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5D depth of field issue

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camerashy

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I have seen a few references in the past over the depth of field of the 5D when compared to the 30D but never understood whether it is better on the 5D or worse..... could someone please enlighten me. If it is 'worse' what precautions do you have to take.
Appreciate any help.
Dave

--
pbase supporter at http://www.pbase.com/dav4184
for equipment see profile
 
Define "better" and "worse"...

Better yet, grab a physics/optics book - a 10th grade science course will do nicely, too...
 
If you like shallow dof -- the 5D is better. Primarily it's because for a given focal length lens you will stand closer to get the same framing on a subject.

Take the 30D and Canon 85mm f1.8. At f1.8 and 16' away, you'd have .72 feet of dof.

The Canon 5D with same lens at f1.8 and 15' would have 1.14 feet of dof. However, you wouldn't stand that far away to get the same shot. You'd stand at 10' and would have .44 feet dof.

Enough to buy the 5D over the 30D for that feature alone? Not really. But in practice, I like the look of my wedding photos on the 5D better than my 20D when it comes to those dreamy narrow dof shots.

Lee
 
LeeBase said:
If you like shallow dof -- the 5D is better. Primarily it's
because for a given focal length lens you will stand closer to get
the same framing on a subject.

Take the 30D and Canon 85mm f1.8. At f1.8 and 16' away, you'd have
.72 feet of dof.

The Canon 5D with same lens at f1.8 and 15' would have 1.14 feet of
dof.
Click to expand...
Wouldn't you have roughly the same DOF in this case? At the same distance and the same lens/aperture the DOF should be the same regardless of sensor size?

I agree that you have to stand closer with the 5D to get the same framing hence the shallower DOF, just not that bit of your explanaition...

http://www.betterphoto.com/?janem
 
but how did you calculate the dof so quickly using the 85mm lens as an example??

My wording of 'better' or 'worse' could have been improved (if I knew what I was talking about) DOF has always confused me.
Thanks for the explanations
Dave
--
pbase supporter at http://www.pbase.com/dav4184
for equipment see profile
 
Very basically, and leaving out a lot of technical stuff, the difference in the depth of field (or amount in front and behind the subject in acceptable focus) is larger with a crop camera because you will be further away from the subject than you will with a full frame camera.

Say in order to get a whole person in the picture with the same lens you will be 1.6 times further away on a 20D than on a 5D

The further you are away, the more your depth of field.
camerashy said:
but how did you calculate the dof so quickly using the 85mm lens as
an example??
My wording of 'better' or 'worse' could have been improved (if I knew
what I was talking about) DOF has always confused me.
Thanks for the explanations
Dave
--
pbase supporter at http://www.pbase.com/dav4184
for equipment see profile
Click to expand...
 
On the first couple shoots with my 5D I blew some shots by under-DOFing (was used to the 30D). I like working closer but I need to learn to stop down more.

If you have a 30D, are there times when you wish you could work closer to the subject and have shallower DOF?

What I like about the 5D is that I don't find myself swapping lenses as often. The 24-105 can practically cover an entire shoot and the 70-200 isn't as long and thus stays on the camera more. So a lot has to do with the particular lenses you have and how you prefer for them to operate.

Also keep in mind that the more megapixels the more your workflow bogs down (you need bigger CF cards, hard disks, faster computer for your raw converter to work smoothly and so on). And it seems like the 5D isn't quite as snappy at the camera either so I guess the file size has an impact at the camera as well.
 
in a sense.

the difference in dof in this case is basically coming from the fact that the smaller sensor image must be enlarged more to get to the same final viewing size as the larger sensor image. this enlargement factors in the determination of coc.

this is why you will have people stating, correctly, that the smaller sensor cameras actually give less dof than the larger sensors; and at the same time, because for comparable framing you will be either further away or using a diff focal length, smaller sensor cameras also offer a perceived dof "advantage" (ie, deeper dof) than larger sensor cameras.

this is a somewhat confusing issue, and unfortunately it is not made more clear in these forums by the amount of polemicizing around sensor size that goes on. (and this is from someone who prefers ff and loves thin dof; there's plenty of unhelpfully polemical posts on both sides. it never ceases to amaze me how many people here will claim that wide apertures are 'unusable' because of the very thin dof, for example.)
 
