DIC Conversion

[gpmatthews]

This is the story of a cloud with a silver lining, which I thought might be of interest to anyone that finds themselves in a similar situation as myself with some bits and pieces that don't fit the equipment available.

Once upon a time there was a lab that owned a Leitz microscope with DIC. Unfortunately someone broke it and the microscope was junked BUT, a few of the bits found their way to a good home thanks to an ex-colleague/good friend ...

... including a Leitz ICT substage condenser with carousel to match 3 Leitz ICT objectives (x16, x40, x100), 2 phase contrast objectives (x25, x50) and one "straight through" position... also, the relevant objectives on a quintuple nosepiece and a sheared off mounting fork with dovetail fitting to take the substage condenser. The objectives are for a nominal 160 mm tube length and the nosepiece has an integral lens, presumably to match the objectives to the Leitz standard 170 mm tubelength.

Unfortunately, I do not own a Leitz stand. My usual "workhorse" stand is a Zeiss Standard GFL of nominally 160 mm tube length.

So... I dismantled the Zeiss substage and borrowed the rack and dovetail slider, manufactured a new substage mounting plate from perspex which was intended to be a trial assembly pending making a metal part. I had to make a minor mod to the Zeiss dovetail (a rectangular recess) in order to permit the assembly to sit far enough back to be centrable. It is still able to be returned to its original function on the Zeiss substage mounting, however. The broken Leitz substage mounting bracket was drilled and bolted square to the new perspex part. This completes a carrier that will take the Leitz substage condenser in the correct dovetail mounting. It turns out that the perspex part is quite rigid enough and so I will not need to remake it in metal.

The rotational position of the objectives in the Zeiss quadruple nosepiece is critical in order to align the Wollaston prisms correctly, so I made spacing washers from polystyrene sheet (approx 0.3 mm thick). These ensure that the objectives are in the correct orientation when fully screwed in.

Finally, as a test piece to demonstrate that the DIC does actually work, I took a stack of 32 images of Actinoptychus (a favourite test subject of mine). It isn't the most technically perfect image, but I think it shows the system is in working order. The objectives seem to match the tube length of the GFL OK, although there is a little spherical aberration detectable with the x16 objective. I have yet to try the x100 oil immersion objective.

Next, some live subjects, maybe with flash...





Zeiss Standard GFL Microscope
Substage: Leitz ICT in modified mount
Objective: Leitz x40/0.70 NPL Fluotar ICT
Ocular: Watson x8 Conmpensating
Stack of 32 images combined with Helicon Focus, only minor post-processing. No artifacts removed or retouched.

[Charles Krebs]

Graham... you have always been very inventive! I look forward to seeing more of the results from your hybrid system.

I have found that occasionally certain diatoms (and some other "hard" multifaceted subjects like certain amoeba tests made up of tiny sand particles) do not always work out well in DIC. I think the subjects composition tends to mess up the "sheared" DIC light in strange ways.

But I know you will have a lot of fun with it!

[gpmatthews]

I've had a few requests for images of my conversion. so here goes:


This first picture shows the condenser in situ (lowered for ease of viewing). The condenser controls are at top for centreing and for flip out top lens, below that slider control for retardation plate and rotation lock for polariser. Below that, thumbwheel for polariser rotation. The back of the condenser actually rests against the mounting plate.


This is with the condenser removed and shows the Leitz mounting bracket fixed to the perspex plate. It is important to get the mounting plate as high as possible, but the position of the 3rd (top) mounting screw for the rack constrains this because of the condenser centreing ring diameter and the need to provide a recess to take this. There is sufficient movement to focus the condenser, however. There is normally a screw-stop in the hole on the LH of the picture above the mounting bracket. This has to be removed.


This is a shot of the condenser. At the bottom, the polariser assembly can be swung out for brightfield work. The top lens can be flipped out for low power work.

I hope this helps explain how the condenser is mounted. There is nothing special about mounting the objectives other than choosing the right thickness shim washers to ensure they screw in giving the correct orientation. This is critical.