Jump to content

Stargazers Lounge Uses Cookies

Like most websites, SGL uses cookies in order to deliver a secure, personalised service, to provide social media functions and to analyse our traffic. Continued use of SGL indicates your acceptance of our cookie policy.

sgl_imaging_challenge_banner_beauty_night_skies.thumb.jpg.2711ade15e31d01524e7dc52d15c4217.jpg

gkec

Members
  • Content Count

    618
  • Joined

  • Last visited

Community Reputation

229 Excellent

4 Followers

About gkec

  • Rank
    Proto Star

Profile Information

  • Gender
    Male
  • Interests
    Electric guitars
    Computer stuff (Not IT!)
  • Location
    Oxford UK
  1. The Isaac Newton Telescope (INT) was moved from Herstmonceux to La Palma. The William Herschel Telescope was built on La Palma under the direction of the Royal Greenwich Observatory (RGO). I have not been there since the 1990s but there were several other observatories there. I don't know how it works now as everything was handed over to Spain but there used to be an office in Santa Cruz on La Palma that used to deal with this sort of stuff. Visitors were restricted but we did have them coming round every so often. It was a while ago so it may be different now. I would suggest contacting the organisations that run the facilities.
  2. OK -- then I would suggest trying the scope with an eyepiece otherwise you have no idea whether it is good or bad.
  3. I have been in this position but with a guitar rather than a telescope. Along time ago about 1981 when I was a poor student I bought a guitar from a second hand shop for £50 which was a lot for me. Once I started working I bought a better guitar but I did still like the cheap one. As is the way it sort of deteriorated and became unplayable. I asked several knowledgeable guitar playing people and they just said it was not worth repairing. I tried to part exchange it but £80 seemed a bit cheap. I found a guy who set up guitars and paid him to setup my "good" guitar. Well it came back better than when I had bought it. So I showed him my old guitar. He said there is no such thing as a bad guitar. So I let him fix it. My niece has starting out glass blowing and she very kindly made me a bottle neck. She wanted to see what the bottle neck was like so I recorded an abridged version of "In my time of dying". I'm no Jimmy Page but it seems like the guitar was made for it. And the bottle neck is a work of art. https://www.facebook.com/graham.newton.35/videos/vob.1612985902/10205429871978898/?type=2&theater
  4. I asked her and she replied "it doesn't bother me so long as I know you are out in the garden so I don't lock you out like last time. Also I can watch what I like on telly and I like the photos". She will come out to have a look but usually trips over the tripod and complains about how cold it is.
  5. I often go for a drink with a friend who I went to University with. I did theoretical physics he did physics and philosophy. He says that we are maybe living in the equivalent of a pre Copernican view of the universe. It all looks great, the astrolabes are fantastic to look at and watch. But maybe someone looks at it from a completely different viewpoint and it all makes sense. He maybe has a point.
  6. I think that article misses the point of binning and draws some incorrect conclusions. First of all you have to consider how binning is performed. If you imagine a CCD as an array of buckets (i.e the pixels) and they fill with water (in reality electrons) depending on the number of photons that land in the bucket. At the end of the columns of rows of buckets there is an extra row of empty bigger buckets and at the left hand end of that row there is a single bigger bucket which we can call the measuring bucket. In a normal 1x1 bin readout what happens is that the first row of buckets is emptied into the bigger row of buckets, the 2nd row into the first and so on until the last row is emptied into the last but one and is left empty. So in effect the image shifts down by one row. Now a similar process happens to the row of big buckets in that the first big bucket is emptied into the measuring bucket, the second bucket into the first, and so on so the image is shifted one pixel to the left. The amount of water in the measuring bucket is measured and that value is taken as the value of the bottom left hand pixel. The measuring bucket is then emptied and the left most bucket in the big bucket row is emptied into the measuring bucket, the next bucket is emptied into the left most bucket so the row again moves one pixel to the left and the measuring bucket is measured again to get the value of the pixel on the bottom row second from the left. This is repeated for the whole row. Once the whole row has been measured and is empty. Then first row of buckets,which hold what was in the second row of buckets, are again emptied into the bigger bucket and the whole process repeated to measure the second row. This rather tedious process is repeated until all the buckets have been measured. Right now for 2x2 binning. The process is the same but instead of emptying one row of bucket into the bigger buckets and going through the measuring process on the row the second row of buckets is also emptied into the single row of bigger buckets. So the image moves down by two rows and the big row of buckets hold the water from two rows of buckets. Similarly for the row, two big buckets are emptied into the measuring bucket so that there is 4 buckets of water in the measuring bucket. Again this bucket is measured and the value taken as the 4 pixels in the bottom left hand corner. Again this is repeated for all the buckets. One thing is immediately apparent is that you can have m x n binning where m and n is any number you like so long as the buckets don't over flow. So we can bin -- so what? Firstly the measurement process is not 100% accurate. You can visualize his as the water sloshing around a bit whilst you are trying to measure it. If say you can measure the water level to say 1 cm then the measurement is more accurate if you measure 4 buckets worth at once than measuring each individual bucket. This is known as readout noise. The readout noise is the same whether you measure a single pixel or a binned pixel. Also the measurement take time compared to all the bucket emptying. So it is quicker to measure 4 buckets at once rather than each bucket. When you have a few million buckets it adds up. Now back to the article. It is claimed that a binned pixel is more sensitive than a single pixel. Well you are measuring 4 buckets of water rather than just one. Of course you get more signal. You should get, assuming equal illumination, 4 times more signal. However only 3 was measured. Lost a whole bucket of water somewhere. There are two explanations for this. 1) To measure this properly you have you use a flat field with constant illumination so that all the pixels get roughly the same amount of light. 