Digital cameras 101

[mrentertainer]

Hi!  I'm new to digital SLR's and I've just purchased a manufacturer refurbished Olympus E-410 with the standard 14-42mm Zuiko lens.

Having read about the 35mm factor I assumed that this lens would give approx 28mm wide angle and 80mm 'portrait' telephoto; but even at max zoom the image is still smaller than life-size, ie the magnification at longest focal length is still less than a factor of 1 ??

Can anyone please advise me about this, thanks

[bdery]

Hi and welcome!

There is a lot of information on the web about "equivalent focal lengths". Not all of it is acurate.

First, let's keep things simple. If you have, say, a 50 mm lens, it will ALWAYS be a 50 mm lens. Nothing changes that. So any depth of field capculation, for instance, must be done with the real focal length of the lens. Same goes for apertures, an f-number of, say, f4, will not change because of the crop factor.

What does change is the apparent FIELD OF VIEW. And that's not the same thing as focal length. So with your camera (which has a crop factor of 2x) a 50 mm lens would have the same field of view as a 100 mm lens on a 35 mm camera.

I hope this clears some things up.

Magnification is a different story, and is related to subject distance. Magnification is calculated as image size (on the sensor) divided by object size. It can also be calculated by using object and image distance, but we're getting into more comple territory here, and I'm not sure it's rlevant (let me know if you want more details).

The image you see in your viewfinder is a representation of your scene, but not up to scale. Viewfinders have magnifications of their own, so you should not relate the size of the image in the viewfinder to the size of the final image. What's more, you can enlarge your image, crop t, or manipulate it with a computer.

For the record, your lens offers a maximum magnification of 1:5, which means that an object five inches tall will, at most, for an image 1 inch tall on your sensor. Lenses with higher magnification ratio s are dedicated macro lenses, and labeled as such.

Let me know if this clears things up.

[mrentertainer]

Hi!  Thanks very much for your quick reply.  I think I understand now - ie it's the crop factor of cmos sensors compared to 35mm format image.
I guess that's why this camera often has a Zuiko 40-140mm zoom lens as an option for, say, portrait work etc?

Thanks again

[bdery]

Hi again,

just a note, the crop factor is not linked to the type of sensor. In other words, a CMOS or a CCD can both have just about any size.

You are right that a 40-140 mm lens would cover what most people consider a good portrait field of view, and it would also act as a moderate telephoto lens. A good balance.