Originally Posted by
Brian Ellis
Layman's explanation (though I may not understand your question, in which case ignore this explanation):
Lens performance at different apertures is affected by lens aberrations as well as diffraction. The more you stop down the more lens aberrations tend to be improved. So the optimum aperture is one that strikes the best compromise between loss of image quality due to diffraction when stopping down and gains in image quality due to minimizing aberrations when stopping down.
Well stated.
The area around the cross over point is referred to as the Sweet Spot.
The Sweet Spot for 35mm is generally around f/8 to f/11.
The Sweet Spot for MF is generally around f/11 to f/16.
The Sweet Spot for 4x5 is generally around f/16 to f/22.
I used the term 'generally' to avoid bickering of this lens maker verus that lens maker.
Also see Ralph Lambrecht's book Way Beyond Monochrome, second edition, for more researched and scientific discussion of this subject. http://www.waybeyondmonochrome.com/WBM2/Welcome.html
For the Hasselblad lenses that I have, the Sweet Spot starts at full aperture and extends to f/22. That is much wider than I stated above. My experience with 4x5 albeit small has consistently shown the Sweet Spot is for f/16 to f/22 on some lenses and to f/32 on the longer focal lengths. My selection of 4x5 lenses is on the plebeian level rather than the level of many of the well established users here. My present goal is to learn to use the hand held 4x5s that I have and get familiar with the basic capabilities. Later, depending on use and interest I will buy better lenses and look to using them in a field camera. One step at a time, I have passed up opportunities to buy well priced monorail cameras because I fear that if I spread out too fast too soon, I will never use anything.
Steve
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