How to test new Sigma 10-20 ?

I've just recieved a new Sigma 10-20 & would like to make sure the lens is a good copy, would appreciate some tips on the best way of testing it ?

thanks

simon

Apart from the obvious things, like consistency across the frame, one thing to look out for is ensuring that it focuses when you want it to, rather than when the camera thinks it should.

I talked a bit about this here.

I don't think this is a fault with the lens, more a consequence of the extreme DOF you get at wide angles.

Thanks for the info Chris, useful to know about the potential focusing issue...

I've taken a couple of tripod mounted shots as a test, would appreciate anyones thoughts...looks a little soft at F8, although F11 doesn't look bad....would this be classed as a keeper ?

(click on "link" text & then again on "pop-up" for full size, these are quite heavily compressed . jpg)

F11
[IMG]http://i37.photobucket.com/albums/e68/STKITCHIN/th_F11.jpg[/IMG]

Edit --large image (I hope)
]link



F8
[IMG]http://i37.photobucket.com/albums/e68/STKITCHIN/th_F8.jpg[/IMG]

Large image ---
link

Can't get the full size ones.

___________

Edit: Ok, seen these now. I'd be inclined to reshoot these, making sure the camera is at right angles to the wall.

On mine, the barrel distortion is symmetrical.

(ie, same right as left).

That's what I call severe barrel distortion.

It's not a lens for brick walls, or architecture generally.

G

This is mine, at 10mm.

[IMG]http://i162.photobucket.com/albums/t244/chris5gd/Technical/IMGP9460-sm.jpg[/IMG]

It is very noticeable, I agree. Still, it's very easy to fix, and it's an awful lot cheaper than the 12-24. I haven't tried the Sigma at 12mm for comparison.

The Pentax 12-24mm is just about perfect as far as distortion goes. It depends what you photograph, but I'd be very unhappy with all that barrel distortion in the Sigma 10-20mm.

It will be interesting to see how the Tokina 11-16mm behaves in this respect.

I wouldn't keep a lens that wasn't becoming sharp till f11 though.

What's it like for purple fringing?

Again it depends on what you are photographing. For architecture it's fine but if you have lots of fine tree branches against bright sky then you will indeed see purple fringing, especially at the edges.

The pity with all lenses is that manufacturers don't give a breakdown of what the design parameters are for a given lens. Obviously the Sigma would not be first choice for an architect. If this were explained upfront, then it would avoid disappointment and wasted cash. This applies equally well to all lenses from all manufactureres - tell us what they are designed for and then we can make an informed choice.

Likewise a statement, for example like "Both 100mm and 50mm macros are superb, sharp lenses, but the 50mm is more suited to the photography of flat subjkects such as documents" (if it were true, I'm not saying it is so!) would be a useful indication in addition to providing distortion figures.

I have a superb loose leaf folder from the Spotmatic era that does just this, including distortion diagrams for all the lenses then available. Very useful stuff, and certainly very interesting.

Couldn't agree more. The lack of sufficient information available to allow people to make informed decisions is scandalous, really. I suppose the manufacturers don't want to give up their secrets if they're not all positive.

The Sigma shows virtually no PF at all, even in the sort of conditions that encourage it - like tree branches as you say.

As you say, it's horses for courses.

When I get a chance I'll throw together a little comparison of its distortion at 10mm and 12mm, since to be fair, the Pentax only goes down to 12.

10mm is a lot wider than 12mm, it has to be said. For the sake of a bit of (very easy) correction sometimes, the extra width, lack of PF, and the hugely smaller price, I opted for the Sigma. So far, touch wood, I haven't been disappointed, although before I realised how to make sure the focusing was happening, I was a little concerned.

The distortion at 10mm was well known to me & isn't really an issue, I have software to correct it & I'm more interested in the 12-18mm range, to compliment my Sigma 17-70...

Chris I'd appreciate your thoughts on the large images I've now posted (have to click on the text "link")

thanks

simon

Are they the same ones I saw after you put the links in, or now re-shot as I suggested above?

Chris,

I reshot some as symmetrical to the wall as I could get, shot on the tripod this time at f8 & F11

thanks

simon

Barrel distortion is only very obvious with the Sigma 10-20 when the lens is very close to the subject. Actually it's remarkably rectlinear considering the extremely wide angle at 10mm.

The distortion compares favourably with the Pentax 12-24's. See:

www.photozone.de/pentax/146-sigma-af-10-20mm-f4-56-ex-dc-pentax-k-review--test-r...


www.photozone.de/pentax/133-pentax-da-12-24mm-f4-al-ed-if-review--test-report?st...

How close is very close? I was about 12 feet from the house in my picture above.