Posted by
bradscopegems-2 on
Feb 12, 2011; 1:22pm
URL: http://imagej.273.s1.nabble.com/affordable-camera-suggestions-tp3685628p3685631.html
Dear Gabriel,
You will not find resolution values in the scant
literature supplied by microscope manufacturers, but you can calculate how
many pixels you will need from the N.A. and magnification written on the
objective. Assuming Nyquist sampling, the pixel separation (assuming no
extra magnification) is 21, 14 and 16 microns for three commonly-used
objectives (60x N.A. 1.4, 20x N.A. 0.7 and 10x N.A. 0.3). So, if we wish to
capture a 20 x 20 mm square area of the intermediate image (a reasonably
large fraction of what we see in an eyepiece) we need 0.9, 2 and 1.5
megapixels minimum (i.e. to record full detail without any empty
magnification. In practice, microscopists usually choose to work with about
3x the linear magnification at the Nyquist minimum, so this means that the
preferred number of pixels would be nine times this, unless the camera was
recording a reduced area of the intermediate image. This means that the high
pixel numbers of the modern DSLRs are not overkill. This is why standard
PAL video resolution (about 0.4 megapixels maximum) is so hopeless for
microscopy, forcing users to capture only a tiny fraction of the eyepiece
field.
Brad Amos
On 12 February 2011 12:20, Gabriel Landini <
[hidden email]> wrote:
> On Saturday 12 Feb 2011, bradscopegems wrote:
> > If your requirement is for still images, even a medium-price digital SLR
> > camera such as the Nikon D90 will give superb results at higher
> resolution
> > (14 Megapixels).
>
> The resolution is mainly driven by the microscope optics. With a 14 MP
> camera
> one gets what is called "empty magnification".
> I would suggest to find out what are the resolution values of the
> microscope
> objectives are (from the manufacturer manuals) and start thinking from
> there.
> Depending on the field width of the camera and the optics, I think anything
> >
> 4 MP or thereabouts will not capture much more detail than the resolution
> of
> the optical system will be able to provide in a relatively good brightfield
> microscope.
>
> Of course one can subsample large images with empty magnification and
> reduce
> file size while keeping the useful amount of detail, but there are other
> disadvantages. With a SLR one will struggle to make illumination
> modifications
> on the fly to correct for brightfield background illumination using the
> transmittance method. You can do it, but it will be more time consuming as
> one
> cannot check histogram saturation on the fly, etc. then transfer the images
> to
> the computer, reload them, etc. Whether this is crucial it depends on how
> many
> images one is expecting to acquire.
>
> Also remember that colour cameras using Bayer masks will interpolate
> colours
> and that reduces further the resolution of the image data. A good
> alternative
> is to use greyscale cameras with a R-G-B filter wheel or tunable filter so
> each pixel is exposed 3 times (R G & B). This avoids the interpolation.
> Such
> things are, sadly more expensive.
>
> If I had to buy a new camera, I would try to find out what is supported
> right
> now (some camera manufacturers produce IJ plugins that can drive their
> cameras, but be aware that some of these only support manual acquisition,
> and
> not driven from a plugin or macro, which is really useful).
> Check the MicroManager pages to see what it is supported too.
> If you decide to get a camera supported by an ImageJ plugin but without
> macro
> support, you could still use the IJ_Robot plugin to try to automate it. It
> is
> an ugly way of doing it, but it works.
>
> I hope this is useful.
> Cheers
>
> Gabriel
>
--
Dr W. B. Amos FRS
MRC Laboratory of Molecular Biology
Hills Road, Cambridge CB2 0QH
telephone 44 (0)1223 411640 (lab)
fax 44(0)1223 213556
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