might find useful...

• The tube has an outer diameter of 56mm and an internal diameter of 52mm.
• There is approximately 21mm of travel in the focuser.
• The tube has a female thread that accepts the body of the focuser. It would be possible to shorten the tube if you had the means to re-cut the thread inside the tube or find a shorter focuser with the same thread or a very sort adapter. Sorry, I have no means of accurately measuring the pitch of the thread but it looks like some sort of standard metric fitting to me.
• The lens cell and green retaining ring unscrew to reveal a 16mm male thread on the OTA. The green ring eats up a minimum of 3.5mm of that thread. The lens cell has a 10mm deep female thread. This means that you could remove 2.5mm from the front of the tube and both would still fit provided you did not destroy there thread on the OTA.
• Alternatively, you could dispose of the green ring and remove 6mm from the front of the tube and re-attach the lens cell without the retaining ring.

I was seriously considering that final option when something struck me! ?⚡?⚡

I have been fitting the Baader T2 prism using the 1.25" nosepiece. The Baader "T2" Prism has...wait for it...a T2 fitting on both sides!!  

I unscrewed the nosepiece and screwed the prism directly onto the T2 thread on the back of the focuser and my prism is now 4mm closer to the objective so I should now be able t reach focus on infinity. Bingo!

Here are some pictures that might help you visualise some of the above...

Back of OTA with the focuser removed to reveal a female thread. Internal diameter appears to be 52mm to thread diameter perhaps M53?

Focuser male thread and OTA female thread are approximately the same length so modification to shorten the OTA here would require the OTA thread to be extended/re-tapped.

 

Green retaining ring fully retracted leaves 2.5mm spare thread when objective cell fully engaged.

Objective end male thread on OTA is 16mm deep, 12mm when green ring retained in place. Green ring therefore eats 4mm of the OTA length.

The lens cell has a 10mm deep female (M56?) thread. Shortening the OTA by 6mm ad not using the green retaining ring would give 6mm of additional inward travel.

 

The Baader T2 Prism lightbulb moment! ?

 

 

It will hopefully be clear tonight so I will give this a go and report back ? 

[happy-kat]

Well done. I'll investigate my two diagonals the WO and the unknown for a T2 thread.

[DRT]

In the last picture I posted you can see the Baader 1.25” Focusing Eyepiece Holder that I have fitted to the Prism. The top ring of that holder is the focusing ring which can be removed to reveal another T2 male thread. Removing it provides another 2mm of inward travel ??

[happy-kat]

I've got one of those baader helical focuser rings too. I'll see later what I can fashion.

[Peter Drew]

Just waiting for them to come back in stock to purchase a couple for a binoscope. I have a keen hacksaw and a lathe so it shouldn't be a problem.

[happy-kat]

No go here by two diagonals that do unscrew are revealing female threads and the WO diagonal doesn't unscrew at all.

[DRT]

38 minutes ago, Peter Drew said:

Just waiting for them to come back in stock to purchase a couple for a binoscope. I have a keen hacksaw and a lathe so it shouldn't be a problem.

Worth checking Rother Valley Optics, Peter. I got mine there same day when all others were declaring out of stock ?

[DRT]

33 minutes ago, happy-kat said:

No go here by two diagonals that do unscrew are revealing female threads and the WO diagonal doesn't unscrew at all.

If I manage to test the Baader Prism works fine I’ll be selling the Meade Prism so I’ll put you down for first refusal of you are interested?

[happy-kat]

I look forward to your results and yes that sounds like a plan for now please.

I'm going to research if I can get some 1.25 what ever that thread is to a T2 male as my unknown diagonal does focus just need a bit more for infinity which I might manage with the baader helical as you are about to test.

[nicoscy]

I asked a friend who sells astrogear and the thread after you remove the green bit is M53.

This whole situation is ridiculous! SW comes out with a very attractively priced, good looking, FPL53 50mm scope and they couldn't just shave off 30mm from the tube and have a longer extension at the back. Had they done so, these things would fly off the shelf like hotcakes!

I applaud all those who are fighting the good fight to adapt this thing for visual but I think I'll stick to reading this thread and give up on the idea of the SW as a mini grab n' go

[Peter Drew]

Any indication as to whether the objective is airspaced or cemented?

[Roy Challen]

This is an interesting thread. It looks like a perfect ultra lightweight travel setup and I would certainly be interested if it can be used for widefield visual. Before anyone goes cutting one up, might it be worth considering using a combination of Borg adapter/mini helical focuser/short-light-path diagonal? I recall that Tak prisms and Tal mirror diagonals both have light paths under 70mm (nearer 60 for the Tal) and one of the huge range of adapters that Borg make must surely (hopefully!) be of use.

