Lens calibration

[Ari]

Well after nearly two years of owning a dSLR, I discovered lens calibration last night!

I was having a play with my new 24-70 F2.8 and on 2.8 it seemed to me to be focusing ahead of whatever it was I was photographing. So a bit of on line research and I learned how to calibrate a lens. Of my five lenses (12-24, 24-70, 70-300 plus a prime 35 and 50) three were spot on, one needed to go to plus 8, but the new 24-70 needed to go right to the end of the scale at +20! And I'm still not sure it's quite far enough.

I need to take it out and try it again now I've calibrated the camera to it. Wondering whether I should take the lens back and change it though, it was a lot of money and that does seem a long way out.

What are people's experiences of lens calibration, is it normal to need to do this?

[K12beano]

Ari said:

What are people's experiences of lens calibration, is it normal to need to do this?

Long laborious task. Needed near to both extremes (can't remember offhand which two). Hardly anything on a couple of them.

Think this is quite normal.

[AndWhyNot]

Ari said:

What are people's experiences of lens calibration, is it normal to need to do this?

I borrowed a fisheye which needed a startlingly massive amount of adjustment, given an advantage of such wide angle lenses is they're supposed to help keep everything in focus with extensive DoF.

My only other 'extreme' experience was with a prime I bought. It was pants, miles off, way beyond what the camera could compensate for. Then I noticed the dealer had sent me the wrong model (AF rather than AF-D) so I sent it back to become someone else's problem.

Up to 20 must be fairly unexceptional for the camera makers to include it.

[illmonkey]

Was about to post something similar. What methods do people use?

I am very unpleased with every photo from my kit lens (yes, its only a kit lens, I know), but get good results from my nifty 50 and the tamrom zoom. Most photos from the kit lens are slightly out of focus, annoyingly, not enough to tell on my 450d's screen, but easily visible on my monitor.

[Ari]

There are a few good tutorials on Youtube if you search for "lens calibration", that's what I did.

[Ari]

AndWhyNot said:

Up to 20 must be fairly unexceptional for the camera makers to include it.

I think my concern is that I've ended up at 20 because that's absolutely as far as the adjustment goes, and whilst I think that's brought it into line, I'm not certain (to be fair I've not had chance to try it yet).

If it were 20, all fine and the scale went up to 25 I'd be quite happy, I'm just a bit concerned that I'm banging off the rev limiter, so to speak.

[Kermit power]

illmonkey said:

Was about to post something similar. What methods do people use?

I am very unpleased with every photo from my kit lens (yes, its only a kit lens, I know), but get good results from my nifty 50 and the tamrom zoom. Most photos from the kit lens are slightly out of focus, annoyingly, not enough to tell on my 450d's screen, but easily visible on my monitor.

Unfortunately with a 450D you're stuck with it, as lens calibration is a feature of the camera, not the lens.

[illmonkey]

Kermit power said:

illmonkey said:

Was about to post something similar. What methods do people use?

I am very unpleased with every photo from my kit lens (yes, its only a kit lens, I know), but get good results from my nifty 50 and the tamrom zoom. Most photos from the kit lens are slightly out of focus, annoyingly, not enough to tell on my 450d's screen, but easily visible on my monitor.

Unfortunately with a 450D you're stuck with it, as lens calibration is a feature of the camera, not the lens.

Ah, bugger. Good excuse for a new lens at least!

[Kermit power]

I have tried looking at calibrating lenses with my 7D, but got thoroughly confused by the whole process...

All the tutorials I've been able to find on the subject talk about setting the camera and lens up parallel to a pattern displayed on a computer monitor at a distance equal to certain multiples of the lens' focal length.

Now, quite apart from the fact that this is bloody difficult to do without knocking the back wall out of our house for the 200mm end of my lenses and deploying multiple spirit levels to get it flat and square on, the end results just don't seem to be all that accurate. I don't know if it's just my eyes, but I struggle to get it to a point where the focus matches how it's apparently supposed to look when it's spot on.

What seemed more logical to me was to set the lens up at an angle to a ruler, focus manually on, let's say, the 20cm line on the ruler, then auto-focus to see if it changes the focal point forward or backward, adjusting the calibration until it no longer does so.

Given that my approach would be a lot easier to set up, I assume that I'm missing some glaring problem with it, but I can't for the life of me figure out what that problem would be. Could anyone enlighten me?

[JustinMinns]

With the 24-70mm at what focal length did you adjust it and was everything still good at oher focal lengths? Never sure how it works micro adjusting zooms

[Simpo Two]

Ari said:

Well after nearly two years of owning a dSLR, I discovered lens calibration last night!

Another reason to RTM when you buy new kit - you'd have discovered it two years ago

[RobDickinson]

I use Focal software to do this.

