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Peter Drew

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Peter Drew last won the day on February 24 2020

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About Peter Drew

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    Astronomy Centre Todmorden U.K.

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  1. The images in the bottom row are indication of tilt, usually. Not sure of the Cheshire image to the right, looks like gross decentring of the individual lens components which is unlikely. If the cell does not have a facility for collimating it I would suggest first rotating the lens pair to see if the deformation turns with it. If it does, remove the lens, mark the original orientation of the two components relative to each other then slightly separate them and turn the front one relative to the rear. Replace the lens complete in its cell and retest.
  2. I can't specifically directly answer the optical characteristics as these will vary being that the optical sets will be unique to each telescope. I can confirm that amplifying additional optics will give increasing back focus dimensions and focal reducing elements, the reverse. As a rule of thumb, the increase of back focus due to an inter mirror change is the amount of change x the amplification factor squared and the amplification factor in your case will be x4. All Cassegrain types are susceptible to inter mirror variation due to varying temperature, one of the reasons one seems to alwa
  3. For housing Dobsonians over 14" aperture I use fixed buildings and the telescope rolls out on rails.
  4. I've had pleasing solar views at 80x using a C8 with a full aperture white light filter. Just pick a good day/time of day.
  5. Probably someone has but not worth doing seriously, you would lose the benefits normally obtained by binoviewing.
  6. I think most amateur available mirrors are overcoated with silicon dioxide as a protection for the softer aluminium. Mirrors, like star diagonals, can be dielectrically overcoated for greater protection but the process is very expensive.
  7. We get several requests each year for recipients of stars etc to help them with the location and the possibility of visiting to have a look at them through one of our telescopes. Almost invariably, the star is far too dim or badly placed for little to no chance of a view. I have often asked whether they had any input with the choice as the high magnitude numbers suggest inexperienced selection, apparently not. We were able, on one occasion to show someone their patch of land on the Moon thanks to the services of Quickmap which zoomed to show that it even had its own small crater. I kno
  8. Another vote for a zoom eyepiece for single unit use. I use binoviewers these days though.
  9. Pity about the distance to Oz. I could fix it in less than 15 minutes if down your street. I would just pop it in the lathe, drill out the remaining bit of thread, re-tap it with the correct thread and screw in a new length with some threadlock. Surely someone close by in Oz could do this for you?
  10. Open a bag of salt, take a large pinch ...........etc,etc.
  11. I'd rather have an achromatic doublet lens made by Skywatcher than a Flourite doublet lens made by me! It's not always just about the glass.
  12. By contrast, I have a 4" Flourite and a 5" triplet that I've used probably no more than twice in the last 5 years. I also have a 150ED that gets used frequently as it's mounted on a larger telescope as a finder/general purpose telescope. I don't need to G & G and I rarely take a telescope anywhere else, usually once a year to Kelling.
  13. @Goldenmole. Your telescope has an erecting prism diagonal, the prism will show a bar across the middle when used at night, if you plan to replace it make sure you get a standard 90 degree star diagonal.
  14. Some years ago now Nigella, life still goes on though.
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