Lens calibration

[Glenda]

I am wondering if you can and if so, what is the best way to calibrate a zoom lens.

[ameerat42]

Do you mean for micro AF adjustment? What's your lens doing/not doing?

[nardes]

I think the theory goes something like this:



On a typical DSLR the AF Sensor is a stand-alone Sensor positioned in a different location to the Image Sensor.
Any difference in "perfect alignment" of these Sensors might lead to the AF Senor reporting that it has found perfect focus but when the Mirror flips out of the way, the exact in-focus plane may be located marginally either just in front of the Image Sensor or just behind it, leading to slightly OOF images.
With a DSLR that allows "Micro Focus Adjustment" (MFA) you use Live View and Manually focus the lens and the camera Menu reports the minor variation as a + or - value which you can then dial in.
For a Prime Lens you do this once as it is a single focal length.
For a Zoom Lens you have to do this at max and min FL and I guess hope that it caters for the in-between values.


Cheers

Dennis

[Glenda]

Do you mean for micro AF adjustment? What's your lens doing/not doing?

Not really having a problem with the lens Am. I have often checked the focus of my prime lenses but never my zooms because I wasn't sure if I had to check a variety of focal lengths and what to do if they were different.


I think the theory goes something like this:



On a typical DSLR the AF Sensor is a stand-alone Sensor positioned in a different location to the Image Sensor.
Any difference in "perfect alignment" of these Sensors might lead to the AF Senor reporting that it has found perfect focus but when the Mirror flips out of the way, the exact in-focus plane may be located marginally either just in front of the Image Sensor or just behind it, leading to slightly OOF images.
With a DSLR that allows "Micro Focus Adjustment" (MFA) you use Live View and Manually focus the lens and the camera Menu reports the minor variation as a + or - value which you can then dial in.
For a Prime Lens you do this once as it is a single focal length.
For a Zoom Lens you have to do this at max and min FL and I guess hope that it caters for the in-between values.


Cheers

Dennis

Thanks Dennis. I've often checked primes but never zooms. I was just wondering how to do one and what to do if the adjustments varied at different focal lengths. Sounds a bit hit or miss if they do.

[Gazza]

Something like this? :url: (https://www.youtube.com/watch?v=5cHhrWF-pqM)

[ameerat42]

Well done, Gazza. I enjoyed that very informative movie :nod:

[Gazza]

Well done, Gazza. I enjoyed that very informative movie :nod:
He has a wonderful way of stretching it out to the max. Must've been getting paid by the minute? :D

[Glenda]

Something like this? :url: (https://www.youtube.com/watch?v=5cHhrWF-pqM)

No Gaz, my camera is too old to have auto AF fine tune - I have to do it manually :(.

[Gazza]

No Gaz, my camera is too old to have auto AF fine tune - I have to do it manually :(.
Time for a new toy. Sounds good to me :grinning01: (I won't tell, Gordon...)

[nardes]

Hi Glenda

I experimented with LensAlign (http://michaeltapesdesign.com/lensalign.html) which involved a straightforward manual set up process, including a built-in method of making the Target used in the MFA process parallel to the camera sensor. I used it on my 7D Mk I and it recommended that I dial in a small +ve amount, I think it was around +2 or +3.

I also had a more recent play with Reikan FoCal (https://www.reikanfocal.com) with offered a software assisted procedure. Some camera models allow an end-to-end software assisted procedure whereas e.g. my Canon 7D Mk II requires some user input during the process which is simple and straightforward.

I no longer have the lenses that I tested for MFA and my current lenses do not appear to require MFA, so I cannot really report on them.

I found Reikan FoCal more suited to my personal style, preferring SW driven test methods over HW centric test set ups. However, I think that both do what they say they do and at the time I used either, they gave me the results that I desired.

Playing around with MFA did prompt me to return a Canon 300mm F4L IS lens that had a case of severely back focusing with my older Canon 40D and the 40D did not have MFA so the lens was useless. This was worse as you approached closest focus and less obvious towards infinity.

In the end, I concluded that unless I was getting consistently poor results with a particular lens (and I was able to discount operator error), then MFA isn't really necessary.

