Focusing an entry-level DSLR

Question

I like really really sharp photos.

Even with a prime lens, I seem to be able to do noticeably better with my 450D by manually focusing using live view at maximum zoom than by using auto focus (even with just the center focus point selected and aimed at the same high contrast region that I am looking at in live view). However this is a painstaking procedure that requires a tripod and a fair bit of time; not really suitable for capturing fleeting expressions on people's faces or rapidly moving children.

Unlike my old film camera, the 450D lacks a prismatic focusing screen, and my eyesight isn't good enough to do better than the autofocus through the viewfinder without one. How do others deal with focusing for candid portraits? Any tips?

Answer 1

The lack of focus could be partially the result of camera shake. Even though the focus is correct, the image may be blurred slightly by the movement, which would go away using a tripod.

If you are looking at 100% crops of digital images, there will probably be some blur unless you make sure to select a high enough shutter speed. The same image viewed as a 4x6 is going to be quite sharp compared to the 100% crop.

Answer 2

It looks like you can put a focusing screen into a 450D. Check out these links for the procedure:

• Canon EOS 450D 500D 1000D Split Screen Installation
• Canon EOS 450D Focusing Screen Installation **

** Beware, that page is written in fairly bad English.

Canon 450D & 500D focusing screens for purchase. I have no idea if the price is reasonable...plain it is $105, with the brightness enhancement and AF points, it is $200:

KatzEye™ Focusing Screen for the Canon® 450D/500D (Rebel XSi/T1i)

Here is a much cheaper one:

Double 45° Split Focusing Screen For Canon 450D 500D 1000D

Answer 3

There have been claims of back and front focus issues on the Canon 450D, but I'm not entirely sure I believe them. I have a friend with that camera that runs around with an unstabilized 400mm Canon prime and takes sharp bird pictures using that lens. So... I suspect that it may be more related to camera shake caused by one or more of the following:

1. Mirror vibration which can have bigger impact on slow shutter speeds.

2. Technique which can cause camera shake. For example, if you stab at the shutter release, that can cause movement.

3. Slow shutter. Hand holding a shot with a shutter speed well below 1/f (f being focal length) is sure to introduce shake, especially with an unstabilized lens.

4. Low light focus hunting. You may have shifted focus as you pressed the release and not realized it.

After all that, it is entirely possible that you have a front or back focussing issue but, as I said, I suspect the general claims of this are unlikely.

Answer 4

Every component (lens and body) have independent tolerances when it comes to focusing. With a the shallower the depth of field, the overall focus offset becomes apparent.

To make things more complicated, the focus offset may change with these variables: focus distance, aperture, and focal length.

Although it is entirely possible that your combination may be front or back focusing, you should look at other factors such as camera shake.

If you want to determine if it really is front or back focusing, or something else, do a focus test. It's important you do this outside with natural light, as artificial, particularly incandescent, will cause front focus with most cameras. If it is calibrated indoors, you'll get back focus with other light.

Make sure to read all the instructions and use a tripod: http://focustestchart.com/chart.html

Answer 5

One trick you can use to avoid camera shake on the 450 is to use the 2 second timer.

You could go so far as to introduce a tripod and muck around with the mirror lock-up.

I use the 60mm prime macro and get reasonable results just using the auto focus stuff even in low light with high ISO.

As soon as I tighten the aperture and use higher speeds I start getting fantastic results.

I think that a bigger factor is the 450s poor performance with high ISO which restricts what you can do in low light.

I have noticed that photos that use flash tend to appear a lot more focused so another trick you could look into is using a fill flash in low light.

Answer 6

You can change the focusing screen of the 450D. (It does come with one, but not a high contrast one). A quick google has found one by katzeye and instructions for changing it.

It is easier for the higher spec cameras, but can be done at your level.

Answer 7

Another thing to think about: If you do change the focusing screen, manually focusing will get quicker over time. You'll learn your lens and you'll be able to do it much faster. Practice, practice, practice!