25mm 2.8 Lens Discussion

Started Mar 5, 2008 | Discussions thread
csgzs Regular Member • Posts: 214
Re: Tech data is on Olympus WEB

I include the MTF of two lenses I consider reference in the ZD/ED lineup, the 50mm f2 macro and the 150mm f2, along with that of the 25mm f2.8 (I am sure they are copyright by Olympus - you can find them on Olympus's USA and UK website, respectively). I also include MTFs for the (perhaps) closest competitors, the 25mm f1.4 Summilux and the Sigma 30mm f1.4.

The 50mm ED macro

The 150mm ED

The 25mm pancake

The Summilux 25mm f1.4

The Sigma 30mm f1.4

Both reference lenses are known as superb in terms of bokeh and sharpness, although the 150mm is noticeably sharper. MTF lines are running high up (sharp) and in parallel (nice bokeh) - OK, it's not that simple, but sort of. Both lenses are of complicated design (11 elements) and have a large rear element (which you see only if you hold them).

Now let us turn to the primes. It is clear that the Summilux is very sharp in the image centre and also shows nice bokeh, but degrades rapidly after about half the diameter is reached. However, as these MTF graphs refer to wide open performance, it might well be the case that at f2.8, it beats the hell out of the pencake. Note that in the came comparison, the Summilux is a real beast. The caveat about measured wide open applies to the Sigma too, but it appears to have superior sharpness to almost .8. But beware! There is a little trick in the Sigma MTF charts, namely that they are calculated with 10 lppmm instead of the four-thirds norm of 20 lppmm. Correcting the graph mentally shows that the Sigma is weak and is only a last resort in low light, but we already knew that (again: at f1.4).

The MTF of the 25mm is not quite the same as the ED primes, but is very promising. Until .8 in the image circle, it performs very well in terms of sharpness, with some falloff thereafter. This is however nothing dramatic - it depends if you expect more from a ZD lens. My opinion is that it is a cost you can feel but something you have to incur for a pancake lens. Bokeh-wise the lens is fine, although not superb. Also, because of the pancake design, I am sure that telecentricity and/or performance with IS had to be sacrifised to some extent (small rear lens and/or smaller - but sufficient - image circle, as it is the case with the otherwise nice 14-42). We shall see what the lack of ED elements mean in practice (re: painful CA with the Summilux). Despide the woes, I would say that on paper it is a very good contender and might be worth the price.

(Remark 1: I truly hope it is focus by wire - without USM, direct manual does not seem to be possible to implement without a clutch which is a big no-no for me.

Remark 2: When first trying the E-400, I felt that I would not use it without a lens that gives it a grip. I am really interested if I can adopt a shooting style with the 25mm that allows me a steady grip.)


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