Search found 120 matches

by Spectral Joe
Wed Jul 22, 2020 2:27 am
Forum: Solar Radio, Magnetometry and Spectroscopy
Topic: SHS/ SHG Holographic Grating choices
Replies: 9
Views: 1927

Re: SHS/ SHG Holographic Grating choices

The box is 1/4" plywood, with a double layer of 3/4" plywood for the bottom. It's internally baffled and divided into five sections, the objective section, the turning and flat field optics, the grating and Littrow lens, the slit, scanner and detector and an intermediate center area that t...
by Spectral Joe
Mon Jul 20, 2020 2:41 pm
Forum: Solar Radio, Magnetometry and Spectroscopy
Topic: SHS/ SHG Holographic Grating choices
Replies: 9
Views: 1927

Re: SHS/ SHG Holographic Grating choices

The whole thing is enclosed and well sealed, it's only opened for occasional adjustments. All the optics stay clean. A safe way to remove dust is to use a regular duster can with a long extension made from thin plastic tubing, the can is left stationary on a flat surface so there's no chance of liqu...
by Spectral Joe
Sat Jul 18, 2020 10:10 pm
Forum: Solar Radio, Magnetometry and Spectroscopy
Topic: SHS/ SHG Holographic Grating choices
Replies: 9
Views: 1927

Re: SHS/ SHG Holographic Grating choices

The rules for resolution and dispersion are the same for concave gratings, Rowland circle mountings aren't used much outside of the vacuum ultraviolet, Eagle or Wadsworth mountings are the usual choice. The astigmatism problem with concave gratings isn't due to the figure of the substrate, it's from...
by Spectral Joe
Fri Jul 17, 2020 4:59 pm
Forum: Solar Radio, Magnetometry and Spectroscopy
Topic: SHS/ SHG Holographic Grating choices
Replies: 9
Views: 1927

Re: SHS/ SHG Holographic Grating choices

The difference in efficiency is due to groove profile. Holographic gratings have a sinusoidal groove profile, because of the way they are made. Ruled gratings have grooves with flat sides, the angle of which is chosen to enhance efficiency in the spectral range of interest, called "blazing"...
by Spectral Joe
Fri Apr 03, 2020 4:29 pm
Forum: Commercial Solar Filters/Cameras/Hardware
Topic: Protuberance approach vs. Coronograph
Replies: 19
Views: 9493

Re: Protuberance approach vs. Coronograph

This is a subject that has irked me for a long time. I've carried a $100 bill in my wallet for more than 20 years, a prize for the first amateur telescope maker that can show me the corona in their "coronagraph". Not that it's impossible, if Lyot could do it in the 1930's it's easier now w...
by Spectral Joe
Mon Jul 16, 2018 5:55 am
Forum: Solar Radio, Magnetometry and Spectroscopy
Topic: Even when there's little going on....
Replies: 6
Views: 3957

Re: Even when there's little going on....

Thanks, guys. I don't get as much time in on this as I used to, another unrelated project is taking up a lot of my time, but for a good cause. The bandwidth is 0.3 Angstroms. Seeing was good yesterday, 2-3 arcsec, and little haze or smoke.
by Spectral Joe
Mon Jul 16, 2018 5:46 am
Forum: Solar Radio, Magnetometry and Spectroscopy
Topic: Recent Digital SHG
Replies: 12
Views: 5366

Re: Recent Digital SHG

If these are trials then you are definitely on the right track! Excellent for initial efforts. Definitely some stray light, have you trapped the ghost images of the slit?
by Spectral Joe
Sun Jul 15, 2018 2:20 pm
Forum: Solar Radio, Magnetometry and Spectroscopy
Topic: Even when there's little going on....
Replies: 6
Views: 3957

Even when there's little going on....

There's usually something to see.
071418 full.jpg
071418 full.jpg (224.83 KiB) Viewed 3957 times
071418 center.jpg
071418 center.jpg (50.42 KiB) Viewed 3957 times
The usual tradeoffs, low stray light, high spectral purity and tunability but lower resolution.
by Spectral Joe
Thu Jun 28, 2018 3:54 pm
Forum: Commercial Solar Filters/Cameras/Hardware
Topic: NEW direction in the solar narrowband imaging.
Replies: 35
Views: 13390

Re: NEW direction in the solar narrowband imaging.

