[sdgreen]

I've just purchased a K5 & intend to pair it with a Sigma 10-20. The questions are :

1 Which 10-20
2 How do I know if I've got a good sample?

1 Regarding which lens : I've read dozens of reviews, online (both users & technical in depth) & in magazines. It seems there's no consistent answer about which is the best optically. For every reviewer who says the 4-5.6 is sharper there'ss another who says the opposite (ie that the 3.5 is better)! A UK retailer (pro centre) advised me to buy the variable aperture for landscape (which is what I'll be using it for) since I'll be shooting f8 - f11 therefore don't need the wide fixed aperture. That makes sense. But I just wanted the sharpest one. It seems as if the answer to that question is....there is no definitive answer! The 4-5.6 is certainly cheaper (filters also) & lighter though.
.
2 I've read that Sigma lenses can suffer quality control variation. (perhaps that may partly explain the review 'inconsistencies'). My question is : how do I know if the copy I buy is a good one? All lenses have optical imperfections so how would I know what is acceptable? I understand in theory what decentering / front focus & back focus is but I wouldn't know if my lens was doing any of that unless it told me! I would probably be blissfully unaware of having a lens that is not performing as it should. I'd prefer to know though so I can return it.. so are there tests I can perform to find out?

Thanks

Yours confused

[drougge]

The f/4-5.6 version has 6 aperture blades, the f/3.5 has 7. If you intend to shoot anything with sunstars, I would get the f/3.5 for this reason. I'm sure sharpness is good enough on either unless you get a bad copy. I don't much test my lenses, so no advice there.

[Pauld]

A good lengthy review of both the Sigma 10-20 lenses was posted on the main page not to long ago. I personally have the F4 version and absolutely love it. It's a very good side by side review that covers all the bases.

Sigma 10-20mm F3.5 vs F4.0-5.6 - Introduction - PentaxForums.com

[JinDesu]

The f/4-5.6 version has 6 aperture blades, the f/3.5 has 7. If you intend to shoot anything with sunstars, I would get the f/3.5 for this reason. I'm sure sharpness is good enough on either unless you get a bad copy. I don't much test my lenses, so no advice there.

I do agree with this statement - the star effects from my F4-5.6 version looks terrible compared to my Sigma 17-70, which has 9 blades. It also looks kinda bad compared to my DA 35 F2.4, which also has 6 stars, but forms them much more clearly.

That being said, there is a big price difference between the two lenses, and I have not yet been unhappy with my 10-20. I don't get to use it much, but when I do, it's always produced lovely shots for me. It's nice and sharp from F8-F11 (I only do landscapes with it).

As far as focusing - I rarely use my Sigma's autofocus (again, landscapes), but at the wider ends and the smaller apertures, the DOF is so huge that focus isn't a big deal. Decentering shows itself very well if you do a shot of a symmetrical subject, and one side is considerably less sharp than the other side.

[savoche]

I don't think there's much of any difference in sharpness between the two. I'm very happy with my f/4. Yes, the sunbursts are much nicer with the f/3.5, but that comes at a price (I chose an even pricier option in the da15...) and weight/size.

As for testing; take a picture of something flat, a bookshelf or something, at widest aperture. Then see if the picture is (evenly) sharp across the frame.

[jezza323]

Dont forget to consider the filter ring size. The f3.5 has 82mm filters, which are hard to find, and expensive. The f4.0-5.6 version uses std 77mm filters

I like using IR720 and ND10 filters on mine so this was a consideration for me

[sdgreen]

Thanks a lot for these replies..I didn't have to wait long.

I never even considered sunstars. It's something I actually like to include in an evening photo sometimes. So what you're saying is that , for sunstars , the 3.5 is better.

Also the advice regarding testing is really helpful. I'll do this when I get the lens.

& yes, I found the 82mm filter prices are significantly higher than the 77 in the UK.

It's really useful to know this stuff before buying.

Regarding the sharpness difference I get the idea that , in practice , there's no difference worth considering - sample (& photographer!) variation being a bigger factor - probably(!).

So , thanks again. I hope to be able to offer advice to others once I've put all this into practice.

NB I already have a Nikon D7000 plus a couple of lenses & decided to invest in a K5 system as well. I'll post something soon about why! It may be helpful to anyone making this choice whilst they're still current.

