[edgedemon]

Saw this over at DPreview

WonderPana 145 System Holder Only for the Sigma 8-16mm APS-C Lens

Looks like an easy way to get a filter on this lens?

[troglodytis]

Couple of SOTC photos of Skyharbor.

[Digitalis]

I put in my order for the sigma 8-16mm f/4.5-5.6 today, I will be keeping my DA15 for IR and shots that require filters. It will be interesting to compare the two lenses on my K5IIs, so far all the Sigma lenses I have bought have been excellent: The Sigma 100-300mm f/4 APO EX DG has been nothing short of stellar apart from some focusing calibration problems.

[Digitalis]

My sigma 8-16mm f/4.5 - 5.6 ASPH arrived today, at some point this week I will be doing some detailed tests comparing it to the DA15mm f/4 ED ASPH on my K5IIs

[joko]

Hey Pentaxians,

you've been posting pictures taken at f-stops like 8 or 11, but the only Sigma 8-16mm I've found so far only has a f-stop range of 4.5-5.6.
Am I missing something?

[Digitalis]

you've been posting pictures taken at f-stops like 8 or 11, but the only Sigma 8-16mm I've found so far only has a f-stop range of 4.5-5.6. Am I missing something?

you're missing quite a bit actually- f/4.5-5.6 is the widest aperture the lens supports throughout the focal length range of 8-16mm - but we all have to option to close the aperture of the lens down further than this in order to increase DOF and improve image quality - I hope that clears things up.

Juxtaposing the DA15mm f/4 ASPH ED Limited and the Sigma 8-16mm f/4.5-5.6 ASPH DG :



But I can already tell that working with the Sigma 8-16mm is going to be a great deal of fun:

[joko]

Thanks Digitalis, shame on me!!

[steve1307]

But I can already tell that working with the Sigma 8-16mm is going to be a great deal of fun:

Yes, Its "mindbending". It's hard to describe but If you use it exclusively for a whole day, then you set it down after shooting. For the next few minutes viewing the world just through your eyes feels a bit strange.
I dont get how straight lines manage to stay pretty straight enven way out at 8mm. Little disappointed the K-5IIs still cant recognise FL <10mm though.

[Digitalis]

Little disappointed the K-5IIs still cant recognise FL <10mm though

I know, 8mm isn't exactly a common focal length so none of my pentax cameras recognise it at 8mm which it is going to make searching for images taken at 8mm in lightroom rather bothersome.

I am going to have fun comparing the DA15mm f/4 to the Sigma 8-16mm though both lenses come with incredibly annoying lens caps. I flogged a 72mm rubber lens cap from one of my 4X5 lenses that does the trick.

[dadipentak]

I am going to have fun comparing the DA15mm f/4 to the Sigma 8-16mm

I'll be interested in your take on that. I have both but haven't formed an opinion (and I'd take yours more seriously than mine anyway.) Basically, I think of the Sigma as an excursion lens for its versatility and the DA 15 as something to pop in a pocket in case I'll encounter a WA opportunity.

[bimjo]

I know, 8mm isn't exactly a common focal length so none of my pentax cameras recognise it at 8mm which it is going to make searching for images taken at 8mm in lightroom rather bothersome.

I am going to have fun comparing the DA15mm f/4 to the Sigma 8-16mm though both lenses come with incredibly annoying lens caps. I flogged a 72mm rubber lens cap from one of my 4X5 lenses that does the trick.

I use ExifChanger for my legacy lenses on my NEX 5N, it (or something like it) should work for the Sigma files as well. It's an extra step in post, but at least you can put the lens info in the file. Keeping track of focal length with a zoom could be a problem, but I almost always shot both my DA 10-17 and Sigma 10-20 at the widest setting anyway.

[Digitalis]

I use ExifChanger for my legacy lenses on my NEX 5N, it (or something like it) should work for the Sigma files as well. It's an extra step in post, but at least you can put the lens info in the file. Keeping track of focal length with a zoom could be a problem, but I almost always shot both my DA 10-17 and Sigma 10-20 at the widest setting anyway.

Thanks, I'll keep that in mind - though I think Lightroom 4 has the ability to edit EXIF information built-in, I just haven't had an excuse to use it. Pentax cameras recognise the 10mm setting so this lens is only going to need editing when I use the 8mm setting.

[Digitalis]

well I will have to book some studio time to do more exhaustive testing of these two Ultrawide lenses but my initial impressions are this:

My copy of the sigma 8-16mm f/4.5-5.6 ASPH I was able to detect very slight de-centering - I can spot it, it is essentially a non- issue as most photographers would completely miss it and considering it is a UWA zoom lens from sigma, with their famous QC.It is going to be hard to find a lens that will be any better.

At 15mm the Sigma lens has considerably less field curvature and marginally lower astigmatism at 15mm than the DA15mm f/4 ASPH Limited, and as a result of this the corners are much sharper. Compared to the Sigma zoom @15mm the Pentax DA15mm lens has visibly more barrel distortion,well over the visually detectable 1.3% the Sigma lens has slight pincushion distortion at this zoom setting. Again, it is difficult to see but with eyes like mine I can spot it.

At 15mm @ f/5.6 the sharpness of the sigma lens is consistent across the frame, it has lower lower CA and less field curvature than the DA15. Vignetting at 15mm on the sigma lens is slightly higher than the DA15 (about 0.2 stops higher) at f/5.6 the DA15mm has central resolution that is spectacularly high on the Pentax K5IIs but this makes the corners look even worse by contrast. Overall f/8 is the sweet spot on the Sigma 8-16mm lens, the sweet spot for the DA15mm f/4 is f/11.

In my testing I have discovered a rather curious discrepancy in exposure between the two lenses, I will confirm this with the studio tests (where I have absolute control over exposure). From what I'm seeing the Pentax DA15mm f/4 ASPH Limited seems to giving almost a stop more exposure than the sigma, and I used Identical exposure parameters between the two lenses. The implications of this are either : Pentax is doing some behind the scenes boosting of ISO figures when lenses that are capable of lens/body communication are being used. Or the simpler construction of the DA15mm f/4 Limited - 8 elements in 6 groups- combined with SMC coatings is transmitting more light at the same aperture than the Sigma lens which has a considerably more complex design- 15 elements in 11 groups- and lets admit it: the coatings Sigma have been using on their lenses don't hold a candle to the coatings pentax use.

[dadipentak]

initial impressions

Interesting--thanks!

[Digitalis]

I had to hand my Sigma 8-16mm f/4.5-5.6 ASPH DG back into the shop - the decentering was really getting in the way of me making a proper comparison with the DA15mm f/4, the thing is the rest of the images from the lens were fine apart from the extreme left hand side and it was really bugging me. The Pentax K5IIs has zero tolerance towards optical faults* - if there is a flaw in the lens the camera will reveal it in pristine clarity. Personally I prefer to use the Zeiss Star chart, projected through the lens mounted on a specialised optics testing bench - the Zeiss pattern which has been used to spot problems like this in photographic optics for decades. However a really quick way to spot decentering is to shoot one frame with a finely textured subject that is preferably at infinity focus with the camera normally - then flip the camera upside down and take a shot with identical framing. Using the comparison tool in Lightroom to show the images side by side - if they look Identical then you have a perfectly aligned lens, if they don't look the same and one part of the image is sharper than the other: Then there is a problem.

My pentax DA15mm f/4 ED ASPH Limited was perfect right out of the shop - a big win for the pentax lens.


Sigma 8-16mm at 8mm showing the degree of decentering I discovered, Image produced by the method outlined above - crops are from the extreme Right corner @ 100% unsharpened

*Neither do I.