As has been pointed out, the 8542 line is similar in width to H alpha, unlike the UV CaII lines. Thus, bandpass requirements for an imaging system at this wavelength are similar to that at H alpha. The reflectivity of the coatings on the etalon plates is a major factor in determining the finesse of ...
by Spectral Joe
Wed May 30, 2018 3:27 am
Forum: Solar Scope Modifications
Topic: WILL IT BURN? - ..Filter Killer..
Replies: 13
Views: 7008

Re: WILL IT BURN? - ..Filter Killer..

I've had this discussion before, it rarely sinks in but I'll try again. Rather than just burn stuff why not just think for a minute about what radiation actually reaches the Earth from the Sun. How many people here have ever seen a solar radiation plot and thought about what it means? The great assu...
by Spectral Joe
Tue Dec 12, 2017 2:13 am
Forum: Solar Radio, Magnetometry and Spectroscopy
Topic: 20Jun2017 Spectroheliograms: Hydrogen
Replies: 25
Views: 9970

Re: 20Jun2017 Spectroheliograms: Hydrogen

Line profile scaled.JPG Here is a spectral scan of a spectroheliograph with a 0.3 Angstrom bandpass, the red curve is the data and the blue curve is a Gaussian fit. This is the instrumental line width, matching the entrance slit and pixel size to the Airy disc size. Narrowing the entrance slit furt...
by Spectral Joe
Tue Oct 24, 2017 3:23 pm
Forum: Solar Radio, Magnetometry and Spectroscopy
Topic: the old way the hard way
Replies: 7
Views: 4187

Re: the old way the hard way

Got me there, I don't do drawings, just visually observe. The instrument is a Wm. Gaertner & Co. L4020 from 1905.
by Spectral Joe
Mon Oct 23, 2017 2:32 pm
Forum: Solar Radio, Magnetometry and Spectroscopy
Topic: the old way the hard way
Replies: 7
Views: 4187

Re: the old way the hard way

"I bet you no one has tried this since the days of queen Victoria"

You lose, I do it on a regular basis, and with equipment from the period.
DSCN6142 (Small).JPG
DSCN6142 (Small).JPG (93.01 KiB) Viewed 4181 times
by Spectral Joe
Fri Aug 11, 2017 1:11 am
Forum: Solar Radio, Magnetometry and Spectroscopy
Topic: question - pre filters for SHG
Replies: 3
Views: 2977

Re: question - pre filters for SHG

For adjusting intensity, yes, but only if you have no other way of adjusting exposure.
by Spectral Joe
Thu Aug 10, 2017 11:43 pm
Forum: Solar Radio, Magnetometry and Spectroscopy
Topic: question - pre filters for SHG
Replies: 3
Views: 2977

Re: question - pre filters for SHG

Two separate things are happening. In case 1), it's important to know that gratings have different efficiencies for parallel or perpendicular polarization, so changing the polarization going in will change the brightness coming out. In the second case, the polarizer has optical thickness, and if it ...
by Spectral Joe
Mon Jul 17, 2017 3:47 pm
Forum: Commercial Solar Filters/Cameras/Hardware
Topic: Realtime Seeing Filter idea - to benefit Altair GPCAM / Hypercam owners and others
Replies: 6
Views: 4102

Re: Realtime Seeing Filter idea - to benefit Altair GPCAM / Hypercam owners and others

Not quite real time, but try converting tiff files to jpeg or bmp, the more detail (better focus or seeing, for example) the less compression you get. Maybe someone can automate the process. On the other hand, the scintillation seeing monitor with Firecapture support thread in the Solar Scope Modifi...
by Spectral Joe
Tue Jun 27, 2017 3:46 pm
Forum: Solar Scope Modifications
Topic: DIY Solar Scintillation Seeing Monitor with FC support
Replies: 127
Views: 69499

