focal lengths and shutter speeds

The Darkroom

Hi, I am using a cropped sensor body and have a question regarding focal lengths and shutter speeds. If I am using a cropped telephoto such as a 40-150mm do I have to obey the shutter speed rules as if it was a full frame body and lens? What I mean is if I am at 40mm do I have to be at a shutter speed faster than 40mm or 80mm in the full frame equivalent? I hope that I'm making sense.

CabanSail

It's not a rule it's a guideline.

However, the guideline is easy to remember for 35mm cameras. With a cropped camera you would use the inverse of the 35mm equivalent focal length.

eg. in your example on a 1.5 cropped body the 35mm equiv is 60-225mm, so at the wide end the you would shoot at 1/60th or faster and at the long end it would be 1/250th.

The Darkroom

So what your saying is a 40-150mm ( eq to 80-300 on full frame ) is that at its widest of 40mm I am to have the shutter speed at 1/40 of a second or more and at its longest no less than 1/160th or 1/200th of a second?

thanks for your reply. I love taking pics of my kids with new camera but sometimes they turn out blurry and I thought this up in my head and thought I'd bring the question here to more experienced minds.

CabanSail

No. You have it the wrong way round.

The focal length of a lens does not vary with sensor size, however we became accustomed to the way various focal lengths appeared on 35mm film, as it was around so long. The Full Frame cameras now have a sensor the same size as 35mm film.

With a smaller sensor it seems to zoom in. The image below shows how this occurs.



So on a smaller sensor the lens image moves towards being telephoto. This is much the same as a digital zoom or cropping the image.

Anyway .... with a cropped sensor your minimum shutter speed will need to be faster than on a full frame sensor or film.

TheQuietFella

The Darkroom wrote: »

I love taking pics of my kids with new camera but sometimes they turn out blurry and I thought this up in my head and thought I'd bring the question here to more experienced minds.

Where are you taking the pictures of your kids. Is it indoors or outside?
What settings are you using or have you just set to auto?

Paulw

Bump up your ISO, open your apreture and shoot at a good fast shutter speed.

Try for something like 1/400 sec or fatser, ISO 800 and f/4. See how that works, and adjust from there by decreasing ISO, upping or lowering the shutter speed.