Sharpness test for the Canon 70-200 f2.8L

Gary.D

Gary.D

Hoodie
Messages
2,499
Name
Gary Derbridge
Edit My Images
Yes
I have just recieved this lens and want to make sure it is as sharp as it should be.
Pic is straight off the camera.

1/500
f8.0
iso: 1600

IMG_7467normal.jpg


100% crop

IMG_7467crop.jpg


Thanks
 
I've got the IS version on a 40d, and even at f/2.8 I get shots consistently sharper than the one you posted. Might be worth taking a few other shots, maybe on a tripod if you haven't done so already, one image alone won't be a good test.
 
I dont think you can really test sharpness at iso 1600
 
If you want to test it you need to test it properly.

You need a proper test chart which you can download and print. Then mount the camera and lens on a tripod and turn off the IS. Take your shots with the lens autofocussed on the target point and again manually focussed on the target point.

This is how you determine whether you have a back focus issue. Don't forget also that the anti aliasing filter over your sensor will cause softening and you will need to work out the best sharpening settings to use.

And the ISO 1600 won't help :)

Hope that helps. :)
 
A lot of physics that make your piccie blurred :)

Basically it is a filter that removes those signals that are outwith the range of the sensor. The net effect is that the removal makes the images look a bit soft. If those signals were left in and got to the sensor they would result in artefacts. Different cameras use differing amounts of ani aliasing which is why I ran some 100% crops with different sharpening techniques until I found which one suited my cameras the best. I use a combination of Nik filters and actions for mine now.

http://en.wikipedia.org/wiki/Anti-aliasing
 
Read post No5 :)

Tripod mount the camera and turn off the IS and focus using autofocus and manual at a spot in the middle of the chart. Download and compare. Don't forget you will need to sharpen the images too. :)
 
You need to establish the focus point so if you are focussing on a number 5 do it on autofocus and again on manual (is switched off) and sharpen them.

Just had a look at the patterns, hold off a mo, I'll find the one you need first. :)

Then post them for us :)
 
Ok have a look 3/4 of the way down this page for a proper chart with numbers on it.

The ones Byker posted are for microadjustment which is available on some newer DSLR's

http://www.focustestchart.com/chart.html

Have a read at the whole article for a good explanation of what you need to do to check it properly. :) It micght say Nikon D70 on the page but it's the same technique for any DSLR

Hope that helps and your lens is good :)
 
Before you go and batter your head with test charts, go and take some more shots at ISO 100 and a decent shutter speed.
 
I would be very surprised if a new Canon L lens was anything but perfect, but if you want to make sure there are two things to check - is it a 'good copy' and is the AF properly calibrated? Neither is hard to test, and you don't need any special targets to do it with - just the opposite I would say.

Taking a one-off shot and posting it in isolation is pretty meaningless TBH. If you want to do that, the only way is to shoot an identical image, processed identically, from a known good lens. Otherwise you have no reference and the test really means nothing. And looking at the centre of the frame at f/8 is also a poor test - any lens will be sharp in that situation, unless it's been dropped.

To check if you have a good copy, select a distant target to minimise focusing errors, like a car number plate or road sign. Tripod, mirror up, mid-range focal length, lowest f/number (ie f/2.8), and the highest shutter speed you can get. Increase the ISO as necessary - a bit of noise won't hurt for this.

Set the exposure and using live view, focus the target in the centre of the frame. Lock everything on manual so that nothing can change, and take four pictures with the target in all four corners of the frame. Do this quickly so that the light doesn't change; if it does, it will throw the whole test. Look at them on the LCD on max magnification to see if all four images are equally sharp. You are not looking to superb quality, which you probably won't find, but only that all four corners are the same.

What you're looking for is to see if every lens element (and there are a lot of them in your lens) is correctly centred, which is by far the most common problem, even if it's unlikely with a new Canon L. A good lens will always pass this test.

Don't use that focus test with an A4 sheet of paper at 45 degs. It is technically flawed, at least when used with some types of AF and some lenses, it is extremely critical, and highly prone to user error. It is also unnecessary and confusing.

I use three cerial packets lined up side by side, and shot at a sensible distance. It must be at least 50x the focal length of the lens to be relevant and meaningful. Set the packets side by side and exactly in line, angle one of them towards the camera by a few cms, and the other slightly away. I also get a 1ft ruler and prop it up beside the middle packet, with the top just behind the front face of the target, and the bottom just in front by a few cms.

Set the camera on a tripod, absolutely square to the target, mid-range focal length, lowest f/number, highest shutter speed, and again increase the ISO as necessary to get it. Set the focus to infinity, then autofocus the target and take a shot. Do the same again. And again.

Chimp the images on the LCD. Chimp one of the images on max magnification and scroll up and down the ruler. You will see it going in and out of focus as the depth of field fades, and of course the sharpest point should be exactly in line with the face of the target. The same effect will also be seen on the faces of the two angled packets. All three images should be identical.

