DOF etc

I have been struggling with a wealth of formulae etc all to do with depth of field. Does this example look reasonable to you? C&C please

If the exif hasn't been preserved:
K100D DA 18-55 @55mm
Av mode
f5.6 1/60 2-sec timer ISO 800
small tripod (v v small!)
subject was close - must have been no more than 2 feet!

Ehm, :
This is a photo with a certain DOF. As you have taken it at f5.6 I would have thought it is reasonable for f5.6.
The DOF is there, whether you can calculate the depth or not. Even if you haven't got the slightest idea what DOF is, it will still be the same at this setting.

A bit like being a little child falling from the chair. It doesn't know anything about gravity but it is nonetheless subjected to it.

Perhaps you were after something else?

Prieni

I miss having DOF indications like I had on my old 35mm film SLR lenses. So I downloaded a nifty small program which claims to calculate DOF. After fiddling about a bit I found I could replicate the program's formulae in an excel spreadsheet. It told me my min DOF (55mm @ f5.6) was not much more than a tenth of an inch!!

I was a bit surprised

What does everyone else do - use the so-called "optical preview" and judge it by eye? Or is it more a case of years (and years!) of practice...?

Well, for a shot like this, where you've got all the time in the world, I would take several shots at different apertures/focal lengths/exposures and pick which one I liked the best. That's one of the beauties of digital.

Dan

Ok, now I see where you are coming from.
These DOF calculators (as well as the scales on the lens of old) are correct under certain assumptions. As far as I understand (and I haven't really dug into it) it has to do with how big an enlargement you are looking at from what distance. So while they are a good indicator, especially when comparing different settings, the absolute values might have a bit different meaning for your viewing/enlarging situation.

The small DOF for macro work is a well known and common problem.

Prieni

Daniel thanks. It is absurd the way I still am so tight-fisted about taking pictures - as if each one was going to cost a fortune to develop and print!

Ralf thanks also. What I want is to develop a good strategy. So the more I can learn about how DOF behaves with my lenses the better equipped I will be when I consider shooting a type of subject

This is one of the beauties of digital - you can do all that experimentation without further cost.

As regards DOF here, the simplest approach is the trial and error one. At least it avoids Excel spreadsheets! I would use the smallest aperture that I could, with the camera firmly clamped to a sturdy tripod. I think I would be using around f11 or f16 for this shot. Not f22 straight away because definition will drop off at the dmallest apertures.

If there was too little or too much DOF then it's simple enough to shoot another frame at a different aperture.

Hope that helps!

It's a hard habit to get out of, and sometimes it's useful to have this mindset anyway - better than firing off 1000 shots in the hope that one is going to be okay. But I often take a lot more shots of a subject than I need, simply because as I start taking photos, the composition starts to develop, you see different ways to approach it, and you hopefully end up with an image that's better than the one you started with.

No substitute for practice here I think, so being a bit more trigger happy, and varying the aperture, focal length etc as you go, will be the quickest way to find what works for you.

Following on from John's post, you might find that when using these smaller apertures the background becomes too focused. In this example, you just need to move it further away. The greater the distance between your subject and the background, the better you can isolate the subject, even when using smaller apertures.

Dan

Thanks John
Thanks Daniel
Not being "too focused" is what my experiments were meant to achieve! This is why I wanted to figure out what ranges of DOF I could play with using a mix of maths and optics. I have certainly learnt that focal length, aperture and distance from the subject all play a part.
Who has the motto "keep on clicking"? - quite right!