Finding DOF with 35mm attached?

[MatthewC]

I've got an upcoming shoot in very low light. Im worried my DOF is going to be extremely small. I've got a iPhone program to show my DOF when I punch in my f stop, distance to subject, and lens being used. However, I'm using a Letus on my HPX170, how do I add the HPXs F-stop into the equation? Also, is it best to have the cameras iris as wide as possible for maximum light? Thanks for the help!

Oh the iPhone program is called Field Tools, and it's free.

 

[Ryan Patrick O'Hara]

Your DoF is ONLY effected by the F-stop of the lens on the adapter, not the aperture of the camera body... you only need to figure it into exposure equations.

To calculate DoF:

1) F-stop of lens on adapter
2) Distance of subject to the ground glass in adapter
3) focal length of lens on adapter


HOWEVER: your iphone program will have you choose a format... be careful. Depending on many factors, the amount the camera is seeing of the ground glass will change which lenses you choose and effect that equation not to mention create false values for field of view numbers. DoF will always be the same due to the three factors I mentioned, but the FoV created by the chip size will effect your decision of which lens to use, and that will effect the DoF. It's simply something to be aware of.