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DrRobin

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DrRobin last won the day on July 29 2016

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About DrRobin

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    Wish I was somewhere sunny!

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    http://www.drrobin.co.uk

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    Astronomy, obvious really.
    Sailing
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    Newcastle Upon Tyne, UK
  1. Well done Alexandra, just seen your photo on the BBC website. Robin
  2. Nice one Steve. All of my solar kit is still in hiding, Sept 2018 was the last outing in Crete, perhaps I will go and have a look to see if it is still there? Robin
  3. It seems to take several seconds (30s?) to transit the disc and is not massively out of focus so it must be a reasonably sized object some distance away. It's random nature, speed and size rule out an aircraft or satellite, if I had to guess I would suggest something at about 500~1000ft away, moving at around 10~30mph. It appears to change shape, so your guess that it is a sheet of something been blown along by the wind (tumbling) is consistent, but not as high as you suggest. It might be a drone, someone at 500ft and moving about 10mph, but been manually controlled and changing angle or been blown a bit in a strong wind? Anyway nice capture. Robin
  4. We have all been there, moving telescopes round the garden, chasing the narrow window in winter. Sadly my solar telescopes haven't made it back out of storage since sometime last year (or was it the year before?), I forget when, but looking at some of the other posts there has been a few spots to look at, so good luck. The other option is to drive out to a car park, you get some funny looks, but that is all.
  5. I saw a bright flash last night at 23:34 and initially thought it was lightning, but a check on lightningmaps.org confirmed it wasn't and anyway the colour was wrong. I assumed it was a meteor and the report below confirms this. https://www.bbc.co.uk/news/av/uk-england-derbyshire-51373851/exploding-meteor-caught-on-doorbell-camera-in-derby I live 10 miles west of Newcastle Upon Tyne and it was due east at 23:34, I guessed somewhere over the north sea. It must have been pretty big to be seen so well in Derby and due east of Newcastle Upon Tyne. My night sky camera caught it, in the 9 o'clock position, due east of me at 23:35, but it runs 60 second exposures. Did anyone else see it and which direction, we might be able to triangulate it?
  6. It's a simultaneous equation, x is the distance of the train from the bridge, y is the length in the bridge (in terms of time) x = y/3 and x+y = 2*(y/3) x therefore equals y and therefore the speed of the train is 3x. We did these in school.
  7. A focal reducer doesn't change the F ratio of the scope, it changes the size of the sensing element. Your 200mm RC is still F/8, but the pixel size has effectively doubled in size (4 x the area) and this makes it more sensitive at the cost of resolution.
  8. Binning doesn't help that much. If you use a 2x2 bin (4 times the area), but they way the signal is read it is more like 2x the signal. To get back to 4x signal you have to use 4x4 bin, roughly speaking. Smaller pixel sizes often have a lower light sensitive area to total area, due to the need for readout registers. It's so dfficult to compare different ccds. If you look at my post from 2013 you will see I differentiated between a DSO (the subject of this thread) and a star. This is important if you are considering point sources or a light spread out of an area.
  9. I was making the assumption that it would be the same camera on both. If you change the pixel size then everything changes, oh and you might as well change location to above the atmosphere where there is less loss. I doubt this is true either, both systems end up with the same amount of sky per pixel, if both cameras have the same sensitivity (difficult to achieve) then both will image in the same time as they both have the same number of photons to play with.
  10. How faint you can see depends on how many arc-seconds per pixel and the signal to noise ratio of the chip. Hubble is in space so has very low noise. The F-ratio, aperture and pixel size all then contribute to the number of photons in each pixel from any given light source. If you increase aperture and as a consequence increase F/ratio (focal length) then the number of photons per pixel might not change and you won't get any more signal. If you increase pixel size then you will see faint objects provided you don't increase noise as a result, but at the expense of resolution.
  11. Simply put..... F ratio determines how long you will image for (your exposure time); Aperture (and focal length) determine how much you will fit in. E.g. a 12" F/5 telescope will have the same exposure as a 6" F/5 telescope, its just that the 6" will cover a much wider field.
  12. Hi, My dad got me out of bed to watch Armstrong and Aldrin walk on the moon, I think it was delayed? but can't really remember, I was only 5. Fantastic achievement, this is what can be achieved when everyone pulls together. Robin
  13. Rear mounted Etalons are designed for a certain f/stop and need to be placed at the correct distance from the objective lens. It's all about the angle of the light passing through. I don't have the physics to hand but a PST is f/10, so really you want to keep the final scope at or near f/10 and the same relative distance from the objective as the PST. In front mounted Etalons the light [from the sun] is near enough parallel, in rear mounted Etalons, the light is converging, but not so much in a f/10 system. Restricting the aperture of a objective lens, results in light which converges less (at the edge of the aperture) and increases the f/stop, so might actually help the Etalon work better. If you use a different f/number then you will need to experiment to find the best place to put the Etalon. Remember that the Etalon has a fixed aperture so it is likely that it will need to move backwards in the tube towards the eyepiece. Using a Etalon on a lower f/stop scope will probably lead to a smaller field of view over which the Etalon will work (smaller sweetspot) which would be counter-productive. Peter [Drew] will know more about this than the rest of us put together, interesting that he uses a 6" f/10 lens. It is the same with a Quark, Daystar recommend a F/4 to F/8 scope although the Quark has a 4.2 x barlow installed, which sets the f/stop to f/16 to f/20 which is the range they decided on.
  14. I didn't say earlier (didn't want to put you off), I was one of the early adopters of a Quark, my first went back twice, it would reach lock and the contrast/detail was very poor. The one that replaced it was perfect, the contrast good a reasonably flat field. Unfortunately that one would reach lock (no green LED, either Red or flashing) either so I sent it back for re-adjustment. They decided to replace it. The replacement reaches lock, but the contrast isn't quite as good as Quark 2 and the field not quite as flat. Perhaps I should have stuck with Quark 2 but the one I have now is pretty good and flats take care of the field. You can have similar problems with a [double stack] Lunt, I have to have my second Etalon in just the right place and right state of tune for it to work well. I found a focuser rotator which was just the right size so my second Etalon is permanently fixed to the front of my Lunt. All that said, I would still go for the Quark, it lets you use your expensive scope for something else. If buying second hand just confirm with the seller what the views/images are like and that it achieves lock for all of the settings. With a bit of luck they will have used it for imaging and can send you some images.
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