DOF and Sensor Size

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Archive 2005 · DOF and Sensor Size

jdaily
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p.9 #1 · DOF and Sensor Size

Turns out I have 5 of his books.

In "Nature Photography Field Guide" (not to be confused with "Nature Photographer's Complete Guide to Professional Field Techniques") he provides details on his "size of the subject" remark:

With any given lens at any given f-stop, depth of field decreases as you decrease lens-to-subject distance. As you move closer to a subject, you see less of it through the lens...

He never clarifies the difference between point 3 (size of the subject) and point 4 (distance between the camera and the subject); to me it seems like #3 is just a mix of #2 (focal length) and #4 (distance). Anyway, his depth of field text in each book is slightly different, and seems to show a lack of precision on his part.

Aug 16, 2005 at 05:10 AM

rcmanoj
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p.9 #2 · DOF and Sensor Size

jdaily wrote:
Turns out I have 5 of his books.

Anyway, his depth of field text in each book is slightly different, and seems to show a lack of precision on his part.

But he takes wonderful photos

Aug 16, 2005 at 05:15 AM

nsbca
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p.9 #3 · DOF and Sensor Size

jdaily wrote:
Anyway, his depth of field text in each book is slightly different, and seems to show a lack of precision on his part.

Or an evolving perspective.

Aug 16, 2005 at 05:19 AM

Pixel Perfect
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p.9 #4 · DOF and Sensor Size

Round and round the merry-go-round, the merry-go-round, the merry-go-round, round and round the merry-go-round, all day long.

I have just graduated from advanced pendantism 101 with honours.

This thread had some very useful information .... Presented from a squillion POVs and still there was a giant CoC for some people.

Aug 16, 2005 at 05:45 AM

nsbca
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p.9 #5 · DOF and Sensor Size

What all this comes down to is the way I calculate DOF is acurate and simple. I do it in my head as second nature. Swapping a lens between bodies does not require a calculator and a formula book.

My thought process: Bigger sensor=bigger print. DOF is unchanged if nothing besides the FoV, the sensor size and the print size has changed. I can make ajustments for those in my head.

Simple.

Someone try and give me a formula if you can for acuratly calculating DOF between a 1.6 and a FF body with while keeping the same FoV and retaining the 8x10 model. (without using a palm pilot or a computer)

Let me guess. It involves determining what MM focal length to use, what the new distance from camera to subject should be, multiplying all of that against some (unknown to me) number and then figuring out how all of that will affect actual DOF.

Not something I want to do in the field.

Aug 16, 2005 at 05:48 AM

slin100
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p.9 #6 · DOF and Sensor Size

nsbca wrote:
Someone try and give me a formula if you can for acuratly calculating DOF between a 1.6 and a FF body with while keeping the same FoV and retaining the 8x10 model. (without using a palm pilot or a computer)

Let me guess. It involves determining what MM focal length to use, what the new distance from camera to subject should be, multiplying all of that against some (unknown to me) number and then figuring out how all of that will affect actual DOF.

It's quite simple, actually. To retain the same FoV at the same subject distance, use a focal length 1.6x shorter. To, additionally, retain the same DOF, open up 1 1/3 stops.

No complicated formulas. I'd wager it's no more complicated than the sunny 16 rule of thumb.

Aug 16, 2005 at 06:18 AM

slin100
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p.9 #7 · DOF and Sensor Size

jdaily wrote:
I have 3 of his books, and only in "Landscape Photography" does he make that statement. I think he was trying to say image size, because image size pops up again (rather obscurely) about 5 paragraphs later. Or...

In "Closeups in Nature", he [John Shaw] says this:

If the image size and the aperture remain the same, all focal-length lenses give the same depth of field...If you photograph a subject at life-size with a 50mm lens and then move back and photograph it again at life-size with a 200mm lens at the same f-stop, the depth of field will be the same.

Perhaps that's where he was headed with "size of the subject" in "Landscape Photography".

Read this article for an explanation of John Shaw's point. It's a handy rule of thumb.

Aug 16, 2005 at 06:24 AM

nsbca
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p.9 #8 · DOF and Sensor Size

slin100 wrote:

It's quite simple, actually. To retain the same FoV at the same subject distance, use a focal length 1.6x shorter. To, additionally, retain the same DOF, open up 1 1/3 stops.

No complicated formulas. I'd wager it's no more complicated than the sunny 16 rule of thumb.

Show me how it works.

I have a EOS-20D with a 1.6 crop sensor.

