50MM 1.4 sharp only at 2.8... Why not at 1.4 ?

[peripatetic]

Yeah OK I stand corrected, but there's not a lot in it, certainly in the centre of the frame. That's some amazing MTF!

Also with the shallow DOF it's entirely possible that viewers would regard the picture as sharper wide open.

[ac.smith]

An advantage of f1.4 vs. say an f2 on a DSLR is that the F1.4 will provide a brighter image in the viewfinder for framing and the narrower DOF makes focusing easier even if you will use F2.8 as the shoting aperture.

[fldspringer]

Just to set the record straight, not EVERY lens performs better when stopped down. There are exceptions to this general rule.

There are several Zuiko lenses that will buck this general rule. There are even some that will resolve the edges better than the center. Different lens design can alter what is assumed to be written in stone.

Most Zuiko lenses perform quite well wide open. Some actually do better wide open. Before someone calls me a liar again, here's a source to verify my claim.

The 11-22 f2.8-3.5 at 11mm:

http://www.photozone.de/8Reviews/len...2835/index.htm

the 50-200 f2.8-3.5 at 50mm as well as 200mm:

http://www.photozone.de/8Reviews/len...2835/index.htm

The 14-45 f3.5-5.6 kit lens at 45mm:

http://www.photozone.de/8Reviews/len...3556/index.htm

All of these examples show what is essentially identical performance wide open to one step stopped down. They list both center and edge measurements and there are increases in one measure or the other.

The buck the edge being softer than center rule, there are also exceptions:

The 40-150 f3.5-4.5 kit lens at 40mm wide open:

http://www.photozone.de/8Reviews/len...3545/index.htm

The 50 f2 macro is also at f11 & f16, but I'm putting the chart up because pretty much puts the myth to rest.

An example of a Canon 50mm/f1.8 stopped down fully. It's not that it isn't sharp, but the chosen focal point is sharp. The smaller f/stop makes you much more careful on the focal point vs the rest of the image.

[Gazander]

philgib wrote:

I do not understand why fast lens are not super sharp at their minimum focal ?

If a 1.4 lens is only very sharp at 2.8, why do people call it a 1.4 ?

I would rather call it a 2.8... :?

Maybe I'm spoiled but all my Pentax 50mm/1.4 lenses have been excellent at all apertures, even at 1.4

Maybe you're misfocusing. DOF is very narrow at 1.4 and focusing is tricky.

Not to toot the pentax horn but despite being 'slow' (which I dispute) the AF is very accurate and unsharpness/softness is never an issue.

Or maybe you just got a bad copy of the lens

[philgib]

Tanner report :

"In fact, the best way of thinking about the Canon 50mm f/1.4 is that it's an excellent f/2.0 lens, with a "special effect" soft-focus option at f/1.4!"

http://www.slrgear.com/reviews/showp...uct/140/cat/10

This is exactly what I mean, in a much better Engish :-)

[TCav]

philgib wrote:

Tanner report :

"In fact, the best way of thinking about the Canon 50mm f/1.4 is that it's an excellent f/2.0 lens, with a "special effect" soft-focus option at f/1.4!"

http://www.slrgear.com/reviews/showp...uct/140/cat/10

This is exactly what I mean, in a much better Engish :-)

But, once again, they market a lens based on what it's capable of, not on what it's especially good at.

That's what SLRGear.com, PhotoDo.com, and PhotoZone.de (among others) are for.

[fldspringer]

philgib wrote:

Tanner report :

"In fact, the best way of thinking about the Canon 50mm f/1.4 is that it's an excellent f/2.0 lens, with a "special effect" soft-focus option at f/1.4!"

http://www.slrgear.com/reviews/showp...uct/140/cat/10

This is exactly what I mean, in a much better Engish :-)

Looking at the plot from that link, it would seem the lens is a bad copy (make that a horrible copy). The traditional behavior is bowl shaped curve that peak at the corners. That thing is a mess.

Lenses that fast are kind of a specialty product. Ones that perform at such an aperture are expensive. Canon has a 50 1.4 L that would certainly do better, and even a 50 1.2 L that would put that lens to shame. Problem is it ain't gonna be cheap!

[peripatetic]

fldspringer wrote:

philgib wrote:

Looking at the plot from that link, it would seem the lens is a bad copy (make that a horrible copy). The traditional behavior is bowl shaped curve that peak at the corners. That thing is a mess.

Lenses that fast are kind of a specialty product. Ones that perform at such an aperture are expensive. Canon has a 50 1.4 L that would certainly do better, and even a 50 1.2 L that would put that lens to shame. Problem is it ain't gonna be cheap!

No I think that's probably a fairly representative sample.

Canon has never made a 1.4L. They currently make a 1.2L and used to make a 1.0L.

The 1.8 is very cheap and has slow and noisy AF. The 1.4 is quite cheap, still made of plastic but better built and has much better AF.

But for portraits I find f2 @50mm is where I like to be most of the time and it's much better at f2 than the 1.8 and almost as good as the 1.2. At f8 they are pretty much all the same.

Also don't forget that the viewer responds to differences in sharpness. At f1.4 the DOF is so shallow that if the centre is focussed well they will think it looks very sharp. (Talking about portraits or photos where the middle of the frame is where the interest is.) The fact that the edges are so blurred is often no big deal, it was probably out of the DOF anyway, and that blurryness may well enhance the appearance of sharpness in the centre of the frame.

[Remember the experiment where you have 3 bowls of water, cold, hot and warm. If you put one hand each in the hot and cold then into the warm the hand that was in the cold thinks its hot and vice versa. The eye responds in the same way. Because the centre is so much sharper at f1.4 than the edges it seems sharp even though it's not in absolute terms.]

Of course on a test chart or a brick wall it looks rubbish, but that's not how you'd use this lens in the real world.