Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
05-19-2020, 01:21 PM   #1
Loyal Site Supporter
Loyal Site Supporter




Join Date: Jun 2009
Location: Tumbleweed, Arizona
Photos: Gallery | Albums
Posts: 5,503
AstroTracing & High Voltage Transmission Lines

A friend and I are thinking about going out this next weekend to shoot the Milky Way (we had probably the best shoot possible last weekend up in Sedona at Cathedral Rock). The particular location we were considering is an old Windmill and water tanks off the highway - in the middle of a large grazing range (Bureau of Land Management (BLM) property). The one drawback is that, there are high power lines running about 35 feet away from where we would need to shoot (about 70 feet away from the windmill/tanks). We can calibrate any distance away, and then walk over to the shooting location, but does anyone have any experience in terms of actually shooting (maintaining calibration with the electronic compass working [K1 & K70 with O-GPS1]) in near proximity (35 feet) to high power transmission lines. The lines appear to probably a full set of 230 KV lines out of Parker Dam to Phoenix.
___________________________
I went back to Google Earth and measured again. We would be almost directly under the lines. See the image below, red X marks the spot. In the second image, you can see the windmill in the center with the transmission towers on both the left and right sides of the frame.



Attached Images
   

Last edited by interested_observer; 05-19-2020 at 01:46 PM.
05-19-2020, 01:58 PM - 1 Like   #2
Loyal Site Supporter
Loyal Site Supporter




Join Date: May 2007
Location: Flagstaff, Arizona
Posts: 662
Flowing electrical currents generate magnetic fields - that's a given fact of physics! So, those fields could affect your initial set up based on the magnetic compass. It might be worth experimenting at home with an astrotracer alignment in one place and then moving your camera a few hundred feet away to see how it works (i.e. how well it tracks). As long as you keep the camera orientation with respect to the sky as fixed as possible while you move, this ought to work. A displacement of position on the ground of about 30 meters (100 feet) corresponds to a change of 1 arcsecond in the apparent position of an object in the sky. The effect on tracking motion is second order and would be much less in terms of accumulated pointing error during an exposure.

If you can reconnoiter during the day, try using a regular compass to see what, if any, effects the power lines cause. Measure the magnetic azimuth to some distant object when you are well away from the power lines, and then move under them and repeat the magnetic azimuth determination.

The lines should not, however, have much, if any, effect on GPS signals. The only possibility might be what are called multi-path effects (reflections of the GPS signals) from either the lines or, more likely, the support towers. I would expect these effects to be pretty minimal at, say, 100 feet away. Again, you could do some experiemnts - determine your GPS position (using the camera, or your phone, or ...) both close and well separated from the power lines. The only differences should correspond to the actual difference in position. At the same level as noted above - moving ~30 meters north should increase your latitude by one second of arc.
05-19-2020, 02:03 PM - 3 Likes   #3
Pentaxian
photoptimist's Avatar

Join Date: Jul 2016
Photos: Albums
Posts: 4,373
Both the in-body and O-GPS1 module absolutely must have a stable, accurate compass reading. That's typically achieved through a good calibration and a stable magnetic environment at the time you hit the shutter button. It's the only way for the camera to know which direction the lens it pointing so the camera knows which direction the stars are turning.

My only tangential experience with power lines is when I looked at the electronic compass of the K-1 while riding the TGV train in France at 180 mph. The reading was jumping around like a caffeinated chihuahua on a hot griddle. Admittedly, I was only 15 ft or so below the catenaries powering the train but it does suggest that powerlines don't play nice with compasses.

So if your vantage point has a crazy, fluctuating magnetic signature, it's doubtful that astrotracer will work, unless...... If you can figure out the exact compass direction you'll be pointing and use a small permanent magnet stuck to the camera to fool the compass into putting out the right reading, it just might work.

Good luck, it sounds like a great trip!
05-19-2020, 05:10 PM   #4
Loyal Site Supporter
Loyal Site Supporter




Join Date: Jun 2009
Location: Tumbleweed, Arizona
Photos: Gallery | Albums
Posts: 5,503
Original Poster
QuoteOriginally posted by AstroDave Quote
Flowing electrical currents generate magnetic fields - that's a given fact of physics! ......<snip>

The lines should not, however, have much, if any, effect on GPS signals. The only possibility might be what are called multi-path effects (reflections of the GPS signals) from either the lines or, more likely, the support towers. I would expect these effects to be pretty minimal at, say, 100 feet away. Again, you could do some experiemnts - determine your GPS position (using the camera, or your phone, or ...) both close and well separated from the power lines. The only differences should correspond to the actual difference in position. At the same level as noted above - moving ~30 meters north should increase your latitude by one second of arc.
My physics classes were 50 years ago - long in the tooth and getting greyer. GPS multi-pathing should not be a problem. The towers are about a mile apart, and it takes large flat faced structures to get significant signal reflections. I was one of the original GPS engineers back in the mid 70's, and have done a fair amount of GPS since.
QuoteOriginally posted by photoptimist Quote
Both the in-body and O-GPS1 module absolutely must have a stable, accurate compass reading. That's typically achieved through a good calibration and a stable magnetic environment at the time you hit the shutter button. It's the only way for the camera to know which direction the lens it pointing so the camera knows which direction the stars are turning.