I had a Borg Mini 60 achro a few years ago. That worked with a Baader Amici prism (the expensive one), Tak prism, mini helical focuser, T2 adapter, Lunt wedge and all of my then current eyepieces except 2 of my Zeiss orthos. Point being, I would be surprised if there isn't a combination of off the shelf parts that didn't work.

[DRT]

2 hours ago, nicoscy said:

I asked a friend who sells astrogear and the thread after you remove the green bit is M53.

This whole situation is ridiculous! SW comes out with a very attractively priced, good looking, FPL53 50mm scope and they couldn't just shave off 30mm from the tube and have a longer extension at the back. Had they done so, these things would fly off the shelf like hotcakes!

I applaud all those who are fighting the good fight to adapt this thing for visual but I think I'll stick to reading this thread and give up on the idea of the SW as a mini grab n' go

 

49 minutes ago, Roy Challen said:

This is an interesting thread. It looks like a perfect ultra lightweight travel setup and I would certainly be interested if it can be used for widefield visual. Before anyone goes cutting one up, might it be worth considering using a combination of Borg adapter/mini helical focuser/short-light-path diagonal? I recall that Tak prisms and Tal mirror diagonals both have light paths under 70mm (nearer 60 for the Tal) and one of the huge range of adapters that Borg make must surely (hopefully!) be of use.

I had a Borg Mini 60 achro a few years ago. That worked with a Baader Amici prism (the expensive one), Tak prism, mini helical focuser, T2 adapter, Lunt wedge and all of my then current eyepieces except 2 of my Zeiss orthos. Point being, I would be surprised if there isn't a combination of off the shelf parts that didn't work.

Nicos & Roy - just to clarify, this scope does work for visual observing provided you find a short prism.

The cheap standard Meade Prism (which looks identical to the Celestron version that comes with their SCTs) works just fine. I have't tested it yet but I am now also convinced that the Baader T2 prism will work when screwed directly onto the T2 thread on the back of the focuser.

Please step away from those hacksaws folks  

Edited June 4, 2018 by DRT

[DRT]

1 hour ago, Peter Drew said:

Any indication as to whether the objective is airspaced or cemented?

Sorry, Peter, I don't know.

Are there any tell-tale signs I could look for without dismantling the cell?

[Peter Drew]

The most obvious sign would be 3 separator tabs but some objectives have a ring separator so does not easily show up. I'm hoping it's not cemented.

[DRT]

39 minutes ago, Peter Drew said:

The most obvious sign would be 3 separator tabs but some objectives have a ring separator so does not easily show up. I'm hoping it's not cemented.

I've had a look and there are no signs of separator tabs. It is possible that there is a ring in there but I cannot see it.

Perhaps ask FLO?

[DRT]

14 minutes ago, DRT said:

I've had a look and there are no signs of separator tabs. It is possible that there is a ring in there but I cannot see it.

Perhaps ask FLO?

I've emailed Skywatcher to ask the question.

[Peter Drew]

Derek. Thanks for looking. The interest is because I'm hoping to make a better small astro binocular than those usually available, cementing often results in star images that look like fly impacts on a windscreen. I've contacted RVO concerning availability and they are out of stock until the end of July.

[Rick_It]

Thanks everybody for all your efforts!

I'm very interested in the Baader T2 prism, because I have a 28mm/68° (2" barrell, but a T2 opening is enough) which would provide me 8.6x!

I bet this objective is the same as the Celestron Hummingbird 50mm ED. Since the Hummingbird exists also in the 56mm ED version, maybe SW will come out with a 56mm Evoguide with enough backfocus for a standard diagonal. They can use the same tube and focuser, just a different lens cell (the 56mm objective has a 29mm longer focal lenght!).

Edited June 5, 2018 by Rick_It

[DRT]

On 04/06/2018 at 12:25, Peter Drew said:

Any indication as to whether the objective is airspaced or cemented?

Here is the reply I received from OVL...

Quote

 

From: "Info@opticalvision.co.uk" <info@opticalvision.co.uk>
Date: Wednesday, 6 June 2018 at 10:10
To: "DRT" 
Subject: FW: RE: Derek Turnbull sent a message from Skywatcher website

They are air-spaced, not cemented
 
Kind regards,
OVL
 ************************************
From: auto@skywatchertelescope.net [mailto:auto@skywatchertelescope.net] 
Sent: 04 June 2018 14:35
To: Info@opticalvision.co.uk
Subject: Derek Turnbull sent a message from Skywatcher website
 
Hi,
 
I have recently purchased a Sky-Watcher EvoGuide ED50.
 
Could you please tell me if the doublet lens is air-spaced or cemented?
 
Thanks
Derek
************************************

 

 

[happy-kat]

That's great to know.

I've shaved about 6mm off yet to be checked for distance improvement.

[Peter Drew]

Thanks very much Derek, even keener to get a pair now.