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I have tested a lot of products in order to make the collimation: reego, catseye, .... At the end, I use two: Reego in order to verify & OCAL pro camera for collimation. You could find some images on this french forum: https://www.astronomie-va.com/forum/viewtopic.php?f=7&t=3166&p=146624&hilit=ocal#p146624 |
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 Can anyone comment on my collimation?i dont know why but the secondary mirror is not in the center of the draw tube |
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Hassaan Zaheer: And neither is the primary. As for the secondary it might be that your offset is wrong and/or the secondary isn't aligned with the drawtube. |
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The primary is centered as good as I can get it. I thought centering the edge of the secondary to the edge of the focuser was "offsetting" it according to your answer above. When you say away from the focuser what do you mean? andrea tasselli:The primary is centered as good as I can get it. I thought centering the edge of the secondary to the edge of the focuser was "offsetting" it according to your answer above. When you say away from the focuser what do you mean? As pointed out by @andrea tasselli above, the offset of the secondary is not something you act on during collimation. An offseted secondary has it geometrical center that is not centered in the OTA axis; it is offset in the direction that is opposite to the focuser axis. In order to collimate your scope, you then start by adjusting the height of your secondary so that it appears perfectly concentric in the focuser tube. As the offset shift the mirror away fro the focuser, you have to bring it higher in the OTA. Then you use the screw to collimate the secondary properly and finaly you move the collimation of the primary. Here is an illustration of the full offset, but from the side :  In slow system, you simply align the geometrical center of your primary with the OTA axis. However, in fast system, the light cone in the OTA is such that you have to adjust the centering the secondary mirror by shifting (i.e. at the time of gluing your secondary, not during collimation) its geometrical center away from the focuser. Otherwise your secondary won't be at the right place to catch the light cone come from the primary. As a result, in order to have the secondary centered in the focuser tube, you need to have it closer to the spider. I hope this helps. Clear skies, Patrice |
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andrea tasselli:Hassaan Zaheer: the secondary mirror is horizontally miss aligned. No matter what i do the secondary mirror is off from the center i have pulled and pushed it towards the primary mirror till it is in the center using a collimation cap. but when i try to allign it vertically it just wont align. vertically means left right in the below image. The secondary is a bit shifted to the right.   |
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| Unless some gross distortions are hampering this you should be able to position the secondary in the center of the drawtube end. This is best done with a cheshire EP or some digital gizmo. As a start I'd measure whether the arms of the spider are of the same length. This should be the fiirst step in centering... Then we need to calculate the offset and for that we need the focal ratio. |
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andrea tasselli: Hi Andrea This is an f/4 quattro 150 Ill check on the veins. I did try to move the veins but it did not move the secondary mirror at all. |
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| Assuming a 50mm minor diameter for the secondary your offsets (both away from the focuser and toward the primary) is of 3.125mm. So your offset on the support along the long axis is of around 4.4mm. |
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andrea tasselli: I think i finally centered the secondary. had to stand the scope straight and use my hand to position the mirror. its still not a 100% but still progress.  |
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| Yes, seems much better than previously. |
