So it would seem it could be alot more than 2 stops.
In sharpness and tonality, it is recognizably a Delta film. If you make an 8x10 inch print from a 6x7cm Delta 3200 negative (at EI 3200), and an 8x10 inch print from a 35mm Delta 100 negative (at EI 100), the grain in the two pictures looks surprisingly similar. Of course, one is only about a 4x enlargement, and the other is around 7x, but the family resemblance is clear.
One more point needs to be dealt with, and it is a fairly fundamental one. Why would you want to use fast film with a roll film camera? Ilford told me that they had two clear groups of reactions during the field trials. One group said, "This is what I have been wanting for years. " The other group said, "What am I going to do with this film?"
At first, we had more sympathy with the second group than the first. After all, when you need the ultimate in speed, 35mm is still more attractive. The lenses are faster, and depth of field is greater. With a fast lens on a medium format camera, you often need to stop down to f/4 or less for depth of field. Even if you can work at full aperture, most lenses for roll film cameras are slow. Speeds of f/3.5 and below are quite common, and f/2.8 is regarded as the normal "fast" lens. There are a few faster lenses, such as the 105mm f/2.4 on the Pentax 6x7, the 110mm f/2 on the Hasselblad, the 80mm f/1.9 on the Mamiya 645 and of course the 80mm f/2 on the new Contax 645. Any of these could be useful for the right subject. But until we tried Delta 3200 in 120, we could not really see why anyone would want to use medium format instead of 35mm for ultra-low-light photography.
Then, when we saw the results, we changed our minds completely. This is magic.
There are two ways you can use it. One is in the same sort of way as 35mm: hand-held, for reportage and similar pictures. The other is where you need depth of field, or action stopping, in low light conditions, while still retaining excellent quality.
When you need depth of field, or action stopping, or both, you can use just about any camera, but the speed of Delta 3200 is a major advantage. For example, where you can use Delta 3200 at 1/60 second and f/5.6, rated at EI 3200, an ISO 400 film at its rated speed would require both a stop wider (f/4) and a shutter speed one step longer (1/30). Given that you can easily go to EI 6400 with Delta 3200, and that EI 12,500 is far better than it has any right to be, the advantages are clear.