I'm sorry if these tests seem a bit crude and unscientific. Actually, they are neither and you really don't need or want pseudo-scientific test charts. This is real world, relevant, and if there is anything wrong these checks will certainly find it.

Good luck :)
 
HoppyUK said:
To check if you have a good copy .....

..... if there is anything wrong these checks will certainly find it.
Click to expand...
This should be a sticky. Preferably with pictures of the cereal box setup, and ideally with some example results (good and bad).
 
HoppyUK said:
IDon't use that focus test with an A4 sheet of paper at 45 degs. It is technically flawed, at least when used with some types of AF and some lenses, it is extremely critical, and highly prone to user error. It is also unnecessary and confusing.

I'm sorry if these tests seem a bit crude and unscientific. Actually, they are neither and you really don't need or want pseudo-scientific test charts. This is real world, relevant, and if there is anything wrong these checks will certainly find it.

Good luck :)
Click to expand...

Come on then Hoppy, that link I posted explained exactly why it is NOT technically flawed, the least you can do is elaborate on why you think it is, being the standard method of testing as well.
 
The test chart is often cited as flawed because the AF points aren't necessarily exactly where the little blob in the viewfinder is. That said I've used them successfully myself.
 
HoppyUK said:
Don't use that focus test with an A4 sheet of paper at 45 degs. It is technically flawed, at least when used with some types of AF and some lenses, it is extremely critical, and highly prone to user error. It is also unnecessary and confusing.
Click to expand...
AliB said:
Come on then Hoppy, that link I posted explained exactly why it is NOT technically flawed, the least you can do is elaborate on why you think it is, being the standard method of testing as well.
Click to expand...
I'm not qualified to comment on whether it is technically flawed. However, I will agree that it is extremely prone to user error. And I'll add two more issues with it:
- it's of questionable relevance, since it's testing the focus at or near the minimum focus distance
- it can't be used with many telephoto lenses, because their minimum focus distances make it impossible to achieve a practical test setup.
 
I found short distance calibration on a long lens to be useless.. I tested my 300 at reasonably close and the pictures looked great.. very happy... But at long distance (full length of a football pitch) it was clearly uncalibrated... I made the micro adjustments on my mkIII and the long distance became perfect... it didnt (to my naked eye) make any difference to the closer pics..
 
AliB said:
Come on then Hoppy, that link I posted explained exactly why it is NOT technically flawed, the least you can do is elaborate on why you think it is, being the standard method of testing as well.
Click to expand...

Most people have already said it already, and yes, the author does go on at some length to justify his test against the waves of protest he's received. And of course he has a position to protect ;) I know that it drives them mad in camera service departments when they get lenses returned for calibration, which are within tolerance and perfectly acceptable in normal use, and then the customer is upset as they get a bill for nothing plus a load of frustration and aggro.

The problems I have with it are because it is shot at 45 degrees (not square on) and at very close distance.

TBH, I don't have a big problem with it being at 45 degs. Not ideal, and it's only done so that you can read off the distance directly very easily, so that is a poor compromise for a start. The theory is that AF points are active over a much larger area than appears in the viewinder, and a larger area than the focus line on the target. There is also some mumbling about the orientation of some focus arrays, but I'm not sure it makes any difference in practise. I haven't found it so, but then I've only checked a couple of different cameras, both Canons.

Now the close distance. Unless you have a macro lens, why would you want to shoot that close? More importantly, lenses are analogue devices - they are not perfectly calibrated to meticulous accuracy over a vast range, they are calibrated to optimum accuracy over more common distances, and they are also calibrated within a tolerance. When the lens gets within that tolerance, it doesn't try any harder to nail perfect focus; if it did, it would hunt and shunt about and be very much slower. Lenses are also often different in this respect, depending on maximum aperture and how much fine movement they have in the focusing helicoids at close range. Only macros are built with this kind of fine accuracy in mind.

Zooms are subject to tolerance over their focal length range, and if you self-calibrate a zoom to focus perfectly at one focal legnth and very close distance, it will quite likely be out both at longer distances, where you actually need it to be spot on, and also at different focal lengths. The web has plenty of examples of this happening, and I've read it on here a few times. Again, all lenses are different in this respect and I guess it is reasonale to assume that a Canon L will be better overall than a cheap mega zoom, but the chart takes no account of that.

User error. When you look at the chart, depth of field is only a few mm. In practice, it is extremely difficult to work to that level of accuracy. Don't ask me why, if you're careful and know what you're doing, but feedback from folks who have done that test, and been disappointed, shows that more often than not they have got it wrong and actually the kit is fine. StewartR can vouch for this, as I guess a lot of people will check out his hire lenses with that chart and tell him they are duff, when they are obviously not.

