da 55-300 problem

LunaS · 06-07-2014, 03:21 PM

Hello. I have this problem with my da 55-300. i turn the lens to 300mm, focus at that mm (auto or manual). then if i turn the lens to any wider position (280, 250, 2oo mm or everywhere else), the subject goes out of focus. So far i l knew that in a zoom lens if you focus on the telefoto end, it will keep being focused at all wider positions. Has enyone else seen the same problem? thanks

calculator01 · 06-07-2014, 03:40 PM

Please, you only need to post your question once. Don't revive old threads... Threads from 5 years ago...

This seems like a very normal issue to me. When you change the zoom, you are effectively changing the length of the lens, therefore you are changing the focus.

**boriscleto** · 06-07-2014, 04:29 PM

There are 2 types of zoom lens, parfocal and varifocal. A parfocal lens will stay focused at any focal length while zooming. A varifocal lens changes focus while zooming.

It's easier to design a varifocal lens, so most consumer zooms are varifocal.

06-07-2014, 03:21 PM	#1
LunaS New Member Join Date: May 2014 Posts: 5	da 55-300 problem Hello. I have this problem with my da 55-300. i turn the lens to 300mm, focus at that mm (auto or manual). then if i turn the lens to any wider position (280, 250, 2oo mm or everywhere else), the subject goes out of focus. So far i l knew that in a zoom lens if you focus on the telefoto end, it will keep being focused at all wider positions. Has enyone else seen the same problem? thanks

06-07-2014, 03:40 PM	#2
calculator01 Veteran Member Join Date: Nov 2010 Location: Edmonton, Alberta Photos: Albums Posts: 817	Please, you only need to post your question once. Don't revive old threads... Threads from 5 years ago... This seems like a very normal issue to me. When you change the zoom, you are effectively changing the length of the lens, therefore you are changing the focus. Last edited by calculator01; 06-07-2014 at 03:48 PM.

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06-07-2014, 04:29 PM	#3
boriscleto Loyal Site Supporter Join Date: Dec 2009 Location: North Syracuse, NY Photos: Gallery Posts: 16,475	There are 2 types of zoom lens, parfocal and varifocal. A parfocal lens will stay focused at any focal length while zooming. A varifocal lens changes focus while zooming. It's easier to design a varifocal lens, so most consumer zooms are varifocal.