Taking a trip with my 20D and very new 70-200 f4 - need advice

[wayne_huang3]

I just bought a new 70-200 for a trip to China. I'll be leaving in one

week and have not had time to thoroughly test the lens in real life

and controlled situations.

 

I've done some shots already just to test the capability of the lens

and have found that some of my shots are in focus while others are

not, even with a tripod. I always use center focus (lock zoom and

recompose).

 

I have not yet determined if this lens has front-focusing problems

that it's notoriously known for, but either way, I will be taking it

on this trip to find out.

 

My biggest concern is that if I rely on AF, I will only find out after

the trip what pictures were bad or good because I won't have access to

a computer.

 

Is there a sure fire way (even if this lens is faulty) to ensure all

my pictures focus as they are suppose to? MF is the obvious answer,

but what else can I do? I will have a tripod with no tripod collar and

a remote switch for the shutter.

 

Thanks a bunch \\

[thomas_sullivan]

"...I always use center focus (lock zoom and recompose)..."

 

It's pretty well documented on this site and on Canon's site under the tutorial section to NOT do that.

[pontus_lindqvist3]

The 9 focus points works perfect on mine, why stick to only one. You get the light metering all wrong by using one too unless you use exposure lock all the time.

[mrspock]

I find when photographing nature/wildlife that using the default 9- zone focus and metering causes focus problems, because the subject (let's say, a bird) is standing in water with reeds and plants behind it. They camera often gets fooled as to whether the subject is a rock in front of the bird, the bird, the water or the reeds behind the bird, so I was getting a lot of out of focus shots. I switched the camera to just use the single, center point, which seems to work better.

 

Are you suggesting that I should be sticking with the 9 zones or was that just a general comment?

[wingedrabbit]

Huh? I never heard of a problem using on focus point. What's the problem and where can I read about it.

 

The lightmetering isn't based on the focus point. I've always thought I was based on the center (that circle in the middle of the viewfinder) or the overall picture.

 

This is news to me.

[erin.e]

The Canon 70-200 f4 L is not notoriously renowned for a front focus problem, that is just internet inspired bullshit, that lens has a great reputation for being very sharp for a zoom lens. Most 'focus problems' with 'L' series lenses and other 'Pro' lenses are derived from poor photographer technique and arrogance in the belief that the lens must be at fault, instead them. This is one instance in where the tired old cliche is indeed appropriate "It is a poor workman who blames his tools"

 

You have an LCD on the back of your 20D plus the ability to magnify that image 10X so you will be able to see almost instantly if the image is sharp or not, one of the many advantages of digital photography.

 

A 200mm magnification lense is quite difficult to hold absolutely still and get consistent sharp images under all conditions, and a tripod would be a drag to lug around on a trip. High shutter speeds, good techique and use of any handy solid item to brace yourself or camera against will help to get some sharp pics on your trip, have fun!

[mrspock]

A follow-up question based on a comment from Erin about using the LCD to check the image.

 

I was recently at a wildlife refuge and ran into a fellow taking photos. The morning sun was to our backs so I was unable to see anything on my LCD screen. He had a bellows-style hood with a magnifying glass hung over his LCD screen. I see it advertised on hoodmanusa.com for about $35. He let me look thru the hood, and it was quite easy to see the image since the hood blocked the sun and the magnifying glass zoomed the image.

 

Has anyone on this forum used such a device, and if so, what did you think of it?

[Greg M]

Didn't you know Erin, the 70-200 f4L's all have front focusing problems, just like all 10D have back focus issues and all 100-400L lenses are soft at 400mm.....

 

If you hear a few(and I do mean a FEW) people say it enough times, don't you know that consititutes a reason for some to assume it's normal?

[phyrpowr]

If you focus lock, then zoom, you change the focus slightly, this is common in zoom lenses, no, I don't know why, I forgot

 

Also, if you don't have your auto focus set for "one shot" you can get focus changes, AI Servo will refocus, as it's designed to keep focus on moving objects., It can't tell that the subject isn't moving but the lens is

 

Use one shot, focus lock after zooming

[scott_milso]

Why not just choose ONE of the NINE focusing points, choose the correct focusing point and then you do not need to recompose.

