![]() ![]() A safety feature can be added by attaching a short, strong string between the mirror and its holder using a strong epoxy. The tape patch shouldn't be too small in order to provide enough grip but also not too large so it won't introduce stress. Special care should be taken when choosing the tape - if it's too soft it won't be strong enough and if it's too hard it won't be elastic enough. It is faster and used by many manufacturers (Skywatcher, GSO), though it's arguably weaker and often avoided when attaching heavy mirrors for large telescopes. In this case the distance between the mirror and the holder should be controlled with matchsticks and the adhesive should be allowed enough time to set.Īnother method is to use a double-sided foam adhesive tape. There are various methods of attaching the mirror to a holder without clips: One is to use an aquarium silicone sealant which is applied to 3 evenly spaced spots or to a large single central spot. In my case I had to replace the stock 58mm diagonal of my Skywatcher 10" Newtonian with a larger 63mm one because it was too small. The solution can be either to move the primary mirror further away from the secondary (often not applicable) or to increase the secondary mirror diameter.Ģ) The telescope is used for deep sky astrophotography and a larger secondary mirror is required to achieve a wide fully illuminated field of view.ģ) The stock mirror is attached in a such way that it's under mechanical stress, which causes astigmatism and image degradation, as described here.Ĥ) The offset of the secondary mirror isn't set correctly, which results in unevenly illuminated field of view and complicates the collimation process.ĥ) The stock mirror is of inferior quality and, usually, causes astigmatism.Ħ) The mirror is too old and needs to be re-coated or replaced. Or calculate if the fully illuminated field of view is less then zero. This issue can be diagnosed by looking through an empty focuser exactly from the focal plane - if you can't see the whole primary mirror reflection (including its clamps as seen in this image) - then the diagonal is too small. This happens because some manufacturers are trying to achieve mutually exclusive features: A short, fast OTA with a long back focus and a small central obstruction. ![]() And calculation of the fully illuminated field of viewġ) The stock mirror is often too small and causes vignetting (darkening) even at the center of field of view. ![]()
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