Re: affordable camera suggestions

Posted by Martin Kielhorn on Feb 17, 2011; 10:16pm
URL: http://imagej.273.s1.nabble.com/affordable-camera-suggestions-tp3685628p3685637.html

2011/2/15 Gabriel Landini <[hidden email]>:

> On Monday 14 Feb 2011 22:41:38 David Gene Morgan wrote:
>>       I'm responding to the question of whether there is a reason for the 3x
>> sampling reported to be commonly used by microscopists.
>
> I think both Brad's and your explanations were very useful, thank you.
>
> There seem to be a variety of possible combinations of extra optics in the
> extension tubes that one could add: x0.25, x0.5, x0.75, x1, x1.2, 1.5, x2.5,
> x3.3, x4, x5.
> Presumably these also have an impact on the resolution of the
> image projected on the sensor. Is that just a multiplicative effect only, or
> it there further deterioration of the image resolution due to these?

In a microscope the tube length (distance between principal planes of
objective and tubelens)
should be the sum of the focal length of the tubelens (f_Tl=164.5 mm
for most Zeiss systems)
and the focal length of the objective (f_obj=164.5/MAG=2.61 mm for a
magnification of 63).

If this condition is fulfilled the system is called 'telecentric' and
has the property that features
in different z-slices don't change their size, when you focus through
the sample.

In our Zeiss Axiovert 200M the tube lenses (Zeiss calls them Optovar)
1.0x, 1.8x and 2.5x are
all in one turret at the same distance from the objective (presumably
164.5 mm). These lenses
look like singlets with small curvature, so I think the principal
planes are close to the center of the lens.
This, however, means that the system is telecentric only for an Optovar 1.0x.

The Optovar 2.5x should actually be in a distance of 2.5 * 164.5 mm =
41 cm from the objective.
I have never figured out a way to quantify the effect of
non-telecentricity on the images.


Regards, Martin

--
Martin Kielhorn
Randall Division of Cell & Molecular Biophysics
King's College London, New Hunt's House
Guy's Campus, London SE1 1UL, U.K.
tel: [phone],  fax: [phone]