Showing posts with label resolution. Show all posts
Showing posts with label resolution. Show all posts

Tuesday, November 26, 2024

Biology resources

There have been many changes in science curricula since I was in school. Most of the stuff back then was descriptive. Physics was more structural mechanics. Now there's a lot more subatomic stuff and cosmology. Chemistry was more about how the elements and their compounds looked and behaved. Now, there's a lot more mathematics....calculating yields and such, and more about what happens at the atomic level.

Biology.....they used to talk about cells, organization of bodies, cell division, and the tree of life (organization of species) but now the tree of life is a different tree. It used to be based on observable similarities between different plants and animals ( and there were only two kingdoms.....plants and animals) but now it's based on similarities between their DNA which reflects how living things are related through evolutionary development.

I'm watching the lectures from the MIT introductory course in biology. They start with molecular chemistry then briefly touch on cellular organization. Then they spend a lot of time on how genetic materials translate into proteins. They end up with considerable amounts of medical biology....stem cells, immunology, cancer...

If you want a deep introduction, the MIT course is at https://ocw.mit.edu/courses/7-016-introductory-biology-fall-2018 .

As usual, there's a lot out there. Let's see. What's in my tool chest? It's nice to have all my tools in one place so I try to consolidate as much as I can on my phone. Beside the general purpose apps I've been using (the calculators, sensor apps, and general purpose tools) there are some useful programs specifically oriented toward biology.

A major emphasis on biology is imaging. Biological entities range from submicroscopic viruses (we won't be looking at them since it would take some very expensive and very non-portable equipment, like electron microscopes. We might do some Internet safaris, though ) to whole forests of Aspen trees (an Aspen Grove may well be a single organism.) The parts of organisms are important also, from the molecules that power them (again, too small for us to actually see) to individual cells, to whole ecosystems.

I walked down to Dry Creek Park the other day to take some pictures. I was a bit disappointed. We're in a period of cooling and frequent storms and everything was quiet......no birds or squirrels in sight. The creek was flowing so that microorganisms are washing downstream.....no stagnant water there to play with and the cold water encourages them to go dormant. Still, I got a few pictures.





This ash tree was still green. The grass in my lawn looks like it's getting ready for fall but the trees haven't quite caught on yet 




I have some identification books stored in my phone but I used Google Lens to check my identification. Once you have an image in Google Pictures, a poke at the Lens button  will search the Internet for a similar image. There are similar apps available for different phones and computers.




I can zoom in with my phone camera to about eight times (8x) but notice that, in the photos of an ash leaf above, the more I zoom, the blurrier the picture is. In an electronic camera, the number of light sensitive elements (pixels) there are in the CCD (charge-coupled device chip...the part of the electronic camera that replaced the film in older cameras and changes patterns of light into electrical signals)  is constant. Since the picture resolution is determined by the number of pixels available, that's constant, too. Resolution is usually specified as the number of pixels on the CCD. In my phone, the front camera ( the one on the same side as the user....the "selfie camera") has 16 mega pixels ("mega"="million") and the back camera (the one I usually use) has 50 megapixels. My phone actually has three lenses that focus the light on different sections of the CCD.

Imaging is important in biology because there is so much detail that matters that is hard or impossible to see. You probably got to use laboratory microscopes in school that magnified to over a thousand times. Field microscopes are usually lower powered for a couple of reasons. Portability is an obvious virtue in a microscope that will be in the field. Often, though, samples are brought back to the laboratory for examination. Most laboratory microscopes used to look at field samples trade resolution for field of view. They're usually bulkier than laboratory microscopes and have two eyepieces ("stereoscopic microscopes") to enhance the dimensionality of the image.

I determined the optical characteristics of my camera here:





I have a very portable clip-on microscope for my phone that is quite serviceable in the field. It's rated at 60x magnification with more magnification possible with zoom.

That's sorta an advertising misinformation. You can get larger pictures with electronic zoom but the resolution remains the same so a zoomed picture will be blurry. Still, you have to zoom to get rid of the "tunnel" effect in the top picture above. I can get a fairly reasonable image at around 80 or 90x. The maximum around 120x is pretty poor.






There are ways to improve a blurry image. Most phone cameras have editing features that allow you to play around with a photo image. "Sharpen" is one that can improve an enlarged image. It senses borders in the image and averages the values of the pixels around the border, replacing the pixels on the border with the averages. It's an illusory improvement that can miss some important details, but with some skill, a photographer can get some decent photomicrographs like that. There are also "magnifying glass" apps that have the sharpen feature built in.

The bottom line is that if you want really good photomicrographs, use optical magnification instead of electronic (zoom) magnification.

I also have a clip-on front camera microscope that has a stage like laboratory microscopes and uses transmitted light (my other clip-on has a built in light that reflects light off the sample). Actually, I got that microscope with the "Cells" Science Wiz kit. 


Here is some stuff I found in Little Dry Creek. It's not very impressive since the water flow was pretty high and the water was cold. All the little beasties were hiding for the autumn. The magnification is about the same - around 60x.



Big things and distance views are important in biology field work also. My Carson telephoto lens will give me a moderate field, zoomable, magnification of six times. That's about perfect for wildlife photography. You want to be far enough from wildlife to avoid spooking them or from being mauled or trampled by them.





