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tumbleweed
Dogsey Veteran
tumbleweed is offline  
Location: East sussex
Joined: Feb 2007
Posts: 2,260
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05-08-2015, 09:41 AM

Camera lens focus issues




Like most products some are made well and some are frankly terrible. It is the same with camera lenses, cheaper ones don't have the lens ground to such a fine precision so they can cause focus issues. That is the foreground may be in focus and the background blurred when the subject is the target say like a person . Same thing again the foreground may be out of focus and the background is in focus.
There are two ways to get over his depending on the camera. Some camera do have a fine adjustment to overcome these problems and some don't, in which case the lens needs to be sent back for recalibration.

Ok so far

Now how do you check to see if a lens is equal in focus at the back and front at the same time?

One way is to use a ruler on a desk and take a picture and then see if both ends of the ruler are in focus or not. The problem with this is getting the camera looking down at the right angle , get it wrong and the check is worthless.

This product in the photo overcomes this issue as the scale is at the correct angle. By having the middle of the lens and the centre of the target at the same height and focus problems will show up worst at the number 6 at either end of the scale.

AS you can see there is hardly and difference in sharpness at either 6 on the scale so the lens is well made and prefocused properly before going on sale.

This is one of the reasons why a quality lens is so much more expensive than a cheap one

So now you may start to know how to fix front/back focus issues
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