Comparing lenses for full frame vs. APS-C sensors

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Originally Posted by ajax

Might it be that on a lens with a fixed focal length (maybe better referred to as a prime lens?) the focal length does correspond to a simply measurable distance?

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I have a number of fixed focal length lenses; the wide angle ones are definitely much longer than the stated focal length. These are referred to as retrofocus lenses (backwards telephoto lenses). A telephoto lens is technically a lens that is shorter than the stated focal length.

My Leitz 400mm Telyt lens is NOT a telephoto and is in fact 400mm long.

A prime lens (a definition I do not care for) is generally a "fast", i.e. wide aperture fixed focus lens. The problem is that this definition is fairly loosely defined as most people would consider an f/1.4 50mm lens "fast". They would also call a f/4 400mm lens "fast".

Another "lie" in the lens business is that the focal length of the lens is what is marked. That value is only correct when the lens is focused at "infinity". As one gets closer to the subject, the focal length will change, as will the maximum aperture. This is especially noticeable with macro lenses.

Let's also talk about "mediocre" lenses. I have won a lot of awards for images that I have taken with "kit" or "mediocre" lenses. These comparisons are only true when you shoot in lab-like conditions. Hand hold a lens and in general, even with a stabilized lens, you will come nowhere close to the stated optical resolution. Shoot with a solid, heavy duty tripod, you might get close.

On the other hand, if all you do is post your images on the internet, your 20 - 150MP camera will get downsampled to around 2MP and you lose all that resolution anyways. If you are a large format print maker (I am), then these issues become more of an issue, especially if you deal with a pixel peeping audience.

My advice to people is that you should concentrate on making the important technical, organizational (composition,etc.) and impact aspects of your photography. Most modern cameras will deliver strong images, even with kit lenses.

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Originally Posted by ajax

... Artistic pictures need to be produced on paper, in that electronic displays cannot begin to do justice to artwork (i.e., each different display device shows something different).

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A little too all-encompassing, IMHO.

It says that only pictures produced on paper can be termed as being "artistic". Neither can it be true that ALL electronic displays are unable to do justice to "artwork".

And, in these halcyon days of almost universal color management, if "each different display device shows something different" then there is something wrong.

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Originally Posted by ajax

Apparently my 75-300mm lens is a FF lens. Based on what I’ve learned herein FF lenses can be used on APS-C cameras but in this case the focal length is actually 120-480mm.

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Nope. Your lens is a 75-300 for all eternity

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Originally Posted by ajax

Is it possible that there is some basic reason one should want to know about this?

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Nope. Just do not expect a 300mm lens to necessarily be 300 mm long. The optical centre of a lens can vary, and even be in front of the front-most element.

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Originally Posted by ajax

Might it be that on a lens with a fixed focal length (maybe better referred to as a prime lens?) the focal length does correspond to a simply measurable distance?

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Maybe. But unless you are a lens engineer, you have no idea where the optical centre of the lens is

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Originally Posted by pschlute

But unless you are a lens engineer, you have no idea where the optical centre of the lens is

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Actually you can determine it with a tape measure. Most good cameras have a little symbol on the body showing you where the plane of the sensor lies within the body. Measure from that forward and it will give you the optical centre of the lens you are using.

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Originally Posted by xpatUSA

A little too all-encompassing, IMHO.

It says that only pictures produced on paper can be termed as being "artistic". Neither can it be true that ALL electronic displays are unable to do justice to "artwork".

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NO DOUBT! I have to admit that finding the right choice of words to try and simplify something that is pretty complicated is problematic. I have spent a lot of time both learning and practicing the development of digital images. Whether or not that is artistic is fair to argue with. However, I will go out on a limb and suggest that just understanding color profiles is every bit as complicated as what is being discussed herein. The display I use for developing photos is calibrated. Like my cameras, my display is NOT the best but it does qualify as pretty good. I have no doubt that none of the other displays I have, on all manner of devices which are but a tiny example of those available to the society, fail to do justice when it comes to faithfully producing the same appearance as what the development process intended. The difference in color profiles required for different printers and paper also complicates the process further. In that, getting a faithful print is complicated. Even with all of that at the end of the day the printed version is going to differ, to some extent, from what was seen on the display. My preference for paper is that it removes all of these variances from what different people get to see when viewing the same printed version. But of course paper also differs. By using the same kind of good quality paper on a fairly good printer I do end up with pictures that look the same to me. Therefore, my preference for paper being the ultimate measure of getting a correct result.

