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Recently I was thinking about the fact that getting longer exposure time results in less impact of the initial vibrations (because of turning on/off of the enlarger) on a print. So my idea is to dim the light as much as possible (by using for instance smaller aperture - but maintaining sharpness of the lens; increasing distance between paper and enlarger, probably by the use of longer lens; somehow utilizing ND filters - probably the most straightforward idea) and of course take into account reciprocity failure.

On the other hand it seems (according to few Youtube tutorials) that nobody opts for drastically long exposures. I conclude that my reasoning has some pitfalls that I'm not capable of noticing and I wonder if you could help me find them.

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Several comments on your idea:

  • in an ideal setup you should have zero initial vibrations - the timer and enlarger are connected only electronically. Your pressing of a switch (or foot pedal in some cases) should not have any impact. If it does stabilize your enlarger - a good idea is fixing your center column to the wall.
  • by setting too narrow aperture on your enlarger lens you are moving away from the sweet spot of maximal resolution (about f 8 for most enlarging lenses) towards dangerous diffraction territory.
  • too long exposure times make for unproductive darkroom sessions

Most printers that I know aim for basic exposure times of ten to thirty seconds. Anything shorter than five seconds is risky because of reciprocity failure and unreliable meters (especially badly calibrated mechanical ones).

If you want to do any dodging and burning basic exposure of 20 seconds is about right for an 8×10" paper.

Short enough that you manage to have something done over your session and long enough that you can move your dodging tool smoothly enough from place to place.

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Stopping down about 2 f-stops will likely deliver the highest acuity. Stopping down all the way will likely degrade due to the twin demons of interference and diffraction. I recommend composing with the lens wide-open and then stopping down 2 f-stops and then refocusing. The re-focus corrects focal length shift that likely occurred when you stopped down. Exposure time is based on a developing time of 60 thru 90 seconds. You can use ND filters to achieved or lamp aftermarket dimmer switch.

It is not likely that vibration will harm provided the enlarger is well mounted.

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