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Leica dioptre


Guest NEIL-D-WILLIAMS

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No.  I believe the phenomenon you are experiencing is caused by uncorrected astigmatism at axis 90° which makes the horizontal lines that you are converging in the RF to be corrected by about half a diopter.  You already got a diopter in your glasses oriented at that axis.  

 

You probably are able to see up close better than your contemporaries because of this as well?

 

Rick

 

Not sure how I compare to others.  I can read without glasses....but can see finer details better with them.  Not sure if thick Corneas have any bearing on anything....but told I have them, which accounts for some higher pressure readings.  I have a couple of other eye conditions, neither of which I think impacts on my seeing ability.....at least for now.

 

Thanks.

 

Jeff

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Exodies,

 

The cornea does not focus.  It does refract (fixed).  It is the strongest refracting surface in the eye!

 

If, you have an IOL then you are stuck at ∞.  That is, if you are corrected for ∞ with your IOL.

 

But, an odd phenomenon;  patients with a fixed IOL actually can accommodate (focus) their IOL.  The IOL can move slightly forward when your eye tries to focus and this gives Mag!  It can be about +0.50D... here we go again!

 

Rick

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Not sure how I compare to others.  I can read without glasses....but can see finer details better with them.  Not sure if thick Corneas have any bearing on anything....but told I have them, which accounts for some higher pressure readings.  I have a couple of other eye conditions, neither of which I think impacts on my seeing ability.....at least for now.

 

Thanks.

 

Jeff

Thick corneas make no difference.  They just make eye doctors want to treat you for glaucoma when you might not need it.

 

Rick

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Jeff, by the way, if you want to see something cool, take your glasses off and look at a grid pattern.  It can just be something you drew with a black ballpoint pen (so the lines are contrasty and sharp.  You just need four lines at 180° and four at 90°.  Then look at which set is the clearest.  One set will be clearer than the other at near.

 

Rick

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Jeff, by the way, if you want to see something cool, take your glasses off and look at a grid pattern.  It can just be something you drew with a black ballpoint pen (so the lines are contrasty and sharp.  You just need four lines at 180° and four at 90°.  Then look at which set is the clearest.  One set will be clearer than the other at near.

 

Rick

 

That is cool!  I can move the grid back and forth to make one set fade and the other remain crisp.  Is there a lesson there in using the M?

 

BTW,  I have an honest eye specialist.....no glaucoma treatment....just annual checks to monitor various conditions.

 

Jeff

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First off, you can determine the axis of your astigmatism by the rotation.  At the point where one set is clearest and the other the blurriest, that is the axis of your astigmatism,  the last number in the line of your Rx.  So, try tipping the chart ever so slightly down on the right side, 5° for your right eye.  That should be the clearest for one set of lines.  

 

Next, the distance from your eye that is about 40cm will be the clearest for one set of lines.  That is because your power is 1/2.25 = the near focal point for those lines. If your Rx was -2.25 spherical, all lines would be in focus at about 40cm.

 

The lesson for the M is that this allows you to line up the vertical lines in an image (I said horizontal earlier, incorrectly) without a diopter because you are probably under corrected in your distance glasses astigmatism!

 

Rick

 

Clear as mud, huh?  :D

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Thanks....I think!...not sure if I should feel good or bad...or maybe if I could see even better....or worse?  Oh my.

 

Not sure if this is related, but I do find it easier to focus with the camera in landscape rather than portrait orientation.

 

Jeff

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Yep, that is because when in portrait you are trying to line up horizontal lines which are less sharp for you.  When you shoot in portrait you can feel the frustration of your Leica presbyopic brethren... in both orientation for the rest of us.   :unsure:

 

So, when dissected, your original statement wasn't quite correct.  You do have trouble with the RF.  Just half the trouble compared to the rest of us.  Or, maybe more accurately, 10-20% of the time (when you shoot portrait).  It's all explainable with optics!

 

Rick

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What's the charge, doc?  Seriously, though, thanks.....that's more than anyone else has ever explained to me (not that I asked them).  At least I now know why I prefer horizontal orientation (insert joke here).   Maybe you should review/re-write any VF related FAQs.

 

I won't be so quick to dismiss the numbers side of things...though I'd like to think there's still some mystery involved!  There of course remains individual variation in preferences and comfort level with various 'solutions'...e.g., use of glasses (and different types like single vs progressives) vs contacts vs diopters....and considering other factors like my own sensitivity to light (use of sunglasses), etc.  

 

For now I still prefer the RF to most DSLR screens when used in MF mode.  SLR screens were better....but I guess so were my younger eyes.

