[Leica] Crop factor ramblings

[mark at rabinergroup.com (Mark Rabiner)]

Photographers usually don't change the format shape of their neg or sensor
to fit the format shape of their print. They adjust the borders which will
not all be equal. The borders don't need to be equal. They even look a bit
bad all equal.  And printing serious full prints with no borders tends be
only done only in very large sizes as in mural sizes. And it those sizes the
paper is just as often adjusted to match the size the photographer picked
for the image. Printing with at least full inch borders is still considered
more archival just like a darkroom print would be.

In making comparisons between aspect ratios we are using the diagonals
anyway so that accounts for some being more squarish and others being more
panoramic..


On 5/5/14 2:47 AM, "Ken Iisaka" <ken at iisaka.com> wrote:

> With Mark's remarks about crop factors and "full-frame" sensors, I was
> inspired to ponder the true meaning of the "crop factor."
> 
> One of the things that is often not discussed is that it is dependent on
> the aspect ratio. Different formats have different aspect ratios, and it
> has a meaningful effect on the "crop factor."
> 
> If you are comparing sensors of the same aspect ratio, it's simple: just
> compare the diagonal measurements, or one of the edges.
> 
> When you are comparing two different aspect ratios, and possibly a third
> aspect ratio for the final print.
> 
> A 35mm "full-frame" is nominally 24x36mm, though it is not uncommon for the
> outermost 0.5mm or so to be masked, leaving us with a 23x35mm frame.
> 
> However, if I want to make a 8x10 print, I would only be using 23x28.75mm
> of the frame.
> 
> Thus, if I am using a FourThirds or 13x17.3mm, the valid comparison would
> be between the short edge of the frame, i.e., 23mm vs 13mm, or 1.77.
> 
> So, my Panasonic 20mm lens really behaves like a 35.4mm lens on a "full
> frame" 35mm film.
> 
> If I want to produce 5x7 prints, however, the factor is different again.
> 
>> From the 35mm film, I'd be using 23x32.2mm, while I'd be using
> 17.3mmx12.38mm of the four-thirds sensor. Here, the "crop factor" is 1.86,
> closer to the "official" crop-factor of 2.0.
> 
> Anyway, I have always felt that the Panny 20mm is too wide for my taste,
> and I expect to be happier with the new Olympus 25mm lens, which is really
> equivalent to a 43mm lens on a 35mm film.




-- 
Mark William Rabiner
Photographer
http://gallery.leica-users.org/v/lugalrabs/