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bobro

DIY EQ2 Economy Autoguiding

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Perhaps DIYers will be interested in a low cost guiding setup for EQ2 mounts. I'm not sure if this approach has been tried before, but it's relatively straightforward to implement and is certainly low cost.

In early 2016 I purchased a Meade Polaris 130 scope, complete with EQ2 mount and Economy RA (clockwork) motor drive with the intention of trying out astrophotography at a low entry cost. Very quickly the prime focus problem arose - so the scope was shortened by 40mm. With this mod 30 second exposures very not too difficult, with 60 seconds sometimes successful. Of course the problem was tracking.

Rather than spend time taking lots of 30 second exposures and knowing that longer exposures were really the way forward, I decided to investigate the Economy RA Motor to see if it could be modified in some way for guiding. The answer soon became apparent - yes it could (with very simple mods) but I had no idea how well it would work.

Next steps were to look for a way to guide the motor - an Orion mini guide scope and Microsoft Cinema webcam (modified of course) plus a Raspberry PI with Lin_guider were relatively painless to get going and the results were good. However, DEC drift could still cause star trails, so a bit of thought came up with the idea of using an Economy RA Motor as a DEC motor, again to be controlled by the Raspberry PI.

This evening the setup was given its for test for dual axis guiding (5 min RA guiding had been successful previously). Not the best sky - very bright due to the moon and clouds appearing. Still, taking no time for polar alignment other than to point the scope slightly to one side of the pole star, a guide star was found, guiding started, guiding gain etc adjusted and a couple of images taken before the clouds got in the way. 

Results - no doubt as seasoned astrophotographers would expect, DEC guiding just needs a bit of correcting from time to time - the gain of Lin_guider had to be brought down to stop oscillation. RA guiding takes much more frequent corrections, again with a low gain for my setup.

My aim with the mods was to see if such a low cost and basic setup could be made to guide - also at a low cost and with simple equipment/mods. On the face of things it is not too involved and I hope that it will be useful to those who don't want to jump into the expense of more mainstream equipment. It could also be a low cost learning curve into guided astrophotography for those who have already purchased a scope with EQ2 mount.

Next steps for me is to find (hopefully!) some clear skies for a chance at decent imaging. Weight hasn't been added to the mount as yet - this should improve stability although the short 650mm focal length is a help when it comes to stability and guiding errors.

Below is a 5 minute (bright) single image taken this evening with dual axis guiding (at 100 ASA due to the moon). The central star seems reasonably round, though coma affects other stars towards the edge of the image. I've also attached diagrams of the setup and another earlier 5 minute single image taken with RA only guiding.

 

 

 

IMG_0003.JPG

Setup2.jpg

DSC_0016.JPG

Single image 5 min exp.jpg

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To complete this post, below is my first attempt at imaging (Flame Nebula) with guiding provided by RA motors for both RA and DEC guiding on the EQ2 - an unusual guiding setup as the motors are not stepper motors. As long as there is no wind, stars are round (ignoring coma). With wind comes some movement, so work is needed in that direction. Need to work on image processing too :happy11:.

Flame9small.jpg

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That's a well thought out budget project, that seems to have produced excellent results.  A good low cost upgrade might be to use APT software to control the camera.

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Really excellent project.  I'm trying to do a similar job, but I'm struggling with the cost of the guidescopes.  I've decided to buy any old frac from ebay as long as it's less than a tenner.

What are your skies like? Once I go over about two minutes, my photos are all washed out by light pollution.  I'm probably going to have to use filters.  Any thoughts?

Regards

Steve.

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Hi Steve,

Yes, the guidescope can be an expensive purchase. I considered using a low cost refractor but finally decided on the Orion 50mm guidescope as, with a 162mm focal length, it is quite fast at f3.3 and so can produce a bright image for the guide camera. With my setup the guide camera is a modified Microsoft Cinema webcam, which is reasonably sensitive. The combination makes it not too difficult to find a guidestar - I simply rotate the guidescope slightly until a guide star comes into view. The Orion guidescope takes standard eyepieces, so it can also act as a visual pointing aid if the main scope does not have goto. The short 162mm focal length also helps with the wide field of view making it easier to locate a guide star as the webcam has a small sensor, which acts to limit the field of view.

Whether a guidescope with a higher f-number will work for you will depend on the sensitivity of your guide camera.

I'm luck that skies here (from my back garden) are quite dark - see the single unadjusted 10 minute 1600ISO image below. If your skies are bright try dropping the ISO whilst keeping the exposure as long as possible - that way the image will capture as much detail as possible.

I'm a beginning imager and one of my biggest surprises was how much an image improved with flats. DSS and GIMP are my processing software. Processing can greatly reduce unwanted gradients due to light pollution.

If you wish to share one of your images I would like to see it.

Hope this helps.

Bob

IMG_0014_1.jpg

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Hi Bob,

Thanks for your reply.  The info about focal lengths is interesting.  Really, I think you're saying if I don't have a sensitive camera, then go for a short focal length.  It's a good point.  Yes I use DSS and GIMP too, both have their problems.  Have you managed to get the astro-exension to GIMP installed?  If so I'd be pleased to hear how.  So far it has resisted all my attempst!!

Here is a single unprocessed picture of the Flame Nebula, the only thing I've done is to convert from raw to .png.  No match for yours:

2017-01-24_21-55-45.png

Here is a fully processed picture of the Orion Nebula, about 8 images cleaned for noise and manually stacked with GIMP:

orion_neb_stacked.jpg

The noise levels is not as bad as some, but I feel UHC filters and guiding is the way forwards.

Tell me what you think.

Regards

Steve.

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Actually, I think that's the dss stacking. Gimp doesn't produce those jitters, it's just time consuming.

