DOF Problem

[digismash]

I have this problem alot and Im not sure if its the lens or camera so hopefully someone can help.

This was shot with a canon 5d and 24-70L lens
f10
70mm
1/100

The problem is too tight a dof, do I need a longer lens?? it happens alot with protraits too when one subject is behind the other at f16 or even f22 the back subject is slightly blurry

any help would be appreciated.

[angryhampster]

Shoot the same thing on your 20D and see what happens. I'm not sure how to explain it, but full-frame creates exceptional depth of field.

[20D_Newbie]

You may want to play around with the DOF calculator at this link.

http://www.dofmaster.com/dofjs.html

[Woolburr]

You will probably get a better answer if you explain what you are looking for. Too tight DOF? Are you looking to have more depth of field or less? If you are looking for more depth of field...a longer focal length lens will help, if you are looking for less, open your aperture up to f/2.8.

[digismash]

Yes I was looking for more depth of field, thanks for the quick replies

[Wilt]

DOF is reduced with closer shooting distances. But doubling your shooting distance and then using 2x the FL, so that you are framed as tightly even though shooting from a longer distance, is NOT the answer! For example with 20D, 50mm f/1.8 at shooting distance of 5' has the same DOF as 100mm f/1.8 lens shooting at a distance of 10'

[Mr. Clean]

Yes I was looking for more depth of field, thanks for the quick replies
Back up from the subject, grab your 24-70, dial in your sharpest aperture and crop it! You got that amazing 5D, it should be able to pull off a 50-100% crop and get you a great pic.

[Rhinotherunt]

You could also do some image stacking. There is some software that helps you do it, but I do it manually in PhotoShop.

Basically take an image where the top of the image is in focus and then next image move the focus down the ring.

Bring the images into PS and line them up and mask in the in focus sections.

[Wilt]

Back up from the subject, grab your 24-70, dial in your sharpest aperture and crop it! You got that amazing 5D, it should be able to pull off a 50-100% crop and get you a great pic.

That will not improve anything for DOF, simply because it is the FINAL SIZE which establishes the DOF for an image. So by doubling the magnification on a crop of the image, you are doubling the COC which is seen in the final print, so DOF is not changed!

[Krapo]

But doubling your shooting distance and then using 2x the FL, so that you are framed as tightly even though shooting from a longer distance, is NOT the answer! For example with 20D, 50mm f/1.8 at shooting distance of 5' has the same DOF as 100mm f/1.8 lens shooting at a distance of 10'

Unfortunately, the focal length and the distance to the subject are not linear in the calculation of the depth of field. It's a pity because it would be much more easy!

[superdiver]

Just open up your aperature (increase the f stop) and get the extra DOF that way...this is a set up so you can add as much light as you need, right...or am I missing sometihng?

[Wilt]

Just open up your aperature (increase the f stop) and get the extra DOF that way...this is a set up so you can add as much light as you need, right...or am I missing sometihng?

He wants more to be in focus, not less. A larger aperture (for the newbies...bigger diameter opening in the lens diaphram --not a bigger number aperture!) gives shallower DOF (less in focus), which is the wrong direction of correction. The only solution here is use of a smaller aperture, to increase DOF.

[sammysmithazt]

stacking two images together is a good way to go. very useful for macro shooting.

[lostdoggy]

Looking at the image it looks more like blown highlights then a DOF issue.

Did you use AF or MF for this shot?

[lostdoggy]

For a shot like that I think you would be better served w/ a true macro lens.

What type of lighting were you using???

[treeshugger]

That will not improve anything for DOF, simply because it is the FINAL SIZE which establishes the DOF for an image. So by doubling the magnification on a crop of the image, you are doubling the COC which is seen in the final print, so DOF is not changed!

wowzers!
I never understood what "acceptable depth of field" meant
now i guess it means sharp down the pixel at current resolution displayed
btw, are you sure about the above? why is dof measured in distance than instead of distance/pixel?

[Wilt]

wowzers!
I never understood what "acceptable depth of field" meant
now i guess it means sharp down the pixel at current resolution displayed
btw, are you sure about the above? why is dof measured in distance than instead of distance/pixel?

I am certain. Get yourself a DOF calculator if you want to prove it to yourself!

Most DOF values in tables assume COC on the film/sensor. COC is often assumed to be 1/100" and a viewing distance of 10", for example, but this is not universal in DOF tables. Most people have no idea that DOF tables are calculated upon an assumed print size and an assumed viewing distance.

