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About festoon

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    Star Forming

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    Cambridge, UK

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  1. Seems there was a bright fireball/meteor tonight visible in the UK. Very disappointed not to have seen it, it happened between me being out observing and putting the kids to bed. Hope some of you managed to catch it
  2. Not sure of your location but SES-4 was pretty close to there at a similar time. Image taken from https://in-the-sky.org/ 29/02/21 at 20:35, location Colchester, UK
  3. festoon


    Images taken with my portable EAA kit - C5 on a AZ GTi, with an intel compute stick PC
  4. festoon

    Samyang 135mm

    Images with the Samyang 135mm on an AZGti mount (with ASI224MC-Cool sensor)
  5. Point taken about zoom and how you sample or re-sample an image - dont go beyond 100% And I guess the point is it depends how you process your data i.e. if you re-sample use a method which smooths. In terms of the specific lens I have (the Samyang 135mm) the measured resolution at the centre of the image plane at f/2.8 is 47 lpmm (as defined by MTF50, reference https://www.lenstip.com/442.4-Lens_review-Samyang_135_mm_f_2.0_ED_UMC_Image_resolution.html). That corresponds to a size of 21 um. To sample 47 lpmm sufficiently you would need a pixel size of 10.5 um or less. If you use a colour
  6. At this zoom you dont see that it is undersampled. I understand that perception and presentation make a big difference. If you look at the stars and galaxy at a higher zoom it is apparent it is underampled
  7. The effect I am thinking is that too few pixels are captured for the resolution of the lens
  8. Just a further thought on this...when I was using the 6.5um pixels at 135mm samyang then if sampling rate is x2 due to it being an osc, the the effective sampling is using an equivelent of 13um. @vlaiv - do you not think that this will be starting to become noticeable in terms of undersampling as you calculated that good pixel size for such lens is about 10-12µm?
  9. super info - thanks @vlaiv So what I take from this is - when using an OSC if doing bilinear interpolation debayering sampling is x2 what it would be with a mono camera However at x2 sampling some sharpness in smaller stars is lost, but image still shows good detail as shown in the GIF comparison you posted. I think the former is what I was experiencing with smaller stars
  10. I'll have to see if I saved any images with the 6.5um OSC. I certainly was not impressed hence why I switched to the ASI224MC Cool sensor with smaller pixels. I guess undersampling may not be the correct word, but with the larger pixel size the stars appeared more square on the monitor. Also purely from a understanding point of view I would like to understand if OSC does effect the resolution of the image
  11. Thanks @vlaiv. So I guess what you are saying is the lens is diffraction limited so having smaller pixels makes no difference. The thing is I saw a massive difference in perceived resolution moving from 6.5um pixels OSC to 3.75um pixels OSC. Obviously less blocky even on widefield targets. Yes this is the Samyang 135mm f/2
  12. Deep sky imaging in general - I did take some images with this set up of M81 and M82 and as expected the resolution was poor. But I was thinking maybe some of that was down to the fact its an OSC sensor. Also from an inquistive point of view is there a way to calculate what sized OSC pixel size would give equivelent results to a mono setup?
  13. Currently I'm imaging at 135mm focal length with a an OSC sensor with a pixel size of 3.75 microns. Thus I'm undersampling at 5.73 arcsex/pixel. But I was wondering is my sampling even worse than this because I'm using an OSC with a Bayer Matrix? If so would I see a noticeable improvement in image resolution if I was to use a mono sensor with the same pixel size?
  14. Yes I'd agree with this...I think there is more signal to noise in the f/2 image (especially on M42).
  15. Thanks @carastro. To the best of my ability yes these images were processed the same (using Startools). The results at f/2 (and f/2.8) are pretty amazing. As I was using a colour CMOS I was not using any filters to begin with, and I did notice bloating of the brighter stars but thanks to advice from @vlaiv to use a UV/IR filter the results were massively improved. I was also advised to try f/2.8 hence the comparison here. I don't think the difference is massive at f/2.8 compared to f/2 but I think it can be detected in the images above. Also I'd agree with the comment abou
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