Need Lens Help--I just don't get it

[MineeBaby]

Hi everyone
I am looking at purchasing the Canon 30D in a kit, and I have come across one that has two lenses. The first is 18-55mm F3.5-5.6 and the second is 55-200mm F4.5-5.6. I found a DIFFERENT kit that had the same first lens, but had a 75-300mm F4.0-5.6 lens.

This is the first camera I would own where I can swap out lenses, which is really exciting, but I just can't for the life of me figure out what the F range means for the photos I want to take. Wouldn't it be good to have a lens with a high F number and one with a low F number so that there were more options? Why would a kit come with two lens with similar F numbers? I just don't get it.

 

[pisco]

The f number refers to the maximum aperture at each listed focal length. So the 18-55 F3.5-5.6 has a maximum aperture of 3.5 at the 18mm focal length and a maximum aperture of 5.6 at the 55mm focal length. In aperture larger numbers are better as it is a fraction that describes the size of the aperture in relationship to the focal length. So an 18mm focal length with an aperture of f4.0 would have an aperture of 4.5mm.

As aperture is an indicator of the amount of light being let in to the camera, lower numbers are better. But as you will find, they come at a premium price.

I would strongly recommend picking up a copy of Understanding Exposure by Byran Peterson. He explains the relationship between aperture, shutter speed and ISO far better than I ever can. It is a great and very easy to follow book on the subject.

 

[handicap18]

the lower the number the bigger the opening. The "f" numbers are listed as fractions f/4 is bigger than f/11. F stands for focal length divided by the number gives you the size of the aperture opening. The smaller the number after the "/" means you are going to be able to get more light. When you see the range of f/numbers like the f/4-5.6 that means that the size of the opening changes as you make the zoom longer. So with the 70-300mm lens, the widest aperture you can have at 70mm is f/4. At 300mm the widest aperture you can have is f/5.6. For the zoom ranges inbetween, the aperture gets small the closer to 300 you get. For example if you zoom to say 150mm your maximum aperture size might be f/4.8.

Here is an illustration of f/stops. You can see the difference in the size of the hole as it relates to the f/number:

 

[jann1033]

Hi everyone
I am looking at purchasing the Canon 30D in a kit, and I have come across one that has two lenses. The first is 18-55mm F3.5-5.6 and the second is 55-200mm F4.5-5.6. I found a DIFFERENT kit that had the same first lens, but had a 75-300mm F4.0-5.6 lens.

This is the first camera I would own where I can swap out lenses, which is really exciting, but I just can't for the life of me figure out what the F range means for the photos I want to take. Wouldn't it be good to have a lens with a high F number and one with a low F number so that there were more options? Why would a kit come with two lens with similar F numbers? I just don't get it.

you might want to check out the lens reviews also www.fredmiranda.com or maybe http://photo.net/equipment/canon/efs18-55/ would have them i think. just a caution don't get to discouraged if they are not rated top 10s, sometimes they compare them with lenses that cost 10x the amount http://www.pbase.com/cameras ( click on the brand of the lenses)has some photos taken with the lenses and you might be able to see what they would look like taken with your camera body also. do you know the brands? are they canon, sigma, tamron? all things considered if the reviews and photos are comparable i'd go with the 75-300 for the extra zoom and the bigger aperture.

 

[Groucho]

If this is your first SLR/DSLR (and you're still learning about apertures - which is fine, we've all been there), are you sure that you need the 30D? Is there a must-have feature that the 30D has that the XTi is lacking?

I just hate to see people spending twice as much as they need to if they don't actually need the extra features. Beach has a silver XTi body for $646 and the 30D body is $1,129 (minus $100 rebate)... that money could definitely help in the lens department! Canon's kit lens is not well-loved and you might do well getting just a body and a better short-range zoom. I'm not a Canon guy so am not familiar with just what's out there but I'm sure there are a variety.