If you enlarge the image by a different amount, you must multiply the COC. If you increase the print size, and fail to also increase the viewing distance proportionately, you effectively have reduced the apparent DOF because the COC has been magnfied!

If you use different focal length lenses, but the image size ultimately is identical for some target object, the DOF is identical regardless of focal length.
Two things really affect DOF, the aperture and the area of coverage (the final magnification)

[Mr. Clean]

That will not improve anything for DOF, simply because it is the FINAL SIZE which establishes the DOF for an image. So by doubling the magnification on a crop of the image, you are doubling the COC which is seen in the final print, so DOF is not changed!
What? You're telling me that if he back up from the ring, stops his aperture down further and then crops the image to get the look he wants that he'll have less DOF? By 2X? Increased distance from subject = more DOF (edit, at equal apertures)

[Wilt]

What? You're telling me that if he back up from the ring, stops his aperture down further and then crops the image to get the look he wants that he'll have less DOF? By 2X? Increased distance from subject = more DOF (edit, at equal apertures)

Perceived DOF is affected by the magnification and viewing distance. Magnify the COC by 2x, but don't move your viewing distance, and COC magnifies. If you move back your viewing distance so that the COC has the same angle of view, it is the same DOF as original magnification.

If you have a 20D and put 200mm f/2.8 lens on it, there is 4.26' of DOF at 100'.
Put a 400mm lens on it, and do not change your shoting position, and there is 1.06' DOF at 100'.
But if you move your shooting position to 200' (to offset the 2x lens focal length) we are back to 4.26' of DOF.
This shows that DOF is COC size related.

Now if you magnify an image of something by 2x, this is equivalent increasing the focal length by 2X as well; but if you do not change the viewing distance, this is magnifying the COC by 2x via focal length change without shooting position change, so the DOF area would be like the 1.06' DOF example. But by moving the viewing distance back 2x then view the larger image, this is like changing the shooting position 2x and we are back to 4.26 DOF.

[Mr. Clean]

I'm only speaking of cropping, not magnifying the image. If he were to crop the original picture posted, it would have the same range of acceptable sharpness.

[René Damkot]

That will not improve anything for DOF, simply because it is the FINAL SIZE which establishes the DOF for an image. So by doubling the magnification on a crop of the image, you are doubling the COC which is seen in the final print, so DOF is not changed!

Not 100% sure, but I think it should work. Just like using a 1.6 crop camera with the same lens should work.

From this article: (http://www.bobatkins.com/photography/technical/digitaldof.html)

"• If you use the same lens on a EOS 10D and a 35mm film body and crop the 35mm image to give the same view as the digital image, the depth of field is IDENTICAL"
and
"• If you use the same lens on an EOS 10D and a 35mm film body, then shoot from different distances so that the view is the same, the 10D image will have 1.6x MORE DOF then the film image."

So the way I read it: Because you back up (using the same lens) DoF gets greater, even if you need to enlarge the resulting image more.

Easiest way would be to just go out and try it... Far faster then jugling numbers around. Way too confusing to me.... Stuff like this makes color management easy ;)

[René Damkot]

Okay. Gave it a try:

Q&D shot of my cell phone.
Once a crop from the image taken with a 50mm at f/5.6, second shot is taken with the 100mm at f/5.6, using an extention tube to allow close enough focussing (hence the image is darker).

Camera was on a tripod and didn't move. Camera was on manual, aperture f/5.6.

I scaled the 100mm shot to fit over the 50mm shot in PS.
The black line is the outline of the 100mm shot. The 50mm originally was a lot wider of course.
50mm, cropped:
http://www.moonglade.net/rene/POTN/50mm5_6.jpg

100mm overlayed on the 50mm image:
http://www.moonglade.net/rene/POTN/100mm5_6.jpg

The 100mm clearly has less DoF. The 50mm clearly has more noise due to extreme enlargement.

[superdiver]

He wants more to be in focus, not less. A larger aperture (for the newbies...bigger diameter opening in the lens diaphram --not a bigger number aperture!) gives shallower DOF (less in focus), which is the wrong direction of correction. The only solution here is use of a smaller aperture, to increase DOF.

Thats why I put in parenthasis (increase the f-stop)...LOL

I thought that would be less confusing..but apperently not...LOL

[LordV]

From a macrophotographers point of view , there are only 3 ways to increase the DOF .
1. As already suggested take the shot from further out and crop it. drawback loss of resolution
2. Reduce the aperture size (ie higher fnumber). Drawback- softening of image due to diffraction softening.

