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07-08-2011, 07:48 PM   #1
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Why hang on to film carry overs??

This applies both to the sensor and the lenses. With the lenses such as the Pentax DA line or the Nikon DX line, both are designed for aps-c sensors. So, if you have say a 100mm DA/DX lens... why not just call it a 150mm lens? This would seem to reduce possible confusion. Same for the sensor, why call it aps when that format doesn't even exist anymore?? Seems to me it's like describing the size of a car as 1.2 or 1.5 wg (wagon lengths as per distance between axles of a covered wagon).

Is there something here I'm missing? As far as I know, focal length is determined based on 35mm camera size and distance from the back of the lens to the film to clear the mirror. If there are large changes because of the move to digital, it seems to me that it would make sense to make a DSLR the standard and base your measurements and such on that rather than hanging on to 35mm film which is nearly gone...

Ok... fire away

07-08-2011, 08:07 PM   #2
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QuoteOriginally posted by mdbrown Quote
This applies both to the sensor and the lenses. With the lenses such as the Pentax DA line or the Nikon DX line, both are designed for aps-c sensors. So, if you have say a 100mm DA/DX lens... why not just call it a 150mm lens? This would seem to reduce possible confusion. Same for the sensor, why call it aps when that format doesn't even exist anymore?? Seems to me it's like describing the size of a car as 1.2 or 1.5 wg (wagon lengths as per distance between axles of a covered wagon).

Is there something here I'm missing? As far as I know, focal length is determined based on 35mm camera size and distance from the back of the lens to the film to clear the mirror. If there are large changes because of the move to digital, it seems to me that it would make sense to make a DSLR the standard and base your measurements and such on that rather than hanging on to 35mm film which is nearly gone...

Ok... fire away
I have a 150mm lens for my medium format and it is a longer than normal lens, and a 150 mm lens for my 4X5 and it is the normal lens, if it had more coverage it would be a wide angle lens for my 5X7 and extreme wide angle for my whole plate. The focal length does not change when you change format. The physical distance does not change only the coverage onto the film/sensor. If you put a 200mm lens onto the 4X5 film and then attached a digital camera onto the back of the view camera the size of an object would be the same on both the 4X5 film and the aps sensor, you would just have more onto the larger format but each component would be the same size on each format.

The focal length is totally independent of the format. A 100 mm lens only 'acts' like a 150mm lens on cropped sensor because it covers the same view as if the full size sensor or 35mm film had a 150mm lens on it.
07-08-2011, 08:10 PM   #3
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...ummm...because focal length is a physical property of the lens and has nothing to do with film format, field of view (FOV), or coverage circle?


A 50mm lens focuses at 50mm from the film plane whether it is mounted on APS-C (a little longer than normal), 35mm (normal), 645 medium format (wide angle), or 4x5 (extreme wide angle). It has nothing to do with mirror box (my 35mm rangefinders have very short lens registration distances, but are still 50mm focal length) and is still true even off camera.


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07-08-2011, 08:22 PM   #4
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Why use ISO?

It's a standard; a benchmark we can all agree on that, at some time in history, developed into a fixed reference by industry consensus.

APS-C sensors were designed to that size in the anticipation that there would be $2,000 digital cameras and $300 film cameras side-by-side on the same shelf. The industry was trying hedge its bets and keep some of the failed investment in APS going. Digital had a very high cost curve and film was mostly sunk cost with huge margins.

35mm (135) was simply the dominant standard from about WW2 on despite a lot of Kodak quirky film sizes. The Argus C3 "brick" and various Leica spin-offs made it the dominant film format in the market, and when SLR's came to the forefront they all universally used 135. So it became common then to relate everything to that standard.

Before digital, and with the advent especially of SLR medium format, there was a need to "convert" equivalence to what people were most familiar with: 135, leaving Kodak's nutball, proprietary flm sizes out of the equation. People wanting to move up to 120 wanted to know what the equivalent FL was in 135, so 80 became 50 and vice versa. This started long before digital because people were shooting different systems, and MF had 645, 67, 69, and a host of other sizes like panoramas and 6x6, etc. So, for each size of film frame, one needed to know what each lens would be equivalent to, and the benchmark was the most common size in use, 135. The same applied to APS and 110 and 126 film sizes as well, but as a rule it made most sense to equate using systems with interchangeable, zoom lenses.

