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DoF scale on Zeiss Zm lens on T

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I have a Biogon 28mm f2.8 on my T - does anyone know if the DoF scale is true as this is a full frame lens on a APS-C crop sensor. Smaller sensors have greater DoF so may it is even deeper than the scale shows - or not as the sensor less than the full frame image circle which is not affected. Great combo but the M-L adaptor adds cost of course. THANKS !

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To the best of my knowledge, the depth of field scale is accurate as read. The fact that you have mounted the full frame lens on a crop sensor does not change depth of field .. imagine taking an 8x 10 photo print and cutting it down to 5x 7. Nothing really changes in the part that is remaining. Essentially you are viewing a section of a 28mm frame.

 

Rick

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From first principles, the DOF scale should be correct as marked, whatever the size of the sensor.

 

The confusion may arise because, for the same scene, the crop sensor camera would have to be further from the subject (i.e. longer focus distance) than for a full frame. Because it is further from the subject, the actual DOF will be deeper than for the full frame sensor.

 

Smaller sensors do not have inherently greater DOF - DOF is a property of the lens.

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Thanks very much - dof scale on the lens barrel is teally useful and a thing of the past with many lenses

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I have a Biogon 28 mm 1:2.8 on my T—does anyone know if the depth-of-field scale is true as this is a full-frame lens on a APS-C sensor. Smaller sensors have greater depth-of-field ...

As a matter of fact, smaller sensors have less depth-of-field, not more, when using the same lens. So no, the depth-of-field scale is not accurate when using the lens on a sensor that is smaller than the format the lens originally was meant for.

 

So—when using the lens on your Leica T at, say, f/8 then read the depth-of-field off the scale at f/5.6. That's not perfectly accurate but close enough.

 

 

... depth-of-field is a property of the lens.

No, it isn't.

 

 

.

Edited by 01af

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As a matter of fact, smaller sensors have less depth-of-field, not more, when using the same lens. 

 

 

Now that'll open a can of worms.

 

Gordon

 

(and yes. it's a correct statement)

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I would bow to the optical physicists on this forum if they can explain how depth of field changes when you cut a bit off the edge of the sensor (same aperture, same focal length, same subject, same distance to subject). It's a bit like taking scissors to a 35mm negative after exposure - how does that change the dof of the recorded image?

Edited by LocalHero1953

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I would bow to the optical physicists on this forum if they can explain how depth of field changes when you cut a bit off the edge of the sensor (same aperture, same focal length, same subject, same distance to subject).

Same size of the print?

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As a matter of fact, smaller sensors have less depth-of-field, not more, when using the same lens. So no, the depth-of-field scale is not accurate when using the lens on a sensor that is smaller than the format the lens originally was meant for.

 

So—when using the lens on your Leica T at, say, f/8 then read the depth-of-field off the scale at f/5.6. That's not perfectly accurate but close enough.

 

 

 

No, it isn't.

 

 

.

 

 

You are totally wrong...

 

Sensor size has nothing to do with depth of field, its the focal length that does!

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You are totally wrong...

 

Sensor size has nothing to do with depth of field, its the focal length that does!

 

 

Annnnnnnd here we go...

 

Gordon

 

p.s you both are right... sort of....

Edited by FlashGordonPhotography

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Please explain.

 

DoF calculations are based on a standard print size and viewing distance. It used to be a 7x5 and 12" V.D. but now I think most calculations are based on a 10" print.

 

You need a larger enlargement factor for a smaller sensor/film to reach the standard print size. So apparent DoF will measure differently. This is expressed in the DoF formula by the CoC (circle of confusion) measurement which is different for different sensor sizes.

 

Gordon

Edited by FlashGordonPhotography

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You need a larger enlargement factor for a smaller sensor/film to reach the standard print size. So apparent depth-of-field will measure differently. This is expressed in the depth-of-field formula by the circle-of-confusion measurement which is different for different sensor sizes.

Exactly. All it takes is a look at the depth-of-field formula ... there you can see that depth-of-field is—among other things—proportional to the linear film or sensor size (via the circle-of-confusion diameter) and inversely proportional to the square of the focal length.

 

So the smaller format has more depth-of-field when equivalent lenses are used; it has less depth-of-field when the same lens is used. And that's why depth-of-field scales on lens barrels are valid only for the image format the lens originally was intended for.

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Okay all that abra cadabra...

 

If I mount a 28mm lens on a full frame camera and then on APS-C and take the same image which in general has less or more depth of field...

 

All this exact shit about circle of confusion nobody cares about since nobody prints large anymore anyway. 

 

And if I make 2 prints of the same size one with the APS-C body and one on full frame both with the same lens again depicting the same scene... then I'm pretty sure the full frame photo still has less depth of field than the APS-C one does.

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Okay all that abra cadabra...

 

If I mount a 28mm lens on a full frame camera and then on APS-C and take the same image which in general has less or more depth of field...

 

All this exact shit about circle of confusion nobody cares about since nobody prints large anymore anyway. 

 

And if I make 2 prints of the same size one with the APS-C body and one on full frame both with the same lens again depicting the same scene... then I'm pretty sure the full frame photo still has less depth of field than the APS-C one does.

Why don't you just try it out?

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I'm going to bow out of this argument, with dignity intact (I haven't shouted or sworn).

There are two approaches to this: the optical physics one, which I follow, and the one based on human perception, which I accept is the basis for the DoF scale on lenses.

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All this exact shit about circle of confusion nobody cares about since nobody prints large anymore anyway. 

 

 

Maybe you should. Then you'd realise that the images you put on line will have a different apparent DoF depending on what device they are viewed on. A 24" monitor is reasonably common. That's the same thing as a large print, isn't it.

 

And yes your basic premise is correct re DoF but it's not the whole story.

 

Gordon

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The two are the same.

The two approaches I was talking about are not the same: light ray paths for in- and out-of focus images, which are dependent solely on lens optics -vs- how such things can be seen by humans, which is dependent on enlargement and how the CoC is calculated/measured etc.

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