Depth of Field

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09-04-2012, 04:17 PM
iND

Depth of Field

I primarily use a single point for auto focus and pay close attention to my depth of field.
I have an iphone app that has replaced my old charts and is extremely useful.
I do wedding photography and make sure my sharpest focus is usually on my bride.
I then use my depth of field (near distance and far distance) to either assign the group or to change one of the
factors that affects my depth of field.(aperture or distance)

Still I have some occasional blurring at the edges of larger groups that is not accounted for in my calculations.

My question is:

Does the depth of field change toward the periphery of especially wider angle lenses?

Thanks
09-04-2012, 06:02 PM
HDNitehawk

I think the answer to your question is probably yes, but how much you would notice and is this what you are seeing is another question. I have had the same question and thought the same thing with really long lenses with narrow DOF.

Another thought;

iND I think if you look at the ISO charts you might figure the answer out on this one. You will notice in the corners that the lens falls off and will be sharp in the center. It seems that newer lenses that Canon has released the corners have improved and the center of the lens has not in comparison. Perhaps this is what you are seeing in your pictures?
09-04-2012, 07:46 PM
Busted Knuckles

The 24-70 version I is particularly well known for having a curved depth of focus at the wide end. If this is the culprit lens, take a photo of something like a break in retaining wall ( 3-4 step stairway) where you can see both the horizontal focus plane - the top of a retaining wall, and the vertical - steps or vertical element of the retaining wall at f2.8 and notice the parts that are in focus as you move away from center of frame.

Once you see the curve, you will suggest that the group shots be done in an arc i.e. closer to the same distance from the film plane - sounds minor but in a large group shot the bride is 10 feet and the outsiders are 15-20, that is a lot of DOF for F4. :)
09-05-2012, 07:40 AM
ham

Was just going to suggest what Busted Knuckles did.
09-05-2012, 02:22 PM
Stephen Probert

Hey, I had an idea to make "flash cards" of focal length, aperture, subject distance and DOF (giving 3 and requiring the fourth) to kind of memorize a spectrum of depth of field values that are relevant to my portrait and wedding work. Has anyone tried this or known someone who has?

Quote:

Originally Posted by Stephen Probert

Hey, I had an idea to make "flash cards" of focal length, aperture, subject distance and DOF (giving 3 and requiring the fourth) to kind of memorize a spectrum of depth of field values that are relevant to my portrait and wedding work. Has anyone tried this or known someone who has?

I don't do weddings or portraits but I did something similar that for a while I carried with me in my backpack. On one of the DOF chart websites it was very convenient to use to copy and paste on to a spread sheet. I did a little modification to get it to read the way I wanted. You could also say I had to much free time on my hands one day at work.

This is the Canon 5D II at 24mm. The site wouldn’t let me post the full chart this is just a segment of it.

f/1.4 f/1.4 f/2 f/2 f/2.8 f/2.8 f/4 f/4 f/5.6 f/5.6 f/8 f/8 f/11 f/11 f/16 f/16

Distance

(feet) Total DOF In Front Total DOF In Front Total DOF In Front Total DOF In Front Total DOF In Front Total DOF In Front Total DOF In Front Total DOF In Front

1 0.04 50% 0.06 50% 0.08 50% 0.12 50% 0.17 47% 0.23 43% 0.34 41% 0.5 38%

2 0.17 47% 0.24 46% 0.35 46% 0.5 44% 0.71 41% 1.04 38% 1.56 33% 2.57 26%

3 0.39 46% 0.56 45% 0.8 44% 1.15 41% 1.69 37% 2.58 31% 4.34 24% 9.88 13%

4 0.71 45% 1.01 44% 1.45 41% 2.13 38% 3.21 32% 5.3 25% 11.15 15% 998 0%

5 1.12 45% 1.61 42% 2.32 39% 3.46 34% 5.49 28% 10.22 19% 40.45 6%

6 1.62 43% 2.34 41% 3.43 37% 5.26 31% 8.88 23% 20.78 12%

7 2.23 42% 3.23 39% 4.86 34% 7.64 28% 14.18 19% 54.27 6%

09-05-2012, 05:54 PM
iND

The culprit IS the 24-70 version I.
This is my primary wedding lens, but have switched to the 17-40 for groups for this purpose.
There are just times that (since I have these on separate bodies) that I have to take a wide indoor shot with the 24-70
I wonder if this would be different with the 24-70 II.
Don't have any trouble with my 24mm 1.4.

I used to carry the charts but when I was using a 5D with a 50D this got too confusing and I found an app (simpeDOF) that works great.
I also tried to memorize the charts but they did not stick, or I could not recall them in the heat of the battle.

Why can we not have a DOF (not a preview) but a reading on the screen, as it should fit into an algorithm.

Or how about outside depth of field 'blinkies' like the overexposed setting.
Good discussion Thanks.
09-06-2012, 01:17 PM
Agilulfo

I'm not sure to understand why you don't rely in the DOF button of your camera.

Another simple solution, I guess you already have tried it, It's work in AV and shot in two f stops (the right one and another with more DOF). It seems faster than consulting charts.
09-06-2012, 02:20 PM
neuroanatomist

Quote:

Originally Posted by Agilulfo

I'm not sure to understand why you don't rely in the DOF button of your camera.

Depends on the lens and the focusing screen. It you've got a lens that's faster than f/2.8, the standard focus screen doesn't show the true DoF, it shows the DoF of ~f/2.8. That means with an f/1.4 lens, unless you're stopped down beyond f/2.5, your actual DoF is thinner than it appears in the VF, and you can't accurately judge focus.
09-06-2012, 02:51 PM
HDNitehawk

Quote:

Originally Posted by Agilulfo

I'm not sure to understand why you don't rely in the DOF button of your camera.

Another simple solution, I guess you already have tried it, It's work in AV and shot in two f stops (the right one and another with more DOF). It seems faster than consulting charts.

That is one of those neat little gizmo and gadgets a manufacture includes to increase sales, they are great in theory but in realty just doesn't work very well. I find it to be about useless.
09-06-2012, 03:51 PM
iND

Hmmm
The thought of f stop bracketing just crossed my mind for large group shots.
Can't really read precise focus on the preview screen.

Does anyone know if the 20-70 II would be an improvement in this area over the 20-70 I

How is the updated (not red) auto focus points working of everyone indoors?

Thanks
09-06-2012, 06:18 PM
Busted Knuckles

I know I get boring on this.... Magic Lantern, Live view, focus peaking. Works like a charm. Just have to flip between liveview and viewfinder. Also focus peaking is displayed in image review on the new version of Magic Lantern if you would just rather take a pic to check focus. Set your image review to several seconds and you can confirm focus. There are a couple of different settings for focus peaking to display (bright dots around the stuff that is in focus) with colors and % of pixels in focus, etc.

Quote:

Originally Posted by iND

The culprit IS the 24-70 version I.
This is my primary wedding lens, but have switched to the 17-40 for groups for this purpose.
There are just times that (since I have these on separate bodies) that I have to take a wide indoor shot with the 24-70
I wonder if this would be different with the 24-70 II.
Don't have any trouble with my 24mm 1.4.

I used to carry the charts but when I was using a 5D with a 50D this got too confusing and I found an app (simpeDOF) that works great.
I also tried to memorize the charts but they did not stick, or I could not recall them in the heat of the battle.

Why can we not have a DOF (not a preview) but a reading on the screen, as it should fit into an algorithm.

Or how about outside depth of field 'blinkies' like the overexposed setting.
Good discussion Thanks.