Cheers

Dennis

[Glenda]

Thanks Dennis. I have heard of FoCal but didn't think it was worth buying a software program. I haven't noticed a definite problem with any of my zooms but thought it would be interesting to see if they were out after reading about a guy who bought a second hand 24-70 and found it was out by quite differing amounts at various lengths.

[arthurking83]

Thanks Dennis. I have heard of FoCal but didn't think it was worth buying a software program. I haven't noticed a definite problem with any of my zooms but thought it would be interesting to see if they were out after reading about a guy who bought a second hand 24-70 and found it was out by quite differing amounts at various lengths.

I wouldn't worry about using AF adjust in camera on a zoom lens.
99.99% sure it will simply shift any focus accuracy issue to another focal length.

With zoom lenses, the most common AF adjustment anomalies will happen only at specific focal lengths, or may be different at the various focal lengths.
Not only do you have those variables, but the other variable that makes AF adjusting a zoom lens worse than nightmarish .. is the impact of focus distance.

I had this exact problem with my Nikon 80-200 AF-D lens.
Focused pretty much fine at 70mm, very slightly front focused at 100mm(but not enough to be an issue, and so that was ignored).
And at 200mm up to about 4-5m focus distance it backfocused badly(very obvious in all images, more so at f/2.8 and f/4).
Beyond about 4-5m, the backfocus issue neutralised itself.

focus adjust feature proved to be more useless than useful in camera(D300 at the time). Fixing the 200mm backfocus issue created worse issues at 70 100 and 135mm.
Took lens to Nikon's local service centre, but they also wanted the camera(not willing to part with the camera for a week), and the cost was going to be unjustifiable. So the backfocus was 'tolerated'.

The best solution from a financial perspective was to sell the 80-200, and replace it with the first version Tamron 70-200/2.8 :th3:
Other than the material types used on the lens, the Tamron was all round the better lens. The only two areas where the Tamron was bettered by the 80-200 comparison was lens body material, and bokeh quality.

For many years since Sigma first introduced their USB lens dock system, I've been a big fan of it. :th3:
And that type of system is really the only way you can account for any discrepancy in a zooms focus accuracy at it's various focal lengths .. on bulk of cameras with the ability to adjust lens parameters within them.
If the camera AF micro adjust allows for various focal lengths, then obviously the lens based micro adjust wouldn't be required.

[Glenda]

Thanks Arthur. The zooms I use most are my Tamron 24-70 and 70-200 and for the subjects, mainly scenes where I just focus approx 1/3 of the way in or if I'm really keen use the hyperfocal distance calculator on Photo Pills, it probably wouldn't make much difference. I've certainly never noticed any major problems. We used to have the Nikon 18-200 which I was never happy with the sharpness but after my husband fell and the lens was broken, we replaced it with a Sigma 18-200 which has so much better sharpness. Possibly the Nikon did have a problem. I could probably check my birding lens as I mostly use it at 500mm but I think any problems with it are caused by user error rather than the lens :D. I would love a better Sigma birding lens complete with the USB dock system but not sure whether I could cope with the weight nowadays :(. Think I'll just stick with checking the primes.

[arthurking83]

After my issues with the Nikon 80-200 lens(this was back in '07-08 ish), I then checked all other lenses, and have checked all purchases since.
The only other lens I had focus issues with was my Tammy 28-75/2.8, which is also AF-D type.
This Tammy was less affected, but a tweak did bring out a bit more 'pop' out of it in use.
Again that tweak, ruined the other focal lengths.

The difference between the two lenses tho(ie. in operation) was that you couldn't quickly/easily manually override focus on the 80-200.
It had this annoying manual-auto ring for doing that, which hard locked the focus ring. So using the 80-200 at 200mm and focus less than 5m was always going to give iffy image results.
OTOH, the Tammy 28-75/2.8 focus ring wasn't hard locked, and could be moved manually. The consensus was that you didn't manually force the focus against the cameras focus motor(apparently not good for longevity).
But because it was a mechanical system, they usually have a very small amount of play(slack) in the mechanical connections), and this is what the 28-75 had too.
There was this 0.5mm of rotational play in the focus ring before the resistance of the focus motor was interfered with.
It was this exact tiniest of slack that made the difference in focus ability, so I just had in in mind that if I had the lens at 75mm, f/2.8 I had to do was to tweak the slack out of the focus ring, and the focus inaccuracy was eliminated.
In practise, it worked well, as long as I could remember the lens settings. At f/4, the slightly deeper DOF hid the issue, and at longer focus distances again the natural DOF even at f/2.8 also masked the issue.

