imagesintime Loc: small town, mid-America

Nikonian72 Loc: Chico CA

Pictures of calculators is not proof!

imagesintime Loc: small town, mid-America

You obviously did not take time to explore the web site or to input information into the provided DOF software.

Nikonian72 Loc: Chico CA

Q

I have properly used DOF calculators for several decades, especially with 4x5 view cameras at full bellows. Just because you have a photo of a calculator, doesn't mean that you know how, or when, to use it.

imagesintime Loc: small town, mid-America

Let me help you use the website. Try this page
http://www.dofmaster.com/dofjs.html
Fill in the camera and lens information for various equipment and compare the results. This site is one of the premier DOF sites on the web. It is doubtful it would have existed as long as it has if the information was incorrect.

imagesintime Loc: small town, mid-America

Let me help you use the website. Try this page
http://www.dofmaster.com/dofjs.html
Fill in the camera and lens information for various equipment and compare the results. This site is one of the premier DOF sites on the web. It is doubtful it would have existed as long as it has if the information was incorrect.

Nikonian72 Loc: Chico CA

http://en.wikipedia.org/wiki/Depth_of_field

Same focal length for both formats
Many small-format digital SLR camera systems allow using many of the same lenses on both full-frame and “cropped format” cameras. If the subject distance is adjusted to provide the same field of view at the subject, at the same f-number and final-image size, the smaller format has more DOF, as with the “same picture” comparison above. But the pictures from the two formats will differ because of the different angles of view and the different viewpoints.

If pictures are taken from the same distance using the same lens and f-number, and the final images are the same size, the original image (that recorded on the film or electronic sensor) from the smaller format requires greater enlargement for the same size final image, and the smaller format has less DOF. The pictures from the two formats will differ because of the different angles of view. If the larger format is cropped to the captured area of the smaller format, the final images will have the same angle of view, have been given the same enlargement, and have the same DOF.

Synopsis:
Same lens on different formats, digital images cropped to same field = same DOF.

This has been true for 150-years, since photography progressed from glass negatives to tin-types (same cameras, same lenses, but different size formats). Experienced photographers who have used various film formats, like me, know this. Photographers with mostly or only digital experience (and little or no film experience), still have a lot to learn about photographic principles. Which are you?

dpullum Loc: Tampa Florida

[quote=Nikonian72]

Sorry NiKonian72, you may be disappointed! When I became a math teacher after retiring from 40+ years of Science in Industry I was amazed to find that "formal proofs" that we had in school are no longer done!! No, if/then/therefore!!! No logic truth tables or formal logic thinking!!!

As I said one one of these pages, the lens is the lens and is not aware of the sensor, thus the DOF of the lens and focus point remains the same regardless of sensor as long as the sensor is smaller than the image circle.

Surly issues of diffraction, circle of confusion, clarity of image, noise come into play, but the lens is innocent of that knowledge, and certainly does not change its optical nature to accommodate the sensor size. The lens only knows its mm value and how much of the target image is used, it is not aware nor does it care. What is in focus is based on the optics of the lens, that is the unchanged. Any defect in image or spot on the lens only appears to be larger, that fleck of dust does not grow, the smear of the fleck may be fuzzy looking, that confusion only is expanded when the final image is "blown-up" like a square on a balloon to fill the screen.

A particular lens has a DOF based on optics within and f-stop settings, again, IF the sensor was changed in the focus area, THEN the lens does not know and the mm and DOF etc remain unchanged.... the sensor only samples a smaller portion of the image area, THUS the resulting image must be enlarged to fill the screen or print area. In the case of a Minolta Lens on a Sony Alpha that enlargement is 1.5

Now, is that 1.5 per side, thus an area enlargement of 2.25?

Nikonian72 Loc: Chico CA

Donald - My point was that Images In Time made a math statement without any cite as to how he arrived at his his conclusion. I did not expect a "proof". Reference to a calculator is not proof.

