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Triple NB imaging rig with remote camera rotation using a turret system.


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Posted (edited)

Shortly I will have a third cooled astro camera and planning a triple imaging rig.  Each camera will be fitted with a NB filter, Ha, OIII and SII.  These are Astrodon 3nm NB filters.  The rig is designed for widefield and uses vintage SLR film camera lenses.  I have a range of these from 28mm to 200mm in sets of 3.

 

This shows an earlier design with Atik 146EX cameras.  The new version will use a ZWO ASI 294MM-PRO and 2 ASI 1600MM-Cool cameras.

post-13131-0-36187000-1443951646_thumb.j

Edited by Gina
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The cameras all have a 4/3" size sensor and the 18mm FL lenses give a field of view of 36.2° x 27.4° while the 200mm FL covers 5.1° x 3.8°.  The lenses are :-

  • 28mm f3.5
  • 55mm f1.8
  • 105mm f2.8
  • 135mm f2.5
  • 200mm f4

The longer focal length will need guiding and this will be provided by a Skywatcher 9x50 finder and ASI 120mm Mini camera.  This guide system will be fitted inside a 60mm diameter aluminium tube forms the the main axle of the turret.

 

Since the guider wants to stay in a fixed orientation compared with the RS and Dec axes, the tube will not rotate itself.  Instead the turret will rotate on the tube.  Not yet sure about the bearings but maybe plain bearings would suffice.  The turret won't be rotated much or often.  I envisage using worm drive on the rim of the turret to rotate it.

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  • 3 weeks later...
Posted (edited)

Thank you Mark.

 

WOW!!  Lot of catching up needed here.  Mind you, a "blow-by-blow" account is not really needed.

 

Current state is that I have a turret made taking 3 ZWO cooled cameras and have recently added the third, an ASI 294MM-Pro.  I have tested terrestrial imaging with the new camera but not the cooling as yet.  New camera is running off an RPi 4B via USB3.  The other ASI 1600MM-Cool cameras are using RPi 3B+ and USB2.  The difference in download speed is amazing!  I'm using the relatively new Astroberry Server as the RPi 4B firmware.

 

 

Edited by Gina
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Before the aluminium tube arrived I went for this design.  It uses a 10mm stainless steel rod for the axle.  A drum was designed and printed to act as an adapter between the axle and the turret plates which have 60mm diameter holes.  A separate gear ring was used to rotate the turret so that parts could be redesigned without printing both parts as one unit.  (These 10" diameter parts take a long time to print.)

1425438581_Screenshotfrom2021-06-0322-44-51.thumb.png.7305a9403192d867d8798529363e4a3d.png

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This model shows the design of the turret plates (sides) to hold the cameras and rotate on the central axle (a 60mm OD aluminium tube).1919162216_Screenshotfrom2021-06-0310-21-44.thumb.png.cf69ed928ff06abb26a9ee3caea7bf5f.png

 

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Posted (edited)

I was going to use worm drive for the rotation of the turret but when it came to testing, there was a problem with tolerances with the mesh of the teeth.  These are curved and the mesh has to be right in two directions. 

 

Consequently, I decided to go for a much more tolerant spur gear arrangement.  With the large drive gear and a small pinion on the shaft of a NEMA17 motor there is still sufficient reduction.  18:1 ratio is readily achieved giving 20° turret rotation for one turn of the motor shaft.  With 1.8° steps this gives 10 steps per degree of rotation.

782426428_Screenshotfrom2021-06-0818-14-00.thumb.png.98c68931a09e163b5628c212acd778c6.png

 

Here are a couple of screenshots of the gears in the slicer (Simplicity 3D).

1247218736_Screenshotfrom2021-06-0817-53-52.thumb.png.43e8472581b7eef3393cbb0ec234ca61.png2059799249_Screenshotfrom2021-06-0817-55-37.png.4650a3015236b693f23b41000b73c802.png

 

Meshing in CAD screenshot.

1432048796_Screenshotfrom2021-06-0821-24-42.png.a7e445f335fc9c427215f30aa026ebb5.png

Edited by Gina
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This shows the remote focus worm drive.  It uses the little 28BYJ-48 stepper motor with built-in gearbox.  The worm gear is clamped onto the lens focus sleeve and the motor bracket onto a fixed part of the lens.  A screw in a slotted hole provides adjustment of the mesh of the teeth (pic 3).

Focuser01.thumb.jpg.ac9f52aacaf2424bfcbb2f984c7ac616.jpg

 

Focuser02.thumb.jpg.d35a32004569fa7992c4e2923da84bd9.jpg

 

Focuser03.thumb.jpg.7534e8d1fb42d5fe64ce236133603557.jpg

 

Focuser04.thumb.jpg.613353caf550eac3c8ab795102267f09.jpg

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This shows the selection of lenses I shall use with this imaging rig.

  1. 28mm f3.5
  2. 55mm f1.8
  3. 105mm f2.8
  4. 135mm f2.5
  5. 200mm f4

Lenses1.thumb.jpg.1b36f0351028fc261098d23719f1d157.jpg

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Turret construction.  Two plates make the sides of the turret.  These have rebated holes to hold the camera casings and 3 spacers.  This shows the version with adapter for the 10mm SS axle.

Turret01.thumb.jpg.d1c9892d042a079fa5346f7641d2d3da.jpg

Turret02.thumb.jpg.b1c9326b042e4783666ae0a9841d3eb1.jpg

TurretRig01.thumb.jpg.6d5263e257d1dcfb93c92ecc59f6f492.jpg

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Have 200mm lenses on and hoping for a rough test run tonight.  This is a "bodge-up" to have it ready for imaging.  More work to do.  eg. focus drives.image.thumb.png.d06cd056cf02e936a1a02bd3c03378a8.png

 

image.thumb.png.1413ec8dfde3a09df175314f14fbeec9.png

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The imaging run showed that to use the 200mm lenses guiding is needed.  Short exposures gave nice round stars but there wasn't sufficient signal in the stars to star align except with the more sensitive 294 sensor  or binned.  The subs taken with ASI 1600MM-C in Ha were no good.

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I tried to implement the 60mm aluminium tube axle to allow guiding but I failed to get a good enough fit onto the tube and there was slop that would would probably make guiding useless.  As a result I have embarked on a different approach abandoning the fixed guider and going for a simple guider attached to the front turret plate.  I have still gone for ann aluminium tube as a conduit for the cables but a smaller one and rotating with the turret.  This makes for a much more accurate setup.

 

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Posted (edited)

This shows the new design.  The axle is a 1" (25.4mm) OD aluminium tube.

207596270_Screenshotfrom2021-06-2517-39-24.png.5cc475261f84cd7237bb4cadab9324c4.png

 

Another view without the rotation drive but showing the new supports.  With the tube rotating, the errors caused by slack in the bearings is much reduced due to the far greater spacing.

1569381008_Screenshotfrom2021-06-2517-08-25.thumb.png.b2d19df5b222ad144275d74f10cde271.png

 

The extra holes in the turret plates allow cables from the cameras to be fed through and into the end of the axle tube, then through the tube and out the right-hand end as shown here and to the control box.

 

Edited by Gina
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