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Film Lenses and the 1.5 factor
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Hi all you guys who use film lenses on DSLR’s.
I have a large range of nikon film lenses (now don’t be jealous) and am toying with the idea of puchasing the film 15mm lens. When this goes on the digital SLR it will become equivalent to about 22mm.
My question is will the same image distortion that occurs with it suse on the film SLR occur when it is used on the digital SLR.
Regards :?:
Hi Mike,
Think of the Image Multiplication factor as a crop. Whatever the 35mm image would look like with the edges cropped off will be what you get with the Digital. Because the magnification is greater, you need to watch hand-hold speeds for shake.
Si
Hi Si
Thanks a lot for your advice.
Still one mystery though:
Does it mean if I were to use the lens in the film camera and then:
a) Print the result (to say 10″ by 8″).
b) Crop approx one third top and bottom.
c) Enlarge the image again to 10″ by 8″then the result is similar to using the lens in the DSLR.
Regards
:?:
Hi Si
Thanks a lot for your advice.
Still one mystery though:
Does it mean if I were to use the lens in the film camera and then:
a) Print the result (to say 10″ by 8″).
b) Crop approx one third on all sides.
c) Enlarge the image again to 10″ by 8″then the result is similar to using the lens in the DSLR.
Regards
:?:
Mike. Answer is no. By crop factor, is meant simply that the full sensor size (about 22x15mm for Canons, slightly bigger for Nikons) is used to capture only about 2/3 the area of a 35mm frame (36 x 24mm). You get that at the full sensor resolution though, so it’s not as if you’d cropped the image in Photoshop and upsampled it to the same print size.
Think of it another way. If you would use a 15mm lens, on a 35mm camera you’ll get the full field of view you’d expect from a 15. On a DSLR you’ll get the same field of view with the 15 that you’d get using a 22mm lens on the 35mm camera. But you’ll get that at the full sensor resolution.
Similarly, with respect to the original question, as your 15 on DSLR would act like a 22 on a full-frame camera, to frame the same pic in the same way you’d have to stand further away, so distortion will decrease. If you don’t move you’ll get the same distortion but a tighter frame.
mike grehan wrote:
Hi Si
Thanks a lot for your advice.
Still one mystery though:
Does it mean if I were to use the lens in the film camera and then:
a) Print the result (to say 10″ by 8″).
b) Crop approx one third top and bottom. (crop the edges so as to trim 1/6th all the way around approx)
c) Enlarge the image again to 10″ by 8″then the result is similar to using the lens in the DSLR.
Regards
:?:
Yes! In terms of the framing and distortions etc, but, upsampling will introduce other distortions relating to the enlargement.
So, if you stand in a spot and took a picture of a subject using a 35mm film SLR and then in the ssame spot took the shot again eith the DSLR.
The DLSR will have the same picture as in the 35mm shot, just with the edges croppped off. All DoFs, distortions etc will be the same, exactly like a 35mm with the edges cropped off.
The effect of this is to give the same field of view as a longer lens. YOu’ll have to move your feet to get the same composition and by moving, the DoFs, “distance compression” of using different focal-lengths etc will change.
I agree with what Steve says as a different way of looking at it.
All best
Si
Every time I read this stuff.. I have to re-read it and get it clear in my mind. :?
Something that hasn’t been mentioned is the benefit of using film lenses on digital sensors in terms of image quality. On lenses, it’s typical for the edges to be softer, suffer from vignetting and distortion (pin cushion/barrel). Obviously the degree of distortion depends on the quality of the lens. However, as the image circle falling on the digital sensor is smaller, the edges of the lens are not used on the digital sensor and as such the image is typically higher quality because it’s using the sweeter part of the glass.
ciaran wrote:
Every time I read this stuff.. I have to re-read it and get it clear in my mind. :?
Something that hasn’t been mentioned is the benefit of using film lenses on digital sensors in terms of image quality. On lenses, it’s typical for the edges to be softer, suffer from vignetting and distortion (pin cushion/barrel). Obviously the degree of distortion depends on the quality of the lens. However, as the image circle falling on the digital sensor is smaller, the edges of the lens are not used on the digital sensor and as such the image is typically higher quality because it’s using the sweeter part of the glass.