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Last edited by sdgreen; 06-11-2012 at 09:19 AM. Reason: Addition

[Michael Shea]

At apertures of between f8 and f11, the biggest risk to apparent sharpness you run will be your shutter speed. I own the f3.5 version and it's sometimes harder than you might expect to keep still enough on the K-5. Personally I find the visible edge distortion on the cheaper version quite hideous at times and that is a factor you might also care to bear in mind. As others have commented, focus accuracy should not really represent a problem at these focal lengths. To be honest though, I think if sharpness is your main concern you ought to save some money with the older model of the lens.

[Tanzer]

I'm borrowing the 4.0-5.6 from a friend, so I'll provide my critique. 1) It is already a pretty large and somewhat clunky lens, so I couldn't see myself actually carrying the bigger/heavier f/3.5. 2) In practice it is a little slow (dark) for indoor shooting, even on the K-5 with it's otherwise great high-ISO capability. In this case the slight improvement in aperture for the 3.5 might buy you something. You mentioned in a follow-up that you are intending this primarily for landscape, but I'll mention this anyhow since a superwide is good for indoor shots too. (You can't use the on-board flash at 10mm because of the shadow created by the big honking front element -- bounce flash should work for this but I haven't experimented enough with this combination. The 3.5 would be even more limiting in this regard.)

Probably I am biased because I already have the 15 Ltd which is so small and light, and doesn't suffer from the flash-shadow problem when used indoors. By the way, the 15 Ltd is very noticably sharper. (In my case I can only speak in comparison to the 4.0-5.6.)

[sdgreen]

In response to Michael Shea:

One of the primary reasons I chose a K5 with that lens in mind is the in body the image stabilization. I have a Nikon D7000 but there are no stabilized wide angles in DX (ie cropped sensor) format. I felt that low light hand held shooting is so important to me (for hiking / mountaineering) that I decided to invest in a K5 + 10-20 for high quality low ISO 'on the move' photography over distance and/or difficult terrain.

Using the D7000 I noticed that , in 'interesting' late afternoon / evening lighting, I was getting shutter speed readings of 1/30 sec or less for high DoF apertures. That's too slow - particularly when it's cold / windy and/or I've been climbing a slope / time is pressing. So the Pentax Shake Reduction was a (the) deciding factor.

I hope it makes a big difference!

[Michael Shea]

The stabilisation of the K-5 body only works with Pentax lenses, unfortunately. My K-5 doesn't fully recognise the Sigma, although EXIF correctly records its focal length. You may need to push up the ISO on occasions, although in reality you'll probably find that f5.6 or f7.1 will mostly do the trick. I've just had a few days on Jersey and the only coastal scenes that I felt were any good were shot at 1/200 or faster.

[Ivor K Ecks]

The stabilisation of the K-5 body only works with Pentax lenses, unfortunately.

That is wrong.....I am pretty sure It will work with nearly all K mount lenses.

[Michael Shea]

Read page 141 of the K-5 user manual or refer to the Pentax publicity material linked. I'm not wrong and wouldn't want to mislead anyone, least of all someone who might be buying something. K-5 - Digital SLR - PENTAX Photo

[Ivor K Ecks]

The manual and the material that you supplied the link for only states that the SR will work with pentax lenses. It does not state that it will not work with other makes of lenses.

That is the beauty of having a Pentax system. Virtually any lens that you mount is stabilized.

[RioRico]

My post #11000: Any lens mounted on a Pentax body with SR can be stabilized, Whether it is stabilized CORRECTLY can be a problem. Here are some possibilities:

* Any MF prime: just enter the actual focal length. Exception: a fisheye has a wider AOV than its rectilinear counterpart. I get better stabilization with my Zenitar 16/2.8 if I tell the SR'bot that it's 12mm, which is the rectilinear AOV equivalent.

* Any MF zoom: the SR'bot does NOT auto-learn the focal length. Some folks, including me for a while, pick a value we hope is optimal for the whole zoom range. Wrong. For best stabilization, either 1) select and enter a focal length AND STAY THERE, or 2) re-enter every time you zoom, or 3) leave SR off and shoot in bright light with a fast shutter, or on a tripod.

* Any Pentax AF prime or zoom: the SR'bot picks up the focal length from the lens. No problem. Unless the lens is damaged.

* Some non-Pentax AF primes and zooms: the SR'bot is NOT guaranteed to get the right focal length, not if the lensmaker was sloppy. I haven't experienced this, but I've read of problems with some 3rd-party glass. We take our chances. At worst, we demand a return+refund.