2.8 lens takes darker pictures than old 5.6

[tryall3]

Hey,

I just purchased a 18-50 f2.8 Sigma for my Pentax and at 50mm and f 5.6 it takes a noticeably darker picture than my 10 year old junky 3.5-5.6 28-80mm

Any Ideas? Is this normal? or maybe a bad lens? oh, Yes the exposure, field of view are the same.

[mjs1973]

Is the exposure of the images you are comparing the same? Can you post some examples along with the exposure info for both images? I'm guessing that one image is under exposed compared to the other.

[Frog]

Have to be same aperture and shutter speed to compare. iso too

[tryall3]

Sorry guys, yes the iso aperture, shutter, and image filed are the same. How do I post examples?

[another view]

Hi and welcome - here's a tutorial on how to upload pictures. Keep them around 600 pixels on the long side and you should be fine as far as file size goes.

The new lens has an f2.8 maximum aperture but that doesn't necessarily mean that it's using this aperture. Faster lenses (ones with larger maximum apertures) are usually better because they give you more options, but the aperture that you actually use to take a photo should be determined by light level and creative considerations (depth of field, shutter speed being used, etc). IOW, it isn't always better to shoot at f2.8 than f5.6.