I'm stuck on a question on my assignment...

[Salma]

This is the question.

Why might you experience light 'fall off' when using a made-for digital lens on a film camera?

I am so stuck, there's nothing I can find about this in my revision papers. Do you guys have any ideas what I should put.?

Thanks :D

[neumanns]

Hmmm.....have you given any thought to digital sensor size vs film plane size?

[Salma]

Hmmm.....have you given any thought to digital sensor size vs film plane size?
I'm sorry, I should've made myself more clear.

This is the question in the test paper that I don't know the answer to:

Why might you experience light 'fall off' when using a made-for digital lens on a film camera?

[-MasterChief-]

im talking out of my a$$ again but here goes nothing .... because digital only lenses are designed to take advantage of the 1.5 or 1.6 crop of non-FF digital sensors.

[Duncan Frenz]

The coatings used on 'digital lenses' filter light in a manner to take advantage of the range of digital sensors. These coatings are not optimized for film which is sensitive to different light spectrum, causing light 'fall off'.

i.e. digital sensors are inherently prone to flare, thus special coatings are used for 'digital lenses'. Theses coatings reduce light transmission which causes light fall off when used with film.

[Matthew Patrick]

The question was not phrased or conceived with clarity in mind. It's a bogus question because you should never try to mount a lens designed for a crop sensor on a full frame camera unless you understand the inherent danger involved. a better question might be "Why might the mirror be damaged when you mount an EF-S lens on a full frame body"

I don't know if "light fall off" is the most accurate terminology for this question. This link might help you figure it out:
http://en.wikipedia.org/wiki/Vignetting

[neumanns]

delete

[jacuff]

Made-for digital lenses (Canon EF-S, Nikon DX, Sigma DC, Tamron Di-II, Tokina DX, etc) are designed to cover a smaller sensor. The image projected onto the sensor plane or film plane is smaller. Some are made to not physically mount on a camera to help prevent this. Others will mount but will show light fall off or vignetting, especially when used at the wider end of the lens.

About lens coatings... let me look up more information for you. I'm pretty sure most digital sensors and film are sensitive to near the same light spectrum.... aka the visible spectrum. (Not withstanding modified cameras and special purpose films such as IR.) The coatings on digital lenses are usually to stop reflections coming back off the sensor, it's fairly insignificant when mounted on a film camera. Light fall off will be very minimal. That's why I tend to think the question was asked so that the first paragraph is the right answer.

[jacuff]

The question was not phrased or conceived with clarity in mind. It's a bogus question because you should never try to mount a lens designed for a crop sensor on a full frame camera unless you understand the inherent danger involved. a better question might be "Why might the mirror be damaged when you mount an EF-S lens on a full frame body"

Not quite. Yeah its true for EF-S lenses, but others are not designed that way. The question isn't really a bogus question at all. A popular lens that people use this way is the Tokina 10-17mm fisheye. It is designed for digital crop cameras but when zoomed to 15mm or higher, it works perfectly fine on a Full Frame camera... and it won't damage your mirror because it doesn't stick any further into the mirror box than any normal EF lens.

[Matthew Patrick]

I just think the instructor should make sure his students don't go out and try to mount a 10-22 on their new 5D without being aware of the inherent dangers involved. I said it's bogus because I don't think that light fall off is the appropriate terminology for this situation.

[Wilt]

The coatings used on 'digital lenses' filter light in a manner to take advantage of the range of digital sensors. These coatings are not optimized for film which is sensitive to different light spectrum, causing light 'fall off'.

i.e. digital sensors are inherently prone to flare, thus special coatings are used for 'digital lenses'. Theses coatings reduce light transmission which causes light fall off when used with film.

'buzz'...wrong

[Wilt]

This is the question.

Why might you experience light 'fall off' when using a made-for digital lens on a film camera?

I am so stuck, there's nothing I can find about this in my revision papers. Do you guys have any ideas what I should put.?

Thanks :D

Hint: image circle size (anything more than that from me is helping you to cheat)

[Duncan Frenz]

It is evident that the question asked is poorly defined and can be interpreted differently leading to widely different, but correct, answers. Does the term 'digital lens' refer to lenses made specifically for smaller sensor formats or is it alluding to the manufacture of lenses optimized for digital sensors regardless of format?

Obviously, if it is in regard to lenses designed for APS-C sensors, the lens would cause light fall off on a 35mm film camera because of the smaller circle projected onto the film from the inherent characteristics of such a lens. However, I read the question as to mean the manufacture of lens optics that are designed for digital to reduce characteristics of the sensor itself versus film and how they are affected by light. i.e. sensors being(more) prone to flare

[Duncan Frenz]

Hint: image circle size (anything more than that from me is helping you to cheat)

You are assuming the question meant digital lenses in the sense of ones designed for a smaller format. There are many lenses designed for 'digital' that are used for FF digital cameras, and project the proper circle to the sensor or film. Furthermore, saying 'film' is generic without specifying a format. They could very well be asking about MF, 35mm, C-126, or 110 film!

