If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. |
|
|
Thread Tools | Display Modes |
#1
|
|||
|
|||
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 |
#2
|
|||
|
|||
Change in Enlarger Head Height corresponds to Change in Exposure Time, but by how much?
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 |
#3
|
|||
|
|||
Change in Enlarger Head Height corresponds to Change in Exposure Time, but by how much?
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 |
#4
|
|||
|
|||
Change in Enlarger Head Height corresponds to Change in Exposure Time, but by how much?
"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 |
#5
|
|||
|
|||
Change in Enlarger Head Height corresponds to Change in ExposureTime, but by how much?
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. |
#6
|
|||
|
|||
Change in Enlarger Head Height corresponds to Change in Exposure Time, but by how much?
"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 |
#7
|
|||
|
|||
Change in Enlarger Head Height corresponds to Change in Exposure Time, but by how much?
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 |
#8
|
|||
|
|||
Change in Enlarger Head Height corresponds to Change in Exposure Time, but by how much?
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 |
#9
|
|||
|
|||
Change in Enlarger Head Height corresponds to Change in Exposure Time, but by how much?
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 |
#10
|
|||
|
|||
Change in Enlarger Head Height corresponds to Change in Exposure Time, but by how much?
"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 |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
TRI-X development time | ATIPPETT | In The Darkroom | 2 | March 5th 04 02:39 PM |
Develper for Delta-100 | Frank Pittel | In The Darkroom | 8 | March 1st 04 04:36 PM |
Adjust B&W paper development time when using Uniroller? | Phil Glaser | In The Darkroom | 14 | January 26th 04 10:04 PM |
Exposure factors to change contrast on single colour enlarger wanted please? | Chris Wilkins | Film & Labs | 2 | October 16th 03 11:20 AM |