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Tuesday, February 20, 2007

Why Film Camera Lenses Aren't Great for DSLRs

How many people out there have bought a film-era SLR lens for their DSLR only to be vaguely disappointed in its performance—even if it's a prime (single-focal-length) lens?

Here's why:

1. Coatings are relatively more important to lens performance than most photographers realize.

and...

2. Digital SLRs require different lens coatings than film SLRs.

What a lot of people don't realize is that when a lens says it's "multicoated," it doesn't mean that every air-to-glass surface in the entire lens is coated as well as it can possibly be. As with every other aspect of lens design, a lot of engineering expertise is invested in most lenses to try to figure out how to make the lens cheaper to manufacture, while still performing at a level that will be acceptable to the market. And applying separate layers of coatings to lens elements is expensive—especially if the lens is a zoom with 10 or 12 or 15 elements. Accordingly, lens designers specify which surfaces have to be multicoated, which can be single coated, and which can be left uncoated. And how many coatings are there in a "multi-"? Two? Six? Sixteen? (Do you know how many coatings the elements of Earth-surveillance satellite lenses get? I'll give you one clue: those lenses can cost half a million dollars and more.) The options available to the designer are more or less infinite. The chief limitation is cost.

The trouble comes from the fact that film lenses need to be protected from stray light in different ways than digital lenses. Not much light bounces back to the exit pupil of a lens from a piece of film. It turns out, however, that rather a lot of light bounces back from a digital sensor, and hits the lens where most lenses are least protected from flare—in the arse end. (That's a technical term.) How to cut corners in a lens intended for digital is a different engineering problem than how to cut corners in a lens designed for a film camera. Not a problem—except with DSLRs, which can accept both kinds of lenses.

This is the reason why you may be naggingly underwhelmed by the optical performance of, say, that older AF 28mm ƒ/2.8 you bought to use as a "normal" lens for your DSLR.

It's also the reason why you probably aren't dissatisfied with the performance of your newfangled, fancy-schmancy made-for-the-digital-age zoom (even the ones that also cover 35mm): it's coated to perform well on a DLSR.

Liz and Ray, Wigilia, 2006—My current main digital lens is a Konica-Minolta 28–75mm ƒ/2.8 made for Konica-Minolta by Tamron. Despite being uncool [see below], it's a great performer, in part because it's been coated specifically to work well on digital SLRs. 30mm, ƒ/2.8, ISO 1600, 1/50th sec.


It's also the reason that film-camera lenses work better for digital if they were made to a higher standard in the first place. Sometimes, a maker's fastest, most expensive lenses work pretty well on DSLRs because they were aimed at pros when they were new. Because they were aimed at a more demanding market and intended for tougher conditions—and sold for more money—they were coated better than consumer lenses. A slower, cheaper lens—despite having fewer elements that would theoretically result in less flare—might not be so good. You don't hear people complaining about the performance of film-era Leica M lenses when they use them on their M8s, because one way to make a premium lens premium is to just not cut any corners. Film-era Leica lenses are already "coated for digital" just because they were well-coated, period.

I keep waiting for the lensmakers to start making new primes optimized for digital sensors—or at least to start making "Mark II" modified versions of their film lenses that are coated for digital. (Maybe they are. They don't tell me. Or you.) Unfortunately, the fact that they're not doing so does limit your lens choices a little more than might be immediately apparent from the catalog. For my DSLR, I'd rather have a lens that I know was coated specifically for digital.

Posted by: MIKE JOHNSTON

23 Comments:

Blogger Peter said...

This is exactly why I completely avoid shooting certain, very specific, contra-jour scenes, with my otherwise completely beloved Minolta 28/2. Under those specific circumstances, it produces a really nasty greenish "ghosting" effect. Consequently, this is the "main" reason for my interest in the Sigma 30/1.4. Because it's DC it's "designed for digital" and because it's EX it's a "premium" lens. Even though I do tend to be a speed queen when shopping for lenses, the one-stop difference in this case is not actually the main attraction.

As an aside, this does not seem to be a problem just with still photography, nor a problem just with moderately priced lenses either. Strictly anecdotally, I've seen this on live digital video feeds, and at the time the lens that produced the green ghosting was painted (Canon) white. (Although to be fair, I don't know for certain if that means the same thing for their cine lenses.)

4:32 PM  
Blogger MHV said...

THANK YOU Mike, for resetting the clocks. If you can induce a feeling of underwhelment and guilt from inadequate equipment in the digital shooters, that will keep their paws off from my beloved M42 lenses that keep rising in price since some smarty pants realized that he could use an adapter for it. Now I hope I'll finally be able to get that 24mm Super-Multicoated-Takumar for my Spotmatic for under 200$. And perhaps the 85mm as well, so I can have a cool short long lense ;)

4:50 PM  
Blogger Chris Stone said...

