Go Back   Steve's Digicams Forums > Digital SLR and Interchangeable Lens Cameras > Canon Lenses

Reply
 
Thread Tools Search this Thread
Old Dec 5, 2004, 9:51 AM   #1
Senior Member
 
WisconsinGirl's Avatar
 
Join Date: Oct 2004
Posts: 606
Default

I've been looking into wide angle lenses (for wide landscape shots) and I'm looking at this one:

Canon Zoom Wide Angle-Telephoto EF 28-135mm f/3.5-5.6 IS Image Stabilizer USM Autofocus Lens

Now I'm really confused, though, about the aperture range. I thought getting this lens would allow me great depth of field (as opposed to my telephoto zoom lens. How can you get crisp details for an entire landscape scene if you have such a small f value? I'm so confused. Maybe this isn't the lens I'm looking for?!?!?!?!:-?
WisconsinGirl is offline   Reply With Quote
Sponsored Links
Old Dec 5, 2004, 10:06 AM   #2
Senior Member
 
Join Date: Jul 2003
Posts: 3,396
Default

That wide angle specification is for "Full Frame 35mm" cameras.

First thing to consider is that a 28-135 on a 1.6 crop body(like the dreble, 10d 20d)acts like a 44.8-216.

Basically starts at what used to considered a "normal" FOV lens (about the same as human vision), and goes into a medium telephoto.

Next is the aperture, 3.5-5.6 is the maximum aperture, at the 28 setting it is f3.5 at the 135 it slides down to a maximum of f5.6. At all focal lengths itcan be set down much further probably down to somewherearound F22.

If you want something "wide" look for lenses starting around the 17mm mark, on a (1.6 canon, 1.5 Nikon)crop body that is about 27.2 effective and is the beginning of the old wide-angle range.

For really wide take a peek at the canon "EF-S 10-22mm f/3.5-4.5" it is a S series lense so can only be used on the drebel and 20d, and itis listing at 1100$cdn but it gets you into some real wide angle views (16-35.2mm effective). :-)IMHO: I think it is a bit on the overpirced side.



PeterP is offline   Reply With Quote
Old Dec 5, 2004, 10:12 AM   #3
Senior Member
 
Join Date: Oct 2002
Posts: 157
Default

The first f-stop number (3.5) is the max aperture value at full wide angle (28 mm.) The second number (5.6) is the max aperture value at full telephoto (135 mm.) Per the Bell & Howell site (ref model Mfr # 2562A002 B&H # CA2813535EF) (I know, I cheated on getting the numbers), the min aperture at 28 mm is f 22 while at full telephoto is f 36. Plenty of opportunity with such a range to get nice sharp images.

Looks like a nice lens!

Paul in NoVA
C-730 B-300 WCON-07
plg3 is offline   Reply With Quote
Old Dec 5, 2004, 10:16 AM   #4
Senior Member
 
Join Date: Oct 2004
Posts: 440
Default

WisconsinGirl wrote:
Quote:
How can you get crisp details for an entire landscape scene if you have such a small f value? :-?
To increase depth of field (dof), you go to the opposite end of the aperture range (the bigger numbers), which means a physically smaller aperture. As mentioned above, you are currently looking at maximum aperture, but you really are in need of is minimum aperture.

Also, in general the smaller the focal length of a lens, the greater the dof at any given aperture.

PhilR.
PhilR. is offline   Reply With Quote
Old Dec 5, 2004, 10:35 AM   #5
Administrator
 
Join Date: Jun 2003
Location: Savannah, GA (USA)
Posts: 22,378
Default

As others have already mentioned, a zoomlens is rated by it's maximum available apertures at it's shortest and longest available focal length. You can still select smaller apertures. As a general rule, the larger the aperture (represented by lower f/stop numbers), the higher the lens quality.A brighter lens with larger available apertures allows you to use faster shutter speeds in lower light for any given ISO speed and lightinglevel (and you can still select smaller apertures with a brighter lens).

Although, you'll want to take size and weight into consideration since a brighter lens is usually larger and heavier, and you may not need a brighter lens for the type of shooting you do.

Also, Depth of Field is based on Aperture, Focal Length and Subject Distance.The smaller your aperture (represented by higher f/stop values), and the shorter your focal length, and the greater your focus distance, the more Depth of Field you'll have.

So, for subjects at further distances (i.e., Landscapes), you'll have a lot more depth of field than you think.

For Landscapes, you'll be shooting at infinity most of the time anyway (or you can use a Hyperfocal Focus Distance if you want more of the foreground in focus, too), and you'll probably be shooting atshorter focal lengths much of the time.

See this handy Depth of Field Calculator to see how these three parameters work together. Plug in a camera model, a focal length (actual, not 35mm equivalent), focus distance and aperture. Play with the values, and you'll see how much Depth of Field you have.

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

Even if you shot with the aperture "wide open" with the lens you're looking at, at shorter focal lengths, your landscapes would still be acceptably sharp from about 38 feet to infinity. But, you'll want to stop down the aperture some anyway, since most lenses are softer at their extreme aperture settings (smaller or larger).

