A refractor is born

Sometime in September I’ve decided that an upgrade for solar imaging is a must.

The goal of such an upgrade would be to have a very portable yet powerful scope that can be easy to set up and without many of the problems encountered with other instruments I have. I’ve concluded that a diameter of 150mm is the minimum, and that the instrument will be a refractor due to lack of the collimation procedure required with a Newtonian for example. Other optical systems were considered but my budget aimed at a homemade instrument. That, again, pointed at an achromatic lens.

The main purpose of the instrument would be H-alpha solar work, but with the ability to do some white-light solar imaging also, and the occasional ISS transit. The Moon would also be fun for such an instrument, and perhaps some deep-sky views at the eyepiece.

I’ve decided that I should go with the iStar company (US based) and their 150mm F/5 achromatic lens. Unfortunately this lens was not on stock, so I’ve reconsidered and selected an improved version, an anastigmatic R50 slim lens. I was hoping that by the time the lens would get to Romania the instrument’s frame would be completed.

So…I had one month to put on paper, select materials, build components and assemble the “thing”.

September 22: The design was more or less selected. Initially I’ve built the lens and focuser flanges by hand, using an aluminum plate and sawing by hand the desired shape.

I was not happy with this setup, so I’ve decided to get some proper flanges built using Laser-cutting techniques. The process took quite a while, so at the end of September I was still lacking the main parts of the frame.

October 5: The new flanges arrived. Using some new components built the days before, I’ve assembled for the first time the frame of the instrument. The focuser system was also modified, with the electric motor now connected to the focuser by a pair of  toothed wheels.

A few more components had to be built by hand, and aligning/realigning the frame took some time.

October 15: One of the most delicate procedure of the entire project was to spray-paint the components. The job was done after 7-8 days of painting/drying/painting/correcting/painting/drying procedures:

Finally, the components were now ready to be permanently assembled.

October 17-18 (the night between): Like some furniture from IKEA or a LEGO set, the components of the soon-to-be optical instrument were “carefully placed” on the carpet:

And they were not left alone until the final shape of the refractor was formed:

Verifying the alignment showed me that the frame was stable and could now receive the main component: the lens.

October 20: The lens was in my hands. I must thank my friend Alin Tolea for the many talks and help with acquiring the lens from the US 😉

Now I was finally touching the “untouched” lens. No dust, nu scratches, no signs of ever being in contact with the air. The first and last time a lens would look like this…

Thanks to my friend Vlad Dudu for this shot.

Of course I’ve rushed back at work, drilled a few more holes, and went home only to start the final and most rewarding procedure: “put a lens on it”.

Now, this strange-looking piece of aluminum, was finally looking almost like an optical instrument. The Lunt 50mm ERF filter was also housed into a homemade cell, and mounted on the focuser; one more component finished.

Next phase: tests. Under the stars at first, to have a proper collimation and some first views of the sky.

The same evening I had the refractor ready, I drove to my usual observing site and had a go at the eyepiece of the new instrument. With a 32mm eyepiece the views of Dumbell Nebula and M 15 globular cluster were very nice, despite the very poor transparency due to cirrus clouds and some light pollution. I did not have much time to do the adjustments, but I did however acquire some frames of M 15 using the ASI 1600MM camera at the focal plane with no filters. This was before I had the lens collimated, so some defects are easily visible on the 50% resized image. Only 50% of the frame was selected due to the uneven star shapes (very normal for such a lens). Using no filters showed that the chromatic aberration is present, but at rather low levels compared to other achromats I’ve used (SkyWacther 150mmF/8, 100mm f/5, 90mm f/8). Of course no match for the Teleskop Service APO 115mm F/7, but again, deep-sky imaging was not the purpose of this lens, at least not in full-spectrum. Some H-alpha might be a possibility as soon as I find a suitable field-flattener. So, the M 15 shot (40 frames, each a 10 sec exposure, no binning, no calibration, just some mild Photoshop):

Pretty nice for a 6 minute-equivalent shot under poor conditions. This scope proves to be a very fast one.

Of course I had to wait a little longer for the true test…

October 21-22: Some H-alpha work was finally in sight. On Oct 21 the seeing was very poor, and the results were not confirming my expectations for the instrument…I was a bit disappointed actually. But on Oct 22 the conditions were not so bad, with some cirrus clouds and 4-5/10 seeing. The Sun had an altitude of only 30-35 degrees, which did not help much…

Still, the “first H-alpha light”looks promising:

Also, this was the first time I could actually see (on Oct 20 I was observing at night) the refractor onto the EQ6 mount. They look happy together 🙂

I still have to build a dew shield, a shroud and some lens caps, but the shape of the refractor will not change.

At the end, I can say that this 1-month project was very rewarding, as I could build the frame in time to receive the lens, and also test the instrument just before the arrival of  a bad weather front.

This time the well-known phenomenon “I’ve got a new telescope, so it will rain for days” did not occur 😉

 

 UPDATE (October 23):

I’ve managed to save a few more H-alpha shots from the first-light tests on October 21-22. All were acquired in poor seeing conditions…