Sorry about sacrilege

[vlaiv]

My case of cloud sickness is still hitting strong and I can't get rid of these crazy ideas - always searching for new project (although I have like tons in backlog waiting for better weather conditions).

I'm sorry in advance for causing any grief among binocular lovers, I truly am. Part of the problem is that I have one good eye (other is astigmatic nightmare) so I observe with telescopes only and really have not developed proper appreciation for binoculars.

Here is the thing - how good is this binocular optically?

https://www.teleskop-express.de/shop/product_info.php/language/en/info/p1421_TS-Optics-20x80-ED-APO-Binoculars-with-two-Triplet-Objectives-and-Tripod-Adapter.html

I see that it is triplet and it has ED and APO monikers in the title. It is 80mm of aperture and I'm guessing somewhere around 320mm to 360mm of focal length (like F/4 to F/4.5? possibly). Maybe even F/5 optics - given the size of binoculars?

I'm going to continue talking and if you feel uncomfortable at any time - just don't read the rest .

It costs 197€ without VAT. That is less than 100€ per what seems to be 80mm F/4-F/5 apo triplet objective. See where I'm going with this?

Sure, you would need to provide tube and focuser and show some serious DIY skill - but hey, 80mm fast triplet APO under 300€ (another 100€ for focuser and rest for other materials) - well that is dream to lot of people. Maybe imagers won't be interested because of residual chromatic aberration - but for wide field visual and EEVA - I don't see why not.

Maybe even "transplant" would be possible - ST80 body and above APO triplet lens. That would be even cheaper and with less DIY skill (although worse focuser).

Alternative to such scope is maybe SW equinox or similar - but that is still F/5.25.

Are these objectives diffraction limited? Do binoculars have lens cell or are lens housed in binocular body?

[Peter Drew]

An interesting project with the potential for two 80mm triplet refractors.  However, as they say, there's no free lunch.  I would be surprised if, even a triplet, from a binocular designed to cope with 20x magnification, would have aspirations much beyond that.  Another caveat could be that the correction of the objectives may be balanced to the optics further downstream which might make their inclusion essential for well corrected performance.  I would certainly try and devise the alternative arrangement to enable the binocular to be rebuilt back to the original should the experiment prove disappointing.     🙂

[PeterW]

Nothing ventured, nothing gained. Maybe knock together some right angled binoculars from the insides of them... more comfortable to use. If you only want one eye at a time then you have a “spare” in case the first experiment doesn’t go to plan.... so tell us how you get on.

 

Peter

[vlaiv]

2 hours ago, Peter Drew said:

An interesting project with the potential for two 80mm triplet refractors.  However, as they say, there's no free lunch.  I would be surprised if, even a triplet, from a binocular designed to cope with 20x magnification, would have aspirations much beyond that.  Another caveat could be that the correction of the objectives may be balanced to the optics further downstream which might make their inclusion essential for well corrected performance.  I would certainly try and devise the alternative arrangement to enable the binocular to be rebuilt back to the original should the experiment prove disappointing.     🙂

That is what I thought as well - hence question on optical quality.

There is another apo triplet - and this one is 70mm, quite a bit more expensive (again cheaper than x2 70mm triplets) but with 1.25" eyepiece connection.

https://www.teleskop-express.de/shop/product_info.php/info/p3830_TS-Optics-70-mm-APO-Binoculars-with-1-25--Eyepieces-and-90--View.html

That one is listed as good for astronomy as well.

I wonder why would anyone go thru the trouble of designing triplet for binoculars if not to get good performance out of them?

It looks like that first binocular is the same as APM 20x80 ED APO that received favorable reviews. With 300mm FL it is F/3.75 - and that is really fast.

[Peter Drew]

The triplet design may well provide an improvement over doublet binoculars, even ED ones but made to perform at 20x there is no incentive for the manufacturer to specify optics for much higher magnifications.  I would expect that the emphasis would have been for colour correction and field flatness for which a triplet should be superior.      🙂

[Rusted]

I would have thought you could obtain a lens to fix your cyclopic astigmatism.
Even cut/grind down a spectacle lens which provides your personal correction.

