field of view - Can I combine a pinhole bodycap with macro extension tube to adjust focal length?

I'm interested in trying out a bodycap style pinhole on my DSLR (a Nikon D3300 in my case).

Can I combine this with a macro extension tube to adjust the focal length?

Calculators such as Mr Pinhole seem to indicate that this would change the focal length and the viewing angle in the way I want, and reduce the amount of light reaching the sensor.

Answer

Yes, you can.

But keep in mind that the optimal performance of a given pinhole is related to focal length used. More on the theme can be found here: How to calculate the optimal pinhole size?.

Using a macro tube extender will give you suboptimal results - the longer focal length of the "camera" would ask for a bigger pinhole than your bodycap.

On second thought: a small pinhole on a long tube will increase your exposure time considerably; possibly into area where noise caused by sensor heatup becomes an issue. This might be a bigger problem than diffraction.

But it will work.