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Jason D

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About Jason D

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    California, USA
  1. I believe the issue reported by the OP could be (and I am speculating) due to the holographic optical piece mounted on its metallic casing at an angle. Referring to the OP's original photo, note how the pattern looks OK along the 2:00<->8:00 line but looks at its worse along the 11:00<->5:00 line. Jason
  2. That does not look right. I would ask for a replacement. Here is mine. Don't mind what I was trying to do in these photos -- just check the uniformity of the rings.
  3. Your collimation as shown on the above photo looks good Jason
  4. Secondary mirror silhouette will always appear skewed towards the primary mirror. It is just more paramount for fast scopes. The cross hairs in the photo are the spider vanes. These should be ignored when collimating. Refer to my photo in the pre reply. My scope's spider vanes intersect slightly to the right of the center spot.
  5. It should look like that (with an offset). Here is a photo of my collimated scope
  6. That does not mean much with respect to collimation. I would ignore that observation if I were in your shoes. Your photo does not provide enough information to evaluate your collimation. The primary center spot is not showing and the focuser edge is also not showing. A good collimation cap will have a reflective (or at leave a white) underneath surface.
  7. As the person who came up with the particular center spot shape (called Hotspot), my main target was to improve stacking the center marker reflections via Catseye XLKP autcollimator collimation tool. The tool will show several reflections of the center marker and some of these reflections will be 180 degree rotated. To stack the center marker reflection against its 180 degree rotated reflection, the radioactive symbol shape (the Hotspot) works best. Another advantage is aligning the Hotspot against the ring of the Catseye cheshire. See attachments. The Hotspot center marker is irrelevant to the collimation cap. Jason
  8. Based on your description, I suggest you leave the secondary mirror alone. Just ensure the primary mirror is adjusted then enjoy the views. Jason
  9. The following statement in the book "For uniform illumination of the focal plane the diagonal must be displaced away from the eyepiece and toward the primary mirror by equal amounts" is wrong!!!! Jason
  10. What you have described only checks for the primary mirror alignment which is the most critical collimation alignment -- the one responsible for coma. However, the method you have described does not evaluate the proper placement of the secondary mirror unless the secondary mirror is grossly (and I mean grossly) misaligned. Jason
  11. I presume the middle figure below matches your concern when mounting a secondary mirror without an away-from-focuser offset , am I correct? That is, as shown in the same middle figure, part of the reflected star light cone will miss the secondary mirror unless it is either properly offsetted away-from-the-focuser or the secondary mirror is large enough to intercept the whole reflected light cone, am I still correct? Well, this is a common misconception!!! If the secondary mirror is mounted with the proper away-from-focuser offset then you will get the left-hand side figure which is the "intuitive" picture we have in mind when we think of the reflected cone. However, when the secondary mirror is mounted without any away-from-focuser offset then we can still intercept the whole light cone as shown in the right-hand side figure. As we go through the collimation steps, we will end up tilting the primary mirror towards the focuser without even knowing it. Now the central star in the FOV is not the one intercepted by the OTA axis and our setup will intercept the whole reflected light cone of the FOV central star. Both methods of secondary mirror mounting will provide perfect collimation if the proper steps are followed as shown below: There is one exceptions when it is desired to mount the secondary mirror with the proper offset which is to improve DSC accuracy but the benefit is small. There are two exceptions when it is a MUST to mount the secondary mirror with the proper offset which are: 1- When tilting the primary mirror causes the incoming parallel light to be clipped by the OTA edge. This only happens with the OTA opening it too tight -- as large as the primary mirror. 2- When the Newtonian has a corrective lens mounted at the OTA opening but most Newtonians do not have it. One more thing, it is typical for off-center stars to have their reflected light cones clipped by the secondary mirror even for a perfectly collimated scope as shown below: Jason EDIT: Added missing last attachment
  12. The slight misalignment you referenced is negligible and has no impact on your views. I would definitely ignore and not be bothered with it. Jason
  13. Hello Tim, With proper knowledge, quality laser collimators are great and accurate collimation tools. The rotational error you have described is hardly noticeable at the eyepiece for visual observation. It does not impact coma or focus but rather it has a "theoretical" impact (that is hardly noticeable visually) on the distribution of field illumination within the FOV. It should be known to any laser collimator owner that laser collimators can only used to achieve axial alignment -- when the eyepiece axis points at the primary mirror center and the primary mirror axis points at the center of the eyepiece center. Unless the laser collimator is equipped with a holographic attachment, it can't be used to optimally center/round the secondary mirror under the focuser simply because a typical single beam laser collimator does not interact with the secondary edge. Jason
  14. To OP, Check this post and the next post https://stargazerslounge.com/topic/186945-collimation-woes-laser-vs-cap/?do=findComment&amp;comment=1946524 Jason
  15. Can you share the "after" photo for comparison?
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