I.m shooting with a 85mm lens set at f/8

I am 100 ft from my subject.

I switch over to my 1Ds body.

What focal length and f/stop setting do I need to retain both Fov and DOF while still keeping the distance to subject a constant?

135mm at f/5?

So what if I want to keep the 85mm on the camera and still retain the same DOF and FoV? I guess I have to move. But where?

f/5 at 160ft?

Now I want to swap the lens from my 20D to my 1D Mark II. Uhhoh! I think we get back to carrying that formula book around with us again.

All of this is a lot of calculation that should not be necessary to an intuitive photographer

Aug 16, 2005 at 06:42 AM

steve_t
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p.9 #9 · DOF and Sensor Size

nsbca wrote:
What all this comes down to is the way I calculate DOF is acurate and simple. I do it in my head as second nature. Swapping a lens between bodies does not require a calculator and a formula book.

My thought process: Bigger sensor=bigger print. DOF is unchanged if nothing besides the FoV, the sensor size and the print size has changed. I can make ajustments for those in my head.

Simple.
...

Actually it only works if your sensor's pixel pitch is the same. Consider a 1Dmk2 vs a 20D for example. They have the same number of pixels but at a different pitch. You wouldn't really want to print the 1Dmk2 image bigger (the pixels become more obvious).

The other, obvious problem is if I normally print from a 20D at 10x15 I'll need to print everything from a 1Ds2 at 16x24 to get the same DOF (time for a new printer)

Aug 16, 2005 at 08:07 AM

nsbca
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p.9 #10 · DOF and Sensor Size

steve_t wrote:

The other, obvious problem is if I normally print from a 20D at 10x15 I'll need to print everything from a 1Ds2 at 16x24 to get the same DOF (time for a new printer)

I can print 62.33x24 if I like on my printer and frame it any size I like without a problem. So ones POV and way of calculating comes down to some extent to what equipment one has. Like I said, I rarely ever consider print size until the image is up in PS.

Aug 16, 2005 at 02:35 PM

Imagemaster
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p.9 #11 · DOF and Sensor Size

Jeff Donald wrote:

I think you're talking minimum focus distance not DOF.

No, I am not.

My 50 mm at f/16 can't focus on something 4 inches in front of it and have an object 100 feet away in focus.

Neither can your eye. Your eye(s) can focus at a minimum distance and a maximum distance, but can't focus on both at the same time.

Prior to Lippershey and Galileo DOF was not known. It requires optical lenses to perform the phenomenon.

And just what kind of lens do you think we have in our eyes if it is not an optical lens?

http://hyperphysics.phy-astr.gsu.edu/hbase/class/phscilab/imagei.html

Aug 16, 2005 at 04:16 PM

slin100
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p.9 #12 · DOF and Sensor Size

nsbca wrote:
slin100 wrote:

It's quite simple, actually. To retain the same FoV at the same subject distance, use a focal length 1.6x shorter. To, additionally, retain the same DOF, open up 1 1/3 stops.

No complicated formulas. I'd wager it's no more complicated than the sunny 16 rule of thumb.

Show me how it works.

I have a EOS-20D with a 1.6 crop sensor.

I.m shooting with a 85mm lens set at f/8

I am 100 ft from my subject.

I switch over to my 1Ds body.

What focal length and f/stop setting do I need to retain both Fov and DOF while still keeping the distance to subject a constant?

135mm at f/5?

1.6x->FF: Use a focal length 1.6x longer. Open up 1 1/3 stops. So, 135mm at f/13.

So what if I want to keep the 85mm on the camera and still retain the same DOF and FoV? I guess I have to move. But where?

f/5 at 160ft?

This is not unlike switching from a 135mm to a 85mm lens on a FF. You would have to move closer, to 100/1.6 or 62.5 ft to retain the FOV of the subject. Of course, perspective will change. Furthermore, you're now working a lot closer to the hyperfocal distance, so it going to be a little harder to retain the same DOF. In this case, you would use approximately f/9.5.

Now I want to swap the lens from my 20D to my 1D Mark II. Uhhoh! I think we get back to carrying that formula book around with us again.

All of this is a lot of calculation that should not be necessary to an intuitive photographer

As I have shown, it's not that bad with two formats. I'll note, however, that 1.6/1.3 is 1.23, so it's not unlike dealing with a 1D2 and a 1Ds. Frankly, I think the number of people who own all three formats is not that common. If DOF is that important, doing these calculations is necessary. Heck, some people still carry DOF charts with them. Nothing is stopping you from carrying an extra set. At some point it will become second nature.

