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Found 12 results

  1. Can someone please take a look at this video and tell me what they think.I've got a horrible noise coming from the Dec motor only in one direction.https://youtu.be/4E-oRAANk_QThanks!
  2. In an earlier post I examined the noise in single dark frames over a range of exposure times. My conclusion was that the Nikon D7500 was a lower noise camera than the D5300. This was also backed up by an examination of master bias frames that again strongly favoured the D7500. However ... The first image I attempted to produce with the D7500 exhibited very strong streaks in the noise. I had been in the habit of not using dark subtraction with the D5300 as it has very low thermal pattern noise. Accordingly, I again only used bias and flat frame calibration in the workflow that produced the above images. Whilst the streaks are due to patterns in the noise being spread across the image due to errors in the application of dithering during tracking, it did indicate that the D7500 did have significant thermal pattern noise. I found this surprising because the noise in individual frames ( when looked at in isolation ) seems to be completely random. I thought that perhaps my memory had failed me and maybe the D5300 has the same level of pattern noise but my memory was being tricked. That is, all my recent images with the D5300 were taken at lowish air temperatures ( ~5 deg or so ) whereas the image above was captured on warm nights ( low 20s ) and so maybe the D5300 would be just as bad at higher temperatures. To test this I produced bias corrected master darks for both the D7500 and D5300 from images all taken at around 20 deg or just over. The images below have all been stretched using the same screenTransferFunction applied to the Pixinsight histogram tool. The results are striking ... D5300 master dark ( 47 subs, bias corrected ) - red channel: D7500 master dark ( 281 subs, bias corrected ) - red channel: D5300 master dark 100% centre crop - red channel: D7500 master dark 100% centre crop - red channel: And the histograms of the full size images ( red channels ) ... D5300 master dark ( red channel ) histogram: D7500 master dark ( red channel ) histogram: The Pixinsight statistics tool calculates the following: D5300: mean 2.3, standard deviation 9.3 D7500: mean 7.5, standard deviation 20.8 ------------- Analysis: The images and histograms clearly show that the D7500 has higher pattern noise than the D5300. In particular, from the histograms, 0.1% ( 6,286 ) of D5300 pixels are more than 44 ADU whereas, for the D7500 this figure is 27 times as great at 2.7% ( 141,305 pixels ). Furthermore, the master dark for the D5300 was only produced using 47 images -v- 281 for the D7500 so I would expect that this difference would be even higher with more D5300 frames. On the other hand, whilst not shown in the histograms above, my D5300 does have more 'very hot' pixels than the D7500 ( 579 pixels greater than 400 ADU -v- 10 pixels greater than 400 ADU ). However, these hot pixels are very easily removed via dithering during tracking and sigma clipping when integrating. The very large number of warm pixels however are very difficult to remove as dithering just places different warm pixels on top of each other. I went back and examined the 'random' noise seen in the individual D7500 dark frames ... and yes they do look random when seen individually, however, when flicking between a number of frames it is clear that the 'random' pattern is repeated in each frame! Conclusion: My D7500 has very significant thermal pattern noise, albeit randomly distributed in a fixed pattern. ............ Next steps (?) - I could use in dark subtraction during calibration to reduce the impact of pattern noise - however, as my camera is not cooled and the night's temperatures are constantly changing, any master dark will not closely align to the actual thermal pattern noise and as such dark subtraction may help but will not solve the problem - Using in-camera dark subtraction ( Nikon's long exposure noise reduction feature ) would almost completely remove the pattern noise from each frame. However, due to the extra random noise being introduced by subtracting another noisy dark frame from each light frame, as well as the reduction in total light frames by 2, the resultant images will suffer from higher levels of random noise. So whilst this would be an improvement with respect to the pattern noise, it is not a complete solution. - Third option, sell the D7500 and go back to using the D5300 ...
  3. Hi, I have a Canon EOS 1000d, which I modded back at the start of the year. I usually capture subs of about 3-5mins duration at ISO 800. However, I'm wanting to image the Deer Lick group with Stephan's Quintet, and I'm going to need to go right the way to 5 min subs for them. I've noticed quite high noise levels at ISO 800, is this the optimal speed to use? Would it be better to capture subs at ISO 400, or would they then be really underexposed? Would I be better doing 3 min subs at ISO 1600? I find ISO a little bit confusing, as far as I know it's a measure of how the camera's computer assigns brightness from the raw pixel values? Thanks for looking! John
  4. Hi - it used to be the case that astrophotographers using DSLRs generally preferred Canon technology to Nikon because of the lower noise Canon sensors. However benchmark tests with organisations like DSomark.com seem to favour many Nikon cameras over Canon and in some of the tests I've seen certainly some of the full frame Nikons appear to deliver images with a lot less noise. If we are focussed on recovering detail in the shadows in post production, much the same as "daylight" photographers, then is Nikon now leading Canon or are there other factors to take into account. Thanks in anticipation of your help.
  5. Ok, so i had my first run at planetary imaging yesterday evening, which was disappointing to say the least :/ I was trying mars. The setup went smooth, and imaging went ok as well, but the seeing was very bad and especially the heat of the atmosphere was high, which blurred the images to the point that mars' image was not even a sphere (see left image). There are , however, also other probable issues: + Short focal length (800mm) with an 8mm EP, resulting in only medium magnification + problems with focusing the blurred image + missing real astro darkness (24th of june) + days' high was around 28 deg c, although it had cooled down to 22c at imaging time... Have you guys & girls tips on how to improve? The resulting image from stacking 1600 out of 3800 images was a mess, but at least spherical
  6. I have completed a comparison of the level and pattern of read noise in bias frames between the Nikon D7500 and the D5300, please see the blog page ...
  7. pixelsaurus


