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Thread: Digital Capture & Standard LF Lenses

  1. #1
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    Digital Capture & Standard LF Lenses

    I heard at a photo studio that standard LF current lenses don't work as well as the new Digitar lenses on digital backs. According to Schneider's LF technician, it's because of color fringing. He said that the Digitar lenses are much better.

    I checked Schneider's webpage, and it indicates that the Digitar lenses are apochromatic, that digital sensors are especially sensitive to non-apochromatic lenses. So, what about the APO-Symmar lenses? Are these lenses not APOchromatic?

    By the way, I'm not forgetting about Rodenstock.

    Does anyone have personal experience with this? Practically speaking, how bad of a problem is this?

    To add to my question, does Canon or Nikon talk about this regarding their digital cameras? I've not heard it, nor do I see mention of this on Canon's website. From my perspective, they regard their lenses as interchangeable between digital and 35mm film.

  2. #2

    Digital Capture & Standard LF Lenses

    As one who has listened in on a lot of conversations over on robgalbraith.com I can tell you that the pro users of the 1Ds and the 1Ds Mk II are less and less happy with many of their canon lenses. Especially wide angle lenses. It is the opinion of many that the present day WA lenses from Canon are indeed inadequate and cromatic aberation is their main complaint. The extreme angle of the light strinking the photo-sites is what causes the purple fringing. It can be toned down with better glass.

    The other complaint about existing lenses is that the new sensor is too good for them. It out resolves all but the best prime lenses. It has always been said that 35mm lenses have better MTF curves than MF or LF lenses. The new digital backs have the same resolution regardless of what camera platform you put them on. If resolving fine detail is your game I would think sharper LF lenses would be necessary.

  3. #3
    Moderator Ralph Barker's Avatar
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    Digital Capture & Standard LF Lenses

    I think there are several things working here, Neil. First is the physical characteristics of the digital sensors, where (I've heard, but don't know for a fact) the angle of incidence of the image-forming light with respect to the sensor surface is (may) be an issue. Second is the bucket of marketing issues at play. Canon and Nikon woul have a harder time selling expensive digital SLRs to their existing customer base if they told us we needed to buy all new lenses, as well. Also, there is the issue of focal length vs. format size - the angle of view or "perspective" of longer lenses designed for larger formats.

    Among the miniature-format (35mm) manufacturers, it is my understanding that Olympus has designed new lenses for their digital cameras. On the flip side of the coin, Leica supposedly has hesitated making a digital M due, in part, to the angle of incidence issue that exists with the current line of M lenses, the design of which often extends farther into the body than SLR lenses, for example. My guess is that this issue may be related to the thickness of the digital sensor, where if the angle of the incoming light is too oblique, it may cause problems with adjacent pixels - the "color fringing" problem, or what might be called ghosting.

    But, Canon and Nikon digital SLR users (including me) seem to be getting nice, sharp (even if dinky) digital images with conventional SLR lenses. So, I'm confused, too, while I wait for a full-sized digital back that I can afford for my 4x5, and which runs for a week or so on a couple of AA batteries. ;-)

  4. #4

    Digital Capture & Standard LF Lenses

    Neil:

    The other issue with the "digital" lenses is higher MTF values at higher spatial frequencies, ie, better resolving power. The trade off is that this better resolving power is realized over a smaller image circle. In many cases, the Digitars have large circles of illumination, but the image circles quoted by Schneider are based on higher resolution/MTF criteria.

    In corresponding with Rodenstock, I have learned that some Apo-Sironar-Digitals such as the 90mm are unique designs. Others, such as the 55mm Apo-Sironar-Digital is a tweak of the Ap0-Grandagon. Element spacing is changed slightly, and some of the glasses are selected from more expensive blanks with tighter dispersion/index of refraction tolerances.

    Apparently, the main result of all of this is "more" Apo-ness, or smaller lateral CA.

  5. #5

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    Digital Capture & Standard LF Lenses

    Speaking only about view camera lenses, the information is scarce and feedback by professionals is hard to find. The last Rodenstock brochure presenting the apo-sironar digital lenses, however, has two interesting technical features briefly discussed.

