RustyBug
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 p.1 #12 · Totally confused about diopter correction - or just ignorant? | |
johnvanr wrote:
I've written before how I've struggled with the lack of a diopter correction setting on the M10 I bought a while back. Since then I traveled to Europe for a little bit and used the Leica alongside my Olympus gear. I did like the Leica overall, but was often still bugged by the need to shoot it with glasses and never really getting a sharp image in the rangefinder. The glasses I wear vary from +1 for driving to +3 for close up reading.
Now, I had tried several strengths correction lenses from Leica before leaving for Europe, but found nothing really did the trick. Upon return I actually bought a used SL2-S with its gorgeous corrected EVF, but I just know I'm not going to carry that around like I can the M10.
Then I'm sitting here at my desk with some cameras lying around. I noticed that my Olympus Pen f shows the correction for the EVF set to negative. Later I notice by checking the manual for the SL2-S that the correction dial on its EVF corresponds to -2.5.
I talk with an optician about whether this means I need a negative correction lens for my M10, but he can't really answer the question. So, I order a -2 correction lens from B&H, which arrived today.
And I can't see a thing in focus through it. Now, I kind of expected that, what with the glasses and all.
What I don't get, though, is how the diopter correction relates to correction lenses. I've got a bunch of cameras and now know that I all turn them into a pretty strong negative correction but I apparently need positive correction lenses.
In other words, anyone with expertise who can tell me how these two things are related and end my confusion and ignorance?...Show more →
I won't claim "expertise" ... but, I went through this with my optometrist to set my distance on my glasses where I want them (for my case, leaving the native -0.5 OEM diopter in the camera). I'm rolling around a -3.5 Rx, so my curve is different regarding my 20 feet vs. 2 meter than yours will be, but the concept of how to get where you want to land things, hopefully I'll lay it out.
FYI, it took me and my optometrist a bit to get him to understand the objective, but once he did, we played well together. It's not the norm, and it's not what they teach in school. Just have to get them on board with the mission, then it's pretty straightforward after that.
Here goes:
The basic premise is that a person with 20/20 vision (i.e. tested at 20 feet) has an optical power of X in their native eye. 2 meters is less than that, so, a -0.5 is a little bit of help for the lesser, 2 meter distance.
So, if you're at a +3 for your distance (measured at 20 feet, although typically simulated via mirror at 10 feet) ... and at +1 for close distance (typically measured at 18" or so), then the Rx you'll need is somewhere between +1 and +3 for your "final" Rx at 2 meters. (For discussion we'll assume +1.75 is the Rx you need for 2 meters. Confirm this with your optometrist by setting something at a 2 meter distance.)
So, if you are looking through your RF using the distance portion of your lenses (if a bifocal), which is a +3, then you'd need a -1.25 to arrive at a final of +1.75. Leica's -0.5 only gets you down to a +2.5 from a +3. So (if you were to stack) you'd need an additional -0.75 to go with the -0.5 to make a total of -1.25. BUT, you likely aren't going to "stack" them, you're going to replace the OEM -0.5 with a -1.25 to achieve your final desired +1.75 for the 2 meter viewing distance in the RF.
The other thing you can do ... is simply this. Take your camera to your optometrist appointment. In addition to the chair, the optometrist will have those glasses which you can interchange the lenses in. Put on a pair of those and look through your VF and see how it plays with your RF patch. Don't like it, change the lenses up / down until you do. Then your optometrist will know what your Rx will be for your 2 meter distance (don't forget the -0.5 in the RF when getting that Rx).
At that point, you have a decision to make for the diopter correction. Will you be using your camera WITHOUT glasses on, in which case you'll need the "final" (+1.75 in our example) Rx. Or, will you be using your camera WITH your glasses at distance viewing (starting at +3, thus needing -1.25 to yield final +1.75. Or, will you be using your camera WITH your glasses, viewing through the bifocal / reading distance of +1, thus needing a +0.75 to achieve your final of +1.75.
So, to summarize.
Step 1.
Determine Rx at RF patch distance (2 meters) with help from your optometrist.
Step 2.
Decide if you are viewing your RF patch via your UNAIDED eye (without glasses), or through your DISTANCE Rx, or through your BIFOCAL / READING Rx.
Step 3.
Compare the Rx for your 2 meter distance with your RX for your viewer of choice (Unaided, Distance or Reading). The math necessary to yield your 2 meter (Step 1) from your starting point (step 2) will be the amount of diopter correction you'll want to have installed on your RF, to arrive at your final Rx for the 2 meter / patch.
You will have to bear in mind if you used the camera's installed -0.5 or just used the chair for your 2 meter Rx. So, don't forget to include that diopter math if you used the camera itself to get your Step 1 Rx at 2 meter.
Hopefully, I laid that out right for ya. If not, it should still be a good starting point to share with your optometrist, so he can understand the mission. You and your optometrist can work out your strategy from there. (Which could be setting your bifocal to the 2 meter Rx and looking through it / adjusted for the OEM -0.5 ... instead of using the bifocal for reading distance altogether.)
NOTE: for bifocal wearers, you may want to adjust your bifocal height to ensure you are consistently looking through your distance (or bifocal, if you prefer). I had my line set in a place that would have me sometimes one, sometimes the other and it would make me fidget around trying to see clearly in the RF. Lowered my bifocal, so I was consistently looking through the distance portion instead.
HTH
There is yet another ...
With the academic out of the way, just go pragmatic.
You're starting point of +3 (distance) -2 (correction) = +1 (your reading).
Obviously, you don't want your reading Rx.
Leica diopters only come in 0.5 increments (iirc).
-0.5 is OEM install and you've tried -2.0.
That only leaves -1.0 and -1.5 left to choose from.
Return the -2.0. Get BOTH the -1.0 and -1.5.
Try them both out, keep the one you like, return the other.
Again, HTH
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