Adding prescription Lenses to Binoculars (1 Viewer)

[mekidear]

Being long sighted with astigmatism I don't wear specs, except for close up stuff.
This is fine most of the time but when looking through my binoculars the view is not as sharp as I would like.
So I have googled 'adding prescription lenses to binoculars' to see if it has been done before - which it has - but there is not much info out there.

I have started my own little project and will post up progress here so there is something for others to find if they want to have a go.

 

[mekidear]

Progress so far

I have purchased a pair of spare eyecups from Opticron. They were not horrendously expensive and I prefer to have the original pair to fall back on if I have a complete disaster.

A pair of round spec lenses to my prescription to fit inside the stock eyecups are on order. I did ask the lens supplier to leave out the SPH part of the prescription but apparently they can only make exactly what is on your prescription - its the rules! So I went with that. Hope they mark the orientation clearly.

I have no clue how thick my lenses will be, so have not yet determined exactly how they will fit into the eyecups. The eyecups are not designed for this and may not be suitable. I want to keep this simple and am hoping the lenses will fit between the twisty section of the eyecup and the ocular lens, with a couple of suitable o-rings. Twist the eyecup down tight and tape/glue in place.

I want to try and keep it simple but If this fails I will machine something from aluminium or black delrin.

Will post again when I have made some progress

 

[delia todd]

I had a lens for my rifle sight (indoor target shooting). I used to ask the optician at the time of my test if I could also have a prescription for this purpose.

Quite happy to do, then I sent it off to whoever it was that made these lenses. This was over 25 years ago, and I can't remember the details.

 

[Binastro]

This has been done before.

I think that Kabsetz gave a detailed description.

There are also Televue astigmatism lenses for their eyepieces.

A friend has done this for years.
He takes prescription glasses and files the lenses down to size.
It takes him twenty minutes but he is an experienced engineer.

Regards,
B.

 

[mekidear]

I was going to grind down some lenses to fit but I needed a new prescription anyway so easier to get them made to size - a bit cheaper too.

 

[kabsetz]

You can search for the thread where I discussed this. I had a Zeiss lens made that corrects for astigmatism for my left eye, with no SA correction so zero diopter. It is held to the area surrounding the eyelense of the eyepiece with three small pieces of the sticky tape opticicians use to hold a lens to the grinding machine. Axis of cylinder correction is marked with a small line at 12 o'clock (although I found that best results come a couple of degrees away from this). I don't have a lot of astigmatism, but this still helps to give a sharper image.

 

[mekidear]

I have read that thread thankyou kabsetz. I did a few searches and read all I could find

I will have to do it differently as the eyecups are completely a different design.

One thing I was wondering from your photo, how far is the prescription lens from your eye? Do you have any issue with eyelashes brushing the lens or body heat fogging it up?

 

[Tringa45]

A pair of round spec lenses to my prescription to fit inside the stock eyecups are on order. I did ask the lens supplier to leave out the SPH part of the prescription but apparently they can only make exactly what is on your prescription - its the rules! So I went with that. Hope they mark the orientation clearly.

I don't understand why the supplier insists on following your prescription. You could just ask for lenses of the required diameter with only the cylindrical correction and a mark for the axis.
Glasses frames are usually much larger than what you require and the larger the diameter of the lens, the thicker it will have to be for a positive correction (far sightedness).
This might interest you DIOPTRX™. However, hobby astronomers often use high magnifications with correspondingly small exit pupils, so if you were using an 8x32 binocular for instance, you would still profit if your cylindrical prescription is 0,5 dioptres or higher.

 

[mekidear]

I don't know if it was their own policy or an industry wide one. I wasn't sure if there was any real advantage omitting the SPH values so just went with the flow

I have looked at the Dioptrx lenses but a pair of prescription lenses made to my required size is half the price of one Dioptrx lens. So it was not really an option worth considering.

 

[kabsetz]

My correction lens comes some 3 mm closer to my eye than the non-corrected right ep eyelens. I have not had fogging issues, and only minimal eyelash issues, but it makes sense to place the lens as close to the eyepiece lens as possible. Do check the orientation that gives you the best image, as cylinder correction is usually not determined to the precision you would like it to be. Best to have the binoculars on a tripod and only view with the one eye the lens comes for.

 

[mmx_4]

For prescription lenses in ocular you need binoculars with long eye relief,
I think, 19-22mm from glass surface will be good (some APM, Pentax, Fujinon, and other models).

 

[mekidear]

My lenses arrived last week and I had a go at fitting them into my binocular eyecups today.

I was prepared to machine my own parts to make this work, but as it turns out this was not necessary, in fact it was really easy, only took half an hour.