That same benchmark continues to this day. FF is 135. APS-C is 1.5 crop. APS-H is in between (Canon only). M43 is 2x crop, and so on. This allows legacy glass to have a quick convert FL for use on different size sensors, something that is common now as we move down in sensor size, where legacy class can be used. This was not common on film.

The same principle applies even more starkly in the P&S world where so many sensor sizes requires some benchmark everyone can agree on so they can pair their FL and DOF needs with exposure values and judge the camera product accordingly.

Historical accident, marketing, and sheer common use made 135 the standard. We'd need to develop a standard (like ISO) if this did not exist or every camera system with slight variation would be incomparable to the one on the shelf right next to it. That might work between brands (Kodak again with their oddball film sizes for decades) but in the long run the market found it simpler to adopt 135 and convert from there, sort of the same way JPEG and ISO were organized.

Make sense?

07-08-2011, 09:12 PM   #5
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QuoteOriginally posted by Aristophanes Quote
Why use ISO?

It's a standard; a benchmark we can all agree on that, at some time in history, developed into a fixed reference by industry consensus.

APS-C sensors were designed to that size in the anticipation that there would be $2,000 digital cameras and $300 film cameras side-by-side on the same shelf. The industry was trying hedge its bets and keep some of the failed investment in APS going. Digital had a very high cost curve and film was mostly sunk cost with huge margins.

35mm (135) was simply the dominant standard from about WW2 on despite a lot of Kodak quirky film sizes. The Argus C3 "brick" and various Leica spin-offs made it the dominant film format in the market, and when SLR's came to the forefront they all universally used 135. So it became common then to relate everything to that standard.

Before digital, and with the advent especially of SLR medium format, there was a need to "convert" equivalence to what people were most familiar with: 135, leaving Kodak's nutball, proprietary flm sizes out of the equation. People wanting to move up to 120 wanted to know what the equivalent FL was in 135, so 80 became 50 and vice versa. This started long before digital because people were shooting different systems, and MF had 645, 67, 69, and a host of other sizes like panoramas and 6x6, etc. So, for each size of film frame, one needed to know what each lens would be equivalent to, and the benchmark was the most common size in use, 135. The same applied to APS and 110 and 126 film sizes as well, but as a rule it made most sense to equate using systems with interchangeable, zoom lenses.

That same benchmark continues to this day. FF is 135. APS-C is 1.5 crop. APS-H is in between (Canon only). M43 is 2x crop, and so on. This allows legacy glass to have a quick convert FL for use on different size sensors, something that is common now as we move down in sensor size, where legacy class can be used. This was not common on film.

The same principle applies even more starkly in the P&S world where so many sensor sizes requires some benchmark everyone can agree on so they can pair their FL and DOF needs with exposure values and judge the camera product accordingly.

Historical accident, marketing, and sheer common use made 135 the standard. We'd need to develop a standard (like ISO) if this did not exist or every camera system with slight variation would be incomparable to the one on the shelf right next to it. That might work between brands (Kodak again with their oddball film sizes for decades) but in the long run the market found it simpler to adopt 135 and convert from there, sort of the same way JPEG and ISO were organized.

Make sense?

All of that makes perfect sense. My point is why hang on to a standard based on something that is completely obsolete? At some point it makes sense to move the standard to something more current. HP in car engines is a good example... they changed the way it's measured several times. APS film is long dead... why keep it as a standard? Just like describing a sensor as 1/2.33"... just call it a 7.5x5.2 (or whatever or call it a 7.8mm diag). Just seems to me sometimes standards hang around long after their usefullness is long gone.

As for the lens focal lengths, if focal length is simply a physical factor of lens design then drop focal length multipliers and crop factors. I know that angle of view does change but if that's it then it seems to me that flm and crop factors muddle the whole thing.
07-08-2011, 09:28 PM   #6
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QuoteOriginally posted by mdbrown Quote
... Just seems to me sometimes standards hang around long after their usefullness is long gone...
Yes, just look at the keyboard you used to type your message.
07-08-2011, 09:55 PM   #7
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Let's not confuse the focal length definition of the lens itself with the apparent effect that a given sensor has when it's inserted in the cone of light projected by that lens. By physical design and definition, a 50mm lens is a 50mm lens no matter what use it's put to.

