Illumination for series 20 dark phase contrast

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bcjolly
Posts: 27
Joined: Sat Jul 06, 2019 2:50 am

Illumination for series 20 dark phase contrast

#1 Post by bcjolly » Wed Sep 23, 2020 8:11 pm

Almost a year ago I purchased a nice series 20 by American Optical. Over time I purchased the correct accessories for dark phase operation. I have gone through the manual and set everything up according to factory recommendations. Using a 10x bright fielld objective and no filters in the carousel I can get full illumination in the field of view. However, when I go to phase operation, I get a bright field of view in the middle and a slightly darker view in the rest of the field. I know that for phase operation there are phase annuli in the turret and phase rings in the objectives. Is this normal for this microscope?
Barry Jolly

PeteM
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Joined: Tue Dec 06, 2016 6:22 am
Location: N. California

Re: Illumination for series 20 dark phase contrast

#2 Post by PeteM » Wed Sep 23, 2020 10:49 pm

Are you trying to get phase contrast using the regular 10x brightfield objective - or a 10x phase contrast objective and a 10x phase annulus in the condenser?

bcjolly
Posts: 27
Joined: Sat Jul 06, 2019 2:50 am

Re: Illumination for series 20 dark phase contrast

#3 Post by bcjolly » Thu Sep 24, 2020 1:35 am

I used a regular 10x to center up the apertures of the AO series 20 and used the phase objectives and anulli in the turret for phase.
Barry

apochronaut
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Joined: Fri May 15, 2015 12:15 am

Re: Illumination for series 20 dark phase contrast

#4 Post by apochronaut » Thu Sep 24, 2020 2:00 am

bcjolly wrote:
Wed Sep 23, 2020 8:11 pm
Almost a year ago I purchased a nice series 20 by American Optical. Over time I purchased the correct accessories for dark phase operation. I have gone through the manual and set everything up according to factory recommendations. Using a 10x bright fielld objective and no filters in the carousel I can get full illumination in the field of view. However, when I go to phase operation, I get a bright field of view in the middle and a slightly darker view in the rest of the field. I know that for phase operation there are phase annuli in the turret and phase rings in the objectives. Is this normal for this microscope?
Barry Jolly
No, you should get a nice even mid grey background with sharply defined objects , seemingly on it or above it. There are a few things to make sure of. Make sure that you remove the thick doublet lens in the bottom of the phase condenser, if the condenser you purchased originally came from a series 10. It is used only for the 10 and removed for the 20. Make sure the condenser is the cat.# 1242 or the cat.# 1201. If you have a 1087, let me know and I will send you the set up for that. Make sure you establish a Koehler condition. Make sure both your field diaphragm and your condenser iris are wide open. They can be adjusted slightly to ameliorate the contrast later. Make sure the annuli are centered.
I am assuming that the illminator has been properly centered and focused and that the objective being employed is either a cat.# 1211, or 1224.

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