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Melitastro

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About Melitastro

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    Nebula

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    Malta
  1. I'm the owner of a GSO RC6 and have just come across this discussion. One point that stands out is that the consensus of opinion for adjusting the secondary mirror to achieve the optimal focal length is by adjusting the centre screw on the secondary support. I'm not convinced this is the best way as the mirror distance can be adjusted by slacking the locking ring (see photo) and screwing the housing in or out as needed. It's much easier than using the centre screw and in theory will not mess up the collimation. However @davies07's post says that Es Reid used the centre screw adjustment method so I'd really like clarification on this as I must be missing something. A better view of the secondary mirror housing construction can be found on Han Kleijn's site http://www.hnsky.org/RC_collimation.htm Tony
  2. I can't remeber 100% which star, there are plenty available from my site. It would have been a 2nd or 3rd mag using APT with Bahtinov aid and mask. Recorded the focus point for each (I'm using a Pegasus focus cube) and then used the same difference between focus positions when imaging. Tony
  3. Mine will have come from stock held by Teleskop Service in 2015, I wonder if they are from the same batch?
  4. As I mention, there are no other optics in the path, these are taken with just the filter and no reducers or flatteners etc. and the camera is ASI 1600MM-Pro at -10°C that has what ZWO refer to as the 'protective window' over the sensor
  5. I'm starting to realise how widespread this issue is. Has anyone had good experience with this filter?
  6. No I didn't, as I say in my post I didn't try to screw it in from the other side. Is that really a solution that's used with mounted filters, I've only seen it discussed with unmounted ones?
  7. Back in 2016 I bought the Baader LRGBC + Narrowband 1.25" filter set. For various reasons I only used the LRGB and didn't use the narrow band filters until a few weeks ago. Those of you who've bought these filters will know they advertise 'NO halos, NO reflections, NO ghosting' on the filter case, so I was really surprised when the images through the OIII filter had a really well defined halo. I looked on Baader's website and contact with them is by using a web form so I posted a description of my filters, a copy of my NB images (Ha, SII and OIII) and a list of the equipment in my imaging train, and asked for their feedback on the OIII image. However, their reply was a copy and paste - or "Because we have such inquiries regulary, we wrote a complete, detailed explanation about such effects" - which more or less said that the problem was most likely due to other optics in the imaging chain (there were none, only their filters) or the window in front of the camera or spacing of the optical elements (none again). The problem is everything but their filter. It even suggested reversing the filter, something I've never seen suggested before for a mounted filter. Are you supposed to dismantle the FW so you can insert it from the back of the carousel? They even had the cheek to try and sell me on the aesthetic value of having halos because they even occur around bright stars when imaging nebulae (ok, we've all seen Alnitak in the Horeshead nebula photos!). They concluded with "Most likely you cannot get rid of the Halo - unless using extensive image processing such as described by our customer Andreas Bringmann in the attached pdf". Having been in charge of management systems before I retired, my approach to problem solving is a bit different to theirs, and with so few variables to consider the use of a different OIII filter seemed obvious. Although I can't really afford it, I opted for the Astrodon 5nm as it is supposed to be the standard by which others are judged. The filter arrived yesterday and these are last night's results comparing the Baader and Astrodon - identical 100s exposures for each, the only difference being the refocus between images. I think the images speak for themselves, so when customer service tell you: what they actually mean is "Most likely you cannot get rid of the Halo - unless..." you stop using our filters!! PS: I've got a Baader OIII filter going cheap - I'm saving for some more Astrodon NB filters Tony
  8. The only thing I can think of, and you've probably done it when cleaning the sensor, is making sure the holes in the carousel are clear so the sensor can detect position correctly. Tony
  9. Something that comes to mind when mentioning errors is that these graphs don't show data points, and along with data points you normally expect to see error bars on them. I have no idea how many variables there are when performing these measurements but as an example how accurate is the temperature? If my camera states that it's cooled to -20°C I have no way of verifying it. It may help to find how much uncertainty there are on these measurements and then see how the graphs compare?
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