An APS-C sensor simply takes a smaller "bite" out of the projected cone of transmitted light and we associate the resulting image with what we have grown to expect from a longer FL lens in the ol' familiar 135mm world view. A medium format sensor inserted in the same cone would appear to produce a wide angle effect (if it weren't clipped) simply because it would take a bigger/wider "bite". Early 35mm-centric advertising added to the confusion. Fortunately the medium format folks didn't join the media party too.

We (most of us here anyway) just happen to be trapped in a world that grew accustomed to the results we see when the FF 135mm format is placed in the image cone projected by any lens and we use that familiar impression as a de facto standard for comparison. If you'd "grown up" in the medium format world you might have the same translation problem but the interpretation would be quite different. Just be glad you don't have a Minox 16mm in the mix too.

Try this: ignore the FL of your lenses and assign them categorical descriptions relative to the results they provide as you use them and regardless of the body-type -- UWA, WA, "Normal", medium tele, long-tele, macro, portrait, etc.

This is especially interesting if you use a given lens on more than one format. I sometimes use a Mamiya M645 150/3.5 with an extension tube on the DSLR's -- same lens but with quite different results and I feel no need to get tangled up translating FL's between 645, 135 and APS-C to understand the expected outcome.

For many years I thought of an 85/1.8 as "normal" and a 50/1.4 as "sort'a wide" on my Spotmatics and never gave a thought to the actual FL. To me, the lenses were task oriented irrespective of their FL. The same thought process worked equally well for the 2 1/2 years I carried a half-frame Oly Pen-F system even though the relative FL's were totally different -- just like APS-C but a quarter century earlier! Become "multi-lingual".

H2
07-08-2011, 10:07 PM   #8
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Many standards were established by common usage. Sometimes it takes many years for one to 'take'. I have two copies of the Argus Cintar 50/3.5 lens from different decades. The new lens has f-stops marked 3.5, 4, 5.6, 8, 11, 16. The older uses a different standard: 3.5, 4.5, 6.3, 9, 12.7, 18. A German lens has aperture marks of 0,1,2,3,4,5 and that's all. Different cameras may have different scales of shutter speeds. Try to get equal exposures, eh? And different nations and times saw various sensitivity standards. H&D, DIN, ASA, BSI, GOST, all finally evolving into ISO. That only took a century.

So we have these filmic standards and conventions because THEY WORK, and they establish common ground for comparing quite different systems. All our gear is chaotic enough; without a common language for discussing this stuff, we'd be pretty lost. As it is, the whole crap.factor and equivalence stuff is more than confusing. So just learn what any given lens does on any given camera, and don't talk about it.

07-09-2011, 05:54 AM   #9
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The changing of now we name the focal lengths would cause two problems. The DA lineup even though they are optimized for digital bodies some of these are still compatible with FF. Therefore if you use a DA lens on a future FF body the focal length is more or less accurate. In addition, used lenses would get confusing but it says 100mm but the new one says 100mm too why do they look completely different issue. Further, the APS-C sensor is used in most DSLR. Yet, it is not the only sensor that can be used the FF offerings from Nikon and Canon use the full frame so 100mm will be 100mm not 150mm on a APS-C.

