Archived posting to the Leica Users Group, 2004/04/15
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Martin, Since no one has replied to your question as we try to roll the rock up the hill I will give you a simple answer or at least a direction. First, you have to assume that the lens is the limiting factor. Using a good extremely fine grain film will net you in the area of 150 LPM. In 35mm the best lenses will resolve about 100 LPM. Therefore, the smallest thing on film that is identifiable will be in the region of 1/100 mm (it takes two to tango). The above assumes that the subject is in the plane of focus, otherwise, all bets are off. You can't really go into coc, atmospheric disturbance, lens aberrations affecting oof areas and lots of other options without experience with a specific lens at specific distances and specific lighting conditions. Personal experience tells me that with a 50mm lens (DR) at optimum aperture at infinity I can resolve hair at more than 500 yards on Velvia and high contrast lighting conditions. As to the satellite thing, think about wavelengths of light and their effect on resolution as well as really and I mean really long base sampling as in side scanning radar and you will get some comprehension of how the satellite boys and girls see the things that they see. I hope this helps. Don dorysrus@mindspring.com -----Original Message----- From: lug-bounces+dorysrus=mindspring.com@leica-users.org [mailto:lug-bounces+dorysrus=mindspring.com@leica-users.org] On Behalf Of Martin Krieger Sent: Thursday, April 15, 2004 10:02 AM To: lug@leica-users.org Subject: [Leica] On-film resolution (if it is X lp/mm, what size letters should I be able to read with a magnifier?) If I use a 22x magnifier to examine optically printed 4x6 prints, I can see the granularity fairly well. I'd like some guidance then: What is the size of the "granules" or grain-clumps on the film? If I use a 22x magnifier (or whatever you use), given that I can discern some letters or numbers, what minimum lp/mm might I conclude. Why do I want this. Some of my work is a survey of neighborhoods. If I want to be sure of the address of a place, I will try to discern its number from the image. Of course I am far enourgh away, so that the number is small on the negative. I need some idea of what kind of limits there are to this process, given reasonable demands on my holding the camera, etc. I might need only 20% (I don't know, maybe it is 40%) on the MTF to do the discernment, so this is not so demanding a task. If you know, please let me know. If you have an idea where I can find out, let me know where to go look. Obviously the spy satellite people have this down to a science. I just don't know where to look. Thank you, Martin Krieger krieger@usc.edu _______________________________________________ Leica Users Group. See http://leica-users.org/mailman/listinfo/lug for more information