Your understanding of microdots is correct. If you look at the timestamp of *9:06* in your post, a completed microdot with the negative backing material removed is just about the size of the dots in the colon between the 9 and the six. The test contained therein is generally found in a near-square format, with one corner of the square at the top and an opposing one at the bottom. That was using fairly low-tech photographic technology circa 1966, probably not greatly different than what Oswald might have either developed on his own through his employer's facilities or having been so trained as a part of his military or intelligence background.
Of course, if you owned a Minox camera in a certain restricted serial number range, it wouldn't necessarily mean you were a spy either; but if the FBI were interested in covering up your possession of that equipment, it might be because that particular item was from a lot purchased by an American intelligence agency.
-archy-/-
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If you have time, a photo of a camera like Oswalds is here. One has to open the camera by sliding it to view the serial #. The camera in the Archives is stuck in the closed position and they won't have it repaired, therefore the serial # can't be viewed. I wonder why. If it's not Oswald's camera, why is it in the Archives?
Also there is a photo of a sack being carried out of the TSBD. It's longer than 36 inches. It looks to be 12"X48". It's not the sack Oswald allegedly carried in. If you'll notice, it's being carried out by being held at the bottom by something unseen. Oswald's MC was carried out uncovered, so the MC rifle isn't in this bag. What is? Curtain rods? Another rifle; a Mauser? HHmmm.... The sack couldn't stand up like it does on its own; it would bend over. Why did the Dallas police have to utilize such a large evidence bag? I haven't the answers, just questions.