Jump to content

Narrowband

MikeODay

Members
  • Posts

    1,388
  • Joined

  • Last visited

  • Days Won

    2

MikeODay last won the day on May 27 2018

MikeODay had the most liked content!

Reputation

1,566 Excellent

3 Followers

Contact Methods

  • Website URL
    www.flickr.com/photos/mike-oday

Profile Information

  • Gender
    Male
  • Location
    Blue Mountains, Australia

Recent Profile Visitors

7,688 profile views
  1. Yes you do need to send a few sets of measurements for the MPC to check and make sure your measurements are within certain bounds. Once they qualify you they issue the code. The code to use for the qualifying sets is XXX.
  2. Thanks! Although I'm pretty sure that the Pan-STARRS guys don't pay too much attention to the likes of me with my little setup - now if I find a comet one day, that might be different
  3. Back in March I was granted an observatory code ( Q69 ) by the Minor Planet Center ( MPC ) and since then I have been spending all my available telescope time ( which due the weather has admittedly not been very much ) to capturing images of asteroids, that the MPC is interested in recieving data for, and sending in the positions that I have determined. Mostly I have been focused on asteroids that have not been observed/reported on during their current return to visibility. 2014 LA21 was my first after getting my code ... Here I was the first to report astrometry for 2014 LA21 since 2016 - not like discovering a new comet I imagine but still, a small achievement and a nice feeling You may have noticed that I don't as yet supply any brightness data; this is because I have not figured out how I can do this reliably ( most of the asteroids I am chasing are very dim and so my 4 minute exposures tend to spread them a little making them hard to compare to nearby stars ). I have been getting reasonably good position data though, with a "variation to average path" across the samples of sub 1 arcsec ( typically less than 0.5 and sometimes down as low 0.15 ) .... Anyway, I was just thought I would let people know what I have been up to and why you have not seem me latley over on deep sky imaging forum and also, I was wondering if there is anyone else here on Stargazerslounge doing the same thing ...
  4. The great Barred Spiral Galaxy ( NGC 1365 ) in the constellation Fornax ( details and access to full size image here ) A Cluster of Pearls in the Southern Skies ( NGC 3766 " The Pearl Cluster" ) ( details and access to full size image here ) A deep look at Omega Centauri ( NGC 5139 ) ( details and access to full size image here ) The Cat's Paw Nebula ( NGC 6334 ) in Scorpius ( details and access to full size image here ) ............................................... And my favourite for the year ... Carina Nebula in HDR and full colour ( NGC 3372 ) ( details and access to full size image here )
  5. I'm in the shed capturing some more subs of Eta Carinae and there is a moquito in here with me - I can hear it but I can't see the little blighter; I'm sure it's going to get me  :eek:

