All images © Bob Atkins

19.jpg

This website is hosted by:
Host Unlimited Domains on 1 Account

5.jpg

Welcome, Guest. Please login or register.

Login with username, password and session length
 
Web www.bobatkins.com
*
+  The Canon EOS and Photography Forums
|-+  Photography Forums
| |-+  The Canon EOS Forum
| | |-+  Long lens optimization?
« previous next »
Pages: [1]
Print
Author Topic: Long lens optimization?  (Read 1058 times)  bookmark this topic!
Frank Kolwicz
Senior Member
****
Posts: 124


Long lens optimization?
« on: February 29, 2012, 05:33:40 PM »

I was under the impression that Canon revised the formula for the 300+mm lenses in the 1990s to give optimum sharpness at near-wide-open where such lenses are used most often and have the most critical need for sharpness rather than at 1-2 stops closed down from wide open.

Is there anything to that?
Logged
Bob Atkins
Administrator
Hero Member
*****
Posts: 1185


Re: Long lens optimization?
« Reply #1 on: February 29, 2012, 11:59:03 PM »

I'd presume that they'd always been optimized that way. If you make a prime telephoto lens as good as it can be wide open, it will also be as good as it can be stopped down. Making it better wide open doesn't make it worse stopped down.

The only reason to make a lens better when stopped down is that it's cheaper. Making a lens that sharp wide open needs extra corrections and that costs money either via extra elements, more expensive optical glass or increased fabrication costs due to more complex element shapes and/or better quality control of surface accuracy and polish.

With wide zooms you can probably make tradeoffs of wideopen sharpness for field uniformity and better performance over some focal length ranges, but you don't need to make such compromises with long telephoto prime lenses.

So my guess is that there is nothing to that rumor. If The Canon telephoto lenses have gotten better wide open, it's because of advances in design and materials, not a change in design philosophy. Their prices have certainly gone up!
Logged
Pages: [1]    
Print
« previous next »
Jump to: