Home · Register · Search · View Winners · Software · Hosting · Software · Join Upload & Sell

Moderated by: Fred Miranda
Username   Password

  New fredmiranda.com Mobile Site
  New Feature: SMS Notification alert
  New Feature: Buy & Sell Watchlist
  

FM Forums | Alternative Gear & Lenses | Join Upload & Sell

  

Archive 2013 · Medium Format FOV Calculation
  
 
Dooglestar
Offline
• •
Upload & Sell: Off
p.1 #1 · p.1 #1 · Medium Format FOV Calculation


HI,

I understand to get the correct FOV on a crop ASP-C sensor, using a lens made for FF cameras (35mm) have to multiply your focal length by 1.6 to get an accurate FOV. So a 50mm will be like a 80mm. Am I correct in this?

My main question is how to calculate the FOV if using a medium format lens, a Mamiya 80mm on a Canon 5DIII?

Thanks.



Jan 26, 2013 at 01:08 PM
mpmendenhall
Offline
• • • •
Upload & Sell: Off
p.1 #2 · p.1 #2 · Medium Format FOV Calculation


The calculation is very easy: an 80mm lens (designed for medium format, used on your 5DIII) will have the field of view of an 80mm lens on your 5DIII

The "1.6x crop factor" that you apply for APS-C sensors is to compare the field of view of the sensors, relative to the "familiar" 24x36mm format. An 80mm lens is an 80mm lens is an 80mm lens, regardless of what film size it was designed for, so if you already have a feeling for how wide 80mm is on your camera, then no further calculation is needed.



Jan 26, 2013 at 03:23 PM
Dooglestar
Offline
• •
Upload & Sell: Off
p.1 #3 · p.1 #3 · Medium Format FOV Calculation


Ok, so that's completely thrown me. So there's no crop factor using a Medium Format lens made for a 465 sensor/film plane on a full frame (smaller)? The FOV stays the same as if I was just using an 80mm lens made for FF (24x36)?

If that's so, why does the FOV change when using a FF lens on a crop sensor? It's effectively the same thing happening with the MF lens on the FF body, no?

Thanks for your reply.



Jan 26, 2013 at 03:39 PM
mpmendenhall
Offline
• • • •
Upload & Sell: Off
p.1 #4 · p.1 #4 · Medium Format FOV Calculation


The field of view does change between sensors. The lens focal length does not. People calculate an "equivalent focal length" (which causes confusion, because the focal length is a fixed property of the lens) because they are familiar with a particular sensor size (e.g. 24x36 "full frame 35mm") and want to know how lenses will look on a different sensor size. Since your familiar "frame of reference" is already the 24x36mm sensor of your 5DIII, no conversion is necessary to understand how lenses will look on it.

On the other hand, if you want to know how wide an 80mm lens will look on a 42x56mm Mamiya 645 relative to use on your 5DIII, then you can figure the "full-frame equivalent" factor the other way around: along the width of the picture, the Mamiya 645 will see the 80mm lens as "equivalent to" if you were using a 36mm/56mm*80mm = 51mm lens on your 5DIII (e.g. an 80mm lens on 645 format is "equivalent" to the "normal" 50mm focal length on 35mm format).

Edited on Jan 26, 2013 at 03:52 PM · View previous versions



Jan 26, 2013 at 03:47 PM
jcolwell
Offline
• • • • • • •
Upload & Sell: On
p.1 #5 · p.1 #5 · Medium Format FOV Calculation


The FOV of an 80mm lens on a 645 camera is "normal", equivalent to a 50mm on FF (135 format) camera. When you put the 645 80mm lens on a FF camera, it captures only the central part of the image circle that comes from the 645 lens, and so it's a short telephoto FOV - same as an 80mm lens "meant for" a FF camera. The big difference is that the 645 lens has a larger image circle which is mostly captured by a 645 camera, but only partially captured by a FF camera.









Jan 26, 2013 at 03:48 PM
Dooglestar
Offline
• •
Upload & Sell: Off
p.1 #6 · p.1 #6 · Medium Format FOV Calculation


Thanks for the diagrams.

If you got a 35mm image circle and put a 1.6 crop image rectangle in it (say a 50/2 R Leica on a 7D) it would look something similar to the 645 image circle with the 35mm rectangle inside (Mamiya 80mm on 5DIII).

Why does the FOV change for the former and not the latter?



Jan 26, 2013 at 04:20 PM
mpmendenhall
Offline
• • • •
Upload & Sell: Off
p.1 #7 · p.1 #7 · Medium Format FOV Calculation


Dooglestar wrote:
Why does the FOV change for the former and not the latter?


The FOV does change in all cases (when moving a lens between different sensor formats). The focal length of a lens, e.g. 80mm, is not the field of view --- it's the combination of lens focal length and sensor size that gives field of view. Change the sensor size and the field of view changes, but not the focal length.

