Could use some help: how to properly use the coverglass correction collar

[deBult]

Ha,

Would appreciate you guidance: I recently obtained a 40* objective with a coverglass correction collar: how do you set up this properly please?

When you turn the collar the focus changes as well: so setting it up requires a balancing act between the focus nob and the correction collar? Could use some help here.

Würde mich über Ihre Anleitung freuen: Ich habe kürzlich ein 40 * -Objektiv mit einem Deckglas-Korrektur erhalten: Wie stellen Sie dies bitte richtig ein?

Wenn Ich den Kragen drehen, ändert sich auch der Fokus: Das Einrichten erfordert also einen Balanceakt zwischen dem Fokus-Nob und dem Korrekturkragen? Könnte hier Hilfe gebrauchen.

Best, Maarten

[limno]

Hello Maarten,
a balancing act is not necessary. But you have to pay attention only to turn the correction collar and not the RMS-screw-thread. I have an apochromatic LOMO- objective (water immersion) with a correction collar and I use thinner coverglasses (100 µm).
Best
Heinrich

[deBult]

Heinrich,

Thanks, I'm using an Olympus lens and the RMS-screw is NOT moving, but still the focus appears to be changing when adjusting the correction collar. Still stuck on how to use this properly.

Maarten

[Soki]

Hallo Marteen,

leider ist das auch bei mir ein Balanceakt. Ich verwende mein Nikon CFN Planapo 60 0.95 160/0.11-0.23 fast ausschließlich im Bereich 0.15 - 0.17, auch bei sehr alten (100+ Jahre) Präparaten.

Ich nehme als Beispiel mal eines von Annes Diatomeen-Streupräparaten:
Ich kenne die exakte Dicke der Deckgläser nicht, aber ich habe fast immer bei 0.15mm das beste Bild.
Je nach Lage verstelle ich auch innerhalb eines Präparats die Deckglaskorrektur.

Besonders gut erkennen kann man es mit höher vergrößernden Okularen oder im LifeView mit Zoom, ob das Bild besser oder schlechter wird. 
Am besten ist natürlich ein eingebauter Fokusausgleich, das hatten aber nur wenige Hersteller im Angebot (Leitz z.Bsp.)

Grüße,
Simon

[reblaus]

Hi -

Seems to be normal - the focus of my Zeiss 40x/0,95 0,11-0,23 mm will change too (considerably!) if I turn the correction collar. I dont know wether this is true for all types of objectives with coverglass correction, though.

Best

Rolf

[Flagellate]

Hi Maarten,

of course, when you change the lens correction the speciement gets slightly defocused (since you change distances between lenses and  thus the focal length). A kind of balancing process between focus and correction is not needed. But you need to balance the correction to your coverglass.

The best is
1. pre set the coverglass correction to the thickness of your coverglass as good as possible (using the scale at the objective).
2. focus and check the image quality.
3. tray to enhance the quality by setting up the thinkness slowly by reducing or raising the correction and focus again.
4. repeat step 3 until you get a sharp image.

In phase contrast the halo-effect is reduced during correction and the image gets sharper. This is a good indicator for the correction. In bright field pay attention on sharpness.

At the beginning you will need more time but after a while it will go fast.

It's helpful to play around with the correction to get a feeling for it. For instance choose the highest or lowest correction value and try to focus. It will work some how but you will see that the image quality is bad. This is not a matter of wrong focus at your microscope. It's due to the worng lense distance of your objective. Now get closer to the correct setting and you will see the image quality gets better.

Tobias

[Rene]

Hello Maarten, focus change is indeed pretty much unevitable, even for the newest optics abeit a lot less than with the 160mm era objectives.

For fine-tuning of the correction collar, set condenser iris to minimal 3/4 of the objective aperture. Focus on a small blackish dot, focus through continually while adjusting the correction collar. The collar is set correctly when the hazy image above focus is more or less similar to the below focus image. You'll get better in time ;-)

Best wishes, René

[deBult]

Thanks for the guidance,

Apparently as with  most topics in life it appears to be practice, practice, practice and practice once more.

Best, Maarten

[Bob]

The collar is set correctly when the hazy image above focus is more or less similar to the below focus image.

Hi Rene, there even is a theory behind the chaos! Thank you, I wasn't aware of this method.

My Zeiss Jena Apo 40/0,95 also defocusses when I change the cover slip correction setting.

Viele Grüße,

Bob