Mamiya C330f Professional Reparaturanleitung PDF herunterladen (Seite 36)

Mamiya TLR Summary 36

9.5 Maxwell screens

Alternative screens can be obtained from Maxwell Precision Optics, (404) 244-0095 (United States of America).

9.6 Long roll Mamiyaflexes

At least two of these are known to exist. They consist of a large film magazine to hold 70mm (?) film mated to a Mamiya TLR body.

The lens in both examples was a 135mm, and one had a self-cocking shutter installed. The film is motor-driven through the camera.

These appear to be non-commercial conversions. The nearest similar equipment would be the Hulcher cameras and some of the

military bomb-bay cameras. These could take 100 feet of film and expose at around 8-10 frames per second. About 480 frames in

under one minute. The Mamiya conversions would appear to be similar. The TLR design would be a good choice – most of the

advantages of a single lens reflex, but no mirror to move.

9.7 Sekonic L-208 light meter mounting

This is a nice item about mounting the basic Sekonic L-208 lightmeter to a Mamiya TLR using the meter’s supplied flash shoe foot.

The article at http://silvergrain.org/Photo-Tech/TLR-meter.html also discusses the Gossen Digisix and Cosina VC meters.

10 Data Tables

10.0 Introduction

Note that you will require a browser with table-handling capabilities to make much sense of this section. The general Depth of Field

tables have been calculated with a circle of confusion of 0.04578mm. This is the 1/1730 of the format diagonal as used by Sinar,

amongst others. It is slightly smaller than the common 0.06 or 0.075 mm value. The close-up tables have been calculated to the finer

tolerance of 0.0254mm.

In the Depth of Field Tables, 'Infinity' was calculated at 2,200 feet. This somewhat arbitrary figure was dictated by the 250mm lens.

The total depth of field section of each table reports infinity where the further limit is undefined. No correction for nodal position has

been attempted, so these tables should be verified by experiment before undertaking critical work.

Depth forward of plane of focus =

c x A x s x (s - f)

_______________________

f x f + c x A x (s - f)

Depth behind plane of focus =

c x A x s x (s - f)

_______________________

f x f - c x A x (s - f)

where c is the circle of confusion, A is the aperture stop, f is the focal length, s is the subject distance.

For a complete description of this formula, see the page on http://oh114.wpi.edu/~nsushkin/dof.html”Depth of Field Calculation by

Nicholas Sushkin. There are alternative formulae available, however at present these tables seem sufficiently accurate for practical

work, given the limited precision of the camera focus scales. These formulae do not appear to take diffraction into account.

Diffraction has the effect of increasing the Circle of Confusion at small physical apertures, and reducing effective depth of field. Note

that the Close-up Tables are taken from the reference cited, and are (probably) not obtained using these formulae.

[Compiler's Note: The tables are in Feet and Inches for purely selfish reasons - that's how my camera is calibrated!

For those who prefer something less cumbersome than tables, I have produced a program that draws a Depth of Field Calculator

(calc1.ps) using the formulae given above. The prototype looks promising. It takes the form of a double-sided dial calculator with the

three widest lenses on one side, and the four longer lenses on the other. It is produced using a PostScript program with either a

PostScript printer or a suitable interpreter and printer combination, and the images stuck to card or plastic discs. It is 12cm in

diameter (Compact Disc size), which is a compromise between resolution and compactness. And yes, it can be modified for any focal

length and circle of confusion, within reason. An alternative version of the calc1.pdf in PDF is also available.

For an alternative depth of field calculator that uses 0.06mm circle of confusion for 6x6, see the

http://people.smu.edu/rmonagha/mf/brondof.html Javascript DOF calculator on the Bronica pages.

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