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Dave 2112

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Posts posted by Dave 2112

  1. I also have the same set up, and like Steve says playing with the settings should get you an image. I used these settings for this Saturn pic a couple of nights ago...

    [Video Camera ]

    Frame Divisor=1

    Resolution=960x720

    Frame Rate (fps)=7.50

    Colour Space / Compression=YUY2

    Exposure=-2

    Brightness=98

    Contrast=38

    Hue=0

    Saturation=53

    Sharpness=0

    Gamma=180

    WhiteBalance=5423

    BacklightCompensation=0

    Gain=0

    saturn

    • Like 2
  2. A first view of Saturn coinciding with getting a decent alignment and getting lucky with the setting in Sharpcap, ran 6 minutes of film through AutoStakker2 and came up with this...

    saturn

    The Sharpcap avi was very watchable, although Saturn seemed to ripple and bounce around. The "how to" AutoStakker2 guide was straightforward and it seemed easy to use. Two great pieces of free software, if I ever meet the people behind them I'd buy them a pint.

  3. I use a BST 8mm for planetary in my 200p, I like it and it works well with a 2 x barlow but the only thing I have to compare it to is the original 10mm that came with the scope. The BST was a big improvement, can't say if it would be worth getting though if you already have a celestron 8mm.

    I might end up ditching the BST when my TV 7mm arrives though!

  4. Is it astronomy instructions in general that are rubbish or just skywatcher?

    I had the same issue with instructions for the 200p, they were junk and I used youtube and Sky at Night guides to set it up. The other thing was it just seems a bit of a bodge job in places...fitting motors shows how the hole for the RA cable is off centre and its a pain to connect and remove. Thinking about it, the PA scope arrived damaged, the cover for it was broken and yes they were replaced a week later but the whole "new scope" experience was a bit rubbish. Then you realise how bad the standard eyepieces are and end up thinking it might have been a less than brilliant purchase.

  5. I got a screw in adapter from ebay with the IR filter, most for the easy of simply screwing it in and not messing about with glue and cutting bits of pipe. Which makes me sound lazy, but so what, I am.

    It works great, I can't say how it compares to the standard xbox IR filter but for making life easy it was worth the tenner or so it cost. Its never going to be Hubble standard, but its a £3 webcam, seems pointless stressing about how good the IR filter is or isn't.

  6. Here's a still from an attempt at Jupiter, done before I had the motors running but I liked how it drifted across the frame and 3 of the moons are visible in the full avi (which I can't convert to anything I can post on here)

    Jup still

    Sharcap settings were:

    [Video Camera ]

    Frame Divisor=1

    Resolution=960x720

    Frame Rate (fps)=7.50

    Colour Space / Compression=MJPG

    Exposure=-4

    Brightness=50

    Contrast=18

    Hue=0

    Saturation=25

    Sharpness=0

    Gamma=229

    WhiteBalance=5511

    BacklightCompensation=0

    Gain=0

    Seeing wasn't anywhere near ideal and jup was quite bright, but I was happy to have got the xbox cam modded, working, and to have finally got an image. I spent the night playing with all the sliders, so long as the gain is 0 seems you can play with all the others and still see something.

  7. This is how I understand ISO in relation to digital sensors specifically in the world of astro. This is my own interpretation and is subject to misunderstanding on my behalf. A lot of assumptions here and trying to explain in layman's terms.

    To make things simple lets assume that we have a 1x1 pixel sensor.

    Assume the sensor is sensitive enough to detect each and every photon that hits it which in turn increases the stored charge/voltage by 1uV (microvolt). The sensor saturates at 3 volts so it can cope with 3V/1uV = 3,000,000 photons hitting it before it is fully saturated.

    Assume that exposing for 1 second on a faint nebula produces 1 photon, 100,000 photons for a magnitude 2 star and exposing on the sun for 1/8000th of a second produces 3,000,000 photons.

    Assume that the ADC (analog to digital converter) in the sensor is 14-bits wide (16384 steps). The ADC runs from 3 Volts and can detect voltages from 0 to 3 Volts so the resolution for each individual ADC bit is 3V / 16384 = 183uV.

    As you can see trying to fit 3 million discrete values from the sensor into 16384 discrete steps in the ADC is a struggle, something is going to get lost/clipped. What we can see is that the dynamic range we are trying to capture is immensely larger than what can actually be captured by the ADC. E.g. a bright star will saturate the ADC long before the faint bits of wispy nebulae are even registered.

