Dear Barbara,
I have a hard time to follow your explanations. The light
gathering capacity in a luminescence detection system is determined by the NA
of the objective, and unless you throw away the gathered light later, I do not
see how you would gain light with a high NA tube lens. A high NA tube lens
will allow to have a short overall optical apparatus, which can then nicely fit
into a small dark box, so one can avoid any kind of stray light to enter, which
is important for the typically very long exposure times in luminescence imaging,
but that’s about it, I would say.
Cheers, jens
From: Confocal Microscopy
List [mailto:[hidden email]] On Behalf Of Barbara
Foster
Sent: Friday, March 06, 2009 17:37 PM
To: [hidden email]
Subject: [SPAM] Fwd: Re: Importance of the tube lens NA
Date: Fri, 06 Mar 2009 10:25:52 -0600
To: [hidden email], Confocal Microscopy List
<[hidden email]>
From: Barbara Foster <[hidden email]>
Subject: Re: Importance of the tube lens NA
Hi, Gabor
This is an interesting concept. If you use the expanded version of the
Rayleigh criterion [1.22 lamda/(NA obj + NA cond)] and also take a look at the
impact on the diffraction image, a number of things emerge which might answer
your question.
For example: if you use a simple ruled grating aligned N-S on your stage,
the diffraction pattern will be a series of horizontal dots (emails don't
permit a full discussion of the physics... see any basic physics review
book). The bright, central zero order spot carries information about the
background. The other spots carry information about orientation, spacing,
and edge information. To convey spacing and orientation from the object
to the image, the receiving lens (the one that FORMS the diffraction pattern)
only needs to capture 2 adjacent diffraction spots. However, the larger
the NA, the greater the ability to capture neighboring spots (ex: moving from
the center of the pattern to the right: 0, +1, +2, etc.). The more spots
collected, the greater the edge definition. Also, the greater the NA, the
greater the summed intensity of the entire pattern. (Again, emails don't
permit much discussion of all the physics).
It is not clear to me why putting the tube lens near the objective is
important... It is more likely that they have put the SAMPLE near the
objective, setting up the condition for infinity corrected optics. However,
there is a rule in physics that says that intensity falls off as the square of
the distance, so perhaps putting the tube lens nearer to the objective allows
them to maximize intensity collected from the diffraction pattern. If you
are using a high NA tube lens, by default, you need to move the detector
closer, since the distance to the image plane will be shorter.
Finally, even though you did not mention it, a higher NA lens is often
engineered with greater aberration correction. That extra engineering is
also likely to increase the throughput, enabling the observer to detect
more.
All of this might add up to 10x improvement in detection and, actually,
resolution and edge information. You've piqued my curiousity... Looks
like time for a chat with Olympu to learn more!
Hope this was helpful,
Barbara Foster
Barbara Foster, President and Sr. Consultant
Microscopy/Microscopy Education
7101 Royal Glen Trail, Suite A
McKinney TX 75070
P: (972)924-5310 Skype: fostermme
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March 2009. Call me for a free assessment and quote.
At 08:19 PM 3/5/2009, you wrote:
Dear All,
We just had a presentation from Olympus about their LV200 bio-luminescence
microscope. As they claim (and demonstrated with some images) this system is
significantly (approx 10x) times more sensitive then a conventional microscope
used with the same objective and camera (and pixel size/resolution). Olympus
argues that the "secret" is that they put the tube lens close to the
objective (probably less important) and put the camera very close to the tube
lens meaning that they use a high-numerical aperture tube lens. Now I simply
don't understand why this should result in a significantly higher detection
intensity (and the Olympus representative was also unable to give a detailed
explanation).
Does anyone of you have an idea why a high NA tube lens would be advantageous?
And if this is so nice - why it is not applied in conventional microscopes?
Thanks Gabor
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