At telephoto distances, tiny movements of the camera can blur the image so a camera tripod with a phone adapter is necessary. For wildlife photography the tripod needs to be set up in a location that's as obsured as possible and a portable blind is useful. On the day I was taking photos for this blog, everyone was at home asleep. Winter does that sometimes. Anyway ....leaves.

And, of course, phone cameras usually have a video mode that lets you take movies of, say, wildlife behavior.

Microscopy requires things like stains, slides, droppers, knives to slice samples. There are good kits that aren't expensive. I have a couple from Home Science Tools and the Cells kit from Science Wiz.

A particularly useful tool is a microtome that lets you make very thin slices of materials to put on microscope slides. You can pay as much as you want for one. Mine:



an economy model, cost less than $20 and came with a razor blade. It's basically a flat plate with a screw piston that pushes the sample by tiny increments up through the center of the plate so it can be sliced off. Table models can run to four figures but you don't want a table models in your backpack, anyway.

I won't be doing any high powered microscopy but it can be pretty fascinating. You can equip yourself for considerably less than a thousand dollars (or more) and a good source is American Science and Surplus. Avoid the cheap kiddie microscopes. The affordable ones have poor, plastic optics and are not worth the savings. A good option, around $100 is the Celestron line of digital microscopes. 

There's life out there (even in the winter.) so go out and study it!
















Friday, May 7, 2021

I am a camera

Actually, I am not a camera. That was a quote from "Into the Lens", a song by Yes. You should find it on the Internet and listen to it while you read this blog.. or not.

Astrophotography is a fun hobby. To get great photos, you need to put out some substantial funds, but to get nice shots, like my shots of Venus...
You just need a phone camera, a way to connect it to a tripod, and an inexpensive telephoto lens.

You also have to have an intimate knowledge of your scope and your camera.

For any photographic work, you need to know your camera's field of view and resolution, and if you don't have this in your phone's specs, you can easily determine them like I did for my phone camera. Here's my setup.
I carried my portable podium onto the patio with a half meter ruler held up by optical bench stands (those are from an inexpensive set I bought from Home Science Tools. Great company. You could probably make your own.) Under the podium, I stretched out 20 feet of a tape measure.

On the bottom photograph above, there's a plumb bob I threw together using a random piece of plastic I had lying around. I hung it from my phone tripod clamp with a 1/4 20 wing nut and cord. I clamped that to my phone so I could tell how far away I was from the ruler using the tape measure.

To figure out the angular field of view, I stood back until the ruler filled the camera view from one side of the frame to the other. 
That was right at 2 feet (27 inches).

Next, to determine the camera's resolution, the distance at which two close objects at a specified separation can just be seen as two separate objects, I moved back until the millimeter markings on the ruler just blurred into indistinguishable marks.
That was at 28 inches.

So, why would I want an angular field of view? Many terrestrial scopes, including binoculars, give their field of view in terms of width in feet at 20 feet. That's okay when you're working at distances that can be expressed in feet, or even miles, but astronomers work in distances from astronomical units (1 AU is the average distance from Earth to the sun) to light years (a light year is about 6 billion miles) to billions of light years.

If you draw a great circle around the Earth, at any distance, it is composed of 360 degrees. The moon, as seen from Earth, has a diameter of about half a degree (we say it "subtends" an arc of 0.5 degree.) So does the sun, although the sun is much bigger. That's why the moon can block out the sun in a total eclipse. Astronomers work with arcminutes (an arcminutes is one sixtieth of a degree) and arcseconds (60 arcseconds make up an arcminute, 3600 arcseconds make up a degree). Binary stars, as seen from Earth have a separation of from 20 to less than one arcseconds.

Next...the math.

I have set up a right triangle here. The angle from one end of the ruler to the camera, back to the center of the ruler is half the angular field of view. I know the distance from the ruler to the camera (d), and I know that the half ruler is 250 millimeters long (it's a half meter ruler). I can use trigonometry to figure out the angle.

I need everything to be in millimeters, so 27 inches is 685.8 mm. The tangent of my angle is 250 mm/685.8 mm, so the half angular field of view works out to be 20° and the full field of view is 40°.

Mount Evans, pictured here, is 40 miles away. The tangent of half my view angle is the half width of my view field divided by the distance. That means the half width is equal to the tangent of half the angular field of view times the distance, or 14.6 miles. My full field of view at 40 miles is about 29.8 miles.

I figure that my measured distance to the ruler could have been off by 2 inches in either direction, so I can calculate my error by recalculating my field of view at 29 inches and 25 inches and that error turns out to be about ±3°.

I can calculate the resolution of my camera using the same method but, instead of using half the ruler, I use half a millimeter. The distance from the ruler where I can just make out millimeter markings is 31 inches or 787.4 millimeters. That gives me a resolution of 0.07° ± 0.005° . That's a far cry from being able to see binary stars as two stars, but, at least, I can see the sun and moon as a disk instead of just a point source of light.

My camera's electronic zoom does not increase resolution at all but my telephoto lens does. If I wanted to check the resolution of my camera with an optical system like a telephoto lens, binoculars, or a telescope, I wouldn't use trigonometry, I would just see if I could see a pair of stars with a known separation.

Angular field of view is a more flexible measure than width of view at a given distance, but now you know how to find your camera's angular field of view.