Camera / lens callibration, help and advice please

[DanK]

This is why im asking for real world advice! do you calibrate?

For the most part, no, although the obsessive that I am, I bought the Reikan software and tested my lenses, some of them a number of different ways. What I found (with my old Canon 50D) is that all but one of my lenses were pretty much spot on. I did have one zoom lens that was a bit off, but as is sometimes the case with zooms, the error varied with focal length. So, I made a minor MFA adjustment for the longest focal length, which is where it would matter most, but the honest answer is that if you were to look at a bunch of my images, you wouldn't be able to tell where I made the adjustment (or at least I don't think I could).

Last year I bought a new FF body, and with the change in format, I replaced a couple of lenses. I keep thinking I should test all of the combinations of lenses with this body, but I keep forgetting to do it, because I just haven't notice a problem. Being compulsive, I will some day, probably some very snowy winter day when I am mostly stuck indoors.

Dan

[Mark von Kanel]

The link I posted provides a target that is just displayed on a PC screen. For telephoto testing some use a laptop because just like many things including the sort of test targets you have posted distance comes into it - more so with those actually whe they are used for their intended purpose. The target in the link isn't terribly sensitive to that aspect.

John
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John .. wrong John it was shadowman who had the temerity to want to look at actual images.., but having thought about itnone of them are tripod mounted and the human factor will creep in so it wont prove much.... and test targets dont winge about standing still

[Glenn NK]

Don't buy AF software.

Google "dot tune".

Glenn

[ajohnw]

John .. wrong John it was shadowman who had the temerity to want to look at actual images.., but having thought about itnone of them are tripod mounted and the human factor will creep in so it wont prove much.... and test targets dont winge about standing still

The method I linked too is to intelligent for photographers - it uses moire's fringes obtained by sampling a pattern with a sensor that has a square pixel array.

Your test targets you posted ain't much use for critical focus checking really the printing isn't up to it. More distance can solve that even if you buy a real target of Thore Labs. Probably the best source from the UK. Edmund's is also probably an alternative.

The dot focus thingy is probably a variation on mtf measurement using a slant edge. That really does need clean edges on the target. Opens source software is available for measuring mtf this way. Pity about the chart.

The moire patterns don't give a dam about that aspect within reason. They are odd things. This is a camera shot crop in focus.



This is exactly the same shot reduced by 50%



The changes are down to the same effect.

If some one wants to really evaluate a lens a chart such as the Koren shown here is needed. The distance it's used at should get round blurry edge problems. This sort of test allows contrast to be judged when the lens is working well rather than at mtf50. It's used by some keem bird people.

http://www.normankoren.com/Tutorials/MTF5.html

John
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[Glenn NK]

Mark
I have used this Dot Tune method to check and adjust all of my lenses, it worked for me. If you do try it dont forget to turn off your lens/camara IS/VR before commencing the testing. My 5D3 body allows you to tune and save the AFMA for each end of a zoom lens.
Prior to using the DotTune method I did try Auto Focus Micro Adjustments (AFMA) using this target (see link below) arrangement and found it to be a far more labour intensive method, but I did enjpoy the Blue Peter element of printing and making the target.
Target LINK

The Beauty of using DOT Tune is that one doesn't need to print out any targets. It's not a lens acuity/sharpness test - it's a focus accuracy test/adjustment.

I know of a wildlife photographer that while sitting in his blind waiting for something to come along, calibrated his lens using the method!!

All it needs is a well defined "something" on which to focus using both methods.

And yes, any brand of camera/lens can be out of whack. Sorry Colin.

Glenn

[ST1]

Nice link John Mr Koren has created/compiled a great deal of information which I have only scraped the surface of. Thanks for the link which I have bookmarked.

[Stagecoach]

This is why im asking for real world advice! do you calibrate?

Hi Mark,

I have never checked or calibrated any of my lenses using these methods because I have never had reason to question them, not because I disagree with some of the methods available. It's one of those things I may do one day just out of interest and as an example recent use of my 10-20 for where I seem to be always using AF now at a subject focus distance of around 2 mtrs may be worth looking at.