Depth of field is effected by several things:

1. Focal length of lens.
2. Distance to the subject
3. Distance to the background
4. Circle of confusion

The aspect that makes the biggest difference between crop and full frame sensors is the difference between where you stand in relation to the subject for a given focal length of lens.

Lee
 
and if one were writing an analysis of dof this would be a good start. (well, it would be if you changed 'effected' to 'affected'.) and of course i was agreeing with you--just trying to connect the link between coc and sensor size for the person who asked the other question.

for photographers who just want to know where to stand and what to use to get a given dof, there are other ways of saying the same thing. not better ways in any absolute sense, just more helpful for people who don't find the first description all that helpful. kind of the difference between knowing and understanding.

i'm not trying to criticize you personally, i am merely saying that if the goal is to help people understand what they want to know, then it matters how things are explained (not simply whether a given explanation is correct or not).

this can all be very frustrating when the same questions get asked over and over, and some of us feel like we've answered them again and again; but in a forum like this, it ought to be expected that new people are, quite reasonably, going to have similar questions time and again.
 
LeeBase said:
Depth of field is effected by several things:

1. Focal length of lens.
2. Distance to the subject
3. Distance to the background
4. Circle of confusion

The aspect that makes the biggest difference between crop and full
frame sensors is the difference between where you stand in relation
to the subject for a given focal length of lens.

Lee
Click to expand...
--

Actually DoF of a lens is dependant upon three things only - your 1., 2., and the aperture set on the lens.

CoC only comes into it when you wish to make prints and have to determine if a point on the print is sharp or unsharp - even then print size, viewing distance, paper surface, film/sensor size and personal preference can affect how you decide this.

Paul
 
LeeBase said:
Depth of field is effected by several things:

1. Focal length of lens.
2. Distance to the subject
3. Distance to the background
4. Circle of confusion

The aspect that makes the biggest difference between crop and full
frame sensors is the difference between where you stand in relation
to the subject for a given focal length of lens.

Lee
Click to expand...
For a fixed aperture, which of course has a huge impact on DOF.

When you're considering constant framing, AND standing in the same place (ie fixed focal distance, change focal length) the DOF is less for FF than APC. The important thing is that it's in your control. Now if only I could remember that!
-Mark
--
http://www.pbase.com/markland
 
LeeBase said:
Depth of field is effected by several things:

1. Focal length of lens.
2. Distance to the subject
3. Distance to the background
4. Circle of confusion

The aspect that makes the biggest difference between crop and full
frame sensors is the difference between where you stand in relation
to the subject for a given focal length of lens.

Lee
Click to expand...
Hi there,

Given a scenerio where your position is fixed in relation to the subject and if you use the 1.6 or FF cameras with a fixed zoom lens (24-105) at 100mm, then the DOF will change...is this correct?

In the shots that I have taken, noticed this behavior ie DOF but am not too sure whether the impact has got to do with FF cameras.

Thanks
--
Rgds
http://www.pbase.com/rakes
 
LeeBase said:
If you like shallow dof -- the 5D is better. Primarily it's
because for a given focal length lens you will stand closer to get
the same framing on a subject.
Click to expand...
Where you are in relation to the subject changes the perspective. For the same shot with two cameras, we want the same perspective. That means using a different lens. If you're going to use an 85mm lens on a 30D, then the corresponding lens on the 5D would be a 135mm lens. Using your example, the same depth of field as the 30D/85mm @ f/1.8 would be achieved with the 5D and 135mm lens at f/2.8.

--
http://www.pbase.com/victorengel/

 
Paul Boothroyd said:
CoC only comes into it when you wish to make prints and have to
determine if a point on the print is sharp or unsharp - even then
print size, viewing distance, paper surface, film/sensor size and
personal preference can affect how you decide this.
Click to expand...
It's part of the formula. It's not under your control as a photographer, so I agree you don't take it into consideration when you are planning a shot.

But when you go to a dof calculator like the one linked -- and you put in the same lens, and same distance to the subject -- and wonder why the 5D has MORE dof -- it's because of the CoC.

Of course -- this "factoid" isn't much relevant in actual use because you won't stand in the same place with the same focal length lens with a crop sized and a full sized sensor. And the change in distance to the subject is much more decisive on why the 5D's dof will be smaller.

Still, had I left it out of the discussion -- someone would have chimed in.

Lee
 
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