As you remarked a couple of times, you cope by outputing smaller prints for smaller formats. That works for you, but I'll wager that the majority of people don't work this way. They print at a few popular sizes (4x6 and 8x10) regardless of the format of their camera.

Aug 16, 2005 at 04:25 PM

nsbca
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p.9 #13 · DOF and Sensor Size

slin100 wrote:

It's quite simple, actually. To retain the same FoV at the same subject distance, use a focal length 1.6x shorter. To, additionally, retain the same DOF, open up 1 1/3 stops.

No complicated formulas. I'd wager it's no more complicated than the sunny 16 rule of thumb.

nsbca wrote:
What focal length and f/stop setting do I need to retain both Fov and DOF while still keeping the distance to subject a constant?

135mm at f/5?

slin100 wrote:
1.6x->FF: Use a focal length 1.6x longer. Open up 1 1/3 stops. So, 135mm at f/13.

Looks like you're getting confused and you're sitting behind the computer. f/5 would be opening up 1 1/3 stops from f/8. Imagine trying to do all of that in the field.

The way I visualize mine is so much easier and fluid, albiet it will not work well for someone who only prints one size or thinks in terms of a standard or rigid output.

Aug 16, 2005 at 05:26 PM

slin100
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p.9 #14 · DOF and Sensor Size

nsbca wrote:
slin100 wrote:
1.6x->FF: Use a focal length 1.6x longer. Open up 1 1/3 stops. So, 135mm at f/13.

Looks like you're getting confused and you're sitting behind the computer. f/5 would be opening up 1 1/3 stops from f/8. Imagine trying to do all of that in the field.

Don't make it seem more complicated than it really is. It was a simple mistake. I meant to say close down 1 1/3 stops. I really did mean f/13.

The way I visualize mine is so much easier and fluid, albiet it will not work well for someone who only prints one size or thinks in terms of a standard or rigid output.

Acknowledged.

Aug 16, 2005 at 08:39 PM

Jeff Donald
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p.9 #15 · DOF and Sensor Size

Jeff Donald wrote:
However my eyes can focus on an object about 12 inches from my face and 100 feet at the same time.

jdaily wrote:
I don't disagree with anything you've said about DoF to this point, but can you clarify this statement?

Perhaps it's just my eyeglasses that are distorting the world in ways that my eyes wouldn't if they weren't astigmatic, but if I close one eye and focus on my finger at arm's length, then switch focus to an object about 3 times as far away (box of Ilford Galerie paper), I can see the text come into focus. Conversely, if I focus on the text, then on my finger (again with one eye closed) my finger appears to become sharper and there's no way I can read the text.

Thus, it would appear that just one eye is unable to focus both on the text and my finger.

I also wear corrective lenses. But with with my lenses I have about 20/10 vision (6/3 vision for the rest of the world) though I'm not sure if this is a contributing factor, but I suspect it is. When I hold a piece paper with writing about 3/4 of an inch high, at a distance of 12 inches, I can also read the word stop on a Stop sign at the end of the street (probably 75 to 100 feet). I don't try to focus on one object or the other, I "relax" my vision and both sets of text are legible.

Aug 16, 2005 at 08:54 PM

nsbca
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p.9 #16 · DOF and Sensor Size

Jeff Donald wrote:
Jeff Donald wrote:
However my eyes can focus on an object about 12 inches from my face and 100 feet at the same time.

jdaily wrote:
I don't disagree with anything you've said about DoF to this point, but can you clarify this statement?

Perhaps it's just my eyeglasses that are distorting the world in ways that my eyes wouldn't if they weren't astigmatic, but if I close one eye and focus on my finger at arm's length, then switch focus to an object about 3 times as far away (box of Ilford Galerie paper), I can see the text come into focus. Conversely, if I focus on the text, then on my finger (again with one eye closed) my finger appears to become sharper and there's no way I can read the text.

Thus, it would appear that just one eye is unable to focus both on the text and my finger.

I also wear corrective lenses. But with with my lenses I have about 20/10 vision (6/3 vision for the rest of the world) though I'm not sure if this is a contributing factor, but I suspect it is. When I hold a piece paper with writing about 3/4 of an inch high, at a distance of 12 inches, I can also read the word stop on a Stop sign at the end of the street (probably 75 to 100 feet). I don't try to focus on one object or the other, I "relax" my vision and both sets of text are legible.

