Summer Project Progress

The 1200 lens project is coming together quickly.

I received the Parallax rings for the 1200 mm lens on Monday.  They fit nicely - I will need to put an additional layer of cork or a thin layer of rubber to help with the grip on the lens.  When I first put the rings on, the lens could slide out under its own weight.  I put a temporary shim of some styrofoam padding to give a little more grab.  Once the rings were in place I measured the center line of the rear standard and noted how much the lens needed to rise.  Just like the 900mm, it needs 6 inches to meet the height of the rear standard.  Luckily, I already have a solution in mind and I ordered the extruded aluminum tube just like last time.  

I put the bar assembly on a pair of jack stands just for the sake of keeping it at a decent working height and being able to access the screws both above and below the bar.  I'm not going to keep it like this, just for the sake of testing.  

It's heavy.  I can see that I'll need a helper to put this up.

I looked through the glass for the first time last night and saw that it's already blackened on the inside.  Some flecks of paint have fallen onto the inner surfaces.  Once I get this assembled, I may consider unscrewing the halves and cleaning it up.  I'm also wondering if there is an adjustment that will need to be made between the halves.  Will see how the images look once I can get this mounted on a G11 to look at the full moon.  I will try projecting an image onto a sheet of foamcore to know the proper backfocus.  Once I have this dimension, I will order a custom tube for the back to span most of the distance.  The last bit will be bridged with wide angle bellows so that I can put an eyepiece or film holder in the rear standard and be able to bring both to focus.

On Thursday:

I found out that the metal bar will be waiting for me when I get home today after work.  This reminds me that I will need to get the hardware to bolt it together.  I am extremely lucky that I can buy the hardware at a discount and have it waiting for me to take home at the end of the day.

I have not had the motivation at the end of the day to put the lens on a mount to be able to check for focus at infinity.  I would like to think that I will get to it tonight - or at least while viewing the moon will be an evening activity.

I looked at the fig tree this morning and I'm going to need to cut it back just to properly view Polaris.  Long term project will see this tree and the mandarin going away in the favor of a larger custom shed within 18 months so I'm not too worried about trimming a few branches now.

The next big star party is in September.  I'm hoping to have most of this project completed by then - the big unknowns are the metal tube dimension and how the transition from an 8 inch diameter circle to a 160mm square will be accomplished.  One option is to get some sheet metal and cut it with a sabre saw.  It'll be ugly but will work fine.  Another option is to get a professional-look with a 3d printed truncated cone.  That will probably cost $300 but will look the best.  I think that could be a second step depending on how it goes.

There are many projects that are on pause that have something to do with astro:

1. hypering fomapan - stuff to do to improve the process (thermal control) and to test the results.

2. cutting the roll of aerographic film (aviphot 200) into sizes to use in the holders (and hypering depending on performance) - depends on blacking out the bathroom so that I can work in total darkness.

3. peeling another few layers off the polar alignment onion - requires time and a view of polaris at home (see above picture)

I looked at the original scan of the TMax and I can see two things for improvement:

1. slight trailing - there is a tiny amount of oblong stars in the central region where the image is sharpest.  I would say that the length of the trail is maybe 2-3 pixels - about 8-10 microns at the surface of the film.  Most of the star images outside of the sharpest region are not tight enough to show this error.  This trailing could be field rotation or it could be the balance issue that I've attacked before.  What it tells me is that I can refine the balance a bit more than I have already.

2. coma is not centered - this tells me that the optical center of the lens is not centered on the rear standard.  I will try to figure out which way they need to move to bring it true.  

I am tempted to send off the remaining C41 and E6 film from the last star party to get developed rather than waiting for myself to mix the chemicals and do it.  I keep trusting my future self to do the effort.  There's a lot of emotional baggage that comes with putting all the chemicals into the kitchen, handling the film, and then putting it all away.  It's a very obvious focus of my energy onto something that has nothing to do with house work or garden work.  It's a thing that I have to rationalize and manage.