[wayne_huang3]

"If you focus lock, then zoom, you change the focus slightly, this is common in zoom lenses, no, I don't know why, I forgot"

 

 

Sorry, I actually meant to say 'lock focus' not 'lock zoom'

[paul_chilton2]

Try this:

http://visual-vacations.com/Photography/focus-recompose_sucks.htm

[wayne_huang3]

The reason I would use one point as opposed to all nine is because the camera can't tell what I'm trying to focus on. Often I find that it focuses on an object that I did not intend to focus on.

 

If the camera could read our minds now that would be something else, but in the meantime I prefer to have selective control.

 

This technique of focus-locking/recomposing has worked fine for me on wider lenses, so I'm thinking that the problem is that it doesn't work well at telephoto range for whatever reason, that the margin for error is increased.

[cliff_shone1]

Wayne,

 

What happens when you center focus and don't move the camera. Are all your images in focus?

 

Have to confess, I frequently do the same as you for portraits. Focus on the eye and then recompose. There's not always time to select the best AF point I find. Can't say I had any consistant focusing problem.

[jim_larson1]

Finally someone posted the visual vacations link.

 

Focus recompose is typically only a problem when working at close distances with fast lenses. Unlikely to be an issue with a 70-200/4L.

 

When you say "focus", do you really mean out of focus as opposed to "not sharp due to motion blur"? Bear in mind that you generally want to shoot this lens at 1/120 to 1/250 as a minimum.

 

Also, bear in mind that the AF sensors on a 20D are MUCH larger than the engravings on the focus screen would lead you to believe.

[dogbert]

"You have an LCD on the back of your 20D plus the ability to magnify that image 10X so you will be able to see almost instantly if the image is sharp or not, one of the many advantages of digital photography."

 

I don't find the LCD a very good way at all to check for sharpness. Its resolution is way to low. It will show things that are obviously way off, but the resolution just isn't there to tell if there is slight misfocus or camera shake.

[steve_dunn2]

<cite>The lightmetering isn't based on the focus point. I've always thought I was based on the center (that circle in the middle of the viewfinder) or the overall picture.</cite>

 

<p>For partial or CWA, this is correct. As hinted at in the manual, evaluative metering takes into account the active AF point(s), so you will mess up evaluative metering by doing the focus-recompose-shoot dance unless you lock the exposure.</p>

[mormegil]

I've got an issue with Focus and Recompose sucking...

 

If you're using it at 200mm, at something 30 feet away, and recompose 5 inches, your new distance becomes 30.0029 feet. That's only a change of 0.034 inches.

 

Even at f/4, your depth of field is 1 foot.

 

So at this distance, focus and recompose would make a negligle difference in focus.

 

 

Secondly, I wonder if the correction of using an off-center focus sensor is worth the difference in focus accuracty of not using the cross-type sensor in the center (or is that only with f/2.8).

[jim_larson1]

<i>Secondly, I wonder if the correction of using an off-center focus sensor is worth the difference in focus accuracty of not using the cross-type sensor in the center (or is that only with f/2.8).</i><p>Yes, the "high precision" mode is only active with a F2.8 lens. Other than that, the cross type is merely sensative to both horizontal AND vertical contrast, where as all the other sensors are sensitive to horizontal OR veritical contrast.

[digitmstr]

>>front-focusing problems that it's notoriously known for<<

 

Says who? A few misguided people who have access to computers and the web?

 

First of all, front/back focusing is NOT a lens problem per se.

 

When ****real****, it is a calibration issue which *may* exist between a particular lens and a particular body. This could happen with any lens and any body.

 

Canon offers a calibration service for these cases. You can send ALL your lenses and ALL your bodies and they will all be calibrated.

 

But, truth be told, I have never had that problem with ANY EF lens or any EOS bodies I have ever owned so far (not a small number). NONE of my photographer friends have either.

[wayne_huang3]

<i>Wayne,

 

What happens when you center focus and don't move the camera. Are all your images in focus?

 

Have to confess, I frequently do the same as you for portraits. Focus on the eye and then recompose. There's not always time to select the best AF point I find. Can't say I had any consistant focusing problem.</i>

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What happens is that some are in focus and some are not. I should mention that I'm also using a 1.4x TC. Some were even shot at 1/500. Right now I'm suspecting it is my technique and that I'm being too critical since I've been looking at some of these at 100%.

[mormegil]

So is the center AF point more accurate than the others, even with a slower lens?

 

The other sensors only do either horizontal or vertical, while the center does both.