Re: DIY Solar Scintillation Seeing Monitor with FC support

With regard to high, thin clouds, these indicate high altitude wind shear that would cause poor seeing. Sounds like you are getting the right number. As for the filters, this combination would give a photopic response in combination with the photodiode spectral sensitivity. This type of detector / f...
by Spectral Joe
Sat Apr 22, 2017 5:32 am
Forum: Solar Radio, Magnetometry and Spectroscopy
Topic: little more help, please. More Lockyer questions
Replies: 19
Views: 5905

Re: little more help, please. More Lockyer questions

Oh, I should add, this is an impressive project, and well executed!
by Spectral Joe
Sat Apr 22, 2017 5:30 am
Forum: Solar Radio, Magnetometry and Spectroscopy
Topic: little more help, please. More Lockyer questions
Replies: 19
Views: 5905

Re: little more help, please. More Lockyer questions

One thing to remember,the photo of Lockyer's instrument is contemporary, it was changed and used by others after the historical observations were made. The drawings in his "observations part II": http://rstl.royalsocietypublishing.org/content/159/425.full.pdf+html tell much more. Another i...
by Spectral Joe
Mon Jan 02, 2017 2:25 am
Forum: Solar Radio, Magnetometry and Spectroscopy
Topic: ROT2 command of IRIS
Replies: 53
Views: 17274

Re: ROT2 command of IRIS

Yes, it's shaping up. I see two immediate issues. First, there's a lot of stray light. This can be due to misplaced reflection traps, but in your case it's likely back reflections from the binoviewer. Second, there is noticeable vignetting in the direction along the slit, usually the result of not h...
by Spectral Joe
Mon Nov 14, 2016 4:50 am
Forum: Solar Radio, Magnetometry and Spectroscopy
Topic: questions about shg images and clouds
Replies: 4
Views: 3384

Re: questions about shg images and clouds

There is some hope, if the continuum near the Ha line (or whichever line you are using at the time) is not saturated. If you synthesize an image using the continuum and use this as a flat it should correct some (most) of this. It will cause the dynamic range in the affected areas to be reduced, thou...
by Spectral Joe
Thu Oct 20, 2016 2:37 am
Forum: Commercial Solar Filters/Cameras/Hardware
Topic: Dream come true!
Replies: 113
Views: 50104

Re: Dream come true!

Bob Before getting violent with the Helios (not that I have anything against C4 in the proper place, having used hundreds of pounds of it in a previous career) I can try getting the relevant parts out without damaging them. If you're heading down to California in the future it would be a good thing ...
by Spectral Joe
Tue Oct 04, 2016 4:25 am
Forum: Solar Radio, Magnetometry and Spectroscopy
Topic: Littrow SHG prototype
Replies: 41
Views: 14668

Re: Littrow SHG prototype

As long as the incandescent lamp is run on DC you should be OK, even incandescents show a lot of ripple, especially at 50 Hz.
by Spectral Joe
Tue Oct 04, 2016 12:56 am
Forum: Solar Radio, Magnetometry and Spectroscopy
Topic: Littrow SHG prototype
Replies: 41
Views: 14668

Re: Littrow SHG prototype

My interpretation of the image is that the slit is horizontal and time is vertical, sampling just the zero order. If that's the case then these are either the result of ripple in the source intensity or some sort of hum pickup. Lamps run on AC have substantial intensity variation, I run all of my li...
by Spectral Joe
Tue Sep 27, 2016 3:25 am
Forum: Solar Radio, Magnetometry and Spectroscopy
Topic: Littrow SHG prototype
Replies: 41
Views: 14668

Re: Littrow SHG prototype

Ken

Try putting a short (<75mm) focal length lens immediately in front of the camera, as close to the chip as possible. That camera has a diagonal of around 13.5mm, so a 25mm diameter lens is big enough. If that helps, try other (longer) focal lengths.

