A visit to the eye doctor and...

I was long overdue for an eye exam. My prescription hasn't changed since my first pair of glasses in 7th grade (over 20 years ago), and my chart revealed today that I haven't been to the eye doctor since 2006. Anyway...I'm pushing 40 now, and I've been noticing some issues that I first started seeing in my photos. I use manual focus a lot, and when I get home and upload photos to my computer, I often see a slight sharpness problem. This isn't about technique or gear. I no guru, but I've been doing this long enough to know how to get a sharp photo. And that's just it: they look sharp in my viewfinder, when when I get home, they're not.

My optometrist revealed to me today that my prescription is set to 20/25, which means my focal point is at 25ft, 5ft beyond "normal" 20/20 vision. This isn't an issue for most people, and many don't know the difference or even prefer it that way, especially for driving. But because I often photograph at that distance, it has become a problem. I chose to go with a new prescription that will split the difference. Instead of 20/20 or staying with my current 20/25, I'm going with 20/22.5.

This can be corrected by adjusting the viewfinder diopter. The doctor gave me the new setting, and after making the change, it does help.

Just a public service announcement in case any of my near-sighted friends are experiencing the same thing.

At 56 I can no longer see close up or at a distance. But I have no problem seeing perfectly through the viewfinder with my contacts in. The problem I have is seeing the controls sharply or reviewing on the LCD, which is why I always have a pair of my reading glasses around my neck.

Thankfully, I haven't had that issue develop (yet). My wife is a bit older than me, and got her first pair of bi-focals last year. She took it pretty hard LOL. I got her one of those grandma neck chains as a gag gift and paid for it by spending the night on the couch.

I'm with you guys except I dont need glasses for distance but when I turned 40, now past, I needed readers. I now purchase sunglasses with readers so I can see the controls and view things on the LCD. Sucks but at least they give you the diopter control for the view finder, I just gave up on using the LCD for the most part because I can't take pictures with glasses so I dont even bother with it. Tried the contacts but that turned out to be a no go. I am due now and may try the contacts again but I got rid of them because they gave me fits when trying to view my computer monitor. I guess I am kind of in betweener so to speak, LOL.

Eyes do change as we age, but I thought 20/25 had a different meaning, about clarity, specifically that we see detail at 20 feet that normal eyes can see at 25 feet. So 20/22.5 would only be partial correction. Does not seem an advantage. I'd let the optometrist prescribe it.

The image we see in the camera is not at 25 feet, but instead we see the image of the lens projection on the ground glass screen, at a few inches.
Like looking at a mountain on the TV... it is no longer at miles of distance, but instead is an image, at maybe 8 to 12 feet to the TV.

The cameras have an eyepiece lens to focus on the ground glass. My D800 manual says the eyepoint is 17mm, which is where the eye should be behind it. Eyeglass wearers can have issues with that, but the camera offers the diopter adjustment to vary it.

They way he explained it to me (and demonstrated by switching lenses on the thingy) is:

At 20ft, I should be able to read the 20/20 line on this chart with proper corrected vision. I can read it, but it's blurry. I can, however, read the line above it just fine.

Great timing ... my ophthalmologist appointment is Monday. Unfortunately, I'm on a recurring 6 month schedule with the eye doc to keep an eye on things, no pun intended. That makes me a little nervous as I get worked up about this passion, but so far everything is staying in check.

OK, but Snellen chart - Wikipedia, the free encyclopedia says:

"The chart is at a distance of 20 ft, but a person with normal acuity could be expected to read these letters at a distance of 40 ft. This line is designated by the ratio 20/40. If this is the smallest line a person can read, the person's acuity is "20/40," meaning in a very rough kind of way that this person needs to approach to a distance of 20 ft to read letters that a person with normal acuity could read at 40 ft. In an even more approximate manner, this person could be said to have "half" the normal acuity."


There is NOTHING there about focusing at 25 or 40 feet. It says you have to stand closer to make out the detail of the letters.

And, even if the subject were at 25 feet, you see it "an image" of it at a few inches in the camera viewfinder.


I am trying to suggest that you would like the correct glasses.

My doctor's been bugging me to go see an eye doctor, since I'm borderline diabetic.
I use reading glasses now, but it is getting worse. Time to make an appointment I guess.

