Lens help

[nwafan20]

When it comes to lenses, well, I just suck. Like, what do the numbers mean? (70-400mm)? I think that is the min/max shooting distance if I'm not mistaken. But if so, how do I know what lens to choose or which one to use? (sorry for being noobish about this)

Thanks in advance,

-nwafan20

[SmAlbany]

Well, this is probably better explained in a text book. You might want to check a basics of photography book out of the library.

I'll attempt at a quick answer: There are 2 important numbers, the focal length (70mm, 200mm, etc) and the aperture(F/2.8, F/4, etc). Focal length equates to magnification. The longer the focal length, the greater the magnification of the image. Aperature equates to how much light the lense lets in. The smaller the max aperature, the more light is transmitted to the sensor.

Does this help?

All else being equal, lenses with larger max aperatures (also known as 'fast' lenses) are more expensive. They are called 'fast' because the greater aperture allows for a faster shutter speed.

[nwafan20]

yeah I know about aperature, but like is there a way to calculate zoom magnification (I.E. 4x) with the focal legnth and what would be good for aviation photography?

[SmAlbany]

yeah I know about aperature, but like is there a way to calculate zoom magnification (I.E. 4x) with the focal legnth and what would be good for aviation photography?

I don't think there is any big secret. A 70-200 zoom is about 3X (200/70). A 100-400 zoom is 4X. A 17-40 zoom is not quite 3X. Any of these could be good for aviation - it just depends on how close you can get to the aircraft. 200 is usually enough for me but many airports require more.

[nwafan20]

Thats what I thought, but what would the difference be between 70-200 and 17-40? I know the focal distances are different, but their zoom is the same. I just don't know very much about lenses. But thanks for all your help!

[SmAlbany]

Well, for comparison's sake, a 50 mm lens is considered a 'normal' lens. On a full frame camera, 50 mm should be equal to the magnification you would see with your own eyes. Less that 50 would be a wider view, more than 50 would be magnified. Of course many DSLRs have a crop factor so this is just for film or FF DSLRs.

In point and shoot cameras, they often give the lens specs in full frame equivalents. A common P&S range would be 35-105 (3X). So even though the 70-200 lens is also about 3X, it would magnify twice as much as the P&S camera (200 vs 105)

Make sense yet?

Bottom line is, don't look at how many times zoom it is as much as look at what the focal length of the lens is.

Hope this helps,
Dan

[nwafan20]

yeah, that makes perfect sense. Thanks.