Joe
by Spectral Joe
Sat Aug 20, 2016 5:41 am
Forum: Solar Radio, Magnetometry and Spectroscopy
Topic: neutral calcium 4227
Replies: 20
Views: 6851

Re: neutral calcium 4227

Here's a comparison from smoky Northern California, with correspondingly poor conditions:

Ca 4227
0819_Ca4227.jpg
0819_Ca4227.jpg (175.05 KiB) Viewed 6781 times
Ha
0819_Ha.jpg
0819_Ha.jpg (189.16 KiB) Viewed 6781 times
Overall transparency is less than 80%, with lots of scatter.
by Spectral Joe
Sun Aug 14, 2016 3:47 am
Forum: Solar Radio, Magnetometry and Spectroscopy
Topic: how hard to capture He 10830?
Replies: 3
Views: 3162

Re: how hard to capture He 10830?

Not a good choice for small instruments. Several things conspire to ruin your efforts, first the diffraction blur for a given system is twice what it is in the visible. Second, refractive optics (unless designed for this wavelength range) are well outside their optimum design parameters. They will p...
by Spectral Joe
Wed Aug 10, 2016 2:32 pm
Forum: Solar Radio, Magnetometry and Spectroscopy
Topic: SHG flats, a suggestion
Replies: 3
Views: 2965

Re: SHG flats, a suggestion

Ken There are no unwanted effects from adding the extra optics, they are mounted on a motor driven positioner and are located just before the focus of the objective. In my instrument there are additional optics between the prime focus and slit that are part of the scanning system, these new lenses a...
by Spectral Joe
Tue Aug 09, 2016 4:05 am
Forum: Solar Radio, Magnetometry and Spectroscopy
Topic: SHG flats, a suggestion
Replies: 3
Views: 2965

SHG flats, a suggestion

"Flatting out" all of the unwanted features in SHG images is a vexing problem. Various means are used, Fourier transforms are effective but using directional filters with them has issues, and the transform itself can cause artifacts that are as bad as the ones being eliminated. Flats using...
by Spectral Joe
Fri Aug 05, 2016 9:59 pm
Forum: Solar Radio, Magnetometry and Spectroscopy
Topic: "Imaging Sunlight - Using a Digital Spectroheliograph"
Replies: 55
Views: 21440

Re: "Imaging Sunlight - Using a Digital Spectroheliograph"

The quicker you can get the data the less likely something will go wrong, a moment of bad seeing, wind shaking the instrument (shouldn't happen if it's made properly, but..), a bird flying through, clouds, etc.
by Spectral Joe
Fri Aug 05, 2016 5:04 pm
Forum: Solar Radio, Magnetometry and Spectroscopy
Topic: "Imaging Sunlight - Using a Digital Spectroheliograph"
Replies: 55
Views: 21440

Re: "Imaging Sunlight - Using a Digital Spectroheliograph"

The only limitations are exposure time (getting enough light) and how fast your camera can acquire the data. My instrument scans the solar image across the slit internally while the telescope is tracking. A full disk is done in 6 seconds.
by Spectral Joe
Fri Jul 15, 2016 2:49 am
Forum: This is SolarChat !!
Topic: Goin' Old School
Replies: 4
Views: 843

Goin' Old School

Here at Casa Spectral we occasionally feel like some regression therapy, and roll out an oldie: DSCN6138.JPG DSCN6146.JPG In this case it's a turn of the (last) century Gaertner spectrometer, with a 1950's Bausch and Lomb grating for some "new" spice. Nice to see the spectrum in a slightly...
by Spectral Joe
Mon Jul 11, 2016 3:30 am
Forum: Solar Radio, Magnetometry and Spectroscopy
Topic: new shg : small improvement and much better results
Replies: 4
Views: 3260

Re: new shg : small improvement and much better results

Can you post the raw images? Much can be told from the raw data, but processing muddies things. Could be alignment, or vignetting (very common). A very good start, at any rate.
by Spectral Joe
Mon Jul 11, 2016 3:21 am
Forum: Solar Radio, Magnetometry and Spectroscopy
Topic: Solar hat trick from 7/10/16
Replies: 3
Views: 3043

Solar hat trick from 7/10/16

I usually don't do this, but I ventured into the blue and UV to look around today:

CaH
0710 CaH.jpg
Hb
0710 Hb.jpg
Ha
0710 Ha.jpg
0710 Ha.jpg (188.72 KiB) Viewed 3043 times
by Spectral Joe
Tue Jun 28, 2016 4:07 am
Forum: This is SolarChat !!
Topic: Nothing going on, you say?
Replies: 7
Views: 1456

Re: Nothing going on, you say?

