From time to time I read how people think their D100 gives them 1.5x focal lenth. That's not right. The 1.5x factor only means the picture you take lookes like taken with a lens that is 1.5x the zoom lentgh of the len you use. In other words, it's the picture's angle of view that changes. If you zoom your 80-200 to 200, you still get 200mm, not 300mm. The picture on the D100 is actually "cropped". Reason why you need the sharpest lens you can get with a D100 or any DSLR that's not full frame.
Corret me if I am wrong.
...Live and learn.
#1. "RE: 1.5X factor--again?" | In response to Reply # 0flashdeadline Nikonian since 07th Apr 2002Sun 15-Jun-03 01:37 AM
I believe it's a "relative" term (the 1.5 factor). Something we can use to gauge the "effective" wide to tele capabilities of a particular lens, given the fact we are now shooting to a smaller "negative."
Were it not for the fact that a wise old sailor once spent three hours explaining to me how his telescope really worked, I'd have no idea about the "cropping" you described.
I can remember way back in the old days when I first saw the 120 and 220 "medium format" cameras that took lenses made for 35mm's. Even then we had to know that we were now working with a different "effective" factor.
Thanks for the reminder, especially the excellent point about putting the best possible glass on the camera.
"Shoot everything f/16 at a 100 and let the lab boys worry about it."
"Shoot everything f/16 at a 100 and let the lab boys worry about it."
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#2. "RE: 1.5X factor--again?" | In response to Reply # 0darrellyoung Registered since 21st Apr 2006Sun 15-Jun-03 02:18 AM
Of course, you are right!
But, you know what! When I stick my 300mm lens on my D100 the image sure does LOOK bigger to me. It is an optical illusion, of course, but a satisfying one. You are filling much more of the frame. A full frame prevents cropping. You can print a full frame more easily. To get a comparable result, you would have to crop a 35mm image. It would look the same, but take a lot more work.
I LIKE the 1.5 factor myself. I shoot many many more long shots than wide-angles. But, I do miss the wides sometimes for big groups shots. I guess I'll just buy myself a 12-24 so I can have a 20mm effect.
#3. "It's correctly termed..." | In response to Reply # 0RRowlett Charter MemberSun 15-Jun-03 04:47 PM
...field of view crop. That is a D100 with a 200 mm lens has the same field of view as a 35 mm film camera fitted with a 300 mm lens. So although the image size is the same for a lens of a given focal length on an SLR and a DLSR, the DSLR frame will be more easily filled by a given subject.
Actually with a DSLR you can get away with LESS well-corrected optics, because the current crop of DLSRs crops out the center of the image circle produced by 35 mm format optics. The center of the optical field is usually better corrected for distortion and freer from various optical aberrations than the edges. So most lenses perform slightly better on a small-format DSLR than on a full frame DSLR or 35 mm film camera.
#6. "I don't think this conclusion is consistent..." | In response to Reply # 4RRowlett Charter MemberMon 16-Jun-03 11:12 AM
...with the physics. Digital sensors have inherently less spatial resolution than 35 mm film, and in addition are almost all fitted with an anti-alias filter which is necessary to reduce moire and related digital imaging artifacts. This further reduces spatial resolution in order to combat aliasing. A sharper lens will not compensate for these resolution-degrading factors. While a sharper lens is never a disadvantage, the importance of ultra-sharp optics in a DSLR is less important than in a film SLR. Put another way, it is possible to get excellent performance from a lens on a DSLR that might only be very good on a film SLR.
Not only is this the theroretical prediction, but professionals have also subjectively noticed in practice (for example see Bjorn Rorslett's lens reviews) for most lenses used on both APS-size DLSR and film SLRs, that the same lenses perform better on DLSRs than on 35 mm film cameras.
#8. "RE: I don't think this conclusion is consistent..." | In response to Reply # 6Jonathan Registered since 10th Feb 2003Mon 16-Jun-03 02:27 PM
Digital sensors have inherently less spatial resolution than 35 mm film
This is not necessarily true. It depends on the film, on the sensor, and on the method you use to measure resolution. I have seen tests that show better resolution for some sensors than for some films and vice versa. It's not cut and dried. The issue is further complicated by the fact that resolution of most films depends on exposure, the processing, and the contrast of the subject, so what someone got in the laboratory may have little to do with how your pictures look in practice.
