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Photo Forum / Film Photography / Darkroom / January 2007How much light fade-off of enlarger is reasonable.
i am not sure whether my fade-off is really a fade-off. the enlarger is an Omega D5XL, it's a color header enlarger which got a soften-box ( light multipler ) soften the light from bulb before pass them to lens. yesterday, i projected and focused a 8x8 inch image on the baseboard from a 6x6 negative, after removing the negative i tried to meter the light strength on the baseboard. i used a Sekonic 508 meter ( yes, it's not a enlarger meter, but i'd not get one ), to meter it's center/corners and found the corners get some fade-off, which is about 0.2ev-0.5ev less than the center. is it normal? - thanks. > i am not sure whether my fade-off is really a fade-off. the enlarger > is an Omega D5XL, it's a color header enlarger which got a soften-box ( [quoted text clipped - 10 lines] > - > thanks. Aside from your rather bizarre speech to typing syndrome-yes it is. Falling off for now. Best regards.  SignatureWould thou choose to meet a rat eating dragon, or a dragon, eating rat? The answer of: I am somewhere in the middle. "Me who is part taoist and part Christian". > > i am not sure whether my fade-off is really a fade-off. the enlarger > > is an Omega D5XL, it's a color header enlarger which got a soften-box ( [quoted text clipped - 12 lines] > > Aside from your rather bizarre speech to typing syndrome-yes it is. sorry, i am not a native speake :-) the below reply said it is bad but you said it is normal. which one is right? > Falling off for now. > Best regards. [quoted text clipped - 3 lines] > a dragon, eating rat? The answer of: I am somewhere > in the middle. "Me who is part taoist and part Christian". > center/corners and found the corners get some fade-off, > which is about 0.2ev-0.5ev less than the center. Is it normal? The 2 1/4 square carrier in a 4x5 enlarger? Down 0.2 to 0.5 EV center to corners. That is very bad, intolerable. Something is wrong some where. Bad even with 4x5 center to corner. Dan Steven Woody a ?crit : > i am not sure whether my fade-off is really a fade-off. the enlarger > is an Omega D5XL, it's a color header enlarger which got a soften-box ( [quoted text clipped - 10 lines] > - > thanks. Sensors are very sensible to the angle of the light that reaches them. With a wide angle, the same light intensity will appear much lower than it really is. So, if you did the measure while keeping the cell flat on the enlarger base, most of the difference could just come from this measure error. When measuring in the corners of the image, you have to turn the cell so it remains perpendicular to the light. Sensitive emulsions, like films and papers, are much less prone to this phenomenon and thus will not show so much difference. To put in evidence how much your enlarger is really affected by the light fall-off, then, just use plain paper, no negative in the carrier and adapt exposure to obtain a mid-grey. A hard paper grade will show the effect the most, the softer the less. Claudio Bonavolta http://www.bonavolta.ch >Sensitive emulsions, like films and papers, are much less prone to this >phenomenon and thus will not show so much difference. [quoted text clipped - 5 lines] >Claudio Bonavolta >http://www.bonavolta.ch And if you get really picky (who me ? !) take the print, hopefully a nice medium gray, to a lab and have them run a densitometer over it. Should take them about 30 seconds to map the corners and middle. You might also consider trying a different aperture. Some lenses cause more falloff than others. == John S. Douglas Photographer & Webmaster Legacy-photo.com - Xs750.net "Claudio Bonavolta" <claudio@bonavolta.ch> wrote Steven Woody a écrit : > > Omega D5XL, color head, projected and focused a 8x8 inch image > > 6x6 negative, Sekonic 508 meter corners get some fade-off > > 0.2ev-0.5ev less than the center. is it normal? It's not great, it's not terrible. FWIW: the intensity map of a Beseler 45 condenser, 150 Rodagon, f11, 4x5 carrier: 8.97 9.08 8.98 9.12 9.43 9.15 9.04 9.22 9.04 Numbers are DA EV's - in stops. Again, outstandingly mediocre. When you measure be sure to close down the lens - wide open any lens's fall off is bad. > > it's not a enlarger meter, but i'd not get one I know this guy, he can get them for you wholesale, straight from the factory. > Sensors are very sensible to the angle of the > light that reaches them. Depends on the sensor. Spotmeters tend read low off-axis... Spherical integrators don't have fall off, or sure aren't supposed to have fall-off. > So, if you did the measure while keeping the > cell flat on the enlarger base, most of the > difference could just come from this measure error. It depends what you are measuring. If it is light from a bulb then the sensor, if angle sensitive, should point to the source. If you are measuring the light as it will affect the paper the sensor needs to be in the same plane as the paper. So a flat detector laying just where the paper will be is the correct measuring instrument. There is often a slight light direction sensitivity, this is lessened if you measure with the sensor oriented radially. For most purposes it doesn't matter. > To put in evidence how much your enlarger is really affected by the > light fall-off, then, just use plain paper, no negative in the carrier > and adapt exposure to obtain a mid-grey. The best and cheapest test: if it looks OK, it's OK. SignatureNicholas O. Lindan, Cleveland, Ohio Darkroom Automation: F-Stop Timers, Enlarging Meters http://www.nolindan.com/da/index.htm n o lindan at ix dot netcom dot com > Steven Woody a écrit : > [quoted text clipped - 30 lines] > Claudio Bonavolta > http://www.bonavolta.ch thanks for your answer and advice. i will redo the test in this weekend according what you adviced and report the result back here. - woody >i am not sure whether my fade-off is really a fade-off. It is and it's common and it's bad. == John S. Douglas Photographer & Webmaster Legacy-photo.com - Xs750.net > i am not sure whether my fade-off is really a fade-off. the enlarger > is an Omega D5XL, it's a color header enlarger which got a soften-box ( > light multipler ) soften the light from bulb before pass them to lens. > yesterday, i projected and focused a 8x8 inch image on the baseboard > from a 6x6 negative, after removing the negative i tried to meter the > light strength on the baseboard. That's not the way to measure the outcome. Make a print with a clear negative with a mark in the center upon which to focus, with the lens wide open. Then at your typical stop (two down). Then judge. |
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