Apperture vs depth of field ?

[Dread Pirate Roberts]

Does anyone know of any resources where I can learn more about the affect of apperture on the depth of field vs different focal lengths?

Things like charts for acceptable depth of field vs distance to the subject and focal length?

Books or web pages that can explain how out of focus a given background will be at an apperture vs camera distance to subject and distance to background. I assume they've the variables.

Still climbing a steep learning curve.

[Honest Gaza]

DPR....just search for "dof calculator" in google (or whaterver you use), and you'll get lots of links where you can enter focal length and aperture.

I've even downloaded one for the Palm which works pretty good.

[Rooz]

do you ever use it gaz ?

[Honest Gaza]

do you ever use it gaz ?

Yep. When I ventured out to Eastern Creek, I prepared a table of what type of DOF's I'd get with nominated focal lengths and apertures as a guide of what settings to use on the camera.

It helps you with the creativity aspect....and also gives you an understanding of how apertures sometimes don't matter at all when the subject is far enough away from you.

[Ken.]

You also need a bit of understanding of the dynamics of the lens itself. This is a very, very loose "guide" but a lens will get softer because of diffraction at smaller f/stops. Because a lens can stop down to f/32 doesn't mean it's at a point on optimum sharpness. At wide open you may end up with fall off or other flaws. Somewhere there's a sweet spot, around 2 to 3 stops down from wide open. Oddly, that was an old rule in film days and it seems to hold true today judging by the lens tests I've read.

Also be aware of the focal length conversion factor. A depth of field chart for 35mm will not work correctly with a sensor smaller than that format. For instance, I have a four thirds camera. 14mm is 28mm in 35mm. If I plug in 14mm in a 35mm DOF chart it will show incredible DOF because in 35mm terms this is either a rectilinear wideangle or a fisheye.

Something else to be aware of is the "bokeh" effect. At wider apertures how will the out of focus areas look? A lens with more aperture blades (forming a better circular iris) will produce a smoother appearing out of focus region than one with less.

[Dread Pirate Roberts]

I've looked through a few websites Gaza. I've seen a million different calculators (and offers to sell me charts) but nothing explaining the physics of what is happening and why.

Does anyone have the formula that underlies those calculators?
Does anyone have a webpage with a great explanation?

[DonSchap]

Check wikipedia (http://en.wikipedia.org/wiki/Depth_of_field#Depth_of_field_formulas) (<- click on the link) ... to start.

One other thing to bear in mind, is that tigher aperture causes a softening of the image due to diffraction. Basically, it is when beams of light interfere with other beams of light, as it is bent by the aperture, causing a softening effect of the image.

This will kind of give you an idea of the effect:

35507

So, even though you may have a lens that can give you f/22 or even f/32 ... your digital image (unlike the response you can acheive with film), instead of sharpening, will be degraded, due to this interference. So ... the "f/64 Club" finally reaches its ignominious end. :rolleyes:

[Geoff Chandler]

Aside from all the complecated diffraction issues and the fact that there is only the point of focus actually in focus etc - remember that wherever you do focus, depending on the aperture - an apparent Depth of in focus field is to be found and that it is 1/3 to 2/3 ie 1/3 behind the focal point to 2/3 in front. With our old types of cameras we could visualise this on the focus rings
http://www.normankoren.com/Tutorials/Canon_DOF_480.jpg
So with a smaller f-stop such as F16 you could rotate your focus to line infinity up with the f16 point to enjoy the max DOF effect
Hope that makes some sense

[JTL]

Does anyone know of any resources where I can learn more about the affect of apperture on the depth of field vs different focal lengths?I think you should just leave your camera on Auto! You wouldn't want anyone accusing you of actually trying to learn something about photography, would you? :eek::D:p:D:eek:

[Dread Pirate Roberts]

Thank you very much, that link to wiki was just the ticket.
I must be from the stone age, I'd completely forgotten about electronic encylopedias.:)

Having read but not absorbed much of the article I can see why everyone does it empirically instead of thinking in terms of formulas.

Still it was interesting to see the formula for background bluriness.
Bluriness tends to lens focal length x magnification / f number (valid for a small subject distances)
In other words to get the background blurry get the subject in close, zoom in and use a small aperture.

And yes JTL just because I argued there's a place for auto doesn't mean I'm not trying to learn as best I can.

[Visual Reality]

Diffraction:

http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm

[Dread Pirate Roberts]

Thanks VR.

I'd been told not to stop down so far unnecessarily to minimise difraction related softness. It helps my understanding to have it illustrated like that.

I didn't know green had twice as many pixels devoted to it either.

[JTL]

And yes JTL just because I argued there's a place for auto doesn't mean I'm not trying to learn as best I can.Awww, I was just kidding around with you...:)

I don't know if you know about this site, but it's pretty good...

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

[Visual Reality]

Thanks VR.

I'd been told not to stop down so far unnecessarily to minimise difraction related softness. It helps my understanding to have it illustrated like that.

I didn't know green had twice as many pixels devoted to it either.

On the other hand, for huge landscapes many stop down to F16 or F22, reason being they want absolutely everything in focus even if that means making a sacrifice in sharpness. It will depend on the lens and each person will need to test how far they can go before it starts giving unacceptable results.

[Dread Pirate Roberts]

Thanks JTL another intersting site I wasn't aware of.

Yeah VR I was also interested by the section on deliberately compromising focus on landscape shots too.

[cwphoto]

Check wikipedia (http://en.wikipedia.org/wiki/Depth_of_field#Depth_of_field_formulas) (<- click on the link) ... to start.

One other thing to bear in mind, is that tigher aperture causes a softening of the image due to diffraction. Basically, it is when beams of light interfere with other beams of light, as it is bent by the aperture, causing a softening effect of the image.

This will kind of give you an idea of the effect:

35507

So, even though you may have a lens that can give you f/22 or even f/32 ... your digital image (unlike the response you can acheive with film), instead of sharpening, will be degraded, due to this interference. So ... the "f/64 Club" finally reaches its ignominious end. :rolleyes:

Film is also affected by diffraction Don.

[AlexMonro]

However, the f/64 Club were using 10"x8" film, so diffraction probably wasn't an issue, though depth of field was - the opposite to the typical modern small sensor digicam! :)