Canon EF 70-300 IS USM lens maintenance

friviloususeofspace · Jul 18, 2010

Greetings,

I'm a very uninitiated hobbyist and got this lens used to try to photograph birds. I know, a long lens would probably work better, but I currently get by on limited funds, so this was the best I could do.

The reason for the post is that the lens works fine overall, but there are times I shoot a picture and the result seems blurred. I know my lack of experience and technique is primarily to blame, but when I depress the shutter button, the red target thing in the viewfinder usually indicates a focused frame.

I've started to wonder if the lens maybe needs some kind of work? It's seems in pretty good shape, the motor for the auto focus works from what I can tell. However, the business end, where the fine focus is, seems be sort of loose, for lack of a better term, if I hold it and try to shift it a little bit. I'm not trying to pry it apart, applying a lot of force, as if trying to pull it loose or anything, I know I should try to leave the lens in one piece as much as possible.

Having noticed this though, and not having experience with zooms lenses beyond my own, I don't know how much play is normal between the end with the glass and the housing. Do lenses such as this one need occasional maintenance? I keep the lens on the camera, in the bag, it's a snug fit, but they work together. If more information is needed, please let me know.

oldmacman · Jul 18, 2010

If you are in lower light conditions and you are using 300mm it may be hard to get good focus. Also, if your shutter speed is slower (<200) any camera movement is magnified when you are at full zoom.

subscuck · Jul 18, 2010

The rule of thumb for minimum shutter speed is 1/focal length. So at 200mm, your absolute slowest shutter speed should be 1/200th. At 300mm, 1/300th, etc. With shorter focal lengths, say 30mm or 50mm, it's a little more forgiving and you can still get some sharp pics below their theoretical minimum. Sometimes. When you start getting above 100mm, it's not forgiving at all, and the tiniest bit of camera shake can cause a blurry pic.

Your lens has IS, but like anything, IS has it's limitations. I can't say for sure if shutter speed is the issue without seeing examples complete with EXIF. If it turns out you're getting fast enough shutter speeds and IS is working properly, then it's possible the lens may need to be looked at. Ditto with what oldmacman said about low light AF. Without sample pics, it's hard to know...

BTW, that's actually a very nice lens, you needn't make any excuses for owning it.

JustAnEngineer · Jul 18, 2010

There was a bit of looseness in my copy of this lens, too. That shouldn't stop it from taking decent photographs.

I'll agree with what everyone else said about needing enough light. The old rule of thumb that exposure time in seconds should be equal to 1/focal length ÷ field of view crop factor may even need to be increased with high-resolution sensors. 1/(1.6 FOVCF x 300mm focal length) = 1/480th of a second for hand-held shots.

The image stabilization in this lens may give you up to three f-stops improvement. 2^3 = 8, so now we're down to 1/60th of a second for hand-held images. I've snapped a few keepers at 1/25th, but I've also gotten a lot of blurs. If you need to shoot in less light, increase your ISO setting or put the camera on a tripod.

friviloususeofspace · Jul 25, 2010

Thanks for all of the responses. I have to slow down and take some time to figure out the settings on my camera. I don't know what shutter speed I use when I take the pictures.

I also don't know how I'd get the EXIF information for a picture, I don't know what that is. Would it come off of the camera when I copy the photo to the computer? Or do I need an application to tell me what that information is in a picture? I use jpegs, I know there is something called RAW and don't know if jpeg will have that kind of information. I'll try to read up a little bit on those things and try to post something that will be more informative for the people who want to help me later on.

Thanks again for the assistance, everyone.