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Everything posted by Piero

  1. I tend to stand while observing as that's my preferred way. This with both my dobson and refractors. The refractor mounts have an extensible column which I love as it avoids contortionism or "yoga postures".
  2. Last Thursday night the seeing was great with very good transparency. Observing Aristarchus crater and plateau from 160x to 630x was amazing. In particular, I was impressed by the kind of "river" approaching the crater to the left and how the light played fantastic shades inside. From Wikipedia: Aristarchus plateau (NASA).
  3. Found these books in the second hand market.
  4. I observed Copernicus past night with my dobson up to 533x without any sign of image degradation. It was wonderful!
  5. Last night I had a chance to try the telescope following the last work on the mirror cell. The sky conditions were clear, windless, and rather stable temperature between 8.20pm and 9.20pm. After that the temperature started dropping. The telescope was left outside with the fan on since 6.30pm. The light shroud was also fixed in order to reduce internal and nearby turbulence. Both telescope focuser and primary mirror axial alignments were adjusted with my 2" Glatter laser 650nm. Several stars were used for star testing: Betelgeuse, Procion, Rigel, Pollux, and Aldebaran. This was
  6. I thought you already used a RACI finder with your dobson. Nice finder! At the moment I have an Antares VS60 with no illuminated field.
  7. I worked another bit last night and this morning: replaced temporary nylon pins + 2mm pad on top with a stack of 2 x 5mm thick pads (20mm diam). This raised the mirror 1mm. the milk cartoon structure to maintain the triangles in position without affecting their movement was moved underneath marked the position of the sling (COG) on four points. These are about equidistant. cut velcro strips in two segments and placed them under and above the COG where the sling will pass. The external border of the velcro strip (which is slightly flat) was placed towards the slin
  8. I ordered a set of felt pads of different sizes and 5mm thick. After taking all the measurements, I need to stack two of these in order to replace the pins. Will do the work tonight or tomorrow morning. What's the diameter of your pads installed by Randy? 1inch, 20mm, or more?
  9. Hey Gerry, Discard the z function (green) as not necessary here. What we care here is the part of the functions where x is from 0 to pi/2 rad (90 deg). This is the movement of the telescope regarding altitude. Basically, depending at 0 deg telescope altitude the weight force is all on the sling (see cos function) and this decreases as the altitude grows to 90 deg (pi/2). Follow the sin function for studying how the weight force works on the triangles. Note that the intersection is not at 0.5 y. Source: Wikipedia.
  10. Here we go You don't need the actual W vector for this, so it can be assured to be the unit vector. What really matters are the sine and cosine functions at different angles alpha. The alpha angle is 90 - telescope_altitude. Sine and cosine receive angles in radians, so you need to covert: 1deg = pi/180 = 0.01745 rad.
  11. Thank you, Gerry. Very helpful. Placing a pad on top of the pin is not a final solution, but only a quick way to test the idea. I certainly need to consider either taller pins or taller pads, once I get the the measure of the exact height. If this is exact there is no friction caused by pins or pads.
  12. Gentlemen, you are too kind! I haven't come up with new products or design, but just put some information together and been trying to analyse / address some issues which are often ignored. Hopefully, this thread will become a useful resource for those of us having to deal with these issues or want to improve their telescope performance. That would be great! I feel the thread title should change. Currently, it is not really informative and this might affect searches. Probably something like "Lukehurst-Nichol classic dobsonian mods" would be more appropriate? If happ
  13. It's late here Gerry! What's your humblest suggestion? I'm curious!
  14. I don't think it is linear. I suspect it is sin/cos, but haven't thought about this properly.
  15. Sling and triangle supports play orthogonal (=perpendicular) forces AND they should do so, otherwise the result is astigmatism (at the least). Triangle support is 0 at 0 deg altitude and 1 at 90 deg altitude. Sling support is 1 at 0 deg altitude and 0 at 90 deg altitude.
  16. Quick solution,for the time being they are on top of the nylon pins. See video.
  17. Absolutely! The problem is not really the lack of contact between 0 and 5-ish Deg of altitude. The problem is the difference in support that the mirror receive from the bottom. The point is that even if the mirror is supported by all pins of the triangles (all pins touch the mirror), this does not guarantee that the mirror is well supported. If the pins touch the mirror at the same time at the same altitude (0deg ideally), then the support is expected to be identical or close enough.
  18. Very low altitude, probably 5 degrees. You need to raise the telescope very gently. I laid down with the mirror box above me, and then pulled it towards me very gently, raising the telescope. The video shows this. The mirror touched the pins of the 2 lower triangles, but the telescope needed to be raised another bit before the mirror was supported by the pins of the top triangle. Adding 1 pad reduced this gap, although there is still a little gap left.
  19. John, here is a photo of an original Glatter sling attachment. As you can see, it is attached to a roller which can slide up and down according to the mirror plane. Together with the velcro strips, the sling remains in place and in the correct position. It's a great design really. The sling does the job, not the person who needs to assess the correct mirror height. Also, that design prevents the sling to squeeze the mirror (and therefore astigmatism). My telescope also works, but this just because of the wood platform holding all the components (mirror, sling attachments, etc). Still in
  20. Thanks Gerry. That's an interesting idea as it minimise the amount of strips, and therefore potential side effects from these. I should do the same. At what angle are these two cruces attached to the mirror? Thanks John. Yes, in my telescope the collimation bolts adjust the alignment of a wood base on which lay the triangles, mirror, sling attachment, sling and edge supports (for safety). This is not generally the case though. In almost all mirror cell designs I've seen, the collimation bolts move the triangles up or down. I think the range can be up to 1 inch
  21. Further tests on the Glatter sling cable. There are several ways to install a Glatter sling. Here I will focus on the 180 deg (or "U-shape") installation. There are a few important aspects to pay attention: the sling must be placed slightly below half of the mirror thickness (see "h" in figure). The exact value can be obtained here http://www.cruxis.com/scope/mirroredgecalculator.htm . For my telescope, this is 17.75mm. the sling must be attached with some vecro stripes, so that it remains in place. These stripes should be minimal in order to avoid
  22. Personally, I would upgrade the telescope rather than getting a coma corrector to be used with that telescope. Then, yeah, at F5 I would use a coma corrector, especially if using eyepieces with 70 Deg AFOV or more. Not everyone, and here on SGL very few, would though.
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