Depth of Field Question

[Spinners]

I know that the the depth of field is reduced when you zoom in given any F stop and increased as you zoom out.

but does the distance from - the camera to the subject -effect the depth of field for a given F stop?


As an example. a 50mm lense set 10 feet from the subject vs a 50mm lense set 15 feet from the subject?

would this depict the same depth of field?

also, anyone have a quick formula for figuring it out. Especially for zoom lenses.

thanks

[DaveG]

spinners wrote:
I know that the the depth of field is reduced when you zoom in given any F stop and increased as you zoom out.

but does the distance from - the camera to the subject -effect the depth of field for a given F stop?


As an example. a 50mm lense set 10 feet from the subject vs a 50mm lense set 15 feet from the subject?

would this depict the same depth of field?

also, anyone have a quick formula for figuring it out. Especially for zoom lenses.

thanks

Yes. The closer you get to the subject the less the depth of field is per given aperture.

This is especially a concern for macro photography. For macro shots you are going to
want to stop the lens down quite a bit. Unfortunately while this helps with D of F. it also
introduces the optical problem of diffraction

But even at moderate distances the closer the subject is the shallower the depth of field.
Most lens manufacturers will have tables that will indicate D of F per aperture but I don't
see how they are of much use in practice. If your camera has a depth of field preview capability,
you can use this to stop the lens down so you can see what's going to be in focus and this
is a much better solution than theoretical tables.

[Spinners]

i have a DOF preview, but it isnt very easy to tell in the viewfinder cause its so small. Is their any rule of thumb to use? i mean how do you know how far to setup from your subjects? trial and error does not seem fitting for this application..

[dtrayers]

An excellent primer on DOF:

http://www.luminous-landscape.com/tutorials/understanding-series/dof.shtml

[jyrgen]

Formulae, calculators, etc:

http://dfleming.ameranet.com/articles.html

[w10d]

An extreme way to illustrate how DoF changes: A standard lens focused at, say, 30 feet - DoF will extend to 'infinity', mountains many miles away will be in focus. Focused at 30 inches (same aperture) and DoF fall off will be measured in feet.


Most lens manufacturers will have tables that will indicate D of F per aperture but I don't
see how they are of much use in practice. If your camera has a depth of field preview capability,
you can use this to stop the lens down so you can see what's going to be in focus and this
is a much better solution than theoretical tables.


I miss the hyperfocal scale marking on modern AF lenses. Do any of the Canon AF lenses have them?

[ron chappel]

Distance from the subject has a massive effect on DOF.To the extent that,at infinity,it is purely lens focal length and aperture that effects dof.(the example you gave with the zoom lens)
At close distances it is far easier to think in terms of 'framing' + Fstop
e.g ..a 50mm lens @f2 focused at 1m and a 100mm lens @f2 focused at 2m (same framing,see?)will have identical DOF.
In fact when you get used to thinking in these terms(same framing at close distances-portrait photographers think of little else) then the Fstop is the ONLY factor effecting DOF

[Spinners]

Hmmmmm.. well im not ashamed to admit this, but i still dont get it. i mean, does everyone measure out where they are going to stand to take shots? then perform calculations to make sure they will come out correctly?

I have a 24-85mm canon lense and lets say i wanted to figure out depth of field for each of my F stops at 85mm.

is there an easy way? do i need to even worry about this? am i crazy?

[hmhm]

spinners wrote:
does everyone measure out where they are going to stand to take shots? then perform calculations to make sure they will come out correctly?


I think of aperture as the primary control over depth of field, not subject distance or focal length.

I think of subject distance as the primary control over "perspective", i.e. how quickly things become smaller as they get further away. Longer subject distances yield "flatter" perspective (e.g. a portrait from too close yields "big nose in the lens" phenomenon).

I think of focal length as the primary means to yield the desired framing, given the subject distance I chose (or which was chosen for me, if my position is constrained, e.g. I'm not wearing my personal jet propulsion pack).

Attempts to influence depth of field through variations in focal length or subject distance aren't likely to be very successful, assuming you have a certain composition in mind. For instance, if you try to increase your focal length, but then have to get further from the subject to compensate, you will not have significantly different depth of field. Increasing focal length reduces depth of field, but the corresponding increase in subject distance needed to preserve the framing would increase depth of field. One rule of thumb for depth of field that falls out from this is to think of small subjects (e.g. bugs) as leading to small depth of field and big subjects (e.g. mountains) as leading to large depth of field. If you're going to fill the frame with an object of a certain size, whether you do it from up close or far away won't change DoF much, but it will change perspective.

All that said, you can increase depth of field by decreasing focal length without getting closer to the subject (or holding focal length steady and backing away from the subject), thus making the subject "smaller in the frame", and the cropping in post-processing, but then you lose pixels, obviously.
-harry

[Yance]

The lens has a minimum aperture of usually f32 so if you are concerned with trying to get the most depth of field possible, try that setting. In critical shots it is always best to make several exposures to bracket the exposure. You can use that concept to bracket for DOF too. I remember on older lenses, they used to come with DOF tables to give you ranges for each of the f-stops at various distances. Try this resource to get some values you can print out:

Depth of Field Calculator (http://www.shuttercity.com/DOF.cfm)

[rdenney]

spinners wrote:
Hmmmmm.. well im not ashamed to admit this, but i still dont get it. i mean, does everyone measure out where they are going to stand to take shots? then perform calculations to make sure they will come out correctly?

