Go Back   Steve's Digicams Forums > Digicam Help > General Discussion

Reply
 
Thread Tools Search this Thread
Old Jul 9, 2006, 8:17 PM   #1
Log
Senior Member
 
Log's Avatar
 
Join Date: Feb 2006
Posts: 394
Default

i was skimming through the internet reviewing the "bigma" (50-500)... while some people have shots at 500 saying wide open at 5.6 and some saying 6.3 am i looking at different lens reviews as the 50-500 on sigmas website says 6.3... while the only 500 5.6 they have is their prime and 300-800... did they make a new 50-500 with a smaller max. aperture?

logan
Log is offline   Reply With Quote
Sponsored Links
Old Jul 10, 2006, 1:55 AM   #2
Senior Member
 
Marc H's Avatar
 
Join Date: Dec 2003
Posts: 130
Default

I'ts quite simple.

Basically the bigma is a F4-F6.3 aperture lens, only the lens reports an aperture of F5.6 to the camera at 500MM , so the autofocus keeps working on some bodies.

Bodies like the Canon 300D 350D, 10D, 20D and 30d, to name a few, don't have autofocus on lenses with an aperture higher than 5.6. Pro bodies like the Canon 1D models go upto F8 (or something like that), before they loose autofocus.

Sigma just tricks the body, keeping the autofocus on.




Marc H is offline   Reply With Quote
Old Jul 10, 2006, 10:04 PM   #3
Log
Senior Member
 
Log's Avatar
 
Join Date: Feb 2006
Posts: 394
Default

thanks for that

-Logan
Log is offline   Reply With Quote
Old Jul 10, 2006, 10:31 PM   #4
Senior Member
 
Justin Hancock's Avatar
 
Join Date: Mar 2006
Posts: 272
Default

Could that concept be explained better? Are you talking about lenses with a maximum aperture smaller than f/5.6 lose autofocus?

So say if a lense has a maximum aperture of f/3.5 but you're shooting in apeture mode at an aperture of f/22, it will still have autofocus.

Do lenses typically autofocus at their maximum aperture?


...Actually thinking out this makes sense...the lense always uses the maximum aperture (i.e. when composing the shot in the viewfinder) but only stops down to the specified aperture when the picture is taken. So it probably does autofocus at its maximum aperture.
Justin Hancock is offline   Reply With Quote
Old Jul 11, 2006, 5:09 AM   #5
Super Moderator
 
peripatetic's Avatar
 
Join Date: Nov 2004
Posts: 3,599
Default

Yes justin that's right.

They focus at max aperture then stop down for the shot.
peripatetic is offline   Reply With Quote
 
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -5. The time now is 6:03 AM.