New Sigma Lens

[daltoned]

I recently bought a Sigma 70-300MM APO lens for my Pentax K10D. Trying out some shots,I notice that some exposures appear a little on the dark side. I know my inexperience accounts for some of the problem but wonder if anyone has any general do's or dont's when using these lens or should I be tweaking the exposure stops. I know I need to learn a lot more and use the bracketing to measure the exposures, just looking for any advice that may be available.
EddieD

[gjtoth]

I recently bought a Sigma 70-300MM APO lens for my Pentax K10D. Trying out some shots,I notice that some exposures appear a little on the dark side. I know my inexperience accounts for some of the problem but wonder if anyone has any general do's or dont's when using these lens or should I be tweaking the exposure stops. I know I need to learn a lot more and use the bracketing to measure the exposures, just looking for any advice that may be available.
EddieD

That's the thing when using the long focal lenses -- you lose f/stops. I forget what the ratio is right now, though.

[Daver art]

Hi are you using the camera in manual mode, the TTL should work as normal no matter whatever lens you put on it, and yes Gary is right that lenses in general have a full stop fall of as you get longer, having said that if you have a lens say 50mm f2.8, you could also have a lens 250mm f2.8 to which both lenses are as fast as each other no light loss or gain from either.

[gocamels]

Without seeing the images it would be hard to say what's happening, but it sounds like you might be trying to get shots that lens isn't capable of (indoors without flash for example).

As a general rule, unless you buy the "pro" series lenses (Canon "L",etc), zoom lenses are going to be fairly slow, meaning that they don't have a large enough maximum aperture to perform well in low-light situations.

Unless there is something physically wrong with the lens (which would show up on every shot, not just some, at least theoretically)then your dark images are most likely underexposed.

Your camera's meter should warn you when you when you are under- or over-exposed.

The best book I've ever read on the subject is Bryan Peterson's "Understanding Exposure." I re-read it every year or two and always pick up something I missed the last time.

[Joel]

I had the same lens but not the APO for my K10D. I didn't really notice anything different except a bit of overexposing.

[owenmorris]

I have the same lens on my Sony A200 and not noticed any problems, I really like the lens.