4:3 vs 3:2 aspect ratio and field of view.

[Sootchucker]

OK, I'll check this for myself tonight on my 2 bodies, but was reading something recently which got me thinking.

I'm sort of transitioning between Micro Four Thirds to Sony APS-C as my smaller everyday camera set up. The body size of the A6700 being smaller and lighter than the OM-1 along with lenses being typically similar size and weight, have made it an attractive option for me. However, aside from a very few expensive lenses, most "standard" zoom lenses for E-Mount APS-C seem to start from 18mm (27mm FF equivalent), whereas a lot of M4/3 lenses start at 12mm (24mm FF equivalent).

However in the article I was reading it was suggesting that using a M4/3 camera in 3:2 aspect ratio (which I've always tended to do as I prefer this to the default 4:3 aspect), that the effective field of view becomes a little tighter, and that the 24mm effective field of view in 3:2 mode ends up being more like a 26mm lens not 24mm, meaning I'd only be actually giving up 1mm of width from using the 18mm lenses on Sony E-Mount (assuming the Sony lenses are a genuine 18mm focal length). My brain is struggling to understand this as I thought that when a micro four thirds camera (say for instance my OM-1) shoots in 3:2 from the native 4:3, it still uses the same width of the sensor but just crops top and bottom, but that the field of view should still be a 24mm equivalent ?

Anyone with a better understanding of this able to comment and explain this please ?

 

[Ed Sutton]

OK, I'll check this for myself tonight on my 2 bodies, but was reading something recently which got me thinking.

I'm sort of transitioning between Micro Four Thirds to Sony APS-C as my smaller everyday camera set up. The body size of the A6700 being smaller and lighter than the OM-1 along with lenses being typically similar size and weight, have made it an attractive option for me. However, aside from a very few expensive lenses, most "standard" zoom lenses for E-Mount APS-C seem to start from 18mm (27mm FF equivalent), whereas a lot of M4/3 lenses start at 12mm (24mm FF equivalent).

However in the article I was reading it was suggesting that using a M4/3 camera in 3:2 aspect ratio (which I've always tended to do as I prefer this to the default 4:3 aspect), that the effective field of view becomes a little tighter, and that the 24mm effective field of view in 3:2 mode ends up being more like a 26mm lens not 24mm, meaning I'd only be actually giving up 1mm of width from using the 18mm lenses on Sony E-Mount (assuming the Sony lenses are a genuine 18mm focal length). My brain is struggling to understand this as I thought that when a micro four thirds camera (say for instance my OM-1) shoots in 3:2 from the native 4:3, it still uses the same width of the sensor but just crops top and bottom, but that the field of view should still be a 24mm equivalent ?

Anyone with a better understanding of this able to comment and explain this please ?

When I had a m4/3 camera I did a rough and ready comparison in 3:2 against a 35mm camera and came to the same conclusion. I think it's because when working out focal length 'equivalence' it's the diagonal that gets used rather than the 'width' of the frame.

 

[nandbytes]

I think the confusion arises when you are comparing aspect ratios cross format.
for a given image circle from a lens (for the same sensor area/size) this is the region you are capture based on the two aspect ratios
(not to scale)


If we work in field of views and converting it to FF terms of FoV, a 24mm FoV in 3:2 aspect will have more width and 4:3 will have more vertical coverage of the same scene capture by a lens. (hopefully this is fairly obvious)
So now if you take an image that's "naturally" 4:3 and crop to a 3:2 you lose some "wideness" because you are cropping in to get your desired ratio and same applies going from 3:2 to 4:3.
So if you are shooting at 12mm on m43 sensor and cropping it to match a 3:2 ratio it will no longer be equivalent a 24mm field of view. similarly if you shooting at 16mm on APS-C sensor and cropping it to match a 4:3 ratio their field of view will no longer be equivalent to a 24mm field of view.

