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DrRobin last won the day on July 29 2016

DrRobin had the most liked content!

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About DrRobin

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    Wish I was somewhere sunny!

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    Astronomy, obvious really.
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    Newcastle Upon Tyne, UK
  1. 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.
  2. 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.
  3. 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.
  4. 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.
  5. 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.
  6. 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.
  7. 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
  8. 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.
  9. 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.
  10. I am still trying to improve in narrowband, but just had a go at the Tadpoles using a modified Hubble palette. I think it came out okay. 24x600s in each Sii, Oiii, Ha (12.5 hours in total) taken over 4 nights in Jan with a RC 250 and SX-35 IC410 The Tadpoles, 4 nights 13-28th Jan 2019, False colour narrowband 24x600s Sii, Oiii, Ha. 12,000 light years away, each tadpole is 10 light years long by Robin DrRobin, on Flickr
  11. There are a number of different i5 processors and the best site to compare on is www.cpubenchmark.net. Go for the fastest you can afford, it will last the longest. I would still get an SSD for the operating system and short term storage, whilst you work on files and then have another disk for larger storage or things you don't use all that often. An SSD will give you an instant speed increase, probably more than moving up on processor spec a bit. A 256GB is big enough for Windows, most programs and a few files, say a months worth. Get a 512GB if your budget stretches. Get a reasonable amount of memory for the operating system you are going to use, 8GB for Win 10 is enough.
  12. I have a Lunt 60 Double stack and a Quark. I mostly image, so not sure if the balance swings for visual, but here goes. A Lunt (without double stack) is much easier and quicker to use than a Quark, the field is more even, well it is in mine. My Quark does give superior views. The warm up time is not really a problem, just plug it in whilst you set the scope up. Add a double stack to my Lunt and this improves the detail to almost the same as the a Quark, but the field flatness changes, well it does on mine. So a Lunt double stack gives similar views to a Quark and is probably slightly easier to get on with. However, in 2019 with falling solar activity I would choose the Quark, it is cheaper than a Lunt and you can use the scope for something else. In the last two years I have used my Lunt once or maybe twice, I have used my Quark a lot more, but only when there is something to look at.
  13. Hi David, The fans on the back of the scope run all of the time the camera is on. I have an extractor fan in the obs to remove air through a duct as well as a desk fan to circulate the air in the obs, these are switchable, but mostly on when I am imaging, even when it is really cold. There is a small PC in the obs, but it is very low power/heat dissipation. I am not sure if the fans in the back of the scope blow or suck, I think they suck in air and across the back of the primary. The more I read the more I think it might be best to have a primary heater, either a tape round the primary or perhaps a heater element next to the fans. I would make it switchable of course. The real problem is my location, the mist forms on the river down the hill (mile and a bit away) and slowly creeps up the hill. Probably for about 1 - 2 hours before it obscures the stars my primary mists up, so a heater gains me that extra hour or so. Usually by Midnight it is a waste of time, too much mist. Have you got a 10" truss tube or is it a solid tube? Robin
  14. I have a 10" truss tube RC and unfortuanetly my location can get a bit humid and damp. It seems to be the primary that gets the dew. I have a small heater on the secondary (not often switched on) and another on the camera, but there is nothing on the primary. My scope is fitted with a canvas light shroud. The whole lot is mounted in an obs with several fans and is usually somewhere near ambient temperature. If I spot it happening during an imaging session then a bit of light heating of the primary with a hairdryer sorts it out for another hour, but I can have dew on the primary for up to 20 minutes before I spot it and this spoils the images, even though it is still relatively clear. I have seen very few dew heaters for a primary and wisdom seems to suggest that they are avoided, the scope has primary cooling fans. Does anyone know if you use a heater tape or similar to prevent primary dew? Ta
  15. Thanks everyone. Just thought I would post a more typical picture of the view, taken this morning at about the same time. Look carefully and you can just about make out neither the Moon, Venus or Jupiter. Taken between snow showers. The view without the Moon, Venus or Jupiter, 01/02/19 by Robin DrRobin, on Flickr
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