I have a friend who is an experienced photographer. He said that an exposure with the "same bucketful of photons" at high or low level for a shorter or longer time with the same aperture, yields pictures of discernably different quality. The low-level exposure gives a clearer picture, and I am curious why.

I seem to remember it is something to do with the fineness of grain of the emulsion. Slow films, (low ASA) always gave finer details. Unless of course, you are talking digital photography, in which case I pass.

I have a friend who is an experienced photographer. He said that an exposure with the "same bucketful of photons" at high or low level for a shorter or longer time with the same aperture, yields pictures of discernably different quality. The low-level exposure gives a clearer picture, and I am curious why.

 

Probably the camera moves more when the shutter is open longer, but frankly I have zero experience or knowledge with "quantum photography."

I'm a photographer and I don't understand the sentence :S

 

He takes a photo on Exposure 1a, apature 1b, and then takes a photon on exposure a/2, apature 2b? (where a and b are some values to expose the shot correctly) or does he change other things like the ISO number?

I am in trouble as I am not a photog! I think he was saying, same setup on a steady tripod with all changes of background light eliminated, same film and aperture. Now I should ask him about the light source, how its intensity is reduced. That has to be done without any change in its quality.

The question makes absolutely no sense in relation to photography *at all*. Perhaps you could ask it in a photographic sense and then those of us who just happen to be professional photographers may be able to give you a conclusive answer?

How about this: If each grain of emulsion or reactive picture cell could change state by the action of a single photon, the resolution would be at the maximum theoretical maximum. But if a whole bunch of photons is required, how can you get anything less than diminished resolution (and possibly high contrast). The same for telescopes: The greater the light gathering power the greater the fineness of detail.

I am in trouble as I am not a photog! I think he was saying, same setup on a steady tripod with all changes of background light eliminated, same film and aperture. Now I should ask him about the light source, how its intensity is reduced. That has to be done without any change in its quality.

 

Ok, you tapped this in while I was responding about the original question... it's considerably better, but doesn't contain a question?

"The same bucketful of photons", namely, longer exposure at lower level.

"The same bucketful of photons", namely, longer exposure at lower level.

 

Do you mean using a slower shutter speed and altering either the ISO or aperture to create the same exposure?

You must define "clearer picture" ,"same bucketful of photons" and "at high or low level".

The thing that is clear is that the shutter speed vary and the not the apperture. What can vary with shutter speed is blur caused by motion of the subject or of the camera and how luminous the picture is.

I called my friend to ask his help. Compare the photo at a certain light intensity for one minute, to the photo at 1/60 the energy intensity, for one hour. Steve S. says there is a clarity in the longer photo.

I've given my answer, seems to have been ignored, so how is this quote:

 

"Grain size, film speed, and film contrast are related. A high-resolution film will necessarily have small grains, high inherent contrast, and relatively low sensitivity (low speed). Conversely, a high speed film will necessarily have larger grains, lower inherent contrast, and low resolving power. These relationships are dictated by the laws of physics and chemistry."

 

A quick google on film speed and resolving power (ability to reproduce detail) will produce many similar answers. The same principle applies to digital cameras.

 

My last word, honest.

I've given my answer, seems to have been ignored, so how is this quote:

 

"Grain size, film speed, and film contrast are related. A high-resolution film will necessarily have small grains, high inherent contrast, and relatively low sensitivity (low speed). Conversely, a high speed film will necessarily have larger grains, lower inherent contrast, and low resolving power. These relationships are dictated by the laws of physics and chemistry."

 

A quick google on film speed and resolving power (ability to reproduce detail) will produce many similar answers. The same principle applies to digital cameras.

 

My last word, honest.

 

But he's keeping the film the same...

 

The two things that are chaning are the light level and the exposure time.

 

by greater clarity I assume he means sharper?

Thank you Klaynos. Is there overlap and wash in the higher intensity field? Like I mentioned, you may not throttle down the light level by, say, making it more point-like. Hang in here, Gcol, we are in danger of learning something. I am not changing grain sizes so this may or may not apply to digital mode; I'll ask my friend who was working with film, I think.

In what context does he take is photos ? With that long exposure it maybe astrophography ???

Steve S. says there is a clarity in the longer photo

What does that mean ?

In the context of astrophotography I can interpret that as the background sky is not realy black... This is caused by light polution (background noise)

He described an inside space with shuttered windows to eliminate change. Then a "controlled" light source. Maybe a heavy smoked glass filter is fair here, what do you think? You may not "dim an incandescent bulb" thus changing its color, etc.

Steve S. says there is a clarity in the longer photo

Maybe it is because I am french speaking , but it is not clear what that means. Could your friend scan these picture and send them ?

It is realy hard to create a completely dark room, specially if you use very long exposure time. Did he tried to take a picture without any light source to verify that his room is completely dark ?

We even have issues with too much light in basements... doing photonics experiments...

Thank you Jacques, good questions. I'd think, though, that any "noise in the signal" would be worse on the long exposure. You would need black walls, actually, right? Otherwise scattering could be above a threshold, on the short exposure???

If the light source does not change, and thefilmstock does not change, and neither does the developing regime, (a given film speed can be artificially boosted by changing formula and temperature of the chemicals), then lens aperture is the only other available variable, surely. A smaller aperture will give a greater depth of field than a large one, exposure time will be longer, and errors in focussing will be minimised.

then lens aperture is the only other available variable, surely.

The light source can be a variable and it look like it is the case here, is it Norman ?

As I understand it, the aperture is remaining the same size...

Come on Norman, fess up, we are in dire need of the exact experimental conditions. You know, the Scientific Method.....

We change only the illumination intensity, and the exposure time. One has to accomplish the first without altering its distribution. You tell me: can we put a smoked glass filter, such as we view eclipses with, in front of the output of our light? Otherwise, could we maybe run a laser a lower power?