Good to hear you have made your adjustments, the beauty of this is that it's so easy to do and non destructive

Off topic but out of interest, for my 105VR macro I undertook an interesting test last year for fun. Using a 0.3mm hypodermic syringe needle as target I took shots as follows;

a) Focused Manually (VR off)
b) Focused with live view (VR off)
c) Focused with AF (Mirror up, VR off)
d) Focused with AF (Mirror up, VR on)
e) Focused with AF (VR on, Instaneous shutter activation not allowing VR time to spin up)

In real world terms viewing the images at 100% nothing to make me worry about leaving VR on or waiting for spin up.

Grahame

[Colin Southern]

Just for the record ...

AF doesn't always get to the same focal point each time - so be sure to work with a batch of images so that a "fringe" result doesn't lead one down the garden path.

[DanK]

Just for the record ...

AF doesn't always get to the same focal point each time - so be sure to work with a batch of images so that a "fringe" result doesn't lead one down the garden path.

Yup. That is one of the advantages of the Reikan software (assuming you actually have a problem to solve, which I didn't). It does the test over and over again, and it will give you an unwelcome message if your camera/lens combination has greater variance than what they consider usual.

[Shadowman]

John, your actually suggesting i take some images of stuff other than a test target???? Wash your fingers off with soap! how dare you type such blasphemy? ill see what i can find john but my catalog is at home not on my lappy.

whilst im at work im pretty much spending my time studying (and shooting test targets) which is why most of my current posts are technical or pp related.... i do have some from an envioromental portrait session that i shot before i came to work. ill have a look and see what ive got.

Mark,

Not suggesting you take additional photos, just display the original images that caused you to doubt the accuracy of your camera's focusing system. It is how you started this thread:

"A while back i invested in an FX camera body and good glass. To tell the truth ive been a little disappointed sometimes with the results, i was putting it down to technique but my technique was fine with my DX, which had the same pixel density as my FX (d7000 d800) and even using a tripod it somehow seemed off."

[Mark von Kanel]

Mark,

Not suggesting you take additional photos, just display the original images that caused you to doubt the accuracy of your camera's focusing system. It is how you started this thread:

"A while back i invested in an FX camera body and good glass. To tell the truth ive been a little disappointed sometimes with the results, i was putting it down to technique but my technique was fine with my DX, which had the same pixel density as my FX (d7000 d800) and even using a tripod it somehow seemed off."

I know John, just my sense of humour kicking in, after all it is all a bit nerdish! this is the first time ive ever shot a test target!

[Stagecoach]

Mark,

Just for fun on the subject of AF checking and calibration here's some real world observational trivia;

a) Using my D300 with an 18-200 lens at 70mm 2.5 mtrs from the test chart you showed I can achieve 20mm linear movement (varying distance from chart) of the camera whilst the green focus dot remains on.

b) AF accuracy in live view was not consistent at all with a well lit target. 50% of the time I could tweak focus manually to achieve a sharper image from what AF had selected.

c) The first article you linked to has two dubious areas;

1) When undertaking the test (after the initial Live View reference shot) it does not advise you to 'de focus alternately between near and far' before taking your AF test shots

2) Reference is made that in Live View because focus confirmation happens electronically through the camera sensor, it will always be accurate

Whilst the above is trivia it does support the fact that if you do not undertake these tests with an awareness of such things as repeatability, dead-bands and tolerances you can simply end up making adjustments which in real world terms you ain't gonna recognise in an image anyway.

Yes it was raining today and I was stuck inside bored.

Grahame

[Mark von Kanel]

Mark,

Just for fun on the subject of AF checking and calibration here's some real world observational trivia;

a) Using my D300 with an 18-200 lens at 70mm 2.5 mtrs from the test chart you showed I can achieve 20mm linear movement (varying distance from chart) of the camera whilst the green focus dot remains on.

b) AF accuracy in live view was not consistent at all with a well lit target. 50% of the time I could tweak focus manually to achieve a sharper image from what AF had selected.

c) The first article you linked to has two dubious areas;

1) When undertaking the test (after the initial Live View reference shot) it does not advise you to 'de focus alternately between near and far' before taking your AF test shots

2) Reference is made that in Live View because focus confirmation happens electronically through the camera sensor, it will always be accurate

Whilst the above is trivia it does support the fact that if you do not undertake these tests with an awareness of such things as repeatability, dead-bands and tolerances you can simply end up making adjustments which in real world terms you ain't gonna recognise in an image anyway.

