That was also part of my test...out of the box first setup Celestron Advanced VX mount. They were/are on sale $699
It has a 30lb instrument rating and with my camera and lens it is as rock stable as you could want. I was able to manually focus on the Trapezium without the mount shaking at all. This is as good a combo Camera, Lens, mount for wide to medium field of view images. I'm sure if I set up auto guiding I could get better results. I did have a bit of problem finding stars through the camera to align the mount, but other than that I'm pleased.

Ok, folks, we’re off on another adventure in photographic exposure. Since a lot of you found the first installment ( https://www.uglyhedgehog.com/t-574357-1.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, (Aperture). This changes the DiAMETER from fully open to something the size of a soda straw. The other fitting is a VALVE, (Shutter). 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 Sensor or Film). These are cylindrical and vary in height (ISO), 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 whichever 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 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 our 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, 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 SENSOR and ISO (GLASS and its SIZE), it can be set 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 (VALVE) controls how much light can flow through. Working together, under your control, the correct settings are made and the optimum exposure is accomplished.
--Bob