  6. The Great Barred Spiral Galaxy in Fornax ( NGC 1365 ) ( image details here ) The Silver Coin or Sculptor Galaxy ( NGC 253 ) ( image details here ) A Peculiar Galaxy in Centaurus, Centaurus A ( NGC 5128 ) ( image details here ) A Million Stars in the Deep South, The Omega Centauri Cluster ( NGC 5139 ) ( image details here ) ( a version of this image was selected as NASA's APOD for 11th July 2017 ) The Fighting Dragons of Ara ( NGC 6188 ) ( image details here )
  7. Hi Mark please see below links to single dark frames: 5300, 240sec, ISO250 : https://www.dropbox.com/s/fu27b1tx5wbu00c/D5300_dark_240s_250iso__030.nef?dl=0 7500, 240sec, ISO400: https://www.dropbox.com/s/cymscuakzpcu9mp/D7500_240s_400iso__0030.nef?dl=0 Cheers Mike
  8. I have taken the master darks, added an offset, subtracted the master bias files, scaled the gains so that the D7500 @ 400ISO is roughly equiavlent to the D5300 at 250ISO, and shifted them so that the medians line up with the following results. Master Darks ( 100% crops of the centre, identical screen transfer function applied via histogram tool ) D5300: D7500: Histograms @ 1x vertical scale: D5300: D7500: Histograms at 23x vertical scale: D5300: D7500: I have positioned the the tab marks at the bottom of the histograms to encompass 99% of pixels in the relevant master dark. That is, 99% of pixels are in the range: D5300 : -8 to + 16 D7500: -4 to + 97 So, I guess I might say that ( in the range ~ -8 to 8 about the median) the D5300 has more cool and slightly warm pixels than the D7500 but the D500 has way more very warm and hot pixels. For example, in the inital examination ( from the initial post above ) the D5300 had ‘only’ 6000 pixels above 44 whereas the D7500 had 140,000 above 44. ( note that whilst subtracting the bias from the offset D5300 master dark did make a difference, the difference was not as large as I anticipated in a previous post ).
  9. Mark, Perhaps it would be more appropriate to add an offset to the master darks before I subtract the bias frames so as to prevent clipping - would that be a better representation of the non-random signal in the master darks that is due to fixed pattern variations in the thermal response of the pixels across the sensor ( what I have been calling “thermal pattern noise”)? What do you think? Cheers Mike
  10. Hey Mark The problem I have is that with an un-cooled camera, quickly changing night time temperatures and no on-sensor temperature sensor it is practically impossible for me to accurately match darks. So, ideally, I want a camera with very low thermal pattern noise ( as opposed to true random noise that I can reduce somewhat with more subs ). My thinking was that the calibrated master darks show that both cameras have thermal pattern noise but I thought they indicated that the level of that signal in the D5300 is much less (?). So I do not really understand your comment that “ Your bias subtracted darks are an anomaly because of the large number of clipped values”. I thought that the histogram of the bias calibrated master darks shows the uncorrected pattern noise that will be present in the bias corrected lights. That is, in my current workflow, I have not found it necessary to use a master dark with the D5300. So I thought that the bias corrected darks indicate how much worse off I will be if use a D7500 without using a master dark. I guess another way of looking at is this... The D7500 has an almost constant value across the sensor in the master bias frame ( with only a couple of ADU variation along the bottom edge ). So, subtracting the master bias ( other than shifting the peak ) has very little impact on the master dark. However, the D5300 master bias has significant variation of values ( ie. a significant pattern in the bias frame ) and subtracting this from the master dark has significant impact. That is, the histogram of the D5300 master dark is made up of a significant ( mostly temperature independent ) bias component + the temperature dependent thermal pattern noise. Subtracting the master bias leaves a relatively small thermal pattern component. Whereas, the histogram of the D7500 master dark is essentially all thermal pattern noise. That is why I thought the calibrated master darks were a good indication of the relative levels of thermal pattern noise in the two sensors. But I guess I am only focused in my analysis on the fixed position signals showing up in the bias and dark frames ( the former because I can simply remove them and the latter because I can’t ). What do you think, is my approach sound or is there a better way of trying to determine which sensor will have the greater problem with patterns in the thermal noise signals? Thanks Mike
  11. Ok some more histograms ... unfortunately I think I might have deleted some of the files so I these are at different ISO values ( 250 for the D5300, 400 for the D7500 ) These have not been bias corrected. D5300: D7500: D5300: D7500: Note that a significant portion of the left hand part of the histogram for the D5300 is due to bias and is removed by subtracting the master bias ( refer histogram in original post ). This is not so much the case with the D7500. The D7500 histogram clearly shows the very large number of ‘warm pixels’ that, whilst randomly distributed across the sensor, are in fixed positions in each frame and result in significant ‘pattern noise’.
  12. Thank you for your reply Mark. I was focused on trying to determine the extent of the differences in the pattern noise and this is why I was looking at the relatively brighter portions of the master darks. I have been less concerned with the true random noise in each sub as I can deal with this by taking more subs but the pattern in that noise is far more difficult to address. I will dig out and post a different view of the histogram with a lower zoom of the Y axis.
  13. I read somewhere that the D7500 uses a two stage amplifier from around 400iso up. In order to see if this was playing a part I repeated the test at 250iso. The result was essentially the same - at around 20deg C, the D5300 has much less thermal pattern noise than the D7500.
×
×
  • 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.