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Physopto

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Posts posted by Physopto

    Flat Issues - Broken Flat Field Generator?

    in Imaging - Image Processing, Help and Techniques

    Posted

    Hi Vlaiv

    Yes I can see your argument. I always use around 50% FWD for my CCD (QSI 683), ( what QSI recommended I believe). So I aim for around the 25,000e ish. It is a long time since I did any maths/statistics on shot and thermal noise. So I just aim for what seems to work. I would guess it may be different for the various makes of CCD depending on how they work. Things have changed greatly in the last 25 years or so since I did my first degree.

    All I was pointing out is where carastro may have seen or gotten the 33% figure from. I use Maxim DL but have never tried their auto routine so far. I get too little time to waste messing about with experimenting. I beleive in" if it ain't broke, then don't fix it!"

    Derek

    Flat Issues - Broken Flat Field Generator?

    in Imaging - Image Processing, Help and Techniques

    Posted

    Hi Vlaiv

    Yes I can see your argument. I always use around 50% FWD for my CCD (QSI 683), ( what QSI recommended I believe). So I aim for around the 25,000e ish. It is a long time since I did any maths/statistics on shot and thermal noise. So I just aim for what seems to work. I would guess it may be different for the various makes of CCD depending on how they work. Things have changed greatly in the last 25 years or so since I did my first degree.

    All I was pointing out is where carastro may have seen or gotten the 33% figure from. I use Maxim DL but have never tried their auto routine so far. I get too little time to waste messing about with experimenting. I beleive in" if it ain't broke, then don't fix it!"

    Derek

    Flat Issues - Broken Flat Field Generator?

    in Imaging - Image Processing, Help and Techniques

    Posted

    Hi Vlaiv

    Yes I can see your argument. I always use around 50% FWD for my CCD (QSI 683), ( what QSI recommended I believe). So I aim for around the 25,000e ish. It is a long time since I did any maths/statistics on shot and thermal noise. So I just aim for what seems to work. I would guess it may be different for the various makes of CCD depending on how they work. Things have changed greatly in the last 25 years or so since I did my first degree.

    All I was pointing out is where carastro may have seen or gotten the 33% figure from. I use Maxim DL but have never tried their auto routine so far. I get too little time to waste messing about with experimenting. I beleive in" if it ain't broke, then don't fix it!"

    Derek

    • Like 1

    Flat Issues - Broken Flat Field Generator?

    in Imaging - Image Processing, Help and Techniques

    Posted

    4 hours ago, vlaiv said:

    Here flats are quite ok as far as saturation is concerned. Not sure where 1/3 rule came from - I've heard it before, but I don't think it is a good rule (unless someone can explain exactly why it is used). Aim at 80% or so histogram is better option. In fact any histogram value is good as long as you don't have low or high clipping. Higher histogram peak value only ensures that you have good SNR for your flats and that you won't be polluting your lights with noise much.

    This is part of a page from the Maxim DL manual

    Sky Flats Assistant MaximDL Application

    This app for use with MaximDL allows the user to take a series of sky flats while automatically compensating for the changing sky brightness. It is also useful for users with light boxes since the exposure duration will need to be adjusted 

    There is some common setup between the two modes - you need to enter the initial, min and max exposure durations, the target ADU level and error range

    The initial exposure duration should be chosen to be reasonable for the desired target ADU count – this reduces the iterations required to get to the starting level. It doesn’t need to be accurate though, the app will iterate to get to the correct value.

    The target ADU selected should be about 33%  of the saturation level of your camera. This will give the most accurate and noise free raw flats which will result in the best master flat once stacked. Going too high can result in pixels outside the linear range of the CCD and too low can result in poor signal-to-noise in the flat. The allowable error percentage allows you to control how close to the target ADU count the flats must be - exposures outside this range will not be saved, rather a new exposure time will be calculated and the exposure retaken. Making this too restrictive may result in a lot of exposures being thrown away.

    The ideal target number of flats somewhat depends on the noise characteristics of your CCD, but after stacking about 10 flats the signal-to-noise ratio in the flat drops to a level which will generally be insignificant once applied to the light image.

    Flat Issues - Broken Flat Field Generator?

    in Imaging - Image Processing, Help and Techniques

    Posted · Edited by Physopto

    I have the same Gerd Neumann flat field generator. I have never tried altering the voltage as I suspect it is better to use neutral density filters with it. I use 2x filter sheets (2 off) and vary the timing of the exposure. It can also be done with a white t shirt but again I don't think it is the best method. Just my opinion! You could try this anyway.

    # Best of luck

    Derek

    Galloway Spring (February) 2020 Star Camp

    in Star Parties & Astro Events

    Posted

    I have just finished talking to Lesley on the phone. She has agreed that there is no objections setting up tents on the hard standing/field edge.

    Cars can be parked around the back of the house in the storage area if need be to allow motor homes parking on the hard standing area.

    Obviously this is all dependent on the field being overly sodden come the Star Party start as no vehicles will be allowed on the grass if it is that bad. BUT it is still some way off as yet and the weather could improve with luck.

     

     

    So as of the present information known even if the field is very wet -------- 

    The 2020 Spring Galloway Star Party is a GO.

    I hope that this is welcome news for all attending and/or for those awaiting more news on what is happening.

    Please book at, your earliest convenience to avoid any disappointments.

    So hoping for good clear skies.

    😂Rain dancers will be shot!😂

    Hoping to see regular and new attendees.

    Derek

     

    • Like 4
    • Haha 1

    Galloway Autumn Star Camp 2020

    in Star Parties & Astro Events

    Posted · Edited by Physopto

    More the merrier 🔭🔭🔭🔭🔭🔭🔭

    I am sure that Lisa will enjoy the atmosphere and company.

    I will be talking to Lesley, probably tomorrow. I was supposed to today but things happen! So hopefully I can find out a wee bit more information to share with everyone tomorrow.

    Derek

    • Like 1
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