General info

[seanm]

I really have no clue about lenses. Could someone please explain to me what "100-400m" and terms like "f/2.5" mean because I want to buy a lens but I need to know the capabilities of each lens before hand, so knowing what these terms mean would help.

Thanks in advance.

[liza]

The 100-400mm is the focal length of the lens. The f/2.8 refers to the aperture setting, which controls the amount of light entering the camera. Buy "Understanding Exposure" by Bryan Peterson. It will explain a lot.

[Lord_Malone]

I really have no clue about lenses. Could someone please explain to me what "100-400m" and terms like "f/2.5" mean because I want to buy a lens but I need to know the capabilities of each lens before hand, so knowing what these terms mean would help.

Thanks in advance.

See Aperture...
http://www.dpreview.com/learn/?/Glossary/Exposure/

See Focal Length...
http://www.dpreview.com/learn/?/Glossary/Optical/

[seanm]

Wow, great replies so quickly..thanks!!

[seanm]

so is a longer focal pointer better? eg f/6 better than f/2?

[Mint_Sauce]

f2 is better than f6. The lower the number the better (when talking about aperture, I'm new to all this too so someone may correct my well meaning help). :)

If there are two lenses both the same price and by the same manufacturer and their lengths are (for example) 24-70 and 24-200. You will generally find the 24-70 will produce better quality shots but at the expense of the extra reach. What type of photography will you be doing?

[Lord_Malone]

f2 is better than f6. The lower the number the better (when talking about aperture, I'm new to all this too so someone may correct my well meaning help). :)



I see what you're trying to get at, but this is not necessarily true. The larger the max aperture of a lens, the faster or better low light performer it is. A larger aperture also allows you a more shallow DOF for those OOF background shots. You'll generally find that the "sweet spot" of a lens is not at max aperture, but stopped down at apertures between the f5.6 and f8 range.

[Mint_Sauce]

I see what you're trying to get at, but this is not necessarily true. The larger the max aperture of a lens, the faster or better low light performer it is. A larger aperture also allows you a more shallow DOF for those OOF background shots. You'll generally find that the "sweet spot" of a lens is not at max aperture, but stopped down at apertures between the f5.6 and f8 range.

Yeah, I was talking generally but you are spot on with your reply. If I was in his position in a shop and had the choice of two lenses which I didn't know much about. I think i'd end up opting for the lower aperture one. Again, it depends on what he shoots I guess. Weddings, definately go for the faster lens (lower number), but scenery on a tripod stuff that doesn't matter so much so other factors come in to play. It's all down to what you want to use the lens for and how much you have to spend. :)

[evandavies]

Sean, actually its the other way around. The smaller the number the better. The f stop it a fractional ratio between the focal length and the aperture.

1/f=focal length/aperture or aperture=focal length x 1/f

So a 50mm at f1.4
50mm x 1/f1.4 = 35.7mm aperture

and at f2.8
50mm x 1/f2.8 = 17.85mm aperture so letting in less light

Hope its a bit clearer... :confused: ;)

There is plenty of info on the net or have a look for some photo books.

Edit: Erm, I think I was getting too technical...
Choosing a lens in general:
1) Look for the range you want to use. i.e. 17mm to 85mm (17-85mm) As Mint_Sauce said, in general its better to choose a smaller range. Making a lens work with a greater range increases the complexity of the lens construction and therefore the more glass is generally involved. This reduces the efficiency and its ability to focus the light properly on the sensor or film.
2) This one is easy. Aim to get a lens with the smallest f number

Once you have a list of a few possible lenses read as many reviews as possible ;)

Cheers,

[seanm]

thank you again, There are many canon lenses of similar price but I really can't decide which is for me. I've settled on the eos 30d as a camera.

I like doing avaition photography, getting the subject focused and a really unfocused background, and preferably a lot of zoom.

I have found canon 70-200mm f4.0 usm motor for 370 quid. Can u tell me anyhting I should know about this lens or reccomend any other lenses for my needs?

Thanks in advance you are all very patient and friendly:)

[evandavies]

I've got the Canon 100-400 which is the most common for aviation photography. Have a look next time you're at an air show ;)

[crn3371]

While the Canon 70-200 f4 is a lovely lens, and will give you the effect you mentioned
(which is usually referred to as bokeh), it's probably not long enough for an airshow. As mentioned, the 100-400 is probably a better choice.

[Cash]

Buy "Understanding Exposure" by Bryan Peterson. It will explain a lot.

What a great book, I purchased one a few weeks a go and it was very easy read with tons of great information.

[theJingster]

i've only been to one airshow ever and i used the 70-200mm f/2.8L non-IS version. i found it long enough for what i was doing. the planes flew pretty low and the longer you go, the harder it'll be to find them in the viewfinder when they're moving across the sky.

also, most of the time, it'll just be plane and sky so bokeh doesn't really play a part.

as for picking lenses, you've already decided on the shots you want to take which helps you judge the focal length you need. larger numbers reach farther and smaller numbers are wider. there are pros/cons for each. i think the best advice i can give you is that you should read a lot on the basics and terminology before spending money on equipment. sure, we can all give you suggestions, but you'll still be the one using everything. personally, i studied for a while before even buying my body.

head over to a book store and spend as much time as you can bear reading up. then you can go home and read some more in this forum, at dpreview (http://www.dpreview.com), photozone.de (http://www.photozone.de) and fredmiranda (http://www.fredmiranda.com/reviews) for equipment reviews.

i don't mean to sound harsh and i'm sorry if that's how i'm coming off. i've just had experiences with people who didn't study up on anything and they went ahead and spent thousands on a dSLR and a high-end lens but were disappointed when the shots they took in full-auto mode turned out much worse than what they were accustomed to seeing from their point&shoot. i just don't want you to have the same experience.

congrats and welcome to the forum.

[liza]

I used the 70-200 for an airshow, too, and got some really great shots. Those planes were flying so low, it looked like the attack on Pearl Harbor. :)

[theJingster]

I used the 70-200 for an airshow, too, and got some really great shots. Those planes were flying so low, it looked like the attack on Pearl Harbor. :)

haha, yeah i shot the air and sea show in fort lauderdale, FL recently and they actually called it "the beach assault"