Digital BW, The Print

>After tweaks 
> and very minor cropping I have roughly a 20 inch image at 300ppi. 
>How large can this go?
> If I want significantly larger prints am I better off shooting large
> format (4x5) and drum 
> scanning the negs? 


Jamie,

one way to test if you like the look of images that have been interpolated
to extremes is to actually perform the sizing of the file to whatever you are
aiming for, then print a section that fits your 3000. Put it up on a wall
and stand back far enough to have seen the whole uncropped image
if it were hanging there. Then judge if you think it's fallen apart or
if it's still "pleasing".

I assume you know all the tricks to interpolation....   and to applying just 
the right amount of usm. If not, experiment a bit, because those variables
may make a big difference in the results.

I'd also offer a little food for thought on the resolution front:
There is one approach to resolution which is by the numbers. You calculate
the original pixels, then the ideal dpi for your printer and that gives you
the limit of a maximum print size.

But there are some questions to consider; and answering them can be a
little more elusive. What actual image information are you going after? 
What distance are you viewing the final print from? 
Is it that you're looking for extra detail or for smoother tonal
transitions? And which of these variables actually matters to the subject-
matter at hand? 

As examples....  I have blown 35mm and 4x5 negs to 24x36", 
6x7 negs to 44x60" etc. all from the same original scan interpolated up.
The end result looks the "same" as the smaller prints as long as your
viewing distance is proportionately  adjusted. Needless to say, the larger
negs look crisper and smoother and with more detail than smaller ones
when blown up to the same print size. That's just physics.

Also there is a scan size below which you really wouldn't want to go
 to do this. Add to this that scan quality (drum vs Imacon vs flatbed) 
is a factor and you do have some of the real limitations to doing this.

In the case of the digital Canon files, your starting point is fixed. 
To find the limits of what looks good you have to actually see it,
the numbers alone won't do it. I'd also guess that if you shot film
with the same lenses you'd get better results. But that's a whole
other topic...

My point here is that often the reasons for making a really big
print is not to actually see more "information" in the original, but 
because print size dictates viewing distance which in turn affects
how we perceive an image in relation to our position in space.
A small print intimately held in our hands, a medium size print
matted and hanging on a wall inviting us to get closer, or a giant
print that dominates the room and forces us to stand back have
a huge impact on the picture and what it communicates. 
That's the elusive part I was talking about. It's not the numbers
so much as it is the "effect" of size.

Antonis