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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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Gina

Posted (edited)

Thank you :)

Already modded and ready to go.  Just been setting it up.

I can add that this Ha solar telescope was developed and produced by Peter Drew and he deserves the credit plus my thanks :)

Edited by Gina

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I had originally intended my Skywatcher Pillar Mount for use with my widefield NB DSO imaging rig but want to try out the Ha solar telescope ASAP.  The dovetail on the solar scope won't fit the EQ8 but the NEQ6 takes both sizes.  I haven't got a spare 75mm dovetail bar for the EQ8.

Progress so far has been to put the NEQ6 onto the pillar and then the solar scope on the NEQ6.  I have added the Coronado with diagonal etc. but not yet sorted out an eyepiece,

Here is a photo of the present setup.

599eb23135748_SetuponPillarMount01.thumb.JPG.587a718edb082d07481309309ed3e218.JPG

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Gina

Posted (edited)

Should have eyepieces but can only find one ATM and that is a 2" fit 8-24mm Baader zoom.  It had various adapters and could be attached to a 1.25" scope like the Coronado but I've mislaid the other bits.  So I'm 3D printing an adapter.  I've also ordered a 40mm Plossl from FLO as this is the recommended eyepiece.

Edited by Gina

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YIPPEE!!  I've seen my first ever prom :)  Quite small but also quite distinctive :)  Sun spots were easier to see.  The sun appeared in a small gap in the clouds for a few minutes.  I think that's it for today - more cloud and the sun is about to set behind a tree.

A few things are clear from this first observation.  The mount support is insufficiently rigid for this focal length and image magnification, and the focussing is rather critical.  I am not surprised at either of these - the pillar mount is really only suitable for widefield imaging.  This ground location is also not ideal - it's too near the fence - the view of the sun will be quite adequate further back and this pier will revert to widefield DSO imaging use.  As expected the eyepiece needs a hood to keep the light out.  The magnification isn't too bad at 24mm focal length though 40mm would show more of the sun's disc.

I shall need to think about a much more rigid pier - either put the telescope on my main concrete pier in the observatory and EQ8 mount or provide a new platform outside the observatory.   There is not really a great need for a full observatory for solar observing and some sort of roll off shed or cover  would do. 

 

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With little chance of dark side imaging for the next few days, I've decided to install the solar scope on my EQ8 in the observatory.  This has several advantages over an open setup on some sort of tripod.  Not only is the mounting really solid and stable but all the tracking, power and other facilities are there.  I just need to sort out the dovetail arrangements.  The forecast is for sunny spells today - I wonder :D  Currently the sun is out but the sky is hazy with loads of contrails.  Still quite low as yet, of course.

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Gina

Posted (edited)

Changed dovetail bars over and mounted the Ha solar telescope on the EQ8, set up for observing ATM.  Sun is out and conditions much better than yesterday.  Opened roof, balanced scope on mount and pointed scope at sun using shadow on warm room door and then the solar finder on the scope.  With further slight adjustment I had the sun's image in the eyepiece (24mm FL).  Adjusted scope focus and then PST and a nice prominence popped into view :)  The magnification is too high to show more than a quarter of the sun's rim so I'm looking forward to receiving the 40mm Plossl eyepiece. 

I shall also start thinking about imaging.  Not sure which camera to try but with the 1.25" size I'm thinking a small and light ZWO CMOS one might be best for first try.  OTOH the only one readily available is colour - ASI185MC.  I have a mono one (ASI178MM) in my all sky night view camera.  The other mono cameras I have are the ASI160MM-Cool and the Atik 460EX mono (CCD).  The latter is particularly heavy.  Maybe I'll try the ASI185MC to get an idea of the image size and then see which mono camera would be suitable and buy that.

Of course, if anyone reading this has any suggestion about a suitable camera I would much appreciate it :)  The focal length of the whole telescope would be 2400mm I think - 1200mm scope and x2 Barlow.  I'll check in a FOV calculator but I don't know yet whether it's the eyepiece or something else limiting the FOV.

Edited by Gina

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If the view is not being limited by the PST this screenshot from FLO's FOV calculator shows the ASI1600MM-Cool and the ASI185MC.  The latter smaller camera would show a very small FOV.  I would want to get the whole of a prom in the frame. 

599ff89b63db4_FOVASI1600MM-Cool01.thumb.png.8087f6fd7ccdcb1745845e4f3b9e1b67.png

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Hi Gina,

The problem with a PST mod for imaging is that the focal ratio is circa f10. You will struggle/ impossible  to get a FD with a camera. Best use it to capture detail.

Also, best to use a mono camera for solar as you are capturing images that are near the infra red, a colour camera will only capture a 1/4 of what is visible, that is why people apply a false yellow/red in photoshop

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Gina

Posted (edited)

Yes, I realise that.  It is detail I wish to capture - an image of the full solar disc would show little of interest.

