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Nauplius

 
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gpmatthews



Joined: 03 Aug 2006
Posts: 1040
Location: Horsham, W. Sussex, UK

PostPosted: Thu Feb 21, 2008 3:58 pm    Post subject: Nauplius Reply with quote


Microscope: Zeiss Standard 16
Ocular: Zarf G9 Photo adapter
Objective: Leica EF L 20/0.3
Substage: Leitz ICT
Camera: Canon Powershot G9
Flash: Vivitar 283
Sample from Warnham LNR (artificial pond at entrance)
Feb 2008

This image involves a little bit of a mystery. The objective is a long working distance conventional objective, with no DIC Wollaston prism (my normal Leitz ICT objectives have integral prisms), but when I swung it into place leaving the polarisers and condenser Wollaston prism in line, there appears to be a distinct DIC-like effect. The highlighting reverses with rotation of the polariser, similarly to DIC. I tried some other non-DIC objectives, and obtained a similar effect. The extinction at the darkest point is only slight, however. The effect is most pronounced with the Wollaston prism for the Leitz x100 ICT objective. Anyone got any theories as to why this works?

I find the LWD objective good for this sort of subject, where the enhanced depth of field is an asset.
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Graham

Though we lean upon the same balustrade, the colours of the mountain are different.
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Charles Krebs



Joined: 01 Aug 2006
Posts: 5805
Location: Issaquah, WA USA

PostPosted: Thu Feb 21, 2008 6:01 pm    Post subject: Reply with quote

That is a real puzzler Graham! Whatever the reason, the effect looks very good. When forget to slide in the upper prism and polarizer on mine, I have never seen anything even approximating this. At first I thought perhaps something was out of alignment and you were getting some sort of oblique effect. But if you can vary the shadow position with the lower polarizer...?

My "upper" piece has the pol and prism combined together. Yours sounds different. So let me see if I have this correct... prism and polarizer in place at condenser. No upper prism, but an upper polarizer. Is this correct?
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discomorphella



Joined: 01 Oct 2006
Posts: 606
Location: NW USA

PostPosted: Thu Feb 21, 2008 9:16 pm    Post subject: Reply with quote

Hi Graham--

One possibility is that your LWD objective has some residual birefringence. This could be due to strain in one or more of the lens mountings. Since (I am assuming here) you have a Smith type DIC rig, the residual birefringence will act like a wollaston, in roughly the correct plane (near the BFP of your objective). That's one possibility anyway. You can check for this by removing the lower wollaston prism from your condenser, retaining the lower and upper polarizers, and viewing the back focal plane of your objective. IIRC, you should see a cross shape if it has simple polarization aberration, and a pair of arcs (more like hyperbolae) if there's birefringence as well. I'll have to go back and check some old references to be sure. This is one possibility of course. I could also be completely wrong and the actual explanation is that you are, as Charlie suggests, making some sort of oblique illumination scheme. Hope this helps.

David
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Perl



Joined: 03 Oct 2006
Posts: 262
Location: Sweden

PostPosted: Fri Feb 22, 2008 1:08 am    Post subject: DIC Mystery Reply with quote

Hi Graham !

Yes i have the same phenomen as you with
objective that not have Wollaston prisma

Also noted that there are very little if not at al
diffrence between the diffrent Condenser Prismas

Have the same setup as you , with Leitz ICT Objectives
16X , L20X , 25X , L32X , 40X , 100X

Prismas in Condenser are 25X , 40X ,100X

Will look in this little more and se if there are an
explanation to it

Best Regards
Pär Lundqvist
Sweden
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Perl



Joined: 03 Oct 2006
Posts: 262
Location: Sweden

PostPosted: Fri Feb 22, 2008 1:25 am    Post subject: More DIC Mystery Reply with quote

See if you have same effect with a Pol Objective ?

Best Regards
Pär Lundqvist
Sweden
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gpmatthews



Joined: 03 Aug 2006
Posts: 1040
Location: Horsham, W. Sussex, UK

PostPosted: Fri Feb 22, 2008 12:41 pm    Post subject: Reply with quote

Well, I've had a chance to do some tests - Charlie's theory wins! There are no indications of stress or birefringence using just polarising filters, but the effect seems to be related to the distribution of the dark band produced by the filters plus one substage Wollaston prism. And, yes, Charlie you understood the configuration correctly. The theory is also confirmed by Pär's similar experience. Unfortunately, I do not have a POL objective to try out as well, but I think that is probably just gilding the lily.

Thanks for the thoughts chaps. Now we just need a special name for this type of oblique illumination...
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bernhardinho



Joined: 13 Aug 2006
Posts: 563
Location: Germany

PostPosted: Fri Feb 22, 2008 1:28 pm    Post subject: Reply with quote

gpmatthews wrote:

Thanks for the thoughts chaps. Now we just need a special name for this type of oblique illumination...


Hi folks

how about "obDICal illusio...errh, pardon me, illumination" Razz


Bernhard
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Frez



Joined: 02 Feb 2008
Posts: 150

PostPosted: Fri Feb 22, 2008 8:08 pm    Post subject: Reply with quote

Great looking little bugger and nice depth too. It makes me feel like having a crab cake.
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Perl



Joined: 03 Oct 2006
Posts: 262
Location: Sweden

PostPosted: Sat Feb 23, 2008 12:26 am    Post subject: Reply with quote

Most be an explanation to this phenomen

If somebody have an nice solution to this
it will be very intressting

Best Regards
Pär Lundqvist
Sweden
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gpmatthews



Joined: 03 Aug 2006
Posts: 1040
Location: Horsham, W. Sussex, UK

PostPosted: Sat Feb 23, 2008 3:22 am    Post subject: Reply with quote

I will post a more complete description and assessment in the Technique gallery. I think, despite Bernhard's excellent(!) suggestion, maybe I'll call it VOILA for Variable Oblique ILluminAtion. So there it is, voila!...

I think, also, that it would require an awful lot of these nauplii to make just one Frez sized crab cake! My wife makes excellent Thai crab cakes, perhaps I'll talk to her... prik nam pla, anyone (very hot Thai fish sauce & chilli condiment)?
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