    At base ISO (ISO100 for Canon), there is no gain applied to the input of the ADC. So if 75 photons hit the sensor during exposure, it will produce a voltage of 75uV. Once digitised this will produce a value of 75uV/183uV = zero, however:

    At ISO200, a 2x gain is applied to the input of the ADC, now the same exposure time as above will produce a digitised value of 150uV/183uV which is still zero.

    At ISO400, a 4x gain is applied, now the digitised value is 300uV/183uV = 1

    At ISO800, an 8x gain is applied, now the digitised value is 600uV/183uV = 3

    At ISO1600, a 16x gain is applied, now the digitised value is 1200uV/183uV = 6

    What a higher ISO is doing is allowing us to get more out of the sensor near the bottom end of the histogram/noise floor, this is especially useful when using short exposures, however it is not all good:

    Each gain step adds more noise to the input signal, however this can be reduced by averaging/stacking multiple exposures.

    On most modern Digital SLRs, ISO values higher than 1600 produce unacceptable levels of noise (tantamount to digital zoom) so it is not recommended, though that may change in future sensors.

    What is important is to get away from the left hand side of the histogram, not too far that you are unnecessarily clipping the highlights, but far enough that you are collecting the data that is near to the noise floor which contains the subtle data that you are actually after.

    In the ideal world, base ISO (ISO100) and long enough exposures would be the best option, however there is noise introduced by having very long exposures so in practice, you want to use the ISO setting for your camera which produces the least noise for the shortest exposure time to achieve a correct histogram. Each camera model is slightly different so for example a Canon 7D may be best at ISO640. If it is possible to do long enough exposures without trailing then use the "ideal" ISO value for your camera, if you can't then use a higher ISO to ensure you are capturing the data.

    In conclusion, I'd say that strictly speaking the sensitivity of the sensor itself is not changed with ISO, however the value presented by the sensor to the outside world i.e. the ADC converter is. I am aware that newer sensors have ADC's on chip, but the same still principle applies.

    If that's layman's terms I think I need the Ladybird book version.

    I can see a few nights of pressing all the buttons and seeing what comes out again, assuming the sky ever clears up.

  8. Sweet. I'm at the MEN. Got the best seats i've ever had at a Rush gig (and there have been many). In the centre 6th row back from the stage. About 10 feet. I'll be able to see the whites of Geddy's eyes.

    Excellent! Then you should get a view even better than this...

    IMG 1117 small

    And Starnut...man flu is what ladies call pneumonia/TB/rabies or many other very debilitating illness that we men get but struggle through with just a quiet groan.

    • Like 1
  9. Ditto instruction manuals, they could at least update the pictures when they change the mount. After covering the floor in strange looking bits of shiny metal I ended up using Sky at Night articles and youtube to figure out what goes where.

    And this week I am a very happy Rush fan. I got tickets to their Sheffield show for me and a friend who is a music producer, he knows a promoter who works for their record label who is friendly enough with "the Holy Trinity" to have got us on the guest list for the show, upgraded seats and a meet and greet! After momentarily impersonating a 14 year old teenage girl who just met Justin Beiber I did eventually calm down. Roll on May for a different type of star gazing!

    • Like 1
  10. ...I could just remember a few simple things.

    Set up basics...

    Polar alignment is easier if you remember to take the cap off the end. Likewise if you don’t see anything after remembering to take the cap off, remember to swivel the mount so the polar scope is clear.

    Know your equipment...

    Fumble around for the RA control and give it a twist, to find I should have twisted the Dec one.

    Once I get the right control and turn it clockwise, I realise I meant to go anticlockwise.

    With the mount motors running, the occasional correction has me pushing the scope left instead of right. When I pause and think “I want to pan left, so I need to push the right button” I’m holding the control box upside-down.

    Know when to call it a night...

    Condensation on the laptop screen that doesn't wipe off is called ice, that’s when it’s time to go in.

    • Like 1
  11. I also tend to spend more time looking at posts of images that include some detail of the camera and settings used. After spending 2 nights thinking I'd messed up an xbox cam because I couldn't get a view through it, copying setting that someone posted along with one of their pictures helped me get an image and understand the settings a bit more.

    And I don't open links to images either.

  12. Taken from "Turn Left at Orion"

    ...How to clean your lens.

    Step one: Don't do it. Period. No step two required. If you still feel you need to clean your lens, our best recommendation is: don't. If the lens really needs it, the safest answer is still: don't...

    Which made me laugh, but I have of course ignored that advice and cleaned fingerprints off with a spectacle cleaning cloth and the lens was fine. Mind you it was the stock (garbage) eyepiece that came with the scope, I could rub that lens clean with sandpaper, it might even improve the view a little.

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