So moral of the story is to stick with the aspect ratio of the sensor if you want to maximise the wideness of the field of view. And if you can't then buy a camera with a sensor that provides your desired aspect ratio. Of course real life is not that simple..... because for example I do prefer 4:3 a lot but I want a larger sensor, so my option would be the large expensive GFX type systems. So I still shoot with FF with higher res sensors and crop in as required and use wider angle lenses to make up as necessary.

an ideal (probably technically crazy) solution would be to have a circular sensor that matches the lens circle and you can crop in post (or via. in camera options) to whatever aspect ratio you prefer. Then there'd be no need for vertical grips too

hope that helps.

 

[JohnMcL7]

an ideal (probably technically crazy) solution would be to have a circular sensor that matches the lens circle and you can crop in post (or via. in camera options) to whatever aspect ratio you prefer. Then there'd be no need for vertical grips too

It's not that crazy and it's possible to partially achieve with an oversized sensor, Panasonic had this on their GH1 and GH2 m4/3 bodies (and some others like their LX3 series) which allowed you to choose between 4:3, 3:2 and 16:9 without changing the focal length. From what I remember they missed a trick because I don't think you could take the full size in sensor and crop it to the ratio you wanted after instead you had to set the ratio before taking the image. I thought it was a good idea but I don't think anyone does that now?

 

[Box Brownie]

FWIW

On my mFT Olympus and now OM1 I set the shooting to 3:2 because in the main I print (as needed) to that ratio.

Now, on these bodies when shooting raw you still capture the whole sensor but in the EVF I see lines across the top and bottom to show the 3:2 on the 4:3 view.

This for me had been ideal because of for any reason my framing and/or composition leaves something to be desired, I have the latitude to crop as appropriate.

NB if shooting in jpeg the ratio is baked in to a 3:2 image.

 

[Sootchucker]

I think the confusion arises when you are comparing aspect ratios cross format.
for a given image circle from a lens (for the same sensor area/size) this is the region you are capture based on the two aspect ratios
(not to scale)

View attachment 424748
If we work in field of views and converting it to FF terms of FoV, a 24mm FoV in 3:2 aspect will have more width and 4:3 will have more vertical coverage of the same scene capture by a lens. (hopefully this is fairly obvious)
So now if you take an image that's "naturally" 4:3 and crop to a 3:2 you lose some "wideness" because you are cropping in to get your desired ratio and same applies going from 3:2 to 4:3.
So if you are shooting at 12mm on m43 sensor and cropping it to match a 3:2 ratio it will no longer be equivalent a 24mm field of view. similarly if you shooting at 16mm on APS-C sensor and cropping it to match a 4:3 ratio their field of view will no longer be equivalent to a 24mm field of view.

So moral of the story is to stick with the aspect ratio of the sensor if you want to maximise the wideness of the field of view. And if you can't then buy a camera with a sensor that provides your desired aspect ratio. Of course real life is not that simple..... because for example I do prefer 4:3 a lot but I want a larger sensor, so my option would be the large expensive GFX type systems. So I still shoot with FF with higher res sensors and crop in as required and use wider angle lenses to make up as necessary.

an ideal (probably technically crazy) solution would be to have a circular sensor that matches the lens circle and you can crop in post (or via. in camera options) to whatever aspect ratio you prefer. Then there'd be no need for vertical grips too

hope that helps.

Nandbytes, thanks but your explanation above is the bit I don't get namely -

"if you take an image that's "naturally" 4:3 and crop to a 3:2 you lose some "wideness" because you are cropping in to get your desired ratio"

If you look at your graphic above, then yes the 3:2 crop has less vertical field coverage (as your image nicely explains) compared to a 4:3 crop from the same sensor, but surely it increases the field of view in the horizontal i.e. you get a more "panoramic" view than 4:3 in the horizontal - not less again as your image demonstrates ?

I'm intrigued now, so tonight I'll take some shots one on my OM-1 with the 12-40 F2.8 Pro at 12mm and one on my Sony A6700 with the Sigma 18-50 F2.8 and see what's what. Of course I'm assuming that both lenses are true to their marked focal lengths, which we know isn't always the case due to rounding up or down.

Basically I wanted to know (and the images tonight will show me), was how much width of coverage (i.e. horizontal) would I actually be giving up by using an 18mm (27mm effective) lens on a native 3:2 APS-C sensor vs 12mm (24mm equivalent) on a Micro Four thirds sensor also shooting in the 3:2 aspect ratio ?

