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Phase contrast microscope for brightfield too ?

 
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Thomas Ashcraft



Joined: 31 May 2006
Posts: 25

PostPosted: Wed Jun 07, 2006 7:21 am    Post subject: Phase contrast microscope for brightfield too ? Reply with quote

Can phase contrast objectives also be used for quality brightfield viewing and photography? Or will you lose appreciable image quality if you use phase contrast objectives for brightfield imaging?

Thanks for any info in advance.

Thomas A
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Charles Krebs



Joined: 13 Jul 2004
Posts: 1200
Location: Issaquah, WA USA

PostPosted: Wed Jun 07, 2006 2:41 pm    Post subject: Reply with quote

You're going to get a variety of opinions on this one! In the books I have read I have seen opinions coming down on both sides.

From what I have gathered, the majority opinion in the various microscope groups is that you can. Sometimes it is mentioned that contrast is somewhat lower.

My experience has been decidedly mixed, and not that promising. I have a set of Nikon CFN Plan phase contrast objectives (10X, 20X, 40X) and IMO their brightfield performance leaves a lot to be desired. Now the only other phase objective I have tried in brightfield is a LOMO 70X Apo, and it was very good indeed. Think

So it may be possible that the reason for the varied opinions is that the performance in brightfield can vary widely with different phase objectives. There are simply too many people whose judgement I trust, happily using phase objectives for brightfield with excellent results (and probably the majority of them are using Zeiss glass).

I really don't think a "blanket" yes or no answer is valid. Which, I know, is not the (non)answer you wanted. Wink
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psneeley



Joined: 11 Dec 2004
Posts: 23
Location: Utah

PostPosted: Wed Jun 07, 2006 4:02 pm    Post subject: Reply with quote

Was that 70x LOMO APO Water Immersion? Just wondering. If so, do you still use it?

To the original question, I have used AO and WILD phase objectives in BF and they are very good. I had one bad experience with an Olympus Phase Objective (short barrell, older objective, 160mm T.L., 20x) where I tried using it in DF (lots of backscatter and dispersion) but in BF it was fine.

FWIW,

Steve
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Thomas Ashcraft



Joined: 31 May 2006
Posts: 25

PostPosted: Thu Jun 08, 2006 8:37 am    Post subject: Reply with quote

Charles and Steve,

Maybe illumination power could also be a factor. In my studies since posting the original question I read on a Meiji microscope dealer's site that:

"Since these new ( BF semi-plan phase ) Meiji objectives have more glass elements, they tend to transmit less light. We recommend for the best results and the brightest image that they be used only on the ML5000 series with the external 50 watt illuminator."

50 watt is pretty high when I compare microscope models as it seems many microscopes only have 20 or 30 watt options.

Also, I have heard good things about a couple of LOMO objectives. I guess every once in a while a company produces a really sweet objective.

Thomas
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psneeley



Joined: 11 Dec 2004
Posts: 23
Location: Utah

PostPosted: Thu Jun 08, 2006 4:03 pm    Post subject: Reply with quote

"Since these new ( BF semi-plan phase ) Meiji objectives have more glass elements, they tend to transmit less light. We recommend for the best results and the brightest image that they be used only on the ML5000 series with the external 50 watt illuminator."

I smell a rat . . . or at least a problem. Either the objectives are truly 2nd rate and have many uncoated elements, or someone is trying to get you to upgrade with a costly, and uneeded, option?
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Thomas Ashcraft



Joined: 31 May 2006
Posts: 25

PostPosted: Thu Jun 08, 2006 4:56 pm    Post subject: Reply with quote

psneeley wrote:
"Since these new ( BF semi-plan phase ) Meiji objectives have more glass elements, they tend to transmit less light. We recommend for the best results and the brightest image that they be used only on the ML5000 series with the external 50 watt illuminator."

I smell a rat . . . or at least a problem. Either the objectives are truly 2nd rate and have many uncoated elements, or someone is trying to get you to upgrade with a costly, and uneeded, option?



Hmmmmm....that's interesting. I'm in the process of researching phase contrast and darkfield microscopes and I thought that company Meiji was reputable and makes decent quality products. ?
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Charles Krebs



Joined: 13 Jul 2004
Posts: 1200
Location: Issaquah, WA USA

PostPosted: Thu Jun 08, 2006 5:53 pm    Post subject: Reply with quote

Thomas... I also think that a dealer recommending only a 50 watt illuminator because of the number of elements in an objective is bogus. (Although it is nice to have with phase contrast and polarization techniques).

Meiji is a very reputable company, better known for their stereo scopes rather than their compound microscopes. The optics on the new Meiji "MX" microscopes promise to be a fairly major step up in image quality over the "older" finite tube length objectives. However I would think the prices would probably exceed the cost of good used equipment from the "big 4".

Steve... yes it was the Lomo 70/1.23, just like the one you picked up on eBay! Wink Wink
I didn't use it often because of the hassle of the shorter parfocal distance on the stands I was using at the time. I think you will like it.
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psneeley



Joined: 11 Dec 2004
Posts: 23
Location: Utah

PostPosted: Thu Jun 08, 2006 6:37 pm    Post subject: Reply with quote

The working distance on the W.I. is purported to be .14 mm, slightly better than an oil immersion 100x (.1 mm). Tight, but . . .

What really attracted me was that it was a Phase, Water Immersion -- never had such a beast -- an maybe more importantly, it has (well, absolutely needs) a coverslip correction collar . . . a device I have no experience with. Just trying to keep learning and trying out a few things Smile I can 'drive' the phase rign with a Heine Condenser from my AO Series 4 scope . . . should be interesting.

Also, I have access to an example of the LOMO 30x W.I. with iris. Maybe I can compete the 70x W.I., the 40x W.I. that I have already, and the 30x W.I., head to head, and see the hubub is all about! Wink
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Charles Krebs



Joined: 13 Jul 2004
Posts: 1200
Location: Issaquah, WA USA

PostPosted: Thu Jun 08, 2006 7:17 pm    Post subject: Reply with quote

Steve.... when I got mine I didn't know it was a phase objective (didn't really want phase) ... wasn't familiar enough with the odd (for me) designations on the objective. Without working up a phase insert, I have no way to use it in phase. It does not match up with any annulus I have now. (No issue for you and your Heine condenser).

The only real downside to the correction collar on mine is that ideally they should move very easily, and on this Lomo (and an older Zeiss Jena Apo I have) the grease has "hardened" enough to make the movement pretty stiff. I have not mustered the courage to try to see if it is something I could "fix".
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