The standard was set at 35mm so it is only logical to stick with the standard and not change it just because the most common at the time is APS-C. Who knows perhaps the APS-C sensors will become useless as m4/3 sensors take over. Thus forcing everyone either into the m4/3 market or FF market. Reviews have stated that m4/3 sensors can produce nearly the same quality as APS-C sensors.
07-09-2011, 08:22 AM - 2 Likes   #10
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QuoteOriginally posted by epqwerty Quote
The changing of now we name the focal lengths would cause two problems.... the FF offerings from Nikon and Canon use the full frame so 100mm will be 100mm not 150mm on a APS-C.
No, lenses won't be renamed because MOVING A LENS DOES NOT CHANGE THE FOCAL LENGTH! 50mm is 50mm whether it's on 4x5, 645, 135/FF, APS-C, m4/3, Q, whatever. Focal length is a property of the lens, not of the mount not frame. A 50mm lens does not magically change its length. Forget that you ever heard of crap.factor. I wish that the marketing wonk who devised crap.factor could be found and tried and tortured and executed. Argh!!
07-09-2011, 09:06 AM   #11
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QuoteOriginally posted by RioRico Quote
No, lenses won't be renamed because MOVING A LENS DOES NOT CHANGE THE FOCAL LENGTH! 50mm is 50mm whether it's on 4x5, 645, 135/FF, APS-C, m4/3, Q, whatever. Focal length is a property of the lens, not of the mount not frame. A 50mm lens does not magically change its length. Forget that you ever heard of crap.factor. I wish that the marketing wonk who devised crap.factor could be found and tried and tortured and executed. Argh!!
My point exactly, if focal length is a product of lens design only then focal length multipliers and crop factors are fictional nonsense and should be dropped altogether. My very limited understanding of lens design led me to believe that the distance from the back of the lens to the imaging surface were part of the focal length.
07-09-2011, 09:14 AM   #12
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QuoteOriginally posted by mdbrown Quote
My point exactly, if focal length is a product of lens design only then focal length multipliers and crop factors are fictional nonsense and should be dropped altogether. My very limited understanding of lens design led me to believe that the distance from the back of the lens to the imaging surface were part of the focal length.
Those are used to compare the field of view from different sensor sizes, such as 4/3, APS-C (Canon's is slightly different than Pentax and Nikon), APS-H, and 24x36. This also applies to comparing medium and large formats whether it is film or digital sensor. These are useful, but often misunderstood and misused and even marketing departments including Pentax has contributed to that.
07-09-2011, 09:26 AM   #13
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QuoteOriginally posted by mdbrown Quote
My point exactly, if focal length is a product of lens design only then focal length multipliers and crop factors are fictional nonsense and should be dropped altogether. My very limited understanding of lens design led me to believe that the distance from the back of the lens to the imaging surface were part of the focal length.
Actually, it's the distance from the lens' optical centre to the imaging surface / frame. And that doesn't change, no matter the size of the frame.

When using or shifting between different frame formats, equivalencies can be useful. An APS-C camera with a 50mm lens sees the same FOV as an 135/FF camera with a 75mm lens, so both could be used in similar situations -- but perspective and DOF will likely change because the cameras would likely be used a bit differently. So thinking of equivalencies can be handy -- both those setups are useful for some portraiture, etc. But we must be aware that the equivalences are rough, imperfect, and have nothing to do with the lens, only with the frame format.

We only need to wrap our heads around the concept. That takes education. Marketing fails to educate. G'zzz...
07-09-2011, 09:41 AM   #14
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QuoteOriginally posted by mdbrown Quote
This applies both to the sensor and the lenses. With the lenses such as the Pentax DA line or the Nikon DX line, both are designed for aps-c sensors. So, if you have say a 100mm DA/DX lens... why not just call it a 150mm lens? This would seem to reduce possible confusion. Same for the sensor, why call it aps when that format doesn't even exist anymore?? Seems to me it's like describing the size of a car as 1.2 or 1.5 wg (wagon lengths as per distance between axles of a covered wagon).

Is there something here I'm missing? As far as I know, focal length is determined based on 35mm camera size and distance from the back of the lens to the film to clear the mirror. If there are large changes because of the move to digital, it seems to me that it would make sense to make a DSLR the standard and base your measurements and such on that rather than hanging on to 35mm film which is nearly gone...

Ok... fire away
Focal length has nothing to do with 35mm camera/film size, so it would make no sense to rename lenses.

Many lenses, such as the many 70-300mm zooms, fit on cameras of different formats, so it would be way too confusing to name according to format. Whatever measure you came up with, except focal length, would always vary depending on the camera you mounted the lens on.

Paul
07-09-2011, 11:18 AM   #15
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Maybe I should clarify myself. I know the focal length doesn't change but the original poster was saying why don't we adopt using APS-C to name it. On the APS-C a 100mm lens would have a FOV of 150mm. I was just trying to point out if APS-C became the new standard. And we through out the original naming, we'd just run into the same problem again when everything went FF or m4/3.

I hope that helps to understand my points earlier.
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