Thursday, January 12, 2017

Comparison of inexpensive digital microscopes, part 2

In the previous blog post, I reviewed one popular USB microscope, an inexpensive one from Celestron, which can be had for about $40. Not a bad price, you say? Well, have I got a deal for you! How does $7.50 sound? Note the decimal point... Yes, I can get you behind the wheel of a digital microscope for less than the price of a hot date at Starbucks.  

I found this little baby at one of my favorite geek-stores, American Science and Surplus. I am lucky enough to live in Milwaukee, one of but a few cities that has a brick and mortar store. But this particular item I ordered online. Note the really alluring name: "95231P1 PHONE PHOTO LENS MICROSCOPE". 

A loupe for your cellphone

As you can see in the photo above, the device is not a USB camera at all, but a lens and illuminator that snaps onto your cell phone. Hence the really low price. It leverages Apple's team of 800 engineers who worked on the camera in the iPhone, and takes advantage the fact that you already spent a bunch of money cuz you just had to have the latest iPhone. Another secret to the low cost is (no doubt) their tight marketing budget for naming the gadget.

Seriously, the little gadget is convenient cuz it uses my cell phone's autofocus, the user interface is the same as my cell phone, and my granddaughter can teach me how to get the images I take onto my computer.

I took an image of a model's eye with the Celestron camera in the last blog post. Below is a quite serviceable image of those same halftone dots taken with my Phone Photo Lens Microscope. My granddaughter was able to help me out, of course.  

I am but a halftone dot in the model's eye

Just in case you were too lazy to read the previous post, I have assembled a side-by-side comparison of the images taken with the two microscopes. I should mention, I did not rely on the 800 engineers who designed the iPhone camera just to make my selfies look fabulous. I relied on the guy in his basement with a soldering iron who developed the camera in my Samsung. He did just as good a job. He just didn't have a good publicist.

My first impression is that the cell phone image is more better. The colors on the image from the Celestron (at left) are a bit washed out. This could be a veiling glare problem, but I did clean the Celestron lens as best as I could. Another thing of note -- the yellow halftone dots are far more discernible in the cell phone image (at right) than in the Celestron image. 

Below, we see a zoomed version of the white of the eye of the model - same digital images, but with a little digital jiggery-pokery. I also did a little enhancement of the brightness and contrast of the Celestron image in order to more fairly compare the resolution. Note the tiny little black halftone dot that can be seen in both images. If I had to make a call, I would say that the cellphone image gives a better rendition. In other words, the cell phone microscope has higher resolution than the Celestron.
  
At this magnification, the original sexiness of the model's eye has significantly diminished

What's the magnification?

I am gonna take a wild guess here. I am gonna guess that a fair share of the folks who read the first blog post in the series and are this far along in this blog post have been wondering about the magnifications of the two microscopes. I have intentionally left that little tidbit out, since it is not quite as relevant as one might think. Permit me a moment to enter the didactic mode of discourse.

Original definition of magnification

The image below illustrates the concept of magnification as it originally was applied to a system with a bunch of lenses. Only one lens is shown below (because I am lazy), but the concept applies equally well to a a combination of a bunch of simple lenses that constitute what we cleverly call a lens, as in camera lens. Yes, a lens (such as you buy at the camera shop) is made up of multiples lenses. I love the English language. This makes it great fun to write patents. 

Lenses can be used to focus arrows - important for deer hunters

In the depiction above, the object is the arrow at the far right of the picture. The lens images this arrow to the other arrow at the right right of the picture. This arrow at the far left is called the image. This is not to be confused with the digital file that comes out of your camera, which is called an image. This makes it great fun to write patents. Henceforth, I will try to remember to use the term digital image to refer to a digital file which is a representation of an object.

The magnification of this configuration is simply the ratio of the size of the two arrows. In this case, the magnification is 2X. The image of the arrow is twice the size of the original arrow.

A second definition

The previous definition of magnification works well for a microscope where you look through an eyepiece, or for those ancient pieces of technology that were called film cameras. Enter the digital camera. The object is now imaged on a CMOS sensor which might be a five millimeters across. If my microscope projects an image onto the sensor of an object that is four millimeters across (such as the first depiction of the model's eye), then the magnification of the lens is 0.80X. Wow. Doesn't sound like such good marketing to say that a microscope has a magnification of less than 1X! I think that even a company that can't afford to pay for a decent name would eschew publishing such a spec.

