Digital Lens Design Compared to Film Lens Design

A recent sunset picture taken with a Canon Rebel by a neighbor showed an unusual

colored object in the center. Several people attribute the image shape to flare,

even though it is unusual and not a normal film flare image. Question, if you

use a lens designed for film on a digital camera will flare be different than

using a lens designed specifically for a digital camera? Regards.

The sensor in a DSLR is flat and relatively reflective compared to film, which may give rise to flare or ghosting unique to DSLRs. The typical effect is more like ghosting, where you lose contrast in a fairly large, circular portion in the center of the image. This is one of the factors considered in the design of DX lenses. That said, I have taken many pictures into the light using a DSLR with standard lenses, without seeing effects of this sort. I have experienced strong flare from off-axis lights on both film and digital, especially from street lights in night shots. This flare is composed of one or more bright areas, often colored, typical of fast and zoom lenses.

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Show us the image, John.

Was there a filter on the lens? There's a specific kind of reflection (sharp copy of a bright object, rotated 180 degrees around the center) that occurs with digital cameras when using a front filter, and that typically gets lessened by stopping down.

One would have to do side-by-side tests with the same lens over film and over a digital sensor.

 

Zoom lenses have variable performance over their range, so I'd stick to single focal length lense comparisons for first comparisons. (My feelings about zooms is that it is not how well they work compared to single focal length lenses, but that they work at all!)

 

Some lenses fare well when pointed at a light source. Some do not. It has to do with coating, of course, but also with lens design. For example, some Biogons do well with a light source in the photograph while other lens designes of the same focal length (for the same format) do not.

I found that a particularly strong flare turned orange and dense on my rebel xt--there was

no transparency to the spot at all. I think it is just the digital overload.

 

The digital lenses

are only designed to take advantage of the smaller sensors--cheaper as they have a

smaller

sweet spot to design to, but possibly (and I say POSSIBLY) with the advantage of being able

to

make them sharper--the larger the format, all things being equal, the lower the overall

resolution of the lens-due to the need to increase the maximum sweet spot. With more

full frame 35mm coming along, this will all be moot, but

that is why there were so many new view camera lenses for digital that came out a few

years back. Super wide

lenses for full frame formats were very expensive (and very limited in selection), while

"digital" lenses could be produced

with a lower price tag to cover the smaller sensors available.

Cheap film lens with circular area of transparency in center of image probably means reflection off the rear element of the lens from the digital sensor as Mr. Ingold suggests -- there was an identical case here recently addressed by very senior folks. The cause is the absence or ineffectiveness of the lens coatings. Even lenses designed for full frame coverage are labeled for digital use when provided with superior coatings, e.g., a number of Tamron and SIGMA FF lenses.

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Show us the image, John.

Peter,

 

It used to be here:

 

http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=00HhlZ

 

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Done E

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Ahh, another place we can't actually see the image.

 

Thanks!

 

:-(

I think it probably is the cheap filter.

My computer stopped after starting this thread. Back in operation now and thanks for all the input. I loaded the picture into My Portfolio so you can see the image. More info on the camera. Body is a Canon EOS Rebel DS 6041 #1660511490, Lens is not an old EOS lens but the kit lens that came with the camera, an EFS 18-55mm f3.5-5.6. Interesting. Regards.

 

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That's "just" plain old flare, which is actually pretty well controlled since you're pretty much in the worst possible scenario (severely overexposed area with reflections being against a black background. Even the best lens coatings can only do so much.

<<I think it is just the digital overload.>>

 

Wrong. CMOS sensors, due to the inherent nature of their design, do not suffer from any sensor blooming effects.