Both pictures are about 45 secs to one minute.

Edited by SteveBz
clarity

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It's the f# (focal length/aperture) that determines how much light falls on the sensor, not just the focal length. The sensor size plays a big part on the final guiding field of view e.g. the final guiding field of view of my setup is actually less than my main scope due to the sensor size being small. The guidescope and guide camera act together so you can't comment on results only knowing one of them. To compare with a cheap 70/400 scope as a guidescope, that would be f5.7 and would give a final field of view of almost 1/3 of my current setup when used with a Cinema webcam. This narrower field of view together with a higher f# could make finding a suitable guide star tricky.

One other reason I went for the Orion guidescope was weight - my setup is pushing the boundaries of weight, so I tried to keep it down as much as possible.

Your image of the Flame Nebula is rather dark - it could take a much longer exposure, which would give more detail. Below is a single unaltered image of 2minutes 1600ISO with my setup. Even this image could do with a longer exposure to enhance the detail.

The M42 image seems to have a stacking issue. The image is also rather dark - perhaps DSS couldn't align it due to this, though it would be better to see a few unaltered images. M42 is very bright and should produce a good image with 30-40 second exposure. Guiding isn't required for this.

I suggest ignoring noise and filters for now - just aim for good single images and the rest will come with practice. Longer exposures look to be required. The grey background will be reduced in processing.

What exposure time and ISO were used for your images?

IMG_0003.jpg

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Forgot to mention that I hadn't heard about the astro extension to GIMP so I'll check it out. One thing about GIMP that is important is to use a v2.9.x version as this supports 16 & 32 bit images - essential for astrophotography. This allows DSS to save a 16bit TIFF file which can be opened directly by GIMP, so preserving the detail in images that very frequently needs to be stretched. The v2.8 version is only 8 bit and won't produce such good results.

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I'm torn then between getting this from China for £65, which I guess will do the job:

http://www.ebay.co.uk/itm/50mm-Guide-Scope-Finderscope-CCD-Image-Bracket-1-25-Helical-Focuser-Astronomy-/172274032837?hash=item281c5520c5:g:q-gAAOSwbYZXVjtn

And a cheap old scope off ebay or somewhere.  Maybe I should do both.  Buy the cheap scope quickly locally, try it out, and then, if I need to, go for the proper guide-scope from China. 

The nice thing is that an old frac could also be used as a grab and go.

For me, my light pollution is not SO bad, that I need monochrome cams and narrow-band filters.  I have a friend who lives near the local Cinema complex who has 974 street lights within 500 metres of his house and he can only do astrophotography with monochrome cams and Ha, OIII filters and whatever the green one is and recombine after stacking. 

Steve.

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17 minutes ago, SteveBz said:

 

OK. Got GIMP 2.9.5, quite easy to install.

 

Good! If you go for it, M42 should provide nice bright images to put through DSS and then process with GIMP v2.9.5. 

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Ok, well Monday is forecast fine, so I'm gearing up to go to a less light polluted site for the evening.  Let's see what happens.

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Very interesting Bobro, I need to get up to speed with the kit I have, then the Raspberry Pi option looks like it could be worth a go, a good bit of additional outlay though with the guidescope, Raspberry Pi etc.

Thanks for point this thread out though, good work!

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Hi there,

I am really interested in building something like this. Could you give a few more details about how you control the motors from the pi especially the relay board and the gpio outputs etc.

I have most of this equipment already so this might make for a cheap project for me.

 

Thanks

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2 hours ago, adder001 said:

I am really interested in building something like this.

Glad you have found the project interesting. Info on the setup, wiring and sample images captured with the setup can be found at http://guiding.web.fastmail.co.uk/

You could start with just the RA motor control to get things going. The RA motor needs a couple of simple mods to its control board as shown. The DEC motor is disconnected from its control board as only the motor is used. The PI GPIO pins used for RA and DEC  will depend on the PI version. Pin allocations are set up in a S/W config file before compiling the program.

Hope this is useful.

Bob

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Thanks for the info,

Is the relay board part of the economy motor drive unit or is it something else you have bought or made.

cheers

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The relay board can be bought at low cost from ebay. Just search for 'Raspberry PI relay board'. Plenty of sellers offer them. Note: a bracket is required to mount the DEC motor on the scope. If you go ahead with the project I can measure up the one I made from aluminium sheet.

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great , thanks. Does this look about right  http://www.ebay.co.uk/itm/5V-1-2-4-8-Channel-Relay-Board-Module-for-Arduino-Raspberry-Pi-ARM-AVR-DSP-PIC-/252051910091?var=550909188171&hash=item3aaf76edcb:m:mdbiogK3bG3MfWb_sjDpLvw..

I think I will use a raspberry Pi zero as they are under a fiver and have 40 Gpio pins and my existing RA motor and if successful then purchase a DEC motor.

At the moment I  thought that I would have a look at the software on my PI3 just to get familiar with it so I have downloaded the tar file for Lin Guider and I have extracted it but I cant seem to set it up. The readme file doesn't seem to give complete instructions on setup or I am missing something anyway further investigation needed.

I will post pics if I have any success.

Thanks for your help

 

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The ebay link is the correct type of relay board. I'm not sure about using a Zero - what about USB for the camera, USB for wireless dongle / ethernet port   to connect to PI? Doesn't look as though Zero has enough ports on board.

This page gives info on compiling Lin_guider  https://hhastrophoto.wordpress.com/2015/07/23/raspberry-pi-b-for-astro-guiding/

Hope you get it going!

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mmm yes I hadn't thought of that, it does only have 1 micro usb port so maybe not that. I do have an older B+ 512 pi somewhere on an old project that I no longer need that I can use. Thanks for the info on compiling Lin Guider.

 

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