Rybak wrote:Fine FD! What is "the right instrument"?
Something with very low stray light and high spectral purity. In this case it's a digital spectroheliograph.
by Spectral Joe
Mon Jun 27, 2016 5:07 am
Forum: This is SolarChat !!
Topic: Nothing going on, you say?
Replies: 7
Views: 1456

Nothing going on, you say?

You just need the right instrument to pull it out.
There's always something to see.
by Spectral Joe
Sun Jun 26, 2016 6:34 pm
Forum: Solar Radio, Magnetometry and Spectroscopy
Topic: do SHG have newton rings like filters can have?
Replies: 18
Views: 6133

Re: do SHG have newton rings like filters can have?

Joe -- Nice tip on lens - thx :bow but how much will it change FL? I got about 3 inch to play with without doing a whole redo right now FL of collminator is 180 mm The shift should be small, 5 percent or so. Depends on how close to the slit you can get, and the actual focal length of the field lens.
by Spectral Joe
Fri Jun 24, 2016 10:54 pm
Forum: Solar Radio, Magnetometry and Spectroscopy
Topic: do SHG have newton rings like filters can have?
Replies: 18
Views: 6133

Re: do SHG have newton rings like filters can have?

Almost certainly vignetting, especially if the grating is a 30mm square one (guessing again). Even with a 50mm grating there is likely an issue if there is no field lens. Try putting a simple lens (plano convex is best, double convex is ok) just after the slit (close, 5mm or so). 125mm focal length ...
by Spectral Joe
Fri Jun 24, 2016 1:29 am
Forum: Solar Radio, Magnetometry and Spectroscopy
Topic: do SHG have newton rings like filters can have?
Replies: 18
Views: 6133

Re: do SHG have newton rings like filters can have?

"tried shorter fl lens in h-alpha" Which lens? With what we have to evaluate, little definite can be said. While we're guessing, I'm guessing that the signal level (brightness) is lower at the beginning and end of the scan, and an extracted flat is being used to flatten out the intensity, ...
by Spectral Joe
Thu Jun 23, 2016 5:46 pm
Forum: Solar Radio, Magnetometry and Spectroscopy
Topic: do SHG have newton rings like filters can have?
Replies: 18
Views: 6133

Re: do SHG have newton rings like filters can have?

Seeing the raw data would help in evaluating the problem, it could well be a vignetting issue. That said, interference fringes were noticed when the Kitt Peak magnetograph (using Reticon linear arrays) went into operation in 1975. It's discussed in Applied Optics Vol. 15 No. 1 Pg. 40, January 1976. ...
by Spectral Joe
Thu Jun 23, 2016 5:38 pm
Forum: Solar Radio, Magnetometry and Spectroscopy
Topic: "Imaging Sunlight - Using a Digital Spectroheliograph"
Replies: 55
Views: 21440

Re: "Imaging Sunlight - Using a Digital Spectroheliograph"

Particularly for those interested in building one of these, and also for explaining the nature of these to the unfamiliar, this is a well written overall view . The details necessary to construct a working instrument are there, the theory and history are explained and examples are given. One of the ...
by Spectral Joe
Mon Jun 06, 2016 11:22 pm
Forum: This is SolarChat !!
Topic: 1,6m telescope, adaptive optics, time lapse. BBSO
Replies: 13
Views: 1467

Re: 1,6m telescope, adaptive optics, time lapse. BBSO

On the Big Bear web page: http://www.bbso.njit.edu, there's a pull down menu for Projects. The links for NST instruments, science papers and instrument papers contain some info. More can be found in papers written by the researchers themselves, but that often requires subscription access to the jour...
by Spectral Joe
Mon Jun 06, 2016 4:52 pm
Forum: This is SolarChat !!
Topic: 1,6m telescope, adaptive optics, time lapse. BBSO
Replies: 13
Views: 1467