Pentax had already recognised the fact that digital lenses need different coating than filn lenses.

Soon after they started producing DSLRs Pentax replaced their 50mm and 100mm macro lenses with digital capable versions with new coating. Pentax have also been retooling their lens production and most of their production is now digital lenses.

Look out at PMA and later in the year for more digital lenses from Pentax.

Regards

Chris Stone

5:02 PM  
Blogger PatrickPerez said...

Mike, you highlight some of the specific reasons I chose the 4/3 Olympus E-1 when I moved to DSLR. Olympus has the largest (as far as I know) collection of for-digital lenses. The kit lens, a 14-54 f2.8/3.5 lens is maybe the best kit lens ever sold (it better, costing $499 outside of a kit).

I didn't see much point in getting a camera that handled great, felt good in hand, and didn't have relatively affordable good lenses available. I made (and kept) a promise to myself, and stuck with just the kit lens for over a year (well, I took Olympus up on the offer of a OM to 4/3 adapter and used a few OM lenses) before buying any more glass. I now have the 11-22, and the 50mm f2 prime macro. This should hold me for another two years, optically. Best to move slowly.

5:17 PM  
Blogger Peterbkk said...

interesting

on the other hand the previous comment was that it doesnt matter what lens one use as no-one can really see the difference

using 5D/35L as my point&shoot and only camera

9:33 PM  
Blogger carpeicthus said...

Sigma not only has a prime made for digital sensors, as you know, but seems to be making a wholesale effort to update the coatings on all its major lenses for digital. Good for them.

Nikon's nano-crystal coat seems to be really good at handling that sensor reflection issue, among others. Interesting that the two lenses it's on -- the 105mm VR Micro and the 300mm f/2.8 VR -- aren't digital-only.

11:14 PM  
Blogger Ken Tanaka said...

Bah.

At the moment I'll call Missouri my home; Show me the practical, real-world effects at issue.

1:12 AM  
Blogger Dr Hiding Pup said...

Presumably this is why I get great results from my Nikkor 85mm f2.5 and 50mm f1.4 - but only when I'm in the dark? If there's hardly any light, there's nothing to reflect off the sensor?

4:15 AM  
Blogger Bob said...

A typical "fault" with any particular lens is that it's soft around the edges, at least compared with the center of the imaging area.

I'm no lens expert, but it seems to me that if you're willing to put up with the extra weight and size (and corresponding cost) of a full frame 35mm lens on your dSLR, you would enjoy illuminating your sensor with the sweet area of the lens while at the same time you throw away the fuzzy edges and corners. I suspect any coating advantage that a pure digital lens may have would be more than offset by the coverage area advantage of the full frame lens.

5:08 AM  
Blogger chrispycrunch said...

A helpful perspective. This certainly makes it less difficult for me to switch over to canon or nikon instead of sony despite having a few minolta film lenses. Still, support forums and current owners of the a100 swear most lenses will work fine with minolta film lenses.

8:28 AM  
Blogger Marcelo Versiani said...

I have this conflict. I treasure my old glass, and no way I will find perfect replacements for my beloved lenses.

It's not only the matter of replacing focal distance and maximum aperture. I'm used to the lenses. I know how they will behavior, on different conditions. I just feel strong with them, and will try to live with the flare.

Well, is there any chance that the future digital sensors will behave like the good old film, or definitely will have to go for digital lenses?

8:37 AM  
Blogger dasmb said...

Peter -- I hear very good things about the Sigma 30mm f/1.4 DC, and had good luck in general with Sigma lenses. They have dramatically lower spherical distortion than even much more expensive Canon lenses and pretty good resistance to vignetting. A shot like this, taken at 17mm and uncorrected for persepective, wouldn't have been possible with my current walkaround (the 17-85 IS) due to barrel distortion.

My major qualms about my old Sigma 18-125mm walkaround were slightly unsharp images (noticable at 6.3 MP, invisible at 3 MP) and a tendency to front focus, problems I've been assured the 30mm does not have. Oh! And it was rather cheaply made and died after only three years of rough use. Acceptable in a $230 lens (unacceptable in a $400 one, but i've handled the 30mm and it definitely feels tougher) and paid for by insurance regardless.

The Sigma 30mm is so my next lens (replacing a pretty nice, but not wide enough Canon 35mm f/2). I only wish it had IS, but Sigma's only recently made a foray into stabilized lenses.

10:51 AM  
Blogger Peter said...

Still, support forums and current owners of the a100 swear most lenses will work fine with minolta film lenses.

