Why can't they?

**THoog** · 10-18-2015, 10:52 AM - **1 Like**

Originally posted by jatrax

I assume the registration distance required to fit it in precludes making it work on DSLR mounts

That's correct - the telecompressor would interfere with the mirror in a DSLR. Another option for making a lens work "correctly" is to put a 0.66x conversion lens on the front of the lens, but that really kills the IQ.

So far as the OP's question about having to think about what a lens is in 35mm terms, I did that for the first couple years of digital, but got over it years ago. When I adapt a Pentacon Six 80mm lens or a 6-inch Rapid Rectilinear and use it on a 35mm body, should I worry that I am not seeing a "normal" field of view? That is "correct" for those lenses on their native sensors (which I have never used). Focal length is just focal length, and 35mm is just one sensor size of many - a very popular one, but that doesn't make it "correct". Anyone who grew up using only micro 4/3 or APS-C is probably tired of being told their wide lenses should "correctly" be considered ultra-wides, their normals wide, their short teles normal, etc.

**jatrax** · 10-18-2015, 11:23 AM

Originally posted by THoog

Anyone who grew up using only micro 4/3 or APS-C is probably tired of being told their wide lenses should "correctly" be considered ultra-wides, their normals wide, their short teles normal, etc.

^^^^^ This

pathdoc · 10-18-2015, 01:09 PM

Given the ubiquity of 35mm film for so long, I think it's probably the best reference point when considering the FOV a given lens will provide on a given sensor/film size. It's also a good way of putting things in context for people migrating to a different system when considering which focal lengths they will need to buy, but even a reference standard is not "the one true way".

mcgregni · 10-18-2015, 02:25 PM

Ha! Here we are having this conversation, well into the digital age, and we don't even HAVE a 'FF' digital camera yet ..... Can you imagine how this topic is going to spiral once we do ??!

**jatrax** · 10-18-2015, 02:34 PM - **1 Like**

Originally posted by pathdoc

Given the ubiquity of 35mm film for so long,

Given most young photographers are used to the angle of view their cell phone has maybe we should use that as the 'standard'.

pathdoc · 10-18-2015, 03:22 PM

Originally posted by jatrax

Given most young photographers are used to the angle of view their cell phone has maybe we should use that as the 'standard'.

So many cellphones, so many cameras... whose becomes the standard? (The cynic in me says Apple's iPhone, of course.) 35mm print film has had many makers across a large period of time but is a repeatable reference across them all and is still in use today. It is ubiquitous and continuous. I'd wager that most adults today have either used it themselves or remember their parents using it - digital did not become a significant force until after the commencement of the 21st Century.

**THoog** · 10-18-2015, 03:26 PM

Originally posted by jatrax

Given most young photographers are used to the angle of view their cell phone has maybe we should use that as the 'standard'.

I was thinking something along those lines, plus very, very few people born after 1990 have shot 35mm (film or digital), relative to smaller digital sensors. While 35mm will continue to be the standard, eventually it's going to be like designating sensor sizes in vidicon tube notation: don't ask why - it's just something we do.

**THoog** · 10-18-2015, 04:54 PM

Originally posted by pathdoc

So many cellphones, so many cameras... whose becomes the standard? (The cynic in me says Apple's iPhone, of course.)

I just looked at the page for the iPhone 6s, and while they brag about 12 megapixels and 4K video and even mention the lens being f/2.2, at no place do they mention the sensor size or lens focal length. I suspect that if Apple made "wide angle view degrees" or "zoom factor" a thing to brag about, that would be the standard, not some arcane optical property. We saw a little of that with superzoom lenses and the zoom X number, inherited from point and shoots.

FantasticMrFox · 10-18-2015, 05:36 PM - **1 Like**

Originally posted by oscaletrains

As we are all too aware, when we grab a lens and stick it on most of our DSLR's, we have to remember that the 15mm we just attached is really acting like a 22mm, or our 55-300 zoom is really like using a 82-450.

Do we? Because all I have ever shot with (excluding compact cameras and smartphones) is APS-C cameras. When I grab a 50 mm lens, I know what field of view it will give me on my APS-C. What do I care that mounted on a FF camera that lens would give me a different angle of view? I have never done so and will not do so in the foreseeable future.

