Checking a lens (canon EF7-300mm IS)

[Tuna]

I got a lens for my birthday this year, a Canon EF 70-300mm F4-5.6 IS USM. The big problem is I'm not sure how accurate it is at the long end. Trying to get a good picture of the moon, on a tripod, reasonably closed down, the resulting image couldn't be described as sharp. I'd expect zoomed photos to be a little bit mushy, especially when hand-held - and they are. But I'm worried that they are mushier than they ought to be.

What's the best (i.e. cheapest and least hassle) way of getting the lens checked out? Unfortunately it was bought by my F-I-L from Hong Kong, so there isn't the option of taking it back to the shop, and I don't have the receipt for the guarantee. It would be embarrassing to let him know I'm concerned about the quality of the lens.

[bacchus180]

think you will find the moon moves quite quickly... if you've closed the lens right up.. no doubt a slow shutter,

if you want to test its sharpness shoot some trees along way off and look at the detail, closed down i wouldn't expect its that sharp

[ed_p]

Yes, movement can be quite a problem, particularly with higher magnifications. Also, the nearer the moon is to the horizon, the greater the atmospheric distortion of the image. Wait until the moon is well up and the sky is clear. As said earlier though, a "terrestrial" subject is better for testing.

[havoc]

There is a known issue with a batch of these lenses...check the Canon website for info...they can be identified by part of the serial number.

[Gemm]

Good 2 comments above.

Use of mirror lock-up can help with the camera shake but, as metioned above, the moon is a moving object, so it wouldn't do much if the movement is causing the issue.

[Gemm]

havoc said:

There is a known issue with a batch of these lenses...check the Canon website for info...they can be identified by part of the serial number.

I think the issue was when used vertically, wasn't it?

[poah]

a bright moon can be taken at suprising fast shutter speeds. best to use manual exposure to get the correct exposure

[havoc]

Gemm said:

havoc said:

There is a known issue with a batch of these lenses...check the Canon website for info...they can be identified by part of the serial number.

I think the issue was when used vertically, wasn't it?

Actually, yeah. Forgot that bit...

[robdickinson]

Dont test on the moon, could be any number of things.


Setup a test scene, use a tripod & mirror lockup, text with/without AF & at a range of appatures starting at wide open.

Also do a AF focus test with a focus chart (at 45 degrees), remembering that tele end will front focus a little.

[Podie]

I've found that at full extension, the lens can be a tad mushy… so I tend to back it off a touch and it seems to help.

[RobDickinson]

Podie said:

I've found that at full extension, the lens can be a tad mushy… so I tend to back it off a touch and it seems to help.

Theres a known fault at 300mm portrait it goes soft badly. Its known and canon will fix it. only on certain early examples.