scanning negatives - resolution

The confusion here is DPI. It is better to work in pixel's dimensions. First
you must know the maximum optical scanning DPI or PPI is more precise. Let
assume 4000 PPI and this is known as max input PPI. Your source is 35mm
negative so for full frame scan is 24x36mm (1x1.5 inches). Apply max input
PPI will give you 1 x 4000 and 1.5 x 4000 = 4000 x 6000 PPI (pixel's
dimensions). Now come to image output PPI and 300 is more than sufficient
for printing. So 4000/300 PPI and 6000/300 PPI will give you print size
13.33 x 20 inches. Remember don't confuse image input and output PPI also
don't confuse image output PPI and printing output DPI. Your lab probably
give you image output PPI 300 which is correct.

"freightcar" <same_as_my_nickname RemoveThis @gmail.dot.c.o.m.> wrote in message
news:1f64c$4377a2ea$d917f89c$19143@news.chello.sk...
>i would like to scan all my negatives to have digital copy of all my
>photos. when I came to lab I asked them to scan them in 2400 dpi. i sure
>sounded like an idiot, because they obviously scan only in 300 dpi but
>my point is, 25x36 (cm) in 300 dpi equals 9.84x 14.17 inch and that is
>2952 x 4251 pixels. if I want to scan negative in this resolution it
>actually is 4251 / 1.41in (36mm) eq 3014 dpi. this ~ 3000 dpi is actually
>an optical resolution of the scanner. so it is a really different if you
>scan at 1200, 2400 or 3000 dpi. is that so the scanner always use same
>optical resolution and the result is sized by the software? am I completely
>wrong? can someone bring more light here?
> thank you
>
>
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