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Lens calibration
Jun 3, 2019 02:15:04   #
dckean Loc: Midlothian, scotland
 
Really strugglin to find info on this, I have a tokina 11-20mm wide angle lens and want to check the overall sharpness by means of a spyderlenscal or similar tool, ie, what distance from the tool would you set up and at what focal length for Good average results, thanks in advance for your advice.

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Jun 3, 2019 06:09:11   #
ceh1024 Loc: Lutz, FL
 
Check out FoCal completely automatic but last checked works for Nikon and Canon only. I have it and it works great.

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Jun 3, 2019 08:57:58   #
rwilson1942 Loc: Houston, TX
 
I've read recommendations to set up at the distance you are most likely to use the lens at.
I would do the calibration at 20mm since the shorter (wider) angles would have greater DoF and less of an issue with focus.
I've never done wide lens so this is my best guess.

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Jun 3, 2019 09:00:47   #
CHG_CANON Loc: the Windy City
 
As well as the tool, the entire process depends also on (1) having a camera that supports making micro focus adjustments and (b) a lens that registers to the camera so the camera knows when the Tokina 11-20 is mounted to the camera.

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Jun 3, 2019 10:26:30   #
CO
 
I have a SpyderLensCal. They recommend 25-50 times the focal length of the lens. That seems too far because you have to crop a lot in order to see the scale. I've been placing the target about 10 times the focal length away.

I've also seen the same recommendation as rwilson1942 above and place the targer at the distance at which you would be using the lens.

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Jun 3, 2019 12:09:45   #
Kaib795 Loc: Maryland, USA
 
Just a note:

If your camera cannot support these adjustments, and you use a tripod so shots aren't random, a work around is to use Live View. It tends to focus better, albeit slower, than thru the view finder. I tested a old D5000 which I shot for some time but not impressed with the focus. I placed it on a tripod and pulled out some sea shells in a woven bowl and pulled both thru the view finder shots compared to Live View. The Live View were much sharper! Surprisingly so. That camera has been passed down to the kids.

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Jun 3, 2019 22:05:05   #
TomV Loc: Annapolis, Maryland
 
On a wide angle lens the micro adjustment is not a necessity since the DOF is deep. If your goal is to check for sharpness, then cropping is not a problem. Iif you want to see how good you can get, set the test pattern at the distance your typical target is at.

I test my lenses by getting the focal length in mm, dividing by 10, and then use that figure in feet from my test target.

500mm lens, divide by 10 = 50, target for MFA calibration is 50 feet.

For a 20mm lens, divide by 10 = 2, target is 2 ft.
Once you get just a few feet further then the DOF is very deep.

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Jun 4, 2019 02:55:58   #
Kaib795 Loc: Maryland, USA
 
TomV wrote:
On a wide angle lens the micro adjustment is not a necessity since the DOF is deep. If your goal is to check for sharpness, then cropping is not a problem. Iif you want to see how good you can get, set the test pattern at the distance your typical target is at.

I test my lenses by getting the focal length in mm, dividing by 10, and then use that figure in feet from my test target.

500mm lens, divide by 10 = 50, target for MFA calibration is 50 feet.

For a 20mm lens, divide by 10 = 2, target is 2 ft.
Once you get just a few feet further then the DOF is very deep.
On a wide angle lens the micro adjustment is not a... (show quote)


Nice tip Tom, will try this as I love to test my equipment and make it perform.

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Jun 4, 2019 10:08:51   #
camerapapi Loc: Miami, Fl.
 
As is usually the case there will be many answers to your question. The Tokina 11-20 f2.8 is a VERY SHARP lens and you will be its only limitation. I am not trying to be the wise man here but I cannot understand why you want to play with the calibration of the lens.
If the lens is brand new it is covered by a warranty and in that case Tokina should be hearing from you if you have complaints. If it is a used lens Tokina is still the answer if you want to keep it.