Because people typically calculate "crop factors" relative to the size of your 5DIII sensor, no "crop factor" (or, a "crop factor" of 1.0) is necessary --- you are asking "putting what focal length lens on a 5DIII would give the same field of view as putting an 80mm lens on a 5DIII?", so the answer is 80mm. You would need a different answer for a different question, e.g. "putting what focal length lens on a 5DIII would give the same field of view as putting an 80mm lens on M645," (in which case the answer would be ~50mm).



Jan 26, 2013 at 04:31 PM
 

Search in Used Dept. 



a.RodriguezPix
Offline
• • • •
Account locked
p.1 #8 · p.1 #8 · Medium Format FOV Calculation


subscribed!


Feb 28, 2013 at 12:17 AM
JohnJ
Offline
• • • •
Upload & Sell: Off
p.1 #9 · p.1 #9 · Medium Format FOV Calculation


The term 'crop factor' came about in the digital age and was never used in relation to film cameras, even those such as Mamiya RZ's where you could insert the 645 roll film holder and shoot 645 instead of 67. The term 'crop factor' relates to the FF or 24mmx35mm sensor and sensors smaller than it. Trying to use 'crop factors' between medium format film cameras and smaller digital sensors is obviously do-able but not everyone will understand your term because that's not really what it's meant for. It's a little like speaking in a language that no one else understands.

FOV is another matter. As said before, 80mm is 80mm regardless of format, but the FOV will vary wildly. It's easier to think in terms of the lenses focal length and how that looks on a sensor (because it's fixed and will always do the same thing) than it is to think in terms of FOV, which is NOT fixed and which varies with sensor size.

I think it's a pointless pursuit worrying about FOV.



Feb 28, 2013 at 03:11 AM
ken.vs.ryu
Online
• • • •
Upload & Sell: Off
p.1 #10 · p.1 #10 · Medium Format FOV Calculation


http://www.sweeting.org/mark/lenses/medium_format.php


Feb 28, 2013 at 03:20 AM
RustyBug
Online
• • • • • •
Upload & Sell: On
p.1 #11 · p.1 #11 · Medium Format FOV Calculation


+1 @ above, i.e. 80mm = 80mm

If you are familiar with an enlarger in the darkroom ... think of it as though you were projecting an image onto an 8x10 piece of paper. Then without changing the height (akin to FL) of the enlarger, you switch out the 8x10 for a 4x5 sheet of paper (akin to smaller sensor). Your projection will have not changed at all, but you will only be capturing a CROPPED portion of that image projection. Then if you switched out the 4x5 paper for an 2x2-1/2 (akin to even smaller sensor), it would be an even further CROPPED capture of the projection.

So without making a change to the enlarger height, when you present the prints captured by 8x10, 4x5 and 2x2-1/2 papers side by side, each one will display a different amount of the image that was projected, but they will be identical for the corresponding areas captured. Hack the 8x10 down to the size of the 4x5, identical. Hack them both down to 2x2-1/2 and all three will now be identical. The cropping is only going to indicate how much of the projection you are throwing away ... i.e. nothing is really getting "multiplied" just because you capture a smaller area of the projection.

The one thing that is definitely different about using MF glass is that the projection is spread over a larger area (image circle). This makes for smoother transitions and reduced vignetting, particularly when only the more centralized (straighter rays) portions of the projection are being captured by the sensor. When I mentally separate the projection (lens) from the capture (sensor/paper) it is much easier for me to understand that 80mm = 80mm. Which body I put on behind that projection will dictate how much of the projection I have captured/cropped from it ... i.e. crop factor.

Whether that is on my FF (1X) or my 1.25X or my 1.5X cropped sensor. It is just telling me how much of my projection I'm NOT capturing RELATIVE to FF.

But for ease of mind/practical use ... 80mm = 80mm.




Feb 28, 2013 at 03:43 AM
a.RodriguezPix
Offline
• • • •
Account locked
p.1 #12 · p.1 #12 · Medium Format FOV Calculation


http://www.betterscanning.com/scanning/vb_mfholder.html


Mar 02, 2013 at 09:38 AM
carstenw
Offline
• • • • • •
Upload & Sell: Off
p.1 #13 · p.1 #13 · Medium Format FOV Calculation


Err, triple-post.


Mar 02, 2013 at 11:31 AM
a.RodriguezPix
Offline
• • • •
Account locked
p.1 #14 · p.1 #14 · Medium Format FOV Calculation


bookmarked


Jan 13, 2014 at 05:34 PM





FM Forums | Alternative Gear & Lenses | Join Upload & Sell

    
 

You are not logged in. Login or Register

Username   Password    Reset password