Minimalist lens converter. (1 Viewer)

[Binastro]

With some places not allowing binoculars but letting through cameras and lenses, there is the option of a lens/monocular converter.

But these are large and may not be allowed in.

However, there is a rare Leica 39mm mount lens adapter that is tiny and converts a Leica lens to a Galilean telescope.

I saw a self made 3D printed opera glass using Edmunds Scientific Grade 2 and Grade 1 lens elements that cost about $4 each.

A double concave single element eyepiece and either plano/convex or double convex objective.

The focal length of the eye lens is minus 15mm to minus 20mm and about 17mm diameter.

Say minus 17mm and 17mm diameter.

I have a tiny 2.4x opera glass.

I unscrewed an eyepiece.

It has a 12mm diameter lens of minus 26mm focal length.

In a very small metal mount with a blackened short tube.

With some lenses no image is formed.

But I used a Minolta MD 200mm f/4 lens in excellent condition from April 1976 I think according to the Japanese oval sticker code.

Holding the eyepiece just a bit behind the lens I get a 7.5x50 Galilean telescope.
At night looking at a brightly lit entrance hall the image is very good, but the field is very small at 3.5 degrees. A 26 degree AFOV.

However, in the day it wasn't so good as there was false colour.
But this is one sided and probably because the eyepiece was tilted and not on axis.

By cutting a hole in the solid plastic lens back cap I think I could just slot this tiny eyepiece in.

For this particular eyepiece a 135mm f/2.8 lens may be better, giving a 5x Galilean upright image telescope with a 5 degree field.

So, definitely not as good as the suggested Opticron 7x24 MCF binocular.
But if binoculars are seized an option is this tiny camera lens adapter.

Regards,
B.

Correction. mm not dioptres.

 

[Richard D]

Interesting - have you any photos?

 

[Binastro]

Sorry, I don't know how to do photos.

The Leica adapter I have somewhere safe in a drawer, but I haven't looked at it for years. It is very small.

Any old opera glass bought in a charity shop probably has eyepieces that just unscrew. These opera glasses cost perhaps £4, from 100 years old to 50 years.

I think that some of the larger field glasses of 5x or 6x may have doublet objectives and maybe doublet eyepieces, but again I haven't looked at these for years.

Interestingly, the tiny opera glass only has an objective of about 17mm. This limits the field, as the field depends on the objective diameter and the length of the opera glass.

This 2.4x opera glass has a focus wheel but a fixed IPD.
As this IPD doesn't match my IPD, the field with one barrel is 6 degrees and with two barrels 7.5 degrees.
So the sideways field is much bigger with both barrels.

By unscrewing one of the eyepieces I get dioptre correction, but need to make sure the eyepiece doesn't fall off.
There is sufficient travel in my case that the eyepiece stays on.

Using the Minolta 200mm f/4 lens at f/4 the image is bright and the aperture 50mm, which is much bigger than the 17mm of the opera glass. Although the Minolta lens is much longer than the opera glass the wider objective gives a wider field.

Regards,
B.

 

[Tringa45]

Sorry, I don't know how to do photos.

Reassuring to see I'm not the only digital dyslexic here!

Regards,
John

 

[Richard D]

From memory Nikon's lens>telescope adapter was fairly small (smaller than a 50mm lens). I've not seen one secondhand for a while, but with a good F-mount manual lens it might make a serviceable monocular.

 

[fazalmajid]

Kenko makes the Lens2Scope, which is reasonable compact. It's fairly dim, however.

What about a monocular that looks a bit like a camera, like the Minox Macroscope?

 

[Binastro]

Hi Richard,

I have the Nikon monocular converter.
It is very good, But I don't know if any of these monocular converters are very bright.

I have monocular converters in numerous mounts, some very obscure.

I prefer the Vivitat TLA-1 to Minolta's own.

The only one I don't have is the Leica normal one, as they were too expensive.

I also have the Tamron right angle version and the back of the Pentax mirror spotting scope fits any T2 mount lens.

Together with 1.4x teleconverters the variety is almost endless.

The Kenkos are bigger and less magnification but angled.
I bought four different as a job lot.
They are narrower angle than the old Japanese versions.

Although none of the standard monocular converted lenses are as good as a dedicated scope, they are far better than the Galilean version.

The point is that monocular converters may be seized but a tiny single element that is negative and looks like a coat button will probably be O.K.

Regards,
B.

 

[Binastro]

My Galilean monocular converter weighs 8g or 0.3 ounces. It is the size of an overcoat button.

The Itorex, Japan standard monocular converter weighs 109g in Pentax PK mount or 141g with the Pentax 42mm screw adapter.
That is 4 or 5 ounces.

These Japanese monocular converters vary in weight a bit depending on mount.

I have used Exakta, Topcon, Minolta MD and MAF, Nikon, Olympus, Canon various, Pentax K and 42, Konica, Sony, T2 and some other lenses with monocular converters.

I don't think I have seen a Petri version.

The Lens2Scope in Nikon mount, Taiwan, weighs 172g or 6 ounces.
It is currently mounted on a Micro Nikkor 105mm f/4 lens.
It is quite good as a scope, but not that bright.

Regards,
B.

 

[Richard D]

Kenko makes the Lens2Scope, which is reasonable compact. It's fairly dim, however.

What about a monocular that looks a bit like a camera, like the Minox Macroscope?

I've not tried the Lens2scope - is it 10x like the Nikon?

I thought the Minox Macroscope performed quite well for the price - it's much better at short distances than approaching infinity. I sometimes carry mine for bugs in the summer, but yes it might pass a lot of checks without comment.

My Galilean monocular converter weighs 8g or 0.3 ounces. It is the size of an overcoat button.

The Itorex, Japan standard monocular converter weighs 109g in Pentax PK mount or 141g with the Pentax 42mm screw adapter.
That is 4 or 5 ounces.

These Japanese monocular converters vary in weight a bit depending on mount.

I have used Exakta, Topcon, Minolta MD and MAF, Nikon, Olympus, Canon various, Pentax K and 42, Konica, Sony, T2 and some other lenses with monocular converters.

I don't think I have seen a Petri version.

The Lens2Scope in Nikon mount, Taiwan, weighs 172g or 6 ounces.
It is currently mounted on a Micro Nikkor 105mm f/4 lens.
It is quite good as a scope, but not that bright.

Regards,
B.

Nice lens - I always prefered it to the 2.8, but I wonder whether something like the 135mm f2.8 might be almost as compact yet brighter?

 

[Binastro]

Yes, Richard, the Lens2Scope is 10mm as are most of the Japanese monocular converters.

I think that the Leica version may be12.5mm, not sure.

The 90 degree Tamron maybe 18mm and may use a mirror with a reversed image but again, I cannot remember.

The Lens2Scope is huge compared to the old Japanese ones, also the 45 degree angle meant I couldn't find Jupiter just now.
It is more than twice the bulk of the old Japanese ones which are straight through. It has a tripod foot, but I think it would break if a 300mm or 400mm lens was added.

The 105mm f/4 Nikon Micro is heavy. The 135mm f/2.8 would be better.

If binoculars are seized abroad, I think the Lens2Scope would also. Perhaps one would be O.K. with a Bob, Itorex, Vivitar or similar old Japanese one, as they are fairly small.

The point about the inferior Galilean one is that it is tiny and I doubt anyone would know it had a use.

Regards,
B.