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03-04-2011, 10:47 AM - 3 Likes   #1
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You do NOT have a soft lense !

Someone posted this link the other day and after reading it I really think it deserves a larger audience. Some of you may have seen this before but it opened my eyes at least !

"This lens is soft" and other myths


One of the most common examples of anti-logic we see at LensRentals is the statement The lens is soft/frontfocuses/backfocuses. Now don’t get me wrong, there are bad copies of lenses out there, as best we can tell ranging from 3% to 7% of lenses. And we know, despite our checkout procedures, that 1 of 400 lenses or so will be damaged in shipping and arrive not functioning. Sometimes there’s actual damage or misalignment of an element in the lens, although the vast majority of the time that’s not the case. Usually the subject of the photograph is soft because the lens is not focusing precisely.

Three to 4 times a week we have the following conversation:

“The lens you sent me frontfocuses, its not good.”
“OK, we’ll overnight you a replacement.”

Then the first lens comes back and its perfectly fine when we check it out. But the customer is very happy with the replacement lens, it worked great even thought the first one didn’t. So what has happened? Its rather simple, actually, and like most examples of anti-logic it stems from a wrong assumption: the customer knows his/her camera is ‘fine’ because it works with fine with their other lenses—none of them front focus or back focus.

The key to the puzzle is the definition of ‘fine’. Most people assume that ‘fine’ means ‘perfectly calibrated’. In reality cameras are like any other manufactured item, calibration is within a given tolerance range. We don’t have privvy to what the actual tolerance range Canon, Nikon, or the other manufacturers (except Zeiss and Leica) consider acceptable, so lets arbitrarily say the manufacturer will consider a camera or lens to be ‘in specifications’ if its + or – 3 ‘focus units’ from perfect. We can assume they reached this number because anything within + or – 3 focus units will be within the depth of field of a wide aperture (probably f/2.8) lens.

Lets consider that I have a camera body that is -2 focus units from perfect, and a lens that is +2 focus units from perfect. Both are considered ‘fine’ according to the manufacturers definition, although they certainly aren’t perfect. However, the combination of a +2 lens on my -2 camera will be absolutely perfect, I’ll love the lens on my camera . After my experience with this one lens on one camera, I will write Sonnets on the various online forums about how great it is, and will tell anyone who doesn’t like it that they must be a bad photographer. I will have become the most dreaded online lifeform, a FLAO (Fanboy with Loss of All Objectivity).

But what if the lens was -2 focus units from the theoretical perfect and I put it on my -2 focus units from perfect camera? Well it depends. If the lens is say an f/4 maximum aperture, probably not much: the depth of field from an f/4 aperture lens may well mask a bit of front focusing or back focusing. You might notice the lens frontocuses 3 feet in front of the subject at 20 feet if you pixel peep, but since the depth of field is 10 feet the subject is still in focus and the lens seems fine. I will probably describe the lens as very good, but not descend to complete FLAOdom.

But if its an f/1.4 lens with a very shallow depth of field, the front focusing will be noticeable: the subject will be out of focus and soft. If I know how to do a front/backfocus test I may have figured out the problem, but here’s the kicker: if I sent the lens in to the manufacturer to fix the problem they would check the lens out, say it was fine (because it is fine, its within specifications) and send it back. Ony if I send the camera and lens together to be calibrated would the fact that the two together are out of focus be apparent, and then the manufacturer would be able to fix the calibration.

Ah, but there’s no free lunch. If the camera calibration was adjusted as part of the fix, I might find that another lens in my kit that used to be great, now backfocuses a bit. In the past, many full time pros who were aware of these issues, would send their entire collection of cameras and lenses to the manufacturer to be calibrated together. This was one of the original reasons Canon and Nikon formed their Professional Services groups. Most of the rest of us just made do, or sent copy after copy of a given lens back until we got one that was sharp ON OUR CAMERA.

The bad thing is many, many people who did this then hopped on their online camera forum and made blanket statements like “I had to try 3 copies before I found one that was calibrated right”. In reality what they should have said was “I had to try 3 copies before I found one that was calibrated right FOR MY CAMERA”. Those other two copies might well have been fine on someone else’s camera.

When you have a few dozen copies of each lens and each camera like we do, you quickly find out this is just a fact of camera reality. And the funny part of all this is the more expensive wide aperture lenses are the ones most likely to show the problem, because their depth of field is so narrow and the in-focus portion of the picture is so sharp compared to the out of focus portion. That $200 f/5.6 zoom is not going to show a minor front focus problem because the depth of field is about half a mile. The $2,000 f/1.4 prime has a depth of field of a few inches and any problems are immediately evident (and the owner 10 times more invested in wanting a perfect lens).

