Beginner's scope

[photosmart42]

Hi, all.

I've been reading up on microscopy lately because I've always had a fascination with small stuff (a primary reason for getting into macro photography in the first place). I'm wondering if there's any compelling reason as a beginner to buy something fancier than a used educational/student microscope that has a turret with objectives, a stage with a light, and a single eyepiece. I can always change out objectives if I want better quality ones, and can mount the camera directly to the viewing tube. I'm still trying to learn about darkfield microscopy and more advanced techniques, but I want to start small and see if I like it.

Is there more to a microscope that would make me want to spend $4,000 instead of $50?

Thank you in advance for your replies!
-Dragos

[rjlittlefield]

What you propose makes perfect sense, particularly if you have a compact point-and-shoot camera with a small lens. Those cameras act so much like the human eye that you can just hold them up the microscope eyepiece and get reasonable pictures. It is a lot more difficult to couple a DSLR or a DSLR-like camera that has a large lens.

You can experiment with darkfield on almost any scope, through the use of a home-made "darkfield stop" consisting of a small piece of black paper that casts a shadow on the objective while still leaving the subject illuminated from the sides.

More expensive scopes will provide more capabilities and higher quality images, of course. But for getting started, there's a lot to be said for using a simple inexpensive scope that you don't have to be scared of breaking.

--Rik

[photosmart42]

Thank you, Rik! I'm thinking specifically of using a DSLR (Panasonic GH1 to be specific), and I can either fit the camera directly to the eye tube using either T- or C-mount adapters, or I can take the Krebs approach of using macro bellows and pointing the exposed camera sensor to the eyepiece (easy to do on the GH1 with the LiveView).

So, having said that, does your feedback still hold? In other words what exactly aside from the objectives give a microscope high quality images? Could I not get high-quality images using quality objectives on a cheap scope mount?

[rjlittlefield]

The approach is still viable, but using the GH1 does add some wrinkles.

I have no idea how much of this you already know, so bear with me.

Most microscope objectives, especially at higher quality, are designed to work in concert with matching eyepieces. Typically the objective is designed to have a certain amount of chromatic aberration, which is removed from the final image by an eyepiece with the opposite aberration. Used as a matched pair, the objective+eyepiece gives a clean image, but the objective by itself or combined with a non-matching eyepiece will show color fringes or other defects.

When you shoot through the microscope's normal eyepiece, using a camera whose optics are small and close like a human eye, then the setup naturally takes advantage of the match between objective and eyepiece. The resulting image never looks as good as you see by eye, but nothing goes dramatically wrong either.

With most DSLRs, this strategy of looking through the normal eyepiece does not work because it gives too much vignetting. The reason is that most lenses for DSLRs have their aperture placed far back within the lens. Pointing one down the eyepiece is like positioning your own eye a couple of inches too high -- you see only the central part of the image.

So, to use most DSLRs you need to take some different approach.

One approach is to remove the camera lens, remove the eyepiece, and let the objective shine directly onto the sensor. This works great under some conditions, notably if you have one of the unusual objectives that is designed to be "color free" by itself. A second is to use a specially designed "projection eyepiece" that has both the proper aberrations to match the objectives and the proper magnification to match the camera's sensor size. These two are the approaches discussed on Charles Krebs' pages, and they can generate very fine images indeed.

There are other approaches that are less ideal. You can use an ordinary eyepiece to project an image, by focusing the scope far away from its design point. This introduces significant aberrations and curvature of field. Or you can mount a small short lens on the camera and point it through the normal eyepiece, rather like using a compact point-and-shoot. This typically produces a small image in the middle of your sensor. Or you can cobble together your own relay optics using an ordinary macro lens to replace the regular eyepiece. This is vulnerable to vignetting and again loses the correction of the regular eyepiece. I have done all of these myself. They all worked, sort of, but I will avoid doing them again if possible.

Aside from the optical problems, there are mechanical issues. Many scopes have a slanting eyepiece tube. This makes viewing convenient for the human, but introduces dangerous torques if a heavy camera is hung off the tube. Other scopes have a vertical tube where torque would not be a problem, but many of those scopes focus by moving the upper assembly, not the stage, and the added weight of a camera can cause focus to gradually creep downward.

With the GH1, it will be challenging to get a setup that allows conveniently switching between direct viewing (eye to eyepiece) and photography. The most practical approach might be to give up direct view, connect a monitor to your camera, and do all your microscopy through the camera and monitor. I confess that I have spent many happy hours watching protozoa on my TV using this approach.

You asked

In other words what exactly aside from the objectives give a microscope high quality images? Could I not get high-quality images using quality objectives on a cheap scope mount?

A good condenser system will provide bright and even illumination that does not add color fringes of its own. The focusing mechanism must be smooth enough and not drift. If your DSLR has shutter vibration (most do), and the camera is directly coupled to the frame, then a lighter frame may give visible motion blur where a heavier frame would not. At higher magnifications, framing is difficult without an XY stage positioner. There are more or less inconvenient workarounds for all these issues, of course.