Yes it was raining today and I was stuck inside bored.

Grahame

LOL hope the rain stops soon.... anyway i got to twist all my knobs and dials so im happy now it was so much simpler in my days of my zenith E with split screen manual focusing..... there was so much less to think about!

[ajohnw]

I'm glad Grahame mentioned the electronic confirmation problem. I thought about doing it but got cheesed off.

Live view's plus is manually focus with a high screen magnification if you are using a test chart that most suggest. it's the only way to get a pixel level view of the focus or is it. D800 ??? and maybe a 1mp rear screen. It's easy to do the sums. The other way is to look at the shot.

John
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[Stagecoach]

The other way is to look at the shot.

John
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The problem with looking at the shot is that it only tells you what you captured, not if it's the best focus the camera 'could' have achieved

[ajohnw]

The problem with looking at the shot is that it only tells you what you captured, not if it's the best focus the camera 'could' have achieved

Yeh. May have to look at a number of them. One quicker way is to "bracket" the focus corrections and look at several images in one go.

The limitation of live view is seldom mentioned. I'm aware of it due to trying to manually focus on m 4/3. With that 7x with a 1.4mp view and a 12mp sensor was reliable for photography. Pass on testing because I did find that focusing on a black and white test image with longer lenses at about 25m was surprisingly critical but the only way of really see that was to get info off the sensor without debayering. That area seems to clean things up a little.

John
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[rubencarmona]

There is a much better way of checking lens focus than these targets, Described here

http://www.northlight-images.co.uk/a...djustment.html

As with any such test squaring up the camera to the target is very important if results are going to be looked at rather critically. This test will even show signs of slight miss alignment. The bulls eye patterns change.

As pointed out when finally checking the AF you need to use it from in front of the target and also from behind. No adjustments for that aspect are available as far as I know.

John
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I'm using the target that is recommended in your link. It is robust and portable.

Using an image on a screen might be good to save some money. But your screen is a light source, while such a target is reflecting light, which is the same as the object that you're photographing later on. Such a light source can be missunderstood by the autofocus due to the light spreading of the monitor backlight.

Better would be to print it. But then you never know if you're alignment is correct. That's why I prefer that lenscal. Once opened, it's well positioned and you only have to care about the alignment of your camera.

[ajohnw]

I'm using the target that is recommended in your link. It is robust and portable.

Using an image on a screen might be good to save some money. But your screen is a light source, while such a target is reflecting light, which is the same as the object that you're photographing later on. Such a light source can be missunderstood by the autofocus due to the light spreading of the monitor backlight.

Better would be to print it. But then you never know if you're alignment is correct. That's why I prefer that lenscal. Once opened, it's well positioned and you only have to care about the alignment of your camera.

All I can say is I used a PC screen and that taget to check mine and it confirmed that they are ok as they turned out to be. I bought a D7000 and some of those have had severe problems. I also used it to check the focus scale on a 16mm 180 degree full frame lens and found that it is very sensitive even on a lens like that.

There is also a person called Black Pearl who is sometimes around. I understand he has made an unusual amount of use of it.

On this to remember on checking something like this that has already been mentioned - the control loop driving the focus will have some sort of dedband other wise it would continually hunt about.

I don't see why there should be a problem aligning to the same target if some one printed it anyway. That is needed what ever type of target is used. The problem with the one initially posted is that for a really critical test the lines aren't really sharp enough which is why these targets can be rather expensive to buy or have to be used from a greater distance.

Each to his own is how I see it. The aim is to check that auto focus is ok. Methods are a matter of personal choice. One method which I feel is a bit iffy is scales at a 45 degree angle - often proposed but viewing the results is subjective. Another uses the same technique as is used on MTF measurements - over the top really if things are done really well as the measurements can be way to accurate for the camera to hold consistently.

John
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