Depth of field of reading specs

[9fingers]

Might be a dumb question but here goes.

My current reading specs I've had for years were a "nothing special" cheapies from Specsavers.

A couple of years ago they started looking tatty and I went back to newer branch in my home town and said please make another pair just like these. No they said we can only make to a recent prescription. Other opticians said the same - must be a union rule!

I duly had an eye test and basic glasses were made but had a much poorer depth of field. When I complained they said there was a way they could do it but at much increased cost. So I took the parts of the new frames and repaired my old glasses using the new parts. I now need a change of prescription and want to maximise depth of field.

Current DoF is around 150-450mm for my first pair and recent SS attempt was more like 150-275mm

What parameters affect the depth of field for a particular lens specification?

After visiting a Specsavers factory year ago I know they have various differing refractive index blanks they use but I did not ask how they choose which type of blank they start with.
Incidentally if you can blag a trip round a lens factory, grab it! absolutely fascinating.


Bob

 

[Pete Maddex]

I have some cheap reading glasses for small stuff and the depth of field is very narrow so I think the problem is your prescription has changed an you need stronger lenses which are giving you less depth of field.

Pete

 

[9fingers]

I have some cheap reading glasses for small stuff and the depth of field is very narrow so I think the problem is your prescription has changed an you need stronger lenses which are giving you less depth of field.

Pete

Maybe but ss said they could provide greater depth of field in exchange for about 4x the dosh. So how do they do that. I know diddly squat about optics.
Bob

 

[Lurker]

I need correction for both long and short.
My optician who also has a place that actually makes glasses made me some “ desk glasses “ these are varifocals but are bias to distance of less than 5 metres. These are great for office use and for the workshop.

 

[AJB Temple]

It is not viable to have a very deep depth of field for reading glasses at a sensible cost in my experience. I use a laptop on the sofa or reading a book, and that is a DOF of around 30-50 cm with perfect clarity. For reading piano music on the music desk, I need need about 90cm and similar (up to 110cm) for my desktop screens. I use two pairs of glasses to achieve this with a good optician in Sevenoaks. Both cheap. I don't both with fancy frames or coatings for these utility specs. Left and right eye are different in my case and the lenses cost £58 for each pair of specs.

For riding a motorbike and general stuff I use much more expensive varifocals. I'm just on the cusp of needing glasses for driving.

Good luck with getting something suitable. Never got on with Specsaver's myself.

 

[RogerS]

Does this help or hinder ?

https://www.researchgate.net/figure/Ref ... _236642055

Personally I'd never go to Specsaver's but a tried and tested optician. Both the missus and I still drive down from Northumberland to Worcestershire to see our optician.

Went to a couple locally and not so locally for the driving-licence eye test and came away distinctly underwhelmed.

 

[9fingers]

Thanks Roger, an interesting read.

Other research suggests there is not a way to increase DoF for spectacles per see but instead a type of varifocal lens can combine with head movement to find a position of focus over a wider distance.

Several of the replies above are supporting this one way or another.

I have to take SWMBO to Specsavers today to collect her new specs so I might try and chat to the optician at the end of the appointment.
I am overdue for an eyetest but have shoved this on the backburner whilst I've been coming to terms with my cancer diagnosis and treatment plan but will get one soon.

I've always been pleased with the optometrist side of our local SS as she is the wife of a work colleague and been very helpful explaining the impact of my mild diabetic retinopathy but now she has retired so will have to see what the replacement is like.

Bob

 

[Woodster]

I had exactly the same problem Bob, also at SpecSavers. I explained the issue and they made new lenses for me which are fine. They did say they may not be able to achieve the specification I wanted as I got older though.
My current “reading” glasses are about 200 - 450 which is what I asked for.

 

[9fingers]

I went into SS yesterday and they were not too busy and had a long sensible chat with the senior dispensing optician.
We covered Monovision specs which he was prepared to make for me but advised the the differing magnification between the lenses could be difficult to get used to and that viewing objects off to the side would suffer differing prism correction and could cause distortion.
I might still experiment in a simple way see below.
We then talked about depth of field and he said this could not be adjusted with simple fixed focus lenses as the range of aperture sizes were fixed by the eye and the focal length was fixed so the DoF was what is was for each combination of lenses and eyes.
SS do offer what they call occupational lenses which are varifocals with a range according to the customers needs. He suggested I bring in my laptop ( which is what I'm doing when my DoF is inadequate) and they would make measurements to define the range of the varifocal/occupational lens design.It was refreshing to talk to a guy who clearly knew his stuff and be treated as someone also knew a bit about the subject and also fairly certain of what was wanted.
As SS is a franchise type operation I guess such expertise can be pretty variable from branch to branch.

