swmcl

11-Feb-2012, 14:27

Hello to all,

I'm doing my sums ... with the aid of Bob Atkins interactive calculator that I've loaded onto the computer.

So I'll put some figures down and I ask if I'm doing things wrong.

I start with a Heliar 300mm f4.5 lens and I take my portrait at 3m distance with an 8x10 camera. The CoC is 300 microns, the magnification is 0.1111 and the DOF is 24.35cm all according to the calculator.

Now. I go the Xenotar 150 on 4x5.

The CoC is 150 microns, the aperture is f2.8 the magnification is 0.05555. I get a DOF of 24.35cm and a distance o 2.854m.

If you can appreciate it, I'm trying to replicate the image on 8x10 with the 4x5 camera. Exactly the same image means half the magnification right ?? But why only the slight change in distance from 3m to 2.854m ? Is this figure correct ?

Also, it looks by the calcs that the Heliar is getting a shallower DOF than the Xenotar for the same image. Is that right ?

I also have another lens of 205mm FL that has a max aperture of f3.5. If I shoot that on 5x7 then the following figures occur. The CoC is 200 microns, the magnification is 0.77777 the distance is 2.843m and the DOF is 25.04cm.

In summary:

The Heliar 300mm f4.5 on 8x10 has the shallowest DOF of all these lenses and beats the Xenotar 150mm on 4x5 easily. The 205mm f3.5 lens on 5x7 also beats the Xenotar 150mm on 4x5. All assuming the exact same portrait image.

I still think something is wrong. Please enlighten me !

Rgds.

I'm doing my sums ... with the aid of Bob Atkins interactive calculator that I've loaded onto the computer.

So I'll put some figures down and I ask if I'm doing things wrong.

I start with a Heliar 300mm f4.5 lens and I take my portrait at 3m distance with an 8x10 camera. The CoC is 300 microns, the magnification is 0.1111 and the DOF is 24.35cm all according to the calculator.

Now. I go the Xenotar 150 on 4x5.

The CoC is 150 microns, the aperture is f2.8 the magnification is 0.05555. I get a DOF of 24.35cm and a distance o 2.854m.

If you can appreciate it, I'm trying to replicate the image on 8x10 with the 4x5 camera. Exactly the same image means half the magnification right ?? But why only the slight change in distance from 3m to 2.854m ? Is this figure correct ?

Also, it looks by the calcs that the Heliar is getting a shallower DOF than the Xenotar for the same image. Is that right ?

I also have another lens of 205mm FL that has a max aperture of f3.5. If I shoot that on 5x7 then the following figures occur. The CoC is 200 microns, the magnification is 0.77777 the distance is 2.843m and the DOF is 25.04cm.

In summary:

The Heliar 300mm f4.5 on 8x10 has the shallowest DOF of all these lenses and beats the Xenotar 150mm on 4x5 easily. The 205mm f3.5 lens on 5x7 also beats the Xenotar 150mm on 4x5. All assuming the exact same portrait image.

I still think something is wrong. Please enlighten me !

Rgds.