It was a very overcast, dark day - so the light is very flat and the contrast low. The bench is at a crossroads called "Rest and be Thankful". I think I understand why.

Andrew

The Miniwide is the 28mm lens, I think. The manual focus Sigma 24mm f2.8 Superwide II that I have is a fine lens.

Yes, you can demonstrate that it's sharper in the centre than in the corners by taking photos of test charts like this (f5.6) ...




and then peering at eye-wateringly small crops (left is centre of frame, right is corner)...




but the results bear little relationship to what real world photos look like.

I'm sure there are lots of photos taken by the Sigma on Flickr and elsewhere that put any of mine to shame, but even on this photo - do the corners really look that much softer than the centre??




I paid way over the top for the Sigma I have - but I'm still happy with it. Mind you, I don't have the Tamron zoom that you have.

I do, though, have and still use the kit lens ....




Can you tell the difference between the Sigma and the Pentax 18-55mm ALII kit lens? No, me neither

Errrr ....... whilst I'm here, same chart, same crop - but a (cheapie, around £15 on Fleabay) Chinon 28mm f2.8 ....




I *think* I can tell the difference now.

Andrew

I haven't seen the AP test of 50mm lenses - is that available online? The "tests" I've done speak only to the resolution of the lens and not to any other measure of goodness.

As an aside, I do appreciate that lenses may perform a little differently close up and at infinity - but I doubt that the Sigma 24mm is going to sharpen up, in the corners, substantially on distant subjects. The difference is gross. Having said that, I've taken hundreds of photos with it and not previously noticed serious corner softness - perhaps because it's rare that anything in corners is the main subject of the photo, so maybe some were soft but it didn't seem to matter. I suspect, though, that it's simply that photos of test charts - limited though they may be - are more discriminating than just taking photos of {whatever} if your primary purpose is to compare lens resolution.

Andrew

I spent much of this morning fiddling with lenses, a K200D, tripod, cable release, Pentax flash and so on to start the process of comparing the three primes I mentioned above with the kit lens. The testing process is limited to comparing the resolution of the lenses using the Amateur Photographer lens test chart and says nothing about colour rendering. Rather than hijack this thread, I'll go into the detail of exactly what I did and show crops of the test charts in another, so that you can judge for yourself whether the results are meaningful or a load of tosh.

I am pretty confident that, for the samples in my possession, these summaries give a reasonable indication of the differences between the lenses when used at f5.6.

Summarising ........

1) I now agree with Algernon that the Sigma 24mm f2.8 Superwide II is poor at the edges and especially in corners. It is, though, obviously sharper than the 18-55mm ALII kit lens in the middle of the frame.

2) I completely disagree with Algernon about the Chinon 28mm f2.8. It is at least as sharp in mid-frame as the Sigma and massively better at edges and in the corners. It is sharper than the kit lens everywhere.

3) The XR Rikenon 50mm f1.7 is much sharper than the kit lens everywhere. Overall, it is by far the sharpest lens on test. It is about as sharp in the extreme corners as any of the other lenses in mid-frame.

The bottom line here, is that if you want a cheapie sub £25 prime lens then you would do well to look at the Chinon 28mm and the XR Rikenon 50mm f1.7. Beware though, that there are several variants of both lenses and some might be better than others. You also risk varying results due to sample differences.

Andrew

It doesn't look remotely like the Sigma that I have. The 24mm f2.8 Superwide II looks like this .....




My bet would be on Cosina.


Andrew

Agreed - but my intention was simply to illustrate that my copy of the Chinon isn't terminally soft in the corners and hence unusable for landscapes. It was just a crop from a "snap" that happened to have material with fine detail in a corner.

It's difficult to draw conclusions about your bridge photos. The left and right screen captures are not of exactly the same part of the frame. Also, the colour is obviously different. The light has changed a bit between shots - the shadows of rivets are more pronounced on the RH centre crop. As an aside, I've never seen CA on a kit lens before (I assume the left shots are the kit) near the centre of a frame.

I must do some more comparisons,some time soon, between the kit lens and the three cheapie primes I have in the same focal range (Sigma 24, Chinon 28, Rikenon 50). If the kit lens really is as sharp as the primes, I can do some considerable decluttering of my kit bag(s). At the moment, though, I'm convinced that it isn't, though my testing has been mostly at f5.6 and is not as rigorous as I would like.


Andrew

This is a 100% crop of the extreme bottom left corner of a photo of Glenuig Bay (might not even have been in focus, as the grass was entirely incidental to the photo).




I'm sure I could find much better examples, but I don't think this suggests that the Chinon (£15 not in box) is "unusable for things like landscapes".

More incidental grass - 100% crop of bottom left corner of a photo of a beach at Muasdale on Kintyre - but taken with a Sigma 24mm f2.8 Superwide II




Andrew

I bought the Chinon only a few months back and it was almost permanently on the K200D during our recent holiday in Scotland. I've just had a quick squint at several shots taken and cannot see any significant tendency to softness at edges or corners. It is very usable for landscapes. You might have a bad sample.

Andrew

Unfortunately, I don't have a "best of" modern zoom with which to compare, but I do have three sub £100 primes that definitely out-perform a Pentax 18-55mm ALII kit lens - though I couldn't guess how they would compare with a Tamron 17-50mm.

You could do worse than have a look at the Sigma 24mm f2.8 Superwide II, which is very sharp and rarely parted company with my K200D for months after I bought one about 18 months back.

A couple of others that equal the performance of the Sigma and outperform the kit lens are the Chinon 28mm f2.8 and XR Rikenon 50mm f1.7 - though you'll probably get mixed views about those from some forum members. Having said that, you'll pick up either for about £20 on Ebay, so your risk isn't that great.

I know that many don't have much time for test charts, but I find that the lens test chart given away recently in Amateur Photographer is a useful tool for comparing the resolution of lenses in a repeatable way (providing your shots of it fill a quarter of the frame and not the whole frame). I've briefly and not very scientifically compared five lenses recently with it - the kit, the three primes mentioned above and also a Kenlock 28mm f2.8 which I picked up on Ebay for little money. The Kenlock didn't come out too well, so I'd be tempted to avoid it.

Best of luck in your search.

Andrew

Just checked mine. It focusses to well under 200mm.