Focal equivalence for display ?

[timb]

I do not understand your term "Focal equivalence for display" as a 50 mm lens is a 50 mm lens the only thing that changes is the crop factor depending on the size of the film or sensor used. for example a 50mm lens on a full frame stills camera will appear to be wider than a 50mm lens on a APS-C sensor sized camera. So to get the same size images on both formats different lens sizes must be used (if keeping the camera and subject in the same position)

Also if I put figures into "Focal equivalence for display" eg real 50mm diplayed as 14mm (for 2/3" video) then the focal length in your program does not match the numbers on my lens.

All my observations are based from shooting motion film and video.

Thanks again !!

Regards, Tim Bradley

[Didier]

I do not understand your term "Focal equivalence for display" as a 50 mm lens is a 50 mm lens the only thing that changes is the crop factor depending on the size of the film or sensor used. for example a 50mm lens on a full frame stills camera will appear to be wider than a 50mm lens on a APS-C sensor sized camera. So to get the same size images on both formats different lens sizes must be used (if keeping the camera and subject in the same position)

Also if I put figures into "Focal equivalence for display" eg real 50mm diplayed as 14mm (for 2/3" video) then the focal length in your program does not match the numbers on my lens.

All my observations are based from shooting motion film and video.

Thanks again !!

Regards, Tim Bradley

Hi Tim,

This is a good question, I know that this part is not very user-friendly. So first of all thank you for asking this question, it gives me the occasion to explain why I introduced this setting.

It is actually principally used for compact cameras. Because most of manufacturers hide the real lens focal of their compact cameras, the user can frequently see more easily the '35mm equivalent' focal than the real lens focal. Let's see an example with the Canon Powershot G10, in the technical specification it is specified that the zoom goes from 28mm to 140mm (5x zoom), but the real lens focal actually goes from 6.1mm to 30.5mm. This is due to the sensor size which is reduced in compact cameras. To calculate the depth of field, we need to know the real focal. When the user wants to take a wide angle picture with its Canon Powershot G10, he will see on his camera 28mm but the actual focal is 6.1mm. So in WinMoDof, the Canon Powershot G10 is configured "Real 6.1mm is displayed 28mm". Thank to this, to calculate the DOF of his picture, the user can select in WinMoDof 28mm for the focal, as displayed on its camera, and WinMoDof will use 6.1mm for the calculation.

This explains why compact cameras have a huge depth of field, because their lens focal is tiny. I don't know if the problem is the same for camcorders... I have to find some information before adding video cameras into WinMoDof database.

You are right when you say that a same lens will appears wider on a full frame camera than a APS-C camera. But in this case, the parameter "Focal equivalence for display" will not help you, because you know the real focal of your lens. So you can configure it as "Real 50mm is displayed 50mm". But the circle of confusion won't be the same for the two cameras, so the DOF shouldn't be the same with the two cameras...

Hope this answers your question. Don't hesitate if you have any remark.