Benefits? What benefits? :cry: The theory sounds good but in practice it doesn’t work like that. When I switched from film to digital, I found that the lenses I had used for years with film gave me appaling results with digital. At first I suspected the camera, but something clicked in my brain and I decided to get new lenses before getting a new camera. Boy, what revelation.
One of the reasons for this is that film doesn’t really care about the angle at which the light incident on it strikes it. Digital sensors are different however, and ideally the light should be striking the sensor perpendicular to the plane of the sensor. That’s one of the reasons behind the emergence of digitally optimised lenses (such as Tamron’s “Di” range).
Thorsten wrote:
Benefits? What benefits? :cry: The theory sounds good but in practice it doesn’t work like that. When I switched from film to digital, I found that the lenses I had used for years with film gave me appaling results with digital. At first I suspected the camera, but something clicked in my brain and I decided to get new lenses before getting a new camera. Boy, what revelation.
One of the reasons for this is that film doesn’t really care about the angle at which the light incident on it strikes it. Digital sensors are different however, and ideally the light should be striking the sensor perpendicular to the plane of the sensor. That’s one of the reasons behind the emergence of digitally optimised lenses (such as Tamron’s “Di” range).
Well I’d love to say I have some hard data to back this up Thorsten, but this is all based on material I’ve read and I guess a degree of intuition. All my lenses with the exception of one are digital lenses (Nikon “D” lenses or Sigma “DG” lenses). I wasn’t aware of them being optimised for the angle of light, I thought it was simply making use of the image circle being smaller, so the lens and glass itself could be smaller, cutting down in weight, size and cost. I do however have a 50mm prime (film) and have zero problems in using it on a digital sensore.
ciaran wrote:
Well I’d love to say I have some hard data to back this up Thorsten, but this is all based on material I’ve read and I guess a degree of intuition. All my lenses with the exception of one are digital lenses (Nikon “D” lenses or Sigma “DG” lenses). I wasn’t aware of them being optimised for the angle of light, I thought it was simply making use of the image circle being smaller, so the lens and glass itself could be smaller, cutting down in weight, size and cost. I do however have a 50mm prime (film) and have zero problems in using it on a digital sensore.
Sigma DG are full-frame digitally optimised lenses. Sigma DC are cropped digitally optimised lenses.
One of the main improvements in some digitally optimised lenses is the application of non-reflective coatings on the rear element to stop light reflecting back onto the sensor.
Ciaran, you’re right in what you say and so are Thor and Carl, one big happy family :)
The problem with older lenses is that they bounce light around a bit more and the light comes in from “Less than perpendicular” angles. With the D2x you can see the minute failings of excellent lenses. You certainly get very good edge-to-edge shaprpness and virtualy no light fall-off at the corners with film lenses.
The next improvement (IMO) for DSLRs isn’t resolution at the sensor level but at the lens level. This will need perpendicular light and anti-reflective rear-element coatings as Carl says. The theory says that if the light travels through the microlenses perpendicularly, there will be less light-loss, less diffraction evident and less overflowing into adjacent sensor cells (this is more your bag than mine). Many people talk about extending the dynamic range capture ability, I think this will happen but I’m getting more than I need now and often have to bump the contrast.
I have an old 135mm nikon prime f2.8, cool. Except when there are specular highlights or when the subject is backlit, bigtime flare issues as the coatings were non-existant or minimal in those days. I think I read somewhere about a new coating that was virtualy reflectively zero. Anyone hear of that?
An advantage to the smaller sensor size is smaller lumps of glass, allowing superzooms (that you can carry) and generally smaller lenses for the same aperture ranges.
The “D” on Nikon lenses (if memory serves) relates to the “Distance” information that the lens is capable of passing to the camera’s computers (Amazing that if the camera knows the distance to the subject (assuming that’s what you’ve focussed on), that it can’t alwayus get the flash spot on.
All best
Si
ciaran wrote:
I thought it was simply making use of the image circle being smaller, so the lens and glass itself could be smaller, cutting down in weight, size and cost.
Yes, yet another factor to consider when buying a lens! I would consider that a digital only lens rather than a digitally optimised lens :D The new Canon EF-S range of lenses are typical of such lenses and they will only work on certain bodies (they are typically sold as a “kit” lens). Personally, I wouldn’t buy an EF-S lens simply because you are then restricted to using it with a limited range of bodies :cry:
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