Newer cameras can have settings for either end of the zoom.

Also note that often critical focus is only calibrated for one focal distance, shoot outside of this and it may still go wrong.

[ian in lancs]

I have used focal http://www.reikan.co.uk/focalweb/

and got the following on a D700

24-70 15
70-200 10
70 sigma 2
85D 1.8 7
85D 1.4 5
50D 1.8 0
35D 0
24D -4

avg 4

Cant say I noticed much!

[Ari]

Kermit power said:

I have tried looking at calibrating lenses with my 7D, but got thoroughly confused by the whole process...

All the tutorials I've been able to find on the subject talk about setting the camera and lens up parallel to a pattern displayed on a computer monitor at a distance equal to certain multiples of the lens' focal length.

Now, quite apart from the fact that this is bloody difficult to do without knocking the back wall out of our house for the 200mm end of my lenses and deploying multiple spirit levels to get it flat and square on, the end results just don't seem to be all that accurate. I don't know if it's just my eyes, but I struggle to get it to a point where the focus matches how it's apparently supposed to look when it's spot on.

What seemed more logical to me was to set the lens up at an angle to a ruler, focus manually on, let's say, the 20cm line on the ruler, then auto-focus to see if it changes the focal point forward or backward, adjusting the calibration until it no longer does so.

Given that my approach would be a lot easier to set up, I assume that I'm missing some glaring problem with it, but I can't for the life of me figure out what that problem would be. Could anyone enlighten me?

Ok, this is what I did. I put a book with a stripy cover (ideal because it's easy to judge which stripes are in focus) on a table at an angle (a bit more than 45 degrees) so the camera is taking the photo along it.

Camera on tripod, use a remote to fire it, set it up on centre point focusing on an exact point, take the photo then put it on a computer to check it accurately.

I used the dot on the i of Riva as my focus point, and the stripes as well as the lettering to determine what was in focus and what wasn't.

This is the result of doing just that with the 24-70, second photo being a crop of the first. You can see how far out it is given that the dot of the i should be the sharpest point!





I then went into the settings menu of the camera and adjusted the compensation by small amounts until the focus was on the i dot.

I went out today and took some photos of the same objects I took yesterday prior to adjusting the compensation and the difference is marked. It now performs as it should.

[Ari]

JustinMinns said:

With the 24-70mm at what focal length did you adjust it and was everything still good at oher focal lengths? Never sure how it works micro adjusting zooms

I adjusted it on maximum focal length as the difference is most exaggerated at that point

[Ari]

Simpo Two said:

Ari said:

Well after nearly two years of owning a dSLR, I discovered lens calibration last night!

Another reason to RTM when you buy new kit - you'd have discovered it two years ago

Now it's interesting that you say that. First thing I did after learning that focus compensation is possible is look it up in the manual. Nothing.

[MonkeyHanger]

Ari said:

Now it's interesting that you say that. First thing I did after learning that focus compensation is possible is look it up in the manual. Nothing.

What Camera is it? If it's a Canon, look in the index for "AF Microadjustment".

[Kermit power]

Ari said:

Ok, this is what I did. I put a book with a stripy cover (ideal because it's easy to judge which stripes are in focus) on a table at an angle (a bit more than 45 degrees) so the camera is taking the photo along it.

Camera on tripod, use a remote to fire it, set it up on centre point focusing on an exact point, take the photo then put it on a computer to check it accurately.

I used the dot on the i of Riva as my focus point, and the stripes as well as the lettering to determine what was in focus and what wasn't.

This is the result of doing just that with the 24-70, second photo being a crop of the first. You can see how far out it is given that the dot of the i should be the sharpest point!





I then went into the settings menu of the camera and adjusted the compensation by small amounts until the focus was on the i dot.

I went out today and took some photos of the same objects I took yesterday prior to adjusting the compensation and the difference is marked. It now performs as it should.

Thanks! That's exactly the way I intended to do it, albeit with a book rather than a ruler. Given that it worked for you, and seems so much simpler than faffing around with being the right distance from an image projected on a screen, I really don't see why this isn't just the standard recommended method!

[Simpo Two]

Ari said:

Now it's interesting that you say that. First thing I did after learning that focus compensation is possible is look it up in the manual. Nothing.

Not in the custom menus?

Don't know what camera you have but Nikon manual indexes are quite remarkable - there are pages and pages of entries but nothing you want is listed. It's there, but called something else or in an unexpected section.

[Speed addicted]

I used a ruler at an angle with a bit of card against one of the numbers, then focused on the card.

I did this fairly close to the camera mainly so I could see what was out of focus easily, with the thought process that it would also magnify the effect of any correction that was required.

Annoyingly the lens that I thought was out was in (nifty 50) and the lens that I though was perfect was out slightly.