Canon says: more EF-S lenses

Started Oct 6, 2004 | Discussions thread
ChuckH
Contributing MemberPosts: 994
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Re: Canon says: more EF-S lenses
In reply to Doug Kerr, Oct 8, 2004

Doug Kerr wrote:
Hi, Chuck,

ChuckH wrote:

The problem is that wide angle lenses introduce a fair bit of
perspective distortion

What exactly do you mean "perspective distortion"? Are you
referring to geometric distortion?

There are many wide-angle lenses with quite modest geometric
distortion. It costs, of course.

Hi, Doug,

I composed that post in a bit of a rush and didn't choose my words as carefully as I should have.

To answer your question, I was thinking of 2 different types of distortion. The geometric (i.e. barrel) distortion that you referred to as well as the tendency of WA lenses to distort certain features of the subject.

The first, geometric distortion, as well as vignetting, is somewhat alleviated by the fact that the sensor captures a smaller portion of the image circle. However, I still think it will always be more pronounced in the case of a "normal-equivalent" 28mm lens (whether EF or EF-S) on a 1.6X crop-factor body than in the case of a "normal" 50mm lens on a FF body.

The second type of distortion is even more of a problem, if I am not mistaken, since it would not be reduced by use of a smaller sensor. I don't know a great deal about optics or lens design, so I could be entirely wrong in my assessment. It wouldn't be the first time, I assure you (grin). But, it seems to me that the tendency of a wide-angle lens to make closer objects appear much larger than distant objects and thus result in long noses, large heads, small torsos and the like would be just as pronounced when used with a 1.6X body as with a FF body. My understanding is that a 28mm lens would, therefore, give roughly equivalent perspective to a 50mm lens on a FF body, but would distort the perspective in the way we normally associate with WA images. Am I incorrect in that assumption? I would be interested in hearing your opinion on the matter.

To go back to geometric distortion for a moment, it just seems to me that they will never be able to produce WA lenses that, when used with 1.6X crop-factor bodies, will equal the performance of normal lenses on FF bodies, much less super-WA lenses to substitute for their WA counterparts.

From all that I have read and from the numerical ratings given the various lenses on the market, it seems that normal to moderate telephoto lenses virtually always rank much higher optically than their WA counterparts, which in turn rank much higher than their super-WA counterparts. I realize that those rankings are generally based upon FF film camera use and that the WA and super-WA ratings would be somewhat higher if restricted to 1.6X digital use, but the discrepancy between the various classes (i.e. moderate tele/normal --> WA --> super-WA) is so great that I don't think the higher ratings would totally eliminate the performance gap.

So, in summary, I find that we have to pay substantially more and still settle for lesser performance at the WA to normal end of the spectrum. This is balanced somewhat, of course, by the ability to save some money at the extreme telephoto end where the crop factor wins us some free added reach. That is useful for sports and nature photographers, no doubt, and shouldn't be discounted. But, I would wager that the vast majority of users take far more photos at the WA to normal side of the equation.
--
Chuck

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