So even tho the Tammy 28-75/2.8 also had back focus issues, in use, it wasn't really a problem. Whereas on the N80-200 lens, it was a major issue, so much so that I had to sell it rather than waste money on possibly having it fixed.
It was this lens/debacle that turned me into a non believer that thirdparty gear is inferior to manufacturer products.

You know! ... buy the name brand lenses and accessories because you're supposedly getting higher quality stuff! :rolleyes:

.. ahhh, yeah .. NOT!

Sigma 150-600S is a nice lens, can see it working well for birding .. but like you said, it is heavy

ps. I've checked my 24-70 Tammy(first version) and 70-200(first version), and neither misfocus.
The major issue I have with the Tammy 70-200/2.8 is that it can't focus (for some reason) in Lv mode, on both of my Lv capable cameras.
it moves the focus system around, goes past the point of focus then on to nothing.
While it is a major problem, I've never been bothered by it, because my only use for Lv mode and focus is manually focusing anyhow.

if you remember the images of the stone structure I recently posted, taken with the T70-200 :th3:

[Mark L]

since Sigma first introduced their USB lens dock system, I've been a big fan of it. :th3:

Agree. Allowed me to make minor adjustments as my 150-600 S was front focusing by a fraction. No paying someone else to do this and no playing with anything in camera, just fix it in the lens.
I thought that USB dock was a bit of a long term game changer. Have others start to offer this yet?

[ameerat42]

Agree. Allowed me to make minor adjustments as my 150-600 S was front focusing by a fraction...

AK here uses it too, I have read in his posts. But it sounds good from all reports.

That dock tells you what's up with your lens :th3:

[Glenda]

After my issues with the Nikon 80-200 lens(this was back in '07-08 ish), I then checked all other lenses, and have checked all purchases since.
The only other lens I had focus issues with was my Tammy 28-75/2.8, which is also AF-D type.
This Tammy was less affected, but a tweak did bring out a bit more 'pop' out of it in use.
Again that tweak, ruined the other focal lengths.

The difference between the two lenses tho(ie. in operation) was that you couldn't quickly/easily manually override focus on the 80-200.
It had this annoying manual-auto ring for doing that, which hard locked the focus ring. So using the 80-200 at 200mm and focus less than 5m was always going to give iffy image results.
OTOH, the Tammy 28-75/2.8 focus ring wasn't hard locked, and could be moved manually. The consensus was that you didn't manually force the focus against the cameras focus motor(apparently not good for longevity).
But because it was a mechanical system, they usually have a very small amount of play(slack) in the mechanical connections), and this is what the 28-75 had too.
There was this 0.5mm of rotational play in the focus ring before the resistance of the focus motor was interfered with.
It was this exact tiniest of slack that made the difference in focus ability, so I just had in in mind that if I had the lens at 75mm, f/2.8 I had to do was to tweak the slack out of the focus ring, and the focus inaccuracy was eliminated.
In practise, it worked well, as long as I could remember the lens settings. At f/4, the slightly deeper DOF hid the issue, and at longer focus distances again the natural DOF even at f/2.8 also masked the issue.

So even tho the Tammy 28-75/2.8 also had back focus issues, in use, it wasn't really a problem. Whereas on the N80-200 lens, it was a major issue, so much so that I had to sell it rather than waste money on possibly having it fixed.
It was this lens/debacle that turned me into a non believer that thirdparty gear is inferior to manufacturer products.

You know! ... buy the name brand lenses and accessories because you're supposedly getting higher quality stuff! :rolleyes:

.. ahhh, yeah .. NOT!

