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About davidc135

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  • Interests
    Astronomy and ATM, science and natural history, trad archery
  • Location
    Hay on Wye
  1. www.ukglasscentre.co.uk sell 10mm float in 50x50cm for 24.00 plus shipping plus vat maybe but your local glazier might be a bit cheaper. Enough for a number of tools. David
  2. Your local glazier might be able to supply 10mm ordinary float (plate) but there may be a minimum size of sheet. For some 'white' float I ordered it was 50cm square. Would you be able to cut it up? There's something to be said for using that 21mm thick tool, especially on a first project. David
  3. I make the spherical aberration of a 130/900 sphere equal .34 waves; acceptable at this price although I think the extra performance of 1/6 wave optics would tell in good seeing. One point that hasn't come up is the smoothness or otherwise of the mirror surface and which could be more relevant than whether it's a sphere or not. For example, Ben's Ronchigram appears to show zone(s) or it could just be turbulence as he says. Reducing the Ronchi lines to three will increase sensitivity as would a knife edge test. David
  4. I used a weatherproof 'Cassini' plaster at a 28 (water):100 mix. Hard, strong and not affected by water, although I did coat it. Loses very little weight on drying at 40 to 50 degrees. I'd have thought 'herculite' would be better than ordinary plaster. David
  5. Good luck with your project. Have you decided on the speed of the mirror? David
  6. Congrats on this project. Where did you get the lens surfaces coated? Ah, scientific mirrors I've just noticed. David
  7. Midges, hedgehogs and a hornet's nest in my garden. Hmm, will I regret my live and let live good intentions? Another evening of fine seeing with the grs very colourful and clearly separate from the seb. David
  8. Yes, great seeing here as well in Wales allowing detailed views of Mars in a Meade 8'' sct. Above the S. Polar cap was a dark band with some structure and above that a featureless equatorial band. Maybe a dust storm? In the Northern hemisphere a smaller dark patch less conspicuous than in the South. A bright crescent along one limb connected the S. ice cap with the North pole. I was joined by a pair of hedgehogs and, less welcome, by the sound of hornets from a nearby nest up and about their business even before dawn broke. David
  9. Had a look through my Meade 8'' sct on the mornings of the 5th and 6th. It was more worthwhile than I expected with the South ice cap prominent, also southern mid latitude dark areas and Syrtis major showing. Northern part all red and featureless. Very good seeing especially on Tuesday allowed some good views in spite of Mars' low position. David
  10. Might be a consideration if imaging along with tube etc materials. David
  11. x450! Great to hear everything has turned out so well and that my pessimism was nonsense. My apologies to you, Mike and Skymaxes everywhere. David
  12. Very interesting. Can you give the diameter and length of the assembly? The corrector (purple at front) looks flat. I'm assuming there is a secondary mirror behind the metal plate in the corrector. Does it seem flat or curved? The camera looks quite tall which suggests that the focal surface is internal. Following on from vlaiv's comments you could attach some paper flat to the end of a tube just narrow enough to be pushed into the back of the camera. A distant daytime view might do. The image will be bright. If the image is internal, that is. There are some components inside the tube. David
  13. Hi Dan It could be that the zone is no more than the expression of the HSA intrinsic as you say in the design. All errors together are probably less than 1/4 wave although it would be fun to quantify if there was the kit. David
  14. Good images. They show the difference in brightness of rings inside and outside of focus that you mentioned due (I think) to a high zone near the edge. Or even a slightly turned edge? Mel Bartels quotes John Dobson who recommended working on a mirror's zones that were bright outside of focus. Have you put this into aberrator? Looks like your original assessment of a small amount of LSA and HSA was right. There seems to be a heck of a lot to star testing! Has Suiter's book been helpful? I must get a copy. David
  15. Looks to have fine optics. 1/8 wave overcorrected or better from that graph. Congrats. Seems there was around 1/8 wave induced SA(as well) in the first test. David
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