I've actually thought a lot about using Raman for nucleotide
analysis... alibaba lists dropoff filters for Raman... at that point
Raman just needs high SNR as far as I know.
What's the point of using Raman? Maybe we could see separate peaks for
each nucleotide, or better differentiation between DNA and protein...
as Simon said, there's lots of variation in the currently used
technique.
On Tue, Nov 22, 2011 at 1:05 PM, Simon Quellen Field <sfield@scitoys.com> wrote:
> You aren't even close to having to worry about dark currents in the sensor.
> Using a slit made by putting a business card into a slice in a rubber
> plumbing
> cap, at a distance of over a foot, and using only a 20 watt fluorescent
> light bulb
> as the light source, my camera was taking shots at ISO 800 using exposure
> times
> between 1/8 second and 1 second.
> Those results allowed me to experiment with the camera stopped way down, to
> apertures as small as F32, and ISO ratings of 100, using 30 second
> exposures.
> You won't be stopping down at all, letting all of the light hit your sensor.
> And the $5 sensors we are talking about can be used at ISOs well above 3200
> before noise becomes a problem for a spectrogram.
> Given that you have been talking about using 500 watt light sources, I don't
> think
> you will be worrying about dark currents or UV absorption in thin films any
> time soon.
> You don't need a sketch to visualize a lens focusing at infinity.
> Just picture a kid burning ants with a magnifying glass.
> The ant is the slit. The sun is effectively at infinity, and the light from
> it is parallel.
> You don't need a cylindrical lens. A regular lens will focus a slit onto a
> plane just fine.
> All we are talking about here is a simple cheap toy magnifying glass, since
> we don't
> care about aberrations. Those are taken care of in the software calibration
> phase.
> -----
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>
>
>
> On Tue, Nov 22, 2011 at 7:27 AM, John Griessen <john@industromatic.com>
> wrote:
>>
>> On 11/22/2011 06:59 AM, Nathan McCorkle wrote:
>>>>
>>>> With that in mind, consider very narrow slits, and compensate for the
>>>> > dimming by
>>>> > integrating over time. You can also do HDR by taking several images
>>>> > and
>>>> > combining
>>>
>>> With longer integration times I feel that dark currents would start to
>>> blur the image to where it couldn't be ignored. Maybe not
>>
>> The way to think of random noise integration is the dark current is
>> an amplitude of light per time just like the signal you are viewing.
>> Integrating makes both larger and smooths out low frequency noise ( 1/f
>> noise).
>> So you do an integration long enough to get more light collected at your
>> imager pixel so it's within the manufacturer's recommended range.
>> That won't help for low levels similar to the dark current.
>> A narrow slit with strong light won't be that bad.
>> Only the astronomers wait for hours staring at regions of cosmos with lN2
>> cooling so the dark current is lower. You'll be integrating for
>> milliseconds.
>>
>>
>> On 11/22/2011 06:59 AM, Nathan McCorkle wrote:
>> > First, you could simply eliminate focusing altogether, by having the
>> > optics
>> >> focus on infinity. The slit then looks like a point source at
>> >> infinity, and
>> >> is
>> >> always in focus.
>>
>> What does the sketch of that look like? A cylinder lens and correcting
>> lens close to the detector? Close to the slit seems like a good place
>> to stop spread...
>>
>> Oh, here's an idea -- Some optical fiber has different refractive index
>> per radial distance
>> from center and the effect is to funnel an input cone of light into
>> smaller
>> bounce angles as it travels down the pipe, and exits with a narrower cone
>> angle.
>> That's what to use for input fiber.
>>
>> John
>>
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--
Nathan McCorkle
Rochester Institute of Technology
College of Science, Biotechnology/Bioinformatics
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