Also (mostly? :)) thanks to those here who though me so much about DSLR and pointed me in the right direction, I am having major fun with my DSLR.

I've been looking at some Canon MTF charts, and I am quite puzzled in what I see, since for some reason I expected expensive lenses to have significantly better MTF charts.

These two very differently priced lenses, though, don't seem to differ much.

EF 50mm f / 1.2L USM: $ 1500 at bhphotovideo.com


EF 50mm f/1.4 USM: $ 370 at bhphotovideo.com


Ok, the 1.2 is .2 faster, and the build quality is L level. But, am I right in thinking that the MTF charts show a quite similar lens quality (sharpness and contrast) to the super expensive 1.2L? If I am right, is the price difference justified in your opinion?
Also, the 1.2L weights almost twice as the 1.4...

In this instance, what you are paying for with the more expensive lens is not additional sharpness and contract... you are buying additional light gathering capability. Don't be fooled into thinking that a 1.2 is only a little bit faster than a 1.4, it is not a linear relationship. Instead of being 15% faster (.2 of 1.4), a 1.2 lens is twice as fast as a 1.4. It takes a lot more glass to bring in twice as much light, which is why the 1.2 lens is so much heavier.

What is impressive is not that the 1.4 lens has image quality equivalent to the more expensive 1.2 lens. Instead, be impressed that that 1.2 lens can match the sharpness and contrast of the 1.4. That is not an easy thing to do with such a wide aperture lens. That kind of performance (light gathering + sharpness + contrast) does not come cheap, as you have discovered.

tanstaafl.

Modest quibble: the f/1.2 lens is a half stop brighter than the f/1.4 lens, not a full stop (i.e., it brings in 1.4x the light, not 2x the light).

For a lot less money, the 50mm f/1.4 lens will be beautiful, sharp, and relatively lightweight. You pay very dearly for that extra half stop of light. Unless you really, really need it, then there's no point in getting it.

Hmmmm, not quite true.

The 1.2 lenses do offer something more than the others in the range. If you are a professional that thing will be in and out of your bag all day so build quality is key, it's weight helps balance the camera better in your hand. This has nothing to do with the optics.

Most people won't use the 1.4 at 1.4 maybe 1.8 or 2 as this is it's sweet spot. However I can tell you from experience that the 1.2 lenses are fully useable at 1.2 and are incredible to use.

I would sum it up in that if you can make images with the 1.2 that will earn you the money back then it's worth it. If not then the 1.4 will be an amazing buy for day to day use.

Edit - I should also point out that the coatings on the 1.2 lenses allow you to shoot into light a lot more effectively. That defiantly makes it worth my money.

Cheers

Cris

Even the MTF charts you posted show the f1.2 to be a lot better than the f1.4 when "wide open" (maximum aperture). That's one big factor when looking at a wide aperture lens: is the quality good enough to actually use it wide open?

Also, I have the f1.4 one here, and build quality is crap. It has a "USM" motor, but not the highly desired "ring USM" style of motor. This thing is noisy, slow, and generally a bad experience.

It's been back to Canon for repairs twice, and still gets stuck sometimes when trying to focus. AVOID.

EDIT: Apparently the real bargain for a 50mm prime lens, is the f1.8 version. Much, MUCH cheaper, but about the same real-life image quality as the f1.4 lens.

Cheers

Don't get the 1.2. DSLRs can't handle off-axis light generated by fast lenses (<1.4 f number) very well and actually automatically adjust there ISO upwards to compensate (without your knowledge). This has generated a lot of debate in the photo community but the evidence seems to suggest that DSLRs do raise their ISOs automatically with these fast lenses. That should be reason enough to save your money and get a slightly slower lens IMO.

I would expect that the primary consideration for getting the f1.2 50mm lens (as being discussed here) is for the f1.2 aperature and associated short depth of field with good bokeh.

Not for the faster shutter speed (at same ISO) that it implies.

None of that changes even if the camera firmware is boosting ISO by half a stop when wide open.

What makes u say it is "a lot" better? Are u specifically referring at the edges of the lens?

Edit:
Of course, i am probably not giving enough importance to the fact that the black lines (full open) of the expensive lens are obtained at f/1.2, while they are obtained at f/1.4 for the "cheap" lens. Which should imply that at f/1.4 the expensive L lens would perform (significantly?) better. Am I making sense?

Again, thank you all. This thread is as always extremely interesting and informative :-)

When in doubt, rent both lenses for a week and work with them enough to form your own opinions. At LensRentals.com, the 50mm f/1.2 costs $63 (plus shipping) for seven days. The f/1.4 version is $36 for a week.

I do this, it is defiantly the best way of picking your gear. At first I thought I was wasting my money, but all I did was build a really good relationship with my local dealer and never buy the wrong lens again!!! Now when I go in, the dealer is always giving me stuff to try and asking me what I thought. Great!

Cheers

Cris

... What a nice service! I am not sure anything similar is available here, but i'll check.

