Originally posted by Parallax Here's my dilema -

I have a 15Ltd, 31Ltd, 40Ltd, and a Sigma 18-250. I am torn between adding the Sigma 18-35 and the 20-40Ltd. If I get the 18-35 I can't really justify keeping the 31, so I could sell it and get the 18-35 making it, for practical purposes, free.

OTH, it would be a $1,000.00 expenditure, but if I get the 20-40 then none of the lenses I have, including the 31 are rendered superfluous, The 40Ltd is faster than the 20-40 (at 40mm), the 31 is much faster, and the 15 fits with either scenario.

I think the first step is going to be to pick up a K-5 on Black Friday.

Come to think of it, with the low-light capability of the K-5 I could still sell the 31 and get by with the 20-40.

Now my head hurts.........................

According to Photozone:

• the FA 31mm @ f1.8 has depth-of-field of f2.7 when compared to full frame

• the DA 18-55mm @ f3.5 has depth-of-field of f5.3 when compared to full frame

So the 20-40mm will not be able to produce the shallow depth of field effect that the 31mm can.

Compact limiteds are small and light but the "smaller" apertures have downsides: darker VF image, "slower" auto-focus and not as shallow depth of field effect.

This is why Pentax really

**must** produce a fast set "standard" focal length lenses:

• DA f2/18mm (~f3/28mm FOV & DOF equiv.)

• DA f2/24mm (~f3/35mm FOV & DOF equiv.)

• DA f1.4/35mm (~f2.1/50mm FOV & DOF equiv.)

• DA f1.8/35mm (~f2.7/50mm FOV & DOF equiv.)

• DA f1.8/60mm (~f2.7/90mm FOV & DOF equiv.)

R