You & I are in complete agreement. My "proof" (all math involved) is found here: http://en.wikipedia.org/wiki/Depth_of_field which I cited above, along with my conclusion.

dpullum Loc: Tampa Florida

Yep, Nikonian, I knew you did not want a "formal" geo proof. And Indeed, the Wikipedia article is a great one. Also some things while in theory affect an image are minor and/or even if not so minor will not show up in the "output device" ... printer, TV screen, or the eye is not capable of remembering and comparing. Again, I admire your work and your knowledge. Kudos! d/p

Bridgeman Loc: Missouri

Since my initial post on this subject, I have done more research. First you need to know what CIRCLE of CONFUSION is. Simply put, it is a factor of the acceptable sharpness of an image. Second you need to know what causes it. See www.normankoren.com/Tutorials/MTF6.html for the mathematical proof of CoC. I do have to agree that the size of the sensor, full frame or cropped, does not have any factor in the CoC. Although other factors are involved, the main factor seems to be the distance from the rear lens element to the focal plane, either the film or the sensor. Thus, the design of the camera body probably has more to do with determining the CoC factor than anything else. This is why the DoF calculator at www.dofmaster.com/dofjs.html ask for camera make and model. Different cameras have a different CoC.

What is Depth of Field? The portion of a photo from near point to far point that is in acceptable sharpness. htp://cameradojo.com/2011/07/08/how-to-calculate-depth-of-field/ has the mathematical formula to find Hyperfocal length . Hyperfocal length = (focal length x focal length / aperture x circle of confusion) x .00328. I added the multiplier of .00328 to convert the mm of the focal length to feet. As this formula shows, the CoC is a factor in determining the Hyperfocal length. Also given are the formulas to find the near and far points of the DoF. These rely on the Hyperfocal length, thus rely on the CoC factor. I would assume that all, or at least most, on this forum would agree that the DoF calulator at www.dofmaster.com/dofjs.html is a reliable source of information. If you punch in the numbers into the above formula and the same numbers into the above mentioned DoF calculator, you will have the same, or very close to the same, results.

Nikonian72, you ask for mathematical proof that CoC affects the DoF. Here it is!!! It is NOT absolute hogwash, but rather absolute mathematical proof. But what do I know? I'm just an old country boy from Missouri who built bridges for 40 years.

Now to re-answer Stephe's question in the initial post of this string. The DoF will change. Not because of the sensor size, but
due to the design of the camera.


:lol:

dpullum Loc: Tampa Florida

Doing a brain experiment, I think if a shot with a full size sensor was maxed with an 8x10 and then an crop-sensor was used without changing the lens, just swapping the sensor, then using the 1.5 factor in reverse the acceptable enlargement with just acceptably fuzzy spots would be 5.3x6.6. AS with taking scissors and cutting out an acceptable portion of the 8x10. :?: :P

Nothing magic, not sophisticated, simple logic, am I wrong? If so please blame it on my age, otherwise skip the age bit and just call me brilliant... :thumbup: :lol:

These types of challenges are of perhaps low level practicality, but are excellent learning tools and brain exercises to increase the glial cells splashing around in our skulls.

"The human brain is able to continually adapt and rewire itself. Even in old age."
http://www.fi.edu/learn/brain/exercise.html#mentalexercise

Bridgeman Loc: Missouri

Nikonian72; You asked for mathematical proof that CoC affects DoF. I have recently posted asked for proof. Please read and comment on my post. In one of your post you stated that DoF is determined by the relationship of apeture to lens length. I assume you mean focal length. I agree. But it is also determined by the focus length (distance to subject) AND the CoC of the paticular camera. I responded because you called my initial post hogwash, knowing that because of the CoC factor, the same lens with the same setting on different camera bodies will create a different DoF. You posted that any given lens used on any camera will result in exactly the same DoF.

I do want to thank you. Because of my research, I now have a greater knowledge of depth of field, and how to use it.

Respectfully, Bridgeman

pounder35 Loc: "Southeast of Disorder"

Thanks to everyone for enlarging MY circle of confusion. Just kidding. Great topic. I agree with the example of cutting out the image from a photo. DOF stays the same."I thought I was mistaken one time but turns out I was wrong."

pounder35 Loc: "Southeast of Disorder"

I may be off base with this example but what the hell. Since on a 35mm camera a 50mm lens is considered normal and an 80mm would be a very slight telephoto. On the 35mm camera the 80mm lens will have less DOF at a certain focus point, aperture, and distance from subject. Now put the 80mm on 2 1/4 format camera. Considered normal for that format. Same framing, distance from subject, distance to focus point, and aperture. DOF + - or the same?