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View Full Version : Canon 350D - possible lens or focus problem



gprior87
10-21-2007, 10:07 PM
Greetings all,

Perhaps some folks here might be able to give me some input on something. I've been wondering lately whether there might be a problem with my Canon DSLR or possibly the lens that I'm shooting with. This is an issue I've had on and off for quite a while now (in fact, ever since I first switched from the Canon 28-105mm USM lens to 28-135mm IS USM).

I've been shooting with the Canon 350D (Rebel XT) for about a year and a half now. Most of the early period I had that camera I was using the 28-105mm USM lens, but upgraded to a 28-135mm IS back in March of this year. For some reason, with that lens I have a much harder time composing a sharp, clear shot than I ever had with the 28-105mm. The problem is most noticeable in rainy conditions, and I'll post a couple of example shots to illustrate that. Hence why the issue has been on and off - the question of rain was relatively moot over the summer, although the problem still was noticeable when shooting outside in overcast conditions.

Here are a couple of examples. I've included the basic settings I used to take the shots (more data is available on request if needed).

First off, a picture taken on Sept 02, 2006, on a rainy day in Hamilton, Ontario, with the XT and Canon 28-105mm USM lens:
http://img81.imageshack.us/img81/2905/8206ffp5.jpg
ISO 400, Shutter speed 1/200 at f/8.0. Focal length was 48.0mm. Notice how this one turned out fairly well, it didn't blur too badly or anything.

Also taken with the XT and 28-105 mm lens (just as a comparison with regards to image quality):
http://img156.imageshack.us/img156/8120/9241351lr5.jpg
ISO 400, shutter speed 1/200 at f/5.6. Focal length was 83.0mm.

Now, enter the Canon EF 28-135mm IS USM lens. This was a whole new ball game. Here's a shot taken with the XT and 28-135mm (IS not enabled) on a rainy morning - March 22, 2007:
http://img153.imageshack.us/img153/7908/7287csho9.jpg
ISO 400, shutter speed 1/30 at f/5.6. Focal length 90.0mm.

Needless to say, I was not impressed by the apparent inability of this lens to focus on targets in the rain, when compared to the lens I'd been using before. Like I said, this issue became relatively moot in the summer, but now the problem seems to be even more pronounced, even when the shutter speed isn't so slow as it was on that last image.

I'm wondering if this is a problem with the lens, or the camera body. Does anyone have any suggestions? I can post another couple of sample shots if need be.

Thanks,
George Prior

TheObiJuan
10-21-2007, 10:58 PM
The problem is the lens. The lens is not designed to snap into focus quickly or accurately. The slow maximum aperture does not allow enough light to have the XT's sensor's lock on. The lighting is horrible in that scene, too.
Overcast days are known for slow focus.

You could try a 70-200 f/2.8L and see the difference on the XT.
When it is overcast or raining there is not enough CONTRAST for the sensors to pick up and focus. This lens being an inexpensive contender, doesn't help.

You could learn to accept this lens' performance or upgrade.

The XTi is a better focuser, but still, a faster and more accurately focusing lens would help even more.

gprior87
10-21-2007, 11:32 PM
The problem is the lens. The lens is not designed to snap into focus quickly or accurately. The slow maximum aperture does not allow enough light to have the XT's sensor's lock on. The lighting is horrible in that scene, too.
Overcast days are known for slow focus.

You could try a 70-200 f/2.8L and see the difference on the XT.
When it is overcast or raining there is not enough CONTRAST for the sensors to pick up and focus. This lens being an inexpensive contender, doesn't help.

You could learn to accept this lens' performance or upgrade.

The XTi is a better focuser, but still, a faster and more accurately focusing lens would help even more.

I suspected it was probably the lens that was the problem. I have a 50mm f/1.4 USM as well, and it's rarely given me any trouble - granted, I haven't used it much lately, so I couldn't be sure if something on my camera body was giving out, or whether the (dramatic) change in weather lately was responsible for the decline in my photo quality.

Do you have any theories as to why the 28-105mm (an even more inexpensive lens) always gave me a better performance, though? I am definitely considering getting rid of the 28-135 IS, but the options I'm considering are
a. the 24-105mm F4L IS
b. going back to the good old 28-105mm USM