Archived posting to the Leica Users Group, 2015/11/18
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]I agree, Nathan. The sharpness issue is not terribly important to me either. It?s just that I was immediately struck by how unsharp the IR images were, and puzzled, because they were done at best focus as determined by trial and error. It?s become a brain-stimulation issue, as Frank said. For me, with a long background in astronomy and an interest in light and optics (as well as photography) from childhood, it?s a neat little problem in physical optics. But that doesn?t stop me from loving the dramatic landscape alteration of IR imaging! ?howard > On Nov 18, 2015, at 1:13 AM, Nathan Wajsman <photo at frozenlight.eu> > wrote: > > Howard, a couple of things: > > - George suggested a procedure for testing sharpness with the camera on > tripod etc. to determine the focus compensation needed. If you really > worry about sharpness, then do what he suggested. > > But? > > - for me, IR photography is less about sharpness and more about tonality > and the special IR effect. In fact, I do not even bother with the focus > compensation. When I shoot IR, I just focus normally. Most of the time, > the subjects are anyway far enough away that precise focus does not matter > that much. > > And finally, do not bother shooting IR on a cloudy autumn day. You need > plenty of sunshine for good IR. Although the pictures you posted earlier > very nice. > > Cheers, > Nathan > > Nathan Wajsman > Alicante, Spain > http://www.frozenlight.eu <http://www.frozenlight.eu/> > http:// <http://www.greatpix.eu/>www.greatpix.eu > PICTURE OF THE WEEK: http://www.fotocycle.dk/paws > <http://www.fotocycle.dk/paws>Blog: http://nathansmusings.wordpress.com/ > <http://nathansmusings.wordpress.com/> > Cycling: http://www.crazyguyonabike.com/belgiangator > <http://www.crazyguyonabike.com/belgiangator> > YNWA > > > > > > > > > > > > > >> On 17 Nov 2015, at 22:33, Howard Ritter <hlritter at bex.net> wrote: >> >> More experimenting. >> >> Today I took some photos with the M8 and Elmarit-M 24/2.8 both with and >> without the IR filter because I was unhappy with what appeared to be very >> soft focus in the IR photos from yesterday. >> >> The first thing I found is that with the B+W 093 (830 nm) filter, an >> exposure compensation of about 5 stops is needed. When the subject is >> predominantly cloudy sky, it?s more like 8 stops, clouds, like blue sky, >> apparently being relatively IR ?cool". >> >> The second thing I found is that the sharpness of the images taken >> through the IR filter really is dismal. Here?s a small crop of the frame >> with the IR filter: >> >> http://gallery.leica-users.org/v/hlritter/For+Gallery/43+IR+tree+crop.jpg.html >> >> <http://gallery.leica-users.org/v/hlritter/For+Gallery/43+IR+tree+crop.jpg.html> >> >> And without the filter: >> >> http://gallery.leica-users.org/v/hlritter/For+Gallery/47+IR+tree+crop.jpg.html >> >> <http://gallery.leica-users.org/v/hlritter/For+Gallery/47+IR+tree+crop.jpg.html> >> >> >> Aperture was f/2.8 for both. Focus was compensated (f/5.6 mark) for the >> IR. >> >> Any thoughts on the dramatic difference in sharpness between the two? >> Given that the filter is a genuine B+W from B&H, I?m thinking it?s not >> because of lousy glass. The only other thing I can think of is that the >> lens might not be achromatic for the full range of IR wavelengths passed >> by the filter and detected by the sensor, so that in wavelengths >> progressively further from the one that?s exactly focused, their >> contribution to the image is progressively further out of focus. >> >> >> ?howard >> >> _______________________________________________ >> Leica Users Group. >> See http://leica-users.org/mailman/listinfo/lug for more information > > > _______________________________________________ > Leica Users Group. > See http://leica-users.org/mailman/listinfo/lug for more information