Problem with a lack of DoF

[Xibalba]

Hi all,

I have a DoF problem when I am shooting fish in my aquarium. I currently use an EOS300D with an EF 28-105 f3.5-4.5 @ 105mm, 1/200, f13 with an external flash and I shoot from around 2' from the front glass. This gives me a DoF of around 1/2". My fish are around 4" long so when I take shots from an angle, often the tail is out of focus.

As I understand it, if I want to increase the DoF, other than by using a smaller f-stop, I need to reduce the size of the subject. Unfortunately, when I do this, the fish is so small in the final image that I cannot get a decent print. It is ok for posting on the web, but I cannot print out any bigger than 6x4.

Do things such as extension tubes and telecomverters affect DoF in the same manner as different focal length lenses i.e. the same size subject has the same DoF? Is there any other way of increasing my DoF and still maintaining the subject size?

TIA

Rick

[robertwgross]

Let's think about this.

Give the whole scene less light. That will force your lens aperture to open up more, and that will limit the depth of field even worse. That is probably the opposite of what you are trying to do, so swing it back the other way. Give the whole scene more light. That should force the lens aperture to close down, and that should deepen the depth of field. Now, how do you give the scene more light? You could shorten the flash-to-subject distance, but then that might get you into an overload. You could slow down the shutter, but then you subject movement might get you some blur. You could crank up the ISO, which is effectively giving the scene more light. Crank it up too far, and you might get a color noise problem, but lots of that can be filtered out with color noise reduction programs.

Maybe you could get your subject to wear lighter makeup! No, I guess not. That sounds pretty fishy to me.

---Bob Gross---

[DC]

What ISO you at?

I'd try putting the camera in Tv mode, set the s/s to 1/60. That should give you a smaller aperture and therefore more DoF

If you got latitude in the ISO setting, you could try changing that too.

[Jon]

You're not going to gain a whole lot by juggling lenses - although a short lens will have greater DoF than a long one when they're at the same distance from the object they're focussed on, to maintain image size, the short lens will need to be closer to the subject, with reduced DoF. So you'll need to stop down. That means a slower shutter speed (on a moving target? Hah! Maybe if you cooled the aquarium down they'd slow down), more light (off-camera, either flash or floods), or a higher ISO setting. Of the three, I'd go with more light, preferably from an external flash, although you'll have to be careful about reflections off the glass and/or the water surface.

[Xibalba]

So I am assuming that using a teleconverter or an extension tube will not help me out?

I currently shoot at ISO100 so I guess I could change that and then use another external flash or 2 to try and get some more light on the subject. Stopping down to f22, assuming I can get that much light into the tank, will still only really get me a DoF of just under 1" so it looks like some part of the fish will end up out of focus no matter which way I go.

Rick

[robertwgross]

So I am assuming that using a teleconverter or an extension tube will not help me out?


Using a teleconverter will allow you to move back and still fill the frame, and then you will have lost one or two stops of light (which is not desired). Using an extension tube will allow you to move closer than the normal minimum focus distance.

---Bob Gross---

[Scottes]

If you're really into this you might want to look at a little P&S. The very short lenses produce quite a bit of DoF.

[slin100]

Another solution, albeit quite expensive, is to use a Canon TS-E lens. DoF can be really tweaked by tilting the lens.

[Xibalba]

Another solution, albeit quite expensive, is to use a Canon TS-E lens. DoF can be really tweaked by tilting the lens.
A TS-E lens sounds like a good solution to my problem, although the cost does introduce some other issues. Does anyone know where I might be able to find a good explanation of how tilt and shift work?

If you're really into this you might want to look at a little P&S. The very short lenses produce quite a bit of DoF.
I thought this might have been my only solution but I am reluctant to get another P&S as the reason I upgraded to the 300D was to solve some of the issues I was having with getting decent pictures with a P&S. I think that I would need to spend a fair amount on one of the better P&S cameras around to get the performace I need such as the fast shutter response time, fast focus and a hotshoe for an external flash. The price for a camera like that may be close to the price of a TS-E lens and I think I would get better clarity from the DSLR/TS-E combo than a good P&S.

Thanks for your help, at least now I know there are some solutions out there :)

Rick

[slin100]

A TS-E lens sounds like a good solution to my problem, although the cost does introduce some other issues. Does anyone know where I might be able to find a good explanation of how tilt and shift work?

I came across this article (http://www.outbackphoto.com/workflow/wf_42/essay.html) the other day. It's a great primer on the terminology and basics. It also has a description about modifying TS-E lenses to swap the operation of some of the controls for greater usability in certain situations.