Go Back   Steve's Digicams Forums > Digicam Help > Newbie Help

Reply
 
Thread Tools Search this Thread
Old May 13, 2007, 10:40 PM   #1
Junior Member
 
chad515's Avatar
 
Join Date: May 2007
Posts: 11
Default

I'm just starting to understand what the aperture specs mean on digital cameras. I've found plenty of pages describing the technical meaning of aperture, but I haven't seemed to find the practical application of that to a point and shoot camera. I know that all the ultracompact point and shoot cameras will have variable maximum apertures, but do I need to pay close attention to those specs when comparing cameras. If so, what will it realistically affect? Low light performance? Something else?

Thanks for any help you can offer.
chad515 is offline   Reply With Quote
Sponsored Links
Old May 14, 2007, 3:04 AM   #2
Senior Member
 
TCav's Avatar
 
Join Date: Sep 2005
Location: Washington, DC, Metro Area, Maryland
Posts: 13,572
Default

Low light performance and depth of field.

With a larger aperature (smaller f/number) more light gets through the lens to the image sensor, so you can use a faster shutter speed to capture motion, or use a lower ISO setting to avoid noise in the image, or other creative and technical reasons.

Depth of field is the range of objects that are in focus. The autofocus systems will automatically focus on whatever object you point the camera at (hopefully). The larger the aperature, the fewer objects in front of and beyond that object, will be in focus as well. A smaller aperature (larger f/number) will increase the range within which objects will be in focus. There are several artistic reasons for having a smaller (shorter, shallower)or a larger (longer, deeper) depth of field, and you will find several examples in these forums.
TCav is offline   Reply With Quote
Old May 14, 2007, 6:16 AM   #3
Super Moderator
 
Mark1616's Avatar
 
Join Date: Oct 2005
Posts: 7,452
Default

To add to the low light performance and dof another aspect is allowing a higher shutter speed in general shooting allowing you to freeze a fast moving subject.

Here are a couple of real world examples to show what the aperture will mean. One thing to be aware of with a P&S camera you are unlikely to get the shallow dof as shown in the first shot but if you frame tight on a face or a flower you should be able to get something where the background is out of focus (this is a function of the sensor being small meaning that the focal length of the lens isa P&S is short. The ability to blur a background is increased with the focal length of the lens).

Wide aperture with long lens (f4 and 380mm). When I mention lens lengths in mm these are the real length of the lens not 35mm equivalent so this is what makes a really huge difference when shooting with a dSLR rather than a P&S.



Narrow aperture wide lens (something like f9 and 35mm but can't fully remember)



Here I have used a lens about 140mm and f9 to reduce the shutter speed to 1/200th which will then allow me to pan with the subject and blur the background.


Mark1616 is offline   Reply With Quote
Old May 14, 2007, 8:40 AM   #4
Junior Member
 
chad515's Avatar
 
Join Date: May 2007
Posts: 11
Default

Thanks very much for the help. I guess my remaining question is how much of a difference in f number really makes a difference. On the wide-end of the range, most of the cameras I'm looking at have f numbers of 2.8, 3.3, or 3.5. Will I see much difference between those? Or will an amateur like me really not notice a difference between f numbers so close together? On the telephoto end of the range, they seem to range a bit more (4.2 vs. 5.8, etc). Perhaps that's where I'll see more of a difference?
chad515 is offline   Reply With Quote
Old May 14, 2007, 8:55 AM   #5
Super Moderator
 
Mark1616's Avatar
 
Join Date: Oct 2005
Posts: 7,452
Default

There will be noticeable differences depending on the focal length etc, do you have any specific cameras in mind?
Mark1616 is offline   Reply With Quote
Old May 14, 2007, 9:00 AM   #6
Junior Member
 
chad515's Avatar
 
Join Date: May 2007
Posts: 11
Default

Yes. I was looking at the Nikon Coolpix S50, the Sony Cybershot T20, and the Canon Powershot SD800 IS. They all have optical image stabilization (which should help with my low light problems), but I want to make sure I don't pick one that has an aperture that counters the low-light bonus I get from OIS.
chad515 is offline   Reply With Quote
Old May 14, 2007, 9:02 AM   #7
Junior Member
 
chad515's Avatar
 
Join Date: May 2007
Posts: 11
Default

Oh, you probably wanted me to tell you the focal length of those cameras.
Nikon S50 - 6.3 mm - 18.9 mm (38 - 114mm 35mm equivalent), f/3.3-4.2
Sony T20 - 6.33 mm - 19 mm (38 - 114mm 35mm equivalent), f/3.5-4.3
Canon SD800 - 4.6 mm - 17.3 mm (28 - 105mm 35mm equivalent), f/2.8-5.8

chad515 is offline   Reply With Quote
Old May 14, 2007, 9:55 AM   #8
Senior Member
 
TCav's Avatar
 
Join Date: Sep 2005
Location: Washington, DC, Metro Area, Maryland
Posts: 13,572
Default

chad515 wrote:
Quote:
Thanks very much for the help. I guess my remaining question is how much of a difference in f number really makes a difference. On the wide-end of the range, most of the cameras I'm looking at have f numbers of 2.8, 3.3, or 3.5. Will I see much difference between those? Or will an amateur like me really not notice a difference between f numbers so close together? On the telephoto end of the range, they seem to range a bit more (4.2 vs. 5.8, etc). Perhaps that's where I'll see more of a difference?
You won't usually see a significant difference in the depth of field between f/2.8 and f/3.5. The difference only really becomes noticeable with at least 3 to 4 f-stops. Another contributing factor to the amount of depth of field is the size of the image sensor, and all the cameras you referred to have pretty small image sensors, so you may not see much difference in depth of field out of them anyway.

And the aperatures you're talking about are the maximum aperatures at particular focal lengths. The difference you'll see is when you compare the depth of field wide opento when you close the aperature down to f/11 or f/16.

TCav is offline   Reply With Quote
Old May 14, 2007, 9:57 AM   #9
Super Moderator
 
Mark1616's Avatar
 
Join Date: Oct 2005
Posts: 7,452
Default

I'm not an expert on any of the cameras so can't give advice on anything apart from looking at the numbers. The longer the real lens length (not 35mm equiv) and the wider the aperture (lower f number) the better as you will have a small chance of getting a reduced dof as in the top photo above and will allow more light into the lens to make them better in low light conditions with the first two options.

style="BACKGROUND-COLOR: #000000"Having said that you are not going to get much blurred backgrounds from small lenses so the only way you will get anything if you want to is buy using max zoom and framing really tight onto objects close to the camera.
Mark1616 is offline   Reply With Quote
Old May 14, 2007, 11:17 PM   #10
Senior Member
 
Join Date: Dec 2006
Location: Davenport, IA
Posts: 2,093
Default

Most of the cameras in the class you're talking about are unlikely to close down below f8. This again is due to the small sensor becoming diffraction limited earlier than the larger DSLR sensors.

The differences between the Nikon and Sony are negligible. The Canon is a bit of an anomaly. It has slight edge, ~1/3 stop faster, which might occasionally make a difference in low light but on the telephoto side it's pretty close to a full f-stop slower which in low light will give the edge to the other two.
ac.smith 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 12:41 PM.