100mm 2.8L vs 135mm 2.0L

[verysimplejason]

If identically framed for both 100mm lenses, then yes the DoF doesn't change. But comparing the 100mm macro with the 135mm at the same framing[
/b], DoF should be less with the 100mm macro.

+1 but at the same aperture.

Body: FF
Aperture: F2.8
Focal length: 135
Focus distance: 10 meters (to get 2X magnification)
Total Depth of field: 0.97m

Body: FF
Aperture: F2.8
Focal length: 100
Focus distance: 6.75 (to get 2X magnification)
Total Depth of field: 0.81m

But you forgot. If you need that bokeh so bad for portraiture, 135 is still a lot better than 100mm due to its bigger aperture at F2.

Body: FF
Aperture: F2
Focal length: 135
Focus distance: 10 meters
Total Depth of field: 0.69m


Source Magnification: http://www.the-digital-picture.com/Canon-Lenses/Canon-Lens-Magnification-Value.aspx
Source DOF calculator: http://www.cambridgeincolour.com/tutorials/dof-calculator.htm

 

[sagittariansrock]

If identically framed for both 100mm lenses, then yes the DoF doesn't change. But comparing the 100mm macro with the 135mm at the same framing[
/b], DoF should be less with the 100mm macro.

+1 but at the same aperture.

Body: FF
Aperture: F2.8
Focal length: 135
Focus distance: 10 meters (to get 2X magnification)
Total Depth of field: 0.97m

Body: FF
Aperture: F2.8
Focal length: 100
Focus distance: 6.75 (to get 2X magnification)
Total Depth of field: 0.81m

But you forgot. If you need that bokeh so bad for portraiture, 135 is still a lot better than 100mm due to its bigger aperture at F2.

Body: FF
Aperture: F2
Focal length: 135
Focus distance: 10 meters
Total Depth of field: 0.69m

Exactly. I said at their widest apertures, the 135 should have a shallower DoF.

For equivalent FoV at the widest aperture the macro should have greater DoF than the 135.

I didn't want to rake up a DoF/FoV conversation- I merely wanted to confirm that a 100mm macro lens is just another 100mm lens, with a really small MFD.

 

[bycostello]

they do seem to overlap quite a bit... i'd sell to fund the purchase...

 

[Loswr]

I merely wanted to confirm that a 100mm macro lens is just another 100mm lens, with a really small MFD.

Yes.

But comparing the 100mm macro with the 135mm at the same framing, DoF should be less with the 100mm macro.

No.

+1 but at the same aperture.

Body: FF
Aperture: F2.8
Focal length: 135
Focus distance: 10 meters (to get 2X magnification)
Total Depth of field: 0.97m

Body: FF
Aperture: F2.8
Focal length: 100
Focus distance: 6.75 (to get 2X magnification)
Total Depth of field: 0.81m

No2

Your math is wrong. 135mm at 10 m will have a wider FoV than 100mm at 6.75 m. For the same framing as 135mm at 10 m, the 100mm lens would be at a distance of 7.4 m [i.e. 10 m / (135mm/100mm)]. When you plug those numbers into your DoF Calculator of choice, you will find that for the same aperture the DoF is identical.

Here's the way it works: when comparing on a given sensor size (so we can ignore the circle of confusion), three factors determine DoF.

• Aperture: wider = shallower
• Focal length: longer = shallower
• Subject distance: closer = shallower

When you are talking about the same framing, focal length and subject distance have equal and opposite effects, and thus they cancel each other out. When comparing lenses of different focal lengths for the same framing, DoF is determined only by aperture. So at f/2.8 for the same framing, there's no DoF difference between the 100mm Macro and the 135L, but the 135L can open up to f/2 meaning it can achieve a shallower DoF for the same framing.

 

[PackLight]

Staying away from the 135mm vs 100mm DOF conversation, and equivalent FOV......

It was worth a try....

 

[The Bad Duck]

Also, perhaps a bit obvious, but the 135 gives more compression that might be a bit more flattering.
Even more obvious is the working distance, most people are not thrilled at a big lens up their nose. They seem to want some space, favouring the 135. On the other hand, in a smaller room the 100 might be more suitable.

50 or 85 mm can give more intimate portratist since go are forcing yourself into the models comfort zone. However then you might have issues with distortion.

It´s always a compromise no matter how much money you throw at your gear. That is why I like the gear-planning so much.

 

[Jesse]

"When you are talking about the same framing, focal length and subject distance have equal and opposite effects, and thus they cancel each other out. When comparing lenses of different focal lengths for the same framing, DoF is determined only by aperture. So at f/2.8 for the same framing, there's no DoF difference between the 100mm Macro and the 135L, but the 135L can open up to f/2 meaning it can achieve a shallower DoF for the same framing."

Mind blown. So would this work for all lenses? Eg. a 24mm and 200mm?

 

[crasher8]

As someone who just received a 135 f/2 yesterday and has worked with a 100 2.8 Macro for some time I can tell you they serve very different purposes. And to boot, the Macro is no where as sharp and cannot even come close to the gorgeous melting out of focus that the 135 produces. My new favorite lens.

 

[Loswr]

"When you are talking about the same framing, focal length and subject distance have equal and opposite effects, and thus they cancel each other out. When comparing lenses of different focal lengths for the same framing, DoF is determined only by aperture. So at f/2.8 for the same framing, there's no DoF difference between the 100mm Macro and the 135L, but the 135L can open up to f/2 meaning it can achieve a shallower DoF for the same framing."

Mind blown. So would this work for all lenses? Eg. a 24mm and 200mm?

24mm f/4, 200mm f/4, 600mm f/4 - for the same FoV, the DoF will be the same (mostly...at very wide angles, the relationship breaks down a little bit, but even then it's <10% difference). Obviously, you'll be further away, the longer the lens. Also, different rules apply at macro distances (1:1 or close to it).