q@a

mysteryscribe · Jul 5, 2006

Someone else brought up the moving object in relation to lense choices
i was just commenting got off base there sorry. I plead guilty to being sidetracked it has nothing to do with the basic question at all.

It's a sure sign of advanced age to get side tracked. But you have to admit this is more fun than, "should I buy a nikon or a canon?"

RoRoCo · Jul 5, 2006

Theoretically speaking of course...Could there be an instance where too small of a fstop could actually distort the light hitting the sensor? Light is subject to gravitational pulls. And although the pull of the shutter is very small, when you get to such a small opening, wouldn't this pull cause some distortion?

Torus34 · Jul 5, 2006

1. Lenses change somewhat in sharpness depending on the aperture. As with telescope mirror objectives [which I make from time to time], there is the possibility of a turned-down edge on any of the lens surfaces. The old rule of thumb is that a lens is usually at it's best 2 stops down from the maximum aperture.

2. The mention of a black background suggests the possibility of some diffraction effects at a very small aperture. f128 should probably not be on the short list of exposure combinations.

Unimaxium · Jul 5, 2006

mysteryscribe said:
This may not be absolutely correct so let's hear others comment on it please

but the answer to the basic question on film is yes but nobody could ever tell.

The reason you dont need a lens in a pin hole camera is because of the properties of light. With every lens it focuses the light beans but it still makes a difference how they strike the film.

Think of it like this. light travels in a straight line and is a beam. Let us consider a paper straw since it is the easiest thing to work with. If you stand a straw on its end on a piece of paper it will have a small round footprint on the paper. However if you were to force the straw to lean at a forty-five degree angle it would hitting the paper at an eliptical pattern not a circle. In other words a larger footprint. The smaller the footprint the sharper the picture. The smaller the aperture the straighter the beam hits the film or sensor. Thats what really makes depth of field.

So in theory the smaller the fstop the sharper the picture... that said I have no idea if that is true in digital since the sensor is not like a piece of film. A sensor, I think, is actually a lot of sensors tied together. It reads in dots not straight lines. So I have no idea if this is true with a sensor or not. Im sure someone here knows.

Im not sure i explained it very well some of the ohters can most likely do better. I am also not up on lenses but it is understanding that to a more or lesser degree this holds true with all lenses.

Again I doubt that anyone in the world could tell the difference between a couple of stops. Or maybe even the full bore but I know my still life camera is f90 and it is a lot sharper than it was at f32... AGain it is film and has a retro lens...

I see where you're coming from with this, but what you just described was what happens when a point is out of focus in the image. You stated previously that the lens we're working with has perfect optics. Since the optics are perfect, and we have nothing out of focus in the image, all points of light converge exactly at the film plane, meaning that they are zero-dimensional points at that spot. Thus, we are not working with hollow straws but rather one-dimensional lines as they pass through the lens. And when the line intersects the plane, it can only form a single point, not a circle or an ellipse. So I still believe that there is no difference between the apertures when working with this theoretical perfect lens. :greenpbl:

mysteryscribe · Jul 5, 2006

Any and all of you may be right. I really have no idea, but I am curious. I'm going to do some heavy reading just to see....

I STAND CORRECTED... I HAVE BEEN LABORING UNDER A FALSE IMPRESSION I FULLY ADMIT I WAS WRONG/ MIA COPA.....

Even so it was a discussion worth having

mysteryscribe · Jul 5, 2006

There may be something here that is interesting in a historical sense. It not a factual point.

quote from clive russ on lenses

[FONT=Arial, Helvetica, sans-serif]Soft Focus lenses all become sharper as they are closed down to smaller apertures. Most of them are actually quite sharp from about f-11 on (the iris diameter gets smaller ) and as the aperture is closed further,(smaller than the diameter at which maximum sharpness is acheived) the image deteriorates as the aberrations increase, but the image looks more clear because the depth of field increases. All lenses have aberrations as they are closed down, and that includes sharp high quality lenses.[/FONT]

I'm wondering now if the maxim, smaller is sharper, wasn't meant for the more retro lenses that I use now. Since the quality of glass has gotten so much better than it was when max f was 11 or smaller. interesting idea since the f64 club was meant for photograpers who shot very sharp images.

