300 2.8 question

I have just taken delivery of a 300 2.8 IS lens. I am using it with my 30D. First test shots were sharp as a tack and everything seems ok. However on my latest outing I noticed it seemed to be struggling to focus on things at infinity. It would either hunt and miss focus or focus on the backgroud.
Is it more likely to be an issue with the camera focus system than the lens? Is the 30D up to the task of focusing the 300 2.8 ok?
Any advice appreciated.

The 300 f2.8 IS is an amazing lens in both IQ and AF. I used one recently on both a 20D and 40D and the AF was flawless. When you say the lens is struggling to focus on things at infinity, what exactly are you shooting? And how small is the subject? And what AF setting are you using? Of all the lenses possible to use, the 300 should be right at the top of the pack in both IQ and AF accuracy/speed.

What is the background for an object at infinity? It's most likely down to the contrast of whatever you had your focus point over. The AF works on contrast and if your focus point is over a bit of pure blue sky, or featureless cloud, or similar, then regardless of light levels it will struggle to focus.

LightRules wrote in post #5272110
The 300 f2.8 IS is an amazing lens in both IQ and AF. I used one recently on both a 20D and 40D and the AF was flawless. When you say the lens is struggling to focus on things at infinity, what exactly are you shooting? And how small is the subject? And what AF setting are you using? Of all the lenses possible to use, the 300 should be right at the top of the pack in both IQ and AF accuracy/speed.

Madweasel wrote in post #5272115
What is the background for an object at infinity? It's most likely down to the contrast of whatever you had your focus point over. The AF works on contrast and if your focus point is over a bit of pure blue sky, or featureless cloud, or similar, then regardless of light levels it will struggle to focus.

I was shooting a Buzzard which was on a fence post @ 40M against a blanket of sunlit green firs the second time it struggled was on a pheasant at around 15-20M on grass in bright sun the third was a small sparrow sized bird backlit on a fence post at around 12M. When it focuses it is sharp as a tack. Perhaps I have judged it on difficult situations but i thought it should have picked the pheasant up easily.
I will post pics tomorrow for you to judge. Thanks for your replys.

Strange, I can't recall what you described ever happening on either of my cameras.

Good luck in sorting it out.

A buzzard at 40M is not a large target. Relying on one of the AF points to lock on is very iffy. Use MF for birds.

Centre point focus only, and if it still misses, you need to work on your tracking.

Its with a collegue just now who has extensive experience with the lens so He will let me know fairly soon if all is well.....or if I need to sort myself out

Did you change one of the three distance length focus settings ?

I think it will be down to you somehow

Light will impact a lot ... notice in some light or specific times of day contrast is reduced and AF can be more difficult, same with certain subjects and their interrelationship with existing light> Things are as they are in specific light. A Phesant in bright mid day light is very different to one during the golden hour early morning. Try it in ideal conditions and if is Ok then probably just lack of contrast at a specific time.

Palladium wrote in post #5272943
Did you change one of the three distance length focus settings ?

I tried it on a few settings but with no considered logic other than making sure everything worked. I will run through this part again.

malla1962 wrote in post #5273018
I think it will be down to you somehow

Oh I hope so. A red face only lasts so long. My lens on the other hand I have saved up for an eternity to get it. Just want to make sure it's 100%

County Man wrote in post #5273117
Oh I hope so. A red face only lasts so long. My lens on the other hand I have saved up for an eternity to get it. Just want to make sure it's 100%

im sure things will be ok in the end.I have used mine on 20d,30d,40d,1dmk2,and 1dsmk2 with no problems at all.

Enjoy your lens - it's a Pleasure to use