Go Back   Steve's Digicams Forums > Digital SLR and Interchangeable Lens Cameras > Canon Lenses

Reply
 
Thread Tools Search this Thread
Old Apr 28, 2005, 10:01 PM   #1
Junior Member
 
Join Date: Apr 2005
Posts: 4
Default

Hi all, this might seem a stupid question for all you pro's but I'm new to this game, .... just purchased a 20D with 17-85 IS lens and wanting to buy posibly a 70-200 or 300 zoom. Can someone give me the formula to work out the magnification factor, (ie; 2x 3x 4x ....etc) all help greatly appreciated.

Brian
Brian210 is offline   Reply With Quote
Sponsored Links
Old Apr 29, 2005, 3:42 PM   #2
djb
Senior Member
 
Join Date: Apr 2003
Posts: 2,289
Default

85/17 = 5 so you have a 5X zoom which is arbitray since a 100-500mm lense will also be a 5X zoom. i think the standard is a 50mm lense as that producees an image as an ye sees it (you pros can correct me if i'm wrong). so a 500mm would be a factor of 1X so you can divide any focal length by 50 and come up with a comparative magnification. in your case wou woul have a mgnification of .34X to 1.7X a normal lense. and as the example of a 100-500mm would be 2X to 10X magnification over the normal lense. i hope that helps and is correct.

dennis
djb is offline   Reply With Quote
Old Apr 30, 2005, 4:35 AM   #3
Junior Member
 
Join Date: Apr 2005
Posts: 4
Default

Many thanks Dennis, that certainly makes things a lot clearer.... so is that the same as say .... my Binoculars as regards magnification, (ie: they are 12 x 50) and that gives me 12 times magnification, so a subject at 1200 metres gives me a field view of 100 metres ? As regards to my future purchase of telephoto lens ...... well I'm still sifting through all the advice on this forum, .... and still don't know whether to go for EF70-200 f4L USM or the cheaper ones EF 75-300 f4-5.6 IS USM or even one of the Sigma brands :? all so very confusing !

Brian
PS. looking at your explanation again ... I've realised that my Binoculars question has no bearing on camera lens !!!
Brian210 is offline   Reply With Quote
Old Apr 30, 2005, 6:25 AM   #4
NHL
Senior Member
 
NHL's Avatar
 
Join Date: Jun 2002
Location: 39.18776, -77.311353333333
Posts: 11,544
Default

I believe that's what djb is trying to convey...

A 50mm is considered a 'normal' field of view for a human
-> a 70-200 is about 1.4x to 4x the 'normal' field of view, ie it 'zooms in' 1.4x to 4x time

ie (70 divide by 50)=1.4 and (200 divide by 50)=4
... and 300 divide by 70 is what's called the zoom ratio and has no bearing since a 400/100 will also have the same ratio but different magnification (or FOV)
NHL is offline   Reply With Quote
Old Apr 30, 2005, 7:02 AM   #5
Junior Member
 
Join Date: Apr 2005
Posts: 4
Default

Thanks very much indeed ...... now, crystal clear !

Brian
Brian210 is offline   Reply With Quote
Old May 1, 2005, 2:25 AM   #6
Member
 
TDM_Canon_User's Avatar
 
Join Date: Jan 2005
Posts: 90
Default



Think of it this way: a 50mm lens on 35mm film provides a view angle equal to what your eye will see looking straight ahead.

100mm halves the angle and provides 2x magnification; a lighthouse that is 1" on a 4x6 print will now be 2".

200mm 4x; 400mm 8x; etc.




TDM_Canon_User 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 3:02 AM.