4 replies to this topic

[DocMD]

Stupid question, guys. I know that IF lenses do not change length during focusing, but I assume they DO change length during the zoom process, as the focal length changes, right?

[Nikon Shooter]

Yes and no.

IF means that the lens shows no sign of change during focusing:
• stays the same in size

• the front element will not rotate — that alone permits the use of
  tulip shaped lens shades.

IF may also include in some high end cases — a zoom function as
in the the older 200~400 ƒ4 and its newer version, the 180~400 ƒ4;
and with the 24~70 ƒ2.8 but may not the case for all zoom lenses.

I always go for the IF lenses when available.
 

[DocMD]

Yes and no.

IF means that the lens shows no sign of change during focusing:
• stays the same in size

• the front element will not rotate — that alone permits the use of
  tulip shaped lens shades.

IF may also include in some high end cases — a zoom function as
in the the older 200~400 ƒ4 and its newer version, the 180~400 ƒ4;
and with the 24~70 ƒ2.8 but may not the case for all zoom lenses.

I always go for the IF lenses when available.
 

Thanks. I had a misconception that the barrel didn’t lengthen when the lens was zoomed either. Then I thought about it and decided I needed clarification.

Thanks again for the help.

[Nikon Shooter]

ADDENDUM

IF lenses share outstanding water — as well as dust
and fungi — resistance.

 

I appreciate their very predictable behaviour of my
long lenses on the gimbal… always in balance.

[Merco_61]

I don't know if you have found Roland Vink's excellent lens resource. To check whether a lens you are interested in has a fixed or a rotating front element, look in the Filter column. r means that it rotates when focusing and z that it rotates when zooming.

 

Link.

 

There are a few rear-zooming lenses that don't change length when changing the focal length. This feature makes for complex linkages in the lens, making them expensive to produce.