Dunno how to better explain it than with a diagram, Wayne:





If the viewfinder diopter adjustment is set at 0, it is tuned to 20/20 vision. My prescription is 20/25. Which means if I'm using manual focus on a subject, I'm actually using a focal reference point (like a person's eyes) that is 5ft beyond where the focal point actually is.

I would strongly hope you review your notions with your optometrist, before you ignore his prescription you paid for. I think you are ignoring 100% of the details.

My prescription is 20/25. Which means if I'm using manual focus on a subject, I'm actually using a focal reference point that is 5ft beyond.

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Your diagram is incorrect, regarding the camera viewfinder seeing 20/20. I don't actually know what that note means, but the subject is NOT about the camera or the viewfinder. The camera projects its image from its lens onto the ground glass screen in the viewfinder. We don't question the camera, it never wears glasses.

But then we look at that image on the ground glass screen (at a few inches, which requires the eyepiece lens to do it), which is much like viewing a projected slide show on a screen... in that the screen is NOT at the same distance as the subject. The camera diopter adjustment does help us see that ground glass image. The subject distance is no longer any factor at all. Eyeglass prescriptions are written in diopters too.

You really should ask your optometrist for his opinion about your prescription.

Know what, you're absolutely right. It all makes sense to me now, thank you for clearing that up. I'm going to call my optometrist and request another exam. After all, his medical expertise has been invalidated by a guy on the internet.

Your statement: "Instead of 20/20 or staying with my current 20/25, I'm going with 20/22.5."

My eyes are sooooo bad, that without my glasses I can't even see the E on the first line enough to tell what it is, more less what letter it is! Lol And yes I know I need new glasses badly. So it's a wonder any of my photos turn out! Lol

The recommendation to split the difference (20/22.5) was the doctor's, not mine. He said that to dial me back to 20/20 after all this time would be a drastic change and I wouldn't be happy with my new glasses. It would be especially noticeable while driving.

Browncoat said:

The recommendation to split the difference (20/22.5) was the doctor's, not mine. He said that to dial me back to 20/20 after all this time would be a drastic change and I wouldn't be happy with my new glasses. It would be especially noticeable while driving.

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OK, then I certainly am sorry that I misunderstood what you said about it.

No worries.

Dunno about you, but I wear glasses with the diopter -1.5 (minus, or negative one and a half) for more than a 30 years now. But I always take them off when shooting. I set my viewfinders (D5100 and D7000) to the position where I get the clearest possible picture (without my glasses being put on) by turning those adjustment knobs, and that's all. It's either you USE your glasses (and set that knob into neutral position) or you look through the viewfinder WITHOUT your glasses, and adjust the viewfinder's diopter until you reach your personal optimum at ANY distance.
Conclusion: you don't need any prescriptions here - simply look through the viewfinder, point your camera at any suitable object (positioned at the distance you believe is your preferable), manually focus until you realize it cannot get any sharper, and turn that knob around until you find your own "sweet spot".

It sounds like you are saying that the viewfinder focus was off which made the images look clear during shooting and that by adjusting the viewfinder focus you are moving the the point the lens appears to be in focus???

I ask because I'm pretty much confused. I can see that having the viewfinder focused will allow one to see the focusing screen better, but I am at a loss as to how it moves the apparent focal point. Or does it???

Eyelight said:

I ask because I'm pretty much confused. I can see that having the viewfinder focused will allow one to see the focusing screen better, but I am at a loss as to how it moves the apparent focal point. Or does it???

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The diopter adjustment simply focuses the eye piece on the focusing screen.
D3200 manual (page 20) says:

1 Remove the lens cap.
2 Turn the camera on.
3 Focus the viewfinder.
Rotate the diopter adjustment control until the
viewfinder display and focus point are in sharp
focus. When operating the control with your eye
to the viewfinder, be careful not to put your
fingers or fingernails in your eye.



It has a footnote that says:

Adjusting Viewfinder Focus
If you are unable to focus the viewfinder as described above, select single-servo autofocus
(AF-S; 035), single-point AF (c; 038), and the center focus point (040), and then frame a
high-contrast subject in the center focus point and press the shutter-release button halfway
to focus the camera. With the camera in focus, use the diopter adjustment control to bring
the subject into clear focus in the viewfinder. If necessary, viewfinder focus can be further
adjusted using optional corrective lenses (0176).