Canon EOS 1Ds DOF

kevindar wrote in post #4113285
cosworth, please reread what I said.
50, 2.8, same as 80 4 (actually 4.5, since its about 1.3 stops)
so to use your example, it will be 160mm, f 4.5, 100 ft, dof 32.7 ft, same as 100 f 2.8

What you're saying is that a smaller aperture is required to attain the same DOF with a larger format camera.

Pretty much what I wrote.

Curtis N wrote in post #4113286
I don't think an equation will help you if you don't understand the concept, and it appears you haven't reached that point yet.

Depth of field is the distance in front of and behind the focused distance that appears acceptably sharp. Print magnification is going to affect that.

I think the full definition is, "Depth of field is the distance in front of and behind the focused distance that appears acceptably sharp in an 8x10 print viewed at 1 foot distance by an average viewer," or probably the metric equivalent. Definitely affected by magnification.

Curtis N wrote in post #4113293
What you're saying is that a smaller aperture is required to attain the same DOF with a larger format camera.

Pretty much what I wrote.

Curtis, Thats an in effect kind of conclusion. However, it all depends on the fixed variables. in the example you gave, you are comparing a 100 mm lens, and a 160 mm lens. you are comparing two different lenses. a 50 mm lens, at a given subject distance, aperture size, and distance to image screen with have a given dof, regardless of how big the screen is.

As to the earlier poster that made the assertion that the sensor size affect subject magnification, again incorrect. Subject magnification is a function of your focal length, distance to subject, and distance to image produced. that image produced could be on a tiny sensor, or the screen in a cinaplex theater.
Its all a matter of technicality I understand. Every one know that a 50 1.4 on 5d will allow you to take images with a shallower dof than 30D. the only reason behind that however is that you can get closer to your subject with 5D to create an image that fills a larger screen now, hence increasing image magnification (by moving closer to your object) and as I said earlier, image magnification (together with F stop) dictates DOF.

The 8x10 standard is generally used for "standard" DOF calculations and lens markings.

But you could calculate DOF for any print size and viewing distance.

The bottom line: If you want a lot of DOF, print it really, really small!

I read what you said, but the educator in me kicked in . You have to compare the same apertures.

Rememebr that people read this stuff that don't chime in and we have to be mindful of how we respond. Things have to be clear.

Especially when talking crop and "magnification".

Right now it's an argument in a circle (of confusion ! sorry)

Your all correct, for Cosworths illustration to work, we needed to make adjustments to compensate for the crop factor, in this case he changed the actual lenses focal length to compensate for a smaller sensors "X-Factor" on the "crop" sensor, then in turn we needed to alter aperture to keep DOF the same to compensate for the change in focal length.. etc..

The point is, by changing sensor size or format as some may refer to it, one needs to adjust aspects such as focal length to maintain similar working distances etc..

If nothing else is changed, focal length, working distance, aperture, and prints are out put to scale with sensor size as opposed to pixel pitch, then DOF will not change only because the sensor size was changed. More needs to change for the DOF to change. And it does, naturally as we work with the changed format.

Every one is right on this one, IMHO
You just have differing opinions on what aspects of the equation must remain "constant"

I knew this would happen. It happens every time.

The relationship of DOF to camera format has been widely understood by pro shooters for at least a century. Anyone who has used both large format and 35mm film certainly understands it. But in this digital age, every time the subject of DOF is brought up, someone with a less-than-complete understanding of the concept jumps in and confuses people.

kevindar wrote in post #4113391
a 50 mm lens, at a given subject distance, aperture size, and distance to image screen with have a given dof, regardless of how big the screen is.

This is simply a false statement. You don't have a DOF until you have an image to look at. Whether it's a print, a monitor or a slide projected on the wall. Failing to understand the impact of print magnification represents failure to understand the very definition of DOF.

And when you're comparing DOF from two different camera formats it's imperitive that you keep all other factors equal. The only way to create two images with the same FOV and the same perspective from two different camera formats is to use proportionately different focal lengths.

