Mobius Loc: Troy, MI

I am like a lot of you, retired. Have been a serious hobbyist photographer sing the early 60s. I have been reading UHH for some time now and have great respect for several of you regulars and not so much for a few others.
I decided that I needed to join UHH so I could chime in on rmalarz’s excellent series of posts on Exposure and How It Works - A Beginner's Guide. The water flow model is right on and should give the beginner a good “feel” of what is going on.
It is however missing one piece. The flow of water through the opening is a function of the pressure of the water the valve is holding back. The higher the pressure, more water will flow through the aperture in a given time. If you have an opening and time that just fill the glass, it won’t be the same if the water pressure changes.
The water pressure is the equivalent of how much light is on the subject. The pressure gauge on the water supply is equivalent to the photographer’s light meter. The shutter speed and aperture vary based on the brightness (pressure) of the subject.
Now for some comments not based on rmalarz’s posts.
It’s a funny triangle that has four sides. The exposure triangle looks at the three controls in the camera; aperture, shutter speed, and ISO. The fourth side and every bit a significant is the amount of light on the subject. Sometime the photographer can control this, sometimes not.
I’ve always like to think of it as 1) How much light do we have (light meter reading), 2) How much light do we need (ISO), 3) what combination of shutter speed and aperture will give the correct exposure (and have the best side effects, motion stopping and DOF) The old fashion light meters made this easy since when you dialed in the ISO and Light reading they showed all of shutter speed, f stop combinations that worked. You could just look and see them, you didn’t need to do the mental calculations. Once you had taken a few thousand pictures the calculation became second nature, but seeing it really helped the novices. With meters built in the cameras you only see what is correct, not as helpful for learning.
If you don’t like the options, change something (put more or less light on the subject, change the ISO). Don’t forget the fourth side of the triangle, use a flash, use a reflector, move the subject closer to the window, get the light source behind you,

cristal-

Bob: excellent tutorial. Easy for me to understand.thank you for doing it for us, who do not remember like me.I joined the ugly hedged hog hopping I will learn. I been reading (every day ) and learning with the articles that some members post.With your post hopefully I will start using only Manual.
my son is learning Manual. He liked this 2 articles. Again thanks, for doing this. Cristal.

rmalarz Loc: Tempe, Arizona

Mobius, I am aware of the pressure issue you mentioned. However, do you remember your old physics classes, massless, weightless wires? From my engineering classes, there were massless mechanical components. That was to keep the issue simple. After those initial concepts were grasped, we moved on to account for the mass of mechanical components, etc. The idea was to keep this more simplified. Besides pressure/velocity ratios, we'd have to take into account turbulence, laminar flow, etc. The idea was the principles, not the actual physics involved.

I do appreciate you bringing these issues up, none the less. Thanks.
--Bob

rmalarz Loc: Tempe, Arizona

Thank you, Cristal. I'm very glad the work is appreciated.
--Bob

Notorious T.O.D. Loc: Harrisburg, North Carolina

Handheld light meters still offer these capabilities and even more today. The difference is that most people don't want to invest in owning one and learning how to use it to their advantage in my opinion. They rather depend on their built in camera metering, looking at a simplified histogram and chimping. To each their own. But shooting film is different and shooting Kodachrome even more challenging than film or digital.

Happy shooting,
Todd Ferguson

rmalarz Loc: Tempe, Arizona

Todd, I'm particularly fond of my Sekonic L758DR. I have profiles stored in that meter for both my D700 and D800. Along with those, I also have a profile for the film I use for my Hasselblad and 4x5. That gives me the best of both worlds.
--Bob

Notorious T.O.D. Loc: Harrisburg, North Carolina

Bob,

The 758 is a great meter. I have one but just last week received a new 858 from B&H. So, far I like it even more than the 758. I expect I will be selling my 758 before too long. I doubt I would reach for it much more with the 858 within reach even though it is a great meter. I think meters are still very useful tools. I wish more people saw it that way.

Best,
Todd Ferguson

rmalarz Loc: Tempe, Arizona

The 858 looks nice, but the 758 does everything I need. I also use a SEI Photometer from time to time. The 758 has gradually taken over metering duties from the SEI.
--Bob

Haydon

I just bought a L-758 DR-U for studio work Bob off of eBay in near mint shape. I'm still very green using one but so far I really like it. I've relied on chimping and using the histogram for most work but incident light can't be done with reflective metering as you are aware in camera. It feels like a cadillac.

rmalarz Loc: Tempe, Arizona

Ironically, I purchased mine from a friend who decided he was going pure digital. "So, I don't need an external meter". Fine. I'll give you $250 for it. Sold. Downloaded the profiling software, did a few hours of work shooting a color chart, etc. and have been using it since. Travels with me and whichever camera I decide to take. Coupled with the Expodev program on my iPhone, I've nailed my exposure/processing quite well.
--Bob

plumber1948

" This is a place where young men stand and listen and old men sit and talk". Today I'm standing with one foot in Michigan and the other in Peoria, Arizona. The quoit is from the wall of the skilled trades room where coffee was purchased.

Notorious T.O.D. Loc: Harrisburg, North Carolina

Bob, You made a good wise buy!

Best,
Todd Ferguson