effect of lens length

[P3D Peter Abrahams <telscope@xxxxxxxxxx>]

It seems to me that the original question here was, do you get the same image:
>>>> if you crop an image taken with a 50 mm lens to the same part as
>>>> an image taken with a 80 mm lens, and make them the same size - would
>>>> you have the same thing as two pictures both taken with 80 mm lenses?

But 3d-ers read this as, would this change
>>the relationship of foreground and background objects.
or
>>the spatial relationships within the frame itself.

Question: wouldn't changing the f.l. alter the:
--depth of field
--aberrations, especially blur at edge (OK, cropping would reduce)
--flatness of the image...pincushion, barrel, or other distortions
--exposure, leading to film effects such as color balance, reciprocity
--don't longer f.l. shots have more 'cardboarding', less of a sculpted
appearance to the objects?

Maybe the original question needs to be more precise, like '50mm lens
stopped  down to same f# as used in 80'.  Even then, if one lens has several
more elements, or is designed as a portrait lens, or is aspheric; it might
alter the image.  
\\\\\\\\\\\\\\\\\\\\////////////////////
  Peter Abrahams    telscope@xxxxxxxxxx
the history of the telescope, the microscope,
   and the prism binocular


------------------------------