Equivalency is preached to a lot of hobbyists who will never use a FF camera, thus do not need to waste a single thought on it.

oscaletrains · 10-18-2015, 05:38 PM

Originally posted by Waratah

Doesn't get any more normal than this

Pentax A*1200mm F8 and Pentax Q10. Effective focal length: 6.6 metres!

Good Lord.

**skunktail** · 10-18-2015, 05:49 PM - **1 Like**

Originally posted by Waratah

Pentax A*1200mm F8 and Pentax Q10. Effective focal length: 6.6 metres!

It was fun to shoot with though.

oscaletrains · 10-18-2015, 06:07 PM

Originally posted by jatrax

Nope. You are missing the point. 50mm on FF is NOT "correct" it is just what that field of view is. It is no more or less "correct" than a 50mm on APS-C or m4/3. Someone who started shooting m4/3 is used to that angle of view and if they picked up a FF camera with 50mm lens it would very different, but not wrong. Someone who shoots with the 645z using a 50mm is going to expect a very different image.

Seriously, how long have you been shooting APS-C? I would think you would have adjusted within a reasonable amount of time. I guess if you shoot film as well that might be difficult but if you are APS-C only it is what it is.

Here is what you are looking for by the way: Amazon.com : Metabones Canon EF Lens to Sony E-Mount Camera Speed Booster ULTRA : Electronics But as far as I can tell it is only available to mirrorless cameras. I assume the registration distance required to fit it in precludes making it work on DSLR mounts but I have no experience with it so that could be wrong.

In my mind, "correct" would be when the lens I am looking through and the photo it produces is in perspective of what our natural eyes see. The person or building and background or whatever you are taking a photo of is the same scale or proportion as to how your eyes see them from where you are standing. Obviously lower than that makes the objects in the photo further away than your current perspective and higher than that makes the objects closer and more compacted.

But whatever. All I wanted to know is why something that bothered me couldn't be done, and now I know that it can but won't be.

**THoog** · 10-18-2015, 10:12 PM

Originally posted by oscaletrains

now I know that it can but won't be.

I'm not sure that it can be done with a DSLR lens on a DSLR body. By definition, a focal reducer works reduces the focal length of the lens - moving the lens closer to the sensor than its normal registration distance. That works with DSLR lenses on MILCs because MILC mounts have much shorter registration distances, and a Metabones or LensTurbo is actually shorter than a regular glassless adapter. Going from K-mount to K-mount, the lens isn't moving any closer to the sensor. You would first have to extend the focal length of the lens, then reduce it by a greater amount. Even if that could be done within the various restrictions on diameter, doing so without serious image degradation would be very hard. At best, light losses would offset any "boost", and you would break even in terms of f-stop.

LensBeginner · 10-19-2015, 05:26 AM

Originally posted by oscaletrains

In my mind, "correct" would be when the lens I am looking through and the photo it produces is in perspective of what our natural eyes see
*snip*

That's commonly called a normal lens.

https://en.wikipedia.org/wiki/Normal_lens

**Canada_Rockies** · 10-19-2015, 10:12 AM - **1 Like**

Originally posted by LensBeginner

That's commonly called a normal lens.

https://en.wikipedia.org/wiki/Normal_lens

And to throw some numbers around, the definition I find most useful for "normal" focal length is the length of the hypotenuse of a rectangle:

Normal lens for 24x36 mm = (SQRT(24²+36²))=43.3mm. I wonder where the focal length of the 43 limited came from?

Normal lens for Pentax APS-C = (SQRT(15.6²+23.5²))=28.2mm. I'm sure we can find one or two of these lenses if we look hard enough.

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10-18-2015, 10:52 AM - 1 Like	#31
THoog Loyal Site Supporter Join Date: Aug 2012 Location: North Carolina Photos: Gallery \| Albums Posts: 3,685	Originally posted by jatrax I assume the registration distance required to fit it in precludes making it work on DSLR mounts That's correct - the telecompressor would interfere with the mirror in a DSLR. Another option for making a lens work "correctly" is to put a 0.66x conversion lens on the front of the lens, but that really kills the IQ. So far as the OP's question about having to think about what a lens is in 35mm terms, I did that for the first couple years of digital, but got over it years ago. When I adapt a Pentacon Six 80mm lens or a 6-inch Rapid Rectilinear and use it on a 35mm body, should I worry that I am not seeing a "normal" field of view? That is "correct" for those lenses on their native sensors (which I have never used). Focal length is just focal length, and 35mm is just one sensor size of many - a very popular one, but that doesn't make it "correct". Anyone who grew up using only micro 4/3 or APS-C is probably tired of being told their wide lenses should "correctly" be considered ultra-wides, their normals wide, their short teles normal, etc.

