| Sign in: |
| Members log in here with your user name and password to access the your admin page and other special features. |
|
|
|
|
|| SportsShooter.com: Member Message Board
"Digital" lenses
Mark Loundy, Photo Editor
 |
San Jose | CA | USA | Posted: 1:03 PM on 03.28.10 |
->> Outside of the manufacturers' sales materials, has anybody ever independently established the value of so-called "digital" versions of SLR lenses? My gut feeling is that film and digital sensors are physically similar enough as to not have different optical requirements.
--Mark |
|
David Manning, Photographer
|
Athens | GA | | Posted: 1:29 PM on 03.28.10 |
| ->> Mark, i thought it had more to do with the optics hitting only the smaller cropped sensor instead of the 36x24 sensor. |
|
Chuck Steenburgh, Photographer
|
Lexington | VA | USA | Posted: 1:57 PM on 03.28.10 |
->> David - There are two kinds of "digital" variations: lenses designed for smaller-format sensors, and supposedly improved coatings. For example, if you look at Sigma's line, you'll see "DC" lenses which are designed for smaller sensors, and "DG" lenses which are optimized for digital. Presumably the "DC" lenses also incorporate the "DG" improvements since they are inherently used with digital cameras.
Mark - I find it interesting that it's primarily the 3rd-party lens makers that make the distinction you're referring to regarding coatings.
I do remember in the early digital days one of my favorite film lenses - the Tamron 28-105/f2.8 - was not a good performer on my digital bodies. Images had a sort of ghosting effect in them. Interestingly, Tamron discontinued this unique lens rather than make a "digital" version.
The only semi-technical explanation of this I have ever heard is that sensors have a higher reflectivity than film (which seems logical from physical observation) and consequently lenses require additional and/or better multi-coating to handle these stray beams of light bouncing around inside the camera.
While I can't claim to have done an exhaustive study, my experience with my Tamron suggests this might have some validity; the fact that Nikon and Canon haven't jumped on the bandwagon with "digital" glass suggests maybe their coating was better all along. Or maybe the emergence of Nikon's "nano-crystal coating" is there version of this 'fix' only deemed necessary in their top-level glass.
One thing I have observed: as sensors are reaching the point where they can out-resolve film, some of my older "classic" Nikons just don't cut the mustard any more. My 85/f1.8 and 180/f2.8 just don't seem as impressive as they once were - I have 3rd-party zooms that are better in almost every respect than the 85, for example. |
|
Curtis Clegg, Photographer
|
Sycamore | IL | USA | Posted: 2:19 PM on 03.28.10 |
->> To follow up on what Chuck said about a digital sensor's reflectivity, there is also the issue of the small "pits" into which the photodiodes lie. Apparently old-style film cameras disperse light at such an angle that the light doesn't "fall into" (for lack of a better term) those micro pits in the corners.
Olympus made much ado about this in the early days of their DSLR cameras, and specially-made lenses for their digital line that made the angle of light hitting the corners less acute. Here is one reference I found to their original digital design (about halfway down):
http://dpnow.com/310a.html
I don't know for sure but I'm guessing all manufacturers are working on designs to make modern lenses where light hits the sensor as perpendicularly as possible. I think some lenses designed for film are more prone to corner shading than others (I read somewhere that the 17-40 L falls into that category). |
|
Robert Hanashiro, Photographer
 |
Los Angeles | CA | | Posted: 3:20 PM on 03.28.10 |
->> Wow!
Great info guys,
A great example of when the ss.com message board works.
Thanks for sharing your knowledge. |
|
Mark Loundy, Photo Editor
|
San Jose | CA | USA | Posted: 3:55 PM on 03.28.10 |
->> Thanks for responses. Has anybody seen any information that is independent from manufacturer sales hype or personal guesses?
Multicoating is a decades-old technology that has been improved incrementally over the years. But I have not seen an explanation of how digital sensors benefit from coatings in any way that is different from film.
Since it's easier to design a wide-angle zoom that covers a smaller area, many so-called "digital" lenses are simply cheaper versions that won't cover full-frame cameras. My suspicion is that the manufacturers are simply performing a marketing slight-of-hand by disguising a weakness as a feature.
Has anybody seen any *independent* information to show otherwise?
