New Lens Arrives

It "should be". But it is not advisable to rely on either SR or the 1/(focal length) rule of thumb if you're trying to judge the sharpness of a lens.

I have the 10-20 Sigma and have had concerns about the focus from time to time. I'd suggest you are very careful to note where the AF has actually decided to set the focus. I thought that a very short lens would very forgiving about focus but it doesn't seem to be the case so I wonder if the AF struggles to decide where to set the focus sometimes because of the wide angle of view.

Anyway I was concerned for a while and then I realsied most of the issues lay with the way I was using the elns so take heart!

Just for fun test it on a flat wall and use different focus positions - the mode where the buttons shift the focus point for the AF about and see what happens.

Mike

Thanks for that, that's the most useful thing I've had back so far. Some of my shots have been as sharp as I'd expect and others seem to have nothing in focus properly at all. I must learn to use this, but I sort of expected everything in focus due to the large depth of field, and infinity being not much after 1 metre. What's to focus on?! If something is 5 metres away surely it must be in focus. Maybe I should use manual focus and leave at infinity for most shots.

This one seems OK; comments please

What shutter speed? It's not as sharp as I'd hope for but it does depend on a steady camera! I have taken a very similar shot of a church porch and I can zoom in to read the notices on the noticeboard and the stonework jumped at me. Your shot also looks a little flat.

My own theory for what it's worth is that the AF sensor struggles to locate any sharp contrasty edges in some shots becuase the field of view is so wide and that it can sometimes latch onto an unexpcted bit of contrast.

The most disappointing shots I have at the moment are those nominally set to infinity focus.

What I did was stick my lens on a tripod in the garden and then take the same shot with the Sigma, the kit and a an old prime. This went a long way to reassuring me that all was well and also tended to make me think that the AF struggled to focus on very distant things or things without much contrast. A wall a few feet away no problem although I did also test to make sure that the red focus area (I was on spot) fell onto either a course of mortar which at 10mm was quite hard or the front door frame and then the focus was fine.

Basically I'd suggest you do sokme tests like that. I also did the front and back focussigng test which showed all was well. As I say it's the distant view shots that seem the most troublesome.

Mike

I think the church door looks OK - not tack sharp but this lens IMHO just isn't going to give you that.

I've not really noticed the lack of sharpness but after looking at a lot of pics - you're right you can see it.

Was out and snapped a few yesterday - you can notice the non-sharpness but the flexibility of the lens far outweighs it for me.

ISO 500 - a bit soft and noisey close in


1/125 7 500 18mm



1/50 7 320 18mm



1/50 5,6 100 20mm

Sharpness looks OK here to me - don't know if this is contrary but 12 at 1/25 seemed sharper to me than 20 at 1/50?


1/25 4.5 100 12mm

Even a bit soft, its still loads of fun

I've not noticed any lack of sharpness with my 10-20, quite the opposite in fact.

I doubt I've used the lens wide open much though.

Does any one who's got the 10-20 and is happy with the results live near me? If so perhaps we could meet and you could try my lens on your camera and compare results.

I was after a 10/20 having seen some amazing shots taken with it!,,,that was until now!. I'm afraid I cant see a sharp shot amongst them,You would be much better of trying a smaller aperture and using a tripod methinks!,the dof shooting around the 5.6 mark cant be very great at all.The stonework on the church tower is terrible,not a patch on what I can produce with the 18/55.......I'll hang on a bit I think until you get the hang of it!.....good luck...............Ken

I'm pants at giving images but I think these might help.


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and I wasn't using much PP sharpening at the time as I didn't understand why it was needed. The ficus is off but I thin k it's sharp.




Pretty close up and this prints a dream.




I forgot to sharpen again in PP.




Very misty morning




I'm not sure what you'd make of any of these at these sizes

Mike

Great pictures Mike - sharp and some cool subjects.

In a black mood so hope you dont mind;

I agree with the other posters that MX's problems are probably down to incorrect focusing (and perhaps camera shake in some, despite the SR). If not that then it may be a faulty example.

What do you think of mikew's shots? They look alright to me.

Also see: www.pentaxuser.co.uk/forum/viewtopic.php?t=6637

Better still, search Google, Google Images and pbase.com. You will find some stunners.

Re infinity focusing: I can't remember if this applies to the Sigma 10-20, but bear in mind that many modern lenses are designed to focus beyond infinity. This allows for any future expansion/contraction in the materials. So don't just use the nominal infinity setting without checking it's correct.

I have had focusing difficulties too with this lens, but usually being more careful about what I'm focusing on, or simply letting the AF have another go, does the trick.

You can't just assume everything should be in focus because it's a wide angle. Remember it's not ultra-wide at 20mm anyway - the equivalent of 30mm on a film camera.

I agree with Pete and I'm pleased he says the lens can focus beyond infinity as I'd say I have had that happen once or twice. The lens does seem to hunt quite violently on some scenic shots, when that happens I get a focus on some clear and distant object where there is some good contrast and that seems to sort it out.

Here are links to some rather large images that I took almost when I got the lens. they seem sharp enough. I warn you now they are in total 6 meg plus.

At 10mm

www.drmikewebb.com/Cornerhouse.jpg

at 16mm
www.drmikewebb.com/porch0409.jpg

They look sharp in PS.

Mike

Robby - I have a print of the nettles in colour which is lovely so while you're welcome to the B&W I have my print that justifies the impulse buy of the printer (thank goodness) and my wife agrees (once again thank goodness) to the extent she has framed it. There's no accounting for taste.

Mike

Lots of light 125/s f11............what can go wrong?




I can't believe that the autofocus gets it wrong EVERY time.
I have contacted Sigma who want to look at some of my pics.