A use for the old linear polarising filter.
I sill have my film equipment from my Canon T70. One item, the linear polarising filter, I had found out is not good for the auto focus system (struggles to focus) on digital cameras and it was recommended to get a circular polariser instead. So this has been stashed away in the old bag with the rest of my film equipment, for years. I was watching the new season of DTOWN TV (Now they cover all things DSLR not just Nikon) where they mentioned that with fast glass (wide apertures like 1.2 /1.4/1.8/2.8 ) it is hard to set a wide aperture to get shallow depth of field when it is bright outside even when you have cranked up your shutter speed and brought down your ISO. The answer is to pop a neutral density filter (or stack if needed) on the lens and if you have not got these at hand the next best thing is to use a polarising filter. This got me thinking as I have now come across the problem particularly using the 50mm 1.8 lens I got last year. I do have a circular polariser in my bag so I thought what if you had two, like if you had two stacked polarised sunglasses, the more you twist them the darker it gets. Tried this with two circular polarised filters but the effect is minimal, id anything there is a colour shift from a yellow to a blue shade. I puled out my old linear filter and bingo! I had a variable density filter. I can turn the circular filter to have the normal polarizing effect and then if I turn the linear one I start to get darker shades the more I turn it. One thing I have noticed is that it gets a dark blue tint when I really crank it up to the darkest. I will be doing some experiments with this and I will keep you posted.
As you can see below two images shot into the sun with a relatively slow shutterspeed of 1/3200 and 1/500 even shooting at ISO 400. With the double polarising filter in its lightest, 1/8000 shutter was not fast enough and was way over exposed. The images are nothing special and it was a quick and dirty test. I will be doing some experiments with this and I will keep you posted.
Exposure: 1/3200 sec at f/1.8
Exposure: 1/500 sec at f/1.8