The good news is newer cameras have taken all this into account and the fix is right at your fingertips. The following cameras all have a “lens microcalibration” feature: Canon 1DMkIII, 1DsMkIII, 5DMkII, 50D; Nikon D3, D3x, D300, D700; the Pentax K20D, the Olympus E-30 and E-620, and the Sony A900. I’m surprised at how many people don’t take advantage of this feature – its a bit time consuming to do, but once done each of your lenses is locked in the camera’s memory and it will automatically compensate so that each lens is at a nearly perfect focusing plane whenever you mount it on the camera. I find the feature makes such a huge difference for most of my better lenses that I consider this feature alone makes the upgrade to one of the above bodies worthwhile.

Bad lenses (and cameras) will still exist, but the vast majority of front and backfocus issues will be a thing of the past. And for those of you who don’t have this feature, we will continue, as we always have, to do our best to get you a lens that works great on your camera, even when it means sending a replacement.

Addendum I recently saw the greatest real life example of this ever, in an online forum where the poster states ’Canon’s New XX camera sucks’ (I’m eliminating names so the bots don’t pick this up and repeat it.) He goes on to say he had a body for several years, and a hand picked collection of lenses that he knew were perfect because he’d gone through several copies of each to get the sharpest one. Now he bought a new body and all his lenses sucked, and he’d now exchanged bodies twice and they still all sucked. So here is the perfect example of a person starting with a camera at the edge of tolerance, choosing through multiple selection a set of edge-of-tolerance lenses, and now generalizing that all the new bodies suck. The sad part is the new body has microfocus adjustment and he never even tried it. Just sent copy after copy back to the store.

03-04-2011, 11:04 AM - 1 Like   #2
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while I don't necessairly disagree with your comments, I think that this is a dead horse that youo are trying to whip back to life.

The biggest issue we have is that we now look at our pictures much much closer than we ever did in the past.

I know because as I write this, I am sitting in front of a 22 inch monitor, which actually, as a full frame constitutes a 13 x 19 inch boarderless print, AND when I zoom in to 1:1 (pixel count that is) I need 9 monitors to look at a complete K7 frame.

that is one hell of a lot bigger than looking at a typical 4x6 inch print now isn't it.

so the issue is that we now have the capability to look at things much more closely than in the past, which demands higher tolorances. Higher tolornances cost more, and therefore, the manufacturers, who all have this problem, are looking at the same time to reduce costs.

The manufacturer's have come up with the solution that is cost effective, allow the user to make the adjustments.

That is where we are now, but the problem is, making sure all users know how to properly make that adjustment. We have had thread upon useless thread about focusing targets and AF errors.

I susect this will continue for quite some time, until the manufacturers can all stand behind a proper published method. It should be part of the instructions for every lens, and every camera.
03-04-2011, 11:15 AM   #3
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QuoteOriginally posted by Lowell Goudge Quote
... until the manufacturers can all stand behind a proper published method. It should be part of the instructions for every lens, and every camera.
Or maybe until there is a provision in the firmware to autocalibrate against, say a standard printed sheet of paper slapped on the wall? Should be eminently possible. This might not even need a special target. Actually, changes are that the undocumented interface at the USB port which PK_Tether uses includes the ability to set these; PC software could probably do this?
03-04-2011, 11:20 AM   #4
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I don't think most people see the things that people tend to see here.

Just saying. Most photographers I know (amateur or otherwise) don't rate sharpness / bokeh / colour nearly as high as image content. I don't even think they know what FF or BF is.

I think frogfish's point is brilliant, actually. I also think most people aren't even AWARE of this supposed problem.

03-04-2011, 11:22 AM   #5
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I agree that we're pixel peeping more than necessary in most instances. I think that contrast can be as important for perceived sharpness than actual sharpness of the lens in normal sized prints.

