I have loaded some DLC images into two folders on the following newly created site.
  Link : http://picasaweb.google.com/selwyn.stleger

One set relates to diatoms and the other to non-repetitive structures.

Diatoms
-------
These images concern F. Rhomboides and AP.

The FR images show surface detail indicative of dotting but are only a marginal test of a 0.95 NA dry objective.

The AP images certainly do not show an order of magnitude improvement in resolution overall but the beading along the edges is interesting. Is some detail emerging? Why should mere diffraction artifacts introduce this impression, perhaps someone knows?

The DLC images involve differing horizontal positions of the DLC plate on the field diaphragm and differing vertical positions of the condenser and may go beyond those recommended by Barry Piekos.
What is interesting is how different some of these images are; for instance concentrate on the detail at the bottom right side in the first set of images. You may find it helpful to download some to compare side by side. Are these all different representations of the same structure? Are some artifacts? How can one know which is which?

In one of the other folders I have some protists which need confirmation of identification.

Selwyn

Selwyn,
It's great to see some new DLC images - thanks.

I don't know how the Picassa site is set up, but it would be very helpful to have a number associated with each image - similar to the Ap label on the top-left image - for upcoming discussions.

For instance, do the 3 images to the right of the Ap labeled image show the subtle effect of a very small movement of the convex edge plate? Or are they intended to demonstrate something different for your DLC setup?

Regards, Keith

Hello Selwyn,
I have read the term -beading- in photo images a couple of times. What is that?

Dan

Dan,
The term 'beading' seems most usually to be applied when a line of dots on a diatom cannot be fully resolved and they appear as beads on a string rather than separate. I was using it to refer to what appear to be rows of beads at the edges of the diatoms which could correspond with the end of rows of dots (dots not resolved). Under resolution high enough to show striae on AP one notices that the edge of the specimen seems to bulge in and out, as in my beads, with each bulge correspnding to the end of a row.

Hope that helps.
Selwyn

Keith,
I am not fully used to Picassa but there doesn't seem to be numbering. However, numbers can be put in the captions; incidentally, if one hovers the mouse pointer over a caption hidden text is shown.

I regret that it has not been possible for me to be systematic about DLC plate positions. The mylar moves unpredictably when I touch it and takes a lot of fiddling with. Ideally one would need some kind of mechanism to track the plate over the field diaphragm. Similarly my condenser tends to slip and it's hard to move it up and down in reproducible increments.

Photographing AP (whether with DIC, DLC or darkfield) is a pain because although I can make the camera reasonably parfocal for general use it is very difficult to correctly focus (using either the camera display or a VDU) when imaging specimens on the edge of resolution and contrast. Thus, I take many pictures whilst twiddling the fine focus. On the Zeiss Standard 16 the fine focus is not designed for reproducible very fine stepping up and down. In general use that's no problem and the optics are excellent but when pushing the system to its limit one begins to envy those professionals who have access to a hundred grand 'scope that makes the tea too.

What I wanted to achieve with these pictures was to further stimulate the discussion.

Regards, Selwyn

Selwyn,
I owe you an apology - I didn't check your other folders before I posted. The simple 'alphanumeric captions' that you have for the DLC-DIC comparison images are just fine.

It's a very nice presentation and there is plenty for the group to "chew on"!

Btw, what stand are you using?

Later, Keith

"selwynstleger" wrote:
> I am not fully used to Picassa but there doesn't seem to be
> numbering. However, numbers can be put in the captions...

It does, thanks Selwyn

Dan

Selwyn,
I re-read your post and it seems that you are using a  Zeiss standard16  stand. As some members will not be familiar with this particular stand I tried to compile some basic information:
  Link : www.kscitech.com/MicGroup/Temp/Pic_Zeiss16.htm
to perhaps assist with further discussions.
Please feel free to correct anything that is pertinent to your particular stand configuration.

You wrote:
> I regret that it has not been possible for me to be systematic
> about DLC plate positions.
I'm assuming that you set the field diaphragm wide open (per Piekos) and then move the mylar disc around on top of the diaphragm iris assembly.
> The mylar moves unpredictably when I touch it and takes a lot of
> fiddling with.
Yes, in posts way back we questioned if it would be possible to manually manipulate the disk to the 'critical position' required to observe a DLC effect.
> Ideally one would need some kind of mechanism to track the plate
> over the field diaphragm.
Yes, this is why the Lomo condenser setup used by DonW was ideal for his experiments.

I wonder if a hole was cut, with a diameter approximating that for the Zeiss assembly, in some material having a height equal to that of this assembly it would allow a better support for the mylar disc? Then it may be possible to mark, on the added part, reference positions for the disc. Also, it might allow holding the disc in position with a weight of some form.
Just some thoughts.....

I'll study your Picassa images some more this evening to try and get back to you with some questions and comments.

Thanks again for making all of these images available to us.

Regards, Keith

Keith,
Interesting idea about an assembly. Not sure if I have enough practical skills but will look into it.

The Standard 16 is equipped as follows.

Trinocular

Zeiss "Inko" DIC/Phaco condenser, achr. apl. 1.4 NA top lens DIC slider in intermediate tube. DIC system optimised (and superb) for planachromats but reasonable with planapo. One is supposed to oil the condenser to the slide for DIC at all powers but not doing so for 40x and below has little effect.

The condenser does not have a true brightfield position but I set it to DIC postion 1 (move slider out of the optical path and remove substage polarizer).

The objective used in these recent two series of tests is Zeiss planapo (Phaco 3) dry 40x 0.95 NA with correction collar (obviously)

Camera: Nikon Coolpix 4500. Leitz periplan eyepiece used to connect to camera (good but not quite perfect compensation for planapo which is not noticeable in direct visual work.)

With regard to comments I made a while ago, I still think it would be useful to identify an easily available static specimen (without linear structure) the structure of which is clearly known in visual microscopy at high power and do DLC tests with a lower aperture objective. I can't think of anything suitable. If we can't standardize the specimen type among investigators then the other possibility is to do high/low NA comparison tests on a range of prepared slides.

Selwyn

Selwyn,
A quick question: during your recent experiments (using a convex mylar disk supported on top of the Zeiss field diaphragm/iris assembly) did you see a "broad band of diffracted light" that can be either blue or red depending upon the position of the condenser (relative to the Koehler position) - per Barry's description of DLC?

Thanks, Keith

Keith,
I don't recollect noticing it. I had forgotten about that phenomenon and wasn't looking for it. The condenser was in various positions relative to Kohler. I always started from where the edge of the plate could be seen near the top of the view and, mostly, moved the condenser downwards. As anyone who has tried this will know one gets various effects including at one point something akin to darkfield. Also, it's noticeable that the degree of obliqueness changes and images can skew. Moreover, in my tests the area of the field of view where contrast was most increased was quite limited. Hope that helps.

Selwyn