Randys Bench

A repository for projects past and present

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Compact Solar Spectrograph Update…

Today is a rather cold and rainy one, a rather nice change from the 90 deg+ weather we’ve been having as of late. But, a good day for a bit of bench fun.

I’m finally moving beyond the world of cardboard mockups into target enclosure territory. I managed a few more solar test spectra before winding down the preliminary design:

Sodium Double D line region

2nd Sodium Double D line region

Magnesium triplet

Atmospheric O2

With these results in place I feel pretty good about finalizing this design and begin the effort of placing the necessary components in a final configuration.

Below shows the configuration for assuring the slit is in the collimator’s focus. This uses a finder scope (partially pictured on the right), focused at infinity to observe the entrance slit. By moving the collimation lens the in-focus spot is obtained. The small drilled hole is then plugged that allows this calibration step.



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Solar Spectrograph Plodding along…

I thought I’d take a moment out of a busy Summer season to provide a development update on the solar spectrograph project. I ended up going back to my original 35mm 150mm FL collimating lens I’d used previously on the original grating spectrograph built around 2003. The proposed lens for this function was rejected since it’s diameter was such as to not completely illuminate the selected reflective grating with collimated light. Sadly it is a fine quality achromatic lens that’s been looking for a home…I’m sure it’s time will come. Below is a photo of the current prototype, in cardboard of course…

Originally I was using a camera / grating angle of 90 deg but found this was too restrictive and produced aberrations at this sharp angle. So I fabricated an aluminum piece to provide an approx. 38 deg angle which is in line with classic spectrograph design practices. And it works alot better as well! At this time I’m using a fixed entrance slit arrangement using cheap razor blades which I manually adjust. Currently they are fixed with an opening of 2mil (~51 um) which provides enough illumination for testing. Recently I purchased a nice adjustable slit from SurplusShed. They rarely are stocked but I got a heads up reading a recent post on the Cloudy Nights forum which mentioned SurplusShed had received some limited stock…I had one on order within the hour and received it 2 days later.

To use this slit will involve extending the slit adjustment screw to extend further out for the enclosure I’ve selected. Speaking of that I ran across a nice softwood box of the right dimensions, rigidity and weight to accommodate the selected spectrograph components.

Once I conclude the necessary cardboard version testing I’ll begin making the needed cutouts (after a lot measurements x2) on the target box and start fitting the components. One thing that is of particular importance is the box weight. I plan on utilizing a new refractor I recently bought off of Amazon a month ago to ideally image the spectra of stellar objects. This will require a means of guiding to keep the object centered on the slit entrance for several minutes. this will be incorporated at some point in the future. Here’s a shot of the Meade 80mm refractor I purchased along with a few adapters and accessories:

So, that’s the current state so far of the project. With that here’s few spectra I captured a few days ago. The first are calibration lamps (Neon bulb and Compact fluorescent) as well as a few solar spectra shots.


Compact fluorescent bulb

Solar Spectrum Magnesium triplet to Sodium doublet

Solar Spectrum Sodium doublet to Hydrogen alpha region

Solar Spectrum Sodium doublet

Hydrogen beta to Magnesium triplet


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Sky Wanderings II

I’ve had a few decently clear early morning skies recently that I tried to take advantage of with some success. The first was actually not so much early morning but near 11pm since sleeping that particular night was a struggle. Cygnus was high in the sky and shooting Deneb turned out to be my choice…I think this was a stack of 75 light frames coupled with 20 dark frames.

The next image was collected around 4am a few days later when M45 (the Pleiades) was up but still a bit low in the eastern sky. The seeing wasn’t great with some intermittent high clouds but we gave it a go nevertheless… This was a stack (DeepSkyStacker) of 140 light frames and 30 dark frames. Not the finest image but as the Summer rolls over into Fall things will improve I’m sure.

