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Old Oct 6, 2006, 10:16 PM   #41
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Ok I tried the one shot on some surfing shots today and it worked well for a short sequence, shooting the surfer moving across, but not enough to get what I consider a complete sequence. I was able to refocus and continue but that put a noticable gap in the sequence. Shooting at an angle with the surfer moving towards you, in combination with the wave moving towards the shore, dropped the number of shots in the useful section of DOF down to around 2. Could probably get a few more depending on distance and aperture but I shoot wide open.

I can definitely see where it would be useful in situations where AI Servo was a problem but so far I have not had a problem with it. I'm doing mostly surfing and birds in flight and use it on both.


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Old Oct 7, 2006, 11:03 AM   #42
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The issue is two folds - and why you don't have a problem in AI-servo:

1. Your subject size is big enough to cover several AF points so the AI-servo algorithm can easily 'predict' where the subject will be when the mirror is up - Notice I say 'predict' because AI-servo does this between frames, several threads up, the poster did describe how it can have a mind on its own (and do not neccessary line up with any of the AF points)

2. You're also using a MrkII where the AF is much more precise - Most other posters use a xxD dSLR where the AF sensors are placed further apart unlike yours (or my) MrkII where a subject can transition smoothly from one AF point to another within its large 45 points array - There's a big gap between the 9 AF points on the xxD cameras and when a subject is small enough to not cover two AF areas, the camera usually have a difficult time figuring which one is the suject and which one is the background (especially when the background is more contrasty than the foreground smaller subject)

It's also a matter of shooting style: Some folks prefer to time and nail their shots others like to 'machine-gun' the frame. Whatever work again this was from a 10D, and the suject is coming straight in one-shot AF:








The problem is when the subject is small and can not cover multiples AF areas simultaneously that the AI-servo do not work well on an xxD camera (in one-shot AF):






I would definetly try both and see which one works best for you. The reason I prefer one-shot is that it's deterministic. The AI-servo IMO is just too unpredictable since it depends on so many variables: http://photonotes.org/other/ai-servo.html
(+ I'm a H/W kind guy :-))
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Old Oct 7, 2006, 2:01 PM   #43
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Try another backfocus/frontfocus test, since your first test was leading you to suspect that.

I use books myself. :-)

For example, when I got my 100mm f/2, I grabbed some of my wife's books off a shelf and set them up on a table. But, the ones in this example are a bit too reflective (which can fool some AF systems).

If the book in front of my target (middle book) was sharper, I'd have front focus (with that lens, at the focal legnth, in that lighting, using the focus point used, etc.).

If the book in back of my target were sharper, I'd have backfocus. The middle book looks fine, so the lens is fine in that lighting in this case (a quick AF test from last year of my Minolta 100mm f/2 on my KM Maxxum 5D):

http://www.pbase.com/jcockfield/imag...3/original.jpg


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Old Oct 7, 2006, 6:53 PM   #44
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Hi Guys,

Well after almost making myself bald I think I finally have a solution!!!! I have bought a new lens (identical) locally and will return the mail order one next week. After trying it out in the shop the results instantly were better and I have now been able to pop to the hockey field this afternoon to give it a quick once over before the 1st teams match tomorrow and guess what........??? It is spot on (well better than I was getting with the same lens (2 versions older) on the Konica Minolta which as far as I am concerned is FANTASTIC. I need to run a few more tests with the 1.4x telecon as this seems to be lowering the quality a little more than I expected (if anyone is using the Sigma 1.4x telecon with this lens please let me know the sort of differences you are getting to see if I am being too picky) but all it good again!!

Thanks for all your help and I'm really thankful that at last the saga is at the end....... or is it???

I have had 3 different bodies, 2 Sigma 17-70mm 2.8-4.5, 2 Sigma 70-200mm f2.8 and lost a lot of hair. The only problem is, the Sigma 17-70 is still back focusing, but I have tried a three of these (only 2 were mine) and getting the same problem so this could be an issue with the batch. Going to continue to investigate this.

Oh one more problem..... I played with the Sigma 120-300 today OOPS...... what a fantastic lens...... hmmmmmm what can I do to get one of those???? JohnG and others who own this baby you are very fortunate people!!!

Here is a shot from today which I am posting as I am sooooo happy that everything is working (OK so it is not my best work however I only took a few to make sure that everything was sorted). I will post some shots from the 1st team match tomorrow later in the week.

Happy shooting!!

Mark
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Old Oct 7, 2006, 11:16 PM   #45
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NHL wrote:
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It's also a matter of shooting style: Some folks prefer to time and nail their shots others like to 'machine-gun' the frame.
With all due respect - just because someone uses servo to capture several frames doesn't mean they are 'machine gunning' and incapable of 'nailing their shots'.

