Standard Primes. Film VS Digital...

[tobiasfeltus]

Hello,

I have been pondering an optical/ethical/purist issue with prime standards. We

have been used to standard prime lenses as being, theoretically, the most

"natural" focal length per format. the one that offers least distortion, and a

view most similar to that of our own piddly vision.

on a 24x36mm negative the standard was a 50mm lens, but now with the dSLR

standard of APS sized chips, the standard on a 35mm mount is around a 28mm. but

we all knew that 28mm lenses had some barrel distortion, and thus we are stuck

with prime standards on our fancy dSLRs that have a significant amount of

distortion to them.

 

I suppose i have no question to pose with the above, but i would be curious to

start a debate on the topic.

 

but returning to my ponderings, i just thought i would have a quick comparison

between my two "prime standards". I am using an S3 Pro, and the clippings are

full size crops from a Sigma 28/1.8 D Aspherical, and a AF Nikkor 28/2.8.

Sharpness does not seem to be different, and neither does distortion, however

the Nikkor seems to have a little more of a vigniette to it, and the sigma has

this odd chromatic abberration, with the sort of green drop shadow.

 

And thus i have no idea which is better. the Sigma is obviously easier to use,

being a lot brighter.

 

t

[vivek iyer]

"optical/ethical/purist issue"

 

Since you mentioned apples/onions/oranges, I will say this:

 

Yesterday, I had a brief chance to look at the ZM Planar 50mm lens on an RD1.

 

Simply fabulous even at ISO1600!

 

Get yourself a 50mm ZF planar.

[johnmarkpainter]

I don't have the 28/2.8 but I do have the Sigma. That is one solid lens. It hangs right in

there will all of my Nikon primes. I have never shot Film with it though...it's been a Digi-

only lens for me.

[EricM]

"...the standard on a 35mm mount is around a 28mm."

 

don't you mean 35mm giving you 52ish?

[Ed_Ingold]

How interesting to learn that the "standard" lenses are now the Sigma 28/1.8 and the (justifiably) maligned Nikkor 28/2.8. It would also be interesting to know how either of these lenses limits the capability of the 6 MP (discounting the fudge factor) S3 sensor. From your samples, the Nikkor has more contrast and is sharper up to the point that aliasing appears.

[pico_digoliardi]

There is no ethical issue, and your presumptions are just plain wrong.<p>

 

Barrel (or pincushion) distortion is not a natural consequence of a wide angle lens; it is the outcome of a highly compromised, poorly designed lens.<p>

 

You can find very sharp lenses for digital or film, but you have to pay for them. The market demand is for cheap, so cheap the people get.<p>

 

Your lens test is no test unless you include the color temperature of the light, the magnification factor, the subject distance, iso setting, sensor type and more. And of course you used a tripd. Right?<p>

 

Finally, sharpness is, of course, dependent upon lens design but in real life applications there are other factors including subject matter (some things are more susceptible to 'sharpness' (actually acutance)) and color, especially in digital sensors that use the bayer pattern, which all but a couple.<p>

 

I nominate your post as #1 this month for the Same Old Silly S*it Sitting on the Sofa award.

[anupam]

It seems from your post that you are using "prime lens" and "normal lens" interchangeably. You know there can be 20mm or 400mm prime lenses, right?

 

And the normal length for an APS-C sensor isn't 28mm.

 

As for your pairing of optical and ethical - it reminds me of Wittgenstein's warning that "philosophy is what happens when language goes on holiday."

 

-a

[ben conover]

I tend to agree with Pico on this thread. I think the Sigma lens is as you say easier to use, so use it. Although, I'd go for the knickers, oops, nikkors.

 

Cheers.

[vinh]

28mm IS the true normal on APS-C. the reason why everyone seems to think 35mm is normal on APS-C is because the 50mm was ubiquitous on film. but 50mm was never the true normal, 43mm was (or 45mm, not 50mm).

 

the normal is the diagonal of the sensor... 24x36, diagonal is 43mm.

 

28mm * 1.52 (APS-C) = 42.56. the 28mm lens is closer to normal than even the 45mm on film was.

 

 

on film, i never liked 50mm all that much. it never looked normal to me, slightly compressed. 40-45mm looked closer to what my eyes saw, and that was even before i learned that 50mm wasn't a true normal.

