Post by BillW on Apr 2, 2012 10:17:35 GMT
Hi,
Some interesting results from the last month.
A wee experiment....
I tried using a variety of lenses for a few nights each and the results are quite remarkable.
3-8.5mm f1, set at ~8mm to cover chip. Only 2 meteors per night.
8.5mm f1.3 ave 6 meteors per night
6mm f1.2, 2 meteors per night.
It then occured to me that the f1 might not really be an f1 at the longer end of the range. Just like most telephoto lenses that have a degradation in f ratio I thought maybe the cctv zoom lens might suffer the same. By a simple examination of the pupil I could see it changing as I zoomed the lens in and out. With refraction I can't guarantee it's not f1 but I have my suspicions!. I decided to try it again but at a shorter focal length.
I examined a white screen and simply estimated at which point it looked brightest on the pc screen. This was around half way on the zoom setting, ~5.5mm focal length. However the problem is that now there was vignetting at the corners. I think this lens in particular is very good as it is (claimed to be) an IR corrected aspheric so it produces pretty good images but it is designed fo 1/3 inch chips. It is however better than the fixed focal lengths which surprised me a bit.
Anyway, over two clear nights I got last week I recorded 19 and 23 meteors respectively. Whether activity has suddenly and entirely coincidently increased or maybe there is some weather issue, I don't know but what an improvement!
I think it's operating at a better aperture ratio (closer to f1) combined with a larger field of view.
I'll live with the vignetting and see how it goes, if that's how it performs in general! As a comparison I would be interested to hear how this compares to what others are getting for nightly rates over the past month.
Cheers,
Bill.
Some interesting results from the last month.
A wee experiment....
I tried using a variety of lenses for a few nights each and the results are quite remarkable.
3-8.5mm f1, set at ~8mm to cover chip. Only 2 meteors per night.
8.5mm f1.3 ave 6 meteors per night
6mm f1.2, 2 meteors per night.
It then occured to me that the f1 might not really be an f1 at the longer end of the range. Just like most telephoto lenses that have a degradation in f ratio I thought maybe the cctv zoom lens might suffer the same. By a simple examination of the pupil I could see it changing as I zoomed the lens in and out. With refraction I can't guarantee it's not f1 but I have my suspicions!. I decided to try it again but at a shorter focal length.
I examined a white screen and simply estimated at which point it looked brightest on the pc screen. This was around half way on the zoom setting, ~5.5mm focal length. However the problem is that now there was vignetting at the corners. I think this lens in particular is very good as it is (claimed to be) an IR corrected aspheric so it produces pretty good images but it is designed fo 1/3 inch chips. It is however better than the fixed focal lengths which surprised me a bit.
Anyway, over two clear nights I got last week I recorded 19 and 23 meteors respectively. Whether activity has suddenly and entirely coincidently increased or maybe there is some weather issue, I don't know but what an improvement!
I think it's operating at a better aperture ratio (closer to f1) combined with a larger field of view.
I'll live with the vignetting and see how it goes, if that's how it performs in general! As a comparison I would be interested to hear how this compares to what others are getting for nightly rates over the past month.
Cheers,
Bill.