Hi Rowland,
When I used to shoot only with the DSLR and lens combination, this was my preferred way of taking flat frames.
I'd load up a new Photoshop document with a white background set to full screen, layer a couple of tissues over the front of the lens, ensure the lens was pointing parallel to the laptop screen and expose at ISO-100 at the aperture I shot my light frames, to give me a histogram (displayed in Digital Photo Professional) that was 1/3rd of the way across the X-axis.
It worked a treat.
H
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