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Astro Projects

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Ha Solar Imaging and Observing Rig

Gina

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I have just acquired an Ha Solar telescope consisting of an Antares 127mm 1200mm FL telescope with Coronado PST.  I plan to set this up for both observing and imaging.  I have yet to decide on the final mounting for this but will start with a Skywatcher Pillar Mount with an NEQ6 SynScan Pro mount for testing as I want to reserve my EQ8 and main observatory for DSO imaging.

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The telescope focussing is not quite so simple as the knobs are close to the body.  The knobs can be taken off but the shaft is only 3mm and quite short.  Might be better to attach a gear to one of the knobs.

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Gina,

You don't have to worry about or consider any focusing of the donor scope.

The etalon NEVER moves relative to the donor after initial set-up. It's always -200mm from the prime focus.

Think about the donor just as a fixed replacement for the original gold tube in the PST.

Final focusing is always achieved behind the etalon - I use a Borg helical focuser on my PST Mod.

 

 

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Thanks Ken :)  I'll have to think about that.

Later...  Decided to go ahead with the telescope focuser motor drive as that is the basic problem and certainly works for visual so I see no reason why it shouldn't work as well for imaging.  The main problem was that manually adjusting caused vibration to be transmitted to the image even when mounted solidly on the EQ8 with concrete pier.  Getting the etalon 200mm from the focus of the camera can be achieved with suitable extension tubes.  Maybe once the prime focus is set up it will not need altering but I would have thought the focus would change with temperature.

Edited by Gina

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I've taken the NEQ6 tripod out and placed it on the concrete by the SE corner of the house.  The house roof will obscure Polaris so I've decided to use drift alignment for PA.  I want reasonable PA so that the sun doesn't drift out of the FOV when tracking solar.  I don't think very accurate PA is necessary like it is for DSO imaging.

Edited by Gina

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With rather a struggle I've moved the NEQ6 mount from the SW Pillar Mount to the tripod.  Wish the NEQ6 had handles like the EQ8.  In spite of being heavier the EQ8 is much easier to handle than that awkward shaped NEQ6.  I think the tripod should be fine - it's heavy and very rigid.

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Not yet ready to do PA on the NEQ6 mount.  I was going to use my Esprit 80ED Pro with ASI1600MM-Cool but I'm missing an adapter - probably in the box of bits I've mislaid  :iamwithstupid:

Anyway, proceeding with the telescope focuser motor drive parts.  Here is first attempt at the focuser gear mounted on a spare knob (exactly the same as the knobs on the Ha solar scope.

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Edited by Gina

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Been looking into where I could put the electronics box (or boxes) and the motor drive box could go next to the telescope focuser with an extension to the clip/bracket that holds the focus motor and another clip further up, the other side of the solar finder.  I think this will want printing in three parts to avoid a lot of support material so I'll print it in ABS and solvent weld the parts together with acetone.  I have yet to make up the electronics yet.  Two or possibly three stepper motor driver modules plugged into sockets on stripboard plus RPi 3 and buck converted to provide 5.1v for the RPi.  The third stepper motor would be if I add a camera rotator - nice but practicality doubtful.

We have rather watery sunshine ATM which might improve later but I can't see my being ready for solar imaging today and I'm not pushing myself - only results in mistakes!

Edited by Gina

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Well, it does need focussing so how do you suggest I do it?  Are you saying that once I get the scope roughly focused I can rely on tilting the etalon to fine focus?

Haven't had much chance to try things as there's been very little sunshine since I got this scope :(  No surprise there then!!

Edited by Gina

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Gina,

As part of the mod it should have already been set up to the correct position.

The focusing on the solar disk is by using the focus knob on the Black body of the PST. The tuning ring is used to fine tune the H alpha wavelength to show the solar detail.

 

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The correct focus position was set up using an optimally tuned PST less its 40mm objective. The subsequent mod is a stage2 so the black box is empty. The digonal containing the blocking filter fits in an aperture machined in the rear face of the black box. Spacers have been supplied that make up any difference in the post etalon focus. Any very small adjustments for different eyepieces are by way of the OTA fucuser and lie within the etalon position tolerances.   :icon_biggrin:

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Ah I see :) And thank you Peter  :) That's what I thought and why I'm using the scope focuser - simplest solution.

I've redesigned the motor bracket and scope ring to allow attachment to the electronics box and also designed another ring for the other end of the box.

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Edited by Gina

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I've ordered a Pine64 processor board for this project.  It is similar to the Raspberry Pi but has a USB3 port I can use for the camera and the Ethernet port is gigabit, so downloading images will be much faster.  It also has a 64bit processor and 2GB RAM so like a Pi with go faster stripes :D  It has a Pi compatible GPIO port and another as well.  This should work like the RPi but faster and with more facilities.

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Received the Pine64 today and looked at it - no USB3 port! :(  Couldn't have checked properly - I blame my cold!!  I'll return it, normally no problem with Amazon.

A bit later... Applied for return and refund which was successful and now have return label to print - return via Royal Mail postage paid :)

Edited by Gina

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Now back to this project encouraged by the amazing weather. 

I have decided to use the EQ8 in my observatory for this rig.  I may end up swapping scopes if I do planetary or narrow field DSO imaging but that will be later when it's dark enough and planetary may wait until the planets are higher in the sky.  Currently I have a problem with the EQ8 which I'm now trying to sort out.  I think it might be a power problem as the power LED has started blinking which means low voltage I gather.  There may be a faulty connection in the observatory wiring as the voltage at the warm room end is 13.8v.  I'm thinking maybe I should have a voltage display on the pier.  That would be easy enough.  Meanwhile I'll check with a DMM.

There also appears to be a fault in the CAT6 Ethernet cable I have from the house to the observatory.  The Raspberry Pi I'm using for control has WiFi capability but isn't capable of image capture at the high rates required for Ha solar imaging.  All attempts at getting a mini PC working have failed so I may go for a laptop or even tower PC for image capture.  There is plenty of room in the observatory.

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Gina

Posted (edited)

Traced the voltage drop to the power distribution box in the warm room.  This connects to the 13.8v PSU, backup battery and power lines to pier plus ground wire which goes to the pier top and earth rod.  It contains a digital ammeter and three fuses.  The ground terminal was slightly loose and may have been the problem.  I've tightened it up and will see if the problem is fixed.

Edited by Gina

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It is ??  EQ8 mount now slewing, tracking and parking fine.  I plan to take the solar scope out and mount it on the EQ8 this afternoon and see if I can get it tracking the sun and see a prom or two.  :)

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I think I shall need to arrange some sort of shading to keep the strong sunlight off the equipment except for the front of the scope, and myself.  Once I get imaging working I can go and hide in the shade ?

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Been imaging it today and seeing is going rapidly downhill, getting difficult to focus now so don't be surprised if the view is rubbish :)

Dave

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Taken the telescope out to the observatory and noticed that the EQ8 needs a wide dovetail bar rather than the narrow one on the scope so I'll have to take the bar off the Esprit scope and put it on the solar one.  I've been thinking though that I might be able to put the solar scope and the Esprit 80ED side by side on the mount using the large 10mm thick aluminium plate I have.  If I can do that it will save either swapping scopes or making another observatory/pier for the Esprit.

It's very warm in the observatory even with the window open and I might wait until it cools off a bit before doing much in there.  I can sort out mounting parts in the meantime.

The telescope that has been adapted for Ha solar has a focal length of 1200mm as compared with 1000mm of my MN190 so could make a good planetary imager with the PST swapped for a colour camera and the ERF removed.  That would be easier than swapping scopes I think.

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