Jump to content

SkySurveyBanner.jpg.21855908fce40597655603b6c9af720d.jpg

andrewluck

Members
  • Posts

    420
  • Joined

  • Last visited

Reputation

357 Excellent

3 Followers

Contact Methods

  • Website URL
    http://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

Recent Profile Visitors

1,887 profile views
  1. It it with much regret that I have to announce Mike's passing on Friday 9th October 2020. This thread seemed an appropriate place to do it as he gave a status update on the completion of his observatory as well as indicating that he was unwell. Deepest sympathies to his friends and family. Clear skies Mike.
  2. If there's no flex then tightening the tension screws won't fix anything. That looks like a pretty big gap to me and I wonder if the black ring has been cross-threaded on the focuser tube. Andrew
  3. 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
  4. 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
  5. 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.
  6. AP 1200GTO mount Takahashi FSQ106 Moravian G3-16200 Baader 4.5nM Ha
  7. 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.
  8. 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
  9. 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
  10. I'm not sure that such an instrument exists and certainly not cheaper than the FSQ85 imo. Takahashi Europe are now quoting a 40mm imaging circle on their website which is closer to reality than the 44 that was originally claimed but when you get close to this the overwhelming issue is tilt in what you hang off the back. Once this is sorted then a small defocus will round out the stars in the corners. I'm not there with mine yet but AstroBruiser is getting pretty close with his judging from the results he sent me recently. There's certainly a case for using an FSQ106 when you get to this size and resolution of sensor. You'll be operating a close further from the edge of the specification. Andrew
  11. My impression was that this will be an additional flattener. Andrew
  12. I flew to Strasbourg last week and took the train down to Colmar to meet with Richard Galli at Optique Unterlinden. Richard speaks excellent English and I was made to feel very welcome while they looked at my Baby-Q. As I've previously indicated, Takahashi recommend that the focuser be extended no more than 15mm and to achieve this I'd purchased a 37mm long 72mm extension tube. With hindsight, this was a mistake and I should have bought an 87mm tube and replaced the 50mm tube with it. More on this later. With the telescope on a table, pressing on the tube and focuser revealed that there was some free movement in the focuser tube. This I removed by tightening the tension screws slightly. Images were still showing a large amount of tilt and running the Wavefront Estimation script in Pixinsight on a set of defocused star images showed some coma and astigmatism. The report I generated is in the post above. I highly recommend running this script to check the performance of any new refractor to ensure yourself that it meets specification. Based upon my experience, the results are very accurate. At this point I was unable to determine the cause of the tilt and took the telescope to France. Once on the optical bench a tiny mis-collimation was evident and the front lens was slightly loose in it's cell. Apparently this is a fairly common problem. Both problems were corrected by reseating the cell in the tube and tightening the locking ring. Collimation is set at the factory by using small pieces of tape under the front cell but the adjustment was so small it was not necessary to replace these. I also took my extension tubes and these were checked on a measurement table with a dial gauge. This is where my main problem was. While each component was accurately machined there is always a small tolerance which in this case was under 0.04mm error in orthogonality. However, when screwed together, in my case these errors added to create a total error of >0.07mm or >70 microns. Their mechanical engineer decided that the likely cause of the issue was the Takahashi 50mm extension and they replaced this FOC. This reduced the total error to <0.04mm. Test images since I returned home show that there is some small residual tilt in the Y axis that is possibly in the camera and I have some thin tape to shim the camera on it's adapter. Wavefront Estimator shows a much improved PSF image and much better aberration figures. So, to summarise the recommendations: 1: Use Pixinsight's Wavefront Estimator to determine optical quality and collimation 2: Use the minimum number of extensions and adapters that you can arrange 3: Use a tilt adjuster in the image chain (or be prepared to shim components as required) 4: Do not assume machined components will have insignificant errors in them There is some residual field curvature. The recommendation here is to either focus on an off centre star or focus on a centred star and then offset the focus about 10 microns. This will result in slightly larger stars but much reduced distortion in the corners. This will only help when you have everything else aligned though. Takahashi Japan attended the recent Paris astronomy show and indicated that they are aware of the filed curvature issue and have a new flattener on the drawing board that will correct this issue.
  13. Thanks Barry. Useful information. I have what appears to be a lot of tilt and Takahashi want to take a look at it. Investigating flights to Strasbourg at the moment! This is despite adjusting the focuser tension and purchasing an additional M72 adapter so the focuser is only racked out 10mm. Have you run the Pixinsight WavefrontEstimation script? If you do, I'd be interested to see the results (especially without the reducer). I've knocked the relevant bits of the test I ran into a pdf report. Test report.pdf
  14. Does anyone have any experience of tilt issues in the CAA for the FSQ85? Andrew
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.