Re: 1,6m telescope, adaptive optics, time lapse. BBSO

This movie was made using VIS, the Visible Imaging Spectrometer. Unfortunately, BBSO hasn't published many details on this instrument, they concentrate mostly on the telescope and adaptive optics, but a lot can be inferred from what is out there. VIS is an imaging Fabry-Perot interferometer with a 7...
by Spectral Joe
Tue May 03, 2016 2:56 am
Forum: This is SolarChat !!
Topic: Really interesting wave length 8542,1A in IR range.
Replies: 12
Views: 1596

Re: Really interesting wave length 8542,1A in IR range.

Looks like this:
Montage_CaH_CaII_IR.jpg
Montage_CaH_CaII_IR.jpg (29.93 KiB) Viewed 1565 times
CaH on the left, 8542 on the right.
From August 2, 2015.
by Spectral Joe
Sat Apr 30, 2016 2:06 pm
Forum: Solar Radio, Magnetometry and Spectroscopy
Topic: "Imaging Sunlight - Using a Digital Spectroheliograph"
Replies: 55
Views: 21440

Re: "Imaging Sunlight - Using a Digital Spectroheliograph"

Walter passed away in November, 1996. Quite the craftsman, anyone who builds a Lyot filter gets a tip of my hat.
by Spectral Joe
Wed Jan 13, 2016 5:50 am
Forum: Commercial Solar Filters/Cameras/Hardware
Topic: Coronado etalon finesse peaks far from H-A
Replies: 5
Views: 3840

Re: Coronado etalon finesse peaks far from H-A

With good conditions they can do pretty well. 112115_dcv_usm.jpg Variable seeing during the scan can be a real problem. On the other hand, no (affordable) etalon system gives comparable spectral purity to a properly constructed spectroheliograph. As for peaks far from the design wavelength, the coat...
by Spectral Joe
Sat Aug 29, 2015 1:05 am
Forum: Solar Radio, Magnetometry and Spectroscopy
Topic: QUSTIONS ABOUT shg IN INFRARED
Replies: 5
Views: 2757

Re: QUSTIONS ABOUT shg IN INFRARED

My last visual instrument was a folded design in 2009, just for old times sake. It was everything I remembered a shs to be, and thus didn't distract me from the digital approach.
by Spectral Joe
Fri Aug 28, 2015 9:25 pm
Forum: Solar Radio, Magnetometry and Spectroscopy
Topic: QUSTIONS ABOUT shg IN INFRARED
Replies: 5
Views: 2757

Re: QUSTIONS ABOUT shg IN INFRARED

CaII at 8542 and, if your optics and camera can support it, HeI at 10830. CaII is usually easy. How to identify them? That was discussed here: http://solarchat.natca.net/viewtopic.php?f=8&t=17192 If you're going to do this sort of thing then a calibrated wavelength scale of some sort is essentia...
by Spectral Joe
Mon Aug 24, 2015 8:49 pm
Forum: Solar Radio, Magnetometry and Spectroscopy
Topic: caK shg and question about bandwidth option in Wah program
Replies: 5
Views: 3166

Re: caK shg and question about bandwidth option in Wah progr

With the SHG the final bandwidth comes down to the dispersion of the spectrograph (A/pixel) and the resolution (A) of the instrument. Using the Nyquist sampling as a guide, you'll need at least two pixel to get resolution. If you have 0.1A/pixel dispersion then a two pixel strip would give around 0...
by Spectral Joe
Thu Aug 20, 2015 2:40 pm
Forum: Solar Radio, Magnetometry and Spectroscopy
Topic: Digital SHG vs commercial filters
Replies: 13
Views: 5209

Re: Digital SHG vs commercial filters

Superb image, Joe. Your SHS isn't as limited by seeing conditions as the digital SHG (especially a drift scan device, like mine). Conceivably, you could take a large number of images and stack, as conventionally done with filtergrams. What is the focal length and f# of the telescope you're using? A...