Need a new grain focuser...

[ic-racer]

The advantage (to me) of the Peak is the ability to see the edges.

The two case that come up most frequently for me are:
1) Negative curvature. The peak allows one to get the focus spread on the baseboard, from center to edge. I always try to use a non-glass carrier if I can get away with it.
2) Flatness of field. When using a glass carrier, you really can tell the magnification for which an enlarging lens is optimized by observing the focus spread from center-to-edge at various magnifications. For example my 300mm Rodenstock does not have (nor is claimed to have) a flat field at 1:1.

 

[dancqu]

Dan I'm not familiar with the term 'diameter',
but I assume it simply means 'times'?

The diameter is the standard unit of measure
when speaking of magnification. A four diameter
enlargement is twice the size of a two diameter
enlargement. All things being equal.

An example; I've enlarged the negative by
five diameters. Dan

 

[RalphLambrecht]

The diameter is the standard unit of measure
when speaking of magnification. A four diameter
enlargement is twice the size of a two diameter
enlargement. All things being equal.

An example; I've enlarged the negative by
five diameters. Dan

I never heard of that, but thanks. I must get out of that darkroom more often! Last time I came out, they had invented color photography. What will they come up with next? Who knows, someone might try to get rid of film altogether.

Of course you're right. I found it in the dictionary.


diameter |dīˈamitər| (abbr.: diam.)
noun
1 a straight line passing from side to side through the center of a body or figure, esp. a circle or sphere.
• the length of this line.
• a transverse measurement of something; width or thickness.
2 a unit of linear measurement of magnifying power.
DERIVATIVES
diametral |-trəl| |daɪˈømətrəl| adjective
ORIGIN late Middle English : from Old French diametre, via Latin from Greek diametros (grammē) ‘(line) measuring across,’ from dia ‘across’ + metron ‘measure.’