Focus preset on canon 300L Q?
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CT
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Are we talking about the 300 2.8L IS?
If so the answer is no - it wont have any effect. For it to work you have to set it to 'ON' then focus on an area where you anticipate some action taking place. You then press the little round 'SET' button adjacent to the 'ON' button. This memorises that focus position.
You're now free to use the lens and focus on any area and take shots where you see action taking place. If you then see some action taking place at your memorised position all you need to do is give a slight twist of the large knurled ring near the front of the lens. It turns clockwise looking from the back of the lens. It instantly recalls your previous focus position very accurately.
I use it quite a bit when I have birds landing at two different locations.
All the Canon super telephotos work in the same way.
If so the answer is no - it wont have any effect. For it to work you have to set it to 'ON' then focus on an area where you anticipate some action taking place. You then press the little round 'SET' button adjacent to the 'ON' button. This memorises that focus position.
You're now free to use the lens and focus on any area and take shots where you see action taking place. If you then see some action taking place at your memorised position all you need to do is give a slight twist of the large knurled ring near the front of the lens. It turns clockwise looking from the back of the lens. It instantly recalls your previous focus position very accurately.
I use it quite a bit when I have birds landing at two different locations.
All the Canon super telephotos work in the same way.
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KIPAX
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Cheers CT and yes I am talking that lens.. I noticed it was at the ON position today.. No idea how long its been there. I check I ahvent slipped into IS a lot but thats all.. hmm well less now as I know the sound and feel of IS is a bit clunky 
I did google focus preset and it used birds as an example of how to use it... I just wasnt sure if it was hunting a stored.....well anyways just wanted to make sure.. Now I dont need to worry about it being ON accidently.
Ta
I did google focus preset and it used birds as an example of how to use it... I just wasnt sure if it was hunting a stored.....well anyways just wanted to make sure.. Now I dont need to worry about it being ON accidently.
Ta
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KIPAX
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Mines only off the monopod to transport.. to be honest focus is so fast with this lens and the mkIII that it would be quicker focusing than using a preset.. hmm I suppose dim light that may require a focus hunt then its usable..I gues sit must ahve its uses but not much in sport
CT
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I'd have thought it might be handy for you to pre focus on say a goal area? Mind you by the time you've twisted the ring, you could probably refocus anyway.
I can't say I've had occasion to use any of the 4 focus lock/stop buttons at all.They seem to be too far forward on the lens anyway for convenient reach.
I can't say I've had occasion to use any of the 4 focus lock/stop buttons at all.They seem to be too far forward on the lens anyway for convenient reach.