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.

sgl_2019_sp_banner.thumb.jpg.a0ff260c05b90dead5c594e9b4ee9fd0.jpg

andrewluck

Members
  • Content Count

    418
  • Joined

  • Last visited

Community Reputation

354 Excellent

3 Followers

About andrewluck

  • Rank
    Star Forming

Contact Methods

  • Website URL
    http://blog.andrewluck.me.uk

Profile Information

  • Gender
    Male
  • Interests
    Member of Breckland Astronomical Society.
    Astrophotography.
    Ex-RAF electronics engineer. Now a consultant with a computer system integrator.
  • Location
    Norfolk
  1. If you're using LRGB then generally you're time limited. The target also matters, it works best on bright objects with a lot of detail such as galaxies. Light pollution levels also have an impact. RGB filter sets usually have a gap in their pass bands that attenuates sodium sky glow. L filters will record this light pollution and generally you will have more work to do removing gradients from the L image. There will also be more shot noise so you need more exposures to drive this noise level down. I should have mentioned this on my original post as it's a another advantage to RGB imaging under typical UK skies. LRGB doesn't work well for me as my targets are often dark nebulae and molecular clouds with extremely low levels of illumination and not much in the way of spacial information. Star colour in the field is also very important and this is captured best with RGB. As usual, astrophotography is an art, not a science (in the context that's being discussed here) so use whatever works for you! If you decide to do LRGB then most, if not all of the spacial information is derived from the luminance frame and most of your exposures will be dedicated to this to reduce the noise level to expose this detail. The goal in the colour channels is to drive the noise level down as quickly as possible. As no fine detail is required from these frames (they're being used to colour the luminance information) then binning is the quickest, most efficient way to achieve this. There's no requirement to balance the RGB exposure times with either method. Another approach is to assess the noise level in each channel and expose more in the channel(s) with more noise. My last attempt at the Iris is here: http://littlebeck.org.uk/?p=1197 albeit with a one shot colour QHY9 so RGB only. I will have to revisit this with the mono camera. Andrew
  2. My preferred approach is to shoot the RGB frames at bin 1x1 and forget about luminance. In my view this has several advantages: Due to the reduced bandwidth of the filters, RGB images will tend to be sharper than L Any faint structures in the data are guaranteed to have matching chrominance information. This is not necessarily the case if you've gone deeper on the luminance As there is only one copy of the luminance data (derived from the RGB images) in the final stack colour saturation is easier to preserve The one downside is that you will be spending much more time collecting colour data and overall data acquisition time will be longer. Incidentally, if you're shooting RGB at bin 1x1 and using luminance as well then this is a mistake as the only advantage of LRGB is being able to shoot the colours in reduced time using bin 2x2. Andrew
  3. This is the area around Eta Carina acquired with 4x 20 minute Ha exposures. Some 5 minute exposures were used for the star cores but these were too long and also saturated (but to a lesser extent). With hind-sight 30 seconds would probably have been long enough for these. I've reduced the image to about half size. Equipment was the same as for my RCW114 image; FSQ106 with Moravian G3-16200. Images taken at Tivoli AstroFarm, Namibia.
  4. AP 1200GTO mount Takahashi FSQ106 Moravian G3-16200 Baader 4.5nM Ha
  5. An image from this year's trip to Namibia, it's a 2 panel Ha mosaic of the emission nebula RCW114 on the Scorpius / Ara border. 3 hours per panel in 20 minute sub frames. This image spans a 4x3 degree area of sky and includes two globular clusters NGC6388 & NGC6352.
  6. This image of the Lobster (Gum 66) in Scorpius is from 10x 20 minute Ha frames acquired over my last two visits to Tivoli in Namibia. The image has been resized to 60% of the original. Mount: AP GTO1200 Telescope: Takahashi FSQ-106 Camera: Moravian G3-16200 Filter: Baader 4.5nM Ha
  7. This is a two panel mosaic of Sh2-155 comprising a lot of 20 minute red, green and blue sub-frames for 28 hours total integration time. Taken with my FSQ-85 with 1.01x flattener and Moravian G3-16200. Processed in Pixinsight. Andrew
  8. No dispute there, you're absolutely correct. Finger trouble with the calculator here. Apologies for the confusion. Andrew
  9. From the specs on Takahashi America I see that the 130d has a 44mm image circle. The diagonal of a full frame sensor exceeds this at 49.5mm. I've no experience with this scope but with my FSQ-85 (same image circle specification), when I switched to a 16200 chipped camera the stars in the corners were very poor. This sensor is considerably smaller than a full frame. Now I've fitted the new flattener this has made a considerable difference. I'd seek the advise of either Takahashi Europe or America and see what they recommend. Andrew
  10. The flattener has now arrived and been installed. As I already had an adapter for the front of the filter wheel to connect to a CA-35 all I had to do was include some M54 extenders between the flattener and the adapter. The ones I used were these: https://www.aliexpress.com/store/product/A-set-of-M54-Extension-Tube-4-9MM/1371081_32819456658.html?spm=2114.12010612.8148356.4.73733ccaSiki3y Originally, I intended ordering a new custom adapter once I'd determined the back focus requirement but I don't think this is essential. The results are interesting. I was previously aware that these FSQ scopes are extremely sensitive to focus position and this hasn't changed with the flattener. Apparent tilt swings pretty wildly either side of focus and on my last trip to Namibia I was manually focusing an FSQ-106 by focusing for minimum tilt (completely ignoring the usual FWHM metric) and achieved good reults with this. Incidentally, using this method the direction of tilt indicates which way to turn the focuser which makes the process quicker. With the Lakeside auto-focuser at home, I'm focusing on a star in the centre of the field and then offsetting 20 steps out. This has the effect of reducing the FWHM of the focus star from 6 to about 4 and reduces the indicated curvature from 30% to around 10%. Some further fine tuning is probably possible here and should yield a small improvement. As CCD Inspector doesn't distinguish between FWHM and eccentricity I also measured the image using Pixinsight with these results: The stars in the corners of the test image look like this: In summary, I'm very pleased and looking forward to the next clear night. If anyone is interested in the 3D plots either side of focus then ask and I'll post them. Andrew
  11. Hi Julian I haven't got a flattener yet but I'll be pressing the buy button very soon. I'll also need a new adapter to connect it to the filter wheel. <Edit> Button pressed. Also a set of M54 extenders </Edit> Andrew
  12. I use one of these: http://www.auroraeurotech.com/CloudSensor.php Works well with CCD Commander to open and close the roof. No wind speed measurement though. Andrew
  13. Filter is the Baader 4.5nM Ha. There's a thread here somewhere detailing some of the work I had to do getting acceptable (to me) results. I've ended up with some tape under one corner of the camera / filter wheel connection and, having focussed on a star in the centre of the field I then step out an additional 10 steps (about 50 micron). There's still some elongation top left, bottom right but I can live with that for the moment. Hint: machined adapters are never orthogonal and sometimes the tolerances will add up the wrong way and bite you! After noise reduction in the linear phase (TGV & MMT) I used a histogram stretch rather than a masked stretch to preserve what contrast there was. Then there's 3 iterations of LocalHistogramEqualisation at scales of 64, 128 and 256 (decreasing amounts each time) to boost the contrast and then some S curves to finish. More noise reduction etc etc etc Andrew
  14. This is the result of 16x 20 minute Ha frames taken over the two clear nights earlier this week with my FSQ85 / Moravian 16200 combination. Processing in Pixinsight and resampled to 45% of the original size. Andrew
×
×
  • Create New...

Important Information

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