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Blog Comments posted by Gina
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Something I've noticed in the diagram above - comparing the bottom two rows, the OAG has to be 16.5mm unlike the one's I have which are 21mm and won't give the right back focus. I wonder if ZWO produce ultra slim ones
A bit later... Yess!! They do :- ZWO Off Axis Guider (OAG) Yippee, just what I might want for the Esprit rig if not for the widefield
I have to say I'm very impressed with ZWO They seem to have everything sorted
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ZWO have added several more adapters to what's in the box since this listing This includes what would appear to be exactly right for the back focus on focal reducers & field flatterers for telescopes (with the ZWO EFW) so I'll add all the bits to my Esprit FF and carefully measure the spacing. Plus, apart from the filter adapter ring a spacer that would appear to give the right spacing for camera lenses though this isn't shown in the diagram. Item 1 in the diagram would be replaced by extension ring and camera lens (with or without "Russian" adapter). Also, new since I bought my last one is a very nice soft carrying bag for the camera. A nice addition though I doubt I'll use it.
This is the an upgrade from the version I bought before which had a tendency for the front to come loose.
I've corrected an error in the diagram. (Spot the slightly different font )
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For some reason I decided to look at what's included with the ASI1600MM-Cool - there must have been something in the back of my mind from when I bought my first ASI1600MM-Cool camera just over a year ago.
QuoteINCLUDED IN THE BOX
- ASI1600MM Camera
- Soft Padded Case
- T2-1.25" Nosepiece Adapter
- 1.25" Cap
- 2-metre USB 3.0 Cable
- USB 2.0 Short Cable x2
- T2-1.25" Filter adapter (3mm Thickness)
- T2 Extender 18.5mm
- Desiccant Tablets
- Driver CD
I've highlighted the relevant item in green Problem solved!! I can use the mini filter wheel with one camera and the adapter ring for a single filter in the other.
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I think I have a 1.25" filter holder amongst my astro stuff. The only one on FLO seems to be Baader and only for the bigger filters (50mm etc.) - when you add up the parts needed it comes to over £150 - it would make more sense to buy a filter wheel. Otherwise it looks like a 3D printed jobby
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Another thought was to buy another ZWO EFWmini but I can't think what for on second thoughts...
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Regarding mono images, if you want to just collect twice as much Ha data on the same object you will need two Ha filters and Astrodon 3nm Ha filters are expensive. 5nm filters are cheaper though. I have both though I don't know how well mixing data from both would work. Have to say, I do quite like Ha mono images - they seem to provide beautifully sharp and detailed images. Adding in OIII for a colour image makes for a prettier result but seems to reduce the sharpness somehow. Or at least that's how it looks to me. A third wavelength makes for a better result and I don't mean a synthetic green. Although some seem to get reasonable results, I haven't had much luck with that.
Another thought I had was to have a 3nm filter on one and 5nm on the other providing Ha data and NII by subtraction. I have tried the subtraction process with two separate batches of data and it works. Using data sets taken at the same time on the same object should produce better results. This data would be collected after a decent run with Ha 3nm and OIII 3nm filters. I could arrange for this if I were to use my ZWO EFWmini on one of the cameras. This could contain 3nm OIII and 5nm Ha filters and save manually changing filters.
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Second ASI1600MM-Cool is due to arrive Monday. There are no clear might skies in the 5 day forecast so I'm in no hurry for it.
To-do list :-
- Sort out adapters and extension tubes plus filter mountings.
- Mounting bracket to attach rig to EQ8 mount.
- Lens focus ring to stepper motor gears.
- Brackets for stepper motors.
- Electronics box with RPi3 and stripboard with driver modules and buck converter for 5.1v RPi power supply.
- Edit INDI software drivers for focusers and second camera.
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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
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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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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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.
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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.
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Tuning motor bracket.
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This results from my experience with years of NB imaging with Ha, OIII and SII filters and finding that the amount of SII around is so small as to be very difficult to capture any significant amount. NII might be a better third waveband but I can't afford another expensive filter ATM. I have tried to develop triple imaging rigs in the past without much success. Otherwise I have used a single rig with filter wheel.
With the lack of clear skies in the UK it does make sense to grab as much data during times without cloud as possible. These CMOS cameras permit many short exposures as opposed to fewer long ones allowing use of short gaps in the clouds. The use of camera lenses results in larger focal ratios and the ability to capture more data in a given time. Achromatic optics are no problem with NB imaging as the bandwidth is so small.
