Erm, I take it you have clicked on them to get the whole frames?

If they're really uncropped, they really aren't bad at all. The display must have been awful low and close to the crowd line to get them that big at 200mm, but credit to the guy, he can pan.

I don't know about "best aviation shots ever seen" level, though.

Talking about flashes, are you planning to stock the Samsung flashguns?

Why does the eye not suffer from Chromatic Aberration?

Doesn't it?

I daren't. I'm getting little enough work done as it is...

Ah, Ok. I'll see what I can do.

Fair point. The weather's been tricky this last week or two - it's been so changeable that the light changes dramatically within the timeframe of a lens change. I might actually ask my dad very nicely if I can borrow his K10D and tripod. Then I can literally press the buttons at the same time, although I'll have to be careful with parallax making the shots different.

I'm still waiting for a decent full moon... you can be sure I'll be trying the Pentax out on that (though it'll have to be cropped ).

Ok, there doesn't seem to have been much interest in this thread, so I'll make this a final post for now with a couple of shots taken with each lens. There's no science in this - I've just picked a couple that seem representative of the way they tend to come out. Any C&C always welcome.

Subjectively, it seems to me that the Pentax colours are warmer than the Sigma's but that's just an impression.

My overall conclusion is that they're both well worth keeping - the Sigma is a lot smaller and lighter, and can still give some nice results. But the Pentax is a better lens, so worth having for the achievable quality.

I haven't really mastered either of them, to tell the truth. But here are the shots anyway.

This is from the Sigma. Hand held at 1/180 at F5.6, wide open. Cropped and sharpened, with a little additional saturation in the red:




This is from the Sigma too, also hand held, 1/350 at F6.7. It needed a bit more work to remove some purple fringing.




This is also the Sigma, on a tripod, 1/125 at F16:




The last two are from the Pentax:

1/180 at F8 on the tripod.



And finally hand-held 1/125 at F9.5. I think the un-resized one looks a lot nicer - the link underneath the inline pic will show it.


http://i162.photobucket.com/albums/t244/chris5gd/Public/IMGP4103-cr-sh.jpg

Right, the CA test.

I downloaded a sharpness measuring chart, and printed it on a B&W 600 dpi laser printer. Not ideal, I know, but as you'll see, it's good enough for the purpose of comparing the two lenses' CA.

I set up the chart about 20 feet from the camera, in a mixture of daylight and fluorescent light. The chart is A4, and I positioned it to more or less fill the frame.

Then I took shots at F5.6, F11 and F22 for each lens. The exposures were exactly the same for each pair of apertures.

Much cropping and stitching later, I made the following three JPG files, showing about 80% of the frame width I should think.

http://picasaweb.google.com/Chris5gd/PentaxSMCA400mmF56VsSigmaA400mmF56/photo?authkey=11FYdj80uQI#5081145732622077778

http://picasaweb.google.com/Chris5gd/PentaxSMCA400mmF56VsSigmaA400mmF56/photo?authkey=11FYdj80uQI#5081146050449657698

http://picasaweb.google.com/Chris5gd/PentaxSMCA400mmF56VsSigmaA400mmF56/photo?authkey=11FYdj80uQI#5081146394047041394

In each one, the Sigma is at the top, and the Pentax at the bottom. At F 5.6, 11 and 22 respectively.

I've pulled out sections from each one, at the left, centre and right of the frame respectively, in the following extracts. Again, Sigma at the top, Pentax at the bottom.

F5.6:



F11:



F22:



I think its very clear that the CA from the Sigma is awful wide open at F5.6; it improves dramatically once stopped down, and is much better at the centre than the edges. It seems slightly better at F11 than F22

Although CA is visible with the Pentax, it's much better than the Sigma, and not at all bad wide open. Still better at the centre than the edges, and the blacks and whites look much cleaner.

I've often thought that the colours with the Sigma wide open have looked a bit muddy - now I'm not surprised. Would welcome any other interpretations from those that know about this sort of thing.

As requested, this thread is intended as a comparison between the Pentax and Sigma 400mm F5.6 MF telephotos. I'll post various different aspects of the comparison over a period of time, and I'm very open to suggestions for more things to compare.

Let me say, the one thing I've learned so far is that comparing lenses is hard. I'm a complete beginner, and I've had to improvise some materials. So please forgive (and by all means suggest improvements to) what will be very obviously amateurish technique. All the comparisons will be qualitative - I'm not intending to do anything like counting line pairs or anything. But I will try to put like with like, so that the difference is visually obvious, or not, as the case may be.

I'll be posting all the pictures as links, not inline. Some of it will involve some large magnifications, so there's no point trying to reduce the sizes and keep the quality. All the shots will be pretty much unprocessed - taken RAW, then just cropped and converted to JPG.

First off, here is a picture (taken with a Sony DSC-T3 compact) that compares them side by side, with the Pentax on the camera (K10D) to give a sense of scale.

http://picasaweb.google.com/Chris5gd/PentaxSMCA400mmF56VsSigmaA400mmF56/photo?authkey=11FYdj80uQI#5081150122078654338

The first thing that hits you is the relative size - excluding the lens hoods, the Pentax is 8.5cm (3.3 inches) longer.

I weighed them both on my kitchen scales. The Pentax is 1320g, the Sigma 840g - more than a pound heavier, if you'll forgive me mixing my units.

Subjectively, though, the Pentax is much, much heavier - quite a beast. I can hold the Sigma all day while I'm chasing critters in the garden, but the Pentax makes my arm ache in quite a short time. I'm getting used to it though, and I've dug out the weights for some training...

The Sigma has a very light touch for focusing. Smooth and damped, but still quick to rotate. The Pentax focusing ring is much larger, and much stiffer, still smooth but not as smooth as the Sigma.

The disadvantage is that it's harder to focus the Pentax quickly on a moving target. The advantage is that once you let go, it stays put. Also, when focusing on a static target with it on the tripod, it seems easier to find the position of exact focus with the Pentax - with the green octagon in the viewfinder lit. With the Sigma it's harder to find that exact spot, and easier to lose it.

Anyway, that'll do for the first instalment. Next up will be a comparison of the chromatic aberration of each lens. Subjectively, having looked at a number of shots taken with each lens, I prefer the colours from the Pentax. I'm suspecting that the CA results will at least partially explain why this is so.

Clearly not, but I don't think anyone's suggesting they should.

However, it is by no means clear to me that SDM support and DR are going to make them more competitive. DR perhaps.

Upgrading the SR to K10 level, replacing the pentamirror with a pentaprism, introducing ISO 100 at the bottom end of the range would all seem more immediately useful to entry-level photographers than supporting lenses that they probably aren't budgeting for (I'm assuming SDM lenses are going to be in the 16-45's price league or more, not the 18-55's).

But maybe those changes would be too major and consequently expensive. I don't know.

Are they likely to discontinue the K100D, now that the Super version is here (did they stop making the ME, when the ME Super arrived?)

If so, then fair enough - better is always better, providing that the price isn't much different.

Otherwise, although enhancing things is good, it doesn't make sense to me to look at enhancements in isolation from the rest of the range.

If they're continuing all three (four if you count the 110D), then presumably the Super will be more expensive than the 100, and less so than the 10. To choose the Super, you'd need to want SDM lenses (otherwise get the 100), ISO 3200, and maybe AA batteries.

So we're looking at the need for superfast, super quiet, AF in low light, maybe somewhere where you can't plug in a charger - and someone with a lot of money for lenses.

Hardly mass-market, perhaps.