10-18-2015, 11:23 AM	#32
jatrax Site Supporter Join Date: May 2010 Location: Washington Cascades Photos: Gallery \| Albums Posts: 12,991	Originally posted by THoog Anyone who grew up using only micro 4/3 or APS-C is probably tired of being told their wide lenses should "correctly" be considered ultra-wides, their normals wide, their short teles normal, etc. ^^^^^ This

10-18-2015, 01:09 PM	#33
pathdoc Pentaxian Join Date: Mar 2015 Photos: Gallery \| Albums Posts: 6,381	Given the ubiquity of 35mm film for so long, I think it's probably the best reference point when considering the FOV a given lens will provide on a given sensor/film size. It's also a good way of putting things in context for people migrating to a different system when considering which focal lengths they will need to buy, but even a reference standard is not "the one true way".

10-18-2015, 02:25 PM	#34
mcgregni Veteran Member Join Date: Sep 2012 Location: Surrey, England Posts: 2,603	Ha! Here we are having this conversation, well into the digital age, and we don't even HAVE a 'FF' digital camera yet ..... Can you imagine how this topic is going to spiral once we do ??!

10-18-2015, 02:34 PM - 1 Like	#35
jatrax Site Supporter Join Date: May 2010 Location: Washington Cascades Photos: Gallery \| Albums Posts: 12,991	Originally posted by pathdoc Given the ubiquity of 35mm film for so long, Given most young photographers are used to the angle of view their cell phone has maybe we should use that as the 'standard'.

10-18-2015, 03:22 PM	#36
pathdoc Pentaxian Join Date: Mar 2015 Photos: Gallery \| Albums Posts: 6,381	Originally posted by jatrax Given most young photographers are used to the angle of view their cell phone has maybe we should use that as the 'standard'. So many cellphones, so many cameras... whose becomes the standard? (The cynic in me says Apple's iPhone, of course.) 35mm print film has had many makers across a large period of time but is a repeatable reference across them all and is still in use today. It is ubiquitous and continuous. I'd wager that most adults today have either used it themselves or remember their parents using it - digital did not become a significant force until after the commencement of the 21st Century.

10-18-2015, 03:26 PM	#37
THoog Loyal Site Supporter Join Date: Aug 2012 Location: North Carolina Photos: Gallery \| Albums Posts: 3,685	Originally posted by jatrax Given most young photographers are used to the angle of view their cell phone has maybe we should use that as the 'standard'. I was thinking something along those lines, plus very, very few people born after 1990 have shot 35mm (film or digital), relative to smaller digital sensors. While 35mm will continue to be the standard, eventually it's going to be like designating sensor sizes in vidicon tube notation: don't ask why - it's just something we do.

10-18-2015, 04:54 PM	#38
THoog Loyal Site Supporter Join Date: Aug 2012 Location: North Carolina Photos: Gallery \| Albums Posts: 3,685	Originally posted by pathdoc So many cellphones, so many cameras... whose becomes the standard? (The cynic in me says Apple's iPhone, of course.) I just looked at the page for the iPhone 6s, and while they brag about 12 megapixels and 4K video and even mention the lens being f/2.2, at no place do they mention the sensor size or lens focal length. I suspect that if Apple made "wide angle view degrees" or "zoom factor" a thing to brag about, that would be the standard, not some arcane optical property. We saw a little of that with superzoom lenses and the zoom X number, inherited from point and shoots.

10-18-2015, 05:36 PM - 1 Like	#39
FantasticMrFox Veteran Member Join Date: Oct 2014 Location: Munich Posts: 2,339	Originally posted by oscaletrains As we are all too aware, when we grab a lens and stick it on most of our DSLR's, we have to remember that the 15mm we just attached is really acting like a 22mm, or our 55-300 zoom is really like using a 82-450. Do we? Because all I have ever shot with (excluding compact cameras and smartphones) is APS-C cameras. When I grab a 50 mm lens, I know what field of view it will give me on my APS-C. What do I care that mounted on a FF camera that lens would give me a different angle of view? I have never done so and will not do so in the foreseeable future. Equivalency is preached to a lot of hobbyists who will never use a FF camera, thus do not need to waste a single thought on it.

