First off, thanks for the interest in these essays. I think your comments and discussion really make this whole thing more interesting, so keep them coming.Just to clear up a few thoughts based on comments of the first section of this essay. I don't believe that prime lenses are the end all be all for all photographers. I fully understand those who like the versatility of zooms for reportage, or travel, or sports, or event photography. Mostly I was talking to those people who have only ever shot with a zoom, and usually a mediocre consumer level one with a 3.5 maximum aperture at that. Neither prime nor zoom is necessarily the only knife in the drawer, but drawers are big, and there is certainly room for both.
And Scott is right, there are downsides to switching lenses. More dust in the body, missing the crucial moment, etc. But to my mind, what's the point of having an SLR if you're only ever going to use one lens with it?
As for bang for your buck. On the Canon side you can get the 28/1.8, 50/1.4, and 85/1.8 for much less than the cost of a single 24-70/2.8 zoom. To my eye, you don't need L level primes to compete with L level zooms. When I first got my 24-70 a couple years ago, I thought of it as a bunch of really great f/2.8 primes, but haven't found that to be true. A decent prime stopped down to 2.8 is going to be sharper, certainly at the edges, than a zoom wide open.
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OK, now that we've got that out of the way. Some new thoughts.
I've got a confession to make. I'm a pixel peeper. The subject and the composition of the shot are all very important, and while I rarely enlarge bigger than 11x14, I want to be able to if I choose. I'm not sure if it's my equipment failing or if my eye is getting better, but lately I've been a bit disappointed with my lenses. I tend to work in low light and like short depth of field so I'm hooked on wide apertures. Stopping down to improve things really isn't an option. And while if my focus is right on and the subject tends toward the center of the lens, I can get the sharpness I want, I can't alway guarantee those things.
When I shoot with my large format, or the 80mm on my Hasselblad, or the 50mm on my Leica, there is definitely a difference in the look of lenses. I'm certainly a pragmatist and a cynic, so I'm not one for mythology or nostalgia, but I've got to say that there is a difference to the look of photographs from those cameras. For the large and medium format, some people say the difference is that the image is not reduced as much to fit on the film. The less manipulation the lens has to do, the more true the light is on the other side. And that might be true, but it doesn't explain the 35mm Leica with a lens from 1955 mind you.. Theoretically, modern lenses should be better than old ones. Computer designed, new aspherical lens elements, modern and more effective coatings to reduce glare and increase contrast. But to me it seems that the pudding doesn't always bare out this proof.
Since I only use a handful of lenses, I figured I'd look into upgrade options. The 28mm I use is the best Canon makes in that focal length. If they made a f/1.4 L like they do at 24mm and 35mm I'd be all over it like Hillary Clinton on a superdelegate, but they don't so I think I'm stuck there. That leaves the 50mm which I tend to use a lot. My 1.4 is a great lens, but is there better? Canon makes a 1.2L but I've heard mixed things about it. And for 6 times the cost of the 1.4, I'd need some serious kudos from other users before I took the plunge.
But if I like the old lenses so much, why don't I go that route? Well that's exactly what I've been thinking. I would certainly give up auto-focus and auto exposure control for image quality. For the work I'd want these lenses for, that's a no brainer. Plus manual focus and exposure is what separates the men from the men who use the green box mode.
Zeiss, the nearly mythical German company who make the lenses for the older Hasselblad and Contax cameras, have come out with modern SLR lenses in the past couple of years. For the Nikon and Pentax mounts natively, but with a quality adapter they'll work on an EOS mount too. And there area a lot of people on the forums of DP review and Fred Miranda's site, who swear by this route. Saying how much better these Zeiss wide-angle primes are than what I'm using now. Many of them also talk about how the old Zeiss lenses for a Contax SLR are also great for this purpose because you can get them for a song on the used market. T* coating magic and all that implies for only a couple hundred bucks. Good thing my economic stimulus check should be here tomorrow.
The thing is, there are also people who have tried this route and say the people praising it are disillusioned and that the differences are not that apparent, and the usability costs great. I really wish there was an option that was very obviously the right way to go.
