Originally posted by kh1234567890 The point I was trying to make is that with telephoto zooms while you might sometimes get away with having the SR focal length set at a half of what it really is, you are unlikely to get away with having it set to twice the actual value. The SR setting is not so critical with wide zooms (e.g. the M28-50).
Well, if you have set the value to half of the actual FL, you'll get half the blur you would get if you had SR turned off, so it's very much OK in that respect. The problem is that we're used to getting
much more blur reduction than that, so the results may appear disappointing.
If it's the other way round, with the value set to twice the actual FL, you'll get, in theory, exactly the same blur as you would if you had SR turned off. But you're right, it is a situation you'd want to avoid, and you'd certainly want to avoid anything more than 2x.
Wide zooms are only less critical in that you tend to get less blur anyway at shorter FLs. But the amount of blur reduction remains the same (it's just that there's probably less in the first place).