I'm not sure what more I can tell you. I don't see this as a "brightline" decision that goes clearly one way or the other. A lot depends on your personal standards for quality in an image and your fondness for fiddling around with less than cooperative equipment. I've spent a lot of time fiddling around with stuff that was either salvaged or bought cheap. I don't regret the effort as a learning experience, but I generally don't post the images either.

The one thing I can tell you for sure is that you're not going to approach the technical quality shown in a Krebs image without making a similar investment in equipment and setup.

--Rik

[photosmart42]

Rik,

Thank you immensely for the time you spent to write all that up! As someone who seeks a lot of detailed information on various subjects, you've more than provided what I asked for, which is a detailed explanation on the various aspects that go into getting a quality image.

I'll save up some cash to get a middle-of-the road used microscope that has some of the qualities you mentioned but still costs a reasonable amount ($300-ish), and invest in some 'color free' objectives since I like the idea of directly illuminating the GH1 sensor (no mirror and short registration distance are a plus here). Are those achromat objectives, or is there a different technical term I should look for?

I only looked at microscopes that have a vertical eye tube, like the trinoculars, which should make camera mounting easier. Worst case I'll mount the camera on a separate vertical rail so the shutter vibration won't interfere with the imaging, but even if I mount the GH1 directly to the eye tube I think I'll be OK since it's so light.

As for the other features like an XY stage positioner, I suppose I assumed all microscopes have them, but I was wrong there. I think those are issues I'll only discover once I start playing around with an initial setup and go from there. If I buy a used setup I won't really lose much when I re-sell it, so it's almost like I'm renting it.

Thanks a bunch, again!!!!
-Dragos

[rjlittlefield]

Are those achromat objectives, or is there a different technical term I should look for?

That's a really good question. In most optics, "achromat" would mean "the ones without color fringes". But in microscope objectives, it can also mean "the ones that are not corrected as well as apochromats, and they all have color fringes"!

The objectives that most reliably work well on bellows are the Nikon CF objectives designed for finite tube length. (The "infinite" ones are designed to work in connection with a tube lens. Use those without a tube lens, and you pick up some aberrations that may be a problem.)

For more detail, see "Which microscope objectives do not need compensating optics?".

Your approach to picking a scope sounds very reasonable to me.

--Rik

[photosmart42]

Thanks! That's a great link.

One of the questions I need to resolve for myself is how far into microscopy do I want to get. At this moment I'd guess I'm sitting at the edge between macroscopy and microscopy in terms of subjects I want to photograph. I can get to about 7x using a reverse lens stack at no additional expense over what I currently own, so I plan on starting there in any event before I pull the trigger on a microscope. I've started seeing some CA on my reverse lens even at 1.7x, so I can only guess what it'll look like at higher magnifications, but at least it's free to me for now.

When I do decide to get a microscope, I think a 10x or at most 20x will be plenty good for what I want to accomplish (stacks of insects and such). The Nikon CF 10x and 20x objectives mentioned in the link you posted would do fine for that if I decide to go directly to the eye tube. Some of the AmScope scopes come with C-mount adapters for the center tube, which is nice since I can hook that up directly to my camera C-mount adapter.

EDIT: Having written all that, I wonder at what point it makes more sense to consider the trade-off between a macrophoto (e.g. Macro-Nikkor) lens+bellows setup, and a microscope setup. The macrophoto lenses are already corrected and setup up to hook up directly to a camera, and they can go up to 40x with a bellows. That should be plenty good for me, and probably less expensive overall. For that matter I could attach a microscope objective directly to the bellows. Food for thought...

[rjlittlefield]

For that matter I could attach a microscope objective directly to the bellows.

I strongly recommend this approach.

You will be frustrated with trying to get high magnification from a macro lens. The problem is that the image will get fuzzy from diffraction. To get sharp images at high magnification, you need optics that are designed to work well with a wide aperture over a narrow field. Those are microscope objectives.

See the comparison HERE and notice the clear improvement of the 10X objective over the other lenses, both of which are highly rated macro lenses specifically designed for use on bellows.

--Rik

[photosmart42]

For that matter I could attach a microscope objective directly to the bellows.

I strongly recommend this approach.

You will be frustrated with trying to get high magnification from a macro lens. The problem is that the image will get fuzzy from diffraction. To get sharp images at high magnification, you need optics that are designed to work well with a wide aperture over a narrow field. Those are microscope objectives.

See the comparison HERE and notice the clear improvement of the 10X objective over the other lenses, both of which are highly rated macro lenses specifically designed for use on bellows.

--Rik

Can't argue with empirical results =). I'll start out with the bellows with a microscope objective first, then decide on a microscope if I want to get into more advanced areas of microscopy.