[borno]

The 200mm f2 (or 1.8) would be more like 135mm f1.2, I would guess on a crop body. Just my 2 cents (1ds III is full frame)

[wallyb]

The 200mm f2 (or 1.8) would be more like 135mm f1.2, I would guess on a crop body. Just my 2 cents (1ds III is full frame)

In what way would it be like a 135/1.2 (a lens that doesn't exist) on a crop body? In terms of bokeh, it would take only a 135/3 to give the same FOV and DOF on a 1.5x crop body. In terms of the amount of light it takes in, the aperture would remain constant no matter which size sensor was employed.

[borno]

My mistake, it would be 133mm f1.3 for the same depth of field and field of view on a 1.5x crop body. Not that I would buy one.

[Ben_Edict]

I
And sorry, Daniel. The 200/2's photos are way better than what you posted. The subjects do an almost 3D "pop" off the background (like some of the stuff you see off the 43Ltd or 77Ltd when something just works right). It's a fairly common effect from a 200/2 (similar for the Canon/Nikon variants) from the images I've seen.

But you should take the colour and brightness contrast between the subject (the male's skin) and the background into consideration. This stark contrast certainly adds massively to the "3D" effect. In Daniel's images, the background and the girls have basically the same colours and brightness, which simply eliminates some of the "pop". If you just look at the bokeh, as Daniel suggested, the difference is not altogether as visible, between f/2 and f/2.8.

Ben

[wallyb]

My mistake, it would be 133mm f1.3 for the same depth of field and field of view on a 1.5x crop body. Not that I would buy one.

No, like I just said it would take a 135mm (133) f/3 to give the same DOF and FOV on a crop body.

[borno]

Here is an interesting link on the subject:
Digital Camera Sensor Sizes: How it Influences Your Photography

[wallyb]

Here is an interesting link on the subject:
Digital Camera Sensor Sizes: How it Influences Your Photography

As you decrease the sensor size, the DOF decreases, as they say on their webpage. So you need only a smaller aperture to begin with, since the bokeh will basically "multiply" in size. What they say is correct, but their calculator is either misleading or wrong. Think about it logically instead of relying on a calculator and you'll get it.


EDIT: I found out why it's misleading. They are not taking into account the same image/print size. They are using hypothetical direct crops of larger sensors. If you take a 12mp full-frame image at 200mm f/2, you would need a 135mm f/3 lens to give the same image on a 12mp 1.5x crop APS-C camera.

Also, the reason why compact digital cameras have such a deep DOF is because their lens' focal lengths are around 2-6mm at f/2.8 to start with, not because of their sensor size. If you put a 100mm f/2.8 lens on a compact digital camera sensor, the image would have such shallow DOF it would be almost impossible to get any subject fully in focus. Who wrote this errant guide?

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Last edited by wallyb; 01-03-2010 at 07:07 AM.

[Diffusion]

There is nothing misleading. The website linked even has a calculator for you. A 200/2 on full-frame can only be replicated by a 135/1.3 on a 1.5 crop factor sensor.

Also, the quote on the website is "As sensor size increases, the depth of field will decrease for a given aperture (when filling the frame with a subject of the same size and distance)."
INCREASES, not decreases.

[wallyb]

There is nothing misleading. The website linked even has a calculator for you. A 200/2 on full-frame can only be replicated by a 135/1.3 on a 1.5 crop factor sensor.

Also, the quote on the website is "As sensor size increases, the depth of field will decrease for a given aperture (when filling the frame with a subject of the same size and distance)."
INCREASES, not decreases.

Then explain why when a 35mm lens, say a 100mm f/4 lens, is adapted to the four-thirds format, it doubles in effective focal length and has a halved DOF, effectively giving the same appearance as a 200/2 lens on 35mm? Assuming the same resolution between cameras.

[asdf]

Then explain why when a 35mm lens, say a 100mm f/4 lens, is adapted to the four-thirds format, it doubles in effective focal length and has a halved DOF, effectively giving the same appearance as a 200/2 lens on 35mm? Assuming the same resolution between cameras.

Focal length does not affect DOF much. Longer focal length causes the background to be magnified, but about the same amount of stuff remains in focus.

DOF2

Since the out-of-focus areas are magnified with the longer focal length, they appear blurrier. But DOF remains about the same.

[wallyb]

Since the out-of-focus areas are magnified with the longer focal length, they appear blurrier. But DOF remains about the same.

You are right, this is what I'm meaning to say. Since this thread was showcasing the particular bokeh of the 200/2 lens, my point is valid. But I used DOF where I should've said bokeh. They're nearly interchangeable in the final image, but not during composition, which might be confusing everyone.

[filorp]

Guys! Wake up! What happened to this thread? It dies.... I really want 135 with f below 2.8 the fact there is no big difference betw f2.0 and f2.8 doesnt talk to me, i want IT and i want it to be really big (like 82mm filter thread) - this is really shout of desperattion!!!!!

[Ben_Edict]

Guys! Wake up! What happened to this thread? It dies.... I really want 135 with f below 2.8 the fact there is no big difference betw f2.0 and f2.8 doesnt talk to me, i want IT and i want it to be really big (like 82mm filter thread) - this is really shout of desperattion!!!!!

If you are so serious about it, buy a used Pentax 135/1.8, which is a wonderful lens. I'ld love to have one...

Ben