[Cuchulainn]

Originally Posted by cloudspirit

I feel the focus is lacking in some of my shots due to my lenses. The lenses that I use now are 35-80mm, 100-300, 28-105.
Thanks for your help

Digital only lenses usually project a smaller image circle than lenses designed for the 35mm format. In other words they are not designed to cover a 24X36mm frame, but are designed to cover the 16X24 or smaller sized sensors of (not full frame) DSLR cameras. Because they are made to project a smaller image circle they can be optimized to use less glass and are often smaller, lighter and cheaper than lenses designed for 35mm and full frame dSLR's.

While the old film lenses that project an image circle that is larger than the DSRL's sensor will work well other than the crop factor as explained by mattdm, the digital lenses usually do not work well with 35mm cameras as the full 35mm frame is not fully covered.

I use a few manual focus (circa early 1980's) lenses with my Nikon D300 and they work well. In some cases I prefer them.

Using your older Pentax lenses on your DSLR should not have any affect on your focus, but your depth of field and perspective may change from what you are used to. There is also an equivalent multiplier in the rule of thumb regarding shutter speed for hand held shots.

This wikipedia article explains this all in more depth...

http://en.wikipedia.org/wiki/Crop_factor