So, mtf charts show a set of curves at f/8 and they are usually quite high up on the chart. Can we assume f/8 is the optimal aperture value for most lenses, in terms of contrast and resolution? I would guess that depends on the lens... But then, why f/8? And where would i find the "best" f/# values for each lens in terms of resolution and contrast?

The general rule is that a lens is sharpest two stops from it's maximum. So a faster lens can have it's optimal aperture at more like f/5.6 than f/8.Some lenses actually are sharpest at maximum aperture though- the 203mm f/7.7 Kodak Ektar large format lens being the only example I can think of. The best way to find out what the optimal aperture for your lens is just testing it on a tripod- take a bunch of shots at different apertures and compare. Empirical results are always better than MTF charts.

Furthermore, as a general rule, when you're buying an exceptionally expensive lens with a very bright maximum aperture, a big part of what you're paying for is usable sharpness at that maximum aperture.

Of course, there are numerous exceptions to this rule...

www.lenstip.com seems to have some interesting reviews and graphs. They seem a good visual representation of what has been said in this thread by all of you, so I thought I'd post them here.

Left: Canon 50mm 1.2L.......................................................................................................... Right: Canon 50mm 1.4


They do show how the 1.2L is significantly sharper, especially at the center. Interestingly enough, sharpness at 1.2 and 1.4 is not super (in general terms. I suppose it is to be 1.2 and 1.4?), even though quite better than the 1.4.

Also, sharpest f/#s are 4.0/5.6 for the 1.2L and 5.6 for the 1.4.

1.2L graph was obtained on a 50D body. 1.4 graph was obtained on a 20D body. I am not sure how that is affecting the results, if it is.

The Sigma Normal 50mm f/1.4 EX DG HSM Autofocus is fairly priced ($ 500) and offers good performances, of course based on charts.



Possibly built quality is not super, but I am rading less disappointed opinons on line compared to the Canon 1.4. In fact, Mark's comments in this thread seem to be matched by few others in other forums/shops here and there.

Just in case you haven't seen it - the stackexchange Photography Q&A site is a pretty good source of info: http://photo.stackexchange.com/

Thanks Rory! No, i had not seen it. That's great info!

Here's their direct link for understanding MTF charts.

The reason why I originally started this thread is twofold. On one end, I was just curious to see and learn what your interpretation is of MTF charts, and fill in some blanks (such as how the MTF curves change when changing f/#). On the other hand, I was in fact timidly considering to get a prime normal lens.
I'll happen to be in NY at the end of September/early October, and I think that it would be nice to stop by BHPhotovideo downtown and take advantage of the currently very favorable exchange rate for us in the €-zone (assuming the money market does nor change dramatically in the short run). I said "timidly" because DSLR photography is just a hobby for me. I am really enjoying it, and while no piece of gear is "needed", many of them are just "wanted".

So, why a prime "normal" lens?
Well, I'd love a really low f/# just because of the creative oportunities that it offers, both in terms of narrow DoF, and in terms of low light shooting. So, wanting to consider a fixed focal length lens, I am thinking that a "normal" one is probably the best choice. But, is it? I am sure this is quite debatable, also considering that currently I own a APS-C-sensor body, and very subjective as well. On my APS-C body, a 35mm would do just as well I supppose. So, I've been looking at a slightly borader range of focal lenghts in the 1.2-1.4 range, and so far it seems to me that there are two main groups of lenses, in terms of price.

Less expensive group:
Canon 50mm f/1.4
Canon 50mm f/1.8
Sigma 50mm f/1.4



The only reason why I included the 1.8 is that, in fact, it seems to perform quite well for its price, not far from the Canon 1.4. However, Sigma seems to outperform Canon here, especially at low f/#, which in the end is what I am more interested in.
This is of course the group which would possibly make more sense for me, at present.


More expensive group:
Canon 24mm 1.4L
Canon 35mm 1.4L
Canon 50mm 1.2L
Carl Zeiss 50mm 1.4


The reason why I included the 24mm is that it seems to be wonderfully sharp, and it's there mostly as a reference point. Also, Carl Zeiss lens is MF only, so I am not sure it would make sense. What I find interesting is that the 35mm L lens is at 1.4 sharper than the 50mm . So, I wonder whether it would make sense to give up some image quality at 1.4 in favor of the possibility to shoot at 1.2 (rather than "only" 1.4).

Finally, these are expensive lenses. But, lenses are quite durable products, they keep their value over time, there is a good used lens market; moreover, a $1500 lens would actually cost me, now, as low as € 1000. This is so temptig that I could even decide to get an expensive one, provided it turns out to be attractive enough.

So, I just wanted to share with you my thinking. Any comment is welcome, as usual . Am I making sense or not at all? Am I forgetting some good piece of info, or lens in the market? Am I wasting my money?

P.S.: Oh, and lastly: I have been looking at lens resolution and image quality because I am assuming that distortion and color aberrations are to a certain extent fixable via lightroom or other software. But resolution and sharpness? Not so much, I am afraid. And, that's what I really like in a picture.