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Message: <blockquote data-quote="Binastro" data-source="post: 3150321" data-attributes="member: 111403">Hi David,I took photographs of that pimple first in poor light, which was unsatisfactory and then on a bright day where the exposure was 1/1000 second at F/5.8 at ISO160. -1/3 stop correction. I was using a 30 times optical zoom and four times digital zoom which gives about 2800 mm equivalent focal length (35mm).The pimple is not the best shape, it is a triangle approximately as seen, but the base slopes at an angle of 15°.There are two chimney pots I use, one at 124 m and the other at 117m. It is the 117m one that I'm using here.Anyway the calculations suggest that the area of the pimple is the same as a square pimple that subtends an angle of 17 arc seconds, so your memory was better than mine.I will check my calculations later to make sure that I have not made any mistakes.Regarding the Easy Jet observation that you made, it is a great observation  as are all yours and Kimmo's careful measurements.However, the observations I made and the observations of the  EasyJet that you made are quite different.Had I seen my aircraft again, and had I been looking for the name on the side of the fuselage or the tail it is a quite different observation to the discovery observation that I made. The discovery observation is an observation of the unknown, which is not the same as observing something that you are looking for and is known.In birdwatching, it may be that most of the observations are of known objects. The bird is large in the binocular and then you look for detail which you know maybe there.As I mentioned earlier, a discovery with a 16 inch telescope is then visible in a 10 inch telescope and later in a 6 inch telescope.There are enormous differences between observations of the unknown and the known.In addition, the great observations that you are making and the measurements are in optimum conditions, both in lighting conditions and generally.But in the real world lighting conditions are often not perfect, and one may be somewhat tired etc.My observations over many years suggest that the difference between a tripod mounted binocular or image stabilised binocular and standard handheld binocular are much larger than 40% for a 10 times binocular, probably about a 70% to 80% improvement.And at night,the improvement with my 18×50 between handheld unstabilised and stabilised is between 100% and 200%.I will recheck my calculations tomorrow all being well.</blockquote>

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