So here's a problem I'm unfamiliar with. Say you've got power lines running right over your back yard, 5 meters above your head - about 10-15mm thick. With your 'scope focussed at infinity, do they show up in the view (eyepiece or image) at all, or do they just reduce contrast a little like a secondary mirror does?
(I can't test this myself, but it could influence choice of properties ... as I looked at one today exactly like that, but was otherwise fine.)
It would act like a secondary, but it would appear and disappear depending on what you where looking at at the time. Try holding your hand in front of the aperture; It affects the image suprisingly little. I often observe through trees which reduces contrast but doesn't destroy the view entirely.
for other reasons i wouldn't get into the property if it were directly overhead - or that close to you. i have hi voltage behind me but no way would like them that close. yes you notice them.
Hi,
as mentioned by Ralph; they would act as a secondary so you'll loose some light, but considering their small size, you'd only loose a really really small amount of light.
I was hoping they'd just have a mild effect on contrast, and it looks like that's right - I guess the larger the aperture, the more that will be the case. I'll try and test it somewhere, when I can, just to be sure.
Thankfully, the lines aren't HV - they look like local 415v three-phase - and it beats me why they're running over a back yard and not down the street. Still, I'm also a bit nervous about power lines overhead ...
... especially if I'm in a metal ROR obs/shed and it's dark ...
I wouldn't have lines over my property anywhere, hi or low voltage. LFE, Low (50 hz) Frequency Emissions. Not good for your health. I turn off my Electric Blanket when I get into bed.
I've seen enough evidence of illness caused by exposure to LFE to want to stay away from large current lines.
Good thing to stay away from HV power lines. Something as simple as a wire fence can zap you (due to induced currents) if there's a fault in the HV lines. There are cases of people being zapped because their local (metal) water pipes were parralel to HV lines.
Thanks for the continued advice, guys. Much appreciated.
Quote:
Originally Posted by AussieTrooper
Good thing to stay away from HV power lines. Something as simple as a wire fence can zap you (due to induced currents) if there's a fault in the HV lines. There are cases of people being zapped because their local (metal) water pipes were parralel to HV lines.
I've had some experience with unearthed conductors in EM fields - earthing and bonding is unfortunately too frequently overlooked in, e.g., transmitter site design.
Quote:
Originally Posted by ZeroID
I wouldn't have lines over my property anywhere, hi or low voltage. LFE, Low (50 hz) Frequency Emissions. Not good for your health. I turn off my Electric Blanket when I get into bed.
I can understand why you wouldn't want to sleep on it (I wouldn't either), but those 50Hz currents are running through wires in your house ... right next to you. I'm not saying they're a good thing, and all other things being equal, I'd put distance between myself and transmission lines, but personally I'm more worried about the shock hazard. Perhaps that's just me.
50 Hz domestic is only small amps, small field of effect. Overhead lines are in the 100's of amps dept feeding multiple houses, that makes big EMF fields. And explains why parallel water pipes and fence lines in dry ground get induced voltage from the magnetic EMF field. If you want any sort of evidence of the range of the effect then there it is.
How many other houses are on those lines ? figure on about 20-30 amps per house for water heating, cooking etc etc
Back to the original question (following all the scaremongering)
I believe that contrast would be reduced more than if a similar sized wire were placed closer to the telescope. I have no proof for this thought, but as the obstruction is moved closer to "infinity" for focus, then it must degrade the image more and more. I have observed in areas of overhead wires and wondered why objects ( say planets) were sometimes soft. A small amount of defocusing would quickly bring up the wire crossing the image. An obstructive secondary will not do this until the image is massively defocused.
One of my observing spots at home has power lines in view and I am dead sure I have tracked across them in my time. I have never noticed a difference in the view at the eyepiece. I would not worry about them too much from that perspective.
If it concerns you, maybe find yourself somewhere to observe one night which has power lines overhead and check it out for yourself by deliberately observing through them. If you can't pick it or can live with anything you can pick then that would be a pretty good answer for your question.
Be aware that your gps probably won't work properly.
I set up under some similar overhead low voltage stuff on a grass verge and my lx90 refused to go at all. Moved it across the verge and it was fine.
I haven't heard of power lines disrupting a GPS (and am going to test this out the next chance I get!), but it will definitely affect compass readings for quite some distance, which mobile astronomy apps use.
We set up in the same spot when a mate comes out to my place for AP. I have never had an issue with the GPS unit on my scope but he used to set up using a compass and inclinometer and we always used to chase his polar alignment for ages before he could get imaging. Then I did a solar noon check for him and drove in some marker pegs and setup has been very quick since. Perhaps the power lines where affecting his compass and putting him off by a degree or more.
The other place we set up is further from the lines and seemed to be less of an issue.
I haven't heard of power lines disrupting a GPS (and am going to test this out the next chance I get!), but it will definitely affect compass readings for quite some distance, which mobile astronomy apps use.
I had an old Pioneer GPS that used to throw a 'route recalculation' every time I drove under the power lines just before getting home. The newer navman never did it though.
