What is the best setting if I want to move the ISO on my FM2 card?
There is no best attitude worldwide … there is only the best setting for the scene. If you get the desired shutter speed and shutter speed at ISO400, there are only a few reasons to move the movie1, If you need either faster shutter speeds or a more open aperture, but you can not because of your ISO, then You should start pushing.
Sliding the film has consequences, namely increased contrast and grain and reduced shadow details. The Kodak Fact Sheet for TMax 400 states:
Because of its leeway, you can underexpose this movie by one level (at EI 800) and still achieve high quality with most developers during normal development. Graining does not change with the final print, but there is a slight loss of shadow detail and a reduction in print contrast by about half the paper grade.
If you need a very high speed, you can expose the T-MAX 400 film at EI 1600 and extend the development time. With the longer development time, the contrast and graininess increase, resulting in additional loss of shadow detail. However, negatives continue to produce good prints. You can even expose this movie on EI 3200 with a longer development time. An under-exposure with three stops and the use of three-stop push processing further increases contrast and graininess as well as additional loss of shadow detail. For some applications, however, the results are acceptable.
This resource also contains the following information:
Push processing allows the film to be exposed at higher speeds. However, push processing does not achieve optimal quality. There is some loss of shadow detail, an increase in graininess, and an increase in contrast. The extent of these effects varies from slight to very significant depending on underexposure and push processing. The results are usually awarded a 2-stop pressure and acceptable with a 3-stop pressure depending on the lighting and the scene contrast.
And further down in the regulatory small print (fat loss):
Exposure and processing of high-contrast scenes, such as B. starring performers, as indicated in the table. However, if details in the dark areas are important to the scene, increase the exposure by 2 levels and process the movie normally,
Think about it for a second – If shadow details are important, increase the exposure by 2 levels! This is the exact opposite of film shots.
To sum up, there is no best shot, only the ones you need for your shot. However, each of these options brings with it a compromise – and whether or not that compromise is worth it is entirely up to you. (As an example, I pushed Delta3200 once to 12800 for a high school football game, and the results were more like a bad halftone blown up than a photo.)
1: A contrast enhancement is not necessarily a bad thing. I live in PacNW these days where cloudy is the joie de vivre – so I'm not worried about a little extra contrast. You can also simply push film because they like "the look"