[Wilt]

You are assuming the question meant digital lenses in the sense of ones designed for a smaller format. There are many lenses designed for 'digital' that are used for FF digital cameras, and project the proper circle to the sensor or film. Furthermore, saying 'film' is generic without specifying a format. They could very well be asking about MF, 35mm, C-126, or 110 film!


Duncan,
Film camera lenses do not care about the angle of the light rays striking the surface of the film, because chromatic abberations are not induced by color-sensitive sensels. OTOH digital sensors care, particularly for wide angle lenses, because of the steeply oblique angles at which the light rays might strike the surface...so the different wavelenghts of light are recorded by the color-specific sensels. For-digital wide angle lenses are designed for less-steep angles of incidence for light rays, to try to avoid/reduce chromatic distortion. So using a 'designed for digital' lens matters not at all for film, because film does not care about angle of incidence of light rays. This is especially true of APS-C format where, for Canon with the EFS design, the rear element of the WA lenses can be much closer to the sensor than a lens designed for a FF body.

Both film and sensors have to record the full range of visible light, they do not need to different in any fashion about this aspect. Notice that film lenses and digital lenses for FF do not differ in ANY way at all!

[jacuff]

Hint: image circle size (anything more than that from me is helping you to cheat)

Wouldn't it be funny if the instructor is also a POTN member and saw this thread? It reminds me of a student back in my C++ class that did something similar by posting to comp.lang.c++.

Oh sweet... I found it (http://groups.google.com/group/comp.lang.c++/browse_thread/thread/bc518f45e8f51c7f/c348e5f950b2cc13).

[Wilt]

You are assuming the question meant digital lenses in the sense of ones designed for a smaller format. There are many lenses designed for 'digital' that are used for FF digital cameras, and project the proper circle to the sensor or film. Furthermore, saying 'film' is generic without specifying a format. They could very well be asking about MF, 35mm, C-126, or 110 film!


A Canon digital forum seldom delves into anything other than 135 sized sensors, APS-H and APS-C sized sensors. So I didn't feel it was necessary to be more specific about format size in this case.

[Jdumas]

Sigma 30mm on EOS 1n
Light falloff:

[Wilt]

Sigma 30mm on EOS 1n
Light falloff:


...Image circle (illustrated)

[Duncan Frenz]

A Canon digital forum seldom delves into anything other than 135 sized sensors, APS-H and APS-C sized sensors. So I didn't feel it was necessary to be more specific about format size in this case.

Agreed. But this was a question from an instructor outside our forum. I took instructor to mean University...

Anyway, if the definition of 'digital lens' is to mean those designed for 'crop' cameras, such as the EF-S line, then of course the answer is the obvious one to which you alluded and many others.

[Wilt]

Agreed. But this was a question from an instructor outside our forum. I took instructor to mean University...

Anyway, if the definition of 'digital lens' is to mean those designed for 'crop' cameras, such as the EF-S line, then of course the answer is the obvious one to which you alluded and many others.

And if the question about 'digital lens' was not in the context of crop and image circle size, I cannot think of ANY parameter which would cause a lens design to be different for 135 format film vs. for 24x36mm digital sensor. Canon seems to have no 'for digital' lenses apart from EFS. And other vendors like Tamron and Tokina and Sigma don't seem to, apart from image circle distinctions.

From Tamron's site: "What about the image quality of 35mm lenses on DSLRs? Much ink has been spilled on this subject, but there are three key factors to consider—the angle at which the lens’s light rays strike the sensor, antireflection coatings, and optimum format coverage. Much has been made of the fact that the edge light rays transmitted by many ultra-wide-angle lenses designed for 35mm cameras strike the image sensor at very oblique angles. This was perfectly acceptable when film was the capture medium, but it can cause image degradation at the edges and corners of the field when CCD and CMOS sensors are used. This effect can certainly be shown in side-by-side comparison pictures shot with 35mm and digitally optimized ultra-wide-angle lenses on professional, 24x36mm-format DSLRs, but it is far less pronounced with consumer DSLRs using APS-size image sensors. It is also true that digitally optimized lenses made by camera makers and leading independents (e.g. Tamron Di and Di-II lenses) use improved coatings designed to reduce flare (wilt: which is not an impact on 'fall off'), which is more likely to affect pictures taken with digital imaging systems. However, the most important lens factor affecting DSLR image quality is optimum format coverage. In general, lenses specifically designed to cover the APS-C format have an inherent image-quality advantage over lenses designed to cover the larger 35mm format because their coverage precisely matches the frame. The bottom line: By all means use your present 35mm SLR lenses on your DSLR, but when buying new lenses for your DSLR, favor those optimized for digital photography."


