[Kristian Wolfe]

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Hi all,

I'm desperately looking for a -3.5 corrective lens (named "Optical Correction Lens" by Pentax) for the diopter of my Pentax 67II. The lens that is currently in my Pentax 67II's diopter is the standard one (-0.5), which only has a diopter adjustment range of +1.5 to -2.5. I need a diopter lens that allows adjustment between -3.0 to -3.5, so the standard diopter lens currently in my Pentax 67II diopter ring won't cut it, since it maxes out at -2.5. I've attached a page from the Pentax 67II manual regarding "Installing The Correction Lens," and it states that with the Pentax Diopter Correction Lenses the "diopter adjustment range can be changed from -5.5 to -1.5 (which I need) or -0.5 to +3.5 by changing the optical correction lens. Doing some simple math, that would mean that there was a Pentax correction lens of -3.5 for nearsighted people like me, as well as a +2.0 correction lens for farsighted people. It's this -3.5 Pentax diopter correction lens that I desperately need.



I've read on a forum that a Nikon F100 diopter/lenses should fit in nicely, so I bought said Nikon diopter with the -3.0 lens inside it, but found that it won't at all fit into the diopter ring of my Pentax 67II - it's far too loose. I've even removed the -3.0 lens from the Nikon F100 diopter to try to fit it into the Pentax diopter lens holder, but the Nikon -3.0 is too large to even fit inside that. I've also even tried sanding the -3.0 Nikon diopter lens down, but that didn't work either; the sanded bits scratched up the entire lens.

I asked my optometrist if he can fix me a -3.5 diopter lens, but he said that he doesn't do these types of things. I've even contacted Edmund Optics to see if they could perhaps make one for me, but I was told that they couldn't do it, but they could try for a whopping sum of $750, money that I, as a student, simply don't have.

I'm so frustrated over this because I've had this Pentax 67II for over a year now, but I can't use it unless use my glasses, which I really hate using when composing my shots.

That said, short of getting laser eye surgery, does anyone know where I can get the -3.5 corrective diopter lens (or even a -3.0 diopter lens) for my Pentax 67II? Can anyone else please help me with this or offer any suggestions?

Any help or guidance would be very much appreciated.

[marcusBMG]

ebay is your best bet IMO. I just did a search, there are quite a few original pentax diopter correction lenses listed, often from Japan, but post for such a small item won't be prohibitive. None exactly -3.5, but isn't there some adjustment on the camera?

[garywakeling]

not what you wanted but how about this ? Pentax 67 Right Angle Finder reviews - Pentax Camera Accessory Review Database

[NeoSpudly]

Sorry to hijack the thread but I'm nearsighted would love to not have to keep my glasses on when using view finder, how do you find out what your + - value is? Is it on my prescription for my eyeglasses?

[kaseki]

One's eyeglass prescription, which includes the spherical correction, will show what it is. Negative is for myopia, positive for presbyopia. For clarity, the term "diopter" refers to the reciprocal of the focus length in meters. An eye focusing at infinity is operating at zero diopters of external power. (The internal power of one's eye's lens plus cornea, however, is high because it is focusing to about an inch, or 1/40 meters.

So, if one had no accommodation (variable focus), and could focus only at infinity, one would need a one diopter positive lens to look at one meter, a two diopter positive lens to look at half a meter, and so fourth. If the eye has too strong of an internal lens, (focus is short of the retina), one need a negative lens to focus at a distance. For example, if one could only naturally focus at 10 inches (about a quarter of a meter), one would need a -4 diopter lens to see at infinity.

And this gets us to making of lenses. Once upon a time optometrists could cut the edges of optical glass blanks to make them fit glasses frames. I think they used profile grinders. This is probably lost as a skill, or the equipment is no longer in use. Pending an eBay acquisition, one might try buying the least expensive pharmacy glasses rated -3.5, (lenses will be plastic) and coring out the [optical] center of one of the lenses to the diameter that fits the camera eyepiece. Tape over both sides of the plastic before experimenting.

[AstroDave]

ow do you find out what your + - value is? Is it on my prescription for my eyeglasses?

One's eyeglass prescription, which includes the spherical correction, will show what it is. Negative is for myopia, positive for presbyopia.

If you are nearsighted (as I am), as kaseki notes, your eyeglass prescription is the key. Typically the first number is the "spherical" correction, and should be negative for you. I am very nearsighted (I need to move up from the 20 foot line to properly make out the big E on the eye guy's chart!), and my prescription has -5 and -6 for my left and right eye.

Also, as kaseki notes, your best (cheapest!) bet may be to get some eyeglass lenses with the correct negative diopter and try cutting out the middle. You can get simple (plastic) glasses at Zenni for less than $10 (plus shipping) here in the US (I think the absolute bottom may be as cheap as $6.95). I use them a lot and have been quite happy with their products. (I have no financial (or otherwise) interest in Zenni.)

[kaseki]

If you are nearsighted (as I am), as kaseki notes, your eyeglass prescription is the key. Typically the first number is the "spherical" correction, and should be negative for you. I am very nearsighted (I need to move up from the 20 foot line to properly make out the big E on the eye guy's chart!), and my prescription has -5 and -6 for my left and right eye. ...

Piker! I was running -10s before replacing my lenses via cataract surgery.