And as for calibration, I've mentioned before there is no reason that the manufacturers can't use the live view focus to calibrate the phase focus system in the viewfinder without any need for charts or any special subject, just a high contrast target. Put camera on tripod, focus in live view which should be perfect because of using the sensor for focus. Then focus with viewfinder and apply an offset between the two.
03-04-2011, 11:29 AM   #6
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QuoteOriginally posted by jolepp Quote
Or maybe until there is a provision in the firmware to autocalibrate against, say a standard printed sheet of paper slapped on the wall? Should be eminently possible. This might not even need a special target. Actually, changes are that the undocumented interface at the USB port which PK_Tether uses includes the ability to set these; PC software could probably do this?
QuoteOriginally posted by VaughnA Quote
And as for calibration, I've mentioned before there is no reason that the manufacturers can't use the live view focus to calibrate the phase focus system in the viewfinder without any need for charts or any special subject, just a high contrast target. Put camera on tripod, focus in live view which should be perfect because of using the sensor for focus. Then focus with viewfinder and apply an offset between the two.
this is the whole point , isn't it. the manufacturers really need to make it easier to calibrate, for those compelled to do so.
03-04-2011, 11:51 AM   #7
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Interesting article, thanks for the link. I know that the + or – 3 ‘focus units’ is not much, but if your camera and the lens are more in the same limit (+3 or -3) then the camera/lens combination will not be the ideal situation and the user easily can spot that there is a front/back focus problem.
03-04-2011, 12:01 PM   #8
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My experience may not be relevant but I want to share it.

My K10D consistently backfocused. I had to adjust +110um to bring it right. Once I did that, all my lenses are getting much better accuracy. How could this camera pass their QA? If manufacturers could ensure their products within specs, our life could be a lot easier.

I think I miss the main topic here, but I feel I have to say this. Sorry.

03-04-2011, 01:12 PM   #9
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Lowell - I quite understand your point and TBH I don't see that manufacturers are now going to deviate from this 'new' self-adjusting option we have been given (and I think it's great that we now have the tools to do something to alleviate the problem) and decrease tolerances on their equipment. They have found a cost effective solution.

However the reason I started this thread is exactly the point that Paper Bag stated (and in fact is covered in your post) .... that many people don't even know that there are these manufacturing tolerances put in place by manufacturers on their prized possessions. If more buyers were aware of this issue then cameras that don't offer this DIY solution would lose popularity and vice versa.
As you say, everyone needs to be aware that these tolerances exist, that in some cases the total of the two tolerances (camera & lense) can lead to unacceptable results, to know how to correct it in-camera if at all possible and that if it can't then the manufacturers should be held responsible for equipment falling outside measurable tolerance parameters (if we can even find a way to measure it).

I knew there was an in-camera solution for K7 & K5 owners (don't know about Kx, Kr or K20D) but I certainly didn't know, or realise, that the total of the two tolerances could even fall outside of the solution we've been given. Judging by this (two+ years old) article many others don't know of this 'parameter theory' either !
03-04-2011, 01:24 PM   #10
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QuoteOriginally posted by Frogfish Quote
Lowell - I quite understand your point and TBH I don't see that manufacturers are now going to deviate from this 'new' self-adjusting option we have been given (and I think it's great that we now have the tools to do something to alleviate the problem) and decrease tolerances on their equipment. They have found a cost effective solution.

However the reason I started this thread is exactly the point that Paper Bag stated (and in fact is covered in your post) .... that many people don't even know that there are these manufacturing tolerances put in place by manufacturers on their prized possessions. If more buyers were aware of this issue then cameras that don't offer this DIY solution would lose popularity and vice versa.
As you say, everyone needs to be aware that these tolerances exist, that in some cases the total of the two tolerances (camera & lense) can lead to unacceptable results, to know how to correct it in-camera if at all possible and that if it can't then the manufacturers should be held responsible for equipment falling outside measurable tolerance parameters (if we can even find a way to measure it).

I knew there was an in-camera solution for K7 & K5 owners (don't know about Kx, Kr or K20D) but I certainly didn't know, or realise, that the total of the two tolerances could even fall outside of the solution we've been given. Judging by this (two+ years old) article many others don't know of this 'parameter theory' either !
K20 for sure has an adjustment that was the one significant change from K10D other than sensor.

K10D has , through the firmware hack a single camera adjustment, although I have never felt I needed it.

I think the K20 is like the K7, you can apply global general adjustment or lens by lens.
03-04-2011, 02:42 PM   #11
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QuoteOriginally posted by Lowell Goudge Quote
I think the K20 is like the K7, you can apply global general adjustment or lens by lens.
It is. and calibrating all 'important' lenses takes lots of time.
I wish it's an easier way to do.
03-05-2011, 05:28 AM   #12
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QuoteOriginally posted by hoanpham Quote
It is. and calibrating all 'important' lenses takes lots of time.
I wish it's an easier way to do.
In the "old days" you would send your camera and lenses to the manufacturer and they would calibrate them all, I guess adjusting the lenses somehow.

I agree that it is useful to have calibration possible for the user, but unless you know what you are doing, you can successfully screw up your focus quite a bit with the wrong adjustment.

The K10 had a debug menu that allowed you to adjust one setting. People would write down the adjustments for each lens then punch it in when they stuck that lens on.
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