DoF scale with M lenses on the T

[Clemgill]

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I thought I was not a beginner...but I made a beginner mistake: I used the depth of field scale of a 28mm M lens to shoot at hyperfocal on the T(no more bothering to adjust focusing)... Had great time until I "developed" the pictures in Lightroom. A lot of nice frames were nicely defocused.... Not grossly but enough to make it obvious, and totally inconsistent with the glass and camera.

Took me bit of time before slapping my forehead... "This is NOT a full frame but an APC sensor...."

 

After tech verifications, I could indeed confirm that you can use the DoF scale of a full frame lens, used on an APC camera BUT only if you divide the actual lens stop by the crop factor (The diameter of the confusion circle on an APC is simply about 1.5 smaller than that of a full frame)

 

Ex: if the lens stopped at 5.6 you should actually align the infinite mark on 5,6 / 1.5 = 3.7 on the DoF scale of the lens, which means between 2.8 and 4. so rule of thumb is " - one and a half stop"

 

Shooting the T with M lenses is a pleasure, with outstanding results. Just remember its a T...!

 

Learned it the hard way...

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[Michael Geschlecht]

Hello Clemgill,

 

Welcome to the Forum.

 

"Depth of Field" is an illusion. There is actually only 1 plane where the image is actually in best focus. Best focus is not 1 plane & some distance before & after.

 

The idea of depth of field tables like those engraved on modern lenses of many manufacturers is based on a certain set of criteria. Some people find this set of criteria insufficient. Even within the parameters of the lenses & formats they were designed for.

 

Going well back into the 20th Century many photographers have used a standard of closing the lens 2 stops smaller than the guide indicated to get appropriate (for them) results. Even though they are using the lens within the format that the depth of field tables were designed for.

 

Example: Focus @ F2.8 & DOF scale reads as OK. Set aperture to F5.6 & adjust shutter speed accordingly.

 

Alternatively: Focus @F2.8 & DOF scale reads as OK. Use the DOF parameters of F1.4.

 

Not long ago there was a Thread in this Forum where some of this was discussed. It had to do with depth of field with the 75mm APO.

 

Best Regards,

 

Michael