Center Filter Questions

[AnzaRunner]

Hi all. It has been a while since I have posted, but all is going well with my LF shooting. I have found that my wonderful 75mm nikkor lens could use the help of a center filter. I can correct for some mild vignetting with photoshop, but it would be nice not to have to worry about it.

A one stop filter would likely do the trick. I have read that the filter must be mounted on the front. What are the consequences of a rear mounted filter? The reason I ask is it would definitely be more convenient if it was rear mounted. I'm sure there are some good reasons why no one does this though.

[Lachlan 717]

Hi all. It has been a while since I have posted, but all is going well with my LF shooting. I have found that my wonderful 75mm nikkor lens could use the help of a center filter. I can correct for some mild vignetting with photoshop, but it would be nice not to have to worry about it.

A one stop filter would likely do the trick. I have read that the filter must be mounted on the front. What are the consequences of a rear mounted filter? The reason I ask is it would definitely be more convenient if it was rear mounted. I'm sure there are some good reasons why no one does this though.

Without going into the physics side of light's travels, I wouldn't rear mount one as it would be a PITA to have to take the lens off each time I wanted to use it!

It is much easier to compose without it in place, and then screw it on once the camera's locked down.

A 75mm is dark enough when composing without having a CF taking more light...

[Nathan Potter]

Lens is not designed for a planar piece of glass in the image path especially wide angle lenses. The exiting off axis rays will be refracted differently than the on axis rays due to the progressively longer path length as one moves out from the center. Very thin filters can mitigate the effect considerably but still you'll degrade your image quality slightly. Also the light falloff is a function of the diameter and design of the lens and these CF are designed for a specific angle of view and FL, to be used next to the front element. Their correction for falloff behind the lens will be, well, "half assed". I guess you could try rear mounting as an emergency measure.

Nate Potter, Austin TX.

[Lachlan 717]

Lens is not designed for a planar piece of glass in the image path especially wide angle lenses. The exiting off axis rays will be refracted differently than the on axis rays due to the progressively longer path length as one moves out from the center. Very thin filters can mitigate the effect considerably but still you'll degrade your image quality slightly. Also the light falloff is a function of the diameter and design of the lens and these CF are designed for a specific angle of view and FL, to be used next to the front element. Their correction for falloff behind the lens will be, well, "half assed". I guess you could try rear mounting as an emergency measure.

Nate Potter, Austin TX.

Thanks, Nate.

I suspected that someone would do the physics side!