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Astrophotography and Sketching >> DSLR & Digital Camera Astro Imaging & Processing

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mmalik
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Lodestar Autoguider
      #5450486 - 10/01/12 05:05 PM Attachment (174 downloads)

I just got Lodestar Autoguider... camera; here is 5sec shot via PHD with lens cap on. Are these dead pixels or what? I tried different caps with same result. Shouldn't new camera have zero dead pixels if that's what they are?

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mmalik
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Re: LodeStar Autoguider new [Re: mmalik]
      #5450499 - 10/01/12 05:17 PM Attachment (54 downloads)

Sensor of the camera, which looks clean.

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David PavlichAdministrator
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Re: Lodestar Autoguider new [Re: mmalik]
      #5450614 - 10/01/12 06:29 PM

Probably hot pixels and it's normal.

David


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guyroch
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Re: Lodestar Autoguider new [Re: David Pavlich]
      #5450624 - 10/01/12 06:34 PM

Looks like hot pixels. New or old _all_ sensors have defects. I don;t think I have that many on my lodestar but I always take PHD darks so I wouldn't know.

If you take darks (in PHD) they should disappear.

Guylain


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mmalik
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Re: Lodestar Autoguider new [Re: guyroch]
      #5450716 - 10/01/12 07:40 PM Attachment (105 downloads)

Here is a 5sec dark taken with PHD; looks the same to me.

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mmalik
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Re: Lodestar Autoguider new [Re: guyroch]
      #5450743 - 10/01/12 07:57 PM

Let me take a dark with colder temp at night; will post results. Thx

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Alex McConahay
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Re: Lodestar Autoguider new [Re: mmalik]
      #5450853 - 10/01/12 08:57 PM

It is possible to get chips with nearly no defects. But they cost a whole whole lot more than those found in cameras for regular human beings. Chips are graded as to how many hot pixels and other "defects" they have. We average consumers do not get the top frade.

These hot pixels will not at all affect your guiding because allost any start will be quite a bit more substantial than these pixels.

Alex


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fetoma
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Re: Lodestar Autoguider new [Re: Alex McConahay]
      #5450915 - 10/01/12 09:33 PM

Maybe ask Terry on the SX Yahoo group?

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guyroch
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Re: Lodestar Autoguider new [Re: mmalik]
      #5450931 - 10/01/12 09:45 PM

Quote:

Here is a 5sec dark taken with PHD; looks the same to me.




That's the point. Now let PHD subtract those hot pixels on each frame it takes a frame for guiding. As long as you keep the same exposure length guiding that you did when you took your PHD dark frame PHD will use it and subtract it.

Hope this helps.

Guylain


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mmalik
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Re: Lodestar Autoguider new [Re: guyroch]
      #5451038 - 10/01/12 10:47 PM Attachment (45 downloads)

Quote:

That's the point. Now let PHD subtract those hot pixels on each frame it takes a frame for guiding. As long as you keep the same exposure length guiding that you did when you took your PHD dark frame PHD will use it and subtract it.




I have never taken dark frames when guiding; explain it a bit for me. So I take a dark (of equal length), save it and then load it into PHD before guiding? Or do I just take dark (of equal length) and just start guiding right away? If not saved, is it held in PHD cache somewhere?

Here is a 5sec dark frame I took with relatively cold camera.


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nwinston
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Re: Lodestar Autoguider new [Re: mmalik]
      #5451063 - 10/01/12 11:01 PM

To take a dark frame in PHD, all you need to do is put the cap on your guide scope and press the "Take Dark" button in the bottom of the window. Make sure the selected exposure is the one you will be using for guiding. The program will automatically subtract the dark frame from the rest of the exposures.

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Nils_Lars
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Re: Lodestar Autoguider new [Re: nwinston]
      #5451066 - 10/01/12 11:02 PM

You just have to do it before you start "capture"

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guyroch
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Re: Lodestar Autoguider new [Re: Nils_Lars]
      #5451089 - 10/01/12 11:16 PM

like everyone said... it's right there in PHD.

