Lenses for substage illumination

[Will Milne]

Hi

Act of madness I know but...... I'm in cheap/DIY mode

I was wondering what the requirments are for a field lens in order to be able to set-up Koehler/Kohler illumination on a scope. Aperture control I have /focusability I have , what I am puzzled by is the info I have found regarding the objective type required. As far as I can tell what is needed is an Aspherical lens .

From what I have seen in terms of definitions an aspheric lens corrects for both spherical and chromatic aberrations or depending on it's design ... one more than the other . In terms of achieving good Koehler/Kohler illumination which of the two parameters is more critical spherical or chromatic aberrations.

Here is my situation ....

I have a Wild M11 scope with the upper tube/prism removed and a dslr on bellows on a post ala Charles Krebs capturing the direct projection image. Since the M11 has a primitive base I have made an elevated platform that the scope sits on, underneath that I have a Zenon light source for viewing and a flash, both mounted on a sliding table so I can switch back and forth.

There is a hole in the M11 base that the illumination comes up through to light the specimen , above which I want to add a "Koehler/Kohler" illumination modifier.

Hope that all makes sense

Basically taking an older scope with basic/limited substage lighting and adding Koehler/Kohler abilities.

My main condenser is a Wild Phase which seems nicely corrected and gives transmitted bright/dark and annulli oblique . I have tried using a Wild aplantic ( spherical aberration corrected) condenser as a field /collector /aperture control modifier and that has been quite successfull but was hoping to get some advice on how to fine tune .

Will

[discomorphella]

Hi Will--

You don't need an asphere to make a kohler system, in fact Edmund Industrial Optics has a "Kohler Calculator" on their applications page you can use to start the design. The asphere just gets you reduced spherical and other aberrations, but for your purposes its probably ok to use a pair of standard PCX lenses or achromat pairs if you're really worried about chromatic aberration. Here's the link:

http://www.edmundoptics.com/technical-s ... chToolID=4

You'll still have to do some tweaking to get the lenses optimally situated, but you can do that "on the bench" too, or use whatever ray tracing software you can get your hands on.

Regards,

Dave

[Will Milne]

Hi Dave

Many thanks for the info and link--- that's a great resource.

cheers

Will

[g4lab]

Does your scope have a mirror holder or a 45 degree mirror in the base.

Then all you need is microscope lamp and an achromatic lens to image the filament on the aperture diaphragm of the final condensor.

Usually an illuminator plugged into the rear bottom of scopes with phase contrast.

You could use an old Zeiss lighting tube with a 6v 15watt ribbon wound square illuminating surface. Or a 6 volt 20 or 30 watt halogen would give you enough light to dazzle yourself.

PM me I probably have the stuff you need in my junk box so you don't need to redesign the wheel

I went back and reread you post more carefully. What kind of Xenon source are you using. Doesn't it have a collector lens? It should.

Gene

[Will Milne]

Hi

Here is my direct projection rig to date , base is on sorbothane feet/riser is on sorbothane sheet/cam is isolated from scope via a PB6 bellows/shade arrangement on a post ala Charles Krebs...



the lighting is .....



Zenon light is a hardware store 12V undercounter puck unit with no collector lens for viewing and a 45 deg. mirror in a diffused Flash box for image capture , with both on a sliding tray - so I can switch back and forth between them and keep centrality.

I was having a difficult time understanding why most setups are diffused after the collector lens if Kohler is supposed to produce even illumination by default, so decided to diffuse the light sources before the collector/field stop - Zenon and Flash to reduce their contrast - slightly so I could get a better histogram . Not sure if that is correct in terms of good Kohler, but photographically it seems to produce a better result in my case than diffusing after the collector/field stop.

Here is the dual condenser arrangement ( the polarizing filter was left there after I was was playing with partial cross polarization). The Phase Main Condenser I have been using simply to get the addition of oblique lighting using the phase annulli...



The lower condenser/collector/field stop is a Wild Aplanatic with the upper cone removed.

Setup has been

- 10x objective focused on dirty slide
- Main Condenser aperture fully open
- Fully close Collector Condenser aperture and center
- Adjust Main condenser height until Collector condenser aperture is sharply focused
- Adjust Main Condenser aperture until flare and colour fringing disappear from edges of Collector Condenser aperture.
- Open Collecter Condenser aperture until illumination fills frame.

With this setup I get dead even illumination across the frame/sensor, CA is not worth mentioning unless the Main Condenser aperture is not adjusted to suit the objective NA and then it's noticable on the RAW captures. Switching objectives I simply adjust both apertures to suit field of view and NA and the high resolution /no CA condition is maintained.

So given that I have never had the opportunity to look through a properly setup scope is this a description of a functional /correct/acceptable Kohler setup? Or are there places I can tweak this to get improvements with a a more refined/dedicated collecter lens ?

I realize I am exploring here but it is my way of learning and do appreciate and act on the help and advice you all offer.

Objectives are

Nikon CF Plan 4x 0.13 160/-
Nikon 10x 0.25 160/- ( till I can find a CF 10x 0.3)
Nikon CF Plan 20 0.5 160/0.17
Nikon CF Plan 40 0.7 160/0.17

Will