Further Notes on the Micscape
Article
'Experiments with a miniature CCD camera'
.... or the 'pros and cons' of infra-red sensitivity!
by Dave Walker
with the help of Tony Dutton (UK), Ron Neumeyer (Canada), Mervyn
Hobden (UK)
and Max Jens Jensen (Denmark)
In the December 1997 issue of
Micscape I reported some trials I made using a miniature black
and white CCD camera for video microscopy. My results were a
little disappointing, as I particularly had difficulty in
achieving good high contrast images.
I've had interesting emails from the people listed above who remark the low contrast may be caused by the CCD's sensitivity to infra-red. Many of the CCD sensors on the market are sensitive to infra-red for low light surveillance purposes. Although the CCD camera I used wasn't catalogued as being specifically intended for IR imaging, it's possible it may have been at least partly sensitive to this end of the spectrum.
I enclose (with their permission) a selection of their comments below as I think they may be of value to other amateurs trying black and white CCD video cameras.
Ron Neumeyer remarks:
'Hi Dave,
Read your article on miniature video cameras, they are also available here (they use a 9 volt battery for power). B&W specifications are better than colour (which is around 230 lines).
I noted you had a problem with contrast. When I first started with video I used a Panasonic like yours. At first the contrast was much less than expected. However, I inserted a dense green filter (thick) in the carrier and wow ... a major improvement! You might want to give it a try.
In addition, I recently read an article on the effect of near infra-red radiation (NIR) on CCD performance. This radiation can seriously degrade image quality. To check the CCD's sensitivity to NIR aim a remote control channel changer at the device. If the transmitter flash is visible then the CCD is sensitive to NIR. A heat filter (e.g. from an old slide projector) can be used to remove NIR. (The thick green glass filter may remove NIR, which might explain its effect on image contrast.)
All the best,
Ron'
Tony Dutton remarks:
'Hi Dave
I have just thought of something that may help you regarding lack of contrast with a monochrome camera, either Vidicon or CCD when used with visible light.
As these cameras are usually very sensitive to infra-red up to about 1000 nm wavelength, it is essential to include a good quality heat filter somewhere between the light source and the substage condenser.
Failure to do so can cause lack of contrast and a less clear image. Obviously this would depend upon how much IR is absorbed in the microscope's optical train. Having experimented with IR quite a bit I have found that a fair amount in the 880 nm gets through if an IR emitting diode of that wavelength is used when working with magnifications up to x 200.'
Best wishes, Tony Dutton, (Quekett)'
Unfortunately, I don't have the camera any more to assess it's infra-red sensitivity and the effect of heat filters in the optical train, but with IR filters these miniature CCD cameras may indeed be a low cost route into video microscopy for the amateur. My colleague Mol Smith also remarked that B&W CCD cameras in surveillance applications may use a cine lens with an IR filter lens coating if not for a low light application. Tony Dutton remarks that colour CCD sensors in video cameras often have a blue IR filter mounted in front of the sensor, an inspection of my colour CCD camera shows this to be the case.
Mervyn Hobden and Max Jens Jensen also remarked that infra-red is not usually a problem with colour CCD cameras.
Max Jens Jensen remarks:
'Dear Dave
Just a few comments on the article.
All color CCD-cameras are equipped with IR-filters, at least all
that I have seen, and that's a lot. It is not normal to put
IR-filters on B&W cameras, but it solves certain resolution
problems to put one there. We use an IR-filter on B&W cameras
to solve some problems on displaying red text on a yellow
background. Also be aware that B&W cameras have their
greatest sensitivity in the green area like the human eye, but
they are also able to "see" heat e.g. IR.'
With best regards, Max Jens Jensen'
Mervyn Hobden remarks concur with Max's with some additional comments on avoidance of IR problems:
'Hi Dave
I read with interest your article on Micscape on the small CCD camera. I have just purchased one of these for use on an infra-red microscope I am constructing at work. ( Using the CTS 4000 ) These cameras have no I.R. filter in front of the CCD chip. Therefore they are very sensitive to the near infrared, up to 1.3 micron wavelength. Trouble is, a tungsten bulb pushes out far more energy in the infra-red than it does in the visible. The result is an out of focus image with lousy contrast. You will need some sort of an I.R. filter between the camera CCD and the illuminator, cutting off all radiation above 0.8 micron to get a decent image. The heat stopping filter out of a slide projector would do.
Best Wishes and a Happy Microscopical New
Year,
Mervyn'
Incidentally, since the December article, a very interesting article has been published in the Bulletin of the Quekett Microscopical Club on the use of sub-miniature CCD cameras for video microscopy (ref. 1). The author Tony Dutton reported that infra-red sensitive video cameras can reveal features in subjects normally opaque to transmitted light when infra-red lighting is used. The black and white miniature CCD camera used was highly sensitive to infra-red. This allowed internal organs and features of a beetle to be viewed through the normally opaque chitinous layers (e.g. wing cases and the exoskeleton). The author reported that horn, skin and other substances of interest are also IR transparent.
Tony has also informed me of two articles that have recently been published in the Proceedings of the Royal Microscopical Society which discuss aspects of infra-red microscopy (ref. 2 and 3).
As the miniature video cameras sensitive to infra-red are quite cheap, it will be interesting to see what the potential of infra-red video imaging has in the amateur microscope community. infra-red lighting (both transmitted and incident) is apparently quite straightforward using the IR emitting LED's (light emitting diodes) that can be cheaply purchased from electronic catalogues.
Comments to the author Dave Walker welcomed.
Acknowledgements
Many thanks to Ron Neumeyer, Tony Dutton, Mervyn Hobden and Max
Jens Jensen for the valuable comments on my previous article.
Also thanks to Tony for the references 2 and 3 and Tony and Max
for other useful discussions on CCD sensors.
A final thought: I was delighted by the valuable information I've received from readers and colleagues on this topic. I hope this illustrates that it's worth writing up your problems with techniques and equipment for Micscape as well as your successes, as there are many people out there who may be able to help, and the feedback may also be a useful compendium of information for other readers who encounter similar problems.
References
1) 'Constructing and adapting sub-miniature CCD TV cameras to
the microscope' by J A Dutton. Bulletin of the Quekett
Microscopical Club, 1997, 30, p. 21-22. Also the record of a
demonstration by J A Dutton at the QMC Annual Exhibition (1997)
on p.41-42 of the same issue.
2) 'Infrared Light in the Microscope: History, Theory & Practical Aspects' by Tim Richardson. Proceedings of the Royal Microscopical Society, Vol 32, Part 4 December 1997, pp. 229-235.
3) 'Practical Infrared' by Tim Richardson. Proceedings of the Royal Microscopical Society, Vol 32, Part 4 December 1997, pp. 236-242. This informative article deals in depth with photon detection and includes a simple DIY circuit and drawing to enable a detector to be constructed. Both articles are aimed at the professional reader but there are useful graphs and definitions included.
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