GH2-to-APSC Crop factor

[Blue Bomber]

This might help:

The 35mm/full frame column relates to the markings you'll see on any lens. They all relate to this. Now, if you're using a GH2 and want to get the equivalent focal length, match the 35mm/full frame focal length with the one in the AF100 column (not exact, but close enough for comparison).

APS-C doesn't really factor in here unless you're using one of those cameras as a second camera, and want the same focal length for whatever reason. It would be roughly the equivalent of Super35, so you'd need the AF100 column's to that.

 

[Barry_Green]

Yes, focal lengths marked on lenses are all related to full frame field of view. Technically it makes things easier, since you only need to know your camera's crop to determine the actual focal length. If they were camera specific, you'd need to know the crop of the camera the lens came from, the crop of your camera, and figure out what that totals.

This is not accurate at all. Lenses are marked as to what their actual focal length is, not in relation to any particular sensor size!

When you see a 50mm Canon EF lens, that means that lens has a focal length of 50mm. When you see a 50mm medium-format lens, that means that lens has a focal length of 50mm. When you see a 50mm Super16 lens, that means that lens has a focal length of 50mm. They are all exactly the same focal length. And if you mount any of them on that Super16 camera, they will all deliver exactly the same field of view.

Now, if you put one of those lenses on a medium-format camera with its big huge 6x45 sensor, and you put another of those lenses on a Super16 camera, will they have the same field of view? Of course not -- the larger sensor of the bigger camera will "see" much more of the image that the lens is projecting.

Think about it this way -- the lens has no idea what sensor it's projecting its image onto. It doesn't change because it's mounted to a different camera! The lens projects the same image whether it's onto a Super35 sensor, onto a 1/3" sensor, or onto a wall. The lens doesn't know or care what it's connected to. So what makes the difference? It's the size of the sensor. Say the lens projects a 2" x 2" image onto a sensor. If you are using a great big 2" x 2" sensor, well, you could capture the whole image the lens is projecting. But if you were using a little 1/3" sensor, you would only be able to capture the very tiny centermost portion of what the lens was projecting, and all the rest would be "cropped off". Hence the term "crop factor". It's the amount of the image that's being cropped off, as compared to the larger sensor.

That's why you see most standard GH2 lenses starting at what would be a very wide focal length for full frame, which is actually a standard focal length for the GH2. Standard wide angle for full frame is about 28mm. APS-C is about 18mm. GH2 is 14mm. They'll all have roughly the same field of view when used on their respective cameras. Start putting different lenses on different cameras, and you need to whip out the calculator.

This is all entirely correct.

 

[j1clark@ucsd.edu]

Yes, focal lengths marked on lenses are all related to full frame field of view. Technically it makes things easier, since you only need to know your camera's crop to determine the actual focal length. If they were camera specific, you'd need to know the crop of the camera the lens came from, the crop of your camera, and figure out what that totals.

The markings on the lens are what they are... they are not marked for 'full frame' or any other frame. They may be in 'error' due to manufacturing tolerances, but they are not marked for specific sensor/film sizes.

A 200mm 4x5 view camera lens, when mounted on a 35mm camera, will give the same 'view' as a 200mm lens manufactured for the 35mm camera specifically. (just a hell of a lot easier to mount the specifically manufactured lens than a 4x5 lens...

Perhaps this sort of thing would be easier to understand if people learned photography with a 4x5 view camera, with 4x5 film, then used a 6x9cm roll film back. The 'lens did not change', the distance of the lens to the film plane did not change... but the FoV was dramatically changed...

 

[janusz]

Okay, wow. Okay, thanks so much everyone.

I have not gotten any of my work done hahaha, but have learned something different instead.

Thanks, all you repeat posters - Clark, Bomber, Gilden, Dingo and Barry!

 

[Barry_Green]

As an example -- a 50mm lens is not a "telephoto" lens. And it is not a "wide angle" lens. It is a 50mm lens. That's what it IS. Now, if you put that 50mm lens on a big medium-format camera, you would see a wide-angle field of view. If you put that exact same 50mm lens on a 5D, you'd see a "normal" field of view*. And if you put that 50mm lens on a 1/3" video camera, you'd see a massively telephoto field of view.

A 28mm lens is not a "wide angle" -- its a normal lens on a 35mm movie camera, and it's a slight telephoto on a 16mm camera, and a pretty long telephoto on a 1/3" camera.

The mm marking on a lens does NOT indicate what type of field of view that lens provides. All it states is: the focal length of the lens. The actual field of view that your camera will get from that lens is all determined by how big your camera's sensor is.

 

[Barry_Green]

Bah -- j1clark was posting while I was typing that...

 

[M. Gilden]

So are the markings on all photography lenses relative to/marked in full-frame? Meaning, if you were to put a 50mm full-frame lens on my GH2 body, then it would see the world the way the 50mm marking on my M43 zoom does?

