Should people use mm equivalence terminology?

Michael Piziak · 10-04-2021, 06:19 PM

I often see people post, on various camera websites and usually speaking of aps-c lens/bodies as "equivalent" to a FF system, they post that people should stop using "equivalent" focal length terminology, because it isn't "true"

So, is it true or not?

For example, in this video, at 10:25, the author says that the 15-45mm tele lens on his Q camera is *equivalent* to an 83-249mm lens....

https://youtu.be/FEF6Ip3gURw?t=625

**pepperberry farm** · 10-04-2021, 06:26 PM - **6 Likes**

I refuse to do so... a lens has a focal length, no matter what camera you mount the lens to, it doesn't change....

**UncleVanya** · 10-04-2021, 06:28 PM - **6 Likes**

This is a huge can of worms. Some will say no and with force. Others will say having a frame of reference across formats is helpful. For the record I’m in the second camp. It is not an issue that matters much if you shoot only one format… but if you have 5-6 like me - it gets hard otherwise.

normhead · 10-04-2021, 06:41 PM - **3 Likes**

I like having the equivalence on the barrel of the lens. Like some others, I use 5 different formats. I don't care with APS-c or FF, I use them so much I don't need to work out the equivalent. But for some smaller formats with say a 6mm to 24mm lens, I definitely need help with that.

The biggest problem I have with equivalence is working backwards because most of my lenses were bought and used on APS_c. So I have to remember, instead of using 300mm 2.8 on my K-1 I can use a much lighter 200mm 2.8 on my K-3.

SO it totally depends on the camera. APS-c or FF no. 1 inch or 1:2.3 I would have no clue. Equivalence is needed absolutely.

ChristianRock · 10-04-2021, 06:42 PM - **2 Likes**

I also think it's helpful...

photoptimist · 10-04-2021, 06:44 PM - **10 Likes**

The focal length of a lens is a property of the lens all by itself. That focal length is independent of what sensor or bit of film is stuck behind the lens. The same 15mm lens could be mounted on a Q, an Olympus M4/3, an APS-C, or a full frame camera and it would remain a 15mm lens. Mounting a 15mm lens on a Q does not change the lens.

Equivalency refers to the field of view of one lens mounted on one camera (e.g., a 15mm on the Q) being the same as the field of view of a second lens mounted on a full frame camera (e.g., an 83mm lens on FF). The focal length of the second lens mounted on the full frame camera doesn't change anything about the first lens and first camera.

Equivalency isn't a truth about the lens, its a truth about how photographers must use different focal lengths on different formats to get the same field of view.

TL;DNR Interchangeable lenses should be labelled with their true physical focal length because the "equivalent" focal length depends on the body the lens gets put on.

**AggieDad** · 10-04-2021, 07:01 PM - **2 Likes**

I really don't care whether folks worry about equivalence or not.

I am, however, interested in the actual focal length of the lens as that is a reference for me.

Michael Piziak · 10-04-2021, 07:15 PM

I suppose it may come down to magnification. For example, will a 15-45mm tele lens on his Q camera have about the same magnification as a 83-249mm lens on say a FF camera (or whatever sensor size he is make an equivalence to in the video)....

**Bob 256** · 10-04-2021, 07:18 PM

I've shot full frame for many years and know what focal length applies to what field of view. For me, it's irrelevant to list these equivalences since I continue to shoot FF. If I were to adopt APS-C or large format, I would memorize a single conversion factor appropriate to each of the new formats and off I would go, just needing to know which to use for each case.

Usually, the equivalence listed is one special case and that's for APS-C versus FF so it's a little like coming up with an accommodation for just one set of photographers as if APS-C is the only group which matters (and this is mostly because of the interchangeability of lenses possible between those two). Don't get me wrong. It's fine to list equivalence values and for those who shoot APS-C and were used to FF from the film days, it serves a good purpose. But, to go hog wild and assume APS-C is the only other format and printing a special case equivalence on everything is taking too much for granted. Just listing the actual focal length and letting one figure the equivalence for their own format makes me happy (well, that's being a bit self-centered since I do only FF, but I hope you get the picture). After all, it's a simple multiplying factor - not rocket science.

**UncleVanya** · 10-04-2021, 07:35 PM - **1 Like**

I’m with Norm. My skill at apsc and FF lenses is good. 1”, 1/1.7”, 1/2/3” not good.

disconnekt · 10-04-2021, 07:46 PM - **1 Like**

Originally posted by UncleVanya

This is a huge can of worms. Some will say no and with force. Others will say having a frame of reference across formats is helpful. For the record I’m in the second camp. It is not an issue that matters much if you shoot only one format… but if you have 5-6 like me - it gets hard otherwise.

