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RichLD

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Posts posted by RichLD

  1. 10 hours ago, Spacehead said:

    "human entertainment"
    Yeah - too many chav scum around these days to be in a public place with expensive kit.  This country has gone down the toilet.

    Quite! I don't think the recent spate of good, unseasonal weather helped TBH. I've imaged there a lot before and it's never been that bad!

    4 hours ago, Paul73 said:

    Can’t be many worse places to image!

    I did enjoy your descriptions though. Could be that secluded car parks atract ‘entertaining’ types. I’ve had success with footpaths where you can park in a field entrance and hide behind a hedge only 10 meters from your car. It does require a scoping trip in daylight. Having a couple of options ready is a good idea, as I once turned up to my chosen spot to find that a brightly lit camper van had chosen my spot for the night. Finding another location in the dark proved difficult.

    Paul

    Surprise View used to be an excellent imaging site but I will definitely take your advice - a scoping exercise in Summer could be very enjoyable in its own right!

  2. I managed to get out to my nearest dark site at Surprise View last night for the first time in 2 years for some widefield Orion action. It was not a successful evening - on top of various antisocial "human entertainment",  5 billion lumen headtorches/cycle headlights and a "sheep in wolf's clothing" Corsa that had clearly ram-raided Halfords parking right next to me and leaving the engine running, lights on and blasting out Niche Bassline at high volume, one of my cameras ceased to function and now appears dead - I'm gutted! I managed 50m luminance, 25m Red and 50m HA...?

    So, to the question - has anyone tried Minninglow Car Park, DE4 2PN for imaging/stargazing? If so, how did you find it? Was it better or worse than my description of Surprise View above?

    I'm also open to suggestions of other sites - it would be lovely if there was a stargazing friendly campsite, farmers field or similar to use, I'm willing to pay.

     

    Thanks!

     

    Rich ?

    • Sad 1
  3. On 27/11/2018 at 00:46, michael8554 said:

    The PHD2 developers say about 5 arc mins is good enough for guiding (as measured by Drjft Alignment)

    In fact they recommend a small drift in Dec if you have Dec Backlash, as you can then guide in one direction without having reversals.

    Michael 

     

    +1

  4. 2 minutes ago, Space_Plane said:

    Hi Rich,

    That isn't something i've come across before, i'm fascinated.  I've only used these lenses with a DSLR before, and it was really picky about focus / infinity.  The slightest movement knocked it off.  Due in part to larger sensor then i presume?

    I managed to get out the other day and experiment a bit, and with the adapters I have, was about 41.5 out of 44mm.  The lens would vaguely focus about half way around the focus ring, but it wasn't great.  I wasn't expecting ~2.5mm to make such a difference to the focus.  Look forward to getting different extensions and trying to get it sorted a bit better.

    Cheers

    I use a variety of focal length camera lenses - 55mm (Super Multi Coated Takumar) 135mm (Jupiter 37A) and 180mm (Nikkor ED180) all manual focus with a Canon adapter. Because I'm a bit short in terms of flange to focal plane distance, I tend to find that infinity focus tends to be around 2/3rds of the focus travel.

    I have always had very sharp focus with all the lenses at this 'virtual' infinity mark on a 4/3 sensor (like the KAF8300). It may be worth mentioning that all of these lenses focus externally i.e. the lens changes in physical length when focussed. I wonder if IF lenses react differently to incorrect register distance?

    • Like 1
  5. Could be pinched optics, it might be worth checking the tightness of the primary mirror clips. The mirror should be able to move slightly - when tightening the screws, a lot of people put a little bit of thin card inbetween the clip and the mirror, then remove it to leave a very small gap.

    It may be that the camera picked up the problem but the mk1 eyeball missed it. Always worth checking anyhow.

    • Like 1
  6. To add to my previous post, I use the SGP Framing and Mosaic wizard and Platesolve2. It really is a joy to be able to enter an accurate rotation figure and see exactly what you're going to get. It also makes multi-session imaging and mosaics a breeze! I'm either at 270/90 (long side of chip parallel to the dovetail) or 360/0 degrees. Once I've used the star trail/slewing technique mentioned by Olly I'll do a quick platesolve to be sure I'm dead on.

