basic abbe condenser use

[petew]

Hello all, thanks to Mr.Microbehunter Oliver's youtube videos, which got me interested in this as a hobby, I bought an introductory Bresser Biorit TP microscope that has an Abbe condenser.

Based on youtube video 001 "How to use a microscope", I follow these steps for using the condenser:
1) start with lowest 4x objective
2) raise the condenser closest to the stage
3) close the condenser aperture diaphragm to smallest for best contrast at 4x
4) when change to 10x or 40x objective, open the diaphragm accordingly.

So far this basic method has been working well for me.

Question:
When would I ever want to lower the condenser away from the stage, closer to the light source?
It doesn't seem to make much difference if I raise or lower condenser...

thanks!

peter

[dtsh]

Typically you wouldn't adjust it but in very small amounts, usually 1mm or so from the bottom of the slide is optimal. That said, do you have another iris below the condenser as part of the illumination system, typically called a 'field iris'? If so, try focusing on a slide, then close that lower iris (field iris) just enough that you can see it intrude into view, then slowly raise/lower the condenser until the leaves of the iris come into focus. At that point, you open the field iris up so it's just outside your view. This helps get uniform illumination, but if you don't have a field iris it's OK, many scopes don't have them and they work just fine.

Closing down the condenser iris increases contrast, but at the cost of some resolution and the need for a brighter source of illumination.

I am sure there are many tricks more experienced people know to get more out of the condenser; perhaps we will both learn some more.

[petew]

Thanks! Nice to know that I can just leave the condenser raised and not worry about it.

There's no field iris diaphragm on this intro microscope, so no uniform Koehler illumination for me.
I hope I'm using all the microscopy lingo that I'm learning correctly

Thanks again

[petew]

Thought of a few more newbie questions related to the condenser and the lack of a field iris diaphragm on my intro microscope :

A) My microscope has a swing out filter holder at the bottom of the condenser, which currently houses what looks like a white diffusion filter.
It also has a LED lamp under what looks like a lamp lens, presumably to focus the light unto the condenser.

For this LED lighting setup with the LED lamp lens and condenser light diffusion filter, is something like Kohler illumination still applicable, neccessary, or desirable?
It seems like this kind of LED lens/diffusion filter setup addresses the issue of uneven illumination from the light filament?


B) I'm enjoying reading/searching through old threads on this forum and found this one quite interesting:

https://www.microbehunter.com/microscop ... ent#p65424

The OP of this thread didn't seem to post a followup of his results of simply adding a field diaphragm to his microscope that was lacking one.

I have the same question as the OP for my microscope:

Since I already have a LED lamp, apparently with a lamp lens, and a condenser...
Would it be a simple matter of me removing the diffusion filter from my condenser, cutting out some cardboard with different sized holes to act as a field diaphragm placed over the lamp lens, so I can try Kohler illumination?

I've spent the money I wanted to spend on my intro microscope with condenser, and may not want to spend the order of magnitude more just to try Kohler, so wondering if Kohler would, in principle, be achievable with my setup if I tried to do it the way I described?

thanks again!

[deBult]

A good explanation on Kohler (and Nelson) plus how to set it up (on a Olympus BH2) from Carl Hunsinger:

https://drive.google.com/file/d/1Hd5lqc ... p=drivesdk

[petew]

That was an excellent article - read it 3 times and saved for future repeated reference!
Particularly helpful for me was the distinction made between "pure Koehler" and "modified Kohler", which helped to answer my conceptual questions regarding historical and modern day equipment setups. Thanks!