FoCal Lens Distance Question(s)

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01-25-2012, 11:50 PM
Bill_in_WA

FoCal Lens Distance Question(s)

Just received my new FoCal Pro program and am very anxious to get started. Other than the "normal" fears of doing something wrong and having the entire unit go up in smoke, I have faith that the program will work as well as it has for others.
I have read through the Manual and I know that many of my questions will probably be answered as I do the tests. I do, however, have a question or two regarding the distances from target to camera. I have read and know that Canon recommends 50X the Max FL... I have seen elsewhere that you could use FoCal at 20X or 30X. I have the following lenes for my Canon 7D and 5D MkII: 17-55 f/2.8 EFS (7D only), 24-105 f/4, 50 f/1.4, 100 Macro f2.8, 70-200 f/2.8. 100-400 f/4-5.6, 1.4X II TC.

Question 1: at 50X the target distance of the 100Macro would be: 100x50/25.4 =98.4252"=8.20' for the 5D MKII would that also hold true for the 7D with the 1.6 factor?

Question 2: My understanding is that the program, in Full Auto, will provide AFMA values throughout the focal range of the zoom lens and, untimately, will apply what it considers the best overall asjustment... Right? (or is it another Senior Moment?)

Question 3: Has anyone out there experimented with diffferent target distances (especially for the longer lenses) that have been aceptable or is the recommendation to adhere to the 50X?

Thanks to all who respond for your assistance.
01-26-2012, 12:17 AM
neuroanatomist

Quote:

Originally Posted by Bill_in_WA

Question 1: at 50X the target distance of the 100Macro would be: 100x50/25.4 =98.4252"=8.20' for the 5D MKII would that also hold true for the 7D with the 1.6 factor?

Math error. 100x50/25.4 = 197" = 16' 5". Same distance for FF and 1.6x.

Quote:

Originally Posted by Bill_in_WA

Question 2: My understanding is that the program, in Full Auto, will provide AFMA values throughout the focal range of the zoom lens and, untimately, will apply what it considers the best overall asjustment... Right? (or is it another Senior Moment?)

No - you have to manually set the zoom (no motor, right? so, no computer control). Full auto determines the best AFMA setting for whatever focal length and distance you've set, then asks if you want to apply it.

Different focal lengths for a zoom lens, and different distances, will give different results. To test different focal lengths, you change the zoom setting, move the camera, and test again.

Quote:

Originally Posted by Bill_in_WA

Question 3: Has anyone out there experimented with diffferent target distances (especially for the longer lenses) that have been aceptable or is the recommendation to adhere to the 50X?

I've tested at 25x and 50x for lenses from 16mm to 200mm on a 7D and a 5DII.

I posted the results on another thread here in pieces, but I summarized everything, including factors leading to the AFMA choices I made from the data, here:

http://www.canonrumors.com/forum/ind....html#msg61329
01-26-2012, 12:22 AM
Dr Croubie

100mm * 50 = 5m.
Ain't metric grand?
01-26-2012, 03:34 AM
Bill_in_WA

Quote:

Originally Posted by neuroanatomist

Math error. 100x50/25.4 = 197" = 16' 5". Same distance for FF and 1.6x.

I've tested at 25x and 50x for lenses from 16mm to 200mm on a 7D and a 5DII.

I posted the results on another thread here in pieces, but I summarized everything, including factors leading to the AFMA choices I made from the data, here:

http://www.canonrumors.com/forum/ind....html#msg61329

Oops, as I said Senior Moment, managed to leave out the 1 on the 198!!!

Just read your write-up and it answers just about all my questions as well as giving me an idea of the various settings on the zooms. It will be interesting to compare the results of the same model lenses on the same model cameras. The only one not common is my 50mm f/1.4.

Like you the 70/200 is about the longest reach I can go to indoors... The 100/400 will have to wait unless I can convince the art store in town to let me use some floor space after hours (The lighting would also be good).

If you happen to have and calibrate a 100/400 I would be interested in your results.

Thanks again for the assistance.
01-26-2012, 08:04 AM
neuroanatomist

I do have a 100-400, and also 1.4x and 2x TCs for the 70-200 II (lens + TC is a separate AFMA setting).

Good luck!
01-26-2012, 12:13 PM
ChadS

Quote:

Originally Posted by Bill_in_WA

Like you the 70/200 is about the longest reach I can go to indoors... The 100/400 will have to wait unless I can convince the art store in town to let me use some floor space after hours (The lighting would also be good).

Ever been to an eye exam where the chart is projected off a couple of mirrors in a Z configuration before you see it? There's absolutely nothing that says you can't do the same thing. If you have access to optical-grade front surface mirrors obviously use them. However, any mirror that you can look into and see a 'normal image' as opposed to a warped, 'fun house' image will work just fine. Be sure the mirrors cover the maximal rays that will enter the pupil of your lens (lines from the edges of the target to the outside edge of the front glass). The partial reflections you'll get off the glass should have nearly no effect at the working distances you're discussing.