Merlin66
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Posts posted by Merlin66
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11 hours ago, vlaiv said:
- Some subs contain no signal. Suppose that we have source that for our purposes emits one photon per hour and we take one minute subs. As many subs would end up with measured value of 0 - if we associate word signal with measured value as opposed with intrinsic property of source - we can conclude that many of those subs are in fact wasted - they did not capture anything - no "signal" is present on them - but we would be wrong in thinking so. If we follow that line of thought - nothing would prevent us from discarding such subs (as they are meaningless contain no signal) - however if one does that - they will end up with wrong image.
Why would we have the "wrong image"???
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If the sensor records say 10 photons in one minute, then over ten minutes it will receive and record 10 x 10 photons.
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Surplus Shed have all the amateur scientist articles available on one CD!!!
It makes fascinating reading, something for everyone.
https://www.surplusshed.com/pages/item/M2071.html
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1. Has the lowest target signal and low SNR
2. Has an improved target signal, but similar to 1. due to the averaging, but an improved SNR (1 sigma)
3. Has a much higher target signal due to sum but similar SNR to 2.
4. Similar to 3.
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Dave,
if you need help.....we're always here.
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Louise,
Yes, I designed and built the Spectra-L200.
I've also designed a FC 120 (folded Classical) and an MG80 (80mm collimator/ 300 l/mm/ Zuiko 50 mm ) using standard components. Details on the forum.
I don't have access to 3D printing so I tend to skip these designs....I haven't looked at Christian's Uvex3 design.
Paul G. and I communicated on his early design concepts.
Ken
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Louise,
Yes, it impacts on the spectral image. I use a hi res, narrow bandwidth, R=10000 Spectra-L200 and have to re-focus between the various target wavelength.
It's very seldom that I add sections of the profile together...if you want a full spectrum spread, then a 300 l/mm grating or similar is used and set to the "average" focus.
I have seen examples where the camera focal plane is tilted across the length of the spectral image, but when compared to the curve above, it's still a compromise.
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I use a Edmund Optics achromat in the Spectra-L200 (similar to the LHiresIII) it's a 30/200.
The attached curve shows the required focus adjustment required over the visible spectrum. I use a Borg helical focuser.
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If you use the spectrograph on an f7 scope, the beam after the slit will emerge at f7 towards the collimator. This acts as an "aperture stop" - if the beam f ratio is > collimator f ratio then the illuminated part of the collimator will be smaller without adding a mask.
I use a 30/200 (nominally f7) collimator which works (no masking) well on f8 to f12 scopes.
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I'm pretty sure there's a "freeware" spreadsheet program which reads Excel files...
https://articles.bplans.com/4-free-alternatives-to-microsoft-excel/
For the Spectra-L200 which uses 30 x 30 mm gratings, I used Optometrics (Now Dynasil) https://www.dynasil.com/company/optometrics/
I made interchangeable holders to allow different gratings to be used - 300/ 600/ 1200/ 1800 l/mm.
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The SimSpec Spreadsheet will help you.....
IMHO I'd go for a 30 x 30 mm grating.
The grating will probably have to rotate to access the full spectrum, you'll need a holder and some means of fine adjustment.
Ken
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The one you removed is a colour correction filter which reduces the red response.
The front, remaining dust shake/ anti alias filter does a good job as a IR reject filter.
I removed BOTH these filters to extend the Spectral response for spectroscopy.
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I agree with Robin!
The Oly Zuiko lenses are pretty good.
I still have some lenses from the ol' film days and use a 50mm f1.4 Zuiko on the MG80 spectrograph.....
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Robin,
My bad.. I meant to say that the PH grism prism was glass and not acrylic.
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I use AstroArt for all my pre-processing, guiding and "tweaking" - sadly underrated - it punches well above it's weight.
A good alternative to PS (layers, histogram. plug ins, etc. etc.) is Corel's PaintShopPro. No subscription....
https://www.paintshoppro.com/en/
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Dave,
I'm pretty sure the PH spectroscope will use a glass prism.
Fulvio "converted" a PH DV spectroscope to his Spec 600
http://www.lightfrominfinity.org/Spec 600/Spec 600.htm
An Amici prism can be used successfully (the late Maurice Gavin's set-up is illustrated in "Astronomical Spectroscopy for Amateurs", p 170) using a barlow lens as a collimator.
The available processing software (BASS Project etc.) can easily handle the prism non-linear spectral image.
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The OVIO slit plate also gives you the option of 12 different slit widths...
Allows you vary the slit gap depending on the telescope, object magnitude and required resolution - SimSpec will show the probable results.
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On my C9.25 and later on the C11 I added a Vegemite lid to aid focussing. Later motorised using a standard SkyWatcher electronic motor and belt drive, mounted from the finder holes in the OTA.
Worked well.
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Dave,
The reflective multi-slit plate is available from Jeulin.
They and some other useful suppliers are listed here:
http://www.astronomicalspectroscopy.com/supplier.html
Ken
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Thanks Andrew....
I prepared a write-up describing the conversion of a Vixen flip mirror housing to a beamsplitter using the microscope slide, "Astronomical Spectroscopy for Amateurs", p220.
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Louise,
No. The front side faces the incoming beam (and the guider).
The rear surface which has the engraved slits sits towards the grating - there's no glass thickness between the slit and the grating.
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OK.
You only need around R=1000 to split the Na lines.....
Have a look at the SimSpec spreadsheet, It may help to firm up your ideas..
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Louise,
If you look at the plate at a glancing angle (it's only 1.5mm thick) you should see the difference....
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Interesting.
I've designed and built a few.....
What focal length collimator are you thinking about?
What resolution?
A reflective slit plate is a better option than the beamsplitter (I've tried both!)
A microscope glass slide works well (4/92)
Checkout our website below for some ideas.
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Does signal strength depend on exposure time and / or number of stacked subs?
in Imaging - Discussion
Posted
Derek,
Hmmm I accept the arrival of the photons is random (shot noise) but they don't vary in position....I believe, based on our spectroscopy work, a combination of subs with some signal give a increased intensity and improved SNR. How else can I record the spectra of faint stars???