Sigma 150-600S is a nice lens, can see it working well for birding .. but like you said, it is heavy

ps. I've checked my 24-70 Tammy(first version) and 70-200(first version), and neither misfocus.
The major issue I have with the Tammy 70-200/2.8 is that it can't focus (for some reason) in Lv mode, on both of my Lv capable cameras.
it moves the focus system around, goes past the point of focus then on to nothing.
While it is a major problem, I've never been bothered by it, because my only use for Lv mode and focus is manually focusing anyhow.

if you remember the images of the stone structure I recently posted, taken with the T70-200 :th3:

Thanks Arthur. I love both my Tamron lenses and my Sigma macro and zoom. As a hobbyist the price of Nikon lenses is the main reason I went with them, after reading positive comments about them on here too of course. I rarely use Lv so wouldn't have noticed any problems in that area.

[arthurking83]

Yeah, I also got the Sigma USB dock for the 150-600 lens.
Haven't needed to tweak focus accuracy, but I did update to a new firmware and I then set up two function/memory thingies, where one focuses faster(1) than the other(2), and the 'other' is more accurate to focus, but slower focusing.


The other nice thing about in lens calibration(as opposed to in camera calibration) is that not only can you tweak focus for a specific focal length, at least with the Sigma software it allows you to tweak it over a few focus distances too for each of those focal lengths.

While it's a seemingly nice feature to have in camera, in reality it ends up more useless than truly useful.
A more detailed version of it would have been better, for example if the manufacturers had a tethered system to a computer, and computer based software to allow the camera/lens combo to be tweaked as finely detailed, or simply ... if at all!

[Tannin]

Glenda, there is nothing wrong with your pictures. You don't need to MFA.

Most people don't. All this yammer-yammer you read on the web about the theory behind it is fine, and quite a lot of it is even true, but the reality is that most cameras and most lenses are just fine straight out of the factory, and MFA is, for most people, a complete waste of time. All the many other errors we make as photographers swamp any miniscule MFA effect. There are better ways to spend your day.

While it doesn't actually do any harm, it is best done in private and is generally not spoken about in polite company. Be sure to wash your hands afterwards and try not to make a habit of it.

[Glenda]

Glenda, there is nothing wrong with your pictures. You don't need to MFA.

Most people don't. All this yammer-yammer you read on the web about the theory behind it is fine, and quite a lot of it is even true, but the reality is that most cameras and most lenses are just fine straight out of the factory, and MFA is, for most people, a complete waste of time. All the many other errors we make as photographers swamp any miniscule MFA effect. There are better ways to spend your day.

While it doesn't actually do any harm, it is best done in private and is generally not spoken about in polite company. Be sure to wash your hands afterwards and try not to make a habit of it.

Thanks Tony. Just thought I'd ask about zooms as a friend recently did a few of her primes and they were quite a bit out. As I said for most of my subjects which tend to be scenes I haven't noticed any problems.

Your last sentence made me -
:lol:

[arthurking83]

.... Just thought I'd ask about zooms as a friend recently did a few of her primes and they were quite a bit out. ....

And with this specific issue, you need to be careful about that 'out' actually is.
Not many people realise that some prime lenses(most of them will be 'faster types') have an issue known as focus shift.

If you don't know what it is, I suggest a google search, and more importantly look for lens review sites that test for it too.
I remember Photozone has a good pictorial description in their reviews.

That is, the lens will be focused at a specific distance, and without touching that focus distance, the lens is then stopped down through it's aperture range.
Focus shift shows that maybe at f/1.8 the image is low contrast/hazy looking, but that the focus zone is pretty much spot on, but as the aperture is stopped down, the focus distance is visibly changed.
From memory this will usually be behind the focus distance set.

Why this may come across as an issue is that the camera holds the lens fully wide open(for more light), but at that point the lens focuses at the perfect distance.
But if you set the aperture to say f/4 or f/5.6 or whatever smaller size, it still focuses 'wide open' but focus shift issue causes the lens to appear back focused.

Focus adjust for these lens is futile, as it then misfocuses wide open, but spot on only when stopped down.

[Mark L]

..........

While it doesn't actually do any harm, it is best done in private and is generally not spoken about in polite company. Be sure to wash your hands afterwards and try not to make a habit of it.


Thanks Tony. ......

Your last sentence made me -
:lol:


I hope you don't follow Tony's advice of not making a habit of washing your hands.