Another Morning of Adjustments

We are somewhere in the midst of unrelenting solid rainfall and flash flooding.  Fortunately, we are in a relatively safe area (meaning higher ground away from rivers) although I suspect the septic tank will be full of water for a while and the yard will likely be mush for a few days if and when the rain ever stops.  Downtown Waterbury, a small town that was devastated by Tropical Storm Irene and a town that just finished rebuilding its infrastructure due to Irene's wrath and high water within just the past month, is likely going to be flooded as badly as Irene caused or worse.  On the plus side, I can't think of any reason why we would need to go anywhere for the next few days and we probably cannot go anyplace because our roads will likely be under water and perhaps washed out.  Bridges and roads are being washed out across our area.

In the meantime, I stayed indoors and worked on more adjustments on the rudimentary spectroheliograph I am building.  I am understanding more and more but I still have some questions.  

Sheila is working from home now until further notice.  Montpelier, just like downtown Waterbury, is supposed to be under water by this evening and not cresting until around 3am.  Sheila's State office complex is in downtown Montpelier and that area will likely be under water so she has been told to stay home until further notice.  Since Sheila is working in our pandemic home office (which is also where I have all my astronomy gear and all my model railroading models), I moved to the desk in our bedroom to do some work on this spectroheliograph.  

Below is a closer image showing the adjustment for setting the instrument to different wavelengths of light.  This is a rather crude adjustment too.  I'm still finding it very difficult to figure out which line is actually the line I want to record.  That is something I'll need to resolve soon.  For now, the main concern is properly assembling and adjusting the instrument...  

This photo, below, shows something I have found to be a bit perplexing.  I understand needing to slightly shim certain areas to get the fine beam of light to hit the exact right areas as it moves through a tiny slit, through a doublet lens, then reflecting off the holographic grating, then going through another doublet lens, and then to the camera but this area needed a lot of shimming!  I think I now have seven or eight layers of aluminum tape built up to shim one side of the holographic grating and it is still not perfect.  The way you need to make all of these "adjustments" is really a quite crude way to do it especially when you expect there to be fine adjustment control.  This makes it difficult to get things exactly right.  Additionally, I'm a bit concerned about how much I have needed to shim here.  I'm getting closer though.  

Now that I am writing about this issue, maybe I should disassemble the slit assembly again to make sure the slit is sitting perfectly flat in its housing...

It is quite dark outside again today due to all the rain but I still set up the spectroheliograph at our living room window.  I have it sitting on our mantle and my laptop is next to it.  Since the sun is so obscured, I've needed to increase the gain to its maximum which, typically, is not desirable but I'm not actually doing any imaging just yet so the extra noise isn't a problem.  I am just looking for the spectrum on the screen...

I added the red line across the screen as a reference line.  That red line is perfectly straight but the spectral lines are slightly curved.  I have them centered and each end is the same amount of distance from the red line so that is good but I'm not sure if there is a way to actually straighten these spectral lines. This may be due to the cheap doublet lenses in this instrument causing distortion.  Or...  maybe it is due to the angle to the direction of the light?  I still need to look into this more too.  

Looking more closely at this photo, above, I can see that the greatest distance between the thick spectral line and the red line is a bit closer to the left side of the screen which tells me that perhaps something is askew.  It is possible that this is an indication of the slit being ever so slightly tilted.  The curvature of the spectral lines might not be a problem but whether the curve is even across the frame might be an indication of a problem.  I'll need to look into that.  

I didn't get a photo of it but I had to disassemble the camera doublet lens assembly.  That whole assembly was wobbling in the housing.  I ended up shimming the end of that lens assembly with a strip of aluminum tape and it is much more solid now with no wobbles.  

As I mentioned above, I need to remember to disassemble the slit again.  I think I'll check to make sure it is seated perfectly flat in its housing.  I suspect it might not be sitting flat and that is why I needed to do so much shimming.  Additionally, the slit might not be perfectly square to the housing either which may be causing the slightly lopsided curvature.  

Of course, if I make any changes to the slit, I'll need to pull off all my shimming again and start the shimming process over again.  I want to get this as good as it can be though so redoing any or all of the steps of the assembly isn't really much of a problem.  Besides, the weather is miserable anyway! 

Little by little, this new instrument is coming together and I am learning more and more (I'm doing a lot of research too!).  

EDIT:  It is later at night and downtown Montpelier, downtown Waterbury and downtown Barre are all under water.  It is highly likely that Sheila's state office building will be out of commission for months due to water damage, electrical damage, and a potential for mold.  If so, she'll be working from home for the next few months.  

So far, we have no damage to our home or septic system although I do suspect our septic will be running extremely slowly tomorrow...  or even stopped up completely.  Sheila's dad's house has a completely inoperative septic system now.   

They are still saying that the river that runs through these downtown areas will not crest until 3am or later tonight (in the wee hours of tomorrow morning).  They are saying that Montpelier is already more flooded than the flood due to Tropical Storm Irene a decade ago and that flood was devastating.  Waterbury is more down river than Montpelier so I anticipate the river to crest in Waterbury later than in Montpelier.  We know that downtown Waterbury is flooded to devastating levels again but we don't yet know just how bad it is this time.  This time estimate and cresting height depends on when the rain will stop.

Hopefully the rain will stop very soon!