But if I wanted to see the world on my GH2 the way a 50mm on full-frame see the world then I would need 25mm/26.8mm M43 designed lens?

NO!! There is NO SUCH THING AS A "DESIGNED" LENS!!

The mm markings are a measurement of magnification. It does NOT (I repeat: DOES NOT) dictate a certain FOV on all cameras. There is no "50mm for micro 4/3" or "50mm for full frame"... just 50mm. That's a measurement of a physical property of the glass, and it is universal. You can, however, figure out what your approximate field of view would be if you know what size sensor you will be using it on.
On a full frame old-school film camera, 50mm will give you a standard portrait sized frame. But on a smaller sensor, you will be zoomed in more. That's why you don't really see super wide 10mm old lenses- back then 10mm was too wide to be useful, its only these days that we have smaller sensors that it is worth manufacturing such wides.

To help understand, let's use a metaphor- Lets say you have two different kinds of cameras with two different kinds of batteries. One camera's battery is 1,700mAh, the other is 1,200mAh. The more mAh a battery is rated for, the longer it will last (since mAh stands for milliamps per hour, the higher rated battery can pump out the same amperage for a longer amount of time). So the camera with the 1,700mAh should last a lot longer, right?
WRONG.
It depends on how much juice each camera is using. Perhaps the 1,700mAh battery is in a larger body with a 3 chip CCD and a large bright LCD with focus peaking and live histograms, whereas the other is a much simpler camera that is a single chip and stingy on power. Now, if you came from smaller single-chip cameras and are used to a small 1,200mAh battery, you might think that a camera with a 1,700 one will last over 40% longer. But its comparing Apples to Oranges. If you had some kind of battery adapter, and could take the 1,700mAh battery out of the larger cam and put it into the smaller one, sure it would last longer. But your 1,200mAh battery which normally lasts 1-2 hours of shooting won't last that long in the bigger camera. The way you are looking at focal lengths in lenses is similar to someone who would compare battery life based on mAh ratings alone. The mAh are a universal physical property of the electrical output of the body, regardless of what kind of camera it is made for. Just like it won't equal the same battery life on different camera models, the mm rating of a lens won't yield the same FOV on different sized sensors.

My problem lies somewhere within this: "If you have a 5D, a medium portrait lens would be a 50mm. On an APS-C, you'd want somewhere around 35mm". That makes sense to me so I've carried that idea over to other focal lengths and when comparing FOVs of different sensors.

My Nikon 50mm lens on my Nikon 35mm still photography body sees the world the way my 35mm EF lens on my 60D body does.

So why does my Panny zoom at 50mm see the world the same way the Nikon 50mm does on the same GH2 body?

That's EXACTLY what it SHOULD do!! Your Nikon 50mm sees the world the same way a 35mm does on your 60D. But put that 50mm on an EOS adapter in front of your 60D, and suddenly your FOV will be about 1.6x bigger than the 35mm was. Why? Because its a 50mm, and not a 35.

So your panny zoom at 50mm should look the same as the Nikon 50mm on the same body because... wait for it... they are both 50mm!!

::waits for it to click::

EDIT: Everyone answered while I was writing this. Bah on all of you. But glad we got the point across (I hope!).

 

[janusz]

This is how I thought I was thinking earlier today.

This is not accurate at all. Lenses are marked as to what their actual focal length is, not in relation to any particular sensor size!

When you see a 50mm Canon EF lens, that means that lens has a focal length of 50mm. When you see a 50mm medium-format lens, that means that lens has a focal length of 50mm. When you see a 50mm Super16 lens, that means that lens has a focal length of 50mm. They are all exactly the same focal length. And if you mount any of them on that Super16 camera, they will all deliver exactly the same field of view.

Now, if you put one of those lenses on a medium-format camera with its big huge 6x45 sensor, and you put another of those lenses on a Super16 camera, will they have the same field of view? Of course not -- the larger sensor of the bigger camera will "see" much more of the image that the lens is projecting.

Think about it this way -- the lens has no idea what sensor it's projecting its image onto. It doesn't change because it's mounted to a different camera! The lens projects the same image whether it's onto a Super35 sensor, onto a 1/3" sensor, or onto a wall. The lens doesn't know or care what it's connected to. So what makes the difference? It's the size of the sensor. Say the lens projects a 2" x 2" image onto a sensor. If you are using a great big 2" x 2" sensor, well, you could capture the whole image the lens is projecting. But if you were using a little 1/3" sensor, you would only be able to capture the very tiny centermost portion of what the lens was projecting, and all the rest would be "cropped off". Hence the term "crop factor". It's the amount of the image that's being cropped off, as compared to the larger sensor.



This is all entirely correct.