 

that said, the 28mm f/2.8 lens is my most used prime on APS-C. it's a pretty mediocre lens, but the focal length is what i like. i'd love a 28mm f/1.4...

[john_stafford2]

<i>As for your pairing of optical and ethical - it reminds me of Wittgenstein's warning that "<u>philosophy is what happens when language goes on holiday</u>." </i><p>

 

Strange how that quote has appeared twice in photo.net today within an hour; once here, one in the philosophy topic, and often before that.<p>

 

Wittgenstein is what happened when people couldn't make bombs with words and reverted to science. :) Logic bedamned. (kidding of course)

[oski]

T Feltus,

 

read this http://www.ephotozine.com/equipment/tests/testdetail.cfm?test_id=349

[john_stafford2]

<i>And the normal length for an APS-C sensor isn't 28mm. </i><p>

 

Yes it is for all practical purposes if you consider angle of view. 43mm (nominal 35mm normal) is within 2 degrees of 28mm to APS-C.

<p>

Angle of view is the rule for perspective comparison, not diagonal. Diagonal works only by accident. Consider comparisons of wide aspect ratios such as in panoramic cameras.

[michaelschrag]

"I nominate your post as #1 this month for the Same Old Silly S*it Sitting on the Sofa award"

 

I'd like to 2nd Pico's nomination.

[pnance]

Don't forget the cropping from film to digital cuts off the worst parts of a lens (if it has any). So a lens with barrel, pincushion or vignetting will exhibit much less an the smaller digital format.

[ilkka]

Cropping works to eliminate vignetting, but distortion goes through the image. If you crop the edges away and then enlarge an image with barrel distortion, the distortion is still there. A good example is a fisheye lens which has not been corrected for barrel distortion at all. 'Normal' lenses are easier to design distortion free. The wider the lens is, the more difficult, and expensive, it is to correct. It would be possible to make a really good 28 mm normal lens for APS sensors, but so far nobody has done it. I suppose the demand is too small.When the lens speed goes up, it becomes even more difficult to make a good lens and that is why the 1.8 Sigma is not that good.

[mike dixon]

I'm so worked up about the ethical issues involved in choosing a lens to shoot test charts that I may not be able to sleep tonight.

[photojim]

I don't think this is a stupid argument, although it isn't exactly an ethical issue.

 

Wide angle lenses for 35mm SLRs are designed to work around the mirror chamber. If you've ever seen a wide angle lens for a rangefinder camera (or even a point-and-shoot camera like the Olympus Stylus Epic/MJU II), notice that the rear element is very close to the film plane. The 35/2.8 I have for my Soviet rangefinder cameras has a huge bulbous element that goes into the camera chamber behind the lens mount. Over 1/3 of the depth of the lens is inside the camera. With an SLR this is impossible.

 

SLR wide angle lenses use a so-called inverted telephoto design that gets around this problem. Thus, they have more optical complexity than would be needed if not for the existence of the mirror.

 

It would be easy to design a 28mm-ish lens for an APS-sized camera (whether film or digital) without needing this optical complexity, but few have done so. (The Sigma 30/1.4 probably is designed like this; I've never played with one.) So yes, a 28 or 30mm lens designed for digital is going to have less distortion than one designed for 35mm film, because it doesn't have to do the same optical trickery that the film camera requires. (A digital SLR will still require it to have a lens that covers like a 28mm covers on 35mm film... there is no getting around that. It won't need this done, however, at 28mm... but perhaps instead at 24 or 20mm. Similarly, a 6x6 SLR will need it for a 50mm lens because, for it, that *is* a wide angle lens.)

 

Using a 35mm-intended 28mm lens on a sub-24x36 digital is a compromise. The lens was designed for something else. Of course it could be made with less distortion, but not easily. That inverted telephoto design is absolutely required to make that lens work with 35mm film... but it isn't required to work with sub-24x36 digital. That's why a specific "digital" design would be better to use on the digital body in this case.

 

This has nothing to do with morality or ethics or anything else... it's just a rule of optics. Digital SLRs are designed to use 35mm lenses, but that is a compromise. 35mm cameras would shoot images of lower quality than they could if they had to use adapted medium format lenses, too.