Jump to content

Stargazers Lounge Uses Cookies

Like most websites, SGL uses cookies in order to deliver a secure, personalised service, to provide social media functions and to analyse our traffic. Continued use of SGL indicates your acceptance of our cookie policy.



  • Content Count

  • Joined

  • Last visited

Community Reputation

95 Excellent

About Whirlwind

  • Rank
    Star Forming

Profile Information

  • Location
  1. Cool, great to see that you have found a solution. I suspect what this is doing is reducing the dynamic range (so most of the walking noise is one/two levels and then the offset is slightly clipping this out leaving just the small remaining edges of the walking noise. It may be worth playing with the parameters slightly starting from this point to see if you can change the gain / offset to see if there are any further improvements (for example to remove the remaining trace of the noise.
  2. In terms of the video, a lot of software allow you to produce a playback of the blinked images which would demonstrate how frequently and what is happening between each image. I'm unsure about colour CMOS cameras in terms of actual settings. I think noise in CMOS is meant to be generally quite low so excess cooling may be unnecessary? It is strange that it has gone from being not a problem to all of a sudden being so which would suggest to me some change in the setup that is causing the issue.
  3. It might help if you posted the video here as it may help in analysing if there is any issues. Have you changed the settings recently on the camera (e.g. gain / cooling etc?)
  4. I think it is better to confirm this first. Have you blinked the sequence of images without a star correction to see whether there is any movement? I am unsure whether SGP can manage the dither to the above degree of requirements, but increasing the dithering pixel step size/duration enough to wind in the backlash should help. Are you guiding at all or is it very short subs stacked? Sometimes placing a slight misalignment in the balance that works against the backlash can also help - but is dependent on where you are imaging. Effectively the slight moment on one side acts to 'press against' the backlash.
  5. Fixed pattern noise is difficult to post process out because it isn't random per se so it is difficult for software to identify it (it appears more like 'real' data). Dithering is meant to resolve this because it adds a random shift in to each image so then the fixed pattern noise then becomes more apparent to the software as the noise it is. The noise in the fixed pattern arises in the read noise so can be more prevalent in CMOS cameras because of the low read noise and the tendency to use very short exposures. Increasing exposure durations so that thermal noise overwhelms the read noise would be one way to overcome this. You could also image with the camera slightly warmer to increase the thermal noise a bit. For this image it may be worth checking that your darks don't need updating if you are using them. Also try blinking you images to check that dithering is actually working as expected. If you have a lot of backlash in the mount then you may think you are dithering but in one direction it isn't and using up the backlash in the mount. The 'rain pattern' might suggest dithering isn't working in one direction.
  6. Is this just for imaging of visual as well? I ask because if you want a longer focal length of about 1600mm and it is just for imaging then why not say the VXL12"? This would be less burdensome mount wise and aperture is less important (compared to visual) when it comes to imaging. It's also not as costly so would allow more funds to be spent on the mount (which is always the critical part of imaging set up). You are saving about £2k. That could then go towards upscaling the mount (which might open up things like the MESU) and/or a cooled CMOS colour camera which would also likely improve your images. If you are committed to going for this weight capacity the only other mount with this capacity and price range that I know of is the JTW OGEM but is relatively untested (the base version is similar to the CEM120 in price). On the other hand if you want a visual telescope as well then a 16" will work wonders and that changes your mount choices.
  7. No you can't control the three cameras in the fully automated route. This only allows you to use two cameras (guider/main imaging camera). In the advanced version you can control 3 cameras though. You can setup one as the guider and two as imaging cameras. You can set a sequence (e.g. LRGB) for each of the imaging cameras and then start them independently whilst guiding, so is a semi-automated sequence but using only piece of software/computer. You can't use dither though because the sequences aren't linked. In principle, as it has a scripting language built in to the software you could set up a script that allowed dithering if you are software minded.
  8. Unfortunately there are a lot of unknowns in both plots to really understand what the differences are. To have a completely scientific comparison they would need to be measured in the same way to ensure that the data is comparable. Statistically assuming a perfect test you should get a distribution of errors over time. If the CEM data is almost an instantaneous sampling of the data and the MESU was averaged (say 5/10 second exposures) then from a simple statistical analysis you would expect more variance in the CEM data -really it should be a median or average over the same timeframe. I hence don't think we can make much of the comparison of the data without some real errors being shown on the data points.
  9. I'd agree that they are relatively unknown in the astroimaging world. However, they do make quite a bit for the more professional community of which they have more telescopes out there (e.g. GOTO). They don't get advertised in the same way... 3-4 months is the quoted time for a Newtonian I believe, 6 months for a CDK or more complex design. I do appreciate that there is always the risk of the unknown.
  10. Is this on a permanent set up? If so collimation should be less of an issue as it should not have to do it very often once set (assuming a stable set up). If you are intending to strip down every night or go to a dark site then refractor will be the way to go because at F4 you will need to collimate a lot more often. An F5 system will be more forgiving. If you ever want to do photometry then the larger aperture will help. If you ever want to use it for visual then the larger aperture will help. Reflectors have much less issues with regards colour correction given a decent corrector. Reflectors need a bath once in a while! The larger aperture at the same pixel scale will allow you to collect more data in the reflector in the same time (helpful in cloudy UK) A faster focal ratio means your focus position is more critical - your focuser needs to be more precise. Diffraction spikes can be a negative for some. Reflectors can have tube currents (most higher quality ones have oversized tubes/fans to mitigate this). Reflectors are more bulky and more prone to wind (less of an issue if in an observatory and shielded. If you continue with a reflector option it might be worth looking at JTW Astronomy. They make custom reflectors and build to your specs (backfocus, focuser etc). Ian
  11. The amount seems about right. You only pay customs charges on items over £135. So all that is left is VAT and the handling fee https://www.gov.uk/goods-sent-from-abroad/tax-and-duty Royal Mail charge an £8 handling fee and you pay VAT on the total amount (about £7) - which is close to the amount you have been charged. It is the handling fee that can be the bad news for small low cost items because it is generally fixed for what is almost certainly an automated robotic process.
  12. If you don't like collimation I would probably stay away from the RASA. At F2 getting collimation spot on is going to take some time (and may need to be tweaked every time you set up). In comparison refractors are reasonably plug and play once you have the flattener distance dialled in. This and that the Esprits have been out for longer is likely the reason you see more images using them.
  13. it might also be worth looking at PRISM then as well if you want a system for automation that is integrated into the software. It also has processing tools.
  14. I'm not doubting that you can make some very fine images with ASA equipment. However, a lot of the images are fast and relatively short focal length. We also don't know how many images were discarded and what post processing was done with the images; averaging over several nights could easily broaden any slight flexure distortions in the combine and process. I can accept long term repeatable flexure can be managed by any mount given the correct software, short term changes at higher resolution are likely to be another issue (obviously better telescopes should have less).
  15. Yeah, I saw that you had one of these on order. It will be interesting to see how well a mount would perform at such a focal length. Short focal length reflectors or something like the ODK maybe OK because of where most of the weight is centred. A longer focal length corrected Newtonian I'm not so sure. I've heard of both good and bad experiences. I also see a lot of people going for AO at longer focal lengths which I think is to accommodate small flex issues that an encoder based mount can't handle on 'short' time frames (though I accept the point that the mount attempts to plan for long term changes). Obviously SCTs are worse but I'd expect to see some in any reflector system (compared to a refractor which is more stable).
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.