For that kind of DOF you must have a very small opening in your pupil or a very short lens. I will take a stand right now and say that retina size has nothing to do with DOF.

Aug 16, 2005 at 11:43 PM

Jeff Donald
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p.9 #17 · DOF and Sensor Size

For that kind of DOF you must have a very small opening in your pupil or a very short lens. I will take a stand right now and say that retina size has nothing to do with DOF.

Bright sunlight (sorry, I live in Florida, with plenty of bright light) will do that outside.

In response to Imagemaster, the closest I can focus with my corrective lenses (single vision) is about 8 inches. If I remove the lenses then I can focus from about 2 inches to 6 inches. While I am probably not the norm for this demonstration, it is a good example how individual viewing characteristics affect things like DOF and CoC.

Aug 16, 2005 at 11:53 PM

AJSJones
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p.9 #18 · DOF and Sensor Size

One last last thought - I'd mentioned this earlier but here's the link. Try this spreadhseet from Jon Wienke and Doug Kerr and see if it matches with your experience of 100% pixelpeeping views. It uses a much more stringent CoC value than the "original" conditions (full 35mm frame to 8x10 viewed at ~12 inches) It uses the pixel pitch as the CoC, so the DoFs are much narrower than "traditional" ones. It may be too stringent but it would seem to incorporate the concept that digital has brought with it : I've got more MP so I'll print bigger...

Aug 17, 2005 at 12:20 AM

Jeff Donald
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p.9 #19 · DOF and Sensor Size

It may be too stringent but it would seem to incorporate the concept that digital has brought with it : I've got more MP so I'll print bigger...

The concept of more pixels = bigger prints is certainly a viewpoint that up until now I'm a bit unfamiliar with. When I taught large format photography it was not required that students produce 30 X40 inch prints. The norm was 11x14 and occasionally 16x20. The print size is only relevant when combined with the proper viewing distance. That is why 30x40 was not used. It would be hard for me to transport and hard for me to view from the correct distance in my office.

I would say that roughly 10 to 15% of my student have 1Ds' or 1DsMkII' and have at best a 13x19 printer. I can think of a good dozen students (with aforementioned cameras) that can print no larger than 8 1/2 x 11. When I give assignments that are to be printed, the maximum size is 8x10. If the file is a digital file then the requirements are 8x10 @ 300 dpi. I give assignments that require the student to demonstrate a proficiency in DOF and therefore have a set requirement as to the file size or print size so that I can ascertain their knowledge in the matter.

Aug 17, 2005 at 12:40 AM

AJSJones
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p.9 #20 · DOF and Sensor Size

Jeff, I hear ya! I don't follow the "viewing distance" guidelines because I really like to get close to my 24x30's - that's why I use a 4x5 for them and 1.6 factor digital for birds. But I did research DoF pretty thoroughly, even to the point of knowing that I should use a stronger loupe than a 6x to check focus on the GG if I wanted to print bigger than 24x30. However, as we are seeing, these issues are becoming esoterica to many folks - pre-digital. you had to be pretty serious to recompose after the shot - with your own darkroom or a pro service to crop as desired, let alone getting "enlargements". (Guess I'm dating myself using that word

) Now it's such a piece of cake the push pixels around and print whatever crop at whatever size, that the "basics" are getting lost in the flood of new users who can do so much so easily without the benefits of the kind of teaching you guys provide. Such is progress........

Aug 17, 2005 at 01:15 AM

jonwienke
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p.9 #21 · DOF and Sensor Size

I've found the predictions of my spreadsheet to be quite accurate for viewing at 100% in Photoshop. If you print everything 4x6, it's a bit conservative, but not as much as you might think. At any rate, try playing around with the sensor specs for the 20D and 1D-MkII (same pixel count, different sensor size) and equivalent focal lengths to get the same FOV, and you'll find that the 20D will give you wider DOF than the 1D-MkII for the same distance, FOV and f/number. And that's about as apples-to-apples as you can get.

Aug 17, 2005 at 02:17 AM

Monito
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p.9 #22 · DOF and Sensor Size

nsbca wrote: For that kind of DOF you must have a very small opening in your pupil or a very short lens. I will take a stand right now and say that retina size has nothing to do with DOF.

Exactly. Short focal length is the key here. The retina size is appropriate for the focal length. There would be no point in having an eye with a retina the size of a dinner plate and a lens one inch away from it.

