EF-S 70-300mm

[peelie]

EF-S 70-300mm f/4.5-5.5. DO IS USM lens with 50D.
When I photograph flying prop aircraft I have the shutter speed set at 350.
When panning with finger ready on the shutter release button, I press the button and starting shooting sometimes the auto focus goes down to zero and I get a blurred blob of picture.
Any suggestion as to what I am doing wrong or does the lens need looking at.
Tks Peelie

[colin C]

Re: EF-S 70-300mm

A few thinks spring to mind Peelie.

First, 1/350sec is just a little too fast for prop aircraft as you will only get a tiny bit of blur at that speed. I try to start at 1/250sec to make sure I have some keepers, then gradually bring the speed down to 1/200s, 1/160s, 1/125s and 1/100s. Every time a new prop aircraft does its display, I go back to 1/250sec and work down again.

I assume you are on A1 Servo, but are you on centre spot focus point only? The centre spot is the strongest of the focus points and the one to use for panning cars, planes etc. Multiple points will do the job, but if they latch onto anything closer, they will try to lock on to that and that is the most likely cause of your blur. As long as you use the centre spot and keep it locked on to the subject, A1 Servo will keep tracking and you should get sharp shots.

I can't think of any problem with the lens that would cause that, so subject to any thoughts from other members, I would rule out a lens problem.

Colin

[peelie]

Re: EF-S 70-300mm

Colin
First of all the shutter speed unfortunately a Stroke made it difficult to work any lower than 350 for flying shots but I will work on it..
Second I was using A1 Servo and now I will make sure I am using centre spot next weekend at Dux.
Tks Peelie