  7. I have used this very combo and it works very well - you will have back focus to spare as it only adds 5.5mm.

    I prefer to have my chip orthogonal to the RA and Dec axes as I find it makes it easier to plan framing and mosaics.  

    I've now sold my Geoptik adapter and have the very rotator pictured in very good condition for sale. If you're interested drop me a PM ?

    Rich

    • Thanks 1
  8. On 08/11/2018 at 09:05, Whirlwind said:

    I think you might be misunderstanding what dithering is there to do.

    At a basic level there are two types of noise that need to be considered. 

    1) There is a type of fixed noise which may be better described as known errors on the camera.  These are things like hot pixels, cold pixels and so forth, bad columns and so forth.  These stay in the same location all the time.  Darks and bias can partially correct for these but they can accrue charge in a non-linear way which means even with dark/bias correction they can still partially exist (this is particularly relevant for non temperature controlled cameras).  If your tracking is so accurate that the points will always fall on the same point in your image then when you combine them it will reinforce this artefact and you will end up with little bright or dark spots over the image.

    2)  There is random noise.  This comes from that it is statistically impossible to measure something at the highest levels of precision.  If as an example the flux arriving at a pixel is 300 counts then when you image the object you would find that the you get a range of values with greater frequency towards the actual value.  So over five images you may get the following values 295, 298,299, 301, 308.  This is called random or gaussian noise.  It is impossible to predict the exact value you will measure from image to image.  However, it is random and follows a gaussian statistical variation.  As such because some values will be lower and some higher you can median or mean (average) combine such data and the result will trend to the 'real' value of 300.  The more images you take the more you can average out these random fluctuations.  Hence this is why you take multiple images and stack them.  When you process the data you exaggerate this effect as you are trying to pull out the slight variations to the signal (for example in a nebula) that might be very similar to the level of random noise you get.  Hence with too few images averaged then what is real and what is noise becomes confused.  This is what causes the mottling effect.  The more images you take the more you can average out the background noise and the more certain you are as to what is data and what isn't.  Hence when people refer to images being overdone, overcooked this is what is happening.  The details have been over processed to the point that the noise is being processed not 'real' signal. 

    So why dithering?  Well dithering is a random jump of your camera close to the target of interest.  It makes no difference to random noise because it is not based on a specific location.  Wherever you point your camera you will get random noise.  On the other hand the fixed point noise (like hot pixels) are tied to specific pixels, columns and so forth.  As such they will move about your image when your slightly shift (dither) the telescope.  Most software when it combines data will reject any that are hugely discrepant from the average data in your image when tied to a fixed position through star alignment.  So suppose you had a hot pixel that had been dithered once at a specific sky position.  You may get something in counts like this:- 300, 299, 306, 295, 301, 2000.  The software will recognise the last value as discrepant and then ignore that data for that specific pixel and reject it.  If you don't dither you would get something like:- 1999, 1998, 2003, 2007 2003, 2000.  Hence the software won't recognise that this is a hot pixel but consider it a real value and include it on your image.  What you end up with is an image that has scattered single pixel bright spots because of this type of fixed noise.

    As such when noted above that your image looks like dithering is working it is because there doesn't appear to be any single pixels that are overly bright for their location.  The noise you are looking at is random noise which can't be fixed by dithering, only by taking more images and you can never get rid of it completely.  So it becomes a balance as to how much time you want to spend on an object and how much processing you can get away with before the remaining noise becomes distracting.

     

    Brilliantly explained!

  9. 1 hour ago, RayD said:

    Holy cow, Rich.  For OSC and relatively limited data that M42 is insanely good.  Bravo, Sir!

    (M31 isn't so shabby either, mind).

    You're too kind sir, many thanks! Yes, good skies make all the difference with OSC I find - I also suspect that the QHY8L is a good match for the ED80.

    TBH it was a pig to process though ?

  10. I have had great results from OSC but find that dark skies are a must. A bright target like M31 gave me a good return after 10 X 600s using a SW ED80 with its dedicated FF/FR and a QHY8L.

    Not sure how this will work with a fixed mount, unless you're planning high gain 'lucky imaging'.

    I find processing OSC to be just as time consuming as mono, although calibration time is of course reduced due to the lower number of subs.

    HTH

    Rich

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