APS-C lens mm are correct

[Random Orbits]

The final print size is related to the sensor "size", but in terms of enlargement, a sensor's size is defined by its digital information - mega pixels bits of information, not by its physical dimensions, as film would be. So yes, an 18MP iphone sensor would give an image the same size as an APS-C or FF or MF when viewed at 100%, that is when your computer program is adding in an equal amount of information in the viewed image. So in terms of enlargement of the displayed image, a 5D mk1 has to be "enlarged" more than a 7D despite the fact that the 7D's sensor is physically smaller.

However, you are quite right about the inability of a lens to resolve onto so many tiny pixels. Unclear information recorded by the very small chip will also result in your computer program not being able to add to the information clearly, resulting in a much poorer "enlargement".  Larger sensors have many many advantages over much smaller ones, but physical enlargement is not one of them - because they are not physically enlarged.

I know this is getting a little of topic, but it is surprising how many people think FF is better because it isn't enlarged as much as a smaller sensor ! Likewise many people don't realise that your computer is adding to the information. And I'm not sticking up for APS because I really dislike the "crop factor" effect for the sort of photography I do.

I think we are on the same page.  My original point was about the lens having to be of higher resolution on a crop than on FF to achieve comparable final resolution.  Keeping the MP constant for FF/crop makes that comparison simpler.

Most FF cameras (independent of the speed demons) have more MPs in general than their APS-C counterparts within the same brand, and I think the APS-C format is further along the MP/IQ curve than FF due to its higher density.  At some point, increasing density will not gain you anything due to optical/physical limitations.  If a FF camera and a crop camera had the same pixel density (akin to grain size of film), then there will be no advantage for a crop camera IQ wise, although other factors such as price, frame rate, etc. will still cause consumers to chose one over the other.

[PackLight]

I think if the rumored 7D II comes out, with the latest technology and a rumored 21mp sensor it may bring the FF vs Crop resolution MP density debate in to another level of sharp focus.

As it is right now there are only a limited number of possiblities and combinations that the discussion has any relavancy. In almost all but limited instances it is FF for the win.

[Daniel Flather]

Focal length is an intrinsic property of the lens, regardless of the sensor at the image plane.

Yes, and that's why people who use the 50mm prime on their APS-C bodies and think they a using the traditional 85mm lens are mistaken.  What that have is a cropped 50mm image, not the more compressed image from a 85mm lens.  Also, an ef 35mm lens is not a standard 50mm lens on a crop.  It's a 56mm view with a 35mm lens' perspective. 

[Sporgon]

The final print size is related to the sensor "size", but in terms of enlargement, a sensor's size is defined by its digital information - mega pixels bits of information, not by its physical dimensions, as film would be. So yes, an 18MP iphone sensor would give an image the same size as an APS-C or FF or MF when viewed at 100%, that is when your computer program is adding in an equal amount of information in the viewed image. So in terms of enlargement of the displayed image, a 5D mk1 has to be "enlarged" more than a 7D despite the fact that the 7D's sensor is physically smaller.

However, you are quite right about the inability of a lens to resolve onto so many tiny pixels. Unclear information recorded by the very small chip will also result in your computer program not being able to add to the information clearly, resulting in a much poorer "enlargement".  Larger sensors have many many advantages over much smaller ones, but physical enlargement is not one of them - because they are not physically enlarged.

I know this is getting a little of topic, but it is surprising how many people think FF is better because it isn't enlarged as much as a smaller sensor ! Likewise many people don't realise that your computer is adding to the information. And I'm not sticking up for APS because I really dislike the "crop factor" effect for the sort of photography I do.

I think we are on the same page.  My original point was about the lens having to be of higher resolution on a crop than on FF to achieve comparable final resolution.  Keeping the MP constant for FF/crop makes that comparison simpler.

Most FF cameras (independent of the speed demons) have more MPs in general than their APS-C counterparts within the same brand, and I think the APS-C format is further along the MP/IQ curve than FF due to its higher density.  At some point, increasing density will not gain you anything due to optical/physical limitations.  If a FF camera and a crop camera had the same pixel density (akin to grain size of film), then there will be no advantage for a crop camera IQ wise, although other factors such as price, frame rate, etc. will still cause consumers to chose one over the other.
[/quote
+1. It's the quality of the recorded information that is the key, and traditionally FF or MF held this advantage, but the APS chips are closing the gap in IQ at low ISO.

[Sporgon]

Just to get back on topic with this one: rather than stating APS-c lens mm are correct, when dealing with the field of view for a particular lens, it would be more accurate to state APS sensor size is incorrect. When using APS you've basically got a whole load of area missing around your frame  problems with any wide (ish) field of view - which is why I don't like 'em ! 

[Tristan944]

For what a fool I made of myself, you guys have been great. I'm glad I made the mistake because I never will again.

I'm still confused as to why Canon and other companies don't print onto the lens the actual focal length that will be utilized. I now know that the 18-135mm lens is an 18-135mm lens, but the camera and pictures being produced are not at 18-135mm, its at 29-216mm. Isn't it more "honest" and more relevant to tell the customer what the "actual" focal length(s) the lens will be giving him? Because zoomed out, its not showing 18mm, its showing 29mm. Telling me that it is 29-216mm lens would make more sense because that is what focal lengths are actually being used.