Look in the lower right corner in PHD, there is a button there to take darks. Press on it, put the cap on, and let PHD take a few darks... it takes 5 actually. Then PHD will apply the master dark to each guide frames and the noise / bad pixels will be removed and you'll be left with clean frames to guide with.

Hope this helps,

Guylain


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mmalik
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Re: Lodestar Autoguider new [Re: guyroch]
      #5451182 - 10/02/12 12:11 AM

I know where the button is; I meant do I need to save in PHD and load the dark in PHD or does PHD saves it in cache?

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guyroch
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Re: Lodestar Autoguider new [Re: mmalik]
      #5451207 - 10/02/12 12:30 AM

Quote:

I know where the button is; I meant do I need to save in PHD and load the dark in PHD or does PHD saves it in cache?




LOL. It's saved in PHD's memory. It's good for your active session... or until you change guide exposure length. If you turn PHD off and on again you need to takes your darks again. Fortunately it only takes 5 seconds.

Guylain


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Footbag
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Re: Lodestar Autoguider new [Re: guyroch]
      #5451957 - 10/02/12 01:21 PM

PHD does it all for you. It's easier then you are thinking.

I don't have a Lodestar, but will probably be getting one soon. There may be slightly more hot pixels then I would've expected, but who cares about that. It's a guide camera. The sensitivity of it may be the reason for more hot pixels.

Like others have said, take the darks in PHD and apply them then point up and you will know whether it's working. You should see at least a few obvious stars.


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mmalik
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Re: Lodestar Autoguider new [Re: Footbag]
      #5452426 - 10/02/12 06:32 PM Attachment (104 downloads)

Thanks everyone for your feedback.

I am using a 4" Orion APO as a guide scope. Below is 1sec light frame I took via PHD through the guide scope (Image is M35). Notice stars a oblong; and I am not sure what's causing it. It all can't be flexure because if you notice all of my darks had oblong hot/dead pixels. Anyway, PHD couldn't guide and kept alarming on decent mid-range stars in this field. I made sure I wasn't guiding on too bright or too dim stars. Long story short, first real test of this camera with this particular setup has been a failure.

I do feel this particular camera has these oblong shaped hot/dead pixels which is odd; I would have expected some but not all defects to be oblong. Also notice, the image is hazy; I never could bring stars to crisper focus besides being oblong. Your suggestions/solutions are welcome before I send it back. Thanks again for all the help!

Note: I have done quite a bit of guiding with this setup via SSAG 1.5 MP and never had a problem; stars have been crisp and round, although Lodestar shows more stars in a given field given the sensitivity/spec difference.

Note: I have brightened image a bit for better visualization.


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pfile
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Re: Lodestar Autoguider new [Re: mmalik]
      #5452503 - 10/02/12 07:17 PM

a short exposure should not really be subject to flexure problems, and anyway, differential flexure does not even enter the picture here unless you were guiding with the main scope and imaging through the guide scope. so the star shape is most likely caused by your camera not being square with the optics, or maybe just poor optics.

PhD should have no problem at all guiding on that image. guide stars do not even have to be round or even particularly well focused for PhD to work properly. you should see the star images coming off of my OAG right now - they look like seagulls.

PhD is probably mad about the star mass, or perhaps saturated stars. although saturated stars seem unlikely with the 16-bit resolution of this camera. unless you tell us the error, we can't help.

if you don't like the lodestar, send it to me because there's nothing wrong with it.


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mmalik
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Re: Lodestar Autoguider new [Re: pfile]
      #5452637 - 10/02/12 08:57 PM

No error; PHD just keeps losing track of the star with usual alarm/sound output.

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guyroch
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Re: Lodestar Autoguider new [Re: mmalik]
      #5452799 - 10/02/12 10:39 PM

This is almost always the case of a low SNR. Can you please provide a print screen of your PHD when this occurs. I'm curious to see the guide frame luminosity as a whole. You might be guiding to long or to short combined with the slider that changes the luminosity in PHD.

Guylain


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