Birds don't blink like humans. They also don't run with incredibly akward leg motions. You also don't typically have other birds that get in a frame (like in sports where a stray arm can enter the frame - if you take only one shot - oops you couldn't predict that other person doing that).

So, burst shots are not just for those unskilled.

It's a little different when a bird is gliding and you have an entire second or 2 where it looks the exact same. Not so with capturing sports - especially sports with multiple players (i.e. opposing teams).

Most pro sports shooters tend to take short bursts - no spray and pray but 3-4 shots. As already pointed out - one focus lock is insufficient for the distances and apertures in play. Remember here - we're often talking 'sprint type runs' not marathons. So, thinking in terms of miles per hour is incorrect. You need to think in terms of 40-yard dash. A slow 40 time is 6 seconds. That's 120 feet in 6 seconds - or 20 feet per second. While a 3 shot burst of a bird gliding may all appear different - a 3 shot burst of a man running will not. And more often than not the man is running towards you (if your positioned right). Your method works for wildlife but we're talking sports here not wildlife. Or at least the original poster was. It has nothing to do with preference in sports shooting. Single shot is less effective because even the best shooters will want several shots and the subject WILL change focal plains during that time. So, for wildlife - yes - it probably is a matter of preference. But for sports it's really not. I haven't met a good sports shooter yet who doesn't use servo for the types of field sports Mark was referring to.


Forgot one thing - nailing the shot does indeed have it's place in sports - but it typically requires you to lock focus and track so when the split second arrives you don't have to wait for the focus. Which again when your subject is coming towards you at a fast rate requires Servo.
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Old Oct 8, 2006, 4:14 AM   #46
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I agree John! When shooting a hockey match I have 2 goals (not literally, I would get in the way of play if I was trying to score as well and don't think the camera would like getting hit by the ball!!).

First goal is a shot that will be published in a local paper, now usually this is a celebration shot or the goal being scored (very difficult with the size of the ballin hockey), and occasionally like last week they chose a piece of action with our guy going around one of the opposition.

Second goal is to get shots that players and fans will buy so for these I get both action shots with just the player, the player and opposition and also quite close shots of the players with head and torso in the frame.

Another think when shooting sport is to get that shot that happens in a split second such as a foul or a fall. If not shooting in AI Servo and in a burstthis would not be possible as you would lose the moment as the event unfolds and possibly get just the first portion and not the rest of it.

There is a time anda place for all modes and yes as sports shooters we do try to nail a shot, but as I found out to my cost recently at a car event where I missed a few cars multiple images are essential just in case you don't manage to nail it with a single frame.

If Pro's were nailing shots buy just shooting a single frame, why would Canon and Nikon for a long time have been producing cameras with high frame rates and since the digital age always looking for longer bursts? OK so lets say I can take a burst of 30+ (not sure what it is in real life but at least 30) do I take those in one hit? No, but when taking a short burst then seeing something interesting happen I don't want my buffer to be full and miss the best bit of action all day. There are times when you want to follow a player as they go around a lot, also when I am trying to get the keeper making a save that I use more than just a short burst. With the keeper I have them framed quite tight so can't see all the action so just stick with it until the shot is taken (sometimes I will shoot with both eyes open to get a 'global' view, but it just depends.

So for those who are budding sports photographers reading this, don't be put off thinking you are not good if you take loads of shots, initially this will help you to see which angles work and which don't etc but always leave some shots in the bag so when something happens you can capture them.

Mark
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Old Oct 8, 2006, 7:15 AM   #47
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JohnG

Sorry about that my intend was never to mean you guys are incapable but just a style of shooting - In my case anyway with small subjects the camera just dither and more often than not I'll get the background in AI-servo

This is the kind of subject I'm talking about (i.e. doesn't fill the frame or cover several AF points on xxD)... and as you know these guys don't glide in a straight path, but zig-zag through the busy weeds on a dime, and they are so fast even a flash burst can't freeze them!







... but I think we are diverging into sport/wildlife :-)

What I try to stress on my posts are the differences between one-shot AF and AI-servo. One-shot AF focus and stop which is what everyone should do when testing for front/back focus (also on tripod and in good light). AI-servo 'predict' hence the focus may not be spot on if movement is involved - Now if you're steady enough on a long zoom (or on a tripod) then the results should be the same, but most often people test their lens on AI-servo without one and if you can hear the AF mechanism is still continuously adjusting in AI-servo before the shutter is released then the results are in doubt!

-> I also stress on subject size which is also very critical - Try to focus on the football 'in-flight' instead of the players for example, it's totally different... the AF sensor can sometime be bigger (or straddle) the subject on the xxD and you can also have front/back focus issue
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