My only tangential experience with power lines is when I looked at the electronic compass of the K-1 while riding the TGV train in France at 180 mph. The reading was jumping around like a caffeinated chihuahua on a hot griddle. Admittedly, I was only 15 ft or so below the catenaries powering the train but it does suggest that powerlines don't play nice with compasses.

So if your vantage point has a crazy, fluctuating magnetic signature, it's doubtful that astrotracer will work, unless...... If you can figure out the exact compass direction you'll be pointing and use a small permanent magnet stuck to the camera to fool the compass into putting out the right reading, it just might work.

Good luck, it sounds like a great trip!
It's really about a half an hour up the road. We saw it last weekend on the road trip up to Sedona to shoot. It looks like there really are two problems - both electrical field and the magnetic field. If there are problems, we can just shoot the old fashioned way with a single frame rather than tracking. Also, my friend has an equatorial tracker, that we can use also. Personally, I just like the no hassle approach with the astro calibration.

QuoteQuote:
The magnetic field from a wire decreases with distance from the wire. Instead of the field being proportional to the inverse square of the distance, as is the electric field from a point charge, the magnetic field is inversely proportional to the distance from the wire.
Thanks!!!!

05-19-2020, 06:57 PM - 1 Like   #5
Site Supporter
Site Supporter
MossyRocks's Avatar

Join Date: Nov 2017
Location: Minnesota
Photos: Gallery | Albums
Posts: 1,503
The problem won't be with the GPS getting an accurate enough fix. It could likely be off by couple miles north or south and it would still be close enough for astrotracer (east west doesn't matter since it isn't a goto). Since they are big high voltage lines you likely will be dealing with detectable magnetic fields that will be flipping back and forth 60 times a second. You are correct that they are 230KV lines and it runs between substations Carefree and Prescott (you can find it on openstreetmap). Given that it would appear to be the main line feeding that area it probably has a pretty good amperage running through it so again likely generating a detectable magnetic field that will cause astro tracer problems. Also be careful out there and you may expect a visit by someone from APS since you will be hanging around some regulated equipment in the middle of the night.

I've accidentally setup directly above buried power lines (distribution ones not big transmission ones) and then not been able to get a good calibration for astrotracer so I wouldn't be expecting much in your chosen spot. However you said you are going for milky way shots so I assume you are going wide. In that case astrotracer may be more of an albatross around your neck since it would likely cause trailing in the corners as it tracks. Instead use the rule of 200 for your shot length so 200/(focal length) to get your shot length in seconds. Then take a pile of shots of that length at some larger ISO (3200 or 6400) and then stack the images in a program like sequator to drive the noise down. It will even make your life easy and can stack and blend the foreground in. Since you are out shooting a pile of shots I also suggest shooting some dark frames (lens cap on, view finder cover on, same ISO and shutter speed as the frames that have real images) at the end. Here you will want to take probably 20 of these as well. Load those into sequator as well and tell it they are dark frames and it will combine them and remove a fair amount of the systematic error from each shot before stacking them. Since you will be shooting on the wide end of things you will also want to use the complex reduce distortion effects which should help a lot. I bring this up because all those canon, nikon, and sony users don't have astrotracer and they manage to take milky way shots.

Here is the sequator manual, it is a free download and for someone starting out with astro it offers a real easy point of entry into stacking.
05-19-2020, 07:00 PM   #6
Site Supporter
Site Supporter




Join Date: Aug 2010
Posts: 502
QuoteOriginally posted by photoptimist Quote
The reading was jumping around like a caffeinated chihuahua on a hot griddle.
Haha, thanks for the morning chuckle!
05-19-2020, 07:10 PM - 1 Like   #7
Pentaxian




Join Date: Jun 2008
Location: Idaho
Photos: Gallery
Posts: 1,002
Actually, you might have more to worry about from the steel towers than from the power lines. The current is alternating current which averages out its effect on compass readings (DC might be another matter). Also high voltage doesn't mean high magnetic field, which depends on the current rather than the voltage. Although these lines might be carrying fairly high currents, the lines are fairly high (distant, you said 70 feet?) and magnetic fields weaken quickly with distance, and again, these are alternating current fields which tend to average to zero.