And yes, I also know a mono camera is required just as it is for narrow band DSO imaging.  The only reason for considering a colour camera is that I have a lightweight one and I don't have a lightweight mono camera available unless I strip down my all sky camera.  I know I would be losing three-quarters of the pixels.  I would like to try my ASI1600MM-Cool but not sure I can support its weight - I might have to make up some sort of support structure.

The ASI178MM camera in my all sky cam would be an ideal candidate with a 6.4Mpx sensor and without the cooling unit is quite light.  Looks like temporarily cannibalising the ASC might be the best option.

Edited by Gina

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Gina

Posted (edited)

I think it has to be the ASI178MM from the ASC.  Much as I would prefer not to dismantle a working system I can't see any sensible alternative.  I have the ASI185MC in front of me which has a very slightly smaller image sensor, so comparable size, but apart from being colour and only using 1 in 4 pixels, there are far fewer of them anyway - 2.3Mpx.  Slightly bigger pixels.  The ASI178MM has 11x the resolution of the ASI185MC for Ha.  OTOH I guess there would be no harm in trying the latter initially - it might tell me if this sensor size is not suitable. 

Going larger the ASI1600MM without cooling may be a good candidate (at twice the price).  Only slightly heavier but great resolution.  That's if the telescope gives that resolution, of course.  Unfortunately, I don't think I can just try this option as I only have the cooled version with a lot of extra weight.

Quote

Sensor          4/3″ CMOS    
Diagonal       21.9mm    
Resolution    16Mega Pixels 4656×3520    
Pixel Size      3.8µm    
Weight          140g

 

Edited by Gina

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Gina

Posted (edited)

Got the ASI185MC camera set up indoors connected to a Windows 7 laptop running SharpCap and working, then took it all out to the observatory to try.

Connected camera and mount to laptop and set up CdC with EQMOD and SharpCap.  Ran CdC and connected mount and set that up with the sun in the middle of the solar finder.  Then connected the ASI185MC camera to laptop and replaced the eyepiece with it.  Watching the image in SharpCap, I finely slewed to get the rim of the sun in the FOV and adjusted exposure and gain to get a better image.  These needed to be quite low - it's quite a sensitive camera.  With the optical setup as before with Barlow I got a very high magnification - something like the zoom eyepiece set to 10mm. 

Tried without Barlow and got focus somewhere near but camera overloaded even at minimum exposure (32µs) and minimum gain.  So went and got an ND6 filter and added that.  Then the software failed and now won't work, even after a cold boot!

Now having a break.  Maybe the laptop is overheating I know I am! - it's very warm out.

Edited by Gina

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It would seem that a larger sensor is required.  Maybe the ASI174MM which it says was designed for solar imaging (as well as lunar and DSO) having a very high frame rate.  Having seen the turbulence from the atmosphere in the eyepiece it's clear that a high frame rate is needed.  A very high resolution isn't.  This certainly seems much more suitable for Ha solar imaging.  Not so happy with the price though!

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The resolutions of the 185 and 174 are much the same but the 174 has 1.56x the FOV in each axis.  So definitely better but I think I shall still need to reduce the magnification of the whole scope.

Still can't get EQASCOM to work and the clouds are back plus the sun is about to set behind the observatory roof so that's it for today! :(

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Gina

Posted (edited)

Due to the problems I'm having with the Windows software I thought of using the Raspberry Pi setup (already to go in a 3D printed box) that I use for my Esprit rig for DSO imaging.  Currently it's set up to work with the ASI1600MM-Cool camera and EQ8 and also includes remote focussing. 

All that works pretty flawlessly for DSO imaging but I've thought of a problem with solar - that of the data download rate.  A full frame of 1600 data takes about 8s to download which is fine for DSO imaging with 60s or more exposure time but solar wants many frames a second not one a minute!  Might work as a test setup with binning to reduce the data rate.  I do this for focussing with DSO imaging.  OTOH if I change the setup to use the ASI185MC camera the data is much reduced and would take just over a second to download.  That might do for testing.

I might look into the possibility of some sort of support structure so that I can use the ASI1600MM-Cool on the Ha scope.  If this were possible it might save me the cost of £615 for an ASI174MM.  I could still get a frame rate of about 30fps with reduced resolution.

I shall have to investigate the whole problem of control and data storage.  Maybe a Linux laptop in the observatory, use INDI as with the RPi and KStars on the client computer but store the image data on the remote laptop and download asynchronously.

Edited by Gina

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Weekends are a nuisance, Bank Holiday weekends are even worse :(  FLO won't be open until Tuesday so the earliest I could get an ASI174MM would be Wednesday!  Unless I took a trip into Exeter on Tuesday :D  The more I think about it the more I think that is the camera to go for.  I know the scope will cover the sensor since the FOV I get with the 40mm eyepiece is bigger than that.  The resolution is quite sufficient and the high frame rate has to be an advantage.

