Go Back   Steve's Digicams Forums > Digicam Help > What Camera Should I Buy?

View Poll Results: My top picks are:
Olympus E-330 3 4.55%
Olympus E-500 9 13.64%
Nikon D50 15 22.73%
Nikon D70s 3 4.55%
Canon Rebel XT 9 13.64%
Canon 20D 11 16.67%
Pentax *ist DL2 5 7.58%
Waiting for Panasonic's DSLR 2 3.03%
Waiting for new announcments this month 6 9.09%
Haven't decided yet !? 3 4.55%
Voters: 66. You may not vote on this poll

Reply
 
Thread Tools Search this Thread
Old Feb 21, 2006, 3:44 PM   #121
Senior Member
 
rjseeney's Avatar
 
Join Date: Dec 2004
Location: Taylor Mill, Kentucky
Posts: 2,398
Default

Idan wrote:
Quote:
So are we lookingmostly at the large aperture number on the lens, or the minimum aperture of the lens has any significant value or all the lenses has the same lowest aperture number ?
What are you asking?? The lower F-stop values (ie f/2.8, f/1.8) are the wider openings. Typically you'll only find these lower numbers on bright primes or very expensive zoom lenses. These lenses are ideal for low light situations or when you want a very shallow DOF. Most consumer grade lenses have max aperatures starting at f/3.5 or even higher.

The minimum aperatures (expressed by higher f/stop number, ie f/22 or higher) allow the least amount of light into the camera. They produce the greatest depth of field, but really can only be used in very bright light. Also, most lenses suffer from poorer image quality due to diffraction at these aperatures. Most lenses go to at least f/22, some even higher.
rjseeney is offline   Reply With Quote
Old Feb 21, 2006, 3:47 PM   #122
Administrator
 
Join Date: Jun 2003
Location: Savannah, GA (USA)
Posts: 22,378
Default

Idan wrote:
Quote:
So are we lookingmostly at the large aperture number on the lens, or the minimum aperture of the lens has any significant value or all the lenses has the same lowest aperture number ?
I probaby woudn't use the term lowest or highest when discussing aperture, since you can confuse as to whether you're discussing aperture size or f/stop value.

You usually see aperture size referrred to as larger or wider (represented by smaller f/stop numbers) or smaller (represented by higher f/stop numbers). Sometimes you'll see the term maximum (for largest available aperture) or minimum (for smallest available aperture), too.

Most lenses can be "stopped down" (a term meaning to use a smaller aperture setting) to around f/22. Some can even be set to apertures as small as f/32 or even f/45 (you'll see this with some macro lenses).

But, you can run into diffraction problems that degrade image quality if apertures are too small.

Most lenses are going to be sharpest at around 3 stops down from their largest available aperture, but this will vary by lens as to where their aperture "sweet spot" is for a given focal length.


JimC is offline   Reply With Quote
Old Feb 21, 2006, 3:49 PM   #123
Senior Member
 
Idan's Avatar
 
Join Date: Jan 2006
Posts: 267
Default

Why can't I get a a sharp image (all sharp) when I am usingsmaller f/stop numbers ?
Idan is offline   Reply With Quote
Old Feb 21, 2006, 3:54 PM   #124
Administrator
 
Join Date: Jun 2003
Location: Savannah, GA (USA)
Posts: 22,378
Default

Idan wrote:
Quote:
Why can't I get a a sharp image (all sharp) when I am usingsmaller f/stop numbers ?

That depend on what you're shooting, how much of the frame your subjects occupy, how far they are separated in distance to your lens, what your focus point is, and more.

You also need to keep shutter speeds in mind if not using a tripod or flash (since you'll get blurry photos if shutter speeds are too slow to stop subject movement or reduce blur from camera shake).

See this handy online Depth of Field calculator to get a better idea of how focus distance, aperture and focal length impact depth of field.

But, keep in mind that if you use a longer focal length, you'd need to shoot from further away to achieve the same framing, and vice-versa (shorter focal lengths will require you to be closer so that your subject occupies the same percentage of the frame). ;-)

http://www.dofmaster.com/dofjs.html


JimC is offline   Reply With Quote
Old Feb 21, 2006, 4:01 PM   #125
Senior Member
 
Idan's Avatar
 
Join Date: Jan 2006
Posts: 267
Default

Those applets really help you understand what many words can't thanks again.

Question:

Is it possible to shoot a subject that is 3 meters away from you at focal length 200mm for example, I just can't get the focal length meaning right.
Idan is offline   Reply With Quote
Old Feb 21, 2006, 4:12 PM   #126
Administrator
 
Join Date: Jun 2003
Location: Savannah, GA (USA)
Posts: 22,378
Default

That depends on the size of your subject and the minimum focus distance for the lens/

This may help. A longer focal length gives you a narrower angle of view for more apparent magnification. A shorter focal length gives you a wider angle of view for less apparent magnification.

Keep in mind that this app was designed for 35mm camers. The same focal length lens used on an entry level DSLR from Canon will appear to be 60% "longer" (it will have a narrower angle of view) and a lens used on an entry level DSLR from Nikon, Pentax or KM will appear to be 52% longer.

Lenses used on the Olympus models will appear to be twice as long compared to the same focal length on a 35mm camera (since they have smaller sensors compared to the other major brands).

http://consumer.usa.canon.com/app/ht...al_length.html

JimC is offline   Reply With Quote
Old Feb 21, 2006, 4:15 PM   #127
Senior Member
 
Idan's Avatar
 
Join Date: Jan 2006
Posts: 267
Default

so the larger the focal number the narrower is the angle is it right ?
Idan is offline   Reply With Quote
Old Feb 21, 2006, 4:16 PM   #128
Administrator
 
Join Date: Jun 2003
Location: Savannah, GA (USA)
Posts: 22,378
Default

Yes, that's what I said (and you can see it in the graphics at the link I posted, and it even shows you the angle of view in degrees for the focal length selected).

JimC is offline   Reply With Quote
Old Feb 21, 2006, 4:19 PM   #129
Senior Member
 
Idan's Avatar
 
Join Date: Jan 2006
Posts: 267
Default

So in order to get much larger focal range you need a larger radius.

My other question is: What is EISA and why did The Canon Rebel XT won this EISA award ? Are those awards have any significant meanings to you deciding which camera to buy ?



Idan is offline   Reply With Quote
Old Feb 21, 2006, 4:23 PM   #130
Administrator
 
Join Date: Jun 2003
Location: Savannah, GA (USA)
Posts: 22,378
Default

If you want more apparent magnification so that your subject occupies a larger percentage of the frame from the same shooting distance, you use a longer focal length.

If you want less apparent magnification so that your subject occupies a smaller percentage of the frame from the same shooting distance, you use a shorter focal length.

But, even if you move closer or further away so that your subject occupies the same percentage of the frame with different focal length lenses, you'll have perspective differences caused by your shooting distance (making your background and foreground elements appear to be closer together or spread further apart).

So, perspective is another consideration, even if you can use your feet for zoom to achieve the desired framing. We discussed that earlier in this thread.


JimC 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 3:50 PM.