I used to be in the audio recording world. And while I was at school, other kids and I would be ogling over some piece of gear or another and I remember one of my teachers saying, "gear is gear". A couple years out I realized that he is right. Not that there aren't differences, but given a decent Canon setup and a decent Nikon setup.. it's the same 'stuff'. Just a tool, like a hammer or a screwdriver. For a while I was a gear hound in the photo world too. But in the past couple of years now, it's been about the images above all else. I don't want to worry about my tools, I want to buy the best ones for what I use them for and then get on with taking pictures. Confident in the knowledge that any deficiencies in the photographs I'm taking are my own fault, and not the result of me now having the new 2008 Widget XLS.
So are there advantages to classic designs? Or is it all in our heads?

For me, I'm all about the older Leica glass but I can only afford so much. For my Canon set up, I enjoy shooting the older lenses because they are not made almost entirely from plastics and they feel more solid, but the prime, non-L lenses like the 50/1.4 and 35/2 are incredible for the cost.
Bill,
As a total admirer of your work,I think for you, your choice of gear works pretty good, but for me ( I am a professional studio/wedding photog.but technically challenged,to say the least),I found buying the Canon 50 & 85 L lens really have made that difference to my work. Particularly for "no light" wedding work or lifestyle kids stuff, I am amazed by the creamy look/feel/color rendition etc(it really is there,to my eye) in the pictures I now get. I regularly shoot 1.2/1.4, shutter as fast as possible and lowest ISO and get pictures I just love and more importantly non photog clients like too.I know people say well you spent all that money now you have to justify it,I do not agree, I bought both these lenses when it suited me financially and they are well paid for in revenue to my business.
My euro's worth!!
Bill,your site is a constant inspiration/benchmark for me and my work to aspire to.
Thanks.
Ed.
Zeiss and Leica in particular design their lenses for a particular 'look', so there very definitely truth in saying they produce images that look different from the norm, a Planar or Sonnar or Distagon is very distinct in look, as is a Summicron or Summilux. And there's a very distinct difference between a Leica and a Zeiss lens. As a rule, Zeiss glass has high micro-contrast and a very distinct seperation between in-focus and out of focus areas, while Leica prefers a smoother transition without the punch of the Zeiss.
Most of the Japanese makers design their lenses for peak performance at their price point rather than a coherent cross-line look, the exception being Minolta lenses designed prior to 2001 or so, which had a very Leica-esque look to them and were designed for consistent rendering and colour rendition across the entire line (Minolta, unsurprisingly, got the idea from their 70's and 80's collaborations with Leica).
I believe that most glass out there today will produce phenomenal pictures in the hands of a competent photographer. Yes, of course there are substandard lenses out there - but these are not what I'm talking about.
IMO, good photography starts with the mind mostly in regards to composition, then the technical, and then finally the gear. A competent photographer with a crappy camera is much more likely to produce a fine picture than a crappy photographer with a fine camera/lens.
So - Order of importance:
1. Mind/Eye (composition)
2. Technical (knowledge of light, DOF, ISO, photographic techniques)
3. Gear (quality, capability and options of the hardware)
As it happens, I believe that the order above not only represents the order of importance, but also the order of difficulty. While there is overlap between number 1 and number 2 I think it still more likely that someone is able to produce a good picture with a great eye for composition than it is for someone with tremendous technical knowledge but no eye for composition. I'm sure there are those who would disagree with me.
Now, having said all that. I do believe that if anyone should be concerned about their gear its the pro photographer. In theory the pro photographer has mastered and/or developed the base photographic techniques encompassed by items #1 and #2. (although it is my belief that they will continue to develop those techniques and learn new things throughout their career). At this level of photography that you are doing it does make sense to be concerned about the quality of the equipment including the glass.
My point above is different, but tangential, from the question you asked and talks more to your last paragraph. I don't know if classic glass is better than modern glass. You seem to have not formed an opinion yourself. Is it within range of possibility for you to buy one of the older lenses that you are interested in and rent/borrow a modern-glass lens and do a controlled comparison test in studio??
If I were to perform such a test I would test both a film body and a digital body (assuming its compatible w/both). For film I would use slide and preferentially two rolls from the same batch or even the same roll of film in both cameras...just to eliminate the differences that occur between chemicals in various batches of film.
-John
Ps. I spoke with someone this past weekend and I understand that you now know who I am...
...I suppose as a practical matter, since you are pro, there should be an evaluation of whether any added gear expense will also add to your income or if it will allow types of work that would not otherwise be feasible without the enhanced equipment.