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Posted in response to Re: Re: Re: Re: Re: Re: Re: Specimen ID Help from Alan on June 06, 2007 at 09:15:30:

Re: Re: Re: Re: Re: Re: Re: Re: Specimen ID Help

Hi Again Mike:

My pardon for the "Two-Part Post" here. I had things about half-done when I had to run, so I posted what I had rather than risk losing any of it.

Let's call this second half "FOV-2."

So, here we sit, wanting to take photos of images 1/8 inch or smaller in size and have them be reasonably focused. The technological fixes I mentioned in the previous post can take us down a bit smaller, but for practical and cost-benefit purposes we have reached a watershed: It gets real expensive real quick to go below about 75X or 80X (lets say 100X max)and bring home a well-focussed shot. In fact, getting good focus in the 60X to 90X range is very difficult using available "fixes" that don't cost an arm and a leg. [For reference purposes, we are now talking about shooting *micros* in which the crystals imaged are perhaps in the 0.1 to 1.0 range.]

What to do...

Well, you could throw more money at the problem - buy better optical elements. There are a number of high-end microscope makers - such as *Wild* - that do produce very high-end optics for scopes if you can afford them. If a price tag of $10,000 to $20,000 or higher doesn't scare you off, go for it! But if it sends you screaming into the hills - as it does most of us mere hobbyist mortals - then you need to find a better/cheaper approach. :~}

The presently emerging technological fix is what I think is becoming known generically as *Combine Z*. (Not really, but let's say so for the sake of argument...)

"Combine Z" (and/or it's emerging equivalent systems) is based on the idea of *stacking* flat photos with different planes of focus and integrating them into a single image with a multiple FOV, each layer of which is sharply focussed. [The "Z" of "Combine Z" stands for the Z-axis of an X-Y-Z grid.]

This technology had to await the development of computers to the point that we have access to enough *computing power* to manage the intricate math/geometry of stacks of photos. This has only come to us in the past few years. Before this, Combine Z was just a nice concept that we were waiting for the development of.

Now, I have to fess up and tell you that my knowledge of Combine Z (generically speaking), is sketchy at best. So while I am going to try to write a bit about it here, you need to take what I say with a healthy dose of salt. It is me fervent hope that if I stray too far afield from things that someone who actually has a working knowledge of it will click in and set things straight. [I'll see if a can get one of the Mindat gang who is using Combine Z to come over and join us - but I can't, of course, promise anyone will be able to do this.]

So... - "Stacking flat photos." What does this mean?

Try this experiment: Slice a 10 centimeter (or whatever...) styrofoam sphere into ten equally thick slices, say one centimeter each. Now stick them back together on a skewer so you have the sphere re-assembled. Then stick the skewer in a base - but with the lowest slice hovering a bit above the base.

Now take some coloring markers and color each slice of the sphere. If the sphere is a 10 centimeter one you will end up with 10 colored layers. The number doesn't matter, though - just the fact that you have different color layers.

Okay. Now set a camera up on a tripod so you can look down on the sphere and get it in focus through the camera - focusing on the dead top center of the sphere. [I'd do this using a digital camera, so you can take a sequence of photos of the sphere and print them on your PC printer. You are going to want to trim out each "layer" you take in the sequence. ] Take a shot and then lift the top slice off the sphere. Now focus on the flat second layer and take a focussed picture of that. Print it and then lift the second layer off the sphere and repeat the "shoot and lift" sequence until you have photographed and each layer. [If you use a 10 centimeter sphere you will end up with ten photos - one for each of the ten slices you carved the sphere into.

Now take each shot and trim it into a flat photo - trimming along the edges of the sphere sections. [If you used a 10 centimeter sphere to start with, you should end up with 10 flat shots.] Now mark your skewer each 0.1 centimeter so it is evenly divided. Then take your stack of shots and poke the skewer down through them, starting dead center in the top slice. Now space out each shot along the skewer. You should end up sort of recreating the solid sphere layer-by-layer on the skewer.

Okay. Now see what happens when you look down through the camera at this sectional recreation. Doesn't the sphere look like a three-dimensional sphere "floating in space?"

What you have done is "combined a Z stack of photos to make a false image that looks three-dimensional." If you did this perfectly, the sphere would look entirely in focus - perfect depth of field or FOV.

Only in reality it wouldn't quite cut it... :~} This is because too much focus is hard for the eye to deal with. The image would not "look right" - there would be eye strain issues, a false blurring of the image because our eyes/brains simply can't see "perfect three-dimensionally focussed images." Ultimately, a perfectly focused image from top to bottom, would give you a headache.

What Combine Z does to combat this is to sort of throw in out-of-focus elements to break up the too-perfect image that our eye/brain can't cope with. The final image ends up looking more natural to us.

The above, I'm sure, is grossly over-simplified. But I think it gives you a fair introduction to the technique: A stack of pictures combined into a single image that looks well-focused, but not perfectly so.

Combine Z: A solution for the photomicrographer.

Hope I didn' bore you to tears... :~}



From Alan - June 06, 2007 at 12:39:46

Message: 64241

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