With that said, it would be quite reasonable to suggest that what counts as art is in the eye of the beholder and simply being different doesn’t make something bad/worse. Then of course there are differences in human vision which are NOT accounted for in any way. In fact, I even find myself polling different viewers in some cases to see which versions of the same picture they like best. There is seldom uniform agreement.

In the context in which I used the term herein, I’d say that what I had in mind was to compare the developing process that I go through with what my parents did when producing paintings. What I end up with is my attempt to match their artistic abilities.

This made me giggle.

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Originally Posted by pschlute

Nope. Your lens is a 75-300 for all eternity



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Looks like another case where my language might have been a bit sloppy. I actually find that B&H Photo does a better job than Canon when it comes to equipment descriptions. I reference their website where is says "Versatile telephoto zoom is designed for full-frame Canon EF-mount DSLRs, however can also be used with APS-C models where it provides a 120-480mm equivalent focal length range.". I also think this is consistent with what I think is the answer to the basic question that provoked my original post. In that, multiple FF value by 1.6 (crop factor) provides APS-C value.

If this lens could only be mounted on an APS-C body (i.e., what Canon calls EF-S) would they NOT need to change what is printed on the lens to be 120-480 instead of 75-300?

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Originally Posted by xpatUSA

It says that only pictures produced on paper can be termed as being "artistic". Neither can it be true that ALL electronic displays are unable to do justice to "artwork".

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Agreed Ted, virtually any image produced today goes through some form of digital process which means some kind of screen is used in the process. The only exception are the prints made on either traditional silver halide based papers processed on an enlarger, in a traditional darkroom. A few folks are out there using even older technology involving processes like cyanotype, coated glass plates, etc.

That being said, the market for "serious" photographic artwork is close to 100% print based, even with the multitude of online galleries. It doesn't matter if these are pieces of art sold at craft shows, small galleries or high end galleries that deal with world renowned photographers. The print is still king, at least for now.

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Originally Posted by xpatUSA

And, in these halcyon days of almost universal color management, if "each different display device shows something different" then there is something wrong.

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Unfortunately, universal colour management is simply not true. Those expensive iPhones and iPads or their Android counterparts are not colour managed at all. There are a lot of low end displays that have abysmal colour performance and cannot even display 100% sRGB (and that is setting the bar pretty low).

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Originally Posted by ajax

If this lens could only be mounted on an APS-C body (i.e., what Canon calls EF-S) would they NOT need to change what is printed on the lens to be 120-480 instead of 75-300?

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No. The focal length of a lens is fixed by its design, it will still be a 75-300mm lens regardless of the camera body you mount it on.

I have an 80mm Zeiss Planar and a 150mm Zeiss Sonnar for my Hasselblad film camera. I have an adaptor that allows me to mount it on both my Full Frame Nikon D810 or my wife's crop frame (1.5x) Nikon D7500. In all cases, the focal lengths of the lenses would be the same as is marked on the lenses.

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Originally Posted by pschlute

This made me giggle.

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Yup. I had someone breaking into modeling make a similar comment to me a few years ago. She said something along the lines of "You still use those big cameras? I though everything is shot with phones these days".

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Originally Posted by ajax

Looks like another case where my language might have been a bit sloppy. I actually find that B&H Photo does a better job than Canon when it comes to equipment descriptions. I reference their website where is says "Versatile telephoto zoom is designed for full-frame Canon EF-mount DSLRs, however can also be used with APS-C models where it provides a 120-480mm equivalent focal length range.". I also think this is consistent with what I think is the answer to the basic question that provoked my original post. In that, multiple FF value by 1.6 (crop factor) provides APS-C value.

If this lens could only be mounted on an APS-C body (i.e., what Canon calls EF-S) would they NOT need to change what is printed on the lens to be 120-480 instead of 75-300?

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When they say an "equivalent focal length range," they mean only that it has the same angle of view on an APS-C that a lens of the equivalent focal length would have on a FF body. The focal length is a physical property of the lens that has nothing to do with the body you attach to it. See this, for example.

Comparing the focal lengths of different lenses is sometimes difficult since some lenses, especially zoom lenses, only measure at the designated focal length when the lens is focused at infinity.

I don't know if the following comment is applicable to this discussion but, lenses used to be designated as long focal length when the focal length was about equal to the physical distance between the optical center of the lens and the focal plane when focused at infinity. Telephoto lenses were long focal length lenses in which the physical distance between optical center of the lens and the focal plane was shorter than the designated focal length when focused at infinity!

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Originally Posted by ajax

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Originally Posted by xpatUSA

A little too all-encompassing, IMHO.

It says that only pictures produced on paper can be termed as being "artistic". Neither can it be true that ALL electronic displays are unable to do justice to "artwork".

