crop factor and lenses(canon camera)

Hi,
I'm starting out with photography (used to shoot with p&s). I have a couple of questions about crop factor & to know the amount of magnification a lens gives you consideing both lens and camera.

I just purchased my first D-SLR, a 450d w/kit lens, so far I'm happy with it! Some of the photos i taken seems soft, is it because of the kit lens?. I have toggled the camera to get a sharper image on different shooting modes, and it improved some way.

Also I'm looking at getting the Sigma 100-300 F4.0 EX DG IF lens (for wildlife and outdoor shooting), I have read that there is 1X Optical Zoom for every 50mm of focal length on the lens. If that's the case the lens maxes out at 300mm, does that mean you have multiply it to 6 to get the equivalent optical zoom? With the 1.6X crop factor my camera and Sigma 100-300 lens, you get 160-480mm = 9.6X Optical zoom?


Third, When looking threw the eye view finder, are you seeing the 1.6X crop factor.. it doesn't seem like you would!? If so, is the view finder magnified in some way?

Thanks, Phil B.

Lets clear a few things here: A lens focal length is the same regardless of which camera you use it on, crop or full frame. The crop sensor is one where the sensor is smaller than the old standard 35mm film area was (a full frame digital being the same size is @ 24x36mm). The changes between crop and full frame sensors is that the angle of view from the lens, which makes the photos out of crop cameras look like a cropped in image compared to a photo from a full frame camera at the same focal length, so people talk about 'effective length' on crop frames compared to full frames.

For your Canon, your 100-300mm lens would give you a picture that would appear the same as a 160-480mm lens on a full frame camera.

As far as I can see reading up on optical zoom, it merely refers to the ratio of the particular lens you're using from its shortest to longest length. So take your 100-300mm lens, that is a 3x zoom, as is your kit 18-55 lens (assuming that's what you got kit wise!). For a compact it would depend on its minimum/maximum focal length what its optical zoom is, but of course many compacts go from optical through to digital zoom without you realising, at which point it's just cropping extraneous pixels at the edge to give you that 'close in' effect, that you could achieve just as well in software at the end.

You see 95% of what will appear in the photo looking through the viewfinder, so you see exactly what the end result would be. Sorry though, I have no idea how that bit works lol

Hi hellokitty_shooter,

You are correct with respect that the 1.6x crop factor means that a 100-300mm lens would in fact be 160-480mm on your camera.

The viewfinder will normally dispay a percentage of what the lensand or sensor is seeing, and this depends on the camera. I believe that the T1i is the equivilant of the Canon 500D here in the UK and this has a view finder coverage of 95%. Therefore you will only see 95% of what the lens/sensor will capture through the viewfinder.

Unfortunately I cannot answer your question aboutoptical zooms

Thanks for the reply guys,

I did, in fact, get the 18-55mm kit lens. I had read elsewhere (maybe somewhere in here phtographytalk.com) about dividing the lens length & getting the "zoom" factor.. 100 / 300 = 3X. As stated in my first post, I had just read someones explanation about how to come up w/the optical zoom. I know you can't think of it like you would binoculars.. 10X50 (10X optical X 55mm objective.)

All I know is compared to the Konica Minolta Dimage Z5 I'm upgrading from, the Canon is day & night! I just took some sunset shots this evening & the colors were dead on.. I never was happy with the Z5's colors & zoom! I guess you learn as you go.. speaking of learning, I picked up Bryan Peterson's Understanding Exposure (revised edition) & like it so far.

Again, Thank you guys.

Yes and no.

100mm-300mm lens has a X3 zoom - as ratesh123 says. However (based on a 35mm camera) a 50mm lens produces the closest image magnification to the naked eye, and is therefore a 1x optical zoom. Therefore at 300mm (6 x 50mm), your lens has a 6x optical zoom -for example. it is magnifying, what the naked eye would see six times. I hope that this is a bit clearer!

Regarding the crop factor, you will find plenty of people talking about the 'magnification effect' of a 1.5 or 1.6 crop. Actually, there isn't one. Like whatratesh said, your Field Of View decreases, but the magnification does not increase.

There is one hidden benefit though, which is that your pixel density is greater. The 15MP canon 50D for instance has an equivalent pixel density on a full frame camera of 24MP so you theoretically get more detail on a 15MP crop camera than a 15MP full frame camera. That is not the whole story, but it is worth noting.