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About skybadger

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  • Birthday 09/02/69

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  1. I was thinking of a central cylinder of around 80mm diameter suspended on a traditional 4-vaned spider in the secondary cage. The cylinder has an internal sliding fit cylinder with a closing plate at one end. On the closing plate is mounted the cameras in a horizontal sliding fit sprung-loaded carriage. Essentially a baked bean can with cameras in it and a hole at one end to let the light in. The challenges are: arrange the sliding fit to be the focuser and add controls - triple rack rails and big exterior gear with drive pinion ? It has to be internal really or it will stick out into the light path. Or focus using the primary... Sliding fit sled - it needs to move about 40mm - half the width of a lodestar and my sx 9X camera combined. So it sounds like its worth knocking up a prototype.. cheers Mike
  2. Hi I'm looking for optical flat mirrors for use in some twisted scopes and for testing optics in dual pass configuration. Useful sizes are 80mm, 120mm and above 6".. I might just build a coelostat or a nasmyth if I get the right sizes. Cheers Mike.
  3. Hi all I'm thinking of a design for a mirror I have . It's a 12" f/2.7 . I was thinking of using it in Newt mode and then wondered, why bother. Why not just place two cameras at the focal plane, a large ccd and a video camera, say a lodestar. The original secondary on the donor Cass scope was 88 mm across so this should fit. I then started thinking about Coma and the video camera being off axis and wondering if that meant that image would be unusable. Then I though about a sliding focal pane, such that I could switch the sensors in and out of the on-axis position. What do people think? Too hard or just a bit of mechanics.? There will need to be a mpcc in front , which is what defines the axis and nulls the coma. Filters will be hard unless screwed to the mpcc each time. I'm expecting a 60' fov at the focal plane. Focusing will need to be by adjusting the entire unit in and out. Other than the big pro scopes, anyone seen this done anywhere else ? Cheers Mike
  4. surely any loss of vibration would be immediate since the vibration is itself quantised ? No tail off there.
  5. One way or another you will end up wearing glasses. What do you want until then is the important question.? You lose both lens elasticity, focusing muscle strength and potentially lens transparency. So let's not worry too hard about the shape of our shrinking heads. Mike
  6. Get your eyes lasered. It will get rid of the astigmatism and while VERY itchy is painless. It will rid you of glasses and contacts both. I had mine done 5 years ago and one remains perfect for distance and the other (mono vision) for reading is acceptable.. M
  7. I'll take this please. Pm me the details for PayPal if successful. Cheers Mike
  8. Where did the rest of the scopes go ? Where can I get one ? M
  9. I have a George Hole cassegrain set too. 12.5" f/10 I think. I am currently using a double-pass ronchi oil mirror rig to work out the secondary spacing distance. What I do know is that one of the mirrors is very zony. I suspect its the secondary which has been polished on a small polishing jig and the primary didn't show much at all at f/2.7 in foucault testing. Once I get the secondary distance right, I'll be sending it to Nicholls for testing and re-figuring. I'm jealous yours is etched. Mike
  10. Machine mart do a set for a good price. Essential. As is a variable diameter tank cutter. I seem to use nothing but holes in my constructions. I'm sure you could have bored it on the lathe too...
  11. Thanks all. I have been searching for the passband info of the filter on the baader website and can't find it. I suspect the tail off might start at 6500 or so. I do need to try a longer focus refractory but all I have here are Petzvals. Might assemble one once I have the time. I shall look into the narrower passband filter too. What do you mean by retune other than to turn the knob? Adding the filter in the way shouldn't provide any interference effect causing the passband to move that I can think off. Do you know one ? Cheers Mike
  12. Hi I'm using a quark chrome H-alpha filter on a skywatcher ST80 and I want to put a pre-filter in front to dump some of the heat. To this end I put a Baader 2" IR cut filter in the train and more or less lost the surface detail. Can anyone recommend a filter for this job and maybe explain why the filter had the effect it did ? Also, my quark seems to be on-band with the knob turned to 1 o' clock when previously it was at about 6. All I did was store it indoors over the winter. Has this happened to anybody else ? Ambient is about 15 to 20 degrees in the info. Finally, do people get better views with longer FR scopes ? This one is about f/5 and the contrast is lower than I am expecting. Cheers Mike
  13. I hope those leds are dimmable, I'd be blind with them in the obbo!
  14. Why is the view upwards a problem ? All our domes need slot clearance overhead. You will face larger problems with sideways wheel forces for dome rotation and bearings gravitating downward to the lower end of the track. Alternatively you might think about making it all alt-az and using a field rotator.