...image circle

(I will still leave it to the student in applying the hint into an answer to the question presented)

Tokina has no mention at all about 'for digital' considerations. Sigma mentions only:
"The most suitable lenses for 35mm film single-lens reflex cameras, as well as for digital SLR cameras. Sigma's development of the DG (Digital) range of lenses has concentrated on the correction of distortion and aberrations. Magnification of chromatic aberration is particularly conspicuous with digital cameras. The optical designs and cutting-edge technology incorporated by Sigma eliminate flare and ghosting from te image sensor and create excellent color balance. Vignetting is minimized whilst marginal illumination is ensured. These high performance lenses are equally suited for digital and analogue cameras. "DC Lens These are special lenses designed so that the image circle matches the smaller size of the image sensor of most digital SLR cameras. Their specialized design gives these lenses the ideal properties for digital cameras, the compact and lightweight construction is an added bonus!"

...and while they mention vignetting, there is noting stated about why digital consideration of vignetting is any different than for a film camera. Actually they state, "These high performance lenses are equally suited for digital and analogue cameras."

[number six]

Wouldn't it be funny if the instructor is also a POTN member and saw this thread? It reminds me of a student back in my C++ class that did something similar by posting to comp.lang.c++.

Oh sweet... I found it (http://groups.google.com/group/comp.lang.c++/browse_thread/thread/bc518f45e8f51c7f/c348e5f950b2cc13).

:lol::lol::lol:

[Salma]

Guys thanks alot for all your responses.

There is no instructor folks. I am sitting a test paper, it's a home learning course and this question came up. That is all :D It's nothing practical.

[Wilt]

Does that mean I can help you cheat? Naw...good learning exercise for you to start with the comments in the thread, and take it where you think it should go, based upon your own conclusion. :cool:

[Karl Johnston]

That's a horrible question.

"A made for digital"

In those words, "Made for a digital crop camera?"

Or a digital lens...like an EFS lens? But then there are EF lenses that are digital, too.

Sounds like a bogus teacher :/

[Wilt]

That's a horrible question.
...Sounds like a bogus teacher :/

I'm certainly not impressed

[Duncan Frenz]

And if the question about 'digital lens' was not in the context of crop and image circle size, I cannot think of ANY parameter which would cause a lens design to be different for 135 format film vs. for 24x36mm digital sensor. Canon seems to have no 'for digital' lenses apart from EFS. And other vendors like Tamron and Tokina and Sigma don't seem to, apart from image circle distinctions. <snip>
...and while they mention vignetting, there is noting stated about why digital consideration of vignetting is any different than for a film camera. Actually they state, "These high performance lenses are equally suited for digital and analogue cameras."

Thank you for taking the time to answer. However, I knew all that (well most) but my answer derived out of the context of the only thing I knew to be different other than the imaging circle. It would never occur to me to put a 'digital lens' on a film body if the definition of a 'digital lens' is one that projects a smaller imaging circle to fit APS-C sensors! That is just absurd to me, thus my answer.

It would be akin to an exam for an EE asking: "Why might you experience an overload if you plugged a 110V device into a 220V receptacle?". It never even crossed my mind that one would ask such an absurd question. It is poorly worded if it meant it in the context described previously. I am curious as to what the answer from the correspondence actually will turn out to be. If their answers are anything like their questions, it should be amusing. Answer: 42!

Oh well. It isn't the first exercise in futiliy that I have run into on the net, and I am certain it won't be the last. ;)

[number six]

Oh well. It isn't the first exercise in futiliy that I have run into on the net, and I am certain it won't be the last.


I'm guessing it's not the first poorly-phrased test question you've seen either. Or, for that matter, the first poorly-qualified teacher.

We've all been there.

Salma, you've got a lot of good things to consider. And you'll decide how to answer.

-js

[Salma]

Ok so now i'm really scared. The question is bogus. Should I complain to my tutor?

[PhotosGuy]

I'm guessing it's not the first poorly-phrased test question you've seen either. Or, for that matter, the first poorly-qualified teacher.

We've all been there. TRUTH! Should I complain to my tutor? I would, but I'm a well known malcontent! :D

[Wilt]

Ok so now i'm really scared. The question is bogus. Should I complain to my tutor?

You might start with a statement that the original question is flawed, then explain the points already made within this thread, and how only the image circle answer seems to apply, but no one in their right mind would use a lens for a smaller format (APS-C) on a larger format camera. It points out clear understanding of the issues, and how there is no proper answer to the question which was posed. It would show understanding and logical thought, and that may be worth something even if the instructor had some other principle in mind.