Michael:Depth of field: FF vs 1.x crop factor???

[Jonathan Wienke]

The short answer is that if one keeps composition (or FOV & subject distance) constant, you are using a shorter focal length lens with a smaller-format camera, which means that given a constant aperture ratio (like f/2) you're also using a smaller physical aperture with a smaller-format camera (like 1.3x) than you are with a larger-format camera (full-frame) with the same shutter speed and ISO setting. DOF is inversely proportional to physical aperture diameter and focal length. Since you have decreased both with the smaller-format camera, DOF must necessarily increase proportionately.

[Jonathan Wienke]

Exactly, it depends on what you want to do.

[bdf]

"which means that given a constant aperture ratio (like f/2) you're also using a smaller physical aperture"

Why is the physical aperture smaller on the smaller format camera?  By the way, what is the difference between physical aperture and the aperture set on the camera?

[BernardLanguillier]

My question is: how visible is this extra DoF?  Is it very noticeable?  Are there any comparisons availible online?

I guess thats 3 questions...

The basic answer is about one stop, or slightly more.

To what extend using F11 instead of F8 is important for you depends on the type of shooting and on how large on intend to print.

Regards,
Bernard

[bdf]

Michael,

I recently read this post on another forum:

"   wow!! You are right! I never realized that before.... Thank you so much for pointing this out........yes...yes...yes.........

To repeat the logic: As long as you own fast glass (I have a couple of 1.4f's in my collection) and given that one is often unwilling to shoot wide open because of the miniscule DOF (about an inch for closeups of people at 1.4) then the max aperture is really limited by the minimum dof one is willing to live with for a given shot. The 1.5x crop factor gives a 1.5x larger dof for the same field of view (i.e. if you use a 75mm ff lens compared against a 50mm 1.5x lens). Then I can shoot at a 1.5x wider aperture for the same dof which is about a stop better iso performance as compared with a ff camera!!!!!

This is the situation I normally shoot in. I will now stop being jealous of all of those good iso noise performance claims of the ff cameras.

Bravo for 1.5x"

I am interested in your thoughts on the matter.  Why is depth of field shallower on a full frame sensor than on a 1.5x crop factor sensor?

Thanks

[lester_wareham]

<snip> ... then the max aperture is really limited by the minimum dof one is willing to live with for a given shot. The 1.5x crop factor gives a 1.5x larger dof for the same field of view ... <snip>

I have always seen more DOF as a limitation of APS-C compared to full frame 35mm, but as you point out in some situations it is an advantage.

[LesGirrior]

My question is: how visible is this extra DoF?  Is it very noticeable?  Are there any comparisons availible online?

I guess thats 3 questions...

[jejv]

<snip> ... then the max aperture is really limited by the minimum dof one is willing to live with for a given shot. The 1.5x crop factor gives a 1.5x larger dof for the same field of view ... <snip>

I have always seen more DOF as a limitation of APS-C compared to full frame 35mm, but as you point out in some situations it is an advantage.

Indeed.

If achieving some minimum depth of field is an objective,
then smaller sensors look much better than if depth of field
is disregarded.

For example, assuming the same subject distance and
field of view (and all other things being equal):
- a 35mm camera at f8
- a 1.6x crop camera at f5
- a 4/3" camera at f4
will give roughly the same depth of field.

That means that the 4/3" camera could
- run at four times the shutter speed for the equivalent ISO setting
OR
- run an ISO setting two stops slower at the same shutter speed

But then all other things usually aren't equal.

On the other hand, if the shallowest DOF is what you seek,
then you want the biggest sensor you can get.

John.

[LesGirrior]

Thanks John & Bernard for information.