Now, I'd probably still focus on yourfurther away main subject for most landscapes, unless you are trying to be creative with something much closer in focus, too. This is because circle of confusioncalculations are based on "acceptable sharpness". But, you'll have plenty of Depth of Field for your landscapes, even if you don't use smaller apertures (and you can select smaller apertures with a lens as previously discussed). Also,keep in mind that smaller apertures require slower shutter speeds. You'll want to balance your ISO speed, shutter speed and aperture settings for best results in a given shooting condition.

As for that particular lens, it's going to have a 35mm equivalent focal length of approximatley 44.8mm at it's widest setting ona Digital Rebel (which is not really very wide if you want a broader field of view forsomelandscapes).

Since this is really a question about the best lens for your landscapes, I'll move this thread down to the Canon Lenses Forum. You'll probably get better advise there.
JimC is offline   Reply With Quote
Old Dec 5, 2004, 5:19 PM   #6
Senior Member
 
WisconsinGirl's Avatar
 
Join Date: Oct 2004
Posts: 606
Default

I thought max aperture was as wide as it can go open, rather than the number value...it is that inverse thing again. I really do get depth of field vs f values, but I just misinterpreted the "max" information. :-)

I'm ok with it then. Thanks for your help!!
WisconsinGirl is offline   Reply With Quote
Old Dec 5, 2004, 6:40 PM   #7
Administrator
 
Join Date: Jun 2003
Location: Savannah, GA (USA)
Posts: 22,378
Default

WisconsinGirl wrote:
Quote:
I thought max aperture was as wide as it can go open, rather than the number value...it is that inverse thing again. I really do get depth of field vs f values, but I just misinterpreted the "max" information. :-)

I'm ok with it then. Thanks for your help!!
Aperture is a ratio, and is determined by dividing the focal length of the lens by the size of the iris opening.

So, if you had a 50mm lens with an 18mm iris opening, then it's aperture would be f/2.8 (50/18~= 2.8 ). Yet, if the physical size of the iris opening (18mm in this example) did not change, and the lens was zoomed out to 100mm, then your aperture would become approximately f/5.6 (100/18=5.6).

As a general rule, metered aperture (amount of light reaching the film or sensor) and physical aperture ratio are roughly the same. That is, less light reaches the sensor through the lens when longer focal lengths are used (for a given physical size of the iris opening).

The aperture scale (in one stop increments) goes f/1.0, f/1.4, f/2.0, f/2.8, f/4.0, f/5.6, f/8.0, f/11, f/16, f/22, etc. With each one stop move to a smaller aperture (represented by larger f/stop numbers), you will need shutter speeds twice as long for proper exposure.

Here is achart you can use to get anidea of the shutter speeds required for any EV and Aperture (but make sure to use your camera's metering, as lighting can vary -- this is only to give you an idea of how it works). It's based on ISO 100. So, each time double the ISO speed, you can use shutter speeds twice as fast:

http://home.earthlink.net/~terryleedawson/dcnotes/tables.htm

Since a brighterlens (i.e., f/2.8 or larger apertures available) allows faster shutter speeds, it'scalled a fast lens. A lens that stops down tof/5.6 is a slower lens (because slower shutter speeds are needed at the smaller available aperture).

Again, just because you buy a brighter lens with a larger available aperture (i.e. f/2.8, f/2.0, f/1.8, f/1.4, etc.), doesn't mean you can't set smaller apertures. Most lenses allow you to stop down to f/22 or smaller apertures (f/32 is common and you'lleven see some macro lenses with f/45 now) So, a brighter lens gives you more flexibilty to go with larger or smaller apertures for depth of field purposes, and gives you the ability to use larger aperture settings for faster shutter speeds to help prevent motion blur in low light.

A 50mm f/1.8 is popular forindoor exiting light use (on your Canon with it's 1.6x crop factor, it would have a 35mm equivalent focal length of 80mm), and you may or may not need a brighter zoom lens. Even a bright (i.e., f/2.8 throught it's focal range),would require shutter speedsmore than twice as long as f/1.8 for proper exposure for any given lighting condition and ISO speed). Remember, for each one stop move to a smaller aperture (for example f/1.4 to f/2.0 which is a one stop move to a smaller aperture, or f/2.0 to f/2.8 which is a one stop move,you need shutter speeds twice as long for proper exposure for the same lighting and ISO speed.

But, you may want to use to smaller apertures for more depth of field in other conditions.As a general rule, you'll usually get sharper shotsif you're not shooting with the aperture wide open orstoppeddown too much either unless you need to, since a lens is usally a little softer at both ends of the aperture scale.

Here is an online depth of field calculator. Select your camera,then change the focal length (for example, 28mm), aperture and focus distance to different values, and you'll see how these parameters work together for depth of field purposes.

http://www.dofmaster.com/dofjs.html
JimC is offline   Reply With Quote
Old Dec 5, 2004, 8:25 PM   #8
Senior Member
 
WisconsinGirl's Avatar
 
Join Date: Oct 2004
Posts: 606
Default

Thanks! I have so much more to learn!!:-)
WisconsinGirl 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 8:12 AM.