How zoom lens work

Started Jul 4, 2011 | Discussions
RoshanL
Junior MemberPosts: 35Gear list
Like?
How zoom lens work
Jul 4, 2011

I'm interested in the workings of the typical SLR zoom lens. If this has been discussed already, please point me in the right direction, since I tried searching on the forums and couldn't find the information I was looking for.

I'm basically interested on how the focal point in varied in a zoom lens and how focus is achieved. What exactly happens inside the lens assembly when the focus ring is rotated. I'm basically looking for a video/animation on the working of a zoom lens. The best I could find was on wikedpedia:

But his doesn't give a clear picture on the zoom lens working.
--
Canon EOS 500D + Sigma DC 18-200mm. OS

 RoshanL's gear list:RoshanL's gear list
Canon PowerShot SD1400 IS Canon EOS 500D Canon EF 28-105mm f/3.5-4.5 II USM Sigma 18-200mm F3.5-6.3 DC OS HSM
Mark9473
Contributing MemberPosts: 733Gear list
Like?
Re: How zoom lens work
In reply to RoshanL, Jul 4, 2011

Actually those are some of the best schematics I've seen, especially the last one. This would be an IF zoom.
--
Mark
my gallery: http://www.dpreview.com/galleries/5120988127/albums

 Mark9473's gear list:Mark9473's gear list
Olympus E-520 Olympus E-30 Olympus Zuiko Digital ED 50-200mm 1:2.8-3.5 SWD Olympus Zuiko Digital 14-54mm 1:2.8-3.5 Olympus SZ-10 +1 more
Reply   Reply with quote   Complain
Mark9473
Contributing MemberPosts: 733Gear list
Like?
Re: How zoom lens work
In reply to Mark9473, Jul 4, 2011

Here's something I bookmarked on another thread:
http://www.pierretoscani.com/echo_telezooms_english.html
Make sure to try out the animation buttons!
--
Mark
my gallery: http://www.dpreview.com/galleries/5120988127/albums

 Mark9473's gear list:Mark9473's gear list
Olympus E-520 Olympus E-30 Olympus Zuiko Digital ED 50-200mm 1:2.8-3.5 SWD Olympus Zuiko Digital 14-54mm 1:2.8-3.5 Olympus SZ-10 +1 more
Reply   Reply with quote   Complain
sherwoodpete
Veteran MemberPosts: 7,761
Like?
Re: How zoom lens work
In reply to Mark9473, Jul 4, 2011

Mark9473 wrote:

Here's something I bookmarked on another thread:
http://www.pierretoscani.com/echo_telezooms_english.html
Make sure to try out the animation buttons!

Very interesting animations, thanks for sharing this.

Regards,
Peter

Reply   Reply with quote   Complain
RoshanL
Junior MemberPosts: 35Gear list
Like?
Re: How zoom lens work
In reply to Mark9473, Jul 4, 2011

Mark9473 wrote:

Here's something I bookmarked on another thread:
http://www.pierretoscani.com/echo_telezooms_english.html
Make sure to try out the animation buttons!
--
Mark
my gallery: http://www.dpreview.com/galleries/5120988127/albums

Thanks a lot for the link. Exactly what I was looking for.

Good write-up with great graphics and animations to explain the concepts in a simple and easy way to understand.

Too bad that most of the website is in French. Its a great resource for beginners to understand the technical aspects of SLR's and lenses.

-- hide signature --

Canon EOS 500D + Sigma DC 18-200mm. OS

 RoshanL's gear list:RoshanL's gear list
Canon PowerShot SD1400 IS Canon EOS 500D Canon EF 28-105mm f/3.5-4.5 II USM Sigma 18-200mm F3.5-6.3 DC OS HSM
Reply   Reply with quote   Complain
Dave Martin
Senior MemberPosts: 2,160
Like?
Re: How zoom lens work - easy math
In reply to RoshanL, Jul 4, 2011

RoshanL wrote:

I'm interested in the workings of the typical SLR zoom lens. If this has been discussed already, please point me in the right direction, since I tried searching on the forums and couldn't find the information I was looking for.

I'm basically interested on how the focal point in varied in a zoom lens and how focus is achieved. What exactly happens inside the lens assembly when the focus ring is rotated. I'm basically looking for a video/animation on the working of a zoom lens. The best I could find was on wikedpedia:

But his doesn't give a clear picture on the zoom lens working.
--
Canon EOS 500D + Sigma DC 18-200mm. OS

Two lenses in a row combine to make a new lens with a new focal length.

The focal length of combined lenses increases with the separation between the lenses.

The animation is good but the math is even easier. Say you have two lenses of focal lengths f' & f" separated by a distance d - this makes a new lens of focal length

f=f'f" / (f'+f"-d)

A Zoom lens has a mechanism that changes the distance between lenses to change the overall focal length. In the equation above, increasing d increases f.

The case of many lenses in a row is handled by using the same equation for each pair.

Practical zoom lenses simultaneously change the focal length and the distance from lens to sensor to keep the image in focus.

Reply   Reply with quote   Complain
RoshanL
Junior MemberPosts: 35Gear list
Like?
Re: How zoom lens work - easy math
In reply to Dave Martin, Jul 5, 2011

@ Dave Martin.. Thanks a lot for the simple and clear explanation of the working of a zoom lens.
--
Canon EOS 500D + Sigma DC 18-200mm. OS

 RoshanL's gear list:RoshanL's gear list
Canon PowerShot SD1400 IS Canon EOS 500D Canon EF 28-105mm f/3.5-4.5 II USM Sigma 18-200mm F3.5-6.3 DC OS HSM
Reply   Reply with quote   Complain
Keyboard shortcuts:
FForum MMy threads