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Varifocal glasses / contact lenses with a microscope

 
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Pitufo



Joined: 21 Jun 2015
Posts: 206
Location: United Kingdom

PostPosted: Thu Jun 14, 2018 7:27 am    Post subject: Varifocal glasses / contact lenses with a microscope Reply with quote

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.
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rjlittlefield
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Joined: 01 Aug 2006
Posts: 19327
Location: Richland, Washington State, USA

PostPosted: Thu Jun 14, 2018 8:49 am    Post subject: Reply with quote

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
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Pitufo



Joined: 21 Jun 2015
Posts: 206
Location: United Kingdom

PostPosted: Thu Jun 14, 2018 9:55 am    Post subject: Reply with quote

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).
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Pau
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Joined: 20 Jan 2010
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Location: Valencia, Spain

PostPosted: Thu Jun 14, 2018 10:27 am    Post subject: Reply with quote

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
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Beatsy



Joined: 05 Jul 2013
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Location: Malvern, UK

PostPosted: Thu Jun 14, 2018 10:38 am    Post subject: Reply with quote

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" Razz

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.
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Lou Jost



Joined: 04 Sep 2015
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Location: Ecuador

PostPosted: Thu Jun 14, 2018 10:55 am    Post subject: Reply with quote

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.
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rolsen



Joined: 01 May 2018
Posts: 76
Location: Finland

PostPosted: Thu Jun 14, 2018 11:28 am    Post subject: Reply with quote

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
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Pitufo



Joined: 21 Jun 2015
Posts: 206
Location: United Kingdom

PostPosted: Fri Jun 15, 2018 8:37 am    Post subject: Reply with quote

Thank you for your all your very helpful comments.

Quote:

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"
Laughing
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svalley



Joined: 03 Dec 2006
Posts: 304
Location: Albany, Oregon

PostPosted: Sun Jun 17, 2018 3:43 pm    Post subject: Reply with quote

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.
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Lou Jost



Joined: 04 Sep 2015
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Location: Ecuador

PostPosted: Sun Jun 17, 2018 3:57 pm    Post subject: Reply with quote

That sounds very interesting!!!!!!
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