Astronomy, Photography and Weather
March 29, 2024, 07:55:09 am
Welcome, Guest. Please login or register.

Login with username, password and session length
News: IAA lecture programme continues alternate Wednesdays from September - an excellent programme of lectures- Queens University Belfast - Bell Lecture Theatre. Also keep an eye out for the Summer Events
 
  Home Help Search Gallery Staff List Login Register  

Taped Contacts - 1.4 X

Pages: [1]
  Print  
Author Topic: Taped Contacts - 1.4 X  (Read 686 times)
brianb
Hero Member
*****
Posts: 1228



View Profile
« on: June 22, 2009, 11:39:22 pm »

Quote
So the shutter speed for f5.6  (with the extender) and f8 (the real f8 without the extender) is the same which suggests to me that the f5.6 in the first photo with the extender is infact f8 even though it's reading f5.6.           
Yes.

But this is absolutely straight forward - with the lens fully open, the linear aperture is obviously unchanged, so the extender must change the f ratio by the same amount as it changes the focal length (since the f ratio is simply the focal length divided by the linear aperture).

What the electronics are fooled into saying is irrelevant - so long as you're using TTL metering. If you're using external metering, you'd better know what the actual f-number is ... this is where one of those old fashioned aperture setting rings comes in handy, even though you do have to do a bit of simple mental arithmetic, there's never any doubt as to what size hole you have set ... and personally I find it a lot less confusing than using those multi mode dials.
Report Spam   Logged


Pages: [1]
  Print  
 
Jump to:  

Bookmark this site! | Upgrade This Forum
SMF For Free - Create your own Forum

Powered by SMF | SMF © 2016, Simple Machines
Privacy Policy