Multi camera adapter

[Jeff Spector]

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Greetings,
 I was asked this by a colleague and thought I'd pass it along to the list
as it may be of value to others. They are designing a mutli-camera adapter
for a Nikon based TIRF microscope using two emccds. They plan to use 1 lens
to collimate the light out of the microscope and two separate lenses (one
for each camera)  to focus on each camera, the second lens will have a
focal length that is twice the first thus giving a 2x mag. I guess they
were thinking f=100 and 200 mm for the lenses. Their questions was, is
there any advantage to using a 2" diameter lens than to a 1" diameter lens,
given that the microscope exit port field of view, and the emccd entrance
port are both less than 1" anyways about 0.7 inches if I remember
correctly. They asked if a larger (2") lens would give less aberration
because you are going "more through the middle" than a 1" lens where you
are getting closer to the edges.
any thoughts?
 Thanks!

[Michael Giacomelli]

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>Their questions was, is
> there any advantage to using a 2" diameter lens than to a 1" diameter lens,
> given that the microscope exit port field of view, and the emccd entrance
> port are both less than 1" anyways about 0.7 inches if I remember
> correctly.

It depends on if you need the added aperture.  When I added a camera
to one of our scopes using a 250 mm tube lens, I ray traced the design
and got that I would need a 30 mm aperture on the tube lens to avoid
vignette on the edges of the sensor (which was only 11 mm wide).  As
you add longer lenses, you will need to make them larger to maintain
the same FOV.

> They asked if a larger (2") lens would give less aberration
> because you are going "more through the middle" than a 1" lens where you
> are getting closer to the edges.

Possibly, but if you are concerned about aberration you should
probably simulate the design first.  The choice and orientation of
lenses is going to have a much bigger impact than the diameter
(assuming you can use a smaller size lens that is).

Mike

[James Kerin]

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*** Commercial Response ***

We hope the following thoughts will help answer Jeff's questions. First,
the focussing power of a lens is proportional to the curvature of its
surfaces, so is independent of its size. However for a given curvature,
the incident angle at the edge of the lens is going to be greater if the
lens is bigger, hence the aberrations will be higher. To keep
aberrations down to acceptable levels, larger diameter lenses therefore
tend to have longer focal lengths. Obviously what is “acceptable” is
going to depend on the application, but one has to consider both
geometric and chromatic effects. “Achromatic doublet” lenses are widely
available, and although their chromatic correction is adequate for most
purposes, they give good geometric aberration performance only for
relatively small fields of view (specifically, they are only corrected
for on-axis images, and they suffer from astigmatism that increases with
the square of the field of view). At Cairn we found their limitations to
be sufficient for us to have moved to custom multielement lens designs
for our camera adapters several years ago. However they do form the best
starting point for a “homebrew” optical solution, where the aberrations
can be reduced by using relatively long focal lenghts, preferably closer
to 200mm rather than 100mm in this instance.

Cairn multi camera & single camera adapters -
https://www.cairn-research.co.uk/products/fluorescence-detection/image-splitters/

The other question concerns lens diameter. 25mm diameter lenses /may/ be
just about adequate for some camera applications, but there is a
potential problem for the “infinity” section between the defocussing and
refocussing lenses. Although the light from any one point on the image
is collimated in the infinity section, its position within the image is
encoded by its angle relative to the optical axis, and this can cause
the diameter of the overall beam to increase as it goes through that
section, although the details of what goes on there do depend on the
preceding microscope optics. Geometric aberrations through the relay
system are likely to be minimised when the length of the infinity
section is close to the sum of the focal lengths of the collimating and
refocussing lenses (a so-called “4f” system), but that means the
infinity section will be relatively long. Our recommendation for this
sort of application is to use lenses with a clear diameter of at least
30mm in order to be on the safe side. This sort of consideration is
going to be increasingly important for the future, as both microscope
fields of view and camera chip diameters are both tending to be on the
increase.

Dr Martin Thomas

President, Cairn Research Ltd.

https://www.cairn-research.co.uk/





On 3/9/2017 5:54 PM, Jeff Spector wrote:

> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> Post images on http://www.imgur.com and include the link in your posting.
> *****
>
> Greetings,
>   I was asked this by a colleague and thought I'd pass it along to the list
> as it may be of value to others. They are designing a mutli-camera adapter
> for a Nikon based TIRF microscope using two emccds. They plan to use 1 lens
> to collimate the light out of the microscope and two separate lenses (one
> for each camera)  to focus on each camera, the second lens will have a
> focal length that is twice the first thus giving a 2x mag. I guess they
> were thinking f=100 and 200 mm for the lenses. Their questions was, is
> there any advantage to using a 2" diameter lens than to a 1" diameter lens,
> given that the microscope exit port field of view, and the emccd entrance
> port are both less than 1" anyways about 0.7 inches if I remember
> correctly. They asked if a larger (2") lens would give less aberration
> because you are going "more through the middle" than a 1" lens where you
> are getting closer to the edges.
> any thoughts?
>   Thanks!

--

*James Kerin
*

*Marketing Director*
Cairn Research Ltd
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UK

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