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Archive 2013 · what is the EFOV of a 1:1 format 28mm lens?
  
 
Kit Laughlin
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p.1 #1 · p.1 #1 · what is the EFOV of a 1:1 format 28mm lens?


I have bought another GXR; I couldn't resist. I want to pair it with the Ricoh A12 28mm f/2.5 GR lens, but using the in-camera square format only.

Assuming diagonal FOV measurements, and further assuming that the diagonal of a 28mm lens is 75 degrees, what will the diagonal of a square-cropped 28 lens be? And what will be the rough EFOV, in 135-land? My guesstimate is around 32mm EFOV, but it is late here...

TIA, KL



May 26, 2013 at 11:24 AM
dcjs
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p.1 #2 · p.1 #2 · what is the EFOV of a 1:1 format 28mm lens?


http://imaginatorium.org/stuff/angle.htm

This widget allows you to calculate the angle of view of any focal length/sensor combination you can imagine.

For calculations like this it is necessary to use the actual focal length of the GXR, which is 18.3mm.



May 26, 2013 at 11:49 AM
kosmoskatten
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p.1 #3 · p.1 #3 · what is the EFOV of a 1:1 format 28mm lens?


I use it like that a lot Kit; the GXR and A12 28 and 50mm modules in square mode.
I can't see myself without them. For some time I was thinking they are a bit long in the tooth but once I start using them again I do like them, a lot. They will be my small kit, and once the GR gets here, my small spare kit, everything fits in a very small bag.




May 26, 2013 at 12:16 PM
genji
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p.1 #4 · p.1 #4 · what is the EFOV of a 1:1 format 28mm lens?


I could be wrong about this (it's late where I am and I've had a beer and a couple of glasses of wine) but here are the parameters:
* the 18.3mm lens in the Ricoh A12 28mm f/2.5 unit has an EFoV of 28mm;
* a (non-Canon) APS-C sensor measures approximately 15.6mm x 23.5mm;
* reducing that to a square format yields an effective sensor size of 15.6mm x 15.6mm (in other words, the horizontal angle of view is reduced by one third);
* therefore the horizontal field of view must be increased by a factor of 1.5.

So the square format Ricoh A12 28mm f/2.5 unit now has an EFoV of 42mm.

Rui Salgueiro's field-of-view calculator confirms this logic:

You submitted the following name/value pairs:
focal = 18.3
format = other
width = 15.6
length = 15.6
Width = 15.6 mm, Length = 15.6 mm, Diagonal = 22.0617 mm
f Hor Vert Diag H/V
18.3 46.1703 46.1703 62.1614 1.0000

You submitted the following name/value pairs:
focal = 28
format = other
width = 24
length = 24
Width = 24 mm, Length = 24 mm, Diagonal = 33.9411 mm
f Hor Vert Diag H/V
28.0 46.3972 46.3972 62.4394 1.0000

You submitted the following name/value pairs:
focal = 42
format = 24 36
width = 24
length = 36
Width = 24 mm, Length = 36 mm, Diagonal = 43.2666 mm
f Hor Vert Diag H/V
42.0 46.3972 31.8908 54.5041 1.4549



May 26, 2013 at 01:06 PM
 

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Tariq Gibran
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p.1 #5 · p.1 #5 · what is the EFOV of a 1:1 format 28mm lens?


Kit Laughlin wrote:
And what will be the rough EFOV, in 135-land? My guesstimate is around 32mm EFOV, but it is late here...

TIA, KL


Effective frame of view between two different aspect ratios - rectangular 35 and square- is the impossible part of course. It seems obvious enough but when you are shooting - and if you are not used to square - it could be disorienting because in the vertical dimension, you get the same as with the 35mm but in the horizontal it would be like shooting with a 42mm lens on 35. Where things get crazy also is when you calculate what is required - effective focal length wise to 35 - to get the same horizontal field of view on the square as you did with 35mm when using the 28. You would need something equivalent to about a 19mm lens in 35mm land.

So, vertical field of view, nothing changes. When "cropping" the 28 to square in the horizontal dimension, it's like using a 42mm lens (as above) on 35 (to achieve roughly 46 degrees). If you want the same 65 degree horizontal field of view on the square as you got with the 28 on 35mm, you would need to be using close to a 19mm lens. All of that is relative to FF 35. I think that's right. Things get confusing after a while.



May 26, 2013 at 01:59 PM
Kit Laughlin
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p.1 #6 · p.1 #6 · what is the EFOV of a 1:1 format 28mm lens?


Thanks everyone; that is brilliant, and the reason is that between 40 and 45 mm EFOV is my absolute all-time focal length favourite.

This is just wonderful and I think the square format as well (as many of those who used to shoot 6 x 6 format in the old days with Hasselblads or other cameras will know) really has a completely different compositional aesthetic and one that I like very much.

Now off to search the B&S for a 28mm module. Cheers and sincere thanks everyone.



May 27, 2013 at 02:47 AM
douglasf13
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p.1 #7 · p.1 #7 · what is the EFOV of a 1:1 format 28mm lens?


Cropping a 35mm lens (on 135) to square (or a 23mm'ish lens on aps-c) is nearly identical to the field of view of the standard 80mm lens on a Hasselblad 6x6.

Shooting the 28/2.8 module on the GXR and cropping it square would be like using around a 70mm f10 lens on a Hasselblad, in terms of field of view and depth of field.



May 27, 2013 at 07:25 PM
Tariq Gibran
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p.1 #8 · p.1 #8 · what is the EFOV of a 1:1 format 28mm lens?


douglasf13 wrote:
Cropping a 35mm lens (on 135) to square (or a 23mm'ish lens on aps-c) is nearly identical to the field of view of the standard 80mm lens on a Hasselblad 6x6.


Funny Douglas, I almost posted the exact same in the RX1 thread!



May 27, 2013 at 07:51 PM





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