AFMA

[traingineer]

So using my 24-70 F2.8 for years, I always wondered why my images were never tack sharp, so I thought stopping down to F4-5.6 and using faster shutter speeds would make my images sharper, and they did. Although I decided to maybe try and see if my lens was calibrated ( just for fun ) So I took a ruler, set it up at an angle against the window, focused at the number 5, and found out that it wasn't in sharp focus ( at F2.8 ) But 8 was in focus. So I calibrated it to -15 and now my lens focuses at the number 5. I also checked if there was any focus shifting but there wasn't any. ° ͜ʖ °

I feel pretty silly now, thinking my images weren't sharp because of slow shutter speeds/using wide apertures.

 

[Jim Saunders]

Re: Lens calibration

A program called Focal (Reikan.co.uk off my head) may be used to partially or fully automate the process too, if you get bored of doing it by hand.

Jim

 

[traingineer]

Re: Lens calibration

A program called Focal (Reikan.co.uk off my head) may be used to partially or fully automate the process too, if you get bored of doing it by hand.

Jims

Pretty kewl, but I only needed to do it to the 1 lens, my other lenses are completely fine.

 

[ahab1372]

Re: Lens calibration

Your result may be even better if you focus on a vertical target (a Siemens star taped to a cereal box) and attach the ruler to the side of the box, with the 5 (or any number of your choice) lined up with the image plane.
When you focus on the ruler at an angle, it is hard to say what exacly the camera focused on - it could be the 5 but could also be the 4.5 or 5.5 or something else.

 

[traingineer]

Re: Lens calibration

Your result may be even better if you focus on a vertical target (a Siemens star taped to a cereal box) and attach the ruler to the side of the box, with the 5 (or any number of your choice) lined up with the image plane.
When you focus on the ruler at an angle, it is hard to say what exacly the camera focused on - it could be the 5 but could also be the 4.5 or 5.5 or something else.

I'll keep that in mind.

 

[StephenC]

Re: Lens calibration

I'll second the Reikan software. It make the process very simple. I may be using it as I wouldn't know how to do the job the manual way though.

 

[traingineer]

Re: Lens calibration

Well after retrying the calibration, I found -7 to be better.

 

[BL]

Re: Lens calibration

Does distance matter for this sort of calibration/testing? I would imagine it's probably best not to calibrate at MFD or infinity for example.

 

[Jim Saunders]

Re: Lens calibration

Does distance matter for this sort of calibration/testing? I would imagine it's probably best not to calibrate at MFD or infinity for example.

Reikan suggests 50 x focal length in millimeters for FoCal, I don't have a reason why off the top of my head but it seems to work.

Jim

 

[Loswr]

Re: Lens calibration

Reikan suggests 50 x focal length in millimeters for FoCal, I don't have a reason why off the top of my head but it seems to work.

The reason is that at the optimal AFMA can change with distance, but by 40-50x the focal length (and a bit less for very long lenses), that variation has asymptotically evened out. The caveat is that if you usually shoot with a particular lens at a much closer distance, you should test at that closer distance. Personally, I test lenses at 25x and 50x the focal length, and if the optimal value is different, I consider how I usually use that lens in deciding on a value to set.

 

[LewisShermer]

Re: Lens calibration

I'm constantly at odds with my FoCal software. Having a 5Diii it doesn't do it 100% automatically and I have to alter the micro adjustment by hand. on longer lenses this must affect the position of the lens even if it's ever so slightly. if I run it more than once the results are all over the place. I have no idea what to trust with these things. I could go totally bonkers with micro adjustment. the ruler method is just as unreliable with just guessing what number you're focussed on vs. what number the auto focus has chosen to focus on in that little square.

Would you do it with a tripod in the same position or by hand and vary the distance slightly between the shots?

 

[mackguyver]

Re: Lens calibration

I'm constantly at odds with my FoCal software. Having a 5Diii it doesn't do it 100% automatically and I have to alter the micro adjustment by hand. on longer lenses this must affect the position of the lens even if it's ever so slightly. if I run it more than once the results are all over the place. I have no idea what to trust with these things. I could go totally bonkers with micro adjustment. the ruler method is just as unreliable with just guessing what number you're focussed on vs. what number the auto focus has chosen to focus on in that little square.

Would you do it with a tripod in the same position or by hand and vary the distance slightly between the shots?

Lewis, have you seen my post on how I use FoCal with my 5DIII and 1D X? If not, you might want to give it a read to see if it helps.