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Thoughts on which imaging rigs to concentrate on


Gina

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The 1600 on the Esprit gives a FOV of 2.53° x 1.92°.  The Esprit and 460EX gives 1.79° x 1.43° FOV so 6 panes covers 3 x 1.43 = 4.29° and 2 x 1.79 = 3.58°.  That's without the substantial overlap.  4 panes with the 1600 would cover 2.53° x 2 = 5.06° by 1.92° x 2 = 3.84° which is more than enough.  2 panes gives 3.84° x 2.53° which doesn't seem enough but I'll check further.

The 2 panels of the 6 have an overlap of 10% so the image width is 3.58° less 10% = 3.22° so more than 2.53° that the 2 panes would give. ie. the 2 panes will not cover it :(  In the other direction, the overlaps add up to 20% and that taken off 5.06° = 4.05° which is more than 3.84° so inadequate in that direction as well.

So the choices if I want to cover the Cygnus Loop are 4 panel mosaic with the Esprit or full cover with a camera lens.  I think the latter wins :D

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FOV with the 105mm FL lens is 9.63° x 7.29° which would cover a field much bigger than the Cygnus Loop - could be interesting for a widefield image.  OTOH a 200mm f4 lens covers 5.07° x 3.83° including all the Cygnus Loop nicely.  I've also got a 135mm f2.5 lens with 7.79° x 5.89° FOV needing less than half the exposure needed with the 200mm f4 lens.  All these lenses are Asahi Super Takumar type and excellent.

I will have to design a mounting for a lens with bracket for stepper motor for focussing.  Could do with including the filter wheel too.  If I want to run the FW as well as focussing and mount I shall run the mount from another port on the laptop and keep the camera USB hub for focussing and FW, keeping cables short and fixed.

Edited by Gina
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Here's a photo of the 135mm camera lens, filter wheel and 1600 camera.  I think this is where I'm going next - at f2.5 a lot more light than with the Esprit even if I stop down a bit and with a much wider FOV there should be no problem using the EQ8 unguided.  The Esprit seems to give round stars with 30s exposure.  The f2.5 lens is 4 stops faster giving 4x the amount of light.  The FOV is about 7x so in theory I could go to over 3m exposure without elongated stars.  That equates to a relative exposure of 12m on the Esprit.  This is looking very promising and ties in with my intention of concentrating on widefield this season.

135mm Lens & FW 01.jpg

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I also have the 105mm f2.8 variant and it really is a super lens for both astrophotography and daytime photography. I love using camera lenses for astro (mainly NB) and find I have a lot more fun with this format. The ZWO camera looks lovely too, I reckon you'll get some awesome fields with that setup and no doubt make some amazing mosaics, nice one!

Edited by RichLD
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Just connected this rig to the laptop, pointed the camera out of the window and looking across the valley to trees out to the horizon.  It's a "goer" - lens reaches infinity focus easily (at 20m on the scale).  Here's a screenshot of TeamViewer showing the Preview image.  It's quite misty so the view at over 5 miles is not good but I have focussed on a pylon on the horizon.

Test 12.JPG

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Designing and 3D printing parts for mounting the 135mm lens rig is going well including the mounting for the stepper motor and gears for focussing.  Just hoping it all fits together well :D

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With the mounting brackets above I didn't get as much available camera rotation as I thought so I've printed new ones.  These needed my home made Titan 3D printer - the UP plus 2 couldn't manage it.  Since the Titan had black ABS in it, I used that.

135mm Lens & FW 07.jpg135mm Lens & FW 08.jpg135mm Lens & FW 09.jpg135mm Lens & FW 10.jpg

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Amazing!  The rain has stopped and the sky has cleared but there's heavy rain and thunderstorms forecast.  Anyway, I'm not risking setting up by lantern and possibly dropping expensive equipment for a possible hour or two of imaging.  Must be patient :D

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I now have the rig mounted on the EQ8 and been testing connections.  None of the underfloor USB cables seem to work with either the camera or the mount HitechAstro USB to serial adapter.  Both work fine with shorter USB cables connected directly to the laptop.  I don't know whether it's the cable length or the quality that's the problem.  The length needed is about 4m to go through the ducting.  Maybe I'll order a couple of new cables.  I'm wondering if the mount would be better run with the serial cable through the ducting rather than the USB.

I'm still running on Win7 ATM with EQMOD-Ascom, CdC, SharpCap/APT etc. Sorting out the Raspberry Pi to take over from the laptop and Win7 is progressing in parallel.  I could use a Linux laptop but the RPi seems very capable.  With RPi control and imaging I won't need underfloor USB cables as the RPi boards can be fitted directly to the imaging rig and mount with just power connections.

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No, it's just that I would like to keep things as simple as possible.  I would need to add a guide camera and lens to the current rig.  So if that isn't necessary it will save me some work.

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Gina, I am no expert, but a quick google suggests that depending on the speed of the device, 3 or 5m is the maximum. I gather you can get some sort of 'booster' to push the length further. You will know your own system best, but it might be worth considering if this would solve the problem better, as new cables of the same length might not help if you are pushing your devices to the limit of length. But, as I say, I'm no expert.

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Had the rig working on the EQ8 mount this afternoon pointing roughly east at trees on the far hill.  Just had the fold down flap/window open and not the ROR as it was showery.  Everything working except the focus motor.  I could hear it running but the output shaft wasn't turning - must be stripped gear in the gearbox.  Manual focussing worked alright.  So I need to swap the stepper motor tomorrow or when the rain stops.  Certainly seems a wide field of view.  I'll post the image next time it's working - didn't have time today - went out.

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Not raining ATM so went out and opened the east end window/flap.  Here's a screenshot from TeamViewer.  Still focussed by hand but I plan to swap stepper motors shortly and hopefully enable remote focussing.

Test 13.JPG

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After faffing about trying to get a good USB connection to the Arduino Nano in the control box I got the focus control working as far as the LEDs in the driver board but the motor is dead - no output and not a sound from it.  So I've found another dud motor :(  I think I've got a few more of them to try.  Next time I'll try the motor loose before mounting it on the rig as one of the screws is difficult to get at.  Why does a simply job always turn out to be more trouble than expected? :eek:

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Wasn't the motor - it was a silly!!  I didn't have the warm room PSU switched on and the backup battery went flat :o  This meant there was no power to the motor.  I now have remote focussing working fine.  It's a little bit coarse though and one step is enough to go out of focus.  The backlash in the motor gearbox is about 3 or 4 steps.  So I shall design and print a smaller motor pinion.  I'll try that first, otherwise I'll need a need a new lens bracket and gear quadrant.  Not a great problem :D

Edited by Gina
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Just reducing the pinion size was not practical so I've redesigned both the pinion and segment gear with smaller teeth - mod 2 rather than mod 1.5.  Here's a screenshot of SketchUp.

Focus Segment Gear & Motor Pinion 01.JPG

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Changed the motor pinion to give a higher gear ratio.  Previous gears were 90t and 9t giving 10:1 while the new ones are 120t and 6t giving 20:1.

Motor pinion.JPG

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