rmalarz Loc: Tempe, Arizona

Ok, folks, we’re off on another adventure in exposure. This time, you'll have to use a bit of imagination. Since a lot of you found the first installment (http://www.uglyhedgehog.com/t-484554-1.html) enjoyable and enlightening, let’s do another installment. This time it’s going to get a bit sloppy, as we’ll be using water, various sized containers, and a rather large pipe with some special fittings. The fittings are composed of a device which will permit us to vary an opening through which the water will flow, the DIAMETER fitting. This changes the DiAMETER from fully open to something the size of a soda straw. The other fitting is a VALVE. This VALVE can be opened and closed very quickly controlling how long the water can flow through the DIAMETER we set. These fitting are in line with one another.

Let’s start with our container. Imagine GLASSES. These are cylindrical and vary in height, but all are the same size around. This is to keep things simple. For our lab work today, our job is to fill a GLASS. It doesn't matter which one. We just need to fill one. The very tallest GLASS is labeled 100. The next tallest size is 200, the next 400, 800, and finally 1600. The 1600 GLASS is the shortest of the group. The idea is that we need to fill which ever GLASS we choose right to the very brim. We can’t allow any water to run over the top. Nor, can we stop filling the GLASS short of right to the top. So, we don’t want to over fill or under fill whichever GLASS we choose to use.

Now our pipe, with an unlimited amount of water, is close to being the size of a fire hose. We can vary the inside DIAMETER with one lever marked DIAMETER. The other lever is marked VALVE. These are fitted in line in the delivery nozzle. So, let’s pick a GLASS and place it under the nozzle and start our adventure in filling a GLASS.

We’ll pick the GLASS marked 400. We leave our DIAMETER setting wide open. We take the VALVE lever and pull it open and push it closed. Wow!!! Water all over the place. The water came gushing out of the nozzle, hit the GLASS, overflowed, and it’s clean up time. That didn’t work so well, did it?. How to solve this problem. Let’s close the DIAMETER a bit. Since we don’t want another mess let’s close it quite a bit. We open the VALVE for the same amount of time and water flows at a much more manageable rate but doesn't fill the GLASS right to the top. Hmmm, we need to make another adjustment. We'll leave the VALVE open for a bit longer period of time. Ah, that worked. The GLASS is filled right to the brim and no overflow. Perfect!!!

What we’ve discovered is that the right combination of DIAMETER and VALVE allows us to precisely control the amount of water entering the GLASS and fill it exactly. At this point, we decide to experiment a bit. We notice that if we open the DIAMETER setting a bit, we don’t need to open the VALVE for quite a long to accomplish a satisfactory GLASS fill. We then close the DIAMETER setting a bit and we now need to leave the VALVE open for a longer period of time to accomplish the same satisfactory GLASS fill. So, there is a relationship between how large the DIAMETER is set and how long we need to leave the VALVE open and vice versa.

We have marked this relationship noting the setting indications on the DIAMETER and VALVE. So, let’s change the GLASS. We take the next smallest size, the one marked 200. We place that under our nozzle and have our DIAMETER and VALVE settings the same as with the GLASS marked 400. We open the VALVE and close the VALVE. Wow!!! The water only filled approximately 1/2 of the GLASS. Hmmm. What happened? The GLASS is taller and therefore needs more water to fill it. We need to either open the DIAMETER a bit or open the VALVE for a longer time. It’s a matter of letting more water in, in the same amount of time, or letting the same flow of water in for a longer time.

After mopping up some of our missteps, we take a few minutes to ponder and observe. There seems to be a relationship between how much water is needed to fill the GLASS we choose, the size to which the DIAMETER is set and how long we leave the VALVE open. We also notice that we can fiddle with the DIAMETER and that requires us to fiddle with the VALVE and vice versa. We further notice that if we change the size of the container, we have to adjust the DIAMETER or the VALVE, or both accordingly to obtain a satisfactory fill. With all of this filling we concluded that if we change one item, we have to change something else to accomplish the same perfect fill.

