Re: [Leica] image quality and format

[Mark Rabiner <mark@rabiner.cncoffice.com>]

Ken Iisaka wrote:
> 
> Erwin wrote:
> > Now the format. A 35mm negative has an area of 864 square
> > millimeters. To make the 6x6 format comparable, we need the same 2:3
> > ratio for the Hasselblad negative and that is 38x56mm or 2101 square
> > millimeters. So the Hasselblad has an advantage of 2.5 times for
> > area. That implies that the same object that fills the frame in the
> > Leica case, will fill the frame in the Hasselblad case with an
> > advantage of  2.5 times. So now we have the situation that one square
> > millimeter of image area in the Leica case has 2.5 square millimeters
> > in the Hasselblad case. Assume that we need the limit of 40 lp/mm for
> > the object details when taking the picture with the Leica. We need
> > only 16 lp/mm for the Hasselblad picture to cover the same detail at
> > the equivalent resolution. So OF COURSE the Hasselblad negative has a
> > big advantage.
> 
> Actually, Hasselblad requires not 16 lp/mm but 26lp/mm (40 lp/mm * 36 mm
> / 56mm) to captures the same amount of information.  lp/mm is a unit in
> one dimension only.  Alternatively, Hasselblad lens needs to perform as
> well as a Leica lens at 40 lp/mm, at only 26 lp/mm.
> 
> With a more square, conventional 4x5 aspect ration photographs, the
> comparison turns in favour of Hasselblad further: the usable negative
> area from a Leica would be 24x30mm, where you could use as much as
> 45x56mm from a Hasselblad negative.  In this case, Hasselblad lens has
> to perform at 21 lp/mm (40 lp/mm * 30mm / 56mm) to equal Leica at 40
> lp/mm.
><Snip> 
Let us not also forget that we may be talking Hasselblad verses Leica or are we
just comparing formats.
I have a 645 back for my Hasselblad so these ratio's of comparison can vary.
And if we talk "medium format" to 35mm than these ratio's vary some more as we
can also be talking 6x9cms.
Mark Rabiner