Varifocal glasses / contact lenses with a microscope

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Pitufo
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Varifocal glasses / contact lenses with a microscope

Post by Pitufo »

Someone asked me recently if they could wear varifocal glasses and/or varifocal contact lenses when using a microscope.

My first reaction was that would it be better to remove the glasses (not so easy with contact lenses) but maybe it is possible to do contine wearing them if you always view with the same part of the spectacle lens.

If so, which would be the best part of the glasses lens to use?

Does anyone have any experience or comments?

P.S. Apologies if this is in the wrong section, I wasn't quite sure where it should fit.

rjlittlefield
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Post by rjlittlefield »

Yes, it should be possible but there may be ergonomic issues. If the microscope is constructed so that the viewer's eyes look straight forward (parallel axes), then probably the upper section of the glasses will work best. If the microscope is constructed so that the viewer's eyes look inward, then lower sections of the glasses are a better bet. Ultimately it will be a matter of trial-and-error to determine the best spot.

As explanation... Varifocal glasses work by having a "sweet spot" for each distance, with graded zones between those where the image suffers various aberrations that are small enough to be tolerated by most users. The sweet spots are placed so that the user's eyes can be looking through the centers of them when converged on a real-world subject that is physically placed at the distance corresponding to focus. So, the sweet spots for infinity focus are positioned as far apart as the user's pupils when looking straight forward, and the sweet spots for closer focus are positioned closer together, matching the corresponding convergence. For use with the microscope, what you're trying to do is match the exit paths of the eyepieces to some pair of sweet spots in the glasses.

I will happily admit that this advice is based on old information. I gave up on varifocal glasses after a one-month trial, several decades ago, because the sweet spots were small and I was neither tolerant of the surrounding aberrations nor willing to swivel my head around all the time so as to point the glasses at what I wanted to look at. I've have since been assured by opticians that the new ones are much better, but they have all given up quickly when I explained what my concerns were.

--Rik

Pitufo
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Post by Pitufo »

Thanks Rik. So there is no reason not to use varifocal glasses as long as they can hit the same sweet spot consistently.

In this case, it was mainly for use with a stereomicroscope. I'm not sure whether that means the eyes would be looking inward or straightforward - if I had to guess then slightly inwards would be may bet as it was a Greenough-type stereo (but I realise it is possibly not this simple).

Pau
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Post by Pau »

I have no experience with varifocals, I'm pretty sure that I'd be uncomfortable with them, even I dislike the sunglasses with non uniform darkness.

Usually, despite that microscope magnification being computed for comparison with the apparent size of the subject placed at 25cm of the naked eye, I think that the best focus point of the eye is to infinite to have a relaxed vision.

Except for people with strong astigmatism, I think is better to use the microscope without eyeglasses, compensating the diopter difference with the eyepiece regulation, in any case having the same correction for the complete field without forcing the eye position seems clearly convenient
Pau

Beatsy
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Post by Beatsy »

rjlittlefield wrote:...I've have since been assured by opticians that the new ones are much better, but they have all given up quickly when I explained what my concerns were.
I can imagine you being an optician's nightmare, "Quick, lock up the shop! That man with the optical bench and lasers is heading this way again" :P

I have varifocals and prefer them. I like being able to tweak the quality of the image I see by moving my viewpoint a bit.

Lou Jost
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Post by Lou Jost »

I tried them and they didn't last a single day, went straight back. They don't work well when hiking on uneven jungle trails where you have to watch your feet and look ahead more or less simultaneously.

rolsen
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Post by rolsen »

I'm old school, one set for normal usage and other for reading and all close-up thingies. They speak very highly about how they are so good and blaa-blaa, but many of my friends don't like 'em and I'm a bit nightmarish customer myself.

- Rane

Pitufo
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Post by Pitufo »

Thank you for your all your very helpful comments.
I can imagine you being an optician's nightmare, "Quick, lock up the shop! That man with the optical bench and lasers is heading this way again"
:lol:

svalley
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Post by svalley »

Every year when I had my annual eye exam I would ask the doctor if there had been any advances in contact technology that would solve my vision problems.

As an entomologist I spent a lot of time looking at small specimens in drawers and under the microscope. Presbyopia is the normal loss of near focusing ability that occurs with age. I used reading glasses and constantly put them on to look at specimens and took them off to look through my microscope.

Finally, about 10 years ago the doctor said yes. Multi-focal contacts were the answer to my problem. They have many concentric rings that bring near and far features into focus at the same time. I have tried several different brands since then and finally found some that suit me perfectly.

I can focus on objects about 3 inches from my eye all the way out to infinity where I can see very fine details. Looking through my microscope is completely natural. It is wonderful to be able to see the controls on my camera in the field without trying to look through bugspray, sunscreen and sweat smeared glasses.

The contacts I am using now are Bausch+ Lomb Ultra Contact Lenses for Presbyopia.
"You can't build a time machine without weird optics"
Steve Valley - Albany, Oregon

Lou Jost
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Post by Lou Jost »

That sounds very interesting!!!!!!

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