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New Contributor
Posts: 2
Registered: ‎10-09-2019
Accepted Solution

EF-S 18-55mm

I am taking an online course on DSLR camera operation and someone posed a question about this lens. At 18 it's extended, at about 34 it's pulled in, but at 55 it's extended again. I see that my lens exhibits the same behavior. Why is this so? I've serach around and cannot find a picture or diagram of the inside of the lens.

 

Thanks

 

Reputable Contributor
Posts: 706
Registered: ‎12-24-2013

Re: EF-S 18-55mm

[ Edited ]

This behaviour is very common with  zoom lenses in the slightly wide to slightly telephoto category. It has to do with the way the internal lenses and groups move inside to change focal length using both retrofocus and telefocus lens design. 

 

This diagram can give you an idea of the complexities involved. 

B7DE8B1A-EB1B-43FA-82D6-5707BAD11CBB.jpeg

Mike Sowsun
S110, SL1, 80D, 5D Mk III
New Contributor
Posts: 2
Registered: ‎10-09-2019

Re: EF-S 18-55mm

Thank you Mike!
VIP
Posts: 11,315
Registered: ‎12-07-2012

Re: EF-S 18-55mm

A more in detailed answer is, not all lenses are designed with internal zoom, constant aperture, and internal focus. The most expensive and difficult designs to make.  Different lenses are designed to do different specific tasks and to be produced at specific price points. Your kit lens the consideration was keeping the cost down. Period. In low cost designs the internal zoom elements might bump into other elements of the lens before they could travel far enough to extend, or contract, to the desired focal length. Compromises are done and room is made for the internals without worrying on what is happening to the outside.

EOS 1DX and 1D Mk IV and several lenses!
VIP
Posts: 11,315
Registered: ‎12-07-2012

Re: EF-S 18-55mm

[ Edited ]

BTW, another factor of this class of lenses, as you close focus, the FL and aperture are effected. The f-ratio can be lesser by 1/3 stop or so. Yeah, it is small but it is there.

EOS 1DX and 1D Mk IV and several lenses!
Esteemed Contributor
Posts: 3,401
Registered: ‎02-17-2016

Re: EF-S 18-55mm

I believe it is the 15-85 that has a mark on the zoom ring at the lower end of the zoom range. I finally figured out that this was the zoom position for the smallest travel and the mark was to indicate where to "park" the lens before you put it in the bag!

Reputable Contributor
Posts: 706
Registered: ‎12-24-2013

Re: EF-S 18-55mm

[ Edited ]

My 15-85 has no markings on the zoom ring. Are you thinking of another lens maybe? 

 

001 a.jpg

 

Many of my other lenses have a mark on the zoom ring but it doesn't always denote the shortest length. I think it is just there because the spacing on the zoom scale markings don't match the travel on the zoom ring. 

001 x.jpg

Mike Sowsun
S110, SL1, 80D, 5D Mk III
Esteemed Contributor
Posts: 3,401
Registered: ‎02-17-2016

Re: EF-S 18-55mm

It is the 17-85:

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