First unscrew the eyecups from the bins and then take them apart. The rubber peels off leaving the twist assembly, this comes apart into two sleeves/collars (see photo - screws not shown) by removing the three small screws in the helical slots. There are also 3 tiny little rubbers squeezed between the two sleeves (to stiffen up the action and stop rattling I presume) Keep these and the screws safe in case you ever want to put it back as it was.



Next take the outer of the two sleeves and drop in an o-ring, then the lens (make sure it is the right way round) then the other o-ring. I had the lenses made 23mm diameter which is a close fit inside the outer sleeve, the o-rings were 30mm ID x 2mm diameter = 34mm OD so they gripped the inside of the sleeve and held the lens in place.



Next put a wrap of electrical tape around the inner sleeves that screws to the binocular - so that the outer sleeve will push on and stay put, but can be turned to make adjustments.

Screw the inner sleeves to the binoculars.

In turn look through each lens and rotate to get the sharpest view, mark the top with a bit of sticky tape then press the outer sleeve+lens assembly onto the inner sleeve/binocular with the mark at the top (with the bins set to your IPD)

Push on the rubber eyepieces and you are pretty much done. You just need to spend a few minutes fine tuning the IPD, then the lens rotation and finally the diopter adjustment.

Your might find that your diopter adjustment has changed - mine did. I put this down to my LH lens being approximately 0.3mm thinner than the RH lens so the LH eyepiece pushes further onto the binocular. This was easily accommodated with the adjuster but could also be corrected using different size o-rings or a spacer ring of some sort.

I have not yet tested this set up in the field but just looking out the window shows that the results are excellent, just what I was after - like wearing my specs but without wearing my specs

The sticky tape push fit between the two eyepiece sleeves is not the best engineering solution, but seems to do the trick and does allow easy adjustment/disassembly if it is needed. If this comes loose with time - or on a hot day - a dab of glue or some other solution might be necessary, I will worry if it happens.

Well worth the effort 🤓🤩

 

[mekidear]

If anyone reads this and would like to do the same to their own binoculars, please note that your eyepieces are likely to be slightly or completely different.

My binoculars are - Opticron Travellers 8x32 BGA WP

Also it would be a good idea to source a spare set of eyecups before you start taking anything to bits, so if the worst happens and you ruin something, you can always put your bins back to how they were.

 

[elkcub]

Being long sighted with astigmatism I don't wear specs, except for close up stuff.
This is fine most of the time but when looking through my binoculars the view is not as sharp as I would like.
So I have googled 'adding prescription lenses to binoculars' to see if it has been done before - which it has - but there is not much info out there.

I have started my own little project and will post up progress here so there is something for others to find if they want to have a go.

Note my old thread from 2005 (go to Post #1): Binocular Prescription Lenses
Ed

 

[mekidear]

Hi Ed Did you ever do it? I would be interested to see how you got on - all those years ago

Having sketched out various eyecup designs dedicated to adding prescription lenses, I don't think it would be difficult for manufacturers to offer such a thing to their customers. I cannot believe they have not considered this numerous times over the last 100 years!

I guess it must be such a small niche market that it is not worth their while. Having said that, with a bit of thought and careful design, a standard eyecup could be designed to accept lenses, giving every customer the option should they wish, with no added cost or supply issues for the manufacturer.

 

[elkcub]

Hello mekidear,

Nah, as usual I let most things drop. So, congratulations to you for actually accomplishing the job. Fantastic!

Ed

 

[mekidear]

A question for the optics experts - I cannot figure this out!

Adding prescription lenses to my binoculars has been so successful that I now need to do the same on another pair I have - otherwise I will never use them!

This time I plan to use an existing pair of specs and grind the lenses to fit. I have several pairs that could be used as donors, long distance/driving, Using a PC and Reading. I am long sited with astigmatism

Which would be best to use? I am thinking two things:

Firstly - the effect of each lens on close focus distance - simple experiments show if doesn't make that much difference. The stronger reading lenses focus a bit nearer.

Secondly - Which would cause less distortion? I would guess the weaker distance lenses. Or as above would it make little difference?

I suspect there will not be a definitive answer to this but if anyone has any knowledge on this that they can pass on it would be much appreciated.

 

[Maljunulo]

Just make sure that the optical centers of the spectacle lenses ends up on the optical axes of the binocular.

 

[mekidear]

Do you know how to locate the optical centre of the spec lenses?

I assume it will be literally in front of my eyes, but if there is a more accurate way of locating it I am all ears

 

[Maljunulo]

No, I don’t. That’s why I carefully avoided any mention of how to find it.

My wild guess would be the highest point on the front of the lens, when it’s resting on a flat, level surface. (assuming it isn’t some odd shape, which would tilt it)

There must be an easy way to find it, but I’m not smart enough to think of it.