It happens because people use math. That's all well and good. Think of it as bolting ACTUAL lenses to your ACTUAL body. If we assume that the only variable is the crop (same focal length, same aperture etc. on a lens you can hold) then it skews the math lovers.

Why the aperture changes is a given, but it's not real world usage.

Cyberdyne, you are correct, and I agree with you. I also agree with Cosworth, that since people are interested in the "in effect" results, sometimes its beneficial to simplify things. I do take exception with the poster who told me to check my facts before I spread misinformation, as all the statements made in my original posts were correct. I think sometimes dumbing down an explanation just adds to the circle of confusion.

Ok, I'm baffled. I think I'm reading DOFmaster wrong, but it keeps showing me that you get greater depth of field with a larger sensor, which I know experientially is wrong. What am I misunderstanding?

Curtis N wrote in post #4113286
I don't think an equation will help you if you don't understand the concept, and it appears you haven't reached that point yet.

Depth of field is the distance in front of and behind the focused distance that appears acceptably sharp. Print magnification is going to affect that.

Alright Curtis, you may be right. I may not be at Nirvana of Dof. I also did not realize an image printed at 5x7 will have a different dof than image printed at 25x35. or I am misunderstanding.

In any case, Peace to all, I think I have beaten this dead horse enough.

I read all of the posts to every one of these threads. I am only starting to get a grip on this. The circle of confusion seems to be a key here and I think I finally got a clue from this thread. The differing methods that everyone uses to discuss this makes my head spin sometimes. I always tried to eliminate parts of the discussion to make it easier for me to understand and I think that made it harder for me to understand. Carry on!

kevindar wrote in post #4113512
I think sometimes dumbing down an explanation just adds to the circle of confusion.

On this I will agree. DOF has inherent complexities. Sometimes people try to simplify it to help others understand, but this is a slippery slope that generally leads to misunderstanding.

tsaraleksi wrote in post #4113523
Ok, I'm baffled. I think I'm reading DOFmaster wrong, but it keeps showing me that you get greater depth of field with a larger sensor, which I know experientially is wrong. What am I misunderstanding?

It's not experimentally wrong. It's common knowledge among people who have used different camera formats and seen the results.

There's a reason why large format landscape shooters feel the need to shoot at f/64 and deal with reciprocity failure.

Curtis N wrote in post #4113915
It's not experimentally wrong. It's common knowledge among people who have used different camera formats and seen the results.

There's a reason why large format landscape shooters feel the need to shoot at f/64 and deal with reciprocity failure.

Yes it is, for exactly the same reason you just quoted. The calculator tells me consistently that for greater depth of field, I should use a bigger sensor, which I know is wrong. What exactly am I misreading?

And I've shot with "different formats and seen the results" which is exactly why I asked my question in the first place.

tsaraleksi wrote in post #4113523
Ok, I'm baffled. I think I'm reading DOFmaster wrong, but it keeps showing me that you get greater depth of field with a larger sensor, which I know experientially is wrong. What am I misunderstanding?

tsaraleksi wrote in post #4115408
Yes it is, for exactly the same reason you just quoted. The calculator tells me consistently that for greater depth of field, I should use a bigger sensor, which I know is wrong. What exactly am I misreading?

And I've shot with "different formats and seen the results" which is exactly why I asked my question in the first place.

Are you changing just the camera, i.e. the sensor? If you are, you aren't getting the same picture with the two cameras until you crop the FF picture to match the crop camera's picture. But then, the 8x10 crop camera picture will be getting compared to a 5x6" print from the FF body. If you want to start with both the cameras taking the same picture, edge to edge, from the exact same spot (so perspective is the same), you'll find the FF camera has a shallower DoF when you compare the two 8x10 prints, because you'll need to use an 80 mm lens on the FF camera to match the FoV of a 50 on the crop.