Greg Hewgill ([info]ghewgill) wrote,
@ 2005-04-26 09:14:00
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Entry tags:telescope

amusing things you can do with a telescope
A new cell phone tower was recently installed about a quarter mile behind my house. This morning I saw a couple of guys scaling it, so I thought it might be fun to try to take a picture. It's surprisingly difficult to get good focus, even in daylight. I need to work on that if I'm going to improve my astrophotography.



It occurs to me that taking pictures of a couple of guys working on a cell phone tower is surprisingly similar to taking pictures of a couple of birds nesting at the top of a tree!


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[info]cowbert
2005-04-26 03:47 pm UTC (link)
you don't want to use an astronomy telescope for this, because as the light is being scattered around too much by the eyepiece lens. This will cause abberations when attempting to focus on objects only several hundred feet away. The aberration worsens as you run wider and wider apertures. You want to use a spotting scope or something that isn't modifying the light path twice.

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[info]ghewgill
2005-04-26 03:51 pm UTC (link)
Yeah, I figured as much. Do you think using a prime focus setup (no eyepiece) would help? That would mean using an SLR configuration camera. I've got a T adapter for my scope but haven't had an opportunity to use it because I haven't got an SLR camera.

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[info]cowbert
2005-04-26 04:25 pm UTC (link)
Well the optics in the telescope don't lend themselves well to close work either because you have to move the focal point so close to the objective (I assume you have a typical refractor). It's like at the optometrists when they dilate your pupils and hold up a piece of paper really close to your face and you have to try to focus on the words.

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[info]ghewgill
2005-04-26 04:29 pm UTC (link)
Yeah, I figure an astronomical scope is designed for incoming light that is pretty much exactly parallel. A quarter mile with a 4" aperture is not really very parallel anymore. :)

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[info]cowbert
2005-04-26 04:25 pm UTC (link)
but getting rid of the eyepiece probably helps somewhat.

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[info]decibel45
2005-04-26 04:04 pm UTC (link)
Actually, I suspect it's much harder to get good focus during the day because there's much less contrast than looking at stars at night.

Funny, I never had any idea those vertical sections on the antennas were actually man-sized.

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[info]willyumtx
2005-04-27 02:11 pm UTC (link)
Are they fighting or mating?

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[info]ghewgill
2005-04-27 05:56 pm UTC (link)
I think just nesting right now. I'll continue to observe them over the coming weeks.

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focus
[info]swimathon
2005-04-28 10:31 am UTC (link)
For what it's worth, if you can focus manually, put it to infinity and it'll be perfect at that range.

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Re: focus
[info]ghewgill
2005-04-28 04:14 pm UTC (link)
I set the camera to infinite focus (so it doesn't try to do automatic rangefinding), but I still have to adjust the focus on the telescope.

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