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How to keep everything in focus?

Steve Ralston , Apr 02, 2007; 08:01 a.m.

I recently purchased a Pentax k100d, moving up from a Kodak C740. With the Kodak it was easy to take a photo, say of a centerpiece on a table, and have pretty much everything in the foreground and background in focus. With the Pentax the default behavior seems to be keeping everything in the center of the focus plane in focus. I'm not having any success trying to figure out how to get that "everything in focus" effect on the Pentax. I have read through the manual extensively, and learned a lot along the way, but haven't figured this one out yet.

I would really appreciate any advice.

Steve Ralston


Geoff Sobering , Apr 02, 2007; 08:15 a.m.

Try a search on PN or Google for "depth of field" (use the quotations) and you should find more than you'd care to know about getting things at different distances in focus. It turns out the small sensor on your Kodak created conditions for very wide depth-of-field (aka DOF), and the larger sensor on your k10d will require you to pay a bit more attention. The good news is this is a proverbial "good thing".

A couple of tutorials I found quickly: http://www.cambridgeincolour.com/tutorials/depth-of-field.htm http://en.wikipedia.org/wiki/Depth_of_field

A DOF calculator: http://www.dofmaster.com/dofjs.html


Geoff S.

Peter Daalder , Apr 02, 2007; 08:19 a.m.

The Pentax K1ooD has a CCD with a dimension of 23.5 x 15.7 mm.
You might like to check up on the size of your Kodak C740's sensor and will probably find that it is smaller...
Have a look here for further information.

Christopher Gervais , Apr 02, 2007; 10:22 a.m.

Depth of field is a very basic thing you should learn. Google "depth of field" and get a good book such as "the camera" by Ansel Adams

Matthew Miller , Apr 02, 2007; 12:28 p.m.

The other posters are definitely right -- knowing how this works is essential for using an SLR well. But the quick answer is: you need a smaller aperture, which means a higher f-stop number. Put the camera in aperture priority mode and experiment.

Andrew Gilchrist , Apr 02, 2007; 12:34 p.m.

The other posters are right, this (depth-of-field, selective focus) is a fundamental factor in photography, and for better or worse, a small-sensor digicam is going to naturally provide greater depth of field than a larger-sensored D-SLR whether you like it or not. You have likely already observed that this makes focusing more critical than it was with your Kodak.

The really simplistic answer to your question is: shoot with a smaller aperture (larger Av (f-stop) value. f/8-f/22 will generally leave increasing amounts of your image in focus. Larger openings (e.g. f/6.7-f/1.4) will introduce increasing amounts of selective focus. f/8 isn't a magic number, just one I selected because its somewhere in the middle.

If you're shooting "scene" program modes, landscape mode will likely boost your depth-of-field while portrait may make it shallower. I recommend shooting Av mode with several different aperture values and look at the difference. Also, try out the depth-of-field preview lever (read about it in the manual--K100D has both optical and digital preview, I'm referring to optical) so that you can have some idea of what will and won't be in focus.


Unca Mikey , Apr 02, 2007; 01:17 p.m.

And the really fun next step is realizing that not having everything in focus can be fun and interesting...

Ton de Goijer , Apr 02, 2007; 05:12 p.m.


Agreeing with all and especially with the last poster before me.

Learn DOF and see how you can make an object (flower building or insect) come loose from the background.

This is a shot that I took this afternoon experimenting with a 100mm lens at 2,8. As you can see, the hair on the rear of the head is already out of focus. It is shot at f/2,8.

Have fun, Ton

Michael Kuhne , Apr 05, 2007; 01:57 a.m.

The good thing is you now have better control. You can select increased DOF, or sometimes you will want reduced DOF to blur background, to make your subject stand out. A "fast" lens that can open to a wider aperture increases that capability. Enjoy.


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