Please don't misunderstand my post. The single mentioned caveat aside, there's absolutely nothing "wrong" with using the 28/2 "film lens" on a digital body, specific to digital. Actually the speed, size, weight, and FOV are all pretty much perfect. Aside from that lens, I'm also use the 50/1.7 (newer version) and the 70-210/4. Functionally, there's no problem with either one. The digital sensor seems to show up a bit more color fringing on the zoom, but then you have to accept some compromises when using a 20 year old design.

11:42 AM  
Blogger Peter said...

I suspect any coating advantage that a pure digital lens may have would be more than offset by the coverage area advantage of the full frame lens.

In what way? I would think that shooting from the sweet spot of the lens and the quality of the coatings address different problems in lens design.

11:47 AM  
Blogger Peter Hovmand said...

Well, I'm a dedicated Nikon-man who loves his old glass. And I don't get many problems with my AI-lenses on my D100. The tones differ from lens to lens. Which I find charming! Really. And I will adjust the collours afterwards anyway :)

All these are done with a 28/2.8 AFD:
studio135.net/cairo

More than happy!

4:15 PM  
Blogger Bob said...

>>In what way? I would think that shooting from the sweet spot of the lens and the quality of the coatings address different problems in lens design. >>

They certainly do, but man does not live by lens coating alone, or at least I don't.

You don't get to pick and choose. You can't say, give me a lens with full frame coverage AND coated so as to be optimized for my small digital sensor.

My point was that when you're shopping for a lens (assuming price plays some part), you might be better off buying a full frame lens vs one especially coated for digital if overall image quality is the goal.

I suppose if internal reflections are the ONLY issue for a particular photographer, then shop for coatings; however, that doesn't describe most of us.

You may like the brakes on a Porsche and the transmision on a BMW, but manufacturers don't sell cars Chinese menu style.

Bob

4:15 AM  
Blogger Mike Johnston said...

"You don't get to pick and choose. You can't say, give me a lens with full frame coverage AND coated so as to be optimized for my small digital sensor."

Bob,
Why not? The Tamron 17-35mm abnd 28-75mm are both coated for digital, and both will cover 35mm.

--Mike

12:13 PM  
Blogger Bob said...

>>......Why not? The Tamron 17-35mm abnd 28-75mm are both coated for digital, and both will cover 35mm.>>

Sorry. My post was poorly worded. I didn't mean to imply that there were no full frame lenses that were also coated for digital. Rather, I meant to say that the option to select a full frame lens and then order it with special digital coating is generally not an option. We also know that you can't order a Nikon digital lens, for example, and then pay extra for the "full frame field of view option". The choice just ain't there.

My point is that choosing a well made full frame lens over a "digital" lens is certainly a viable option, at least for some of us, in spite of the fact that the coating may not be "digital".

Bob

3:56 AM  
Blogger Mike Johnston said...

It may be that my generalizations on this topic are just confusing people.

--Mike

7:58 AM  
Blogger Bob said...

>>It may be that my generalizations on this topic are just confusing people.>>

Funny, I have the exact same impression about what I've posted here.

Bob

7:14 AM  
Blogger Dan said...

Gee well my film lenses are amazing on my Canon EOS 30D.

Such as my Olympus G.Zuiko 50mm f/1.4 from the 70's that performs so similar to my Canon EF 50mm f/1.8 in sharpness and tone, colour, saturation and contrast at equal apertures i cant tell the difference between them, other than the olympus having superior bokeh (8 blades vs canon's 5).

My asahi takumar's are sharper than any zoom lens, including Canon L zooms.

Zoom lenses tend to be rubbish in sharpness at the telephoto end.

I also use my Canon EF lenses on my Canon film EOS camera.

10:22 PM  
Blogger Ronald said...

I just got back from MickeyMouse Land in Fl. having taken over 400 shots with a CanonXTI that I had just purchased, and using both an older Canon (film) EF 35-80mm,f 4-5.6, and a new Tamron 18-200mm zoom.
I am a newbie when it comes to digital photography, especially with composition and using all the bells and whistles on this XTI. I shot most of the pix using the 'P' program mode and many of the pix came out dark or darker than I think they should have. Most of the pix were shot with the Tamron and those were the pix that seemed to be darker when shot in bright conditions.

Is it my lack of knowing my camera and its settings that seem to have caused this condition?

I like to keep up with technology thats why I went from film to digital(point and shoot) and then to DSLR. I'm confused and frustrated.

RonC

11:09 AM  
Blogger Mike Johnston said...

Ron,
Sorry to hear about your difficulties. This isn't an active comment field, however (this posting is from February 2007) so I would recommend finding a good forum in which to ask questions. There are many people on the internet who will help you troubleshoot, but no one is likely to see your query here.

Good luck to you. Despite your frustration I'm sure you'll figure it all out.

All best, Mike J.

6:53 PM  

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