I'm in the 2nd group too. I see it as a good "rough reference guide" for those who shoot full frame (film & digital) that are looking at other formats to give them a rough frame of reference, especially with Field of View

**UncleVanya** · 10-04-2021, 07:57 PM - **8 Likes**

Originally posted by disconnekt

I'm in the 2nd group too. I see it as a good "rough reference guide" for those who shoot full frame (film & digital) that are looking at other formats to give them a rough frame of reference, especially with Field of View

It would be easier if rather than equivalence we had all learned the common angle of view of the lenses we typically use - then we would only need to speak of the angle of view when that’s all we meant.

**mikesbike** · 10-04-2021, 07:58 PM

Since I have been at times over the years shooting with both Pentax 35mm film bodies and APS-C DSLR bodies, knowing which lenses will provide what FOV when used on each has real-life practical value, and even more true now that I am shooting with my FF K-1 II as well as with my APS-C bodies.

Paul the Sunman · 10-04-2021, 08:39 PM - **2 Likes**

I don't know why we don't just go with "angle of view". That's what we're actually interested in ultimately. Of course, that depends on both focal length (lens) and sensor size (camera), not to mention focus distance if focus breathing is an issue. But "angle of view when focused at infinity" is then precise and comparable between systems.

**luftfluss** · 10-04-2021, 09:00 PM

Originally posted by UncleVanya

It would be easier if rather than equivalence we had all learned the common angle of view of the lenses we typically use - then we would only need to speak of the angle of view when that’s all we meant.

This, so much.

10-04-2021, 06:19 PM	#1
Michael Piziak Closed Account Join Date: Dec 2013 Location: West Virginia Posts: 2,815	Should people use mm equivalence terminology? I often see people post, on various camera websites and usually speaking of aps-c lens/bodies as "equivalent" to a FF system, they post that people should stop using "equivalent" focal length terminology, because it isn't "true" So, is it true or not? For example, in this video, at 10:25, the author says that the 15-45mm tele lens on his Q camera is equivalent to an 83-249mm lens.... https://youtu.be/FEF6Ip3gURw?t=625

10-04-2021, 07:18 PM	#9
Bob 256 Site Supporter Join Date: Jun 2008 Location: Idaho Photos: Gallery Posts: 2,378	I've shot full frame for many years and know what focal length applies to what field of view. For me, it's irrelevant to list these equivalences since I continue to shoot FF. If I were to adopt APS-C or large format, I would memorize a single conversion factor appropriate to each of the new formats and off I would go, just needing to know which to use for each case. Usually, the equivalence listed is one special case and that's for APS-C versus FF so it's a little like coming up with an accommodation for just one set of photographers as if APS-C is the only group which matters (and this is mostly because of the interchangeability of lenses possible between those two). Don't get me wrong. It's fine to list equivalence values and for those who shoot APS-C and were used to FF from the film days, it serves a good purpose. But, to go hog wild and assume APS-C is the only other format and printing a special case equivalence on everything is taking too much for granted. Just listing the actual focal length and letting one figure the equivalence for their own format makes me happy (well, that's being a bit self-centered since I do only FF, but I hope you get the picture). After all, it's a simple multiplying factor - not rocket science. Last edited by Bob 256; 10-04-2021 at 07:26 PM.

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10-04-2021, 06:26 PM - 6 Likes	#2
pepperberry farm amateur dirt farmer Join Date: Dec 2014 Location: probably out in a field somewhere... Photos: Gallery \| Albums Posts: 41,766	I refuse to do so... a lens has a focal length, no matter what camera you mount the lens to, it doesn't change....

10-04-2021, 06:28 PM - 6 Likes	#3
UncleVanya Loyal Site Supporter Join Date: Jul 2014 Photos: Gallery \| Albums Posts: 28,454	This is a huge can of worms. Some will say no and with force. Others will say having a frame of reference across formats is helpful. For the record I’m in the second camp. It is not an issue that matters much if you shoot only one format… but if you have 5-6 like me - it gets hard otherwise.

10-04-2021, 06:41 PM - 3 Likes	#4
normhead Pentaxian Join Date: Jun 2007 Location: Near Algonquin Park Photos: Gallery \| Albums Posts: 40,451	I like having the equivalence on the barrel of the lens. Like some others, I use 5 different formats. I don't care with APS-c or FF, I use them so much I don't need to work out the equivalent. But for some smaller formats with say a 6mm to 24mm lens, I definitely need help with that. The biggest problem I have with equivalence is working backwards because most of my lenses were bought and used on APS_c. So I have to remember, instead of using 300mm 2.8 on my K-1 I can use a much lighter 200mm 2.8 on my K-3. SO it totally depends on the camera. APS-c or FF no. 1 inch or 1:2.3 I would have no clue. Equivalence is needed absolutely.