I have a 24-85mm canon lense and lets say i wanted to figure out depth of field for each of my F stops at 85mm.

is there an easy way? do i need to even worry about this? am i crazy?

In the old days, we had focusing scales and depth-of-field scales printed on the lens barrels, so, yes, we did just what you say. I still do it on my medium-format cameras: I move the focusing ring so that all distances that are important to me are within the depth-of-field marks for the aperture I'm using. I may even choose a smaller aperture if experience tells me that the depth-of-field scale on the lens is not conservative enough.

With view cameras, I measure things when reasonable, but I still check focus using a high-power loupe on the ground glass. I've found no other way to be sure.

That new lenses don't have those scales is really annoying to me, and one of the weaknesses of modern autofocus equipment.

Rick "who uses experience to set depth of field nowadays, and then checks focus on the LCD after shooting" Denney

[Spinners]

does anyone know where to find DOF charts for canon and sigma lenses? that would be of help.

[w10d]

spinners wrote:
i mean, does everyone measure out where they are going to stand to take shots? then perform calculations to make sure they will come out correctly?


No, well, perhaps when making movies :)

A lot comes down to experience and familiarity with your equipment. DoF is about the most powerful technique available to photographers - and using it can seperate you from the casual snap-shooter. As I mentioned earlier, unfortunately modern AF lenses no longer seem to carry the markings that would make DoF and hyperfocal distance calculations easy :( I think Canon tired to offer a solution with the DEP setting, but the version of it on the 10D seems useless to me.

[mishkin]

spinners wrote:
As an example. a 50mm lense set 10 feet from the subject vs a 50mm lense set 15 feet from the subject?


at 15ft the DOF is 2.25x larger than at 10ft. DOF is approx. proportional to the square of subject distance.

Same for misfocus error. 0.5" misfocus at 2ft. becomes about 50" (4ft!!!) misfocus at 20ft.

Mishkin

[iwatkins]

Canon used to have a great feature on one of my old film bodies (650F or might even have been my 1000F).

It had a DOF mode. You used auto focus to focus on the point you wanted the DOF to start. You then focused again on the furthest point you wanted the DOF to extend to and then you recomposed and it would take the shot with the DOF you setup. I loved that feature. :)

Cheers

Ian

[w10d]

iwatkins wrote:
Canon used to have a great feature on one of my old film bodies (650F or might even have been my 1000F).

It had a DOF mode. You used auto focus to focus on the point you wanted the DOF to start. You then focused again on the furthest point you wanted the DOF to extend to and then you recomposed and it would take the shot with the DOF you setup. I loved that feature. :)

Cheers

Ian



Yup, I think thats what they 'updated' on the 10D, with the A-DEP setting. By automating it they have made it pretty much useless. Oh well, so much for progress...

[ron chappel]

They still have the proper version on better film bodies.basically i don't know why they bother with the A-DEP

[DonCoon]

spinners wrote:
also, anyone have a quick formula for figuring it out. Especially for zoom lenses.

thanks
http://www.nikonians.org/html/resources/guides/dof/hyperfocal2.html

Use .019 for a 10D/D30/d60/300D

[DonCoon]

Yance wrote:
The lens has a minimum aperture of usually f32 so if you are concerned with trying to get the most depth of field possible, try that setting. In critical shots it is always best to make several exposures to bracket the exposure. You can use that concept to bracket for DOF too. I remember on older lenses, they used to come with DOF tables to give you ranges for each of the f-stops at various distances. Try this resource to get some values you can print out:

Depth of Field Calculator (http://www.shuttercity.com/DOF.cfm)

Can't use this calculator with a Canon 1.6X DSLR. There is no selection option for a .019 CoC :(

[Spinners]

sigh.... is there anything that would cause a camera to focus fine on close shots, but not fine on far away shots? I purchased another 10D body to see if my existing body was messed up. It's shots don't seem to be much different from that of my 'about to drop out 2nd story window body'.

could i just misconstruing softness for out of focus? when i zoom in the pictures look like crap. which means when they're blown up they will look bad?

any more ideas? i am going to post a picture today to show you guys.

[rdenney]

spinners wrote:
sigh.... is there anything that would cause a camera to focus fine on close shots, but not fine on far away shots? I purchased another 10D body to see if my existing body was messed up. It's shots don't seem to be much different from that of my 'about to drop out 2nd story window body'.

could i just misconstruing softness for out of focus? when i zoom in the pictures look like crap. which means when they're blown up they will look bad?

any more ideas? i am going to post a picture today to show you guys.

Remember that at maximum zoom, you are looking at an image that if you saw all of it would be around 20x30 inches. This is beyond the capabilities of most 35mm film cameras. I can easily check focus and lens quality looking at the zoomed-in images on the LCD.

You have to make some prints so as to calibrate your eyes for the relationship between what you see on the LCD and how it looks on a print. My prints are generally looking much better than what I see zoomed in all the way on the LCD.

Rick "whose 10D usually focuses well enough for a 13x19 print to appear quite sharp" Denney