We also notice an oddity here. There seems to be somethings that don’t make intuitive sense. The larger the number on the GLASS the smaller the GLASS. We also notice some setting markings on the DIAMETER and the VALVE. The first marking on the DIAMETER is a small number, but the opening is the largest. As we move to larger numbers the opening gets smaller. It’s odd, but with practice, we’ll know exactly the DIAMETER we’re setting and can repeat that setting whenever we want. The same can be said of the numbers on the VALVE. There's a whole number, 1, followed by fractions. The smaller the number on the bottom of the fraction, the faster the VALVE will open and close.

Well, we’ve been at this quite a while now, and it’s getting late. What’s going on? It seems that the later it gets, the less water pressure we are seeing in the system. No worries, we can still fill a GLASS, but we’ll have to adjust for the less pressure by using a larger DIAMETER or leaving the VALVE open longer. If we really need to get a GLASS filled, and don't want to spend a lot of time, we might have to choose one of the ones marked with the larger number. Remember the object is to fill a GLASS, we’re not fussy about which one.

This, very simply put, is the way exposure works in your camera. The light sensitive material is the GLASS (ISO), it can be chosen to fill more quickly or slowly as needed. Once set, the Shutter (VALVE) allows light to flow through the lens for a precise amount of time and the Aperture (DIAMETER) controls how much light can flow through. Working together, under your control, the correct settings are made and the optimum exposure is accomplished.
--Bob

rjaywallace Loc: Wisconsin

Thanks, Bob. Great explanation. Jokingly...all these years we've looked for a better camera manufacturer, instead we should be looking for a better plumber.

rmalarz Loc: Tempe, Arizona

--Bob

BebuLamar

You should talk about how to meter or determining exposure without a meter. It's much more important than what you post here in the 2 threads.

rehess Loc: South Bend, Indiana, USA

The OP is addressing conceptual issues that seem to flummox so many.
You need to understand those issues before any other discussions have value.

BebuLamar

What do you mean? What he said is simple stuff. Similar to the lousy "Triangle thingy". The stuff you do after you know what kind of exposure is needed.

Bill_de Loc: US

Exactly. If you don't understand what the aperture is and does you will only be turning dials until the camera says ok. You won't really know why the camera said ok.

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rehess Loc: South Bend, Indiana, USA

I tend not to think in terms of the "triangle thingy", because when I learned ASA/ISO was mostly fixed
http://www.uglyhedgehog.com/t-484554-1.html#8146039

But, no, I see the OP trying to approach these issues at a more basic level. The "triangle thingy" can lead to rigid thinking - actual understanding is much better if someone can reach that point.

BebuLamar

I see that the OP is addressing the easy part of exposure after you already know what the exposure needs to be. Once you know what the exposure has to be choosing the aperture, shutter speed and ISO among the possible choices is easy.

rmalarz Loc: Tempe, Arizona

BebuLamar, please, calm down.

We'll be getting to that. But, for right now, and from the responses I've received, this seems to be a very appropriate way to go. Work on the very basics first. From many years ago, I felt the triangle was a very poor way to explain exposure. Apparently, a lot of folks have found this and my previous contribution very understandable. What you said is absolutely true. It's simple stuff.

if you noticed the "A Beginner's Guide" in the title, that will provide a huge clue as to how simple this approach was going to be. Let's let those who wish to walk before they run benefit. We'll, get to the running part soon enough. Then, we can discuss all of the accoutrements that accompany our camera settings.
--Bob

Sirius_one Loc: S.F. Bay Area

Some of us (like me) need to learn to walk before running. Thank you for this informative explanation.

rmalarz Loc: Tempe, Arizona

You're quite welcome, Sirius_one. I'm glad you found it informative.
--Bob

Tikva Loc: Waukesha, WI

Thank you for the wonderful explanation of exposure. I think I have sort of mastered it, but it always helps me to read it put in different terms. I shoot manual and can usually get what I want, but I still have to take multiple exposures to get there. Again, thanks and I look forward to your next installment.

rmalarz Loc: Tempe, Arizona

Thanks for the kind words, Tikva. They are appreciated.
--Bob

msk Loc: North Carolina

Thank you again for taking your time to help those like me who need to learn the basics.