What's wrong with Exposure time?
Nothing is perfect in real world but that's a different thing.
May 31, 2023
181
-
-
H = E * t in its various incarnations, H_e, H_v, H_ph, H_m etc. (likewise E_e, ...) uses Standard International unit notation so that things not get confusing once one starts digging deeper into the subject.
-
It's an age thing. If you're as old as us you learned E = I × t. During the 60's and 70's science became internationalised, adopted the SI system and more standardised signifiers were used. So E for 'exposure' became H, 'I' for intensity became 'E', and 'T' for time remained as it was. It is as you say the same formula just with different letters. The point I was making is that Porky, who likes to criticise Danno's explanation of exposure, cannot recognise that it is the same as E = I × t but in a different form. He claims differently now, but that is standard behaviour for this individual, who is actually learning while trolling (an interesting concept) but since his starting position was that he knew it all anyway, must deny it. The problem with the troll is that it creates currency for the idea that Danno's formulation is actually wrong in any substantive way - and it isn't.
-
Nothing, except the exposure time may be set to 1/100 while light hits for only 1/500. Or light painting.
-
Oh, good one, all our angst about how the camera gates light doesn't take into account light that doesn't have a constant intensity. Reminds me of an article in a photography magazine from long ago about a fellow who'd set up a view camera on one slope of a valley, open the shutter, then run around the other slope setting off all sorts of illumination. Neat images...
-
But all this preciseness of language really detracts from the problem at hand, considering so-called "proper" exposure. Me, I'm really getting reinforcement here for my perspective, "proper" is a poor adjective to prepend to the word "exposure". The needed exposure for an image depends on what you're trying to do...
-
IMHO another problem is that the light spectrum is ignored in all popular definitions, and thus we end up with colloquialisms like "blue channel is strongly underexposed", or don't have means to formally and uniformly describe what was the exposure for a shot combined from 3 exposures made with colour separation filters, while a customer demands a valid EXIF ;)
-
Indeedy!! Spectrum aside, What Do You Record for the exposure tags in EXIF of a HDR amalgam JPEG? Or, a conglomeration of a stack of 19,000 captures to render the Milky Way?
To mis-appropriate Paul Simon, There are 50 ways to
leaveexpose yourloverphotograph... 😆
-
I think that all definitions involving light intensity automatically include a spectrum i.e. the CIE luminous efficacy curve.
-
What I doubt is the usefulness of such inclusion without allowing for exceptions, that is without a possibility / option to describe particular exposure conditions.
-
And, in the case of the 1931 2 degree SO, not completely representative of the population. Collectively, that group was somewhat blue-deficient.
-
You'll need to define sensor for this definition to have precision. Are you talking about the silicon? The CFA? The microlenses? The top of the sensor stack?
-
In your way of thinking, does the CFA spectral response affect the exposure? Does the hot mirror affect the exposure?
-
Depending on definition, orthochromatic film is already a problem, X-Ray is another problem, including "actinic light" into the definition is a partial solution.
-
With X-ray plates, you can have density without light (measured in lux) hitting the sensor.
-
What does exposure mean for a sensor with a IR-pass, VIS-rejecting stack, and a 950 nm low-pass (for frequency) filter on the lens?
-
Absolutely.
-
That is a great pity because most, if not all, light meters (external or in-camera) are calibrated to that curve as I am sure you know!
I don't understand what an exception might be. Is it possible that I have missed such an exception in this thread?
With a spot meter going around a scene it would give different exposure recommendations for evenly-lit, equally reflective, equally distant objects if they are, for example, red, green and blue.
If the blue is 450nm and the green is 550nm then the perfect spot meter would recommend about 5 EV more than the green. But if someone exposed for the green then the blue would be rendered pretty dark - which could naïvely be called "under-exposed".