But my question would simply be, why use a small chart like that, which is so prone to errors, variables and irrelevances, when all you need to do a proper test is three cerial packets and a ruler in the kitchen? The benefit of that test (intellectual copyright HoppyUK :D ) is primarily in that it is shot at a reasonable distance - about the same range as you might shoot a portrait, and therefore within the range that you want, and would also reasonably expect the lens to handle perfectly. The other thing is that the target is flat, and much larger than the AF point, with lots of easy detail for the system to lock on to. Even so, I would not use the cerials packets test, as I've described it here, for wide angles. You would have to move too close and field curvature at least is a concern. It could be modified though.

I will try to find a link to the instructions that Canon issues for self-calibration of lenses, which are broadly similar to the method I've described. The key aspect that they stipulate is, I think, that any tests should be done from a distance of at least 50x focal length.
 
Further to my post #25 above, here is how Canon suggests you set up to check focus micro adjustment. It is by Chuck Westfall, and although he says it is unofficial, since he is Canon's chief technical guru and knows absolutely everything there is to know about how these things work, and there isn't actually an official version, I guess we should listen to him.

It is taken from here http://www.digitaljournalist.org/issue0812/tech-tips.html
and if you click the link, and that is highly recommended, you will see he also adds some explanation and also caution about why you should not shoot close targets, that are not square to the camera, or expect your zoom lens to be perfect at all focal lengths. Well, there's a thing. He fails to mention cerial packets, but then perhaps he skips breakfast :D

1. Mount the camera to a sturdy tripod.
2. Position a reference target for the camera to focus on. The reference target should have sufficient contrast for the AF system to read, should be flat and parallel to the camera's focal plane, and should be centered with respect to the picture area.
3. Lighting should be bright and even.
4.Camera-to-subject distance should be no less than 50 times the focal length of the lens. For a 50mm lens, that would be at least 2.5 meters, or approximately 8.2 feet.
5. Set the lens for AF and the camera for One-Shot AF, and manually select the center focusing point.
6. Shoot at the maximum aperture of the lens via manual mode or aperture-priority AE, and adjust the exposure level if necessary to achieve an accurate exposure of the reference target. Use a low ISO setting to reduce noise.
7. If the lens has an image stabilizer, shut it off.
8. Use a remote switch and/or the camera's self-timer to release the shutter. Use mirror lock as well.
9. Take three sets of images at microadjustment settings of -5, 0 and +5, i.e, three consecutive images at -5, three consecutive images at 0, and three consecutive images at +5.
10. Examine the resulting images on your computer monitor at 100% pixel magnification.
11. Take additional sets of test images at different microadjustment settings if necessary until the sharpest image is achieved.
12. Register the corresponding microadjustment settings in the camera.
 
Yes, and I still do. I have read so many conflicting reports but coming from a scientific background I'm far more tempted by a proper scale than some cereal boxes. :)

Although I have to admit to never having tested a lens in anger. As far as I'm concerned I do tend to agree with you in that they either work or they don't.

Yes I'm well aware I have just contradicted myself. :)
 
AliB said:
Yes, and I still do. I have read so many conflicting reports but coming from a scientific background I'm far more tempted by a proper scale than some cereal boxes. :)

Although I have to admit to never having tested a lens in anger. As far as I'm concerned I do tend to agree with you in that they either work or they don't.

Yes I'm well aware I have just contradicted myself. :)
Click to expand...

Ali, yes it would be nice if instead of cerial packets, I had used the vastly expensive ISO 12233 resolution test targets, mounted on titanium stands, laser aligned and plane parallel to the camera, set on a spirit levelled granite slab, illuminated by colour certified halogen lamps, and so on. A white lab coat would also look nice, but none of it wouldn't make a blind bit of difference.

What is important is a sound understanding of what the camera is trying to do, in the context of real field photography, and then devising a relevant test to see how well it performs. I would rather be approximately right, than be precisely wrong.

How to really get it wrong is demonstrated at www.the-digital-picture.com which is a massively popular lens review site. Here is a quote from their test set up procedure:

"The camera is mounted on a very expensive (and very nice) Arca-Swiss C1 Cube geared head which is mounted on an 145 lb (65.8 kg) Bogen / Manfrotto 809 Salon 230 Camera Stand. The camera stand is positioned on a custom designed, perfectly level, specially painted, 6" (152mm) thick concrete floor. The camera/lens is multiple-laser-aligned to the target which is mounted on 60" (1524mm) square, 1/2" thick glass. Focus assist lighting is from 2 Solux continuous lights. Primary light is provided by 4 Canon 580ex II Speedlites."

But unfortunately, the lens test itself is fundamentally flawed and despite huge amounts of fancy window dressing, the results are often plain garbage.

Check out their tests of the Canon 17-55 2.8 vs 18-55 IS kit lens, and then the Canon 70-200L 4 vs 70-200L 4 IS, and then 50L 1.2 vs 50 1.8. The test chart images, which they have gone to such lengths to create, are a travesty.

I won't go on.
 
You must log in or register to reply here.
Back
Top