Finally, even when film is potentially better than the CCD, in practice the resolution limit of good lenses tends to be close to the CCD dimensions. For portraits at f/1.2, good film, such as velvia, can be much better than CCDs, but then again medium and large format are used so often because even 35mm film shows its limits.
But if you're shooting at small aptertures, the difference between film and CCD rapidly vanishes. At f/8, the physical diffraction limit to a lens's spatial resolution at the film plane is about 5 microns, which close to the size of a CCD pixel. Since it's rare for general-purpose lenses to get within a factor of 2 of the diffraction limit, it's unlikely that you would see any noticeable difference in resolution between film and a high-quality CCD at f/8 or higher. For this reason, you DO want to pay attention to the quality of a lens for digital just as you would for film.
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#5. "RE: 1.5X factor--again?" | In response to Reply # 0
I like the crop factor. That 80-200 f/2.8 become a really nice lens on a D-series camera. I think that if you compared photographs, (200mm on D-series, and 300mm on F-series) you will end up with the same result. I'm not sure about the sharpness issues, and I'm sure someone will correct me. It makes sense, but I still think it would be better than cropping the 35mm image taken with a shorter lens. All other things being equal.
Allan, A Comox Valley Nikonian
#7. "RE: 1.5X factor--again?" | In response to Reply # 0
This is correct. And also, a 35mm format is a cropped version of a 6x7cm medium format negative, which in turn is a cropped version of an 8x10 negative. Thus, a 300-mm lens is "really" a wide angle lens (on an 8x10, it gives an equivalent angle of view that a 43mm lens would on a 35-mm camera), but it "seems" to be a long lens when you crop the image down to 36x24 mm. The argument that there's something bad about the 1.5x factor because it's "only cropping" is just like arguing that there's something wrong with 35mm because it's cropped down from 8x10.
Of course it would be silly to think that a 300mm lens on an N80 or an F5 is "really" a wide angle lens with a large cropping factor because in the context of the 35mm format, 300mm is a pretty long lens. Similarly, in the context of APS format, 200mm is just as long as 300mm is for the 35mm film and 2100mm for 8x10.
Now the actual effect on your picture taking is this: At a given distance, the only effect of changing lenses is to "crop" your image on the film. A number of good books (my favorite for this is Ansel Adams's The Camera) demonstrate that changing lenses without moving the camera has the same effect as cropping an image. The way you change the perspective is by moving the camera.
By concentrating only on the cropping question, many people forget to ask the question, "how far away will the photographer stand from the subject," which is the really important question. Because the APS-sized sensor makes you stand farther back when using a given lens than you would with 35mm film, the net effect is that photos shot with a 200mm lens on a D100 will be like photos shot with a 300mm lens on an N80.
When you move your camera to compose the image, how far back you stand is not a function merely of the focal length of the lens, but of the ratio of the focal length to the size of your sensor (film or CCD). Let's say I have three cameras. One is an N80 with film and a 300mm lens, another is a D100 with a 200mm lens, and the third is a D100 with a 300mm lens. I compose a picture in the viewfinder of the N80 and try to replicate it with the D100s. The D100 with the 200mm lens would go at the same place as the N80. The D100 with the 300mm lens would have to go 50% farther back to fit the whole scene in tht viewfinder. Thus, the perspective in the N80/300mm and the D100/200mm images would be the same and the perspective in the D100/300mm image would be flattened by the additional distance between the camera and the subject.
As to sharpness, lenses generally produce sharper and less distorted images near the center than at the periphery, so the cropping factor crops out the areas where most 35mm-format lenses have the worst performance and the greatest distortion. Thus, a given lens will tend to give better performance for a D-1/D-100 than with film.
Thus, what the cropping argument really amounts to is that with an APS-sized sensor, you end up paying more than you need to for lenses because some of the money you're paying goes to minimizing aberrations in the corners of the negative that your CCD won't even see. If you don't mind paying a little more for film lenses than for DX lenses, there's no problem using an APS sensor and treating the 1.5x factor as a real enhancement of the lens's focal length.
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#9. "RE: 1.5X factor--again?" | In response to Reply # 7
#11. "RE: 1.5X factor--again?" | In response to Reply # 0
Having tested many lenses on the D100 in side by side comparisons, I
have not seen repeatable variance among my very good and better lenses
in terms of resolution. In many tests, my 28-105mm Nikon AF-D, a
very good lens, will as well as and in some cases better than my Nikon pro level lenses. Bad lenses do give bad results however.