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Lab Report

Analytic Essay










Our project in principle seemed extremely fascinating and simple. The idea of how vision is affected underwater was very interesting to us. However, as we progressed through the various stages of the DEEP program there were problems that we had to overcome.
Our very first problem to overcome had to do with putting our results into numerical data. We tried to solve this by calling various opticians and asking them if there was an actual way to measure "blurriness" in a photograph. They told us that there was not a way to numerically measure the amount of distortion in a photograph. This meant that we were forced to look at the picture and merely rank it on a scale of 1-8 of "blurriness." This was our very first inconsistency. This is not a very accurate way of taking data, because it is based purely on opinion not fact.
As an alternate way of taking data, using the photographs we decided to blow the pictures up as much as possible to make the picture of the chart appear like an actual chart. This way we would, in effect, have a copy of the Snellen chart for each two foot interval underwater. However, this made it so that we ran into even more inconsistencies. The mere act of blowing up each picture would increase the amount of blur in each chart. This alone would affect our results. Our solution to this was to use the blown up photo from the surface as our control not the actual vision chart.
In addition to these things, we had a problem with the vision chart itself that went on our project. We had ordered the chart two weeks in advance and on the Sunday before we went to Pepperdine it had still not arrived. This meant that we had to go online to fine one. We were lucky enough to find a website where a doctor had converted a ten foot vision chart to be printer size. However convenient this may appear, this for sure will have affected our results. Even though "real" Snellen charts are printed, they most definitely use far more sophisticated printers than a common home printer. While printing this chart there was definitely some added blur that will have affected things.
When we went to Pepperdine, we had a few more problems that may have affected our results. As we went deeper with our construction, (see picture of our "construction" on the lab page) there was no way of keeping it perfectly straight or level. This meant that each time we took a photograph the chart had a different amount of light onto it. A main principle in our project has to do with refraction. Refraction is mainly about light, so this will have changed our data. Also, at around 13ft underwater our chart became detached from the frame and we had to hold it manually. This meant that the chart for the last two pictures was not level and the same as the others. This is another inconsistency. The underwater camera that we used said not to go below 14ft. The reason for this is at depths such as that, the pressure from the water will start to bend the lens. This could definitely explain why in our results there seemed to be a definate change from 14ft to 16ft. At the depth of 16ft the lens could have bent enlarging the chart.
In addition to these things underwater we also had one more flaw. It is extremely difficult to use a form of measurement that is not effected by water. We chose to use a tape measure, which was probably not the best idea. When under-water and extended to 16ft it started to bend. This meant that our measurements for the two feet intervals underwater were off. As well as this, the depth was off because of how the structure could have been tilted.
Our next inconsistencies occurred when we were taking our results. The way we worked it was to line up our blown up photographs on a wall. We were unable to blow them all the way up to actual size, only to 1/3 of the original snellen chart size. This meant that we needed to use that same proportion as the distance the person stood from the chart. The chart we used was a standard 10ft chart, so 1/3 of 10 is about 3.3 feet. It was almost impossible to get that exact measurement each time we tested their vision.
Secondly, as we moved onto each chart, our tester became more and more familiar with the letters used. They had to look at the same letters eight times. This meant that by the last few charts it was almost a memory test not a vision test. According to our hypothesis, we thought that as a person went deeper underwater their vision got worse. Our results did not back up this idea. However, these unexpected results could be explained through this idea of memorization.
Another large problem was our intervals. In our hypothesis our reasoning had to do largely with the difficulty in seeing the chart as the amount of light decreases. At depths differing by only 2ft, this cannot be a huge factor. If this experiment was to be done perfectly, it would probably be more accurate and interesting if done at ten foot intervals, so as to make the change a lot more noticeable. The amount of refraction does change depending on the amount of light there is, but not at depths of only 16ft. Also, if the day had been darker, we would probably have seen a greater change because there would be much less light at these lower depths.
In the results graph, we can see the change in each person's vision as they look at the deeper chart. You can see that it is a very steady line, until the last depth, where there is a little change downward. This downward change shows a better vision level. From these results, it is not safe to draw the conclusion that their vision got consistently better as they went deeper. If this was the case the graph would show a consistent curve downward.
Science is all about getting things wrong. There are never experiments that go perfectly. 99% of doing experiments is about error. Then you have that 1% where you get it right and you learn something. I would say that, after having done this experiment, we would know how to do it next time in a much better way.