Originally Posted by CSpronken
If the optical quality of the Sigma 24-135 would have been as good as the Tamron 24-135 I would have bought the Sigma for it's aperture.
Reason not to buy the Tamron (I nearly bought it though):
- 24 is a bit narrow for APS-C (but still ok for a walk-around)
- Lens is designed for FF so bit large for APS-C
- Aperture is slower than Sigma
Reason not to buy Sigma:
- 24 is a bit narrow for APS-C (but still ok for a walk-around)
- Lens is designed for FF so bit large for APS-C
- Optical quality not as good as the Tamron
The 18-200 has more zoom than I need for a walk-around thus compromising IQ too much.
I expect the Tokina's optical quality to be very good, I mean it has to be otherwise it's rather strange it has a smaller range than the Sigma which has the same maximum focus length AND was designed for APS-C. I really wished the Tokina was 2.8-4.5 like the Sigma though.
But Pentax just shouldn't make it this hard for potential customers it just need a good and reasonbly fast 1x-135 for the Pentax mount.
Pentax prides on their primes.
Actually the quality is more then decent on the Sigma. If you want quantitative results, chop off the right end of the 24-135 MTF chart (account for APS crop). You'll see its amazing for $100-200 lens to produce that result. The Tamron rides it a bit slower at 3.5-5.6 and costs more.
I find that we don't need the 18mm all that much. Useless involved in special applications, most of the general photography falls into the slightly wider than eye to portraiture. (~35mm to ~135mm).
A 28mm lens yields a resultant focal length of 42mm. Very close to the FA Ltd. 43mm f1.9 which is claimed to be the 'true normal focal length' for film rather than the commonly accepted 50mm.
Although I would agree its not as good as say if the lens had a wide end in the teens. Looking at the MTF charts provided my Sigma, it seems like trying to maintain IQ for wide angle is a rather hard reality to physically achieve. You'll see even on their EX wide angle lenses, the lines waver quite drastically. This is probably due to the fact that light must be coverged at such extreme angles. Anything wider and having larger zoom capacities is going to be very detrimental to IQ let alone rather expensive. I know Nikon made a 18-135. Sigma has a 17-70mm 2.8-4.5 DC Macro which performs very well across its focal range. It goes for around $400-$500. Pentax is realizing its own 17-70 in the coming months and maybe that will be a good option to consider. (Maybe its a rebrand of the Sigma. Who knows? Olympus rebranded the Sigma 75-300)
I have the Vivitar Series 1 28-90mm f2.8-3.5 as my standard walk around and it covers most of the stuff I do. (42-135mm) and its very sharp. A fellow photographer (shoots Nikon DX lenses) marvelled at its sharpness (it was wide open too).
So you don't have to look far for a good standard solution. Pentax may not have larger zoom ratios but it makes it up in IQ. The DA18-55mm may very well be the best standard kit out there. (Leica D 14-50 excluded). If Pentax standard options don't work for you, there are plenty of film lens options. (Remember just because a lens is digitally cropped doesn't necessarily mean its better than full frame lenses. When using full frame lenses on aps, you crop the center which is essentially the 'sweet' spot.)