Not only is it bad marketing, but it is a downright useless as a spec. I will never view the digital image at a size of a few millimeters. That digital image might be magnified to fit my cell phone, which is 110 mm across. In this case, the effective magnification is around 110/4 = 27.5X. Then again, I might view that digital image on my computer monitor which is 480 mm across. The magnification is now 120X. Or, of course, I could zoom in on the digital image as in the illustration where the field of view is big enough to capture five halftone dots across. I could make that into a billboard, and get a magnification of a gazillion X. Or, I could set up a high power projector to project the digital image onto the moon and be able to say that the magnification is a gazilliontillion.

Microscope with high mag wheels

But, the Celestron microscope mentioned in the previous blog has a spec of 150X. What does that mean? Their spec is base don blowing up the image to full screen size on some monitor. Whether the monitor is a 14" or a 36" monitor is unknown, at least from the Amazon website. This is a useless spec. (I should point out that the Celestron webpage for this model gives a complete (and hence useful) spec. They say the microscope is 150X on a 19" monitor. 

I think you see my point that magnification is kind of a meaningless spec without qualifying the spec by saying what size display is to be used and how the digital image was zoomed.

A third definition

There is a third definition of a quantity that relates to the power of a digital microscope which I kinda like. It's simple to calculate, even for the layman, and it is more useful than the X number: object pixel size. You simply determine the size of a pixel.

As an example, we look at the first digital image of halftones in this blog post, the one captioned "I am but a halftone dot in the model's eye". The field of view is about 4 mm horizontally. I look at the digital image of that on my computer, and find that my cell phone gave me an image that is about 4,000 pixels wide. The object pixel size is thus 4 mm / 4,000 = 1 micron. This is the highest magnification available with this lens and my cell phone. 

(I measured  the catalog page with a ruler to determine the 4 mm wide field of view. If your measurement is critical, I would suggest buying a thin ruler and placing that in the field of view for at least one of the pictures. Note that until you refocus the microscope, the pixel size of the object will be the same - if the object is still in focus.)

As a second example, we look at the Celestron microscope that was reviewed in that spectacular blog post that preceded this one. This is a 1.3 MP camera, which means that the entire field of view is 1.3 million pixels. So, the horizontal pixel count is around 1,000. When this microscope is adjusted so as to have a field of view that is 4 mm wide, then the object pixel size is around 4 microns. Of course the Celestron can go higher in magnification by moving the camera. I figger the tiniest object pixel size (highest magnification) of that Celestron microscope is about 1 micron.

This is image is four mega pickles

Based strictly on that number - minimum object pixel size, the effective magnification of the two microscopes is pretty similar.

A third definition

But that still doesn't tell the whole story. In the side-by-side comparison of the little black halftone dot in the white of the model's eye, I made the call that "the cell phone microscope has higher resolution than the Celestron". This is an incorrect statement, if we define resolution as the object pixel size. But resolution is a fuzzy thing. Or, to be literal, resolution is the opposite of fuzzy. Resolution means that the image is "sharp". And sharpness is a fuzzy thing to measure.

If I were a real scientist, and not just someone who plays a scientist in the blogosphere, I would start talking about using "resolution targets to determine the modulation transfer function". In simple terms, you point your microscope at a test target with finer and finer sets of lines. When you can no longer see (resolve) the lines, then your microscope has run out steam.

Everybody needs one of these in their wallet, by golly!

But alas... the test target sells for more money than the microscopes that I am looking at. My dear readers will have to settle for a picture that is worth 1K words.

The second test

I almost forgot about the second test that I did with the Celestron microscope, which was looking at the pixels of my Kindle display. Speaking of fuzziness and resolution...

Fuzzy Wiki was a bear...

This is an excellent example of an image with object pixel size that goes way beyond the inherent resolution in the image. Basically, no matter how hard I pleaded with my cell phone, I could not get it to focus on the Kindle pixels. There will be no discerning of red, green, and blue pixels in Mudville tonight.

Note, for this microscope to work, you need to set the lens atop of whatever you are looking at. On the plus side, this makes it easy to position the microscope. On the minus side, this makes it impossible to adjust to a different working distance. What you see is what you get.

Overall

The Phone Photo Lens Microscope is downright cheap. It's a bargain if you are in interested in a handy tool for looking at the quality of print, and documenting that. But it is a really a fixed focus device. Aside from the digital zoom of your cell phone, you have little control over the magnification of this puppy. But it's downright cheap. The image quality is good. And I should also mention that it is cheap.

I know there are other cell phone loupes on the market. I don't know if they work as well as this does. But I know you can get this one at American Science and Surplus. Buy one quick... I'm sure they will go outa stock as soon as this blog hits.

Disclaimer

So far, I have not received money from either Celestron or from American Science and Surplus in exchange for my reviews. Not that a little kickback wouldn't be appreciated. My granddaughters are starting to think about college. I'm just saying...

No comments:

Post a Comment