The sensor size issue remains an issue for DoF for cameras because it is one of the five factors in the "equation", directly relating to the amount of magnification that has to occur to produce the print or monitor image.

Aug 17, 2005 at 04:28 AM

Imagemaster
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p.9 #23 · DOF and Sensor Size

Monito wrote:

The sensor size issue remains an issue for DoF for cameras because it is one of the five factors in the "equation", directly relating to the amount of magnification that has to occur to produce the print or monitor image.

It may be an issue, but it is such a small issue in comparison to the other factors that it does not even require any consideration. To think that it is a necessity to worry about sensor size for DOF, whether planning on making an 8x10 print or a 30x40 print, is a joke.

Aug 17, 2005 at 03:35 PM

Monito
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p.9 #24 · DOF and Sensor Size

Imagemaster wrote: It may be an issue, but it is such a small issue in comparison to the other factors that it does not even require any consideration. To think that it is a necessity to worry about sensor size for DOF, whether planning on making an 8x10 print or a 30x40 print, is a joke.

The sensor size is not a joke. If a 22.5mm x 15mm 8 MegaPixel image is enlarged to 8x10 and compared to a 36mm x 24mm 8 MegaPixel image enlarged to 8x10, it makes a huge difference to how much the circle of confusion is enlarged. Joke's on you.

We'll keep on saying it because it is true: perceived depth of field depends on linked factors: 1) Chosen acceptable circle of confusion size in the print, which is related to 2) print viewing distance, 3) print size, 4) degree of enlargement of image to print size, 5) focal length of the lens, and 6) distance to subject focus plane. The sensor size directly interacts with the focal length of the lens, the distance to the subject and the desired angle of view.

Note that circle of confusion at the sensor is not the same as circle of confusion at the print. Most DoF calculators pick a CoC at the sensor based on assumptions about final print size and viewing distance and acceptable print CoC that are often hidden and not stated. Properly done, DoF calculations start at the print and work backwards or include all the linked factors in an interactive application where some are declared fixed and others are declared variable.

Some of the factors are interconnected because you can hold one constant and calculate a couple other in terms of each other or in other combinations of constant and variable. This is why some people will say sensor size doesn't matter because they can make it a dependent variable by holding other factors constant or alternatively they can adjust focal length and distance to compensate for sensor size.

Because of the inherent variability of so many factors, if DoF is critical to a shot, I bracket for DoF by using several apertures.

Do the math (geometry). Math rules the universe.

Aug 17, 2005 at 03:50 PM

Imagemaster
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p.9 #25 · DOF and Sensor Size

Monito wrote:

The sensor size is not a joke. If a 22.5mm x 15mm 8 MegaPixel image is enlarged to 8x10 and compared to a 36mm x 24mm 8 MegaPixel image enlarged to 8x10, it makes a huge difference to how much the circle of confusion is enlarged. Joke's on you.

Actually, the joke is on you. If it makes such a HUGE difference, then why are you using a 20D

We'll keep on saying it because it is true: perceived depth of field depends on linked factors: 1) Chosen acceptable circle of confusion size in the print, which is related to 2) print viewing distance, 3) print size, 4) degree of enlargement of image to print size, 5) focal length of the lens, and 6) distance to subject focus plane. The sensor size directly interacts with the focal length of the lens, the distance to the subject and the desired angle of view.

And why do you keep saying it? Are you trying to convince yourself? You don't seem to comprehend that good photography is not dependent on mathematics only. In most cases, the photographer has no control over the print-viewing distance, the eyesight of the viewer, nor the tastes of the viewer. Next you will be trying to tell me that there is a mathematical formula for determining the "best" DOF.

Try running a little photo contest right here for the photo with the best DOF. Do you really think that the judges in such a contest would all agree on what the "best" DOF would be

Because of the inherent variability of so many factors, if DoF is critical to a shot, I bracket for DoF by using several apertures.

Exactly my point, you don't need three different cameras each with a different sensor size.

Do the math (geometry). Math rules the universe.

Don't need to do the math, photography is more about aesthetics. Study people's reaction to DOF in photographs. Some people will say, "Gee, I like the way everything is in focus", while others will say, "Gee, I like the way the foreground is out of focus".

That is called "different strokes for different folks", and has nothing to do with mathematics.

"You can please some of the people all of the time and all of the people some of the time, but you can't please all of the people all of the time." I think that is a quotation referring to depth-of-field, made by some famous math professor.

Aug 17, 2005 at 04:50 PM


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