Jump to content

sgl_imaging_challenge_2021_annual.thumb.jpg.3fc34f695a81b16210333189a3162ac7.jpg

Karen

Members
  • Posts

    217
  • Joined

  • Last visited

Everything posted by Karen

  1. Collimation cap or cheshire to centre and "round" the secondary mirror under the focuser. Even with a self centering adapter fitted directly into the focuser tube I find a laser is too sensitive to slop. Then a barlowed laser or cheshire crosshairs the collimate the primary.
  2. Remember the 10" Dob is f4.7 So 82 degree eps need to be good to work with this short f-ratio.
  3. Add a good quality barlow lens. I have a 10" Dob and have concluded that I really only need two quality eyepieces and a barlow.
  4. I have a laser collimator which would be brilliant if it wasn't for the focuser slop. And using a cheshire I have terrible trouble focusing on the crosshairs. They are just a blurry mess. So I had a brainwave and fixed an old usb webcam over the sight tube pin hole. I have ordered a 2" to 1 1/4" self centering adapter to get better results with the laser. This is the result with the webcam.
  5. "Modesly priced" wide angle 72degree eyepieces usually fine for telescopes over F6. It is when using fast telescopes they produce distortion. For Swan eyepieces note: "They are remarkably good all-round eyepieces when used with telescopes with focal ratios up to f/6 and above."
  6. Not that good here. The moon looked like it was under water and l could only see the two central cloud bands clearly on Jupiter. It is all to do with the temperature drop. Warm day, cold night.
  7. The important bit of a finderscpoe are the cross hairs. Binoculars could be a problem unless you can get accurate centering .
  8. The binoculars are not collimated. That means the optics have not been aligned properly. Get a refund or replacement.
  9. It's the camel poo content that is good for the garden.
  10. Congratulations. I'm going to put some wheels on mine!
  11. They do come with instructions but if you get stuck l'm sure someone on SGL will help.
  12. Primary mirror knurled screws are here http://www.rothervalleyoptics.co.uk/bobs-knobs-skywatcher-newtonian-primary-collimating-thumbscrews.html
  13. If it has to be a plossl then a 8mm and 2x Barlow would be easier to use.
  14. The trapezium is what I have been studying lately. I think l have managed to see 5 stars but definitely no coma or astigmatism on them at 170x.
  15. I am going to have a good look for abberations with various EPs next time the clouds vanish and report what my less than perfect eyes are seeing!
  16. I found this info on Astronomics.com. With flat field planetary (high power) eyepieces coma should barely be noticeable. "The diameter of the effectively coma-free field of a reflector is roughly equal (in millimeters) to one-half the square of its focal ratio. An f/5 scope has a coma-free field of approximately 12.5mm (5 squared = 25, divided by 2), an f/4 scope has an 8mm field (4 squared = 16, divided by 2), etc. A 40mm eyepiece usually looks at an area about 28mm in diameter in the center of the telescope image. At low powers, then, up to 50% of a fast reflector’s image can show coma’s distracting fan-shaped stars. Inexpensive modified achromatic eyepieces typically suffer from curvature of field (an inability to bring the center and edges of the field into focus at the same time). Not only are some of the stars fan-shaped in a modified achromatic eyepiece due to coma, but they’re out of focus as well! Reflectors with fast focal ratios (below f/6) are therefore at their best with flat field eyepieces such as Plössls and those designed for fast focal ratio use (Naglers, Panoptics, Super Wide Angles, etc.) rather than modified achromatics. Coma is not usually a problem at high magnifications. A high power eyepiece looks only at the central 5mm to 12mm area of the image and doesn’t see the comatic outer portions."
  17. A good idea to fit a shroud on the truss tube. I always worry about dropping something on the mirror.
  18. Just had a look at my 250px and the focuser wheels are not lopsided. But if you look at your focuser the tongue at the bottom has a bigger gap on the right side than the left as if the focuser barrel needs rotating anticlockwise a bit. Is this a 250px? I thought they were all metallic black with white fittings.
  19. My EP collection was originally bought for my 5 inch f11 maksutov. If I put a 13mm wide angle eyepiece in the 250px and get bad coma I know it is not the fault of the 'scope, it is my fault for not buying very expensive medium power wide angle eyepieces! There is a much cheaper alternative of course, a coma corrector. There is no coma at high power and it is a 10 inch reflector which blows the 5 inch maksutov away with it's performance, even with a bit of coma.
  20. Checking and adjusting the primary mirror clips takes just a few minutes and then you will be sure the mirror is optimised. Coma will happen in a f4.7 'scope with medium and low power EPs. I mostly go 170x upwards for Jupiter and just about everything else and don't notice any coma. A CC must be the way to go but coma doesn't bother me that much.
  21. Nope, I don't see any coma on Jupiters moons. Not with TMB planetary type ep's anyway. Hyperions are poor towards the edge but still give pleasing widefield views. I did have a problem with astigmatism which turned out to be overtight primary mirror clips. Synta employ gorillas with screwdrivers.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.