Focus and re-compose advice

[ajax_andy]

Hi Richard,

Thats a lot of excellent info that i'll need to go through a few times to fully digest I think, and I appreciate the depth you have gone in to there

I purchased the 50mm f/1.4 not the f/1.8... is the quality much sharper on the f/1.4? I had hoped it would be and that's why I purchased that one over the f/1.8.

With the pics you posted as examples of shooting at f/2 I noticed that both subjects were standing side on and so it was almost a 2d plane that you were having to get in full focus... I'm imagining it's harder if both eyes were visible as that would create a larger area that would need to fit in the very shallow depth of field?

I think I need to just get out there and practice lots to work out what I can and can't do with the lens. i'll probably start off using a fairly safe f/2.8 and once I'm comfortable with how this works then start pushing the boundries a little more.

[RichardTaylor]

Thanks, it can work, sometimes.

Here's one almost head on (A larger version is on my flickr stream) although I can't remember the shooting distance.

Camera Canon EOS 40D
Exposure 0.003 sec (1/400)
Aperture f/2.0
Focal Length 135 mm
ISO Speed 100
Exposure Bias -2/3 EV
Flash Off, Did not fire

Re the 50mm F1.4 - I havn't used it, however I believe it is sharper than the 50mm F1.8 especially from around F2.

[ajax_andy]

Originally Posted by RichardTaylor

Thanks, it can work, sometimes.

Here's one almost head on (A larger version is on my flickr stream) although I can't remember the shooting distance.

Camera Canon EOS 40D
Exposure 0.003 sec (1/400)
Aperture f/2.0
Focal Length 135 mm
ISO Speed 100
Exposure Bias -2/3 EV
Flash Off, Did not fire

Re the 50mm F1.4 - I havn't used it, however I believe it is sharper than the 50mm F1.8 especially from around F2.

That image is nice and sharp... I need to practice lots I think. I posted a couple of pictures in the critique section as wasn't happy with the results of my 1st try with the prime lens and the feedback I got was that even though i'd shot at an aperture of f/3.5 I only had DOF of a quater of an inch!

I was shocked by that as had deliberately not shot wide open to give myself a deeper DOF, however it seems that I'm not completely grasping the maths of it all. However I think it's making a little more sense now (not much but a little), so i'll go back through everything you posted and see if I can pick it up a bit better.

Thanks again for your help

[Johninbigd]

I'm pretty new to this. I had a basic idea of what depth of field was and how to control it, but I wasn't really familiar with the details. This past weekend I shot a picture of someone with a 50mm lens that turned out blurry in areas I thought should have been sharp. It turned out pretty cool, but it was not what I intended. I was trying to blur out the background, but I was at f/1.8 and only about 4 feet away! It sure blurred the background, but my depth of field was only about an inch, as I recall. Luckily, I was focused on her eyes and the result was pleasing, but it made me do some research to find out more about DOF calculations.

The DOF calculator that someone posted is pretty fun to play with. Think about some shots that you've taken recently and go plug those numbers into the calculator. Once you see what the calculated DOF is, go back to your images and compare. It's enlightening!