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Old Feb 21, 2007, 3:08 PM   #1
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On a lot of cameras, including the *ist series, you can adjust the eyepiece for your own eye.

This would mean that you can have the eyepiece way out of whack and take a shot, say, with an AF lens that is in great focus. So theoretically that means that if you are going to manual focus, you might "see" through the viewfinder that your subject is in focus, and yet it really is not as far as the sensor is concerned.

I imagine this would make manual focus with a telephoto and a short depth of field pretty tricky.

How do you calibrate this with an MF lens? I can imagine how to do it with an AF lens. Anybody have any tricks? Or am I all wrong on this?


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Old Feb 21, 2007, 5:17 PM   #2
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No, you got it right. Diopter correction is irrelevant for AF, but can really screw you up with MF. But remember that on the Pentax DSLRs you get the little focus indicator when the camera thinks you're in focus. With 3 or multipoint AF, it'll beep when you're in the ballpark. Using center point focus, it'll be very accurate. Even if you don't use it, it'll still tell you if your focusing makes any sense or if you're way off.

My eye sight isn't so hot, so what I do is adjust the dopter all the way out (towards the left--- WAY wrong for my eyes) and focus the lens to infinity.

Then I try to find a faraway object, or poster or whatever and play with the diopter knob until I can clearly resolve the image or text.

In my case, that's one click away from complete right.


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Old Feb 21, 2007, 11:35 PM   #3
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No it should make NO difference AF or MF all you are doing is correcting the VF without having to wear glasses (and worse FOV) to see things are sharp.

Sharp is sharp. Where as uncorrected diopter VF and AF or MF nothing would ever be sharp.

Something I remember from my EVF P&S days... VF had higher res than the LCD... and people would say its blurry... that was the FOR ME diaopter correction.

With a DSLR not an issue as they see everything from the LCD.... and only I look through the VF.
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Old Feb 22, 2007, 12:36 AM   #4
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If I think my dioper adjustment has gotten knocked off is put on an AF lens and then adjust the viewfinder to match. Then switch to a manual focus lens. While the green dot is close, in some cases I've found that it has focused on something I wasn't intending when the subject is small and/or it is at a distance.

Another way to do it is to set the lens to infinity and look at something in the distance. Change the dioper until the subject in the distance is in focus. Only problem with this is that you have to be able to make out clearly what you are focusing on in the distance (giggle, giggle - I once tried to use a fence, but couldn't see it clearly because it was so small!).
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Old Feb 22, 2007, 1:51 AM   #5
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wrong on the mf... if i'm focusing by eye.... and i see blurry, i'll adjust focus to correct it..... if the diopter is wrong, you can't focus reliably

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No it should make NO difference AF or MF all you are doing is correcting the VF without having to wear glasses (and worse FOV) to see things are sharp.
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Old Feb 22, 2007, 3:00 AM   #6
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That just doesn't make sense.....

The only thing the diopter is doing is correcting the focus to your eye between VF lens and the VF screen... it has nothing to do with the lens or anything you do with it...

as again it is NOT a direct link... you are seing the VF screen which is at the same FP as the sensor/film..... but a wholly separately focused image.

Again if diopter not right nothing you do with the lens will bring it into sharp (though maybe seeming better if still not sharp) focus, as it is focusing on the VF screen not your eye...

I have used my lenses in both AF and MF and see no difference in resuts... though do have the diopter adjusted for my eyesight, where most would see a bit blurry.... but again adjusting the lens would never make that sharp only adjusting the diopter would do that for them.

Maybe you just don't have your diopter adjusted properly for optimum sharpnes for your eyesight. Does AF ever look really sharp to you???
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Old Feb 22, 2007, 12:23 PM   #7
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I thought that the VF (viewfinder, I assume) went through the lens on an SLR -- that there's no screen involved at all -- and therefore you in fact are seeing what the sensor will be seeing when the mirror flips up and the shutter trips. As a matter of fact, I thought that was basically what the mirror is for -- to re-direct the image to the VF.

There is obviously some reduction being done from the mirror to the VF, so there must be some lense(s) between the mirror and the eyepiece - which the diopter would adjust the focus for.

My concern would be that you could focus the light path through the lens to the mirror, then through the secondary lens path to the eyepiece where the diopter is, and it would in fact focus correctly (that is, sharp focus) at the back of your retina, but the light path to the sensor when the mirror flips up would be different and therefore the focus on the sensor might be off of what your eye sees through the other path to the VF.

Does that make sense?

The alternate explanation that would jive with Hayward's view (I don't remember my physics that well which is why I'm even asking the question) .... would be that the lens focuses on the mirror and there's no correction that you can do with the reflection from the mirror between the mirror and the VF -- so if you can get it sharp at the VF at all, that means the image was focused correctly at the mirror.

Maybe that's the way it works. Who has a physics degree around here? :G

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Old Feb 22, 2007, 4:43 PM   #8
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Take the lens off and look up.... you will see the translucent screen the image is focused on, again at the same focal plane distance as the sensor is.

The diopter is purely to correct from it to your eye.

PS you can get dust and dirt on it too (very easily in fact, as it has neither the mirror or shutter curtain covering it) which will not effect the image, just what you see in the VF.
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Old Feb 22, 2007, 5:32 PM   #9
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AHA!

(lightbulb goes off -- perhaps that should read flashbulb)

That makes sense now.
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Old Feb 22, 2007, 11:07 PM   #10
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mtngal wrote:
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If I think my dioper adjustment has gotten knocked off is put on an AF lens and then adjust the viewfinder to match. Then switch to a manual focus lens. While the green dot is close, in some cases I've found that it has focused on something I wasn't intending when the subject is small and/or it is at a distance.

Another way to do it is to set the lens to infinity and look at something in the distance. Change the dioper until the subject in the distance is in focus. Only problem with this is that you have to be able to make out clearly what you are focusing on in the distance (giggle, giggle - I once tried to use a fence, but couldn't see it clearly because it was so small!).
The recommended way is to adjust the diopter to bring the grid etched on the focus screen, and VF displays into sharp focus. Best done while sighted on a blank wall. Also can do it with lens cap on. This prevents distraction from scenery. Try it a few times bringing camera to eye, and checking focus immediately. If you give it time, your eye will adjust to the slightly OOF display.

Be careful when using infinity focus, as some lenses focus 'past' infinity (Infinity and Beyond!, as someone else famous once said)

As Hayward mentioned, an incorrect diopter adjustment won't make something look in focus that isn't, it just makes everything look out.

brian
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