Magnification Extension - Scoping through Binoculars? (1 Viewer)

[Will K]

Hi all,

To fill an idle moment, I tried looking through my spotting scope using a pair of binoculars as a makeshift magnification extender. I ended up with some very intriguing results.

All the following images were captured on an iPhone through a Vortex Razor 85mm, at a distance of about 10m. The first at 27x, the second at 60x, and the final two at 60+12x, having been ‘supercharged’ though an NL Pure 12x42 (very simple method illustrated below).

The results are very far from satisfying, of course, containing many imperfections and distortions, but I was actually really surprised that it worked at all! I’d love to hear someone explain the science behind this.

Also, might there be a way to make this viable as a bootstrapped high-X method?

Thanks!

 

[Binastro]

Hi Will,

This is called empty magnification.

A truly fine 85x astro scope can probably be pushed to 250x in actual use and 350x in testing.
Spotting scopes are less good.

However, you are using a very good 12x booster giving about 700x magnification.
It may be that close up the magnification is nearer 600x.

Realistically about 200x is usable with these good quality optics, so the extra 400x or 500x is empty magnification.

I used 600x and 700x regularly on a 317mm custom Dall Kirkham.
Also, 1100x but this was empty magnification.

Terrestrially I used 250x on three identical 120mm astro refractors at 3 a.m. on rather many occasions viewing a clock tower 4.7 miles away.
The results were excellent with one arc second resolution.
This was over built up areas and parks.
I was viewing 10 metres up and the clock was 25m above the ground.

I have used a very good Japanese Celestron 20x80 c.1975 binocular with a Soviet 7x binocular behind it, also very good.
The resulting 140x magnification enabled me to read a hotel sign 11 miles away.

William Herschel regularly used 900x on his home made 6.2 inch telescope.
To discover the planet Uranus, he used about 250x, 450x and 900x before declaring it was not a star.

It might be more sensible to use a low powered monocular or binocular for your set up.
The Libra 4x22 is cheap and probably good enough or the 4.4x25 (5x25) Bushnell extra wide or a 5x25 Foton.

Or the expensive Zeiss 3x monocular.

Regards,
B.

 

[henry link]

I prefer to increase magnification with short focal length eyepieces, but when a spotting scope design won't allow that I'll resort to the Zeiss 3x monocular as an auxiliary scope placed behind the scope eyepiece. Adjusting the zoom for 120x-180x produces ample magnification for measuring the revolving power of an 85mm scope using the USAF 1951.

 

[tenex]

Where are the filaments/specks that are somehow brought into focus in the 60 * 12x images, and why?

 

[henry link]

Detritus associated with the binocular optics (probably dust on the eye lens), brought to focus by the high DOF imposed on the binocular when its aperture is reduced to 1.41mm by the exit pupil of the scope. Add well focussed eye floaters to that from the eye's effective aperture of 0.0112mm imposed by the binocular's reduced exit pupil and the view is certain to be pretty awful.

 

[Will K]

Fascinating stuff!

What factors prevent a clearer image at this 'empty' magnification range, exactly? Is it mainly to do with disproportionate alignments in exit pupil, as mentioned by Henry - not all the light going where it needs to go?

If someone wanted to find out more about this, might anyone be able to recommend some useful reading: books, articles, blogs, etc.?

 

[Binastro]

The magnification limit is imposed because of the nature of light.

There is a resolution limit, which has different aspects, but depends on the aperture of the front elements, the objective.

Bigger aperture means smaller detail is seen.

Short focus telescopes, such as spotting scopes, have to have extra elements or special glass types to reach near to resolution limits.

Long focus telescopes only need two element or the best, three element objectives that actually reach the highest limits.

Once the limit of an excellent 85mm spotting is reached, say 200x, then increasing the magnification provides no extra information.
In fact, information can be lost because the image gets dimmer and dimmer.
At 600x one will see less than at 200x.
In addition, the human eye, at least in most people has a minimum exit pupil that it can use.
Those with near perfect eyes can use very small exit pupils.

Usually, the atmosphere limits the magnification at medium to long distances.
Some bird watchers complain that only 30x can be used because of boiling images.

At my location, 100x can nearly always be used even during the day.
Often 135x or 150x is also fairly steady.

When observing stars, which are very high contrast objects, higher than normal magnifications can be used, say to separate very close double stars, or even to give a hint that the star is double.

So basically, the magnification is limited by the local Seeing conditions i.e. atmosphere, the size of the front objective and the observer's eyesight.
High mountain sites or high plains usually beat sea level sites.
In addition, the best Seeing occurs when sea, air and land temperatures are the same.
Especially when around 16C or 61F.

Regards,
B.

 

[Will K]

Thanks for the additional context for this effect. Very interesting.

I probably wasn't helping things by shooting these test images through a closed double-glazed window, too. Forgot to mention that!

