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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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I've ordered a neutral density filter with 12.5% transmission - I'll try that.  At least the tests showed that the image sensor size is roughly right, just that the camera was too sensitive for this particular setup.  This was with the camera directly on the 2x Barlow whereas the observing system has an additional extension tube giving more like 3x from the Barlow.  I'll take and post some photos later to show what I'm talking about.  Another test I can apply is to add in a short extension tube between the 2x Barlow and camera to reduce the brightness.  Not today though - the sun is too low now.  Anyway, that laptop is driving me nuts!!

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Here are some photos of the telescope and imaging setup.  Not very good I'm afraid - the sun had set behind the observatory roof.  I'll take some more tomorrow.

59a30f63ed12e_SetuponEQ8Mount01.thumb.JPG.2c40de465bedc15e923d3b30d7993556.JPG59a30f5e82332_SetuponEQ8Mount02.thumb.JPG.6a24e9386a1031a27f4ba81e1d83a074.JPG59a30f56e492a_SetuponEQ8Mount03.thumb.JPG.c590acb7e51cb6057f433201c07b7b84.JPG

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Being in strong direct sunlight the camera got pretty warm so I think a sun shield is indicated.  Apart from that I don't think any camera cooling will be required as the image is bright but if it were wanted I could use a Peltier TEC.  The sensors in these cameras are thermally connected to the case.  I tried Peltier cooling in one of the versions of my all sky cam and it was pretty efficient.  Then I changed to a much better lens and no cooling was needed.

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Gina

Posted (edited)

Hazy sunshine so far today but hoping the sky might clear later.  Micro PC plus SD cards have arrived but the thin cloud seems to be here to stay all day :(  Too hot to do much anyway. 

I've got an electronics control box for my rotating widefield imaging rig but I've mislaid it.  That has two stepper drivers.  I have the one off my Esprit imaging rig but that only has one driver for the focussing.  Both are set up with INDI drivers for the camera and mount controls plus focussing.  I had auto focussing working from KStars/Ekos with the Esprit :)  Probably won't want auto-focus for solar imaging as the procedure uses stars for focussing for dark side imaging.  I guess I can use the single motor drive control box for now for testing.

Edited by Gina

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Gina

Posted (edited)

Time for summing up I think.  This scope has definite possibilities and the FOV with the proposed ASI174MM camera should be fine.  I'm sure the resolution will be more than adequate and the high speed capabilities of this camera plus the slightly bigger image sensor would seem to make it ideal. 

The other camera I've been looking at is the ASI178MM.  This has a smaller image sensor but much higher resolution.  It also has a rolling shutter which is not ideal.  Probably because of this the frame rate is limited.  It does higher frame rates at lower resolution but it doesn't say if this is by binning or reduced ROI (region of interest).  If the latter, it would make it unsuitable.

Looking at these two cameras' capabilities then, plus the information about the intended use, everything points to the ASI174MM as the one for solar imaging.  All in all, the 174 comes out strongly on top.  The downside is the price but I'm reminded of the phrase "spoiling the ship for a h'aporth of tar" :D  Anyway, with the telescope costing less than expected the better camera still comes within my original proposed budget.

That is the camera decided then :)  So I'll order it from FLO.

Edited by Gina

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Another conclusion I have come to is that the present observatory does not provide the best environment for the Ha solar telescope.  The orientation prevents use late in the afternoon.  I'm thinking that a pier nearer the house would be more suitable but this will be a future project - I'll make do with my present observatory for testing.

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I think the Raspberry Pi 3 will provide control of the mount and stepper motors for focus, tuning and possibly camera rotation.  It can also handle the camera for initial testing but when I want high frame rates I plan to use the micro PC for data storage.  Fortunately INDI can handle multiple processors for device control.  The RPi provides hardware IO and the micro PC a USB3 port and gigabit Ethernet plus micro SD data storage.

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Hey Gina, 

I have sent you a message, I would love to hear your response :) 

Either way thank you! James

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Here are some photos of the back end of the solar scope.  A couple of different eyepieces on an extension on the 2x Barlow giving about 3x magnification.  Then imaging with ASI185MC and ASI1600MM-Cool cameras either right down on the Barlow or spaced a bit further away to increase magnification and reduce brightness slightly.

40mm Plossl eyepiece.
59a47971b6ffa_VisualSetUp01.thumb.JPG.d3fc7836674a8f940a4c0731b4d88ede.JPG

Baader Hyperion Zoom eyepiece set to 24mm
59a479672b2cd_VisualSetUp02.thumb.JPG.21d7b9f6a3ebc193c78315b9517e622b.JPG

ASI185MC camera directly on 2x Barlow.
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ASI1600MM-Cool directly on 2x Barlow.
59a479491a248_ImagingSetUp03.thumb.JPG.f7410bace747ac4124f31b86af41de84.JPG59a4793d7e040_ImagingSetUp04.thumb.JPG.317dedee6b438f2d3a8ca483b5bea327.JPG

 

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Field of view calculation with ASI174MM and ASI1600MM and 2x Barlow.  I'm hoping to get the chance to check the FOV with my ASI1600MM-Cool probably with the help of the odd rubber band to help with the weight :D  It's totally overcast ATM but sunshine is forecast for this afternoon - I won't hold my breath.  Meanwhile, I shall try to get the RPi 3 set up for control and imaging.