--Mark |
|
Chuck Steenburgh, Photographer
|
Lexington | VA | USA | Posted: 4:46 PM on 03.28.10 |
->> Mark,
Go to your nearest research university library and look for this book:
http://books.google.com/books?id=cuzYl4hx-B8C&source=gbs_navlinks_s
Chapter 70 is devoted to digital lens considerations. Unfortunately, it's not shown in the Google Scholar preview, but I suspect this may offer you the 'independent' proof you need to determine whether your suspicion of camera company marketing is just a "personal guess."
Chuck
:) |
|
Mark Loundy, Photo Editor
|
San Jose | CA | USA | Posted: 6:11 PM on 03.28.10 |
->> Chuck,
Good find. A lot of the relevant pages are visible there. None of them address any special optical requirements for digital cameras, but it does talk about the capability to engineer smaller lenses due to the typically smaller imaging area.
I've been thinking for a number of years that the third-party manufacturers have been increasing their profit margin by selling less expensive designs and marketing them as special "digital" lenses, when there is, in fact, nothing about the designs that is actually particularly beneficial for digital cameras.
Still hoping to see reliable independent evidence one way or the other.
--Mark |
|
Chuck Steenburgh, Photographer
|
Lexington | VA | USA | Posted: 7:27 PM on 03.28.10 |
->> Mark,
I suspect there is a grain of scientific basis that has been overblown by marketers; nothing new there. But I still want to read chapter 70!
Chuck |
|
Michael Fischer, Photographer
|
Spencer | Ia | USA | Posted: 10:31 PM on 03.28.10 |
->> Mark, would MTF data help, assuming the data for particular lenses were available?
Certainly, if the claim is that the design and coatings were specially designed, then a improvement would / should be obvious in the MTF curves. If the coverage area is actually less, but the MTF curves for it and similar "full frame" were about the same, it would certainly go a long ways towards confirming your suspicions.
FWIW, Mark, I suspect your impression about marketing the lenses as digitally optimized are correct. As a marketer, it FEELS that way.
In this day and age, making a very minor change in manufacturing something and then blasting it out to the world as the second coming is what goes on across almost all consumer industries. Consumers latch on to a meaningless statistic or number and believe themselves "knowledgible".
It's scary how many people look at Consumer Reports as a example, and think those folks have a clue regarding producing good consumer survey results. |
|
Mark Loundy, Photo Editor
|
San Jose | CA | USA | Posted: 11:44 PM on 03.28.10 |
->> Michael,
What I think they've done is make cheaper lenses and sell them for a premium by calling the "specialized."
It's marketing genius, but it demonstrates the gullibility of photo consumers.
--Mark |
|
Mark Loundy, Photo Editor
|
San Jose | CA | USA | Posted: 11:45 PM on 03.28.10 |
->> Michael,
What is MTF? I know Mean Time Between Failures, but I think you're referring to something else.
--Mark |
|
Chuck Steenburgh, Photographer
|
Mark Loundy, Photo Editor
|
San Jose | CA | USA | Posted: 10:54 AM on 03.29.10 |
->> Chuck,
Nope. I usually don't get into this stuff.
Now I know.
--Mark |
|
Al Goldis, Photographer
|
East Lansing | MI | USA | Posted: 12:19 PM on 03.29.10 |
->> I have always considered "digital" lenses to be a limitation (smaller image circle) not an enhancement.
Maybe because I'm not a fan of small-sensor digital cameras and don't look for lenses with a limited image circle, but I wasn't even aware they were trying to market them as better. Cheaper was the only advantage I was aware of. |
|
Michael Fischer, Photographer
|
Spencer | Ia | USA | Posted: 2:25 PM on 03.29.10 |
->> Mark, MTF curves are as close as I've seen for a down and dirty quick way to judge optical performance short of camping out at MIT.
I'm not a optical data kind of guy; but in my long ago days as a tech rep for Polaroid I started to do a little research to understand better.The Polaroid MP4 Camera was a huge camera that used flat field lenses that had a maximum ap of f4.5 Not a lot of glass and the front elements were essentially flat - pretty easy to build a sharp lens for cheap. ( Planars they weren't..)
I still think that if you can get REAL MTF curves for some of these "digital" lenses, your suspicions will be confirmed. Now, here's the hard part: If they provide theoretical guides, it may not do you a lot of good if the manufacturing standards are somewhat "looser". Or it might because they assume consumers aren't looking at MTF curves.
What I learned so long ago was essentially this: The more glass surfaces, the more glass, the harder it is to build it "right'" In theory, the digital lenses should be as sharp if not sharper because there's less glass and less glass surface compared to full frame. If you have less glass and raise the price... well, you get my point.
Michael |
|
Return to --> Message Board Main Index
|