10-18-2015, 05:38 PM	#40
oscaletrains Senior Member Join Date: Jul 2014 Photos: Gallery Posts: 172 Original Poster	Originally posted by Waratah Doesn't get any more normal than this Pentax A*1200mm F8 and Pentax Q10. Effective focal length: 6.6 metres! Good Lord.

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10-18-2015, 05:49 PM - 1 Like	#41
skunktail Site Supporter Join Date: Jan 2013 Location: Sydney, NSW Photos: Gallery \| Albums Posts: 287	Originally posted by Waratah Pentax A*1200mm F8 and Pentax Q10. Effective focal length: 6.6 metres! It was fun to shoot with though.

10-18-2015, 06:07 PM	#42
oscaletrains Senior Member Join Date: Jul 2014 Photos: Gallery Posts: 172 Original Poster	Originally posted by jatrax Nope. You are missing the point. 50mm on FF is NOT "correct" it is just what that field of view is. It is no more or less "correct" than a 50mm on APS-C or m4/3. Someone who started shooting m4/3 is used to that angle of view and if they picked up a FF camera with 50mm lens it would very different, but not wrong. Someone who shoots with the 645z using a 50mm is going to expect a very different image. Seriously, how long have you been shooting APS-C? I would think you would have adjusted within a reasonable amount of time. I guess if you shoot film as well that might be difficult but if you are APS-C only it is what it is. Here is what you are looking for by the way: Amazon.com : Metabones Canon EF Lens to Sony E-Mount Camera Speed Booster ULTRA : Electronics But as far as I can tell it is only available to mirrorless cameras. I assume the registration distance required to fit it in precludes making it work on DSLR mounts but I have no experience with it so that could be wrong. In my mind, "correct" would be when the lens I am looking through and the photo it produces is in perspective of what our natural eyes see. The person or building and background or whatever you are taking a photo of is the same scale or proportion as to how your eyes see them from where you are standing. Obviously lower than that makes the objects in the photo further away than your current perspective and higher than that makes the objects closer and more compacted. But whatever. All I wanted to know is why something that bothered me couldn't be done, and now I know that it can but won't be.

10-18-2015, 10:12 PM	#43
THoog Loyal Site Supporter Join Date: Aug 2012 Location: North Carolina Photos: Gallery \| Albums Posts: 3,685	Originally posted by oscaletrains now I know that it can but won't be. I'm not sure that it can be done with a DSLR lens on a DSLR body. By definition, a focal reducer works reduces the focal length of the lens - moving the lens closer to the sensor than its normal registration distance. That works with DSLR lenses on MILCs because MILC mounts have much shorter registration distances, and a Metabones or LensTurbo is actually shorter than a regular glassless adapter. Going from K-mount to K-mount, the lens isn't moving any closer to the sensor. You would first have to extend the focal length of the lens, then reduce it by a greater amount. Even if that could be done within the various restrictions on diameter, doing so without serious image degradation would be very hard. At best, light losses would offset any "boost", and you would break even in terms of f-stop.

10-19-2015, 05:26 AM	#44
LensBeginner Veteran Member Join Date: Sep 2014 Photos: Albums Posts: 4,696	Originally posted by oscaletrains In my mind, "correct" would be when the lens I am looking through and the photo it produces is in perspective of what our natural eyes see snip That's commonly called a normal lens. https://en.wikipedia.org/wiki/Normal_lens

10-19-2015, 10:12 AM - 1 Like	#45
Canada_Rockies Loyal Site Supporter Join Date: Nov 2007 Location: Sparwood, BC, Canada Photos: Gallery \| Albums Posts: 12,385	Originally posted by LensBeginner That's commonly called a normal lens. https://en.wikipedia.org/wiki/Normal_lens And to throw some numbers around, the definition I find most useful for "normal" focal length is the length of the hypotenuse of a rectangle: Normal lens for 24x36 mm = (SQRT(24²+36²))=43.3mm. I wonder where the focal length of the 43 limited came from? Normal lens for Pentax APS-C = (SQRT(15.6²+23.5²))=28.2mm. I'm sure we can find one or two of these lenses if we look hard enough.