Manipulating Cir. Pola. for Rear of Lens use.

[Stan. L-B]

Has anyone used a Circular Polarizer behind the lens of large format?
If so at what stage was it manipulated for best effect, can it be done before attaching it to the rear of the lens?
Any optical complications involved in such a set up?

 

[rbarker]

Ouch. Putting a polarizer on the rear element would have to top my list of things most inconvenient to do.

Filters behind the lens cause focus shift, and a polarizer would probably cause more shift than most, making it essential to focus after the polarizer was in position. Considering how much light the polarizer eats, the GG is gonna be pretty dark.

If that is the only option, my suggestion would be to use twins - one mounted on the lens, and another to sight through hand-held to determine positioning of the rotating element. With index marks on both, you can then transfer the setting from the one you're holding to the one on the lens. Not all polarizers have good index marking, however, so you might need to add markings yourself.

 

[glbeas]

I would wonder if the orientation would be the same when using the filter behind the lens, since at that point the image is reversed and upside down. I've never tried that before and am clueless about how it would work.

 

[Stan. L-B]

I understand the necessity to focus with any filter in position, on the front or behind the lens, and that I would need to compensate about two stops for the filter factor.

The lens in question is my schneider 300mm Apo Symmar 'L' of 5.6. for 5X4 & 10X8
It has a rear of lens screw thread for filters of 3" in diameter. The front of this lens has a screw filter thread of 4"

My existing filters are 'P' series of Cokin - so will fit the rear of the lens.

I understand that the index mark on the lens should be towards the main light source to obtain the best effect.
I am confident I can do this with the filter in hand, rotate as necessary, note the position of the index to rear of filter, then mount the filter behind the lens.

The fact that the filter is at the rear, to my way of thinking, should not effect the performance of the polarization as the polarized light is then in a single plane, this being so, the fact that the polarized light is reversed is of no consequence.
I have no problems with mounting any with other type of filter, to the front or rear.

Am I being over simplistic with my understanding of polarized light?

 

[Jorge]

Place filter on rear element, open shutter to find best polarization. Once best setting is found, place the lens on the camera and then focus. I have done this way for the same reason you state.

 

[Stan. L-B]

Thanks all for your comments, time for a 'field test'