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

Reply
 
Thread Tools Search this Thread
Old Oct 27, 2005, 11:11 PM   #1
Senior Member
 
Join Date: Oct 2005
Posts: 133
Default

Hi,

What effect does the lens diameter have on the quality of a picture taken?

What effect does the lens diameter have on the "width" of the image taken?

For example, some cameras have a lense that is about 1 inch in diameter (eg a common digital camera), whereas others have lenses with very large diameters (eg a typical SLR)....and then there are digital cameras that are somewhere in between and have lense diameters that are about 2 inches in diameter.

How does this affect the image taken?

Does a larger diameter lense have a larger field of view? Does a larger diameter lens give "wider angle" images?

Is a larger diameter better?

Thanks!
Juggernaut
Juggernaut is offline   Reply With Quote
Sponsored Links
Old Oct 28, 2005, 12:46 AM   #2
Senior Member
 
geriatric's Avatar
 
Join Date: May 2005
Posts: 326
Default

1/ none

2/none

3/none

4/ no no

5/ yes it is faster
geriatric is offline   Reply With Quote
Old Oct 28, 2005, 6:32 AM   #3
Senior Member
 
Join Date: Jun 2002
Posts: 394
Default

I like number 5. I have also read where larger CCD's require a larger dia lens?
normc is offline   Reply With Quote
Old Oct 28, 2005, 6:57 AM   #4
Senior Member
 
Carrots's Avatar
 
Join Date: Jun 2005
Posts: 377
Default

Although I am no expert on this, I know that larger CCD's require lenses with a larger diameter. If you mount a "for digital" lens for your typical Rebels XT's etc on a full frame CCD (or rather CMOS)camera (like the 1Ds mark II), your photo will have a nice round black circular "frame" (vignetting I think its called)on it.

This Canon 5D review explains it nicely.

http://www.mobilityguru.com/2005/10/...als_a_new_era/


I would also like to explain #5 of Geriatric a bit better, as it took me a while to figure it out. Because the diameter is larger, the apperature can also be larger. This lets more light in, and allows you to use faster shutter speeds.
Carrots is offline   Reply With Quote
Old Oct 28, 2005, 1:58 PM   #5
E.T
Senior Member
 
E.T's Avatar
 
Join Date: Jul 2003
Posts: 921
Default

geriatric wrote:
Quote:
5/ yesÂ* it is faster
Wrong, it's both yes and no.
What decides which lens is faster is aperture ratio/F-ratio. (focal length divided by lens diameter/aperture)

So lens whose diameter is only 0.5" and has 1" focal length is faster than 5" diameter lens with 15" focal length.


Now because most digicam sensors are smaller than size standard film they don't need so long real focal lengths to get equal "magnification"/field of view. This is where that "35mm equivalent" mentioned with digicams comes.
For example lens of my KonicaMinolta A2 is 28-200mm equivalent while lens' real focal length is about 7-49mm.
So because aperture ratio (how fast lens is) depends on focal length and real focal lengths are small even small diameter lens is enough to give good aperture ratio.

So here's simple example calculation:
KM A2's lens is F3.5 at tele ("200" mm).
Basing to aperture ratio's formula that would mean ~57mm as required aperture size/lens diameter. Now camera's filter threads are 49mm sized and diameter of lens itself is ~40mm!
That's because of smaller real focal length.
E.T is offline   Reply With Quote
Old Oct 28, 2005, 2:03 PM   #6
DBB
Senior Member
 
Join Date: Jan 2004
Posts: 2,483
Default

The expression "Lens Diameter" means absolutely NOTHING.

Every lens that you purchase, or the fixed lens on a point and shoot, are rated. This rating tells you it's maximum aperature, minimum aperture, etc.

Often enough a lens will have a large diameter because of the mechanics involved with it's ratings. For example, you can have a prime lens, with an extremely LARGE aperture (1.4, 1.8, etc) and yet it's diameter will be dwarfed by the diameter of an f8 500mm lens.

Moreover some of the cheaper manufacturer's have an extrmemly large diameter and yet poor light gathering ability.

Look for the rating of the lens, for it's statistics, and look for reviews of the lens for the optical quality.

Dave
DBB is offline   Reply With Quote
Old Oct 28, 2005, 3:22 PM   #7
Senior Member
 
Join Date: Jun 2002
Posts: 394
Default

Ok, but this still leaves the question of lens dia relative to the size of the CCD?
normc is offline   Reply With Quote
Old Oct 28, 2005, 3:32 PM   #9
E.T
Senior Member
 
E.T's Avatar
 
Join Date: Jul 2003
Posts: 921
Default

normc wrote:
Quote:
Ok, but this still leaves the question of lens dia relative to the size of the CCD?
The bigger the "sensor" (CCD/CMOS or film frame) is, the bigger lens diameter it requires for same aperture/f-ratio ("speed") because of longer focal length.
E.T is offline   Reply With Quote
Old Oct 28, 2005, 4:05 PM   #10
Senior Member
 
geriatric's Avatar
 
Join Date: May 2005
Posts: 326
Default

As I said carrots, it is faster. Faster shutter speed. I am assuming Juggernaut was writing about a given focal length. Take a 50mm lens, f3.5 lens to F1.2 a great increase in size.
geriatric 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 5:33 AM.