Archived posting to the Leica Users Group, 2015/01/05

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Subject: [Leica] The myths of crop factor
From: sonc.hegr at gmail.com (Sonny Carter)
Date: Mon, 5 Jan 2015 20:53:47 -0600
References: <CABXy406V9Nuhx8KY2nEw4j8bR=F5tZM9Q_2QsvEY4RRsQ+3uZg@mail.gmail.com> <D0D0AD68.2F841%mark@rabinergroup.com>

Yes, and the first thing the picture editor did when he got that uncropped
print was to mark it for cropping and send it to be made into a cut.



On Mon, Jan 5, 2015 at 8:06 PM, Mark Rabiner <mark at rabinergroup.com> 
wrote:

> People always spoke of the sanctity of never cropping their pictures.
> People
> in Magnum even did that. But I suspect it was all about the precious thin
> black borders. A print in the stack with no black border stood out as weak.
>
>
> On 1/5/15 8:46 PM, "Ken Iisaka" <ken at iisaka.com> wrote:
>
> > Yes, Mark, been there done that.
> >
> > Also, when using shorter lenses, such as Zeiss Hologon, the actual
> exposed
> > area on the film was slightly larger than the actual aperture of the
> > shutter, since the rectangular aperture was a millimeter or two in front
> of
> > the film surface itself.
> >
> > On Mon, Jan 5, 2015 at 5:23 PM, Mark Rabiner <mark at rabinergroup.com>
> wrote:
> >
> >> Most people I knew in the 90's and before filed out their negative
> carriers
> >> of their enlargers so they'd both get black borders from the clear
> edges of
> >> the film before the sprocket holes; and also insure the people looking
> at
> >> it
> >> that not cropping had been done. We did this with our medium format
> negs as
> >> well. And our 4x5 sheet film. Full frame black borders. Soon at least
> the
> >> Omega company started making the neg carriers already wide enough so
> we'd
> >> not have to file them.
> >> On the paper we'd leave ample white borders. Minor White said if you
> don't
> >> leave am inch border you're print was not archival.
> >> So no your image size or magnification was not determined so much by
> paper
> >> shape. We printed the entire neg. if we were shooting with a Nikon F and
> >> other flagship cameras which gave us 100% viewing then we were seeing
> >> exactly what we'd be getting at the edge.
> >>
> >>
> >> On 1/5/15 6:06 PM, "Ken Iisaka" <ken at iisaka.com> wrote:
> >>
> >>> When comparing sensors with different aspect ratios, the use of the
> >>> diagonal to calculate the factor is overly simplified.
> >>>
> >>> With the diagonal measurement of roughly 21.6mm, the FourThirds sensor
> is
> >>> often said to have a crop factor of 2.0, compared to a "full frame"
> 35mm,
> >>> which has a diagonal measurement of 43mm. This implies that a 25mm lens
> >> on
> >>> FourThirds is thought to work like a 50mm lens on a "full frame" 35mm.
> >>>
> >>> But it's not quite that way.
> >>>
> >>> What you should be comparing is NOT the diagonal measurement of the
> >>> sensors, but the dimensions of the actual area of the sensor that will
> be
> >>> used for the final image.
> >>>
> >>> So, if you are creating an image with an aspect ratio of 4x5, you are
> not
> >>> using the full area of the sensor, but only a smaller area of 24x30mm,
> >> and
> >>> 13x16.25mm. When doing so, the "crop factor" is not 2.0, but is merely
> >>> 1.846. The different is not all that big, but is not insignificant
> >> either.
> >>> A 25mm lens on FourThirds works more like a 46mm lens, not 50mm. There
> >> are
> >>> some of us, who split hair between smaller than that.
> >>>
> >>> If you're creating an image with an aspect ratio of 5x7, the situation
> >>> changes. You'd be using an area of 24x33.6mm from a 35mm sensor, but
> >>> 12.38x17.33mm. Here, the effective "crop factor" is 1.9386.
> >>>
> >>> Want to make it more complicated? Sure, I can do that.
> >>>
> >>> We didn't really use the full 24x36mm area of the 35mm camera. The
> slide
> >>> mount or enlarger negative carrier usually cropped the image to 23x35mm
> >> or
> >>> so. So, if you are creating an aspect 4x5 image, the effective crop
> >> factor
> >>> was only about 23/13 = 1.77, since you only used an area that measures
> >>> 23x28.75 to create your image.
> >>>
> >>> So, a 12mm lens on FourThirds behaves more like a 21mm lens instead of
> a
> >>> 24mm on a 35mm film camera (12*1.77 = 21.24)
> >>>
> >>> With hidden complexities such as this, I find all the discussions about
> >> the
> >>> crop factor, etc. to be absolutely absurd. Sorry, Mark.
> >>>
> >>
> >>
> >>
> >>
> >> --
> >> Mark William Rabiner
> >> Photographer
> >> http://gallery.leica-users.org/v/lugalrabs/
> >>
> >>
> >>
> >> _______________________________________________
> >> Leica Users Group.
> >> See http://leica-users.org/mailman/listinfo/lug for more information
> >>
> >
> >
>
>
>
>
> --
> Mark William Rabiner
> Photographer
> http://gallery.leica-users.org/v/lugalrabs/
>
>
>
> _______________________________________________
> Leica Users Group.
> See http://leica-users.org/mailman/listinfo/lug for more information
>



-- 
Regards,

Sonny
http://sonc.com/look/
Natchitoches, Louisiana
1714
Oldest Permanent Settlement in the Louisiana Purchase

USA


In reply to: Message from ken at iisaka.com (Ken Iisaka) ([Leica] The myths of crop factor)
Message from mark at rabinergroup.com (Mark Rabiner) ([Leica] The myths of crop factor)