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Apologies if this isn't the right place for this--it's the closest match I could think of. Please feel free to move it if it should be elsewhere.

At my work, I use a microscope on a regular basis. Because of the way it's set up, it's much easier to attach a microscope camera to it and use that, connected to a monitor, for most work. However, when I put the microscope camera on, it seems to be zoomed in, meaning I can only see a very small portion of the center of the image on the screen. The camera is zoomed out as far as it goes, but I still see even less than just the middle ninth of the image, compared to looking through the eyepiece.

Is this indicative of a problem with the setup, perhaps some adapter I should have that i don't? Or just that buying a cheap microscope camera wasn't the best idea? Or is this somehow just an intrinsic problem with using a microscope camera in general?

The microscope, if it's relevant, is a Seiwa PS-888, and the microscope camera is a super cheap Omano TMS-HDMI-1.

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  • What's between the camera and the microscope camera port? The optics between the camera and microscope make a difference in field of view.
    – qrk
    Jul 9 '21 at 17:16
  • @qrk Nothing but the adapters that came with it, which have no optical elements in them--they're just tubes, basically.
    – Hearth
    Jul 9 '21 at 20:41
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Your microscope camera sports an imaging chip that is labeled 1/3 inch. This is a misleading nomenclature. It’s origin is the diameter of a glass vacuum tube used in TV cameras of the past. Your imaging chip’s measurements are approximately 3.5mm height by 4.66mm length.

Your 1/3 inch imaging chip is typical of low cost point-and-shoot still cameras.

For example, a high-end microscope camera sports a full frame imaging chip that measures 24mm height by 36mm length.

The best way to explain the difference is to compute the diagonal differenced thus: Your chip has a diagonal measure of 3.5mm. The full frame camera has a diagonal that measures 43.26mm.

The difference is: 43.26 ÷ 3.5 = 12.36. This value is called the crop factor or magnification factor. It tells us that your camera yields a tiny image that must be magnified 12 1/3 times to produce an image the same size as a full frame camera. Another way to state this: 1/12.36 X 100 = 8%. In other words, you camera's imaging chip is only 8% of the size of a full frame camera.

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  • I know I didn't ask this in the question itself, but do you have any suggestions for how to fix it? I guess just some kind of zoom-out lens like someone else suggested?
    – Hearth
    Jul 10 '21 at 1:17
  • Crop factors can be a bit misleading. A 12:1 ratio covers 1/150 of the area. Jul 10 '21 at 20:23
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I looked at the specs for the camera and microscope and I think you're running into a crop-sensor problem. The camera you're using has a 1/3" sensor, which means that if the image the microscope is projecting is 1" across at the camera's focal plane then you're only looking at the middle 1/7 of the image circle.

Of course, the eyepiece you're using affects the image you see vs what the camera sees. if your eyepiece had more magnification then it might be a perfect match for the camera setup you now have. The source I link to below has a table that shows, for a 10x eyepiece, that a 1/3" sensor needs a .3x reducer for the image to match what you see through the eyepiece.

Usually (when using an eyepiece adapter) you can get C-Mount adapters that have a reduction lens built in so that the small sensor size is better matched to the image size.

If the C-Mount adapter comes off of your 'scope and leaves an eyepiece sized tube you might be able to use one of these. A discussion of C-Mount reduction adapters (with useful links) can be found here.

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  • Wouldn't it be 1/9, if it's a third the linear dimension? Anyway, I'm not sure if it does--how would I know if the tube is the right size for that adapter? How would I know that the adapter is the right length for it to focus properly?
    – Hearth
    Jul 9 '21 at 15:56
  • It's an image circle so area-wise it would be ~1/7. Your other questions are good ones, but I don't have a lot of answers. Check the 2nd link for an in-depth discussion. I will say that a camera with a larger sensor will give you less magnification and be closer to what you're seeing through your eyepiece.
    – BobT
    Jul 9 '21 at 15:59
  • A 1/3” sensor is not one third of an inch. It has a height of 3.6mm. An image circle of radius 1.8mm fits within it. The area of that circle is about 1Omm^2. An image circle of 1” diameter has an area approximately 49Omm^2. Jul 9 '21 at 19:52
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    @Bob, Thanks for the correction. The world of camera sensors is one where 1" is actually 16mm, and the diagonal of a 1/3" sensor is 6mm. Thank video camera tubes for the confusion...
    – BobT
    Jul 11 '21 at 15:12

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