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Lodestar Autoguider

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#1 mmalik

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Posted 01 October 2012 - 04:05 PM

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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#2 mmalik

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Posted 01 October 2012 - 04:17 PM

Sensor of the camera, which looks clean.

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#3 David Pavlich

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Posted 01 October 2012 - 05:29 PM

Probably hot pixels and it's normal.

David

#4 guyroch

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Posted 01 October 2012 - 05:34 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

#5 mmalik

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Posted 01 October 2012 - 06:40 PM

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

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#6 mmalik

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Posted 01 October 2012 - 06:57 PM

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

#7 Alex McConahay

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Posted 01 October 2012 - 07:57 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

#8 fetoma

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Posted 01 October 2012 - 08:33 PM

Maybe ask Terry on the SX Yahoo group?

#9 guyroch

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Posted 01 October 2012 - 08:45 PM

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

#10 mmalik

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Posted 01 October 2012 - 09:47 PM

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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#11 nwinston

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Posted 01 October 2012 - 10:01 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.

#12 Nils_Lars

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Posted 01 October 2012 - 10:02 PM

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

#13 guyroch

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Posted 01 October 2012 - 10:16 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

#14 mmalik

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Posted 01 October 2012 - 11:11 PM

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?

#15 guyroch

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Posted 01 October 2012 - 11:30 PM

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

#16 Footbag

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Posted 02 October 2012 - 12:21 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.

#17 mmalik

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Posted 02 October 2012 - 05:32 PM

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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#18 pfile

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Posted 02 October 2012 - 06:17 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.

#19 mmalik

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Posted 02 October 2012 - 07:57 PM

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

#20 guyroch

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Posted 02 October 2012 - 09:39 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

#21 srosenfraz

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Posted 02 October 2012 - 11:17 PM

Mike - you don't want the stars to be sharp pinpoints - Phd can guide more accurately if the stars are a bit out of focus. Bu having the image out of focus, the light from a star is spread over many pixels. Phd uses this information to more accurately calculate the center of mass of the guide star. This allows Phd to do sub-pixel accuracy guiding. This is also why its not an issue if the guide star isn't round - Phd is only calculating the center of mass for the guidestar.

My ONAG guider gives me guidestars that are actually donuts. Even though the guidestar is CLEARLY out of focus, I'm guiding right now at about 1/2 arcsec accuracy (RMS).

As far as the alarming - I'm not sure if this is the problem, but the field you have with M35 could be difficult to isolate a good guide star. Many of the bright stars you might choose for guiding are very close to another bright star (and even some not so bright stars). Is it possible that your alarming is coming from Phd picking up another star wandering into the guide box?

#22 pfile

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Posted 02 October 2012 - 11:39 PM

if that's the case then he can reduce the guide exposure length, or maybe make the search box smaller.

#23 Footbag

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Posted 03 October 2012 - 07:19 AM

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.



This picture really makes me want a Lodestar. I typically have no more then 4 stars in my field.

Until you said you were losing stars, I though maybe it has to do with you specific star selsction. Too bright or too dim, etc... But I had one problem with my SSAG that exhibited behavior like you are seeing. The St-4 cable became unseated from the mount. Everything worked fine until it was time to calibrate. Maybe given the poor connector on the Lodastar, that has something to do with it.

#24 mmalik

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Posted 03 October 2012 - 08:11 AM

Is it possible that your alarming is coming from PHD picking up another star wandering into the guide box?


Scott, you may be right; will try another test soon on a different target.

On a side note, I wanted to ask folks what their thoughts are about SBIG's ST-i monochrome autoguider; has anyone used it? How does ST-i monochrome autoguider compare to Lodestar autoguider?

#25 Alex McConahay

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Posted 03 October 2012 - 08:15 AM

That picture had a lot more stars than I usually get in a field of view in my off axis guider. So, unless you are using a full separate scope, I would not buy a Lodestar based on that picture alone.

I have actually done some studies with Starshooter, Image Source, and Lodestar, and did find the Lodestar pulled in more stars. But the difference was not so great as that picture would lead one to believe.

Alex






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