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Gina

Posted (edited)

If I want to control this remotely as is my usual practice, I shall want both the main scope focus and the PST tuning sleeve remotely controlled in addition to slewing the mount.  It would also be nice to be able to rotate the camera.  My RPi control unit for one of my widefield imaging rigs already provides focus and camera rotation, I would just have to allocate a couple more RPi GPIO lines to cover step and direction for another stepper driver module.  This would be easier to allocate to INDI drivers than to use an Arduino under USB control.

Of course that is for the future, I need to get the camera working first and data saved to local storage.  The connection to the camera will have to be USB3 which rules out the RPi.  I shall need a small computer unit with a USB3 port and gigabit Ethernet.  It's possible that this computer may have output data lines available to control stepper motor driver modules but even so I think the RPi with INDI drivers would be a simpler solution.

The image data storage computer could have any suitable operating system though I guess it would make sense to use Linux with INDI drivers.

Edited by Gina

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Gina

Posted (edited)

Searching Amazon UK I have found this :-

Micro PC, SEGURO V11 Mini PC Intel Atom x5-Z8350 Processor 2GB DDR3 32GB eMMC Intel HD Graphics / 4K / 1000Mbps LAN / VGA Port / Dual Band WiFi, Micro Computer Support Windows 10

Has dual boot Windows 10 and Linux 16.04 operating systems.  3 USB3 ports, micro SD, HD port and gigabit Ethernet plus a rang of WiFi options.  Just a pity the HD isn't internal though maybe the SD port might do for data storage.  I'll have to investigate the speed capabilities.  Designed primarily for video streaming I think this machine should do for video data storage and transfer.

Any comments would be much appreciated - TIA :)

Edited by Gina

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Gina

Posted (edited)

Checked SD card speeds and Class X should be fine, being rated at 10GB/s minimum (that's 10 gigabyte not gigabit) and the micro PC can take up to a 32GB card.  Camera data rate will be 2.3 x 2 (2 bytes per pixel required even for 12bit data width) x framerate MB/s so much lower than the card's maximum.  I tend to get confused between MB and GB :D

The frame size is very similar to 1080p HD television but 2 bytes per pixel rather than 3 so I would guess that the micro PC should be able to handle something like 70fps.  All this is rather guesswork for me but that seems to be adequate.  That would be a pretty enormous amount of date collected over just a few minutes.  The ASI1600MM with 16Mpx sensor at one frame per minute collected oodles of data when run overnight for 6 or 8 hours.  This sort of data would be collected in a minute or less from the solar camera running at it's full capacity.

Applying a bit of calculation :- 2.3x2x70 = 322 MB/s so a 32GB card would fill up in about 100s.  Maybe a 500GB SSD would be more suitable :D   Looking now at the LAN data rate, we are generating data at 322x8 = 2576Mb/s or 2.6 GBps.  Maybe best to collect data on an SSD and physically take it indoors :D

This Ha solar imaging is a "whole new ball park" to me :D  Exciting :)  I'm thinking that short bursts of recording solar data may be the way to go.  We seem to get many more sunny days than clear nights so it's looking like light side  is going to predominate over dark side though I would still like to do a bit of dark side.

Edited by Gina

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Gina

Posted (edited)

Bitten the bullet and ordered that micro PC plus a couple of 32GB SanDisk Ultra micro SD cards to go with it.  Amazon Prime delivery tomorrow :)  So if I can't get the video recording going today I stand a chance tomorrow.

Edited by Gina

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Gina

Posted (edited)

Just been out and tried things again with full sunshine.  The software worked after a reboot for a few minutes.  I was able to slew the scope to point at the sun but got no solar image.  Looked at the setup and saw that I wasn't using the Barlow but had the ND6 filter on.  Put rig back to "normal" with Barlow and without ND filter.  That's when EQMOD failed again and nothing would persuade it to work again :(  The laptop was feeling rather warm!  It's hopeless trying to point the scope manually by releasing the clutches on the mount - just far too coarse.  It was easy doing it the proper way through software - when it worked.  Time for a break.

I've decided not to order an ASI174MM camera until I have imaging working with the ASI185MC as this is an adequate test camera to at least get some sort of image.  It is well sensitive enough in spite of light loss through the Bayer matrix.

Edited by Gina

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My astro laptop worked well enough this afternoon to capture a somewhat washed out solar image.   EQMOD worked just long enough to enable me to point the scope at the sun and set tracking to solar before it crashed again.  Took a while to get the image lined up correctly because EQMOD had stopped working and I had to use nudging with the mount clutches eased slightly to do the required fine slewing.  I had to add the ND6 filter to reduce brightness but it was still too bright and the sun's surface saturated the image sensor even with minimum exposure and gain.  It needs a denser filter.

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