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

Reply
 
Thread Tools Search this Thread
Old Jan 21, 2012, 4:34 AM   #1
Senior Member
 
MartinSykes's Avatar
 
Join Date: Feb 2010
Location: Cheshire, UK
Posts: 854
Default actual aperture

Was trying to explain a question in another thread but not sure of the correct answer myself. Here's the same shot taken at f/4 with a small sensor and APS-C sensor:

I *think* the explanation is that the dof on the small sensor is more because f/4 means the *actual* focal length divided by 4 and although both cameras may have said 28mm focal length, that's 35mm equivalent. The actual focal lengths are more likely something like 20mm and 5mm (or something like that) so the f/4 aperture on a small sensor camera is a lot smaller than the f/4 aperture on an APS-C camera.

Am I anywhere close?

__________________
AutoHDR - Free HDR software for Windows at http://www.autohdr.co.uk on Facebook at http://www.facebook.com/home.php?sk=...36045126467361
My Flickr stream: http://www.flickr.com/photos/martinsykes
Panasonic DMC-FZ38, Sony ­α580
MartinSykes is offline   Reply With Quote
Sponsored Links
Old Jan 21, 2012, 7:44 AM   #2
Senior Member
 
Join Date: Apr 2010
Posts: 584
Default

Quote:
Originally Posted by MartinSykes View Post
The actual focal lengths are more likely something like 20mm and 5mm (or something like that) so the f/4 aperture on a small sensor camera is a lot smaller than the f/4 aperture on an APS-C camera.

Am I anywhere close?
Yes. Aperture is just a simple ratio of FL/aperture-diameter. Small sensors
use smaller lenses with shorter focal length. The FL range of the FZ38 is 4.8mm-86.4mm. This gives a field of view which would be equivalent to 27mm-486mm on 35mm film or a full-frame digital camera. As you can see in your example shots, for a given value of f,
the small sensor gives a greater DOF.
corkpix is offline   Reply With Quote
Old Jan 21, 2012, 3:19 PM   #3
Senior Member
 
Join Date: Jan 2011
Location: Australia, New South Wales central coast
Posts: 2,907
Default

G'day Martin

This is a great topic for discussion & I am sure that lots of responses will come out of the woodwork

My curiosity also comes in here too > forget sensor size for a moment
Several thousand years ago - back in the 60s - one of the units I did with the 3-year diploma of photography course [at what's now called RMIT university] was Photographic Optics. One of the 'golden rules' that I've always remembered was the mantra "when the image size is the same [regardless of lens used] then the depth-of-field will be the same

This was in answer to so many people saying "use a wide-angle lens to get more DoF" ... not realising that the w/a lens reduces the size of every detail within the image - but we didn't go into differences between lenses for differing film formats. For most of our work we used 4" x 5" sheet inside the studio and a choice of 2-1/4" sq or 35mm outside ... I and most others chose 35mm for the choice of lenses available

In the current climate of sensor sizes of 1001 shapes & sizes I am now wondering more about this topic > but not in an academic way, more the day-to-day practical way

I have noticed with my FZ cameras that the DoF is 'beaut' regardless of aperture settings, and that I achieve shallow DoF best via use of zoom rather than use of aperture ~ though the aperture selection does make a difference too

More experimentation needed & I'll follow this thread with interest too

Regards, Phil
__________________
Has Fuji & Lumix superzoom cameras and loves their amazing capabilities
Spends 8-9 months each year travelling Australia
Recent images at http://www.flickr.com/photos/ozzie_traveller/sets/
Ozzie_Traveller 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 8:04 AM.