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ZEISS. Discover the fascinating world of birds, and win a birding trip to Columbia

Investigating the Potential of a Small Newtonian Reflector used in Spotting Scope Mode (1 Viewer)

wllmspd

Well-known member
Interesting. Does it need much infocus travel… for which the imaging newtonian version would be better? (Wondering if you could shrink “the stack” length somewhat)
Do you have a link to the erector you’re using? Does it have any field stop or other limitations to the powers available? Would be interesting to put 2 together to make a bino!

Peter
 

henry link

Well-known member
Hello Neil,

Thanks! You might be interested in this effort at making a Newtonian spotting scope almost 30 years ago.


One optical problem that appears to be inevitable with using obstructed scopes at such low magnification in daylight is that the pupil size of the eye will effectively stop down the aperture until the the diameter of the secondary becomes excessively large as a percentage of the primary. For instance, your scope at 20x in front of an eye open to 2.5 mm in daylight would effectively become a 50mm scope with a 35mm secondary, or 70% instead of 26%.
 

Dipperdapper

Well-known member
Hiho folks,

Thanks for the feedback. The blog was the result of a Sunday afternoon's worth of quality Tomfoolery lol

Peter: I think I picked the erecting adapter up from Tring Astro. I believe you can order one up from any authorised Vixen dealer, but rumour has it it might have been discontinued. Like a Barlow, it will restrict the field of longer focal length eyepieces but doesn't with shorter focal length oculars. When I first received it I giggled to myself; such a long tube but I was surprised how well it worked. I'm sure better designs could be explored to truncate it more but I reckon that would a project for an optics nut.

Henry: thanks for the info on the Russian Zuka Scope; looks really cool - like firing a bazooka lol!

Found a couple of images of it here:


I take your point about the issues at very low powers. I've used it at powers well over 100x though with no issues; really comes into its own in low light.

With best wishes,

Neil.
 

Hauksen

Forum member
Hi Henry,

You might be interested in this effort at making a Newtonian spotting scope almost 30 years ago.

Thanks a lot, that's fascinating with regard to the utility of having a way to brace the optics against the shoulder, too. I've experimented with shoulder stocks for conventional refectors (the Nikon ED50), so seeing that there's a scope purpose-built for shouldered use is quite a revelation!

I also wonder if the effectiveness of the setup could be improved by adding electronic stabilization, but I have not idea if mirror telescopes are actually suitable for these (consumer-grade) systems.

Regards,

Henning
 

Binastro

Well-known member
Hi,

I agree with Henry regarding low powers with obstructed optics.

Then there is the viewing at 90 degrees to the object.

In addition few birdwatchers will be able to collimate any telescope.

Also getting a custom made small high quality secondary and Hilux coatings.

Jim Hysom made me several high quality Newtonians.

Personally I favour 150mm Maksutov Cassegrains.
The f/15 had a 25% obstruction.
The f/10 had a larger secondary but was superb terrestrially at 95x with a Porroprism adapter.

Spotting scopes of the normal kind and astro refractors are mostly trouble free, although the optical standards lately seem to be questionable.

As to Newtonian binoculars.
Well I'd rather not.
Some of the large systems take over an hour to collimate.

Regards,
B.
 

wllmspd

Well-known member
Would a normal 90degree diagonal (like the Zuka) give the correct orientation views? An imaging newtonian and maybe some mirror shifting would deal with any focus position issues.An imaging scope would have a larger diagonal, which would lead to the issues highlighed which could get annoying. (Small replacement secondaries are quite cheap) I would probably not try too high power as you are relying on yourself for stability and breathing/pulse rate will cause little jumps. An ideal scope would be able to provide a full range of magnifications and also bright views, but aperture and sacrificing the lower power range would seem like a good trade off.
Collimation…. If it stops others wanting to use my stuff, then great ;-)

Peter
 

Binastro

Well-known member
Hi Peter,

I am not sure of the orientation, but maybe normal.

I suppose a zoom eyepiece would work, but high powers couldn't be used hand held unless braced on a wall or similar.

