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Everything posted by Merlin66
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ASI1600mm Cool - Flats nightmare, Pt 3
Merlin66 replied to Tommohawk's topic in Imaging - Discussion
Yes. I use AstroArt and the only time bias is mentioned is when you need to compensate your darks to another temperature.... -
Yeah, I'm only doing spectroscopy.... I'm interested in the target star - not the whole field. In the spectroscope slit, normally 3-4 pixel wide and covering 90% of the FWHM image, it's the photons I can collect which makes the difference. I believe in this application, the "arrival times" are important.
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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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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. http://www.msb-astroart.com/ 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. Vixen mod.pdf
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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.. http://www.astronomicalspectroscopy.com/instrument.html