Search found 123 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: 598

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 the light 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: 598

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: 598

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: 598

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". Hologra...
by Spectral Joe
Fri Apr 03, 2020 4:29 pm
Forum: Commercial Solar Filters/Cameras/Hardware
Topic: Protuberance approach vs. Coronograph
Replies: 19
Views: 6779

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 with improv...
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: 2919

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: 3801

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: 2919

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

There's usually something to see.
071418 full.jpg
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071418 center.jpg
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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: 9638

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
Sat Jun 23, 2018 2:38 pm
Forum: Solar Scope Modifications
Topic: Narrowest 393.37 ever by Apollo Lasky
Replies: 117
Views: 26740

Re: 393.4 bp0.1 - yes it does exist.

Thanks, guys! Sorry about the wavelength labeling confusion, 5461 should be 4861, it was late and I had something else on my mind.
by Spectral Joe
Sat Jun 23, 2018 4:42 am
Forum: Solar Scope Modifications
Topic: Narrowest 393.37 ever by Apollo Lasky
Replies: 117
Views: 26740

Re: 393.4 bp0.1 - yes it does exist.

080715 Ca montage.jpg 052017 3lamb montage large.jpg 021716 montage.jpg For some perspective, here are some images comparing CaII H (3968), Ha (6563), Hb (5461) and CaII (8542). In each case, the images were taken within minutes of each other, with a bandpass of 0.3 Angstrom. Just to provide images...
by Spectral Joe
Thu Jun 21, 2018 4:46 pm
Forum: Solar Scope Modifications
Topic: Narrowest 393.37 ever by Apollo Lasky
Replies: 117
Views: 26740

Re: 393.4 bp0.1 - yes it does exist.

with the plot visualized you can see that half bandwidth at 44% is 16 milli-angstroms wide/ or 1.6 angstroms. This is definitely lower than a complete Lunt CaK system in terms of FWHM, and definitely higher transmission than both the lunt and coronado filter. 16 milliangstroms is 0.016 angstrom, no...
by Spectral Joe
Wed May 30, 2018 3:27 am
Forum: Solar Scope Modifications
Topic: WILL IT BURN? - ..Filter Killer..
Replies: 13
Views: 5166

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: 7577

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: 3150

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: 3150

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 3144 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: 2315

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: 2315

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: 3163

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: 113
Views: 36816

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: 4295

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: 4295

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 instrument,...
by Spectral Joe
Mon Jan 02, 2017 2:25 am
Forum: Solar Radio, Magnetometry and Spectroscopy
Topic: ROT2 command of IRIS
Replies: 53
Views: 12966

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: 2747

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: 33689

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 ...