Scaffold poles. (1 Viewer)

[Binastro]

I was surprised to see vertical scaffold poles appear 25m or 80ft up and higher 120m away.

Despite awful vision without glasses they were obvious and one correctly was identified as double with a small gap.

With 8x32BA reversed binocular, I could not focus without glasses.
But with glasses, which are old and I need new glasses, I could see the poles, even though not in perfect focus.

The double poles are easy.
The 10ft high pole above the roof is easy, but the 8ft high pole above the roof more difficult but seen.

The poles are grey, the sky is grey and it is raining.

I guessed the poles are 2 inches thick.
Good guess.
U.K. poles are 48.3mm thick outer size with 4mm walls inside.

So, with 8x reduction an apparent width of 6mm.
120m is 120,000mm.
So one part in 20,000 or 10 arcseconds.
Someone with good vision and good focus could, I think, do much better.

Barnard saw a wire against the sky at 0.44 arcsecond thick, but this is much longer than the scaffold poles, especially when reduced by an 8x binocular.

Perhaps a really long scaffold pole covering most of the eyes field, could be seen down to one arcsecond in ideal conditions.
Maybe up to 10 km distance?

The poles here are vertical, I usually do better with horizontal lines.

It is interesting that the length of the poles is so important.

Regards,
B.

 

[Binastro]

Last night I got a white card and drew black lines using a normal black ball point pen with a ruler.

300mm, 100mm, 50mm, 25mm and 12.5mm long.

With an 8x measuring magnifier the lines are about 0.38mm wide.
Although black ink, using the 8x magnifier they are not very black with a slight greyness. Not jet black.

Also the card is not very white but fairly white.

The biggest distance I could use indoors is 10 metres.

With my old distance glasses I could see the 50mm line but not the 12.5mm line at 10 metres.

By moving the glasses 3cm forward, which is close to my current prescription I could see all the lines, including 12.5mm.

This is with indoor lighting.

Also reflected light is not the same as seeing wires or scaffold poles against the sky in daylight.

The lines at 10m are about 8 arcseconds wide.

My eyes in the last two years are now poor and get tired quickly.

I could not get to, say, 20m to see if the 300mm line would be visible.

Observations made include the fact that moving away from the lines I could continue seeing them at further distances than approaching them from invisibility.
This is an expected result.

Also I know the lines are there, so this is not the same as detecting unknown lines.

Also the ends of the lines were sometimes perceived as slightly drooping, when in fact they are straight as drawn by ruler.
This may be personal to me, or a more general observation.
Sometimes the ends seem straight.

Up to 5 years ago my sight was good and I think I would have done much better.

The length of the lines does not dramatically alter visibility, but short lines such as 12.5mm are difficult

I was hoping to make a graph of arsecond visibility at different distances, but my eyesight is not good enough to do this nowadays.

Perhaps someone with good eyesight has already done this.

Regards,
B.