    From the album: Pix pix

    Horizontal banding generated by a Pentax *istDS @ISO3200 at 30s exposure. This is a jpg from the original PEF with no corrections.
  8. Below is a comparison between single dark frames taken with the Nikon D7500 and D5300 with exposure durations varying from 1 sec to 240 sec ( my usual main light frame exposure ) all at ISO400. Firstly a graph of the standard deviation of the noise in the dark frames versus exposure time: The standard deviation of the noise is a fairly constant 2 ADU less for the D7500 compared to the D5300 ( pretty much the difference in the read noise between the two ) However, the difference is not just in absolute terms but also in the quality of the noise ... Below are the dark frames - ranging from 240 sec exposures at the top to 1 sec at the bottom: D7500 D5300 The D5300 dark frames clearly show the pattern in the read noise ( banding down the bottom ) and also have far more chrominance noise compared to the D7500. At 240 seconds ( the main exposure I have been using ) the difference is starkly different; the D7500 produces images with much lower noise that is significantly more even and random and hence more likely to be reduced during integration.
  9. Hallo! I have written earlier about using dithering technic instead of traditional dark and bias calibration. I have updated my tutorial with a calculation of the noise from Dark/Bias vs Dithering calibration: http://astrofriend.eu/astronomy/tutorials/tutorial-dithering/tutorial-dithering.html#part06 Of course it's simplified but still show you what to expect, it depend very much on the camera and your site's darkness. This is a way to reduce the static pattern (column defects, hot pixel etc) in image. I hope you find it interesting! /Lars
  10. The Nikon D5300 has a well-earned reputation as one of the lowest noise DSLR cameras used for Astrophotography. Now that I have a new Nikon D7500, I was keen to see how it compared to the D5300 in terms of the level of read noise and the extent to which that read noise is non-random ( and thus needs to be removed using a Master Bias frame to prevent it summing up during image integration). So here goes ... ......... A single bias frame Nikon D5300: ISO400, 1/4000th second: This may look pretty bad but really the extreme stretch is bringing out the very small variations across the frame: Standard Deviation: 3.53 ADU ( note: in this context, 3.53 ADU means 3.53 "units" on a real number scale ranging from 0 to 16,383 ( ie. a real conversion of a 14 bit digital scale )) The master bias frame looks like this: Nikon D5300: ISO400, 1000 x 1/4000th sec frames Standard deviation: 0.48 ADU The bands at the bottom are each 1 ADU brighter than the one above. Now for the D7500 ... A single bias frame from the Nikon D7500: ISO400, 1/4000th second: It is immediately clear that the single bias frame is cleaner. The statistics confirm this: Standard Deviation: 1.37 ADU And the master bias ... Nikon D7500: ISO400, 1000 x 1/4000th sec frame Standard deviation: 0.07 ADU The band at the bottom is 1 ADU brighter than the background. The improvement is very obvious Std. Deviation single bias frame: 1.37 versus 3.53 Std. Deviation master bias ( 1000 frames ): 0.07 versus 0.48 In graphical form ... Conclusion: The read noise in a single frame from the D7500 is around 40% of that in one from the D5300. This should give me greater flexibility to reduce exposure times and still ensure that the read noise is only an insignificant component of the overall noise. I will need to consider further the impact of the very low level of pattern noise in the Master Bias; it is so low that I will think about whether or not I still need to calibrate my lights with a Master Bias ( particularly for long exposures when the noise is dominated by light pollution and thermal noise ).
  11. My setup: Telescope: Skywatcher ED80 Camera: Modified 700D Guiding: QHY5L-ii m + finderscope Image Capture: Astrophotography tool Processing: DSS + PS or Pixinsight Filters: Astronomik CLS clip on Over the last week I managed to get two nights with the telescope, both of which were spent capturing the iris nebula. On the first night I got about 1.5 hours and on the second night I managed a whopping 7.5 hours. I give thanks to the recently purchased 700d AC power adapter for that long stint. I live in a relatively light polluted area, but I can still manage to see the milky way on a clear night. Now, I usually image relatively easy images ... orions nebula, horsehead nebula, rosette, heart and soul, using the above setup as well as with the canon 200mm lens. The iris nebula on the other hand I wouldn't consider as easy a subject as the rest, given my FOV and the fact that most of the interesting artefacts around the nebula consist of VERY FAINT dust lanes. In any case, I decided I wanted to take the leap and just go for it. A concern of mine was the colour of the stars; I wanted to make sure that I didn't clip any of them, and so I decided to expose my subs to accommodate this, which lead me to 240s subframes at ISO1600, dithered. This is what the histogram looked like for one sub: And this is what a single sub looked like without any processing/calibration: The stars seemed sharp enough and I had both the Iris in view as well as the ghost nebula (just about) keeping it company. My train of thought has always been that even if a single sub doesn't show the detail I'm after, stack enough of them and it'll soon appear. I went ahead and captured the images, got the corresponding flats, darks and bias frames and then ultimately started to process the images. This is what the histogram looks like in PI before and after I apply the DEFAULT screentransferfunction curve: And this is what the image looks like, without any post-processing other than Automatic Background Extraction and a 180 deg fast rotation: There are a number of things that concern me about this image. The colour motle/noise what ever you want to call it. There are blotches everywhere. The level of luminance noise which for 8+hours worth is simply disappointing. The lack of detail in the dust lanes. I come back to the title of this thread: Where did I go wrong? I apologise for the length of this post, I was just trying to be thorough.
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