85mm f1.2 on Medium Format

[Shashin]

Lens aberrations do contribute to blur, which directly relates to circle of confusion. Again, a very soft lens will limit its depth of field compared to a very sharp lens. And, you cannot subjectively change the circle of confusion to make a soft lens any sharper. This is ultimately limited to how well the aberrations are controlled by the lens itself.

Sergei is going to kill me. But the answer is no. You have a lens that is sharp or unsharp. How can you even determine DoF in an unsharp image?

 

[David Klepacki]

I am using the comparative "smaller." If the permissible CoC is X, than a CoC of X/2 is not going to change DoF.

This is simply not true.

 

[David Klepacki]

Sergei is going to kill me. But the answer is no. You have a lens that is sharp or unsharp. How can you even determine DoF in an unsharp image?

A sharp lens will support a smaller circle of confusion than an unsharp one.

 

[Shashin]

This is simply not true.

Actually, it is true. If the permissible CoC defines the DoF, then all the CoCs smaller than that does not change the DoF.

I think you are confusing DoF with resolving power.

 

[Shashin]

A sharp lens will support a smaller circle of confusion than an unsharp one.

Yes, but the unsharp lens has CoCs larger than the permissible CoC and so the unsharp image has no DoF that can be determined. So to even talk about DoF in an unsharp image is pointless.

You really should read the document I linked to in a pervious post.

 

[MarkoRepse]

See (the middle of) my post above. I think the confusion comes from how you define DOF

 

[David Klepacki]

Yes, but the unsharp lens has CoCs larger than the permissible CoC and so the unsharp image has no DoF that can be determined. So to even talk about DoF in an unsharp image is pointless.

You really should read the document I linked to in a pervious post.

First, no one is talking about an unsharp image here. A lens that is characterized as being "unsharp" is simply a statement that its MTF is not as high as a lens that can be characterized as "sharp". So, in the context of CoC and DoF, "sharp" and "unsharp" refer to relative MTF performance.

I understand CoC and its relation to DoF. What you don't seem to understand is that lens aberrations and lens MTF/OTF performance do affect what can be used as a permissible CoC.

 

[Shashin]

See (the middle of) my post above. I think the confusion comes from how you define DOF

I am using the standard technical definition. Which is really the only way you can define it.

 

[Shashin]

First, no one is talking about an unsharp image here.

A sharp lens will support a smaller circle of confusion than an unsharp one.

Well, if the lens is unsharp, the image from that lens must be unsharp. How else can you define unsharp>

A lens that is characterized as being "unsharp" is simply a statement that its MTF is not as high as a lens that can be characterized as "sharp". So, in the context of CoC and DoF, "sharp" and "unsharp" refer to relative MTF performance.

I understand CoC and its relation to DoF. What you don't seem to understand is that lens aberrations and lens MTF/OTF performance do affect what can be used as a permissible CoC.

You are talking about contrast and how an image is rendered. This is not DoF.

Since the permissible CoC is defined by the format size, the MTF is really not a factor. The MTF of a lens does not change no matter what format you use it with, the DoF will as the permissible CoC is different.

 

[Vivek]

This is simply not true.

+1

(If anyone has a problem with that, I have two suggestions.

1. Look up the actual origins of CoC in detail. Hints: There are a lot of variables. DoF are approximations based on a big list of assumptions.

2. Better yet, use a camera and make some images.)

 

[Shashin]

+1

(If anyone has a problem with that, I have two suggestions.

1. Look up the actual origins of CoC in detail. Hints: There are a lot of variables. DoF are approximations based on a big list of assumptions.

2. Better yet, use a camera and make some images.)

So you are saying that the smallest CoC defines the DoF, not just the permissible CoC? I would suggest you look up the origins of CoC in detail.

 

[Vivek]

Square

Street

Two more gems, Marko! :thumbs: