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Opinions on the QHY5L-II

choochoo_baloo

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lensman57

lensman57

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Here's a TIFF of a dark frame. Gain was 500 with 500ms exposure. The white pixels are consistent between shots. It looks like a star field all by itself!

So are the white pixels stuck, or just due to the low level of excitation or some other factor of having no photons hitting the sensor?

attachicon.gifoaCapture-20140522-195054.tiff

Any help/reassurance greatly appreciated!

These are hot pixels, they exist in the most expensive of CCDs including the military grade ones. They are more prominent in the cmos sensor of an ASI120 or a QHYLii and other cameras, firstly because of the lower grade of these sensors and secondly because these sensors are not cooled. Stacking 500 or more frames as in planetary imaging will help get rid of most of these if not all and also the random noise pattern. This method is very effective, as when imaging planetary with the target bobbing up and down is  similar to employing a very high dithering in long exposure DSO imaging. Problem is more complicated when trying to push the exposure beyond a few seconds while attempting to do " Long exposure" DSO imaging with these cameras. At a 15s exposure the sensor has an unacceptable number of these Hot Pixels, however I have  seen captures of 10s exposures that do not look too bad provided that a large number of these frames have been stacked, under these conditions and with full calibration frames ( Drak, Bias, Flats ) properly applled, will help a great deal to cleaup an image so long as a heavy stretch is not applied during the processing.They are ceratinly capable of imaging small planetary nebulae using a fast enough scope, albeit quite noisy.

If you are good with DIY you can even attempt to install a home made open loop peltier cooling system to bring the noise and the hot pixels under control, I think that this is easier to implement with an ASI 120 ( due to the shape of enclosure ) than a QHY 5Lii, BTW these twocameras have the same sensor.

Regards,

A.G

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mitchelln

mitchelln

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Posted

Thanks for all the replies on this.

Hopefully once I get a decent night (come on Sunday!) I can try it out for real on a planet.

I've posted my dark frame on the QHY forum. Let's see what response I get.

Sent from my GT-N7105 using Tapatalk

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frugal

frugal

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How do you use one of these cameras to successfully guide if there are so many hot pixels? Does the guiding software automatically deduct a dark frame for every guiding frame? That seems like quite a lot of processing for something that needs to be done a couple of times a second.

Sent from my SM-P900 using Tapatalk

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Pete Presland

Pete Presland

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How do you use one of these cameras to successfully guide if there are so many hot pixels? Does the guiding software automatically deduct a dark frame for every guiding frame? That seems like quite a lot of processing for something that needs to be done a couple of times a second.

Sent from my SM-P900 using Tapatalk

take a dark frame, before you pick a guide star.

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lensman57

lensman57

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Posted

How do you use one of these cameras to successfully guide if there are so many hot pixels? Does the guiding software automatically deduct a dark frame for every guiding frame? That seems like quite a lot of processing for something that needs to be done a couple of times a second.

Sent from my SM-P900 using Tapatalk

The guiding software such as PHD will apply a mild stretch but the guide star is always brighter and in most cases larger than the hot pixels, defocusing the star a touch always helps.  I have not had any problems with  getting a good guide star using either the ASI 120 MC or MM with my 50mm or 60mm guidescopes for a very long time using a 1s or 1.5s exposure loop so long as the gain and the exposure settings in the camera driver are set correctly.

A.G

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Notty

Notty

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Not sure if this relevant to anyone but just to add to the body of knowledge on this camera I can confirm that for Solar imaging the mono version of this camera gives bad Newton rings on capture.

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lensman57

lensman57

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Not to everybody...

My cam only has one hot pixel and it comes up as a black pixel on a image, so not easy to mistake it for a star.

Don't mistake noise for hot pixel, noise is due to heat.

I think that if the pixel is black then it is a dead pixel, hot pixels are the opposite I believe.

Regards,

A.G

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tingting44

tingting44

Posted
Posted

Here's a TIFF of a dark frame. Gain was 500 with 500ms exposure. The white pixels are consistent between shots. It looks like a star field all by itself!

So are the white pixels stuck, or just due to the low level of excitation or some other factor of having no photons hitting the sensor?

attachicon.gifoaCapture-20140522-195054.tiff

Any help/reassurance greatly appreciated!

Just done a dark frame with my QHY5:-ii (mono) with the same settings as above.....this is surely not good either is it....? :Envy:

14264005385_c1fe895b21_z.jpgQHY5L-ii Dark Frame by tingting44, on Flickr

EDIT> just thought this was the dark frame with the QHY connected to my guide scope with the cap on the guide scope, i should really take the QHY off the guide scope and put the QHY cap on and do a dark frame with it not connected to the guide scope right....?

EDIT> here is the dark frame with the QHY not connected to the guide scope.........still same results?

14077533777_c03780f5fd_z.jpgQHY5L-ii Dark frame (not connected to guide scope) by tingting44, on Flickr

this is really not good is it?

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hobsey

hobsey

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I put mine in the fridge for half an hour to see if that made any difference but it did.

Also tried as the capture programs just to see if it was Sharcap but they are also show the pixals.

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tingting44

tingting44

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might be a faulty batch, not looking good tho is it :( i wouldnt know how its going to effect the final image really tho as ive only guided with it twice so far, i must try it on planetary, going to message bernhard just to keep him in the loop tho...

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mitchelln

mitchelln

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I do wonder why the QHY has so many hot pixels (in the same locations) at whatever temp whilst my £50 Microsoft LifeCam Studio does not.

I've asked QHY what their hot pixel policy is, but have not had a reply yet.

Sent from my GT-N7105 using Tapatalk

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