Change in Enlarger Head Height corresponds to Change in Exposure Time, but by how much?

In article ,
"Alparslan" wrote:

Hi,
I am planning to make small B&W prints until I find my desired print and
than print it on a bigger scale. Is there a formula I can convert the
printing time for the new scale? It sounds logical to me that if I double
the height of the enlarger head I should double the exposure time. Is it
this simple? What if I additionally raise the enlarger head less (say 2/3)
than the previous height of the head? Regards



My experience tells me it doubles as you double the size, yet it is approximate.
In other words.....going from an 8x10 enlargement exposed at 10 seconds
to a 16x20 would give you an exposure time around 20-22 seconds at the same aperture.
One factor you may encounter is that a larger print seems to require a little more contrast
filteration than a smaller print to look the same......never the less that could be deemed
subjective. If that is the case it may make the exposure a little different towards the plus side.
--
LF Website @ http://members.verizon.net/~gregoryblank

"To announce that there must be no criticism of the President,
or that we are to stand by the President, right or wrong,
is not only unpatriotic and servile, but is morally treasonable
to the American public."--Theodore Roosevelt, May 7, 1918

I don't have the formula handy right now but it's not quite double the size
double the time. BTW it's much more direct to measure image size on the
baseboard or easel than to measure the height of the enlarger head for such
changes. I have an old slide rule that GraLab used to sell that calculates
such things easily but it's probably easier still to get an Ilford EM-10
($20 US) and calculate exposures. Since what you meter affects your results
I always pull my carrier and measure the intensity of the raw light on the
baseboard and "null" the meter using the aperture ring exposure time is then
constant.

--
darkroommike

----------
"Alparslan" wrote in message
...
Hi,
I am planning to make small B&W prints until I find my desired print and
than print it on a bigger scale. Is there a formula I can convert the
printing time for the new scale? It sounds logical to me that if I double
the height of the enlarger head I should double the exposure time. Is it
this simple? What if I additionally raise the enlarger head less (say 2/3)
than the previous height of the head? Regards

Hi,
I am planning to make small B&W prints until I find my desired print and
than print it on a bigger scale. Is there a formula I can convert the
printing time for the new scale? It sounds logical to me that if I double
the height of the enlarger head I should double the exposure time. Is it
this simple? What if I additionally raise the enlarger head less (say 2/3)
than the previous height of the head? Regards

"Craig Schroeder" wrote in message
news
Try this....

http://www.chibardun.net/~craigclu/enlargecalc.xls

I did this some time back and believe it is accurate.

Assuming that what you call "original and new positions" are the distances
from lens stage to baseboard, I believe the formula in cell "B7" is not
quite correct, I think it should be just B6*((B4)/(B3))^2 But then
again, I've been found confused and incorrect a number of times!!. Care to
explain how formula in cell "B7" came about?

If you were dealing with magnifications instead of distances to baseboard,
then, to find the exposure time factor, you would add 1 to each
magnification before dividing them and squaring them: exposure factor =
[(M+1)/(m+1)]^2

Guillermo

Alparslan wrote:
Hi,
I am planning to make small B&W prints until I find my desired print and
than print it on a bigger scale. Is there a formula I can convert the
printing time for the new scale? It sounds logical to me that if I double
the height of the enlarger head I should double the exposure time. Is it
this simple? What if I additionally raise the enlarger head less (say 2/3)
than the previous height of the head? Regards



Doubling the enlarger height will double the print dimensions, spreading
your light over four times the area -- so you'll need to increase
exposure by two stops. You can do that by opening the lens two stops,
if you were already stopped down beyond optimal to get a longer
exposure, but more likely you'll have to add time -- which means you'll
also have to account for reciprocity failure, and will need somewhat
more than four times the exposure time at the same aperture. How much
more than 4x? Depends on the paper; it's been twenty-five years since
I've done much printing, and in those days it would have been about
double the 4x figure. Modern papers may have less effect -- but bottom
line is you'll have to test the paper you're using, but once you have a
ratio between (say) a 4x6 print and an 8x12, it should remain pretty
constant (though a denser negative may require still more additional
time on the larger print, again because of reciprocity failure).