 

[Binastro]

Actually, in this extreme case, the closed window was an asset, as an open window today at 5C or less and a room at 20C, maybe more. would create such an exchange of air through the window gap that the view would be disastrous.

Double glazing can usually take 50x if viewing at right angles to the glass.
My unusually good kitchen window can take 135x easily with an 85mm scope.
A large scope, say 150mm aperture will only take 100x.
Small scopes do better through double glazing.

The actual image at 600x will be badly degraded by the window glass, but the empty magnification will hide this.

I used Horace Dall's 8 inch Maksutov at 400x viewing Mars through his selected and hand worked plate glass window in his loft, and the image was one of the best I have ever seen of Mars.
Unbelievably good.

Mars is now bright, as is Jupiter.

Regards,
B.

 

[wllmspd]

I remember holding some 8x behind some 10x bins when I was a lad and getting a dark but super zoomed view of a distant flat block.

Peter

 

[Will K]

I remember holding some 8x behind some 10x bins when I was a lad and getting a dark but super zoomed view of a distant flat block.

Peter

I assume that at 80x, thereabouts, if the glass was good, and the further objective was relatively large, the image might have some clearer detail.

 

[Hermann]

I prefer to increase magnification with short focal length eyepieces, but when a spotting scope design won't allow that I'll resort to the Zeiss 3x monocular as an auxiliary scope placed behind the scope eyepiece.

I use the Zeiss 3x12 quite often when I've got one of the wideangles on my Nikon Fieldscopes, for instance the 24x WA on the EDIIIA or the 30x on the ED82. The advantage is that I get more magnification without having to change the eyepieces. 72x on a 60mm scope or 90x on an 82mm scope is quite feasible.

Works just fine for a quick ID.

Hermann

 

[yarrellii]

I've been fascinated by this for quite a while. A few years ago I did a similar test with the Moon and the humble Opticron MM3 ED 60 combined (if I remember correctly) with the Nikon EII 8x30.

Following order:
x1 (directly looking through the smartphone); x8 with binoculars
x15 scope at min zoom; x45 scope at max zoom
x120 (8x binoculars + 15x, min zoom); x360 (8x binoculars + 45 x, max zoom)





While the x120 image offers a relatively nice view, the x360 is really soft and dirty. I've been wanting to repeat this with the updated equipment I have now (say a 65 ATS HD and 8x32 EL SV), maybe I'll repeat it if I get a nice clear sky

 

[Will K]

I’m sure an ATS and an EL would give a relatively clear image, at low x.

At the moment, I’ve only got one pair of binos - the 12x42 NL is my ‘all rounder’. So with so much empty magnification created, I’m not going to get great images with my current kit.

I’m very curious to try the Razor with a Zeiss 3x12, though! I might invest in one next year.

 

[yarrellii]

I use the Zeiss 3x12 quite often...

Do you need any sort of "adapter" to make it fit eyepieces/eyecups with different diameters? For example, the change from the Opticron SDLV2 to the Swarovski 20-60 is really noticeable. The latter is way wider.

 

[Will K]

I wonder if I'm right about this: It seems possible to use the binos to fine-tune the focus of the scope.

When looking at a fixed object, I can initially bring the scope into (what appears to be) perfect focus, and then, when looking through the binos and the scope together, see that the focus is a little bit off. I can then adjust the scope accordingly, so that the image seen in 'empty magnification' is as clear as possible.

Would this then equate to maximum clarity when looking through the scope alone? The difference is almost imperceptible, to my untrained eyes. But am I correct in assuming that this method maximises 'normal' focus precision?

 

[Hermann]

Do you need any sort of "adapter" to make it fit eyepieces/eyecups with different diameters? For example, the change from the Opticron SDLV2 to the Swarovski 20-60 is really noticeable. The latter is way wider.

Zeiss made a number of adapters to use the 3x12 with various of their binoculars. I've got them all, and one of the adapters fits into the eyecup of the Nikon 24x/30x WA quite nicely.

However, I think it's quite possible to make your own adapters.

Hermann

 

[yarrellii]

Zeiss made a number of adapters to use the 3x12 with various of their binoculars. I've got them all, and one of the adapters fits into the eyecup of the Nikon 24x/30x WA quite nicely.

However, I think it's quite possible to make your own adapters.

Hermann

That's very interesting and good to know! Thanks. I'll look into that. I'm curious a how could you make an adapter, you mean like 3D printing or a more direct approach?

 

[Will K]

I’ve also noticed that changing the focus on the binoculars makes no noticeable difference to the image. Scrolling from infinite to close focus positions seems to not affect the clarity in any way, whereas the scope focus operates as usual.

I’m not quite sure why this should be. Can anyone enlighten me?

Thanks!

 

[tenex]

The scope has 5x the magnifaction, and a powerful focusing element designed to compensate for that. The binocular focuser will have a modest effect in comparison, though it might affect how close the scope can focus... have you checked?