DISCLAIMER: I'm not a pro. So if there are deficiencies and errors in my testing (and I'm sure there are), sorry!!!
Here are some 100% center crops of a very unscientific test that I conducted. The test parameters were:
- tripod
- body IS turned off, and lens IS (in Sigma) turned off
- lots of tungsten lighting
- running firmware 1.01 on Pentax K-5
- 2 second shutter timer
- I took photos at 17mm, 35mm, and 50mm
- apertures used at each focal length were 2.8, 5.6, 8
- photos in JPG, natural
- cropped in Lightroom 3.3 (tried my best to crop the same size image)
- focus point was single point centered on Polish flag
- ISO 800
My observations:
- Phase detect Tamron AF was a bit off at 17mm, 2.8, and image looked soft; however, using live view yielded a crisp image
- Phase detect Tamron AF was a bit off at 50mm, 2.8, as well. I forgot to take a live view shot at this focal length though.
- Phase detect for Sigma seemed right on at all focal lengths and apertures
- Notwithstanding the Tamron phase detect AF problems, the Sigma seemed a bit sharper
- Sigma is not much bigger than the Tamron, lengthwise. However, the diameter is relatively bigger. Sigma is also relatively heavier. IMO, the Sigma lens is disproportionately too fat for the K-5. However, It's my understanding the DA*16-50 is even chunkier than the Sigma.
- AF speed seemed about the same on both lenses. However, the HSM motor on the Sigma is nice and quiet. The Tamron is painfully loud.
- AF accuracy, as noted above, was lacking on the Tamron lens that I got. Bummer.
- The in-lens IS on the Sigma works pretty well. It's nice to see the IS working while looking through the OVF. However, when I first played with the Sigma in live view, with in-lens IS on and in-body IS off, the battery of the K-5 went from full (green) to empty (red). I turned the K-5 off and on, placed it in the OVF, and got a green battery sign again. Put it back on live view, and it went to red again. I put the Tamron on the K-5, put it in live view, and the battery was green. One day later, I did the same thing with the Sigma in live view, and the battery was green all the time. Weird.
Also took some shots at 22mm to compare with the Pentax DA21. My observations:
- Sigma is sharper than DA21 at 3.2
- Tamron is comparable to DA21 at 3.2
Overall conclusions:
- The Sigma seems to perform better than the Tamron, and performance wise (silent AF, more accurate AF, sharper, nice in lens IS), it's worth the extra $240. But it's a bit too chunky for me.
- 50mm is a little restrictive for me too. I am returning the Tamron for sure. I may return the Sigma as well, and try out the Pentax 18-135. Maybe I don't really need the constant F2.8.
I am not posting the full size photos as they are about 10 megs each. If you want them, and also want the F8.0 photos, PM me. Enjoy!
Here is the first batch of crops - 17mm at 2.8
Tamron 17mm, 2.8, using phase detect:
Tamron 17mm, 2.8, using live view contrast detect:
Sigma 17mm, 2.8
Last edited by Armanius; 04-03-2011 at 01:25 AM.