Janice,
I can't directly answer your questions since I don't do that many gels
anymore, however, my hobby is photography, and I have spent a lot of time
working with scanners and digital cameras.
It sounds like your main problem is that you are not able to adequately
image bands you can see with your eye. All but the cheapest scanners should
be able to do as well as your eye, but usually not using the default
settings. I don't know what software you are using to capture images, but
be sure you have the black and white points set appropriately in the
prescan. These are usually set using the "histogram" tool. With the black
and white points set correctly, the range of 255 levels of grey (or
individual color) the scanner can capture will start at the lightest part
of the gel and end with the darkest. Without setting these points manually
the range will often be much wider than the range of the gel, and the steps
will be larger, possibly missing your faint bands. You can also adjust the
"Curves" to get more sensitivity at the light end of the scan (the steeper
the curve in that region the greater the difference between steps). Setting
both histogram and curves for the color specific to your stain should also
boost sensitivity.
Another thing you can do to improve the results from your scanner is to use
a filter to boost the contrast. I remember that Kodak used to sell a kit
for recording Coomassie stained gels on photographic paper that included an
amber filter (the complimentary color to the blue of Coomassie). You would
lay the gel on top of the filter and expose the film through the filter
plus gel. That would turn the blue bands black, and increase the contrast.
I can't remember the Wratten number of the filter, but that is something
that can probably be looked up. Note you could use an appropriate filter
with a digital camera as well.
So, is a scanner better that a digital camera? How much quality do you
need, and what are you willing to spend to get it? An average 2 megapixel
digital camera, like the Olympus ($500 - $1000) that many people here at
Berlex use for recording their gels, will give you a picture that is
equivalent to a point and shoot film camera. It will look fine if you don't
print it larger than 5 x 7 in. The dynamic range of most digital cameras is
pretty good, I think better than most low end scanners (scanners can have
up to 5 mirrors in the light path, cameras 0-1, each causes a little loss
of light). The resolution of a 2 megapixel camera is around 2000 pixels in
the long direction. That will be the maximum resolution across your gel, no
matter what size the gel is. In a scanner like the Epson 1200 (~$300) the
resolution is 1200 pixels per inch. So, if your gel is larger than 1.6 in
wide you will get more resolution from the Epson scanner (probably too much
if your used full resolution). More expensive scanners (Microtek Artixscan
T1000, $1500) have resolutions of 1000 pixels per inch, but with 14 bits
per color, and Dmax (density range) of 3.9. Compare this to the Epson with
a Dmax of 3.2 (note it is a log scale) and 12 bits per color. The
additional bits and wider density range would make it easier to detect, and
accentuate, through software, the small differences in color between your
faint bands and the gel background. On the other hand, a small digital
camera is easily portable and requires minimal knowledge to use...
Sorry for the long post, but what I mentioned only briefly usually is a
chapter or more in a book on scanning. To try to condense this in to a
couple sentences; In the price range < $2000 scanners are capable of a
higher quality images than the digital cameras, but may require some
training to get the best possible image from them. The cameras are easy to
use and very intuitive. Image manipulation either by the use of software of
colored filters can improve the image from either source.
If you have questions about what I was trying to say let me know and I'll
try to explain it in a way you can use. Also, in your area there are two
good resources: Keeble & Shuchat on California Ave in Palo Alto (327-8996)
(talk to their industrial department they used to set up camera based gel
recording systems. They also have a digital department and can supply
Wratten filters). and Bear Images 417 Lambert in Palo Alto (813-0409). Bear
has everything digital, you want a $30,000 digital camera with a 15,000 x
12,000 pixel image?
Tim Slattery
Berlex Biosciences
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