--
I may be a scwewy wabbit, but I'm not going to Alcatwaz!
-- E. J. Fudd, 1954

Donald Qualls, aka The Silent Observer
Lathe Building Pages http://silent1.home.netcom.com/HomebuiltLathe.htm
Speedway 7x12 Lathe Pages http://silent1.home.netcom.com/my7x12.htm

Opinions expressed are my own -- take them for what they're worth
and don't expect them to be perfect.

"Dan Quinn" wrote in message
om...
"Mike King" wrote

"...not quite double..." The lens becomes faster as enlargement size
increases. I think the area method one I'd go with. Dan

I think the opposite is true, the lens becomes slower as enlargement size
increases.

Guillermo

In article m,
"f/256" wrote:

"Dan Quinn" wrote in message
om...
"Mike King" wrote

"...not quite double..." The lens becomes faster as enlargement size
increases. I think the area method one I'd go with. Dan

I think the opposite is true, the lens becomes slower as enlargement size
increases.

Guillermo

I think your both wrong,....b ut - Tu' es mas correctamundo ;-). The slowing is more
likely reciprocity,......or the need for a greater degree of filteration.
--
LF Website @ http://members.verizon.net/~gregoryblank

"To announce that there must be no criticism of the President,
or that we are to stand by the President, right or wrong,
is not only unpatriotic and servile, but is morally treasonable
to the American public."--Theodore Roosevelt, May 7, 1918

In article m,
"f/256" wrote:

"Dan Quinn" wrote in message
om...
"Mike King" wrote

"...not quite double..." The lens becomes faster as enlargement size
increases. I think the area method one I'd go with. Dan

I think the opposite is true, the lens becomes slower as enlargement size
increases.

Guillermo

I think your both wrong,....b ut - Tu' es mas correctamundo ;-). The slowing is more
likely reciprocity,......or the need for a greater degree of filteration.
--
LF Website @ http://members.verizon.net/~gregoryblank

"To announce that there must be no criticism of the President,
or that we are to stand by the President, right or wrong,
is not only unpatriotic and servile, but is morally treasonable
to the American public."--Theodore Roosevelt, May 7, 1918

In article m,
"f/256" wrote:

"Dan Quinn" wrote in message
om...
"Mike King" wrote

"...not quite double..." The lens becomes faster as enlargement size
increases. I think the area method one I'd go with. Dan

I think the opposite is true, the lens becomes slower as enlargement size
increases.

Guillermo

I think your both wrong,....b ut - Tu' es mas correctamundo ;-). The slowing is more
likely reciprocity,......or the need for a greater degree of filteration.
--
LF Website @ http://members.verizon.net/~gregoryblank

"To announce that there must be no criticism of the President,
or that we are to stand by the President, right or wrong,
is not only unpatriotic and servile, but is morally treasonable
to the American public."--Theodore Roosevelt, May 7, 1918

"Gregory W Blank" wrote in message
...
In article m,
"f/256" wrote:

I think your both wrong,....b ut - Tu' es mas correctamundo ;-). The
slowing is more
likely reciprocity,......or the need for a greater degree of filteration.

Gregorio, me think tu no es correctamundo :-)

Reciprocity does not affect the speed of a lens (where speed is expressed in
f/stops), reciprocity does affect how long you have to expose the emulsion,
though.

The lens "slows" down as the enlargement increases because the effective
focal length of the lens increases directly proportional with the
enlargement/magnification (actually proportional to the infinity focal
length of the lens multiplied by the sum of the magnification plus 1), so if
you increase the enlargement/magnification you then have a larger distance
lens to image (baseboard) but you still have the same lens diaphragm
aperture diameter, consequently, the numeric value of the lens' effective
f/stop would be greater (f/stop = distance lens to baseboard divided by the
diameter of the aperture, assuming a thin lens, for the sake of simplicity),
the greater the numeric value of the f/stop the slower a lens is. The
lens "slows" down as the enlargement increases and that may or may not cause
the exposure time fall into the realm of reciprocity. The above is not
different than what happens when you use bellows extensions greater than the
focal length of the lens. Comprende compadre Gregorio?

Guillermo