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NO DOUBT! I have to admit that finding the right choice of words to try and simplify something that is pretty complicated is problematic. I have spent a lot of time both learning and practicing the development of digital images. Whether or not that is artistic is fair to argue with. However, I will go out on a limb and suggest that just understanding color profiles is every bit as complicated as what is being discussed herein. The display I use for developing photos is calibrated. Like my cameras, my display is NOT the best but it does qualify as pretty good. I have no doubt that none of the other displays I have, on all manner of devices which are but a tiny example of those available to the society, fail to do justice when it comes to faithfully producing the same appearance as what the development process intended. The difference in color profiles required for different printers and paper also complicates the process further. In that, getting a faithful print is complicated. Even with all of that at the end of the day the printed version is going to differ, to some extent, from what was seen on the display. My preference for paper is that it removes all of these variances from what different people get to see when viewing the same printed version. But of course paper also differs. By using the same kind of good quality paper on a fairly good printer I do end up with pictures that look the same to me. Therefore, my preference for paper being the ultimate measure of getting a correct result.

With that said, it would be quite reasonable to suggest that what counts as art is in the eye of the beholder and simply being different doesn’t make something bad/worse. Then of course there are differences in human vision which are NOT accounted for in any way. In fact, I even find myself polling different viewers in some cases to see which versions of the same picture they like best. There is seldom uniform agreement.

In the context in which I used the term herein, I’d say that what I had in mind was to compare the developing process that I go through with what my parents did when producing paintings. What I end up with is my attempt to match their artistic abilities.

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Thanks for clarifying what you meant. Manfred supports your view by narrowing the all-encompassing field down to marketing:

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Originally Posted by Manfred

That being said, the market for "serious" photographic artwork is close to 100% print based, even with the multitude of online galleries. It doesn't matter if these are pieces of art sold at craft shows, small galleries or high end galleries that deal with world renowned photographers. The print is still king, at least for now.

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Leaving "the print" as king and leaving people who don't print incapable of producing photographic artwork, it would appear. ;)

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Originally Posted by xpatUSA

Thanks for clarifying what you meant. Manfred supports your view by narrowing the all-encompassing field down to marketing:

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No Ted, not marketing. Demand. People, in general, are not interested in paying for art that they can only display on screens.

That could change some day with the right technology, but it does not appear to be available today. I have seen some galleries experimenting with digital art, but the large (expensive) screens are usually tucked into a dark spot where they are not overwhelmed by ambient light sources, especially daylight.

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Originally Posted by xpatUSA

Leaving "the print" as king and leaving people who don't print incapable of producing photographic artwork, it would appear.

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Not at all Ted, it's just that the channels for distribution are limited. I know a lot of artists who do not print. They are reliant on third party print makers and framers to prepare the artworks that they are trying to sell. There are a LOT more artists around than competent fine art print makers.

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Originally Posted by Manfred M

No Ted, not marketing. Demand. People, in general, are not interested in paying for art that they can only display on screens.

That could change some day with the right technology, but it does not appear to be available today. I have seen some galleries experimenting with digital art, but the large (expensive) screens are usually tucked into a dark spot where they are not overwhelmed by ambient light sources, especially daylight.




Not at all Ted, it's just that the channels for distribution are limited. I know a lot of artists who do not print. They are reliant on third party print makers and framers to prepare the artworks that they are trying to sell. There are a LOT more artists around than competent fine art print makers.

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Thank you, Manfred, pardon my recalcitrance ... Looks like ajax was right all along!

OK, it looks like Manfred is confirming the point also made by Peter correcting my erroneous view that the same lens can have different focal lengths. Rather a given lens has a structure (i.e., glass and related parts) that determine the focal length.

Going back to Trev’s excellent article titled “Focal Length, Field of View, Shutter Speed, Sensor Size & Equivalence” on Page 9 where he discusses Field of Capture there is a comparison depicting what results when the same lens is used on sensors of different sizes. This is what would happen with my 75-300mm lens when used on FF verses APS-C camera. When they say the APS-C is equivalent to 120-480mm might that imply that it is theoretically possible to construct a lens that would fill the APS-C sensor in the same manner as the FF sensor in Trev's example. Such a lens would be different and have the 1.6 times, at least in the Canon case, longer focal length. Maybe yes?

I think I can also see why it likely makes no sense for the producer to make such a (different) lens given the price/cost along with mediocre optics and build of the one that also does FF.

