Hey guys,
I have a problem with understanding how to properly set the FOV of my 35mm Adapter. In other words, how far to zoom in onto the ground glass. I found this article here from Barry and Steven Dempsey:
http://dvxuser.com/jason/Letus/
It explains how to do the setup. However, I don't agree with the numbers. The article says that the FOV of a 50mm lens at 2 feet distance should be 10.5 inch (given the size of the filmback of 22mm). I made a little drawing that explains how the resulting FOV is calculated (top drawing):
As can be seen in the top drawing, the FOV at 2 feet distance should be 10.5 inchs. However, to my understanding there are two errors in this calculation. First, the distance of the object to the camera (d) is measured with respect to the lens. But if I set the focus of my lens to 2 feet, it means that the filmback (or ground glass of adapter) has a distance of 2 feet to the object in focus. That's why I put a second drawing underneath the first one where this fact is taken into acount. And as you see, the FOV ends up to be only 9.7 inchs.
But that's still not the whole story. In the drawings above a pinhole camera was assumed although we deal ith lens systems where things are a bit different. So here is a third drawing where I replaced the pinhole camera with a 50mm lens and did the math.
Long story short, the FOV is further reduced to only 8.75 inchs. Now, am I doing something wrong here? Or is the FOV actually that much smaller on a real 35mm camera?
The background for this question is that I use FrameForge to block my shots and in order to get the right FOV in the software I wanted to calibrate my adapter setup to correctly reproduce what a 35 mm camera sees. Then I can simply set FrameForge to its 35mm preset to match the FOV.
Hope this post isn't too confusing.
Cheers,
Raphi
I have a problem with understanding how to properly set the FOV of my 35mm Adapter. In other words, how far to zoom in onto the ground glass. I found this article here from Barry and Steven Dempsey:
http://dvxuser.com/jason/Letus/
It explains how to do the setup. However, I don't agree with the numbers. The article says that the FOV of a 50mm lens at 2 feet distance should be 10.5 inch (given the size of the filmback of 22mm). I made a little drawing that explains how the resulting FOV is calculated (top drawing):
As can be seen in the top drawing, the FOV at 2 feet distance should be 10.5 inchs. However, to my understanding there are two errors in this calculation. First, the distance of the object to the camera (d) is measured with respect to the lens. But if I set the focus of my lens to 2 feet, it means that the filmback (or ground glass of adapter) has a distance of 2 feet to the object in focus. That's why I put a second drawing underneath the first one where this fact is taken into acount. And as you see, the FOV ends up to be only 9.7 inchs.
But that's still not the whole story. In the drawings above a pinhole camera was assumed although we deal ith lens systems where things are a bit different. So here is a third drawing where I replaced the pinhole camera with a 50mm lens and did the math.
Long story short, the FOV is further reduced to only 8.75 inchs. Now, am I doing something wrong here? Or is the FOV actually that much smaller on a real 35mm camera?
The background for this question is that I use FrameForge to block my shots and in order to get the right FOV in the software I wanted to calibrate my adapter setup to correctly reproduce what a 35 mm camera sees. Then I can simply set FrameForge to its 35mm preset to match the FOV.
Hope this post isn't too confusing.
Cheers,
Raphi
)