Originally posted by zoomlens For nature and wildlife photography a 400mm or larger is often quoted as being necessary. Then when I look at the lens for sale, the listing confuses me. For example: A 300mm lens will then say 35mm equivalent of over 400mm. So, would I be getting the size that is needed or should I just forget the 35mm equivalent ratings and make sure that it is 400 or over?
Equivalence is important here, and cannot be dismissed.
If the "400mm or larger is often quoted as being necessary"
appears within the context of "full-frame" 35mm photography,
say by respected wildlife photographers working with full frame cameras,
while you are planning to apply that advice to APS-C photography,
you _will_ need to understand "400mm" as a 35mm equivalent,
and then interpret it as an actual focal length of around 250mm
when you go shopping for a suitable lens.
A lot of people wish equivalence would go away,
and it can get confusing at times,
but it's a fact of life whenever the discussion involves different formats.
My 90mm Apo-Lanthar is a long way from 400mm in actual focal length,
but it's my lens of choice (within the Q system) for what little casual wildlife photography I end up doing.
Why? Exactly because it's a "400mm equivalent"!