Short DOF

[vinnyveez]

What is better at producing a short depth of field, a long lens or a large aperture?

I am looking to buy the 50/f1.8 and am wondering if it will be long enough to be unobtrusive while trying to get candids. maybe a longer zoom lens will be a better option, as it will keep me far away from my subject yet still provide the short dof i want.

[robertwgross]

The aperture number of any given lens is relative to its focal length, so they kind of work together.

Therefore, the answer to your question is "yes".

Why don't you figure out the effective field of view that you need, get the right lens or zoom lens focal length thought out to do that, then see what kind of apertures are available in that length? If you are concerned about low light, then go for the smallest aperture number you can find, or that you can afford, at that length.

---Bob Gross---

[Monito]

It depends on focal length, aperture, sensor size, sensor pixel size, sensor resolution, print size or monitor magnification, and viewing distance. Note that the three sensor factors are really two because they are interdependent.

The only way to know is to calculate it. There are programs and websites that will do it for you.

[Kennymc]

Three thing control DOF.
1... The lenses field of view in relation to the medium in which it is used...
2... The aperture the lens is set at...
3... The distance you are from the subject...

To be unobtrusive while taking candids with a full 35mm frame SLR I would suggest a 200mm f/2.8 lens used at f/2.8...
To be unobtrusive while taking candids with a digital SLR camera with a crop factor of 1.6 I suggest a 135mm f/2 lens...
Just my views...