i'd go for it, if i were you. i'm not a fan of the 43/1.9 images i see (the bokeh is a bit jangly wide-open), but i suppose this must be expected of such a small and fast lens—there have to be some trade offs.

the 35/2.8 that you're thinking of has a similar rendering, imo, to the 43/1.9. sharp, contrasty, but the bokeh is a bit rough around the edges wide open. do you think it's worth the effort in changing? you go 8mm wider, gain macro abilities, but lose a stop of speed. i'm not sure it's worth the swap, since if you are disappointed with the 43mm, i think you might be disappointed with the 35/2.8, since they render similarly to me.

the 15mm is a completely different lens. i like the colours, the contrast, the sharpness stopped down, the flare resistance, the lack (well, subtle) distortion, and the size. it's a really unique lens to pentax, and one of the reasons i bought into pentax. i think a 15mm is a good idea for anyone.

but, first and foremost, you should decide what it is that you want this lens to do. you are considering two quite different lenses which would serve quite different purposes in my eyes.

I really think you'll struggle doing better than the SRS price. They are the cheapest I've found by a fair amount. I've been keeping my eye peeled. Would be a great lens to own, but I suspect I'd always reach for my 70/2.4 instead...

Not really. I'm not suggesting the light changes after it passes through the lens, but only that certain parts of the light might not be the easiest to pick up on a digital sensor. That's the whole point of the debate, no?

Digital sensors don't pick up light coming in at an angle (which is why the Leica M9 has those really fancy microlenses). If you have a wide-aperture lens, you have a large exit pupil, so the sensor consequently sees light hit from many angles. Mark Dubovoy thinks this is significant in current DSLRs (I disagree) and that the manufacturers mask it by tweaking ISOs. It's certainly a big deal in rangefinders, but I think we're safe in DSLR land.

[quote="Algernon"]It's probably better to forget DOF and just look at the exposure, which I previously found to be in line with the DxO. My results shown below.
[/quote]Isn't it likely that this drop that you see is from lens vignetting? The 50/1.4 A vignettes quite a lot at f/1.4, doesn't it?

If you look at what DXO talks about, it's just sensor gain. They are not backing Mark Dubovoy—they are simply stating what they measured. I have nothing wrong with what DXO says, but I don't think it should be taken as evidence for the lack of effectiveness of wide-aperture lenses or of camera-makers tweaking ISOs.

don't know much about the matter, so here's some wild unfounded speculation :

perhaps they just want to test it on the same body as yours, but little reason other than that.

i disagree. the contention made in the LL article is that the light coming from the edge of the exit pupil is coming from too sharp an angle for the sensor to pick it up, so the manufacturers sneakily up the iso to balance the exposure.

BUT, if you see a change in the depth of field, then this light from the edge is being picked up. even though the depth of field it's an optical property, it remains for the sensor to detect it.

the LL article even says this in the open letter they wrote:
[quote="Mark Dubovoy"] In fact, is not even clear that large aperture lenses will deliver a shallower depth of field as intended. The DxO measurements to date prove that the marginal light rays just don’t hit the sensor. The point regarding depth of field is that these rays are also responsible for a larger blur spot when out of focus. If they are lost, they not only don’t contribute to the light intensity at the sensor, but they also don’t blur the out of focus planes as much as you would expect at wide apertures. [/quote]

thanks for sharing those results.

i think a mountain out a molehill is being made of the LL article. i suspect it was meant to be provocative, and it was always meant to be a talking point. but i find it astonishing that hardly any people decided to check it.

my main reason for fast glass is the rendering, so long as that's in tact, then i'm happy.

cool. i might have a go at that.

actually, i might have a go at switching it to a k-mount too. looks like a straight mount swap should be ok. only if it doesn't sell, that is.

thanks algi!

here are the pictures of the helios 58/2.

this thread has been good for my product photography—these are looking much nicer than the 35/2.8 shots earlier.

Sorry for the late reply! I'm at work now. I'll put pictures of the Helios up this evening.

i'm not so sure i agree with your assessment about it being better than the macro, stu.

it does seem to have a bit of a stronger contrast in the centre, which is very impressive for a zoom when pitted against a top macro lens.

but in the corners the 18-135mm outright worse.

also, there's significantly more fringing around the white chairs in the 18-135mm compared to the macro.

a good performance for a zoom, but still, the macro is my choice in those images.