Dave, good synopsis of how many of us proceed thru image focusing.
Once, I'm not trying to argue about you're comments but I'd like, out of curiosity, to know what your focusing procedure is. Can you describe how you go about it.
Nate Potter, Austin TX.
Dave,
Thanks for restating what I said. You did a much better job of it than I did.
Let me add a couple of other comments.
If your eye is roughly at 6 inches when looking at a 4 x 5 ground glass image or at 8 inches when viewing a 5 x 7 image, what is recorded on your retina will be the essentially same as when you view an 8 x 10 print from 12 inches. That is just simple optics. But, I don't mean to claim that someone can't do good photography if his eye is not at the `correct' point.. The human visual system is good at correcting for such things. It is called size constancy; Smaller objects interpreted as being in the distance look larger .It works very well when looking at the actual scene, and it still works somewhat when looking at a print of the scene, even if there is a shift in point of view, provided it isn't too great.. After all, we can still make sense of a 4 x 5 contact print viewed from 12 inches, although we might have trouble with a 6 x 6 mm contact print and we certainly would have trouble with a 24 x 36 mm contact print if both were viewed from 12 inches.
So whether or not it is worth worrying about this is a personal matter. Many people are so used to evaluating the scene from 12 inches that they automatically make the necessary compensations. I find I do better by looking at 6 inches. As it happens, using the near point far point method to focus, that also provides enough magnification for me to focus accurately, so I seldom need to use a loupe.
Another related, but different, point came up. For what you see on the ground glass, or in a print, to correspond to what you see looking directly at the scene, again by simple optics, the focal length of the lens should also be the diagonal of the format. This fact explains the common `distortions' which result from using short focal length and long focal length lenses. For example, if a 4 x 5 picture is taken with a 75 mm lens and one views a resulting 8 x 10 print from about 12 inches, objects in the distance will look further away and smaller. In addition, a spherical object at the edge will appear to be stretched out into an ellipsoid. If you want to restore proper perspective you should view the 8 x 10 print from 6 inches. ( Of course an adult with normal vision won't be able to do that without a magnifier, but a myope without his glasses may be able to do it.) Then everything will look much more `normal'. Similarly, if the picture was taken with a 300 mm lens, distances will appear compressed. If you get back to 24 inches, things will look more normal.
It should be noted on the other hand that often this is a feature rather than a problem. When using a wide angle lens or long lens, we expect these things to happen and we use them aesthetically by causing the viewer to see the scene differently. So I am certainly NOT arguing that one should adjust the viewing distance to the print to match the focal length of the lens. Just that knowing about this will help you understand what happens.
Nate, the original discussion I was involved in was about the "evaluating the scene" as Leonard called it, on a gg, not image focusing.Originally Posted by Nathan Potter
The advice Leonard gives, to evaluate the scene, is to look at the gg in a way people with a normal vision cannot use. Just say to somebody with a normal vision to look at the gg of his roll film back 6x9 format from 4in of the distance and insist that it is the normal correct way of doing so, to "evaluate the scene"... If they look at you with a question mark in their eyes start to tell them that your sister/daughter/friend with a severe eye handicap can do so from just 3 inches... You got the point.
A totally different point, I did not discuss, is the focusing procedure. I use 8x Schneider Lupe - the same I inspect my slides with. Works well for me. My vision is normal, good, no eye glasses. Totally irrelevant to the discussed point of "evaluating the scene" on a gg.
No, it's not, Leonard. A normal seeing adult person cannot focus at the gg from a 6in distance. What would be recorded on your retina would be a fuzzy, non sharp, painful image. Is it really so difficult for you to understand the basics of human vision? Or do you want to continue to force people's eyes to work in a way they cannot without special optical device?
Look, this is getting annoying. You pull out of context quotes from what I said. I don't know if you do that because you can't read or because you intend to mislead. Please stop claiming I've said things that I didn't say.
Let me say it once again. Most adults with normal vision can't view the ground glass from closer than about 10-12 inches without aids. Due to personal experience, I've learned quite a lot about human vision, normal and abnormal. I believe I understand how it works pretty well. I've repeatedly said in what I posted that such people would need magnification provided by a simple magnifier or perhaps reading glasses of the right strength to view the ground glass closer than the normal near distance.. I also explained the reasons for choosing to view from such close distances, but I certainly don't believe everyone must do it, just because I said it. People can decide for themselves whether or not to try it.
Finally let me also say once again that the reason I brought this up in the first place is that the original post described someone who, from what he said, is clearly nearsighted in one eye, and I was trying to respond to him. He may very well be able to view a 5 x 7 screen from 8 inches without an aid. There is no way to tell how close he can get without knowing how much myopia and presbyopia he has.. But he will certainly be able to tell, and he can decide what to do.
I won't say any more on the subject, but I'm sure you will arrange to have the last word, whatever it may be.
Yes Leonard, believe me, it is equally annoying for me too (at least something we can agree about
Take it for a normal fact, that you cannot advice something as a normal procedure that should be done (evaluating the scene) when you need a magnifying hood (that's what you speak about, in fact) for that. That is a special procedure, not a requirement for a normal setup.
The fact that after being pushed like a mull you agree that people would need a magnifying device to follow your "normal" scene evaluation says that you finally got it. After all the stories of people with eye handicaps that don't need the device 'cause....
And yet we didn't speak about other nonsense that you spread with your posts - like not being possible to focus at something far away more that 1500 focal lengths etc. I just don't take whatever you come with.
The last word? I'm sure we will get yet another of your inventions soon...
Did I mention that using a 4X loupe on the ground glass that I can see a fly relieving itself out to 500 yards?
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