All for now…see you later



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Sky Wanderings

I finally had some descent skies the morning of June 25th (early morning 3am) and was able to do some more testing with the ASI120MC camera and Sharpcap software. Although the Moon was out in the Southwest (92% illuminated) the seeing appeared pretty good for this time of year so I gave it a go…besides I was already up anyway! As a target I chose the area around the star Mirfak in the constellation of Perseus situated in the northeast. This area is also termed the Alpha Persei Association. This association covers about 5 degrees around Mirfak. The image below comprises 75 light frames of 5sec each stacked in DeepSkyStacker. Mirfak is the bright star in the upper center of the photo…

Here’s the area covered in the excellent Stellarium sky simulator:

Hopefully I’ll get some more clear skies this Summer for imaging…We’ll see


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Re-imagining my Imaging setup

This will be a rather short post since I’ve been spending a bit more in the outdoor world now with summer here as opposed to my bench. I mean who doesn’t like to dig up weeds right? With that I decided to finally upgrade the Astro imaging camera I’ve been using for the last 12+ years. The LX converted Logitech QC3000 pro, once modified for long exposure capabilities it’s been a solid performer. However it was never originally designed for this type of application and is a bit noisy (hot pixels and background banding). Moreover the resolution leaves something to be desired. So I took the plunge for a rather moderately priced ZWO ASI120MC camera which I’m slowly putting into play.

And below is a shot of the mostly completed mount plate with the major pieces in place. Not the neatest setup but wanting to use the bits & pieces I’ve got…

Looking thru my bins and drawers for what was needed I ran across a photo of the moon I’d taken back in late ’71 or 1972 which I had completely forgotten. Taken on a city rooftop thru a Sears 60mm refractor and an old instant Polaroid camera it was the 1st astro image I’d taken. Extraordinarily poor by any standards¬† then and now…well here it is:

Looks like lots of camera shake….I guess one has to start somewhere.

I did get a chance, on a rather cloudy and muggy evening to capture a few image with the new setup. Mostly being anxious to give it a go and at least get some familiarity with the imaging software (Sharpcap) and get the finder scope properly lined up. Still have a bit to learn but did produce an image from somewhere in the Cassiopeia region:

The seeing on this evening was frightfully bad but that was fine…other chances will come…



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Compact Solar Spectrograph – Back to the Drawing (Card) Board

Based on my recent experiments…I’ve not been able to coerce the performance I was looking for with the current compact design. I thought I’d take small step in reverse and examine a more “traditional” layout approach which I had utilized on my previous spectrograph build.

The 1200l/mm reflective grating I’ve now used for many years

Here’s a few photos of the previous spectrograph build from about 2003 or so:

At the time the imaging camera was a long-exposure modified Logitech QC3000 which did a far job with it’s resolution limitations.

The 1st image shows the magnesium triplet (right of center). The horizontal lines shown in both images are known as “tranversalium” caused by irregularities along the slit edges.

The 2nd image shown below is that of the hydrogen beta line left of center…

Back in the 2nd half of the ’90s I used a homebrew Cookbook 211 camera as an imager for the spectrograph and was pleased at that time how well it performed for such a small monochrome CCD (192×165) image sensor. Here’s a PDF I created demonstrating it’s capability of imaging the solar spectrum.

But now back to the present…here’s the current mockup I’ve now built with the ever popular cardboard construction technique:

You’ll notice the use of a guitar pick to raise the height of the grating mount a slight amount! Whatever is handy… Below are some preliminary images of reference lamps used as part of the tests. 1st is a neon source:

Next is a compact fluorescent lamp:

So far so good with quite a bit more to do…See you next time

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Neon Wavelength Calibrator

Since I’ve finally started back to do some work on a sadly neglected project, the Compact solar spectrograph, I thought it time to put together a proper neon-based spectral (wavelength) calibrator for this instrument.

I researched a few designs for the power supply, including a older Forrest Mim’s engineer’s notebook 555-based design shown below:

As well I took a look at the internal calibrator incorporated in Shelyak’s Lhires III spectrograph design which is the one I decided on. This uses a UC3843 PWM controller which, coming from the power supply industry, I’d used in design’s back in the 90’s and became familiar with. This circuit incorporates both PWM regulation control and voltage multiplier circuitry to provide a DC output of 100V. It appears to work well with a variety of neon bulb types.

Here’s a look at the completed card assembly:

This will be a nice addition to the spectrograph redesign upcoming over the next few months. Here is a nice document describing the general attributes of neon bulbs and a few silly circuits as well…Neon Lamp Information. Below is a wavelength chart of the neon gas spectral signatures to give some idea of the calibration coverage one would expect. There’s also some finer lines in the deep blue and violet end of the spectrum:

And speaking of the spectrograph redesign underway, here’s what it look’s like at this stage of development:

Quite a ways to go yet….back soon