High quality secondaries of the correct thickness to prevent bending are not very cheap.

Also fast Newtonians have problems.

Regards,
B.
 

opisska

Jan Ebr
Czech Republic
Well, when it comes to sharpness, a newtonian on axis is extremely hard to beat, but how do you deal with off-axis aberations? Coma is inevitable - the solution is a coma corrector, but the only one that actually works perfectly for visual observations is paracorr from televue, which is quite bulky. At the end of the day, the whole setup, especially if upright image is required, is gonna be just that - bulky.

I have been for many years using Maksutov scopes for birding - those are less bulky, but they suffer from inevitable parasitic light during the day - there is geometrically no solution, any baffle system either leaves some stray light or cuts some desired light. However, these things are silly cheap and compared to the performance of refractors at the same price bracket, they work wonders.

Then I got older and richer and bought an actual quality spotter (Meopta S2 HD) and it pains me to say, but I am never coming back. Not only is the image fantastic, but the whole thing is just so small and lightweight and that completely changed how much I actually pull it out to use it. That's simply unachievable with a mirror system, no matter what.

Newtonians still remain my favored system for astronomy. I have my half meter Dobsonian and you won't get anywhere close to a one-man mobile scope of that aperture with anything else.
 

DRodrigues

Well-known member
... I believe you can order one up from any authorised Vixen dealer, but rumour has it it might have been discontinued. Like a Barlow, it will restrict the field of longer focal length eyepieces but doesn't with shorter focal length oculars. When I first received it I giggled to myself; such a long tube but I was surprised how well it worked. I'm sure better designs could be explored to truncate it more but I reckon that would a project for an optics nut.

...
The Vixen lens erector induces a magnification increase about 1.5x, variable with eps models - see Test of image erectors
 

DRodrigues

Well-known member
Hello Neil,

Thanks! You might be interested in this effort at making a Newtonian spotting scope almost 30 years ago.


One optical problem that appears to be inevitable with using obstructed scopes at such low magnification in daylight is that the pupil size of the eye will effectively stop down the aperture until the the diameter of the secondary becomes excessively large as a percentage of the primary. For instance, your scope at 20x in front of an eye open to 2.5 mm in daylight would effectively become a 50mm scope with a 35mm secondary, or 70% instead of 26%.
At the end of the 90ies I purchased a UK made scope of this type (don't remember the brand), the tube was in carbon-fibre, but I send it back not because low magnification eps problems but because of lack of resolution at higher powers - I attributed this to the probable lack of quality of the image erector - it used adapted Opticron eps.
 

Binastro

Well-known member
There have been some UK made optics that promised a lot but didn't deliver.

Nowadays I have not heard bad things regarding Orion Optics U.K.
They make different quality optics at different prices.

I got an Orion Optics U.K. 20cm Dobsonian for a friend and it seemed to be good, although I didn't personally use it.

Regards,
B.
 

Dipperdapper

Well-known member
Hi David,

Thanks for the feedback. I wasn't aware of the 1.5x amplification. I contacted a Vixen-Opticron( though they no longer deal with Vixen products) staff member and asked him about the amplification. The gentleman I talked to said that they would have clearly stated that in the advertising description if it were the case.

I attach two images I took today; one without the adapter and one with the adapter, both using the 32mm Skywatcher Plossl. Both uncropped. The one in brighter light is the erect image caught in slightly better light.

Kind regards,

Neil.
 

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pete_gamby

Birds? What Birds?!
Hi Neil

Good to speak to you the other day :)

Measuring your photos in Photoshop there's a 1.05x difference in the height of the dish in the erect image shot. Measuring David's photos shows 1.25x increase.

David notes in his text that the erect image adapter increases focal length (something I hadn't considered) so that would of course mean increased magnification even though that is not, as we discussed, mentioned anywhere by Vixen.

Cheers, Pete
 
ZEISS. Discover the fascinating world of birds, and win a birding trip to Columbia
ZEISS. Discover the fascinating world of birds, and win a birding trip to Colombia
ZEISS. Discover the fascinating world of birds, and win a birding trip to Colombia

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