Infinity Focus with Telephotos.


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Jed

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#1
Following this discussion in another thread and several people saying that to shoot a fast moving subject in the distance, you can just prefocus on infinity, and my insistence otherwise and several people disagreeing, I took a few shots in between overs at the Durham v Glamorgan game this afternoon. Don't worry, you're not meant to understand that. About the only person with a decent chance would be Ian *wink*

This is the full frame version of the shot:


Shot details:
400mm lens, 1.5x focal length multiplier, f5.6
Identical levels adjustment and unsharp masking applied to all the crops. Sorry for the levels of grain involved, light wasn't great and I was shooting with a fairly high EI.


This shot was taken with visual focus through the viewfinder on the power cables/structure in the distance.


This shot was taken with visual focus through the viewfinder on the tree immediately to the right of the power cables/structure in the distance. By my estimation this was about 3-400m or so away from the camera.


This shot was taken with visual focus through the viewfinder on the light coloured tree that's in focus. By my estimation this was about 250-300m away from the camera.


This shot was taken with the lens preset as close as possible to the infinity marking on the lens barrel. Bearing in mind that lenses expand and contract, the temperature was about 20 degrees and the sun was out.

Now, from close comparison, the following is apparent to me.

[1] Focus is different in all four pictures. Look carefully, even between 1, 2 and 4. 1 is farthest out, 4 seems to be between 1 and 2, and 2 is the closest (obviously 3 is closer).
[2] This is all already virtually infinity. The closest tree was at least a good 250m away.
[3] A 1mm turn of the focusing ring either side of infinity completely throws the focus off that point.
[4] Focus at "infinity" on the barrel did not result in the sharpest picture of the furthest object.
[5] An F16 shot to the same composition as Mylau's shot would have been about the distance of the mid-distance in the overall shot that I've displayed here (look at the size of the people in the crowd as reference). Considering they are nearer than the nearest tree, it should be clear that accurate focusing is needed. See how out of focus the nearest tree looks in the picture with the focus furthest away.

Bottom line, infinity focus doesn't work for a lot of stuff once you hit reasonable telephoto range. Or you stop down a stupid amount. In the case of Mylau's picture, infinity focus would not have worked.
 

Jed

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#3
Originally posted by StreetShooter
Ah, but with a Canon EOS 1D, an L zoom and AI autofocus, that's a different story.
No no you're wrong there. You need an EOS 1D, an L zoom, and USM autofocus for it to be a different story.
 

Goondu

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#4
Originally posted by Jed
Following this discussion in another thread and several people saying that to shoot a fast moving subject in the distance, you can just prefocus on infinity, and my insistence otherwise and several people disagreeing, I took a few shots in between overs at the Durham v Glamorgan game this afternoon. Don't worry, you're not meant to understand that. About the only person with a decent chance would be Ian *wink* ....

Hey, I used to watch cricket games, especially the one day series. :p

(Sorry, for being OT) :D
 

Jed

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#5
Originally posted by Goondu


Hey, I used to watch cricket games, especially the one day series. :p

(Sorry, for being OT) :D
Heh, ye of the great fortune. This one was pretty dire.
 

Jed

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#7
Not if I can help it! I shot some of the One Day games earlier in the summer. I hate the four day game, too little happens from the photographic standpoint. First match was during the Commonwealth Games so that took precedence. Second match was over the last few days, over which I shot one Nick Barmby press conference, Man Utd v Boca, Bradford v Wolves, and one Falcons media day. So it's not like I haven't been busy, and ultimately, the football is a bigger money earner than the cricket.

However the next one's at Headingley so I might well have to do the first two days. Sat and Sun will definitely be reserved for the footy.
 

Ian

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#8
Originally posted by Jed
I took a few shots in between overs at the Durham v Glamorgan game this afternoon. Don't worry, you're not meant to understand that. About the only person with a decent chance would be Ian *wink*
Gee thanks mate! After Meelup I'll take a few days at the cricket anyday as it beats sheltering (ok drowning) under trees while trying to work in torrential rain sans lens capes.

Speaking of cricket .. looks like I'm going to have the choice this year, cricket or lawn bowls ... oh what a decision!
 

Jed

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#9
Yeah well I managed to not do a single session of lawn bowls at the recently concluded Games.

But speaking of the third Test, my office rung me this afternoon and sure enough I'm down to do Thurs, Fri, Sun and Mon... apparently there's no footy worth shouting about on the Sunday.

Foiled!
 

nhyone

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#10
Originally posted by Jed
Bottom line, infinity focus doesn't work for a lot of stuff once you hit reasonable telephoto range.
I appreciate your testing very much. I have a 70-210/4 where infinity is really infinity. One day, I told my friend to just focus at infinity for his 80-200/2.8 lens.. guess what the result is? ;)

But.. I still haven't learnt my lesson. Recently I shot my 135/2.8 at infinity. No prizes for guessing the result.

However, one thing you are not clear in your post: do you mean,
1. infinity as far as the focusing ring can turn? I presume most telephotos are able to focus past infinity.

2. infinity as in, where in infinity mark, since the symbol is so big.

3. the subject is between the last focusing mark and infinity.
 

Jed

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#11
By infinity, I mean exactly what I say. I.e. infinity. The added focus area beyond infinity (note, *beyond* infinity) is to compensate for when extreme temperatures cause the dimensions of a lens to change and hence the focus might need to be shifted beyond infinity to be able to focus at infinity. However at any given point in time, infinity is still infinity, if you get what I mean. Which is why I quoted my estimated temperature and weather conditions.
 

Ian

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#12
Originally posted by Jed
Yeah well I managed to not do a single session of lawn bowls at the recently concluded Games.

But speaking of the third Test, my office rung me this afternoon and sure enough I'm down to do Thurs, Fri, Sun and Mon... apparently there's no footy worth shouting about on the Sunday.

Foiled!
Isn't that fun (not) ... Hehe time to take up "bird" watching in the stands mate.
 

Jed

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#13
Yeah, we're into the middle of August, and summer's finally here... whoever invented the sun and heat (well, 27 degrees heat anyway) should be given a medal... I tell you there was some *serious* jail bait this afternoon, and there'll be more tomorrow in Glasgow. Now all I need to do is keep eyes on the road...
 

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