broken lens?

Just bought this Sigma 17-70 and I feel it is not sharp at all. I have posted some pictures below and I would really appreciate to hear what other think.

Back/front focus issues?

Exif: 1/800, f4.5, iso 100, 70mm, K10D


Full size

Entire image





Entire Image

Full size


100% crop

Not very good at all. At distances such as even at f4.5 there should be enough DOF to cover any slight error, but this is just not sharp at all.

I'd chuck it back from whence it came and order a Pentax one. I know you'd expect me to say that, but it's issues like this over the years that have led me to the conclusion that I only buy Pentax. It is cheaper in the long run.

The "S" of HSBC at extreme left looks sharper to me. Not good.

I would love the Pentax version but it is just to pricey for me. I know I am paying for quality and I tend to prefer quality of quantity in many ways but I can't quite justify the expense at the moment.

I will probably just settle for the Tamron 28-75 for the moment.

You already have three lenses that give you 18mm, and one of them goes to 10mm. Why do you need another?

And why buy a Tamron 28-75 when you have a Pentax 28-70?

If you are short of cash, the sensible thing to do would be to buy nothing, or even to sell something.

G

I really like the Tamron 18-250 as a walk around lens but it is not fast enough at times (I have also just sent it back to Tamron to be looked at and hopefully fixed). I was hoping I could use the Sigma 17-70 as a general purpose faster lens and only move to the Tamron if I wanted to go longer than 70. The 17-70 range seems very useful. I bought the Pentax 28-70 as it was very cheap and I wanted to test that focal range before considering the more expensive Tamron 28-75. 28 seem to long for a walk around though hence why I considered the Sigma. But after trying the Sigma I think I would rather have the speed and make do with the lack of width. I still have the Sigma 10-20 for that. I don't use the kit lens at all - has always been a spare.

Also, I am not short of cash. I am just not willing to pay £375.00 for a lens right now. I may do so in the future but I have a limited budget right now.

Your point about selling a lens or two is valid though.

The most cost effective solution IMHO would be to buy the SMC Pentax-DA 50-200mm and use that alongside the 18-55mm kit lens and the Sigma 10-20mm. The other lenses could be sold.

Your requirements seem confused so this could be a very expensive exercise as you buy things, find them unsuitable and then buy others.

After you have sold the unwanted lenses, this course of action would have cost you nothing and could well fit the bill anyway.

Maybe it is due to my ignorance, but all my photos look not sharp when seen at 100%.
In which condition shall I do the test?
I did the 3 batteries test for F/B and looked fine to me, but now I have doubts

Sorry to say m8 but i think its more user error than broken Lens.
Its woefully underexposed to try and control the sky blowing out but in this type of scene something has to give.
As for it being sharp, of course its not but i doubt anyone has really sharp pictures straight out the camera. (If the picture has had PP done to it then you need to do a little more work on your PP).
I downloaded the Large version and 30 seconds later ended up with this.
Looks ok to me.
Due to the sky being a little blown i would have been tempted to do this in Black and White.

[IMG]http://i271.photobucket.com/albums/jj132/CraigF1969/private/_IGP8283.jpg[/IMG]

Heres a Black and White Version.

[IMG]http://i271.photobucket.com/albums/jj132/CraigF1969/private/_IGP8283bandw.jpg[/IMG]

It's probable that the OP has resolved this issue in one way or another since he raised the topic in August 2008.