10-04-2021, 06:42 PM - 2 Likes	#5
ChristianRock Pentaxian Join Date: Jul 2013 Location: People's Republic of America Photos: Gallery \| Albums Posts: 9,912	I also think it's helpful...

10-04-2021, 06:44 PM - 10 Likes	#6
photoptimist Pentaxian Join Date: Jul 2016 Photos: Albums Posts: 5,128	The focal length of a lens is a property of the lens all by itself. That focal length is independent of what sensor or bit of film is stuck behind the lens. The same 15mm lens could be mounted on a Q, an Olympus M4/3, an APS-C, or a full frame camera and it would remain a 15mm lens. Mounting a 15mm lens on a Q does not change the lens. Equivalency refers to the field of view of one lens mounted on one camera (e.g., a 15mm on the Q) being the same as the field of view of a second lens mounted on a full frame camera (e.g., an 83mm lens on FF). The focal length of the second lens mounted on the full frame camera doesn't change anything about the first lens and first camera. Equivalency isn't a truth about the lens, its a truth about how photographers must use different focal lengths on different formats to get the same field of view. TL;DNR Interchangeable lenses should be labelled with their true physical focal length because the "equivalent" focal length depends on the body the lens gets put on.

10-04-2021, 07:01 PM - 2 Likes	#7
AggieDad Site Supporter Join Date: Jan 2015 Location: Houston, TX Photos: Gallery \| Albums Posts: 1,456	I really don't care whether folks worry about equivalence or not. I am, however, interested in the actual focal length of the lens as that is a reference for me.

10-04-2021, 07:15 PM	#8
Michael Piziak Closed Account Join Date: Dec 2013 Location: West Virginia Posts: 2,815 Original Poster	I suppose it may come down to magnification. For example, will a 15-45mm tele lens on his Q camera have about the same magnification as a 83-249mm lens on say a FF camera (or whatever sensor size he is make an equivalence to in the video)....

10-04-2021, 07:35 PM - 1 Like	#10
UncleVanya Loyal Site Supporter Join Date: Jul 2014 Photos: Gallery \| Albums Posts: 28,454	I’m with Norm. My skill at apsc and FF lenses is good. 1”, 1/1.7”, 1/2/3” not good.

10-04-2021, 07:46 PM - 1 Like	#11
disconnekt Pentaxian Join Date: Oct 2011 Location: SoCal/I.E. Photos: Albums Posts: 1,702	Originally posted by UncleVanya This is a huge can of worms. Some will say no and with force. Others will say having a frame of reference across formats is helpful. For the record I’m in the second camp. It is not an issue that matters much if you shoot only one format… but if you have 5-6 like me - it gets hard otherwise. I'm in the 2nd group too. I see it as a good "rough reference guide" for those who shoot full frame (film & digital) that are looking at other formats to give them a rough frame of reference, especially with Field of View

10-04-2021, 07:57 PM - 8 Likes	#12
UncleVanya Loyal Site Supporter Join Date: Jul 2014 Photos: Gallery \| Albums Posts: 28,454	Originally posted by disconnekt I'm in the 2nd group too. I see it as a good "rough reference guide" for those who shoot full frame (film & digital) that are looking at other formats to give them a rough frame of reference, especially with Field of View It would be easier if rather than equivalence we had all learned the common angle of view of the lenses we typically use - then we would only need to speak of the angle of view when that’s all we meant.

10-04-2021, 07:58 PM	#13
mikesbike Site Supporter Join Date: Dec 2016 Location: Southeastern Michigan Posts: 4,558	Since I have been at times over the years shooting with both Pentax 35mm film bodies and APS-C DSLR bodies, knowing which lenses will provide what FOV when used on each has real-life practical value, and even more true now that I am shooting with my FF K-1 II as well as with my APS-C bodies.

10-04-2021, 08:39 PM - 2 Likes	#14
Paul the Sunman Pentaxian Join Date: Aug 2011 Location: Melbourne Photos: Gallery Posts: 4,847	I don't know why we don't just go with "angle of view". That's what we're actually interested in ultimately. Of course, that depends on both focal length (lens) and sensor size (camera), not to mention focus distance if focus breathing is an issue. But "angle of view when focused at infinity" is then precise and comparable between systems.

10-04-2021, 09:00 PM	#15
luftfluss Site Supporter Join Date: Jun 2011 Location: NJ Photos: Gallery \| Albums Posts: 11,627	Originally posted by UncleVanya It would be easier if rather than equivalence we had all learned the common angle of view of the lenses we typically use - then we would only need to speak of the angle of view when that’s all we meant. This, so much.