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AstroTim

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  1. Thank you all for the warm welcome messages. I have also signed up to the East Midlands site. Tim
  2. Hi Ed, Thanks, while I do often start observing while it’s still cooling down, just in case the clouds roll in, I left it outside for a couple of hours before checking and correcting the collimation. Tim
  3. Hi Geoff, thanks for the reply. I also suspect that there is little to worry about, but thought it worth checking. I’ve also read that angular rotation is less of a concern nowadays. I think in the more distant past they used to sometimes mount the secondary off centre within its mount in order to counter any error in the centering of the drilled corrector hole. Rotating the secondary would have more of an impact in that scenario but I’d hope that modern manufacturing processes can drill a hole centrally with much better precision. The only thing I was thinking is that if the secondary was too far off centre then despite being in collimation tilt wise, some of the light cone reflected from the primary would miss it. Using a slightly oversized secondary would give you some margin for error here but at the cost of increasing the central obstruction, so wasn’t sure if they would have done that. Hopefully I’ll get a clear night soon to check things out and put my concerns to bed. Tim
  4. Hi Ed, Thanks for the reply. I haven’t noticed an issue as such, but don’t seem to get as sharp a view as others have described with similar scopes, or the same level of magnification without it starting to blur. To date I’ve assumed / hoped that was just due to poorer seeing conditions. However, I made my first attempt at collimating the scope recently, as a star test had showed it to be slightly out. When I tried to turn one of the collimation screws the whole secondary moved very slightly sideways. It did move easily back to it’s original position and upon further examination I noticed that the secondary holder locking ring wasn’t fully tightened, so nipped it back up tight. This did then make me wonder whether the secondary had been off centre to start with and maybe that was why I’m not getting sharp views, hence why I wanted to check it’s position, or indeed whether it being exactly central mattered. Previous star tests did show the scope to be in rough collimation at least. I wasn’t sure if measuring to the tube edge would be sufficient as that assumes that the primary is also mounted dead centre. I know the corrector plate is shimmed to align it with the primary. I was able to complete the collimation just before the clouds came over and haven’t had a clear night since to check things out on a familiar target. Tim
  5. Thank you all for the welcome messages. I haven’t really looked into the use of filters at all, but reading up quickly on the HA filter and does sound interesting. Would it improve nebula for visual, or just imaging purposes? I have also seen a couple of comments that indicate a skyglow filter might be a worthwhile purchase, as it sounds like they might also help with planetary detail, but need to read up on how effective they are first. Tim
  6. Nice pictures. It’s amazing how good phone cameras have become over the last few years.
  7. Yes, having “lurked” on a few discussions to date, there are clearly some very knowledgable people around, who are prepared to give balanced advice i.e. that bigger isn’t always better, and not just recommending the most expensive equipment. Tim
  8. Hi All, I’m a relative beginner at astronomy. I’m primarily doing visual observing (mainly planets and lunar at the moment) but hope to progress onto some simple imaging in the near future, again starting with planets. Tim
  9. Hi, It’s my first post as an astronomy newbie but hopefully not too daft a question. What is the best way to check that the secondary mirror on an SCT is centred (laterally) with respect to the primary mirror and optical axis? It’s a non-Fastar SCT so the secondary can’t be as easily removed and replaced. I’ve read conflicting statements as to whether it’s even important or not (at least to within a few mm). What are peoples thoughts on that? I can see how you might still be able to achieve collimation via the secondary tilt angle even if it’s off centre, but are there any visible side effects compared to it being centred e.g. increased coma elsewhere in the FOV, some of the light reflected from the primary missing the secondary? Thanks in advance, Tim
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