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canon 1dmk+300 2.8 focusing

sjk123 11 286 England
3 Apr 2013 5:38PM
i have noticed that when i have this set up the focusing on my mark 4 twitches back and forth .
is this normal or do i need to send the lens +camera to canon ?
set up is AI servo 300 2.8 cmk4.. some times with the converters on same thing
used resting on a window or bean bag ... not tripod...
single AF point with surrounding .
And i have moved the tracking to slow and to fast does the same .
IS on IS off same thing happens

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3 Apr 2013 6:13PM
It might be a daft question but have you got what ever it is you are focusing on within the lens range, and has the target got contrast
sjk123 11 286 England
3 Apr 2013 6:43PM
not a daft question at all .
if you look at the pic i just up loaded it was taken with this set up .
for a static subject it should lock on.
the lens seems to focus on the subject and then flicker . i get 3-4 in focus out of 10.
it has the same effect in good sun light
the subject was about 20m 25m away.
3 Apr 2013 7:04PM
Its clearly not focus limiter or MFD then

My suspicions are two fold, if you look on DPP and ask where the focus point is, it may be that its on a planer green area, ie there isn't much contrast

The second thought is that you are using AI servo for a static subject, that can be a lot more fickle than one shot
tomcat 12 6.4k 15 United Kingdom
3 Apr 2013 7:22PM
Whatever the issue, your two Green Woodpecker uploads are as good as it could get from that distance, especially with the 2X TC on

sjk123 11 286 England
3 Apr 2013 7:32PM
your right in what saying i don't disagree with you .
but they are one out of 5-6 shots taken at the same time . all the rest are out of focus . and if i hold down the shutter button to take the shot it flickers .
it is fine if i put my 70-200 on with converter 1.4x and 2x .
and if use the 300 with my 5dmk3 its also fine .
sjk123 11 286 England
3 Apr 2013 7:57PM
here is a pic focus point was on his head .d08e0338.jpg

tomcat 12 6.4k 15 United Kingdom
3 Apr 2013 8:05PM
Are you sure the IS is off - Number 0

I personally do not agree with the Servo being on

Giving the camera to much to do and have you checked the Servo settings
Is it set for first shot and then continuous on the same focal point, or set to pick up the next moving object after the first shot

I perhaps have not worded that correctly, but a look in the book should explainWink


Post edit - Green Woodies are very skittish birds - he could just have been moving slightly - the head is in the air, on alert - the Servo won't pick that up
3 Apr 2013 8:14PM
Could I suggest that you try taking the same shot, possibly using a tin can, and then try one shot focus mode, and if the results are the same you could try cleaning the contact points on the lens, it could be a slightly poor electrical connection
Luxin 4 7
3 Apr 2013 8:53PM
When I got my EOS 60D I had some focus problems (Sigma 120-400) especially when backgrounds are grass, plants, trees and so on nearby to subject. I tried all sorts... then it struck me "Focus Assist Lamp"! The image focussing sensor was trying to get locked on to the subject but the "FA Beam" was hitting all sorts of other obstacles, at all sorts of ranges. Went into menu > Focus Assist... turned it off and no problem since... apart from when critter hide amongs branches, then you use manual if you have time!

Many cameras and lens combos have either "Forward Focus" or "Back Focus" problems too, in which case you can get new kit calibrated under warrenty. Your problem though sounds like Focus Assist to me.

tomcat 12 6.4k 15 United Kingdom
3 Apr 2013 9:08PM
Are you using continuous shooting

One out of six would be a good returnWink
Luxin 4 7
3 Apr 2013 9:49PM
Hi Tomcat.
Yes, often. I find that on my 60D with the "Bigma" 120-400 the focus is pretty quick, quiet and locks on quite well. Usually I only fire off about two to four frames as the best actions happen; e.g. bird dives, turns towards you, flaps wings, etc,.

Are you using Av? If you use Av for wildlife, with wides aperture, then your DoF will be narrow, but set the focus for "Centre spot" only and learn to get that little red square dead on the target and you should find you get a few more sharp ones; providing you are not jerking the camera - keeps left elbow agianst chest, hold breath, squeeze button gently, etc,. I'm sure yo know this already! I get about 1 out of 3 that are usable, sometimes about 4/5 out of 6/7, depending on the subject. You will always get some that the focus can't keep up with, or some slightly blurred.

Technique and timing are crucial. Try leaning against a tree, support camera on hide ledge (but don't rest it on the focus wheel as you may damage the motor if theis moves when AF is used!) or sit on the floot and rest arm across knees, if subject is low. Elbow to chest, the "triangle" shaped fram is always good.

Hope this helps with the AF Light "off" suggestion. Let me know.
sjk123 11 286 England
3 Apr 2013 10:03PM
Hi .
I don't have a problem with focusing . It picks up the subject with no problems at first .
But then start flickering in and out .
It's like it can't lock on . I know it's a prime lens but it acts like a zoom lens zooming in and out .
I use manual some times and set the iso to set it self unless its a really good day . And then I use AV
With the pic above the IS was on . But have taken some with it off with the same settings . Same problem .

Luxin 4 7
3 Apr 2013 10:20PM
As I said above, have you checked the Focus Assist lamp?
(see my 1st post)
sjk123 11 286 England
3 Apr 2013 10:26PM
Sorry do you mean the AF assist beam . Just looked in the manual .
Can't seem to find focus assist lamp

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