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| Night Sky Photography - Page 1 | |
| An Equatorial Mount: My lucky day! | Rate Topic |
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| Posted: Wed Mar 6th, 2019 14:03 |
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1st Post |
Robert
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One of the inconveniences of dark sky photography is the Earth keeps moving, nothing new I know but still a nuisance when trying to take a still picture of a particular part of the sky. I mentioned this to a friend because I was considering utilising an old mixer worm drive gearbox to create my own rotating mount with which to track the stars. My friend called after a few days and asked if I was interested in a motor which moved 15º every hour, the penny didn't drop but I'm always interested in anything mechanical so I agreed. Cutting long story short, I now have my own somewhat old, equatorial mount. The price? 50 used paving bricks. At first the mount wouldn't work, the motor drive lead was broken and the control unit wouldn't power up. I figured out the pinouts for the six core cable myself, little or no info on-line. The mount is a Vixen Optics Photo Guider, apparently good for a 15 Lb payload, provided it's counterbalanced. What I didn't realise at first was the motor is a stepper motor, I was expecting a synchronised DC motor regulated by a timer circuit. These devices sell for between £500 and £10,000, depending on size and power. Eventually I discovered the reason why the controller wouldn't work, somebody had reversed the polarity of the voltage regulator inside the controller.  I now have it running beside me as I type. I started it at 10:00pm last night, I am interested what it will say at 10:00pm tonight, it has clock calibrations on the head which you use to help with tracking. It has a polar scope which has to be aligned with Polaris with an offset because as well as spinning, we are drifting in space compared with Polaris. I need to create a red LED illuminator to illuminate the polar scope, the calibration markings are clearly visible in daylight but not in the dark. I am considering a fibre optic bonded with a small red LED in shrink sleeving, with a small button cell battery and switch, it's only needed when setting up the tripod at the beginning or after making adjustments to the setup. I am hoping it will handle my 300mm f/2.8 lens on the D800. As soon as I get a clear sky I will try it out. This was the battery pack:  This is the mount, with the Nikkor 300mm f/2.8 and D800 mounted.  I am investigating various forms of power supply, the controller will handle from about 6Volts to 30Volts but the higher the voltage the more heat it dissipates, so I am working on a maximum of 12 nominal. I do have ideas for using EN-EL4 D3 batteries which are nominal 10.8Volt, 2600mAh or perhaps some racing pack batteries. It's been a very interesting few days. I need to make a new 'wedge' mount to adjust the elevation, the one which was fitted wasn't fit for purpose, too small and seized up. I intend to craft one from solid aluminium bar, with a fine tune adjustment for Polaris alignment. I also need to create a counterbalance bar so I can slide a weight into the correct position to counter the weight of the camera and lens.
____________________ Robert. |
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| Posted: Wed Mar 6th, 2019 14:36 |
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2nd Post |
chrisbet
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That's my sort of challenge - well done. I love rescuing equipment - my wife hates me cos I keep repairing the washing machine instead of buying a new one! I fitted an MGA with a red top racing battery - made up a special cage to mount it in the engine bay ( they usually live in inaccessable cages by the rear axle! I was very impressed with its power for such a small battery - you could hold it in one hand easily!
____________________ If it is broken it was probably me .... |
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| Posted: Wed Mar 6th, 2019 15:04 |
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3rd Post |
jk
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Nice mount. The motor will drive well off the powerpack that you made for use for your Nichai UV light. Double utility.   You can use an LED off that powerpack as well but you will need a dropper circuit to reduce to 3v for the LED. You might be able to use a direct feed off an additional Lion battery (3.7v) but that seems huge overkill for that. There are some nice torches on ebay. https://www.ebay.co.uk/itm/Rechargeable-USB-Mini-Ultra-Bright-LED-Torch-With-Beam-Focusing-Flashlight-UK/153232085887?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649 I got one of these recently. Great little torch. Needs one of the Lion batteries that we use for D3 replacement battery.
____________________ Still learning after all these years! https://nikondslr.uk/gallery_view.php?user=2&folderid=none |
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| Posted: Wed Mar 6th, 2019 15:28 |
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4th Post |
Robert
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Have now set it up in back bedroom, abandoned the 24Hr test because I had moved it several times and even switched it off, so hardly a valid test. I have the D800 clicking away every 15 minutes taking a photo of a clock, the mount is zero'd in on the hub of the second hand. I intend to leave it running for 24Hrs to see how it performs with weight on the arms, I have a crude counterbalance to offset the camera and lens (Nikkor 105mm f/2.5) intentionally not perfectly balanced to see what happens. The UV power pack uses 18650 cells, the output for the LED is current regulated. I could modify it to provide a full current output via an XLR socket or similar. I need to keep weight down because I intend to use this kit on mountain tops. The camera, lens and tripod with the mount will be heavy enough without adding heavy lead acid batteries. I don't expect sessions longer than a couple of hours, the current draw for the motor is 300mA so well less then 1Ah for two hours use (I think!). I could do with a right angle viewfinder for the polar scope. I'm told the Nikon DR-3 (about £25 on eBay? a little more for DR-4 ) works with this setup and is easy enough to fit. A modified Nikon DK-22 can provide the threads for the adapter that the DR-3 screws into.