 

Jeff

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On the official leica shop websites I see that the diopters for M are offered from +3 to -3 diopter.

Important to know that the M finder is a -0.5d already.

So if your shooting eye has +2, you need to get a +2.5, with the minus of course just the other ways.

I saw on Ebay that the leicahop in Vienna is offereing diopters up to -7d.

Didn't know that these exist.

Must be a own production as they are not offered by leica.

Right now I'm looking for another -3.0d for my second M!

John

 

The Leicashop in Vienna has new old stock. Leica/Leitz used to offer many more diopters beyond -3, ..... which is as high as they go now. I bought 2 -4 diopters from Leicashop ..... paid through the nose .... but am happy I did. Regarding the built in factor in Leica viewfinders affecting the diopter you should get; I don't think it matters. A minus -4 diopter for my 400 nearsightedness is perfect. Also I can use a -3 or a -5 diopter ..... the rangefinder on an M is not like focussing on an SLR. Superimposing a rangefinder is easier than focussing a groundless. (for me anyway) One of the good things/pluses of using a rangefinder.

If Leicashop has your diopter grab it. They are genuine.

Edited by rafael_macia
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Guest NEIL-D-WILLIAMS

Rick, I have never experienced normal vision, but at Seventy years-old I have adapted. I will close by stating that the Leica M, my long-time friend, is so difficult to use that I'm about to go back to a high-point view Nikon. Tragic, eh?

 

ASIDE AGAIN, AGAIN, AGAIN! The sever for this site is redirecting or tracking replies so that the delay is entirely unacceptable. If it continues, I'm out of here. As if the admin cares. Just stop it!

Get a Leica Q mate...............so so easy to use and its light, fun to play with and it takes great pictures :) :)

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Guest NEIL-D-WILLIAMS

Neil, ugh... Is that oil rig job is starting to get to you?  :huh:

 

Rick

 

No idea what you are talking about Rick.............. hahahahahhahaha :) :) :)

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  • 2 weeks later...
Guest NEIL-D-WILLIAMS

Yah you do.  I'm confiscating your browser history.   :p

 

Rick

 

by the way, when you get back, send me your Rx in a PM and I'll try and help you with some ideas.

Here it is Rick

Something amazing happened today when I tried the rangefinderon my M6. it was same as my old M240. It was okay but not 100%. I then tried it without my glasses and it was the same so I first tried a 0.5 Diopter and it looked the same. My mate Raymond said it's impossible if it's the same, so he said don't look at the focus patch look at everything in the frame. So we took the diopter off and started again. Without it was shite. So we put the 0.5 on and it was definitely better, we then tried a 1.0 and it was great. He didn't have a 1.5 so he got me to hold the 0.5 in my fingers and then looked. It was fantastic everything was sharp sharp

So to cut a story short I left the shop with a 1.0 Diopter and Raymond is going to order me a 1.5 and swap them out when he gets it.

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Guest NEIL-D-WILLIAMS

Great news!  I assume you use your right eye.  With that Rx you should be +1.00 or +1.50.  So, it sounds right.

 

Now about your avatar... has something happened to you?   :o

 

Rick

 

Right eye mate

Without the correct Diopter I've never been able to the see the avatar clearly..........looks good now :) :) :) 

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The diopter cancels out the "overcorrection" Leica has added to the viewfinder.  Some may need a little more due to the way their eyes are corrected with their glasses or how their own eyes are naturally.  A little more than +0.50D will also make the viewfinder clearer inside 2m.  So, it seems some folks here like to little bit extra and are going for +1.0.

 

Hope this helps,

 

Rick

 

Hi There Rick

it does indeed. . . . .

I've been doing 'monovision' for around 15 years now - it's been really fantastic: I have a reading lens in my left eye (+2.75) and a distance lens in my right eye (+1.5). I can see that it's not the right solution for Neil, but I really really recommend anyone who hasn't tried it to give it a whirl. Previously I used vari-focals, which caused a real pain in the neck working on a big screen and made focusing pretty tough. 

 

Question:

I'm in the very early stages of developing cataracts (my rangefinder eye is slightly ahead). The real question is going to be whether I should have variable focus replacement lenses . . or stick to the monovision principle which has served me so well. It's not a decision I need to make for a year or so, but I'd be really interested in your feelings about this.

 

I can still focus perfectly with the M at the moment, it doesn't seem to be getting worse, which is great.

 

Many thanks for your input to this thread, it's seriously appreciated.

 

Best

Jono

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