Subject: Gnomon & nodus distortion As several of you have mentioned, digital or optical photo perspective rectification works great on the sundial's face, but worsens the look of a gnomon or nodus.
There are two ways to minimize gnomon and nodus distortion. When taking your picture, stand due south of the dial's center so that your camara lens is in the N/S meridian plane. This way, you see the gnomon edge on. The object being to make it as small and unobtrusive as possible. (Or build your sundials with a thin monofilar cable gnomons!) Or, you can use one of the photo digital editing programs to remove the gnomon or nodus. After you erase the gnomon, you can digitally paint the face where the gnomon was attached (the substyle). Use the color match feature when painting. If I were to go this extra step on my Flandrau dial, I wouldn't erase the cable gnomon since it is so thin that distortion is unnoticible. But I would erase the nodus. Then I would copy and paste a little photo of a round nodus onto the cable gnomon at its proper position over the substyle, south of where it is now. And voila! A perfect photo of the dial face! John John L. Carmichael Jr. Sundial Sculptures 925 E. Foothills Dr. Tucson Arizona 85718 USA Tel: 520-696-1709 Email: [EMAIL PROTECTED] Website: <http://www.sundialsculptures.com> > ----- Original Message ----- > From: "Andrew James" <[EMAIL PROTECTED]> > To: <sundial@rrz.uni-koeln.de> > Sent: Wednesday, October 10, 2001 2:55 AM > Subject: RE: Sundial Trick Photography > > > > For vertical dials I would still rather stick with an SLR with a long lens > > (and a tripod!) because of the effects of perspective correction on the > > gnomon. > > Incidentally, the effect of a rising front / perspective correction lens > can > > be more or less equalled - at no cost except a smaller image - by > resolutely > > pointing the camera horizontally in front of your eye rather than tilting > it > > upwards. You need a wider angle lens from the same distance, or > > alternatively have to move further away; and then you need to enlarge the > > image more as it will include the wall up to the dial and lots of ground > > (half the picture). Moving further away helps with the gnomon distortion, > > too - looking at it not up its length. > > > > The perspective correction or shift lens (and the view/technical camera > > equivalent Super Angulons and the like) is very expensive because quite > > apart from the mechanics it has to produce good images a long way off the > > optical axis - which is what you are doing when you move it right up its > > travel to take the high sundial. > > > > While John's photo of his Flandrau dial well illustrates the correction of > > the lines, if you look at the nodus it appears to lie NNE of its shadow, > > whereas the sun was really somewhere in the SE at the time. That's meant > > with no disrespect to his adjustment of the view of the dial plane, it's > > just a fact of geometry. > > > > But it occurs to me that one big advantage of a digital camera in all this > > is that with an ordinary horizontal dial on a high pedestal (not so easy > > with a very big dial, I agree) you can hold the digital camera at arm's > > length vertically over the dial and press the shutter, immediately examine > > the results, and repeat until you're quite satisfied. You will get the > > proper edge-on view of the gnomon (though its top will appear bigger as > it's > > nearer the camera), whereas correcting perspective of a photo taken from > the > > side appears to fold the gnomon down away from you. When I try this > > overhead method with a film camera I often wait days or weeks to receive a > > skewed blurry print of half a dial or one of my own feet. > > > > Andrew James > > >