 

[MineeBaby]

Haha! Oh, I know I am a dork for not knowing the relationship of the aperature to, well, pretty much anything (though your posts have helped explain it well) and still wanting the fancy pants camera. I currently have a Canon Powershot S50 which is really lovely, but my friend has a 20D and I love love love it. I am tired of my camera having so much noise in all of the low light photos. I absolutely love photography and figured that if I were going to upgrade that I would REALLY do it right and then learn the science behind it once I have it to play with. Thank you for all of your explainations and recommendations. I might get that book so that I can grasp the concept to the point where I can see what I want to take a photo of and grab the perfect lens and set it up just the right way. I will check out the websites too, and I will even look closer at the Rebel, though everyone I have spoken to has said that if I am going to think about the Rebel, I should just spend the extra bucks to get the 30D. Lots to think about.

Any more opinions are welcome. In the mean time, I need to study more about aperature and how it relates to what kinds of photos I want to take.

Thank you!! Heidi

 

[Groucho]

I think that picture quality-wise, the XTi should be pretty much a match for the 30D, the 30D just has more features to play with (and more size and weight) - a Canon expert could probably say for sure better, but generally if you're just getting in, I think it's a lot better to start with a slightly cheaper body and have some money left over for lenses, a good tripod, bag, etc.

Certainly, a good lens on an XTi should produce a better photo than a crummy lens on a 30D!

 

[MassJester]

I would strongly recommend picking up a copy of Understanding Exposure by Byran Peterson. He explains the relationship between aperture, shutter speed and ISO far better than I ever can. It is a great and very easy to follow book on the subject.

Just ordered it -- what I don't understand about that is...well...a lot.

 

[seashoreCM]

For outdoor pictures in sunlight or under not to heavily overcast skies you pretty much don't have to worry about f-numbers. It is the nighttime or indoor shots where a smaller f-number (larger aperture; larger f/stop) comes in handy. Whether or not the camera is automatic, the aperture can be made smaller as needed for brightly lit scenes but the aperture can only go as large as that stated for the lens and its current zoom setting.

A typical kit with a camera and several lenses will have not so low f-numbers on the telephoto lens(es). Faster telephoto lenses (lower f-number, larger possible aperture) cost a lot more as well as being somewhat fatter and heavier.

>>> why two lenses with similar f-numbers?
You put on one lens or the other depending on the angle (wide angle, telephoto) you want to take. You have to live within the f-number limitation of the lens you just put on, perhaps using a tripod when you have to use a slower shutter speed to get the proper exposure. For an SLR camera or a digital camera you will see the exact view you will get in the viewfinder so you might not have to worry about millimeters as discussed below.

Is this a 35mm film camera? If so, than the pair of numbers 18 to 55 mm is for the wide to standard angle lens (with zoom) and the 55 to 200 (or 75 to 300) mm lens is a telephoto lens (with zoom). Regular angle for a professional 35mm camera is 50 mm while standard angle for a point and shoot or pocket 35mm camera is a wider view corresponding to around 36 mm.

For a digital camera, SLR or pocket, the standard angle almost always corresponds to a different smaller number of millimeters becaue the sensor is smaller than a 35mm film frame. There will usually be a second number published (a second pair for minimum and maximum zoom on a zoom lens) called 35mm equivalent focal length(s) so if you talk with a camera expert, he can easily figure out what field of view you will get with the lens and camera combination you are using. In 35mm equivalents, 36mm for the lens corresponds to the typical pocket camera standard angle and 50 mm corresponds to the typical professional 35mm camera.

Other quick hints:
http://members.aol.com/ajaynejr/digicam.htm

 

[Groucho]

A lower F-number can be useful during the day in order to control depth of field better, but few zooms are fast enough to really do fine control. For "everyday" shooting, yes, aperture doesn't matter much in the daylight.

An example of daytime large-aperture shooting. 50mm 1.4 at F2.0, 1/1500th second, ISO 200. This is in the World Showcase at Epcot.