[LRflex] Africa art NOW DoF issues on digital cams. - to Bill
- From: Philippe Amard <phamard@xxxxxxxxxxxxxx>
- To: leicareflex@xxxxxxxxxxxxx
- Date: Tue, 13 Nov 2007 07:24:27 +0100
Bill
On the LFI Leica writes :
"The smaller that crop is, the smaller the angle of view and field of
vision; and the greater the enlargement. Since Leica's M and R systems
were built around 35mm cameras, the 35mm format is still considered
standard - here, certain focal lengths are expected to deliver certain
angles of view. For example, the 50mm lens is commonly referred to as
'the standard lens', delivering the standard angle of view; but since
the sensors of the M8 or R9+DMR are 25 to 32 per cent smaller than the
35mm format, these cameras require a 35mm lens in order to arrive at a
comparable angle of view. The multiplication of the focal length by crop
factors 1.33 (M8) or 1.37 (R9+DMR) simply illustrates the angles of view
and enlargements that 35mm photographer can expect from their lenses - a
faithful 50mm standard will mutate into a humble telephoto, a 35mm in
turn into a standard focal length.
As mentioned above, the Digilux 3 is the product of the FourThirds
system. It was designed as a digital camera. The corresponding Leica,
Olympus and Sigma lenses are also designed specifically for the
FourThirds standard, and not for 35mm format. Hence, when a four-thirds
focal length is converted into 35mm terminology using the related 2.0
crop factor, what you get is of course fictional - but the same applies
for the M8 and R9: the multiplication merely serves to help 35mm
photographers refer back to what they've learned from the 35mm medium.
In other words, when a 35mm photographer mounts a D-Vario-Elmarit
14-50mm Asph on the Digilux 3 and imagines it as a 28-100mm lens, he
will be able to visualise just how much of a telephoto the zoom lens is.
While the conversion is helpful, it applies only to the angle of view
and the enlargement. The depth of field, on the other hand, will be
greater than what one has come to expect from certain focal lengths
(while still smaller than the physical focal length may suggest). The
aperture size of an aperture value depends entirely upon the physical
focal length, meaning that the optimum aperture will be a little bigger
than that of a 35mm camera; diffraction-induced blur begins to show a
little earlier due to the shorter focal length.
End of quote
Source :
http://www.lfi-online.de/ceemes/page/show/questions_and_answers/#question1
It is unclear to me if paragraph three applies exclusively to 4/3
cameras, see their remark about DMR and M8 crop factor; are they to be
included in the whole reasoning?
It might be helful to sort that out.
And from the pix you sent me, I can only regret you didn't use the
on-camera viewer to check on your photos before it was too late as it
seems to have been a very enjoable event.
to be continued probably
Yours
Phil...x
William Abbott wrote:
On Nov 12, 2007, at 12:36 PM, Philippe Amard wrote:
you might also consider that once on the DMR your lens is no longer
70 or 90 but must be multiplied by the crop factor. Hence less of DoF.
Philippe,
Having given it some thought, I believe that the DOF is a function of
lens focal length and aperture, both properties of the lens alone, and
an assumed maximum circle of confusion. Thus, DOF is a property of the
lens, and is uninfluenced by the camera or the size of the image
detection and recording system.
For example, if I load my R9 with film and mount a lens, the DOF will
be a property of that lens. If I install a DMR, the same DOF will
pertain, no matter what size of detector I mount.
If the sensor is smaller than the film size, 24 X 36 mm, I will have a
smaller image and have the illusion of a longer focal length lens, but
the DOF will still be that associated with that same lens.
That's the way I understand what is happening.
All the best,
Bill
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