Ok so I got fed up with trying to figure out how to attach one of those pack filters and decided to use the perfect accessory holder already produced by Polaroid.
I am using the Polaroid SX-70 Accessory Holder
And a flat square Neutral Density Filter like the Cokin style.
Even when very carefully trying to cut the filter in to 4 small pieces, I destroyed the first quarter, but the second try came out almost perfect and after a bit of sanding fit right into the accessory holder.
Please let me know if you are interested in purchasing one of these and I'll figure out how much it will cost to produce them.
Here's a photo taken with the filter on.
Feel free to let me know what you think...
Peace - Lance