Strange texture on the bokeh
in [35mm]
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From: Paul Furman on 28 Jun 2007 22:45 I was playing with getting the biggest OOF circles I could get out of my 'new' old 135mm f/2 lens and noticed an odd effect which I cannot explain: <http://www.edgehill.net/1/?SC=go.php&DIR=California/Bay-Area/San-Francisco/gritty/2007-06-28-traffic&PG=1&PIC=3> -click for enlargements and the following shot is the same uncropped scene simply cranked further out of focus. Any guess where the moon craters are coming from? 1) grime on the lens elements 2) grime on my car windshield Any guess what would cause that banding/striping? -- Paul Furman Photography http://www.edgehill.net/1 Bay Natives Nursery http://www.baynatives.com
From: Colin_D on 28 Jun 2007 23:08 Paul Furman wrote: > I was playing with getting the biggest OOF circles I could get out of my > 'new' old 135mm f/2 lens and noticed an odd effect which I cannot explain: > > <http://www.edgehill.net/1/?SC=go.php&DIR=California/Bay-Area/San-Francisco/gritty/2007-06-28-traffic&PG=1&PIC=3> > > -click for enlargements and the following shot is the same uncropped > scene simply cranked further out of focus. > > Any guess where the moon craters are coming from? > 1) grime on the lens elements > 2) grime on my car windshield > > Any guess what would cause that banding/striping? > Have you cleaned your sensor at all? It looks to me like cleaning streaks on the AA filter, plus the odd piece of dirt. Colin D. -- Posted via a free Usenet account from http://www.teranews.com
From: contaxman on 28 Jun 2007 23:10 Paul Furman wrote: > I was playing with getting the biggest OOF circles I could get out of my > 'new' old 135mm f/2 lens and noticed an odd effect which I cannot explain: > > <http://www.edgehill.net/1/?SC=go.php&DIR=California/Bay-Area/San-Francisco/gritty/2007-06-28-traffic&PG=1&PIC=3> > -click for enlargements and the following shot is the same uncropped > scene simply cranked further out of focus. > > Any guess where the moon craters are coming from? > 1) grime on the lens elements > 2) grime on my car windshield > > Any guess what would cause that banding/striping? > > -- > Paul Furman Photography > http://www.edgehill.net/1 > Bay Natives Nursery > http://www.baynatives.com Can you redo the shot, this time without the car windshield (to eliminate at least one possible cause/factor). Could even be some kind of weird reflection off the digi sensor in your camera. At least try the same shot (with or without the windshield with different lenses' bokeh to see if this is a lens specific phenomena. Looks like multiple Jupiters or Saturn without the rings (or the moons ;-)). The "moon craters"/"dimples" look likelens imperfections either in the lens glass itself or in the lens' coating (fungus, mold?) but I could be completely wrong on this since this is only a geuss of mine not a scientific assessment.
From: Nicholas O. Lindan on 28 Jun 2007 23:30 "Paul Furman" <paul-@-edgehill.net> wrote > <http://www.edgehill.net/1/?SC=go.php&DIR=California/Bay-Area/San-Francisco/gritty/2007-06-28-traffic&PG=1&PIC=3> > Any guess what would cause that banding/striping? > 1) grime on the lens elements > 2) grime on my car windshield When you focus close you are in fact focusing on [close to] the car windshield Your light source is a point - it is going to produce a detailed shadow-gram and diffraction pattern of everything that is between the lens and the point source. My guess: o A refractive pattern from molding or cooling when the windsheild was made. Possibly from the slab of glass from which the lens elements were cut. o When you focus close to get the bokeh you are in fact focusing on or close to the windshield. Could be streak marks from cleaning. o A diffraction pattern, possibly due to the geometry of the 'almost a point source' reflecting surface? Diffraction patterns get to be a bother if the source is monochromatic or a point source. o Space aliens -- Nicholas O. Lindan, Cleveland, Ohio Darkroom Automation: F-Stop Timers, Enlarging Meters http://www.darkroomautomation.com/index.htm n o lindan at ix dot netcom dot com
From: Roger N. Clark (change username to rnclark) on 28 Jun 2007 23:43
Paul Furman wrote: > I was playing with getting the biggest OOF circles I could get out of my > 'new' old 135mm f/2 lens and noticed an odd effect which I cannot explain: > > <http://www.edgehill.net/1/?SC=go.php&DIR=California/Bay-Area/San-Francisco/gritty/2007-06-28-traffic&PG=1&PIC=3> > > -click for enlargements and the following shot is the same uncropped > scene simply cranked further out of focus. > > Any guess where the moon craters are coming from? > 1) grime on the lens elements > 2) grime on my car windshield > > Any guess what would cause that banding/striping? > Your lens is out of focus, so any lens imperfections would be very out of focus too. The small spots appear to be dust on the sensor. If you look closely at the banding, you'll notice the bands cross over the out of focus light circles. That proves it is not the lens. The banding is independent of the position of the bright circles, so it must be near the focal plane. To test the focal plane issues: image in focus the clear blue sky at f/22. I bet you see the same spots and banding. Another test would be to move the lens on the other side of focus (e.g. a close bright spot). Lens imperfections are almost always different inside versus outside of focus. Roger |