It might have been a necessity since the glass was a poorer quality and the glass in my stuido camera is from about that period. Also curious was about that time the popularity of the soft dreamy shots was being replaced by realism. Don't get me wrong there are some very sharp images from the mid eighteen hundreds but the hollywood glamour shot was very popular in the thirties.

Unimaxium · Jul 5, 2006

mysteryscribe said:
There may be something here that is interesting in a historical sense. It not a factual point.

quote from clive russ on lenses

[FONT=Arial, Helvetica, sans-serif]Soft Focus lenses all become sharper as they are closed down to smaller apertures. Most of them are actually quite sharp from about f-11 on (the iris diameter gets smaller ) and as the aperture is closed further,(smaller than the diameter at which maximum sharpness is acheived) the image deteriorates as the aberrations increase, but the image looks more clear because the depth of field increases. All lenses have aberrations as they are closed down, and that includes sharp high quality lenses.[/FONT]

I'm wondering now if the maxim, smaller is sharper, wasn't meant for the more retro lenses that I use now. Since the quality of glass has gotten so much better than it was when max f was 11 or smaller. interesting idea since the f64 club was meant for photograpers who shot very sharp images.

It might have been a necessity since the glass was a poorer quality and the glass in my stuido camera is from about that period. Also curious was about that time the popularity of the soft dreamy shots was being replaced by realism. Don't get me wrong there are some very sharp images from the mid eighteen hundreds but the hollywood glamour shot was very popular in the thirties.

I think I've heard this too, and I think someone mentioned it above (but I'm too lazy to scroll up). My guess is that the aperture blades show their flaws more as they are stopped down (perhaps that as the iris diameter becomes smaller the circumfrence-to-area ratio becomes larger?). And at wider apertures the glass shows its flaws more. I wonder how much this still applies to modern lenses, with new construction materials and technology and all that.

elsaspet · Jul 5, 2006

Answer is I use my feet and my brain, and I move in.

mysteryscribe · Jul 5, 2006

Unimaxium said:
I think I've heard this too, and I think someone mentioned it above (but I'm too lazy to scroll up). My guess is that the aperture blades show their flaws more as they are stopped down (perhaps that as the iris diameter becomes smaller the circumfrence-to-area ratio becomes larger?). And at wider apertures the glass shows its flaws more. I wonder how much this still applies to modern lenses, with new construction materials and technology and all that.

Supposedly the small aperture allows the light to spread again instead of hitting hte film straight. Modern lense have much better glass for sure. I wonder what their film to aperture length is. Old lenses on large old cameras have very long distances from the aperture to the film plane. I wonder if that made any difference.

AS for the walk up and use your head, that is prezoom thinking and I like it a lot. My basic wedding lens was a fixed 35mm 1.4 though I never shot it anything but 5.6... Actually i had it super glued at that aperture. I had to change lenses to shoot outdoors. Which I seldom did.

Unimaxium · Jul 7, 2006

Ooh, look what I just found! Ken Rockwell has just written a whole writeup on diffraction as it applies to camera apertures. Apparently due to the laws of physics, apertures that are too small will cause unsharp images because of diffraction. So I guess you are right that f/128 will not create an optimal image. Also, I was surprised to find out that this is something that apparently occurs regardless of the build quality of the optics. The article doesn't seem to explain precisely why diffraction occurs, but I bet if I do a little more research I can find out.

The first link is a shorter writeup on diffraction itself (with examples), and the second link is a rather involved article (that I didn't read fully) about applying the theory of diffraction to find the sharpest aperture on a lens.

http://www.kenrockwell.com/tech/diffraction.htm
http://www.kenrockwell.com/tech/focus.htm