Re: affordable camera suggestions

Posted by melkor2.0 on Feb 12, 2011; 3:09pm
URL: http://imagej.273.s1.nabble.com/affordable-camera-suggestions-tp3685628p3685641.html

Dear Brad,
I've been reading about Nyquist theorem and so, and I don't get the math, it
seems 3x it's at the maximum limit of the linear region, but how do you
calculate the final total resolution required? you say for 60x - 1.4 we need
0.9 megapixels and to work with 3x linear maginification, that is nine times
this, can you explain or reference the math?
thanks indeed,

ramon

On 12 February 2011 14:22, Brad Amos <[hidden email]> wrote:

> 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 [phone] (lab)
> fax           [phone]
> Emails [hidden email]
> or [hidden email]
> Websites:  (Lab) http://www2.mrc-lmb.cam.ac.uk/SS/Amos_B/
>  (Personal) http://homepage.ntlworld.com/w.amos2/
>