3. Focus stack from several images taken from the same point of view but at different focus depths. Drawback- takes more than one shot to do it.
If you are interested in this approach, I did a tutorial here
http://photography-on-the.net/forum/showpost.php?p=1113413&postcount=36

Brian V.

[Mr. Clean]

From a macrophotographers point of view , there are only 3 ways to increase the DOF .
1. As already suggested take the shot from further out and crop it. drawback loss of resolution
...

Thank you! I think that's one of his easiest solutions considering he has huge resolution on his 5D. 100% crops on 5D's are still very very impressive.

[Wilt]

Thats why I put in parenthasis (increase the f-stop)...LOL

I thought that would be less confusing..but apperently not...LOL

Methinks the confusion is in the use of the jargon!.

'Aperture' is the opening in the diagram...Larger aperture= larger opening = smaller f/number = shallower DOF or less DOF

You seem to be referring to larger aperture = larger DOF, in saying "open up your aperature (increase the f stop) and get the extra DOF that way"; but a larger aperture results in LESS DOF not larger DOF, .

[superdiver]

If I go from f2.8 to f8 (an increase in the f-stop) the DOF increases...is what I was getting at ever so poorly....LOL

[Wilt]

Okay. Gave it a try:

Q&D shot of my cell phone.
Once a crop from the image taken with a 50mm at f/5.6, second shot is taken with the 100mm at f/5.6, using an extention tube to allow close enough focussing (hence the image is darker).

Camera was on a tripod and didn't move. Camera was on manual, aperture f/5.6.

I scaled the 100mm shot to fit over the 50mm shot in PS.
The black line is the outline of the 100mm shot. The 50mm originally was a lot wider off course.
50mm, cropped:


100mm overlayed on the 50mm image:


The 100mm clearly has less DoF. The 50mm clearly has more noise due to extreme enlargement.

If you had moved the shooting point 2x when mounting the 100mm lens, the DOF would have been the same.

[René Damkot]

If you had moved the shooting point 2x when mounting the 100mm lens, the DOF would have been the same.

Sure, but that wasn't the point as I read it: The post you replied to was talking about backing up and then cropping. That's what I did here...

Might be a bit of a misunderstanding going on throughout this thread ;)

[Wilt]

Sure, but that wasn't the point as I read it: The post you replied to was talking about backing up and then cropping. That's what I did here...

Might be a bit of a misunderstanding going on throughout this thread ;)



Yes, I think misunderstanding.

My interpretation of the suggestion was that

A: if you back up and use the same lens, you increase DOF. But, then you would need to crop and magnify to the same subject final size. By multiplying higher to same subject size, you increase the CoC size in direct proportion, too. So DOF ultimately would not change.

B: I then commented that if you doubled the shooting distance at the same time as doubling the focal length, you end of with the same DOF, so nothing accomplished by this technique, either. This can be proven with DOF calculation programs on line.

What you did...

C: Same shooting distance, put on 100mm lens (which achieves less DOF than 50mm lens, of course). Then you sized the output of the two to be identical in overlaying them. Neither situation A nor situation B. And you accomplished a reduction in DOF, what we expected.

It would seem that the DOF lost by increasing focal length is not directly proportional to the DOF change by magnification. I needed to scratch my head a bit over that one, and it has been puzzling me since earlier, to explain. The outcome of scratching my head is the recognition that doubling shooting distance does not double DOF...DOF change is far greater (doh, I knew that!) :o . So situation A shooting distance change actually has more increase in DOF than the DOF which is lost via higher magnification to final print size...a small difference, but one which could make a difference! The original conclusion I had jumped to, without giving thought, was wrong. :oops:

Similarly, your 2x focal length change does not result in 2x DOF change, the change in DOF is actually shallower by 4.13x (at shooting distance of 5' f/5.6).

[treeshugger]

you're quite right btw
personal experimentation confirms

[LordV]

Just one additional thought. Using a P&S camera in macro mode (ie small sensor small focal length lens) whilst not actually giving you significantly more real DOF at the same magnification does seem to give more apparent DOF- the OOF areas are not as OOF as they would be a more normal lens and can give the impression of much greater DOF.
Brian V.

[20droger]

Much confusion in this thread.

I suggest anyone interested in learning the facts about depth of field go here:

http://www.dofmaster.com/articles.html