The best test might be to find some equivalent lines nearby and experiment with the camera right underneath them and see if it affects tracking - doubt it will have much effect, but stay away from the metal towers which could harbor some constant polarity magnetic field (think bar magnet) and cause problems.

Good shooting.
05-19-2020, 09:24 PM - 1 Like   #8
Loyal Site Supporter
Loyal Site Supporter




Join Date: May 2007
Location: Flagstaff, Arizona
Posts: 662
QuoteOriginally posted by interested_observer Quote
The towers are about a mile apart, and it takes large flat faced structures to get significant signal reflections. I was one of the original GPS engineers back in the mid 70's, and have done a fair amount of GPS since.
OK - you know how multi-path works, etc! I supported the NASA geodynamics program back in the 80 and 90s as a contractor for Goddard Space Flight Center. We did VLBI, but got to know GPS capabilities and foibles as well.

Next time you are headed for Sedona, come on up north a bit further (Flagstaff) and we can get together (when closer than 6 feet is legit!). Send me a PM.

05-20-2020, 01:10 AM   #9
Loyal Site Supporter
Loyal Site Supporter




Join Date: Jun 2009
Location: Tumbleweed, Arizona
Photos: Gallery | Albums
Posts: 5,503
Original Poster
QuoteOriginally posted by MossyRocks Quote
The problem won't be with the GPS getting an accurate enough fix. It could likely be off by couple miles north or south and it would still be close enough for astrotracer (east west doesn't matter since it isn't a goto). Since they are big high voltage lines you likely will be dealing with detectable magnetic fields that will be flipping back and forth 60 times a second. You are correct that they are 230KV lines and it runs between substations Carefree and Prescott (you can find it on openstreetmap). Given that it would appear to be the main line feeding that area it probably has a pretty good amperage running through it so again likely generating a detectable magnetic field that will cause astro tracer problems. Also be careful out there and you may expect a visit by someone from APS since you will be hanging around some regulated equipment in the middle of the night.

I've accidentally setup directly above buried power lines (distribution ones not big transmission ones) and then not been able to get a good calibration for astrotracer so I wouldn't be expecting much in your chosen spot. However you said you are going for milky way shots so I assume you are going wide. In that case astrotracer may be more of an albatross around your neck since it would likely cause trailing in the corners as it tracks. Instead use the rule of 200 for your shot length so 200/(focal length) to get your shot length in seconds. Then take a pile of shots of that length at some larger ISO (3200 or 6400) and then stack the images in a program like sequator to drive the noise down. It will even make your life easy and can stack and blend the foreground in. Since you are out shooting a pile of shots I also suggest shooting some dark frames (lens cap on, view finder cover on, same ISO and shutter speed as the frames that have real images) at the end. Here you will want to take probably 20 of these as well. Load those into sequator as well and tell it they are dark frames and it will combine them and remove a fair amount of the systematic error from each shot before stacking them. Since you will be shooting on the wide end of things you will also want to use the complex reduce distortion effects which should help a lot. I bring this up because all those canon, nikon, and sony users don't have astrotracer and they manage to take milky way shots.

Here is the sequator manual, it is a free download and for someone starting out with astro it offers a real easy point of entry into stacking.
I agree, the problem will not be with the position fix, but the pointing (electronic compass). I think that I'm probably one of a few to run into a potential problem like this. I guess we'll just go find out what works and what doesn't.

The lines are between the PRS and GPK substations on the map (page 10 of 227). It's the 230KV leg into Phoenix.The grazing range is on BLM land, and there is a sign on the fence to "go enjoy". So, we will see. There is a public access road, but there is also a gate along the highway (a couple of hundred feet off the highway). We haven't decided if we are going to just try to hop the gate off the highway - or drive up to cross road and take the dirt BLM access road back down. At 70, I'm no longer hopping over a lot of gates any longer.

I usually shoot stitched, so that I wind up using only the centers of each frame, which essentially removes the edge/corner distortion on wide angle lenses. Either 2 or 3 frames is sufficient for this.

I've used Sequator several times before. It works well. I do like this link a bit better than the rule of 200. They are close, but I also cheat and use a pixel tolerance of 4, which is a bit less forgiving.
QuoteOriginally posted by Bob 256 Quote
Actually, you might have more to worry about from the steel towers than from the power lines. The current is alternating current which averages out its effect on compass readings (DC might be another matter). Also high voltage doesn't mean high magnetic field, which depends on the current rather than the voltage. Although these lines might be carrying fairly high currents, the lines are fairly high (distant, you said 70 feet?) and magnetic fields weaken quickly with distance, and again, these are alternating current fields which tend to average to zero.

The best test might be to find some equivalent lines nearby and experiment with the camera right underneath them and see if it affects tracking - doubt it will have much effect, but stay away from the metal towers which could harbor some constant polarity magnetic field (think bar magnet) and cause problems.