After coming back home, it dawned on me that I could pretty easily experiment with monovision. I only need very marginal correction for distance viewing and so I plan to get a pair of occupational glasses and remove one lens and then the other to see how I get on. If its OK then next time I'll get a fixed focus distance lense and a occupational for the other.

Hope this might help someone else too.

Bob

 

[RogerS]

:text-goodpost:

Glad to hear you're on the way to getting sorted.

I had forgotten that I also fell foul of DoF last time we flew to Japan. Comfy class, the screens are much further away than cattle class and the distance fell between the DoF of my close-work glasses and the long-distance ones. So no films for Roger

 

[Phil]

:text-goodpost:

Glad to hear you're on the way to getting sorted.

I had forgotten that I also fell foul of DoF last time we flew to Japan. Comfy class, the screens are much further away than cattle class and the distance fell between the DoF of my close-work glasses and the long-distance ones. So no films for Roger

Must have been some p-o-r-n :lol: :lol:

Mine are are multi-focals from reading a book to computer screen of arms-length and +

 

[Eric the Viking]

DoF is really a function of two things:

It's inversely proportional to the diameter of the relevant bit of the glass lens*, and it also depends how much focus accommodation the mk 1 eyeball has.

Our eyes become less flexible as we age, and/or the muscles get weaker. The result, in my dad's case was quite a few sets of glasses.

I have one pair of trifocals, intended for screen-based office work: close at the bottom, most of the lens is about screen distance, and there's a dimple in the middle at the top, for distance. The idea is that you shouldn't need to keep swapping pairs over. Unfortunately it also means lots of head movement for longer distance movement, which is tricky for me, so I hardly use them. And they are verboten for driving, too.

I don’t think there is an easy answer.

E.

*I find the easiest way to understand this is to consider a pinhole camera. Its "lens" has everything in focus, from infinity right to the front (first order approximation). It's sharp, but too dim for practical use. Conversely, a big camera lens (with a wide lump of glass at the front) lets in lots of light, but has a very sharply defined plane of focus. That's why they are popular for portraiture, and Hollywood - the image is usually defined more by what's out of focus than in.

PS: By the way, there's a trick if you forget your close-up glasses: make a small hole between the tips of fingers and thumbs, and squint through that. It works like a pinhole camera, and I sometimes use it to read the bathroom scales!

PPS: if you only have your close-up glasses handy, you gain slightly more distance if they are slightly closer to the bridge of your nose than normal - it's notmuch but may help. Conversely, for a closer-up improvement, you can slide distance lenses down a bit.

 

[9fingers]

I recall someone at work experimenting with Veroboard lenses that worked surprisingly well

Bob

 

[Eric the Viking]

I recall someone at work experimenting with Veroboard lenses that worked surprisingly well

Bob

 

[AJB Temple]

Eric has nailed this I think. I've had numerous pairs of varifocal lenses, but they are a definite compromise. They also tend to have quite obscured peripheral clarity if, for example, you wear a motorcycle helmet and need to catch peripheral movement. Crucial to get suitable shaped and well fitting glasses.

I tried bifocals recently (as I barely need distance lenses) but for things like playing the piano and sight reading a score (which I do a lot when accompanying or teaching). However they are very annoying as I have to tilt my head back to see the score through the reading part of the lens. Nodding donkey effect.

 

[droogs]

No idea what they are called but I got new prescriptions late last year. It was at spec savers and they gave me glasses that they said were a new type of lens and I was getting the first pair the branch had done. The glasses actually had 3 different prescriptions in them as I now need 3 pairs for short medium and long distance. There is no demarcation line or anything but if I read a book in my lap it is clear and then if I sit and look at the computer screen about a metre away it is clear and I can wear them for driving to see out the windshield. I notice that my eyes will raise or lower very slightly depending on what I am looking at. Found them to be very easy to get used to unlike bifocal things