That of which shall not be spoken...... (1 Viewer)

[Troubador]

I have a Zeiss 6x18 too. It fits easily in a shirt pocket. However it has draw tube focusing and it gets longer the closer you get to the subject you are viewing while its depth of field gets shorter. You really need to be well braced to use it on close objects and plenty of light on the subject also helps.

Bob

Hi Bob

Yep I agree and most of the time when I am using it at very short distances including its minimum focus of about 1 foot I am either laying down and using both elbows or braced with one elbow against my knee or a rock. For this type of observing of sea-anemones, molluscs and crustaceans its pretty much unbeatable. But much of the time I make full use of both eyes, bins and their close focus.

Lee

 

[Stephen Prower]

Russian v Chinese 2.5x17.5 monocular

Binastro

Hi Stephen and Clive,
My 2,5x17,5 binocular (actually opera glass) doesn't have a V.
The one in the photo linked was probably for the film V, where they had an interesting way of changing the government.

The Russian one is multicoated. From the photo the Chinese one may be single coated.

More importantly, if the Russian one has triplet objectives, does the Chinese one have doublets? ...

The two little Chinese 2.5x17.5 monoculars have arrived.

To complete the irruption into CliveP's thread, I report:

1. The Chinese monoculars, as the photos in the URLs I gave show, are of a completely different design to the Russian 2.5x17.5 monocular.

2. In answer to your particular speculation, the Chinese monoculars incorporate just two lenses, one at the eyepiece end, the other at the objective end.

I haven't opened up the Russian monocular to inspect and count lenses.

I can't speak re the respective coatings.

3. The big difference in specification is the closest focus distance:

For the Russian specimen, the distance is 2ft (0.6m).

For the Chinese specimens, the distance is 9ft or 14ft (2.7 or 4.3m).

As far as I can see from opening up one of the Chinese specimens, the reason for the discrepancy in closest focus distance between them must lie in the distance of separation of their two lenses.

4. Otherwise:

The Chinese specimens:
* Have superior ergnomics to my taste. The attached finger ring is most useful
* Give a slightly brighter and more contrasty image to my eyes
* Have the above mentioned 'inconsistent assembly' fault
* With focus adjustments, give a fully resolved image only out to about 60% of radius
* Give a blurred image with marked Chromatic Aberration in the outer 40% of radius.

The Russian specimen:
* Has, as above, a far superior closest focus distance
* Has the previously mentioned irritating, but in practice non-vital, assembly fault of a loose focus mechanism
* Gives a more highly magnified image
* With focus adjustments, gives not only a fully resolved image out to about 60% of radius, but also a usefully resolved, CA-free, image continuing right out to the edge.

5. In short you get what you pay for!

The Russian 2.5x17.5 specimen has a full range of utility, and, outside the central zone, usefully performing optics.

The Chinese 2.5x17.5 specimens lack both of the above. Nevertheless, by virtue of their equally well resolved central zone, and better ergonomics, they remain potentially useful to clarify and slightly magnify vision out beyond closest focus distance (whatever, given the vagaries of assembly, that distance may happen to be!).


Stephen

 

[Binastro]

Thanks Stephen.
The brighter Chinese image might be because of lower magnification and fewer elements.
It will also depend on your pupil size if used in the dark.
Are the Chinese elements coated on all surfaces?
The Chinese one may have a wider field because of lower magnification if they are both 17.5mm aperture..

The difference in image off centre is because of the most basic 2 element design.

P.S.
I can get a 2x magnification by holding my distance glasses a distance in front of my eyes, particularly using the right lens with my left eye.
The image is good and useful, and costs nothing.

I also have a tiny opera glass from the charity shop that magnifies 2x, maybe old French. £2.50?

 

[Binastro]

The fields of view of Galilean optics varies with distance between optics and type of optics and eye position.
So it is difficult to predict and varies a lot.

 

[Stephen Prower]

Binastro & CliveP

1. 2.5x17.5 Monocular

I don't normally dismantle optics! So I am not sure what to look for re coatings. I only went into the Chinese monocular to see if I could set a closer near focus point. I'm sorry about that.

Many thanks for the observations! Apart from the nearest close focus measurements, I reported impressions. You supply explanations of the impressions.

I am lucky enough (I don't run a car) not to need or carry glasses for far sight. So I use the Russian monocular instead, as I have said, for the exceptions, eg viewing pictures between the heads of visitors in a crowded art gallery, or reading the numbers off buses. If I was caught at a zoo or aviary without binoculars, I could see a use there too.

2. 12x45 Monocular

Back on the subject of 'serious' monoculars, the tripod adapter for mounting a mobile phone also arrived recently from China, and with the help of:
* Some of the hard foam used by manufacturers to protect bicycle frames in transit (Compressible spacer)
* A stout pair of women's hair bands (Elastic bands),
I have firmly attached the 380 gram (13.4 oz) Chinese 'Military' 12x45 Porro monocular that I mentioned in passing earlier to the adapter.

A selfie stick adds 235 gram (8.3 oz), and belt pouch a couple of ounces more. But I use stick and pouch equally to support 10x42 binoculars for lengthy scanning (and probably would find them useful also with binoculars of less weight and power). So the comparative weight of monocular vis-a-vis binocular remains 380 gram.

Now I wait for better weather to experiment with the new toy: large objective and handy dimensions versus small apparent image size and need for lightweight second optic for close viewing!


Stephen

 

[CliveP]

I stumbled across this:

http://www.monocular.info/index.html

Brilliant what you find at times even if I say so myself 8-P

The knowledge increases.