#55
Post
by PeteM » Sun Apr 09, 2023 8:01 pm
This will be a long post, Antartica, but I wanted to give you a detailed response to your personal message.
It sounds like your quest is to find a good DIC system at a reasonable price.
Most any day, a good transmitted BH2 DIC system can be bought on eBay for around $9-10K with tax and shipping. That might seem "reasonable" if your other hobbies involve boats, planes, race cars, horses, gambling, collecting art, attending the Super Bowl, or maybe golf course fees.
Most of us might hope for something at half that cost - and ideally some spectacular deal. I don't know any spectacular deals, but can help fill out the picture for saving a bit of time and money.
The plan for BH2 and BX Differential Interference Contrast systems is similar, with a pair of polarizers and pairs of matched DIC prisms (along with DIC-compatible objectives, which are generally easy to find). Either a BH2 or a BX system might cost around $4000 with a bit of luck and patience once fairly complete:
1) Between the stand and the microscope head you need an intermediate piece with a single DIC prism slider and a polarizer above it. This intermediate part with a good prism and polarizer typically costs around $800 (a relative bargain) to $1500 or more. An intermediate piece with just a polarizer will not work. These parts (mainly the prism) are hard to find for the BH2 and easier for the BX series. For the BX, the slider fits in a DIC turret instead of an intermediate piece. It's pricey, but fairly commonly available. BX polarization turrets will work and can be had for around $300 minus the DIC slider/polarizer.
2) Below the stage, you need a condenser with an assortment of DIC prisms and another polarizer below it. This polarizer is often integrated below the DIC condenser or, if missing, replaced with one placed above the field lens. These condensers and prisms are pretty easy to find - at a price - for either Olympus BH2 (BHT, BHS) or BX systems. The DIC condensers for BH2 can be as little as $500 for ones with fixed prisms. The DIC condensers for BH2 or BX with individually replaceable prisms might run from $1000 to $2000+ after populating them with prisms.
Where the systems differ is that BH2 "finite" objectives have a converging beam exit their back end, while BX "infinite" objectives have a parallel beam leave their back end. This parallel or "infinite" bundle is then converged in a "tube lens" to form an image at the eyepieces (or directly to a camera sensor). The tube lens is usually located at the bottom of the infinite head.
The so-called infinite portion allows additional accessories such as fluorescent and epi-illumination, analyzers, extra camera adapters, magnification changers, or confocal heads to be inserted in the optical path without needing extra lenses to re-converge the image for a 160mm tube length. It's now the standard for research-grade instruments.
For finite microscopes, each additional intermediate piece (such as a DIC intermediate adapter) typically adds about 1.25x magnification and also additional lens surfaces to gather dust or scatter light. Since researchers might often want to add two or more of these intermediate pieces (thus adding cost, extra lens surfaces, and possibly pushing objectives into empty magnification), infinite optics have become the standard for research-grade microscopes.
Given that computer-controlled lens grinding machines are used for almost all objectives these days, we also see infinite optics at the low and mid-range, even from suppliers who don't have much in the way of intermediate pieces to sell. It doesn't cost more to grind the lenses for an infinite objective. The research-grade ones will have better glass, coatings, corrections, and precisely parfocal and parcentered housings. However, an ordinary plan achromat, built to sell at a modest price, might just as well have infinite as finite optics.
Today's infinite optics generally don't require eyepiece corrections. This is sometimes an advantage in fitting cameras of various sensor sizes to a microscope. For example, an APS-C mirrorless camera might be great for videos, and would easily adapt to a BX stand. Otherwise, you need to find just the right projection optic for both image size and image corrections.
The bottom line, for a hobbyist, is that more than one intermediate piece, adding 1.25x magnification, is rarely needed and something like Olympus SPlan or Plan Apo objectives (or their Leica, Nikon etc. equivalents) are so good, that a more modern (and expensive) research-grade microscope doesn't make sense. It seems natural you should just be able to add DIC as well. Olympus BH2 2.5x projection optics are also widely available and work fine for full-frame cameras. As a point of reference, back around 2007, the amazing and mulitple-award-winning micro photographer, Charles Krebs, put a system together like this. Sixteen years later, he's apparently only looking for one more prism.
The reason you might keep an eye out for a BX-series microscope is that many of us have waited years to find a BH2-NIC intermediate adapter or just the BH2-NA prism up for auction - and then found others bidding it up to semi-insane prices. If a knowledgeable user has a BH2-era DIC prism they'll probably want a fair price for it. If a dealer finds one, he will likely want to incorporate it into a complete system. So, you're not likely to find a cheap one on eBay or a microscope forum. Meanwhile, at least two dozen of the newer BX upper prisms have sold in the $800-$1200 range.
This is why it was suggested that you consider buying either a complete BH2 DIC system when you see one reasonably priced or consider a newer BX era system (or even another brand) for not much more. It may be a long wait to find just the prism. Meanwhile, DIC could surely add something to your already-wonderful synth-accompanied videos.
I'd add that if you find a complete and good DIC system at a bargain price for Leica (DM), Leica (DM) Nikon (-phot or Eclipse), or Zeiss (Standard versions or Axio), they all provide excellent images. As witnessed by several posters here. In any case, here's what you'll need for Olympus DIC:
BH2
1) An upper BH2-NIC system or at least the BH2-NC prism (which could then be mounted in a polarization intermediate piece). An older Vanox transmitted prism can also work if it is labeled "LB" for Long Barrel. This is the hard part to find.
2) A DIC condenser. Tom's post, above, for a BH2-UCD is an example. There are at least four other options: an older Vanox-era LB DIC condenser modified to mount on a BH2, the BH2-era DIC condenser with fixed prisms, and either the U-UCDB or U-UCD8 condensers for the BX, fitted with four or so BH2-era interchangeable prisms. You have options here, from about $500 to $2000 or more.
Plus, the polarizers and compatible objectives
BX
1) A turret with a slot for polarization or DIC, plus a U-DICT prism to fit that slot. BX40 systems are often sold a very reasonable price, but you have to make sure they have the adapter to take interchangeable nosepieces. Most of the other BX systems will take interchangeable turrets. There are also high-resolution and high-contrast versions of the DIC prism, requiring matching condenser prisms. The U-DICT is the most common. It's likely to be easier and cheaper to find - and well suited to tasks like making videos starring various protists.
2) A DIC condenser with interchangeable prisms to match your objectives. The older finite BH2-UCD could house these. The U-UCDB (5 positions) and U-UCD8 (8 positions) condensers are the official choices. All these options tend to be somewhat expensive, but easily available. I've also modified a regular Olympus phase condenser to house a mix of PZO and BX prisms and found it works well.
Plus, the polarizers and a turret with infinity objectives. These will be best (cheapest) found along with a DIC-compatible BX stand.
Good luck. If you broaden your search a bit, to include full BH2 systems, BX compatible systems, maybe even Leica, Nikon, or Zeiss - you may double or triple your chances of finding a bargain. Meanwhile, you're already making some great videos.