 

[nandbytes]

Nandbytes, thanks but your explanation above is the bit I don't get namely -

"if you take an image that's "naturally" 4:3 and crop to a 3:2 you lose some "wideness" because you are cropping in to get your desired ratio"

If you look at your graphic above, then yes the 3:2 crop has less vertical field coverage (as your image nicely explains) compared to a 4:3 crop from the same sensor, but surely it increases the field of view in the horizontal i.e. you get a more "panoramic" view than 4:3 in the horizontal - not less again as your image demonstrates ?

yes correct.
hence I said "wideness" in quotes because normally people refer to horizontal width only like you are doing but you are indeed losing some coverage vertically.
so overall "wideness" in field of view is a combination of both. of course you may be more interested in more achieving horizontal width in which case 3:2 of Sony is more useful.

I'm intrigued now, so tonight I'll take some shots one on my OM-1 with the 12-40 F2.8 Pro at 12mm and one on my Sony A6700 with the Sigma 18-50 F2.8 and see what's what. Of course I'm assuming that both lenses are true to their marked focal lengths, which we know isn't always the case due to rounding up or down.

Basically I wanted to know (and the images tonight will show me), was how much width of coverage (i.e. horizontal) would I actually be giving up by using an 18mm (27mm effective) lens on a native 3:2 APS-C sensor vs 12mm (24mm equivalent) on a Micro Four thirds sensor also shooting in the 3:2 aspect ratio ?

if you are only concerned about the horizontal you won't be giving up much if at all.
if my mental math is correct, you might even have a wee bit more coverage horizontally on the Sony.

 

[myotis]

Nandbytes, thanks but your explanation above is the bit I don't get namely -

"if you take an image that's "naturally" 4:3 and crop to a 3:2 you lose some "wideness" because you are cropping in to get your desired ratio"

If you look at your graphic above, then yes the 3:2 crop has less vertical field coverage (as your image nicely explains) compared to a 4:3 crop from the same sensor, but surely it increases the field of view in the horizontal i.e. you get a more "panoramic" view than 4:3 in the horizontal - not less again as your image demonstrates ?

I'm intrigued now, so tonight I'll take some shots one on my OM-1 with the 12-40 F2.8 Pro at 12mm and one on my Sony A6700 with the Sigma 18-50 F2.8 and see what's what. Of course I'm assuming that both lenses are true to their marked focal lengths, which we know isn't always the case due to rounding up or down.

Basically I wanted to know (and the images tonight will show me), was how much width of coverage (i.e. horizontal) would I actually be giving up by using an 18mm (27mm effective) lens on a native 3:2 APS-C sensor vs 12mm (24mm equivalent) on a Micro Four thirds sensor also shooting in the 3:2 aspect ratio ?

If you ignore the vertical angle of view and only look at the horizontal angle of view:

The 18mm lens on APS will give the same horizontal angle of view as a 13.6mm lens on M43

The 12mm lens on M43 will give the same horizontal angle of view as a 15.7mm lens on APS.

These have just been calculated based on the ratio of horizontal sensor dimensions to focal length.

 

[Sootchucker]

wow, thanks both (we have some real mathematician's here on the forum)

 

[Faldrax]

...However, aside from a very few expensive lenses, most "standard" zoom lenses for E-Mount APS-C seem to start from 18mm (27mm FF equivalent), whereas a lot of M4/3 lenses start at 12mm (24mm FF equivalent)....

The four main 'standard' zooms for E-Mount:
Sony 16-50 kit - if you get it bundled with the camera, ~ £130, cheap, very compact, but slow aperture and average IQ.
Sony 16-55 f/2.8 G - £939 - Best available, but also most expensive
Sigma 18-50 f/2.8 DC DN - £449 - Cheapest of the three f/2.8 options, but least zoom range
Tamron 17-70 f/2.8 Di III-A VC - £578.50 - Pay a bit more than the Sigma, get more zoom range.

As usual, it comes down to how much cash you have