In real life a lens is judged by the technique we use and the results it gives us. I have never been in need of a lens calibration but instead of fooling around with it I would simply send the lens to be calibrated by the manufacturer or a competent technician.

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Jun 4, 2019 11:22:39   #
ggab Loc: ?
 
ceh1024 wrote:
Check out FoCal completely automatic but last checked works for Nikon and Canon only. I have it and it works great.



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Jun 4, 2019 13:09:17   #
amfoto1 Loc: San Jose, Calif. USA
 
dckean wrote:
Really strugglin to find info on this, I have a tokina 11-20mm wide angle lens and want to check the overall sharpness by means of a spyderlenscal or similar tool, ie, what distance from the tool would you set up and at what focal length for Good average results, thanks in advance for your advice.


With a zoom you need to check both ends of the zoom range... so in your case the focal lengths you should check are 11mm and 20mm settings.

The distance you should set up the target is either 25X or 50X the lens focal length, depending upon the manufacturer. I think the Spyder instructions are 25X. With their calibration target, I know Reiken FoCal recommends 50X focal length (but I thin they say 25X is okay when calibrating really long telephoto focal lengths where that distance might be impractical).

11mm x 25 = 275mm. If you're "metrically challenged" like me, convert that to inches: 275 divided by 25.4 = 10.8". I'm sure 11 to 12 inches would be fine!

20mm x 25 = 500mm. Converted to inches: 500 / 25.4 = 19.68... call it 20 inches.

Be sure to set up the lens wide open, at it's max aperture, so that depth of field is as shallow as possible. Focus on the portion of the target that's parallel to your camera's sensor, then see where the focus falls on the angled portion of the target. The shallow depth of field from the largest possible aperture will give the clearest indication where the lens is focusing.

What to do with the info depends upon your camera. Some (most Canon with Micro Focus Adjust produced the last 8 or 10 years, for example) now have two adjustments for zooms... one for each end. If your camera only allow a single adjustment, then you may have to arrive at an average of the amount of adjustment suggested for the two different focal lengths.

I agree with a previous response... there's less need to fine tune focus with an ultrawide lens like the 11-20mm, simply because that type of lens has a lot of depth of field and can tolerate quite a bit of focus error.... especially whenever you use it stopped down to smaller apertures (which further increases depth of field).

Lens calibration is more critical with telephotos.... especially those with large apertures that are often used "wide open", or close to it, to render very shallow depth of field... such as 85mm f/1.2 and f/1.4, 135mm f/2 and f/1.8, 200mm f/2 and 300mm f/2.8 or 400mm f/2.8 lenses.

ceh1024 wrote:
Check out FoCal completely automatic but last checked works for Nikon and Canon only. I have it and it works great.


The FoCal system is good... but if you already have the Spyder LensCal or the Lens Align or other similar, those are more "manual", but will work fine, too.

It's easy to do and might be worth checking your 11-20mm, especially if you suspect a problem. But unless it's badly out of calibration, thanks to the lens deep depth of field you're unlikely to see much difference from any adjustments you make.

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Jun 4, 2019 13:57:11   #
dckean Loc: Midlothian, scotland
 
That's a great explanation, I don't suspect my lens is out of focus, it is very sharp and I'm glad I bought it, I got it mainly for interior shots and for historical buildings, thankyou for your input and for others in the forum for their personal advice

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Jun 4, 2019 20:37:46   #
claytonfm
 
First, a Canon 80D camera allows two microadjustments for a zoom lens, one at the low end and one at the high end. Second, the easiest approach is to assume that Live View (LV) yields the "best" focus you can achieve with your camera because the focus is achieved directly on the sensor. If that is the best, then why not use it as the standard and do the following. At a given focal length and distance, say 10-20 times the focal length, focus on the target in LV, then switch to the eyepiece view (EV), refocus and observe in which direction the focus ring turns. Assuming it turns, make a micro adjustment and repeat the process until the two focus techniques agree.

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