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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.
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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
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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.
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I have copied the relevant posts in my tutorial thread on Setting up a Raspberry Pi for Astro Imaging and Hardware Control into a blog which will remain readily available rather than sinking into the dust of old threads.
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END OF TUTORIAL (At least for now)
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PART 9 - Hardware for remote focussing.
This is the RPi plus HAT and other components for the scope imaging rig. The focus make use of the Astroberry Focuser driver to control a Pololu A4988 stepper driver module which in turn drives a modified 28BYJ-48 little stepper motor with built-in gearbox.
Here are some photos showing the electronics and the hardware with the gearing that drives the telescope focuser from the stepper motor. The gears and motor bracket were 3D printed in ABS plastic but for those who don't have a 3D printer, the gears can be replaced with a timing belt and pulleys and the motor bracket with bent up aluminium sheet.
The power input is filtered from interference with electrolytic and ceramic capacitors. Fuses supply the electronics and the camera. The 13.8v power input is dropped to 5.1v for the RPi with a buck converter - attached to the HAT. Provision was also made for a dew heater switch using a power MOSFET. This can be seen near the middle of the HAT between stepper driver and buck converter.
This shows the Astroberry Focuser connections for the stepper driver.
And this shows the Pololu A4988 stepper driver.
The first photo above shows the connections on the HAT. That should show how the connections are made but if anyone wants more I'll produce a wiring diagram. M0 and M1 in the Astroberry diagram correspond to MS1 and MS2 of the A4988 PCB.EDIT :- One thing I've noticed that may not be clear. The RESET input on the A4988 needs connecting to logic "1" ie. +3.3v (Note voltage). The link on the HAT is partly obscured by the blue SLEEP wire in the photo.
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Below is the modification of the 28BYJ-48 5v stepper motor to enable its use with a bipolar stepper driver such e Pololu A4988 (as can be seen on the HAT above).
On 28/08/2016 at 15:56, Gina said:This mini-project is as a result of the focussing on my lens + FW + ASI1600MM-Cool widefield imaging rig being too coarse with 28BYJ-48 stepper motor and usual driver board.
The ubiquitous little 28BYJ-48 stepper motor is connected internally as a unipolar stepper motor with the centre tap on the windings connected together. This prevents it from being used as it is with bipolar motor drivers such as the A4988 which provide micro-stepping. These drivers need the two windings to be separate as it uses them in an H bridge. However, there is a relatively simple modification that can be applied to the 28BYJ-48 to break the link between windings for anyone capable of handling small things and pliers or wire cutters and a craft knife.
The motor is held together by 4 tiny lugs on the casing which are bent inwards to secure the output shaft plate. Using strong small pliers or wire cutters these little lugs can be prized outwards to release the end plate. Then the innards of the motor can be extracted carefully from the round casing complete with wires and blue plastic piece. Sliding the plastic bit up the wires reveals the coil connections as shown below. Next job is to cut the track on the PCB that joins the two windings and cut off the red wire, which is no longer used. Finally the motor can be reassembled. For use as a bipolar motor the coils are yellow-blue and orange-pink.
One further point to note... Each half winding is rated at either 5v or 12v as printed on the back of the motor so when the whole of each winding is used this doubles the voltage rating. Also, the A4988 or similar has a current setting and this is used to control the power to the stepper motor, so the supply voltage can be more than twice the voltage printed on the case. Thus a 5v motor can be run on 12v or even 13.8v as often used in observatories and provided by a nominally 12v car or pleasure battery.
With this modification and A4988 stepper motor controller with micro-stepping, finer control can be provided from a 28BYJ-48 stepper motor used in a remote focussing system.
Here are some photos :-
- Coils and connections
- Link severed
- Other parts of the motor
- Plastic part pushed back into position and assembly put back in case
- Rotor replaced
- Gearbox replaced but not yet aligned - care must be taken to engage the teeth of the rotor pinion with the first gear in the train.
Finally, here's the circuit diagram for the dew heater.
That completes the hardware description.Hopefully the above will enable anyone to build a similar remote focuser but I'll be happy to answer any questions.
END OF PART 9
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Widefield Narrowband Dual Imaging Rig
in Astro Projects
A blog by Gina in General
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Here is a photo of the two cameras, one with EFWmini and the other with single filter in filter adapter inside the 11mm F-F gender changer extension tube with a pair of 55mm f1.8 Asahi Pentax Super Takumar prime lenses.