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Originally Posted by ajax

Going back to Trev’s excellent article titled “Focal Length, Field of View, Shutter Speed, Sensor Size & Equivalence” on Page 9 where he discusses Field of Capture there is a comparison depicting what results when the same lens is used on sensors of different sizes. This is what would happen with my 75-300mm lens when used on FF verses APS-C camera. When they say the APS-C is equivalent to 120-480mm might that imply that it is theoretically possible to construct a lens that would fill the APS-C sensor in the same manner as the FF sensor in Trev's example. Such a lens would be different and have the 1.6 times, at least in the Canon case, longer focal length. Maybe yes?

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I am thoroughly confused. Which of the seven 70 to 300mm Canon lenses do you own?

https://www.imaging-resource.com/len...ws/#zoomLenses

Telling me "the kit lens" doesn't help me, I've never owned a Canon anything.

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Originally Posted by ajax

OK, it looks like Manfred is confirming the point also made by Peter correcting my erroneous view that the same lens can have different focal lengths. Rather a given lens has a structure (i.e., glass and related parts) that determine the focal length.

Going back to Trev’s excellent article titled “Focal Length, Field of View, Shutter Speed, Sensor Size & Equivalence” on Page 9 where he discusses Field of Capture there is a comparison depicting what results when the same lens is used on sensors of different sizes. This is what would happen with my 75-300mm lens when used on FF verses APS-C camera. When they say the APS-C is equivalent to 120-480mm might that imply that it is theoretically possible to construct a lens that would fill the APS-C sensor in the same manner as the FF sensor in Trev's example. Such a lens would be different and have the 1.6 times, at least in the Canon case, longer focal length. Maybe yes?

I think I can also see why it likely makes no sense for the producer to make such a (different) lens given the price/cost along with mediocre optics and build of the one that also does FF.

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David - while the focal length does not change between lenses made for full frame and crop frame sensors, one thing that does change is the "image circle", i.e. the amount of area that the lens has to project onto a sensor. With an APS-C sensor being smaller than a full-frame sensor, the image circle will be smaller. This allows the lens designer to use smaller optical and mechanical components in the physical lens body = potentially lower manufacturing costs, especially when coupled with other variables (smaller maximum aperture, less expensive anti-reflective coatings, etc.).

This is why a full-frame lens can work on a crop sensor body, but a crop frame lens would only light an area the size of the APS-C sensor. Cameras that allow crop frame lenses to mount on FF bodies generally automatically adjust and create an image that is crop-frame sized.

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Originally Posted by ajax

OK, it looks like Manfred is confirming the point also made by Peter correcting my erroneous view that the same lens can have different focal lengths. Rather a given lens has a structure (i.e., glass and related parts) that determine the focal length.

Going back to Trev’s excellent article titled “Focal Length, Field of View, Shutter Speed, Sensor Size & Equivalence” on Page 9 where he discusses Field of Capture there is a comparison depicting what results when the same lens is used on sensors of different sizes. This is what would happen with my 75-300mm lens when used on FF verses APS-C camera. When they say the APS-C is equivalent to 120-480mm might that imply that it is theoretically possible to construct a lens that would fill the APS-C sensor in the same manner as the FF sensor in Trev's example. Such a lens would be different and have the 1.6 times, at least in the Canon case, longer focal length. Maybe yes?

I think I can also see why it likely makes no sense for the producer to make such a (different) lens given the price/cost along with mediocre optics and build of the one that also does FF.

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David, your 75-300mm lens fills the sensor on your camera the same way that a 120-480mm lens fills the frame of a FF camera. Or put another way, a 47-187mm lens on your camera would fill your frame the same way that the 75-300mm fills a FF sensor.

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Originally Posted by Round Tuit

David, your 75-300mm lens fills the sensor on your camera the same way that a 120-480mm lens fills the frame of a FF camera. Or put another way, a 47-187mm lens on your camera would fill your frame the same way that the 75-300mm fills a FF sensor.

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I think that is the way I understood it. I don't think what said is inconsistent with that. What I'm thinking I got wrong is my posturing about a hypothetical lens. Possibly what I'm confused about is what it means to be called a full frame lens or conversely an APS-C lens. In the case of Canon it is my understanding that the EF-S series lenses do not work on a full frame camera. Might it be simply that, larger Field of Capture (FoC) works on smaller sensor but NOT the converse and where, as with focal length, FoC can very by design.

What really matters to me is what focal length lens would I need to acquire for a full frame camera to match the range of view/perspective (? FoC) that I'm getting with my 18-55mm lens on my APS-C camera. What I've deduced so far is that the 24-105mm full frame lenses provide slightly more range (i.e., equivalent to 15-65mm) than that when used on a full frame camera.