    The first point deals with vignetting due to the recessed position of digital sensors. To address this problem, opticists have an old trick, using asymmetric lenses with a pupillar magnification greater than one, the rule in all regular retrofocus wide-angle lenses like Zeiss distagons. The information brochure of the new Olympus digital SLR mentions an oversized bayonet diametre in view of accommodating extremely asymmetic lenses in the limit of a quasi-telecentric lens. So there is some serious ground to modify the classical quasi-symmetric lens design used for standard and wide angle view camera lenses.

    In the last Rodenstock-Linos 'digital' brochure, there is a comparison of lens designs between the classical 35 mm 'film' apo grandagon and the new 35 mm 'digital' lens. Clearly extreme rays are less slanted in the new design, but Rodenstock does not say anything about less extreme wide-angle lenses, and if you look at pupillar magnification ratios in 'digital' lenses, except extreme wide angle lenses, you find a ratio close to one like in standard film lenses. So the question of slanted rays might not be so important for 70 degree lens.

    The second point does make sense to those who have worked with biological microscopes. Rodenstock mentions that since silicon sensors are recessed behind a certain thickness of glass (silica ?) an optical correction is required. It is well-known for biological microscopes that you are supposed to look trough a glass of .18 mm thickness, and that the lens is corrected for the supplement of spherical aberration induced by this thickness of glass, but again the effect is visible for slanted rays mostly. a 'biological' microscope lens of high power is supposed to deliver bad quality images if you do not look throught the standard .18 mm flat glass.

    A third point seems obvious by reading the specs is that 'digital' lenses being optimized for small sensors, the engineers have changed the traditional trade-off between performance at the centre and homogeneous image qiality over a wide image circle in favor of more sharpness at the centre and less image circle.

    The real puzzling point is the interaction between residual aberrations and a bayer pattern of colour pixels. If the image is not good on silicon on certain circumstances behind a 'film' lens, I'd like to know, conversely, what is magic in film, that makes the same lens acceptable on colour film !!

  6. #6
    Doug Dolde
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    Digital Capture & Standard LF Lenses

    I have deliberately avoided Canon for this reason as well as the fact that I am not a big fan of the 2:3 aspect ratio. I recently purchased a Contax 645 system with the Kodak 645C Digital Back. Not only do I get Zeiss lenses but they only use the sweet spot as the sensor is about 37mm square. Some images from it are on my website now.

  7. #7

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    Digital Capture & Standard LF Lenses

    Emmanuel, my guess is that the difference lies in aliasing, particularly with Bayer sensors. There may be a bit of 'noise pumping' going on too although that's less likely with modern high-bit backs. Film has built in spectral and spatial dithering, but digital doesn't, and current cutting-edge digital is undersampled at the 'resolution' limits claimed in advertising and reviews.

    Take a look at the high magnification images of the York hotel towards the bottom of Luminous Landscape's review of the Canon 1DS


    http://www.luminous-landscape.com/reviews/cameras/Canon-1ds-mkii-p1.shtml


    See the bands of yellow and turqoise in the scrolled railing at the bottom of the DCS proback image - I'd lay money that is caused by aliasing accentuating residual colour abberations. It's a very subtle thing in the overall image for this case, but when you remember that one large target market for these tools is people who shoot catalogues full of textiles I can see why 'digital' lenses with low lateral CA become important.

  8. #8

    Digital Capture & Standard LF Lenses

    "By the way, I'm not forgetting about Rodenstock. But, Schneider has a webpage! (Hint, Hint.)"

    So does Linos - that is Rodenstock's owner.


    http://www.linos.com/en/prod/index.html


    Been there for quite some time.

    And yes we also have lenses for digital applications and yes they do produce better images then traditional optics and yes there is more then one type of digital lens for backs on LF cameras.

    We also have brochures that spill out the differences and the reasons.

  9. #9

    Digital Capture & Standard LF Lenses

    Neil, Struan, Emmanuel

    I have just picked up an Apo-Sironar-Digital 90mm. I will shoot some tests and report back. Hopefully I won't need to cement a thin glass sheet to my rollfilm backs.

  10. #10

    Digital Capture & Standard LF Lenses

    " Hopefully I won't need to cement a thin glass sheet to my rollfilm backs."

    Only the Apo Sironar Digital HR series require a glass corrector plate when shooting on film.

    The reason for this is that these lenses were designed with the glass cover plate on the scanning backs they were designed for as being the last element in the lens formula. Without the corrector plate you would have a focus shift.

    With the Apo Sironar Digital no corrector plate is needed.

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