2) The bucket emptying mechanism is done hurriedly so water is split. I sort of imagine an "It's a knockout" competition where you have to empty buckets dressed as a dragon on a moving roundabout, for those who remember that. This is true in practice as the electronics that effectively do the bucket emptying have to strike a balance between speed and accuracy. Too fast and you empty stuff all over the floor, too slow and it takes forever The binned pixels were shown to have less noise. Well statistically the noise reduces by the square of the sample count. So a sample count of 4 gives a times 2 noise reduction. Which was sort of what was measured (50 cf 70), the 15 difference was quite possibly the readout noise difference. This is not altogether a direct consequence of binning on chip, you could do this after acquisition in software and get the same result. To compare directly you should compare CCD binning with software binning and I don't think this was done in in this case. As for FWHM you are measuring the width at different resolutions so that needs to be taken into account. Exercise for the reader as it is too late too think.
  7. Just have a go with it. It will be fine. There is far more to be learnt from having a go than the finer details of IR filters.
  8. Webcams are great for planetary stuff like Jupiter. All telescopes have "natural" magnification which is dependent on the aperture so to start with find a way of securing the webcam in the focuser and have a go. This is how I started and it is very rewarding. It won't just be a point of light but it won't be huge. Although in an 8 inch it will be reasonable. Before trying for higher magnification there are challenges in get the planet on the sensor as the sensor covers a lot smaller field of view than you can see in the eyepiece( eta happy-kat ^ makes a good point here). This can be very frustrating but once you have achieved it the rewards are worth it.
  9. Probably because it is not that unusual, just a bit bigger than normal http://neo.jpl.nasa.gov/ca/ It is the media who are blowing it up out of all proportion as usual.
  10. Having worked extensively on Cassini Huygens and have had involvement with Rosetta I feel I have to point out a few "don't let the facts get in the way of a good story". Cassini Huygens would never have worked on solar power. Saturn is too far away from the Sun. The Cassini probe is nuclear powered and Huygens was battery powered. The Cassini Huygens launcher a Titan iVB was more powerful than the Russian Proton rocket that launched Rosetta. However both missions have provided immeasurable scientific data and I do hope Philea is able to provide more data once it gets enough power.
  11. I feel that is really bad customer service. So people buy cheap scopes? Don't they sell them at a profit? I have a Columbus Les Paul in a nice cherry sunburst. I bought it when I was a student in 1980 for about $70. I chose it because it looked like the one Jimmy Page played. Anyway across the years it became unplayable. I asked friends and tried to part exchange it and the comments were along the lines of "Oh I remember them, maybe $100". or "Not worth the money". I have another rather more "well respected" guitar that I took to a local guy who setup guitars and he did a fantastic job on it. It was better than it was when I had bought it. So I brought along my old student guitar. He looked at it and said there is no such thing as a bad guitar. I was doubtful. He then immediately noticed that the bolts that were holding the neck on were coming away from the the neck which was why it was unplayable. A week later I had a guitar that was better than it had ever been. Well worth the money which was about what it was valued at. Photo attached which doesn't quite do it justice.
  12. It is amazing to see the orb of Jupiter hanging in the blackness with the moons spread out on either side. This was a game changer. The four main moons are known as the Galilean moons because Galileo the very first telescopic astronomer first saw them. He realised after several observations that the small points of light were orbiting Jupiter. Indicating Copernicus was probably correct in his assertion that the Earth orbited the Sun (not as answers.com suggests that Copernicus was Galileo's BFF!) Whilst the Vatican were not that happy the rest is history. The point being, observing the moons of Jupiter might be common place today but it is significant historically.
  13. My Nexstar controller remembers the latitude/longitude. It also does remember the time BUT only what you last entered. It doesn't keep time whilst switched off. With my Maplin power tank I can charge it whilst using it.
  14. The eyepiece that fits in the ring is a 1.25 inch eyepiece, i.e. the diameter of the metal eyepiece tube is 1.25inch so the inside diameter of the ring should be 1.25inches or just over. This is almost certainly the case. The thread that screws the ring onto the scope is probably a T thread (M42x0.75mm, note standard M42 has a 1mm pitch) but that needs checking. Just to confuse things T2 and T thread tend to be used interchangeably.
  15. He also says - I tried getting it out with tools - I tried using heat to expand the plastic
×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.