 

[janusz]

Yes.

As an example -- a 50mm lens is not a "telephoto" lens. And it is not a "wide angle" lens. It is a 50mm lens. That's what it IS. Now, if you put that 50mm lens on a big medium-format camera, you would see a wide-angle field of view. If you put that exact same 50mm lens on a 5D, you'd see a "normal" field of view*. And if you put that 50mm lens on a 1/3" video camera, you'd see a massively telephoto field of view.

A 28mm lens is not a "wide angle" -- its a normal lens on a 35mm movie camera, and it's a slight telephoto on a 16mm camera, and a pretty long telephoto on a 1/3" camera.

The mm marking on a lens does NOT indicate what type of field of view that lens provides. All it states is: the focal length of the lens. The actual field of view that your camera will get from that lens is all determined by how big your camera's sensor is.

 

[janusz]

This proves my previous thought process, however unexplained it is, correct:

I need a M43 lens that "1.86"x wider than an EF lens on a full-frame Canon 5D body. Or "1.18"x wider than an EFS lens for an APSC Canon 60D body.

Example: Panasonic's 25mm/1.4 on a GH2 sees the world approx. the way a 50mm sees the world on a 5D or D800, etc because the 5D/D800 sensor has approximately a 1.86 wider field of view.

So, with that EFS 10mm lens on a 60D, I would need a 8.47mm M43 lens on my GH2 to see the same image.

This might help:

The 35mm/full frame column relates to the markings you'll see on any lens. They all relate to this. Now, if you're using a GH2 and want to get the equivalent focal length, match the 35mm/full frame focal length with the one in the AF100 column (not exact, but close enough for comparison).

APS-C doesn't really factor in here unless you're using one of those cameras as a second camera, and want the same focal length for whatever reason. It would be roughly the equivalent of Super35, so you'd need the AF100 column's to that.

 

[Barry_Green]

So, with that EFS 10mm lens on a 60D, I would need a 8.47mm M43 lens on my GH2 to see the same image.

Correct.

With the understanding that different manufacturers might calibrate any particular focal length slightly differently, for whatever reason. For example, in Matt Duclos's review/comparison of the Zeiss 35mm vs. the Rokinon 35mm, he found that even though they were both mounted on the same camera body, the Rokinon was just a little bit wider field of view. Apparently their design lent itself to a slightly shorter actual focal length than Zeiss's did, even though both manufacturers christened both lenses as "35mm".

 

[j1clark@ucsd.edu]

EDIT: Everyone answered while I was writing this. Bah on all of you. But glad we got the point across (I hope!).

I don't know... the Wife still talks about multiplying 35mm full frame values to 'figure out' for the different digital sensor sizes...

This is rather ironic since she has never made a 'big deal' about figuring out what her 80mm lens is on her Hasselblad, relative to the 35mm camera... it was just 'normal'... and the 40mm on the "Hasselblad" was 'wide'... and the 150 on the Hblad was
'telephoto'...

But for some reason on the digital cameras we have to 'discuss' that the 35mm full frame 'was' relative to what the digital camera 'is'...

I think it went like this... she bought the 35mm, shot it for a while... decided to get a medium size camera... the store clerk said 'here this is the normal lens for the Hblad'... and that was that... no mention about 'oh, well you have to do Yx multiple of the 50mm to get equivalent...'. I wasn't there at the time... so I don't know... but I don't recall someone trying to relate 35mm lens lengths to my medium and large format cameras... it was just stated.. here's the 'normal' lens... based on the diagonal of the film size... rounded to some 'reasonable' near by lens length...

 

[M. Gilden]

I don't know... the Wife still talks about multiplying 35mm full frame values to 'figure out' for the different digital sensor sizes...

This is rather ironic since she has never made a 'big deal' about figuring out what her 80mm lens is on her Hasselblad, relative to the 35mm camera... it was just 'normal'... and the 40mm on the "Hasselblad" was 'wide'... and the 150 on the Hblad was
'telephoto'...

But for some reason on the digital cameras we have to 'discuss' that the 35mm full frame 'was' relative to what the digital camera 'is'...

I think it went like this... she bought the 35mm, shot it for a while... decided to get a medium size camera... the store clerk said 'here this is the normal lens for the Hblad'... and that was that... no mention about 'oh, well you have to do Yx multiple of the 50mm to get equivalent...'. I wasn't there at the time... so I don't know... but I don't recall someone trying to relate 35mm lens lengths to my medium and large format cameras... it was just stated.. here's the 'normal' lens... based on the diagonal of the film size... rounded to some 'reasonable' near by lens length...

Yeah, its really just there for people who are used to shooting 35mm full frame, since that was "the standard" for so long. But more often than not, it just confuses people these days.

 

[janusz]

Like me!

Thanks again everyone.