Problem after D80 focus adjustment (back focus)

Started Dec 9, 2006 | Discussions thread
PhotoLeon1935
Senior MemberPosts: 2,305
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Looking forward at Back Focus –NEW
In reply to SteveL54, Dec 19, 2006

I finished the test target and the procedure -- Check it out. Let me know how it works.

After publishing targets and information on Back Focus issues I kept running into people who, no matter how careful and meticulous they were kept getting unexplainable problems in focus.

Phil Askey says that back focus is way overblown. Cameras come out of the factory with reasonably correct focus. I agree with him. The methods used by Nikon and other manufacturers are able to let the computer on the factory test bench adjust the focus and the mirror stops are set at an arbitrary position to allow minor adjustments in the field if needed later.

However all test targets used by the consumer including my own are flawed. They do not account for the myriad of flaws, compromises and various astigmatisms that are in the lenses sold in today’s market. A lens that starts at 18 mm and goes to 70, 135 and 200 mm was unheard of just a few years ago. In designing this new generation of compact, wide lenses there had to be some shortcomings to accommodate the problems of “wide”.

A new form of astigmatism was created that as far as I know has not even been given a name yet. We know about cylinder astigmatism if we wear eyeglasses. This new astigmatism appears in different areas of the image and maintains geometry at the expense of focus.

I have created a new focus target and method which will allow you to see what is happening. It uses a new and accurate method to apply the statistical tools built into PhotoShop to measure Standard Deviation to an accuracy of three significant digits. There is now no guessing at what is sharp and what is not. You can see the numbers.

If you go to my site you will learn:
1) How the DSLR phase based focus works.
2) How to absolutely identify the sharpest point in an image
3) How to identify the flaws in a lens and map them
4) How tell whether the problem is with the camera or the lens

If you go to this site you will be there for a while. Don’t forget to leave a comment or the thread will roll off page one and I will have to shamelessly bump it. Sorry, Phil,

Go now to:
http://www.leongoodman.com/d70focuspart5.html

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