Tuesday, January 19, 2016

Lens Back Focus Test

Lens back focus has been a known issue for a long time.  With the arrival of 24mega pixels entry DSLRs, this issue become more prominent.

You can follow a simple test on your lens and camera to check for any auto focusing issue, below is simple video by a Malaysian young chap, but it is very to the point.

However, there is more to it.  From my own experience, I would like to add some points.

1. The focus chart that you use.  If you just download it from the internet, and print it out on normal print paper using your office laser printer, the print and paper qualities are not that high in the first place.  It is more difficult to tell which point is sharp, which point is not.

Sample Auto Focus Test Shot 1

The sample test shot above is an example.  Can you tell whether the word 'sharp' is sharp, or the numbers 2 & 4 below it are sharp?  Or the number 2 above it is sharp?

2. If you are doing this test with a zoom lens, you need to do it at the extreme ends of the zoom range, as well as the mid point.  You expect the performance to be consistent over the zoom range, but the actual fact is not.  You may have good auto focus at the mid point, but your auto focus may be off at the extreme ends.  You have to decide what is considered to be good for you.

That's all for today.  Happy shooting photos!

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