Some new user questions

[Michael Tapes - (MichaelT)]

I will begin to post questions that come to me via email here at the forum so that all can share in the discussion.

A new LensAlign user writes:

Q:
The threaded insert at the bottom of the LensAlign Pro is angled and the unit mounted on top of a light stand looks ugly as heck. I guess this may not have any bearing on the unit's practical use, but aesthetically it is not very kosher looking. Do you want me to live unhappily with this?

A:
Well, actually yes. We are aware that the brass insert is not perfectly perpendicular to the LensAlign floor. To be honest we have not come up with a good way to make it so. We will work on it, but our design assumes that the LA will be mounted on a tripod in which case the angle discrepancy is absorbed by the tripod. Mounting on a light stand is good practice in absence of a tripod but you lose all of the benefits of tripod mounting including fine adjustment during back-sighting. So please live with this aesthetic displeasure. We will work to improve it in the future.

Q:
A couple more questions: The little holes inside the red areas are not dead centered within the red circles. Will this lead to any errors with respect to the unit being nonparallel to the sensor plane?

A:
When you do the sighting use the hole (not the red color) as your guide. Each LA PRO is Laser certified to have accurate sighting, and this is based on the precision location of the bulls-eye "hole", not the color.

Q:
The ruler is concave on the reading face. Is this OK, or should I try to gently straighten it?

A:
I would gently straighten it. If it remains a problem we can send you a new ruler.

Q:
And lastly, given the fact that the depth of field extends a little farther to the back of the target compared to the distance that is in focus in front of the target, should that be taken into consideration and fine tune the focus on the camera to reflect a slightly deeper sharpness behind the zero point compared to the area in front of the zero?

A:
A 2-part answer...
1 - This is one of the beautiful things about LA. You get to "tune" the AF front/back relationship to your liking. (more below)
2 - Most people have a mis-conception about the front/back relationship of DOF. While at Infinity and long distances the classical thinking is true...33% in front and 67% in back. But rapidly as the distance comes off of infinity, the front/back relationship speeds toward 50%/50%. Here is an example...

70mm f2.8
distance - % in front - % behind
100 - 33% - 67%
50 - 48% - 52%
25 - 46% - 54%
15 - 48% - 52%
10 - 48% - 52%
8 - 49% - 51%
6 - 49% - 51%

So to answer the original question, you can use a DOF calculator to find the "true" front/back relationship and set it that way. Or you can be creative and the it for your shooting style. For example if shooting head/shoulder portraits in close you may want to set a front focus bias (80/20) so that when focusing on the leading sys of your subject mode of the back eye and facial features are within the DOF. Just be careful that you always check how your micro adjustment settings affect other distances. The MA is not designed to be set at a close distance if you are going to do generalized shooting. So be creative and change the AF setting when necessary or shut it off if you have it set for specialized shooting.

Sharp shooting!