59a511278ee12_FOVASI174MMASI1600MM01.thumb.png.6d4a91f71e4867e660f06c193de9d823.png

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Why the x2 Barlow???

I use the ASI 174MM but need a tilter (1.6 degree) to suppress the Newton Rings.

 

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13 minutes ago, Merlin66 said:

Why the x2 Barlow???

I use the ASI 174MM but need a tilter (1.6 degree) to suppress the Newton Rings.

 

The original configuration was for the inclusion of a binoviewer which required a Barlow to reach focus. The surprising side effect of this was the increased field of view of the eyepiece in conjunction with the 5mm blocking filter as well as better performance. (The "how and why" of this is currently a subject of debate). As a binoviewer is not being used at present, an extension piece takes the place of it.   :icon_biggrin:

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Gina

Posted (edited)

The sun came out briefly and I caught a glimpse of the limb in the ASI1600MM-Cool image.  Looks like the image disc would cover this size of image sensor, not that I'm planning to use this camera as it won't do the fast frame rates.  This is with the camera as close as I can get it to the Barlow which puts the image sensor some 20-25mm from the top of the Barlow.

Edited by Gina

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1 hour ago, Merlin66 said:

I use the ASI 174MM but need a tilter (1.6 degree) to suppress the Newton Rings.

Thank you for posting in my blog :)  I have ordered the ASI174MM so it's good to know that's what you use.  Do you put the tilter in front of the camera?

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Yes, the tilter sits immediately in front of the ASI 174.

Normally you'll need around 1000 frames per exposure - this allows AS! to select the best frames for subsequent stacking, then apply Registax wavelets to bring up the image.

 

100_3362.JPG

Edited by Merlin66
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Gina

Posted (edited)

Occasional holes in the cloud let the sun through now and again but it's only a few minutes at a time with complete cloud cover mist of the time.

I've ordered a tilter from FLO.

Edited by Gina

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Gina

Posted (edited)

I generally use remote imaging and control for my DSO imaging and may do the same for solar imaging.  If so it would be nice to have a remote solar finder.  For this the RPi camera would seem ideal, looking at the solar finder attached to the telescope.  OTOH using the KStars map I can simply move the telescope to the sun - assuming the mount has been polar aligned and set up with Home pointing to Polaris.

If I use a different pier for the solar scope it will have to be with a view north to align it with Polaris on a clear night so immediately in front of the house would not do as the house faces south.  I don't really want to hog the main observatory with the solar telescope - I would like to keep a dark side imaging rig set up on the EQ8 mount.  Solar imaging doesn't need such a good mount - the NEQ6 should be perfectly adequate.

I think I shall try the NEQ6 tripod on the concrete to the side of the house where I should be able to align the PoleMaster with Polaris and yet still be able to point the solar telescope at the sun for longer than is possible in the observatory.  I this proves satisfactory I may build a concrete pier later.

Edited by Gina

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Checked the azimuth and it turns out that north is about 15° the wrong way and I'm not sure that Polaris is going to be viewable from within the concrete path round the house.  I'll have to check at night when we get a clear one.   There are other ways of PA without needing Polaris though.

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Gina

Posted (edited)

Later this afternoon the clouds parted a bit to reveal some strong sunlight so I had another go with solar imaging, this time with the ASI1600MM but the readout speed of this camera is too slow for this job even though it was connected to a USB3 port.  I continued testing during periods of strong sunlight until the sun set behind the observatory roof.  No further tests are proposed for this camera.  The ASI185MC with fewer pixels and hence a faster readout rate can be used until I get the ASI174MM camera.  Use of the ASI1600MM has shown that the image should well cover the ASI174MM sensor - a useful result and worthwhile test.

Unfortunately, the use of manual control on telescope focuser and etalon tuning ring causes vibration to be transferred to the imaging system making adjustment virtually impossible so remote controls will be needed before further progress can be made.  I plan to work on this next.

Edited by Gina

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Gina

Posted (edited)

ASI174MM and tilter have arrived but so has the rain !!  Fortunately I have the back end of the imaging rig indoors so I can sort out the motor drive to the tuner ring.  I shall use the ubiquitous 28BYJ-48 mini stepper motor with built-in gearbox modified for bipolar connection and drive it with the A4988 driver module with Step and Direction lines driven from GPIO lines on a Raspberry Pi 3.  The 5v version becomes effectively 12v with the bipolar mod.

See Setting up a Raspberry Pi for Astro Imaging and Hardware Control - PART 9

Edited by Gina

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I can use the PST mounting holes for a bracket to hold the motor and either 3D printed gears or timing belt and pulley on the motor shaft.  For gearing the tuner ring wants an ID of 60mm and the pinion a 5mm hole with flats.  Done this many times for camera lens focussing.  OTOH a suitable length timing belt will drive the ring directly.

59a7f2cf2bdbd_TuningDrive01.thumb.JPG.56580f87637208ba554cdbbce3644468.JPG

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Tuning motor bracket and motor attached to the PST body and the gear that fits in the tuning ring being printed.  This is TPU which is a flexible rubbery type of filament.

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Gina

Posted (edited)

Here is the gear fitted to the tuning ring - fits perfectly :)

59a8763b7d933_TuningRingGear02.thumb.JPG.a4a3b5377211c1285d2555b7de91539b.JPG

Edited by Gina

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