RE: continued solarplate notes
I see. Indeed UV levels increase with elevation (because of thinner atmosphere on top) but fractionally and most importantly you're located 320 miles (~ 5 degrees) North of Istanbul... I checked the UV in Montana (Bozeman) and it was less than we had in Istanbul in the same conditions (= open weather. Bozeman was 3, Istanbul was 4.5). Snow/ice reflect UV quite strongly (along with water/sand) that's why you get skin burns in the winter (or at the beach even if you're under a parasol). See: http://en.wikipedia.org/wiki/UV_index It says "...The numbers are directly related to the amount of UV radiation reaching the surface of the earth, measured in W/m2...". Therefore - in my understanding - this should give a person the make quite accurate exposure time predictions under sun (after some testing and evaluating of the results). Of course, if you have a UV light integrator than you should be able to make very accurate exposure under sun. (Apart the fact that there may be slight contrast variations depending on direct / indirect exposure and scattering on air. Not that I tested this; just transferring you what I've read on this subject before...) BTW, see this page for info how UV Index is calculated: http://www.epa.gov/sunwise/uvcalc.html Regards, Loris. -----Original Message----- From: Christina Z. Anderson [mailto:zphoto@montana.net] Sent: Friday, April 13, 2007 6:08 PM To: alt-photo-process-l@usask.ca Subject: Re: continued solarplate notes Loris, I never thanked you for this message.... I know that the worst sunburn I ever had was in MT. I forgot to put sunscreen on the tops of my legs and went for a 4 hr bikeride in shorts. Wow. Sun here is incredibly strong with the thin air, but I do not know when that begins. Our rule of thumb is sunburn outside skiing begins on Feb 1 but before that time if you aren't wearing sunscreen you're pretty OK. Here is a UV light meter: http://www.safesun.com/ Do you or anyone think this is an accurate device that could give relative indications of outdoor UV light for photographic purposes? Or is there a more accurate photographic one for outdoors use? Chris ----- Original Message ----- From: "Loris Medici" <mail@loris.medici.name> To: <alt-photo-process-l@usask.ca> Sent: Monday, April 09, 2007 3:54 AM Subject: RE: continued solarplate notes > Hi Christina, > > It depends on time (UV level peaks between 11:00AM and 01:00PM), > season / weather and how north and south you're located... > > Currently the UV index here in Istanbul is around 4.5 at max. -> it > can go up to 11 in mid-summer (see http://www.enka.com/weather/ - this > particular station is located 200 yards away of my house). I guess UV > index doesn't go above 3-4 right now in Montana; this is pretty weak. > A definite test can be made by using a light integrator. > > Regards, > Loris. > > -----Original Message----- > From: Christina Z. Anderson [mailto:zphoto@montana.net] > Sent: Monday, April 09, 2007 5:44 AM > To: alt-photo-process-l@usask.ca > Subject: Re: continued solarplate notes > > ... > > Considering that Mike Ware says the sun is several times more powerful > than UVBL (anyone know the exact comparison?) this is enough proof to > me that > > there is a quite wide range of acceptable exposure and that the ratio > is > > where it's at. > > ... > >
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