____________________ Robert. |
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| Posted: Wed Mar 6th, 2019 15:52 |
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5th Post |
Robert
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Thanks Chris and JK for commenting. Nothing I love more than making something work, or creating something from nothing. I just spent the last week making a block cutting saw for cutting paving blocks. It works perfectly and has reduced the probability of my cutting off my toes! I also get better cuts. I visited a friend the other day and he is resurrecting a 1935 Triumph 250 motorbike, he is fitting a 500cc JAP speedway racing engine into it, making a wonderful job. When it\'s finished he will have something really special. He intends to speed hillclimb it. Not outstanding iPhone images in mixed lighting...  
____________________ Robert. |
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| Posted: Wed Mar 6th, 2019 17:03 |
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6th Post |
jk
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Robert wrote:
I thought you were using 18650 batteries. Four of those in series will power the motor. There are Seagull magnifying right angled eyepieces that also work on D3. I have one in Spain. Great for macro work. https://www.ebay.co.uk/itm/Seagull-1-2X-Right-Angle-View-Finder/323719897956?hash=item4b5f35a364:g:81AAAOSwo8NceVDr
____________________ Still learning after all these years! https://nikondslr.uk/gallery_view.php?user=2&folderid=none |
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| Posted: Wed Mar 6th, 2019 17:36 |
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7th Post |
Robert
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jk wrote:I thought you were using 18650 batteries. Four of those in series will power the motor. Have just looked, it consists of two pairs of 18650 batteries, the way I have configured it it's entirely possible to add another socket for the Equatorial mount, which can be switched from the current limited UV LED outlet to a separate outlet which could be unrestricted. I will check out the link you have given me. I could do with one for close up work with the D800 anyway. It can be hard to get one's head in the position needed when the camera is on a stand. Not a great fan of live view if I can avoid it.
____________________ Robert. |
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| Posted: Fri Mar 8th, 2019 18:03 |
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8th Post |
Robert
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Well, the mount is up and running. I ran the first test revolving with a clock for 24 Hrs, it was within half a second in time, accurate on rotation over 24 hrs. I took it out after the test finished at midnight Thursday, night I got up there about ten to one, set the Vixen mount up and tried to zero it on Polaris. Initially the lenses of the finder scope misted up and internally as well. Eventually I started to get somewhere when it all went dim. I couldn't understand it the stars were so dim, I thought the finder scope was defective, I looked up at the sky and realised a herd of clouds had wandered in and obscured the stars so I went and had a sandwich and a coffee in the hope it would clear. I was almost ready to pull sticks and head home for bed when suddenly the clouds melted and I was back to a lovely clear sky. The gear had cooled nicely and after a break, everything kind of fell into place. I made a few trial exposures, set the Vixen mount motor running and left the D800 clicking away with the 70-300 VR lens, AF and VR turned off of course. I went with 25second exposures, f/5.6 and ISO3,200, intervalometer set to take an exposure every 40 seconds. I should have left it at 30 seconds but it was OK. The 25 second exposures produced an almost round star with very little elongation, I haven't got my head around the slightly erratic movements but it's WAY better than anything I have seen before. Room for improvement of gear and technique but that's to be expected. I never handled an equatorial mount before, I need to get used to setting it up to align with Polaris. I will post some images tomorrow, too tired right now. Quite amazing, really pleased, it's better than I hoped with a ton of scope to improve.
____________________ Robert. |
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| Posted: Sat Mar 9th, 2019 03:04 |
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9th Post |
jk
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Sounds like you have found a treasure. Look forward to seeing some of your images when you get up and running. I never like the streaky stars effect that comes with long exposures made without an equatorial mount. At least I now know a man who can work one of these things. Will be interested to follow the story and learn more.
____________________ Still learning after all these years! https://nikondslr.uk/gallery_view.php?user=2&folderid=none |
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| Posted: Sat Mar 9th, 2019 03:09 |
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10th Post |
jk
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I am interested in your exposure time. From some of my reading it seems that they recommend 20-25sec maximum to eliminate movement abberations. I guess that drives you towards a 2 frames per minute rate. Limitations are (I guess): How fast can the camera process in between frames? How much does the camera heat up working continuously? How long does your battery last?
____________________ Still learning after all these years! https://nikondslr.uk/gallery_view.php?user=2&folderid=none |
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