Good shooting.
The steel towers are 1800 feet and 800 feet away respectfully, as the location is somewhat between the two. The backup is my friend has in addition to the o-gps1 unit, a tracker unit that we can put the bodies on, and get around the problem. Although I like the astro tracking a bit better - as I hate aligning trackers.

Actually, I'm hoping that there is sufficient height to the lines, that there is sufficient distance - where all of this will just average out to not being a problem. This was something of a unique situation that I thought I would post and ask if anyone else had happened across a similar situation.

QuoteOriginally posted by AstroDave Quote
OK - you know how multi-path works, etc! I supported the NASA geodynamics program back in the 80 and 90s as a contractor for Goddard Space Flight Center. We did VLBI, but got to know GPS capabilities and foibles as well.

Next time you are headed for Sedona, come on up north a bit further (Flagstaff) and we can get together (when closer than 6 feet is legit!). Send me a PM.
I will....

05-20-2020, 01:21 AM   #10
Pentaxian




Join Date: Jan 2018
Location: Jersey C.I.
Posts: 671
Don't know about high-voltage overhead power lines, but I do know that my O-GPS1 can be unreliable if I'm within about 10ft of my parked car (Renault Twingo), and that's with everything switched off 'cept the interior light! An old-fashioned hand-held magnetic compass can be a useful diagnostic tool
05-20-2020, 08:17 AM   #11
Site Supporter
Site Supporter
MossyRocks's Avatar

Join Date: Nov 2017
Location: Minnesota
Photos: Gallery | Albums
Posts: 1,503
QuoteOriginally posted by interested_observer Quote
I've used Sequator several times before. It works well. I do like this link a bit better than the rule of 200. They are close, but I also cheat and use a pixel tolerance of 4, which is a bit less forgiving.
Night Sky Photography Shutter Speed Calculator – tl-photography
I am aware of things like that it is just that the rule of 200 works well enough for non deep sky objects where some amount of trailing is ok. At 200 you are always going to get oval shaped stars but they are round enough, especially if one is doing a stitched panorama where you have even more pixels to hide the ovalness of the stars with.
05-20-2020, 06:24 PM   #12
New Member




Join Date: Apr 2020
Location: Independence MO
Posts: 13
QuoteOriginally posted by Bob 256 Quote
Actually, you might have more to worry about from the steel towers than from the power lines. The current is alternating current which averages out its effect on compass readings (DC might be another matter). Also high voltage doesn't mean high magnetic field, which depends on the current rather than the voltage. Although these lines might be carrying fairly high currents, the lines are fairly high (distant, you said 70 feet?) and magnetic fields weaken quickly with distance, and again, these are alternating current fields which tend to average to zero.

The best test might be to find some equivalent lines nearby and experiment with the camera right underneath them and see if it affects tracking - doubt it will have much effect, but stay away from the metal towers which could harbor some constant polarity magnetic field (think bar magnet) and cause problems.

Good shooting.

Actually while the steel towers present their own problems the magnetic field around the wires throw compasses off. A few years ago we were at a Boy Scout camporee and someone laid out a compass course with their GPS. It ran under high voltage lines on wooden towers. The kids all got lost (not badly) because the voltage affected their magnetic compasses. Think of it this way. You have 3 magnetic fields 120 degrees out of phase with each other. Each are stronger than the magnetic north pole. Since they kind of cancel each other, the compass can't find any constant attraction and the needle floats aimlessly while standing directly under them.

A lot of years ago, we were backpacking at Hercules Glades wilderness and the kids found a bench mark near the fire tower. We explained the meaning and showed them the arrow pointing to north. They tried to check their compasses with it but since the bench mark was within 50 -75 feet of the steel fire tower the compasses showed around 15 degrees off.

Needless to say, this area is likely to present problems for a magnetic compass.

Last edited by bgm1956; 05-20-2020 at 06:41 PM.
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
camera, dslr, feet, lines, location, photography, power, transmission, weekend
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
For Sale - Sold: B+W 77mm XS-Pro Kaesemann High Transmission Circular Polarizer MRC-Nano Filter blumoon722 Sold Items 0 01-03-2020 02:40 PM
Abstract Lines, lines everywhere henrikpedersen33 Post Your Photos! 4 12-31-2019 09:10 PM
For Sale - Sold: B+W 82mm XS-Pro Kaesemann High Transmission Circular Polarizer MRC-Nano Filter les3547 Sold Items 2 09-10-2019 09:28 AM
Fixed my astrotracing mount aitrus3 General Photography 4 09-26-2018 07:14 AM
Stupid question ahead concerning Astrotracing & GPS on K3 II MyTZuS Pentax K-3 9 08-16-2015 12:26 AM



All times are GMT -7. The time now is 10:51 AM. | See also: NikonForums.com, CanonForums.com part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top