[PackLight]

Why do car dealers post the highway mileage on cars, when they know you live in the city and all of your driving will be in town?

Why do they call 2% milk 2% milk? In reality the regular milk you buy in the store has 4% fat, so in reality your only getting 50% less fat. Why don't they call it 50% less fat milk? (actually in small print the 2% milk in the frig says 37% less fat than whole milk, even more false advertising)

Same answer I think applies to your question?

[cinema-dslr]

For what a fool I made of myself, you guys have been great. I'm glad I made the mistake because I never will again.

I'm still confused as to why Canon and other companies don't print onto the lens the actual focal length that will be utilized. I now know that the 18-135mm lens is an 18-135mm lens, but the camera and pictures being produced are not at 18-135mm, its at 29-216mm. Isn't it more "honest" and more relevant to tell the customer what the "actual" focal length(s) the lens will be giving him? Because zoomed out, its not showing 18mm, its showing 29mm. Telling me that it is 29-216mm lens would make more sense because that is what focal lengths are actually being used.

being confused doesn't make one a fool 
For a ef-s (aps-c only) lens it doesn't make much sense to call a 29-216 lens a 18-135 lens because that lens will never be put on a FF body.
but then the confusion starts when you put a 24-105L (FF) lens on a crop body eq  38-168mm.
The numbers on the lenses are correct you just have to multiply it by the crop factor. FF=1x aps-h=1,3x and aps-c=1,6x 

[TexPhoto]

Focal length is an intrinsic property of the lens, regardless of the sensor at the image plane.

Yes, and that's why people who use the 50mm prime on their APS-C bodies and think they a using the traditional 85mm lens are mistaken.  What that have is a cropped 50mm image, not the more compressed image from a 85mm lens.  Also, an ef 35mm lens is not a standard 50mm lens on a crop.  It's a 56mm view with a 35mm lens' perspective.

The thing is, a 50mm image cropped down to the perspective of an 85mm lens will have the same perspective and compresion as the same image taken with an 85mm lens.  DOF will even be the same assuming they were taken at the same aperture.  And this applies for an image cropped in photoshop, or an image cropped via a smaller than FF sensor, or printed and cropped with scissors.

In the sample images I provided above, the 800mm photo is the same perspective and compresion of that part of the photo in the 50mm photo.  It has to be unless you move the camera.

[emag]

Ol' Paint is dead

[Daniel Flather]

The thing is, a 50mm image cropped down to the perspective of an 85mm lens will have the same perspective and compresion as the same image taken with an 85mm lens.

So if I frame a photo the same with my 24mm lens and then with my 200 lens, the photos will have the same perspective?  Perspective, like the mm length, is part of the lens, not the sensor behind it.

[Sporgon]

Simple 
The perspective of pictures 2 and 3 is identical

[neuroanatomist]

The thing is, a 50mm image cropped down to the perspective of an 85mm lens will have the same perspective and compresion as the same image taken with an 85mm lens.

So if I frame a photo the same with my 24mm lens and then with my 200 lens, the photos will have the same perspective?  Perspective, like the mm length, is part of the lens, not the sensor behind it.

No. Perspective is determined by the distance from the camera to the subject.  Focal length, sensor size, cropping - none affect perspective.

If you frame the same subject with a 24mm vs. a 200mm lens, you've changed the distance and that's what changes the perspective.  If you took the two shots from the same distance, the perspective would be the same, but the framing would be different. If you then cropped the 24mm shot to the framing of the 200mm shot, both the perspective and the framing would be the same.

[florianbieler.de]

I'm still confused as to why Canon and other companies don't print onto the lens the actual focal length that will be utilized. ... Isn't it more "honest" and more relevant to tell the customer what the "actual" focal length(s) the lens will be giving him?

The focal lenghts on the lens are correct! The values on the lenses are the actual focal lengths of the lenses, just because the sensor limits the field of view doesn't mean the focal length on the lens is wrong. Can you imagine how confused people would be if a crop sensor 17-50mm produced another field of view at 50mm than the EF 50mm - we somehow would see postings like why don't they print the actual focal lengths on the lenses

It would be just way more complicated if you'd print crop sensor field of view focal length equivalents on crop sensor only lenses, and full frame field of view focal lengths on full frame lenses, as you can use these on your crop too. I vote for printing actual focal length and full frame equivalent if used on aps-c on the lens! Here comes the new Canon EF 17-50mm EF-S 27,2-80mm 2.8 IS II! 

[Daniel Flather]

The thing is, a 50mm image cropped down to the perspective of an 85mm lens will have the same perspective and compresion as the same image taken with an 85mm lens.

So if I frame a photo the same with my 24mm lens and then with my 200 lens, the photos will have the same perspective?  Perspective, like the mm length, is part of the lens, not the sensor behind it.

No. Perspective is determined by the distance from the camera to the subject.  Focal length, sensor size, cropping - none affect perspective.

If you frame the same subject with a 24mm vs. a 200mm lens, you've changed the distance and that's what changes the perspective.  If you took the two shots from the same distance, the perspective would be the same, but the framing would be different. If you then cropped the 24mm shot to the framing of the 200mm shot, both the perspective and the framing would be the same.

My 8-15 and 200 have the same perspective?  If I cropped the 8-15 to the same framing of the 200 it's the same perspective?

An ef 35mm lens on a on a crop is not the same perspective as a 56mm on full frame.