If you wear specs you may have an old lens handy to sacrifice to science.
Tape that over the eyepiece and pray. [If that isn't sacrilege.]
Make sure it is the correct eye lens or it won't be useful.

The lens will obviously have to be rotated to find the correct orientation to cure your astigmatism.
Talk to your optician about this if you make no progress with hacking an old pair of specs.
The optician may be able to source a suitable cylindrical lens for you.
They should at least know the required cylindrical power you need.

 

[vlaiv]

2 hours ago, Rusted said:

I would have thought you could obtain a lens to fix your cyclopic astigmatism.
Even cut/grind down a spectacle lens which provides your personal correction.

If you wear specs you may have an old lens handy to sacrifice to science.
Tape that over the eyepiece and pray. [If that isn't sacrilege.]
Make sure it is the correct eye lens or it won't be useful.

The lens will obviously have to be rotated to find the correct orientation to cure your astigmatism.
Talk to your optician about this if you make no progress with hacking an old pair of specs.
The optician may be able to source a suitable cylindrical lens for you.
They should at least know the required cylindrical power you need.

 

It can be only slightly improved but not corrected - or at least I did not try hard enough?

I recently started wearing reading glasses and when I had eye examination - I did point out that I have astigmatism and that it can't be easily corrected, so optician tried - but no luck.

I was wearing glasses when I was a young lad, but decided to stop wearing them and since I was farsighted - things actually improved on their own, so one eye corrected to excellent vision (very sharp as well) - and brain just started primarily using that one.

When I started being interested a bit more in optics in relation to astronomy - I did some tests on that eye - I examined PSF of star or distant light and this is what it looks like:

Single star is smeared into three images - connected but having distinct points of light.

Moon for example gives tree images in that same order - well two top images overlapping as distance is not that great and bright patch between all three prominent images.

I did try to view at high power in order to reduce astigmatism with small exit pupil and I have the feeling that things did improve somewhat - but I could never achieve sharpness and clarity of my left eye, regardless of focus position and pupil size.

[Rusted]

Interesting. I wonder if your retina is "wobbly" rather than the lens or cornea at fault?
I am not an optician. Just wildly guessing here. Your optician should be able to confirm the cause.

After wearing glasses for decades I started cycling high mileages when I retired.
My eyes went from needing one diopter correction to becoming completely neutral.
 

[vlaiv]

I think that curvy retina could be diagnosed by changing aberration with respect to incident angle.

PSF would change depending on angle between the star and eye.

[Captain Scarlet]

4 hours ago, vlaiv said:

... I examined PSF of star or distant light and this is what it looks like:

Single star is smeared into three images - connected but having distinct points of light.

Moon for example gives tree images in that same order - well two top images overlapping as distance is not that great and bright patch between all three prominent images.

I did try to view at high power in order to reduce astigmatism with small exit pupil and I have the feeling that things did improve somewhat - but I could never achieve sharpness and clarity of my left eye, regardless of focus position and pupil size.

How did you do this? Are you looking at a point source and simply drawing what you can "see", i.e. the light-pattern on your retina/s? I've often wondered about my own distinctive point-source-retinal-patterns and whether anything useful can come out of inspecting them. I can easily draw them and even see their relative sizes. My spherical correction is around 4 in one eye, with bad and multi-axis astigmatism, and 1.25-1.5 in the other without much astigmatism.

[vlaiv]

2 hours ago, Captain Magenta said:

How did you do this? Are you looking at a point source and simply drawing what you can "see", i.e. the light-pattern on your retina/s? I've often wondered about my own distinctive point-source-retinal-patterns and whether anything useful can come out of inspecting them. I can easily draw them and even see their relative sizes. My spherical correction is around 4 in one eye, with bad and multi-axis astigmatism, and 1.25-1.5 in the other without much astigmatism.

I can do that whenever I sit relaxed outside and look at the stars. I look at the bright star with my left eye and I can see it as I should - single point of light. If seeing is good it won't flicker - maybe slightly changing brightness every so often. Then I switch to my right eye and that is pattern that I see instead of single pin point star.

It is quite distinct and I just remembered it - no need to draw it or anything.