CentaurusA mono with QHY9

[Hagar (Doug)]

Here is the latest quickie. Centaurus A 5 X 5 minute images taken at 4X4 binning as an experiment.
Binning is suppose to make the camera more sensitive but produces a lower resolution. This exercise would make the pixels 21.6 X 21.6 microns. I am reasonably happy with the results and can see some uses for this in the future. The biggest problem I have found is I am unable to use my EL sheet for taking flats. They are totally blown out at 0.001sec exposure. I may have to contact EL Australia and see if I can get one with a much lower light output.
Needless to say this image was totally non calibrated so a bit of work in photoshop to correct a few dust motes etc.

Hope you enjoy. Still awaiting filters and very excited with results to date.

This is a full size image at 4 x 4 binning with no cropping what so ever.

[Terry B]

Originally Posted by Hagar

Here is the latest quickie. Centaurus A 5 X 5 minute images taken at 4X4 binning as an experiment.
Binning is suppose to make the camera more sensitive but produces a lower resolution. This exercise would make the pixels 21.6 X 21.6 microns. I am reasonably happy with the results and can see some uses for this in the future. The biggest problem I have found is I am unable to use my EL sheet for taking flats. They are totally blown out at 0.001sec exposure. I may have to contact EL Australia and see if I can get one with a much lower light output.
Needless to say this image was totally non calibrated so a bit of work in photoshop to correct a few dust motes etc.

Hope you enjoy. Still awaiting filters and very excited with results to date.

This is a full size image at 4 x 4 binning with no cropping what so ever.

Try covering the scope with a T-shirt as well to reduce the brightness.
Doe's the camera have a mechanical or an electronic shutter?
If it is mechanical then those very short exposures will not give good flats as the shutter takes a finite time to completely cover the CCD giving uneven illumination.
Great shot of the galaxy.

[Jazza (Jay)]

That's a very beautiful image... I think sometimes this galaxy looks better if you don't try to get the colour!
Jay

[Omaroo (Chris Malikoff)]

Excellent Doug. I've been experimenting with 3x3, which is all the ST-8 will give, and it's fantastic for focussing and, more importantly, for centering the object in-frame. At 3x3 mine gives 27x27 micron pixels - which is getting pretty jaggy using my 820mm f/length scope. Yours still looks nice and smooth.

[renormalised (Carl)]

Nice Cen A there, Doug....I quite like it....not too "busy"

[iceman (Mike)]

Nice effort Doug. When will you start taking flats?

[TrevorW]

It has that classical image look to it

well done

[Hagar (Doug)]

Originally Posted by iceman

Nice effort Doug. When will you start taking flats?

Hi Mike

I have been taking flats for a while now but this camera blows flats out the front of the scope. I actually took a set for this image at 0.001 sec and they were completely saturated at about 47Ke. I have to get some method of reducing the intensity of the EL sheet or another method of taking flats. Back to a tea shirt although this mornings effort with Tea shirt was no better at about 42Ke.
I will work something out which will work. The fix has to be portable so I will keep experimenting. Full well for the QHY9 is 27Ke so I am looking for exposures of around 9,5Ke at an exposure of a second or two to allow for the mechanical shutter lag.

[RB (Andrew)]

Yes I agree with Trevor, it does have a classic look about it. Very nice.
Sorry to hear about the EL panel being too bright for you though.

[Tilt (Michael)]

Thanks for showing us some of the early images you are capturing with this camera, I've been very interested. Was this taken with the Vixen?

Michael

[strongmanmike (Michael)]

Hmm? Centaurus A huh?...you've given me an idea, I haven't imaged that in a while.......

Keep having fun Mr Horrible, you look to be doing so

I assume you won't be imaging at 4X4 bin very often anyway and I also assume that flats wont blow out at bin 1X1..?

Flats

[gregbradley]

Good shot for 4x4. I use 4x4 for focusing but wouldn't use it for imaging. I don't think it gains that much in sensitivity for the amount of loss of resolution. That chip is very sensitive anyway - around 55-60% QE depending on the camera.

As far as flats go I think they are almost not needed with that chip although there is some gain.

As pointed out with a mechanical shutter you need about 3 seconds for a flat exposure.

I use twilight or dawn flats (mostly twilight) with a white T-shirt over the end of the scope and point towards the west. Usually go for 20,000 ADU and around 3 seconds. I take 3 exposures and use average to combine and subtract a bias.

Greg.

[Omaroo (Chris Malikoff)]

Originally Posted by gregbradley

Good shot for 4x4. I use 4x4 for focusing but wouldn't use it for imaging. I don't think it gains that much in sensitivity for the amount of loss of resolution. That chip is very sensitive anyway - around 55-60% QE depending on the camera.

As far as flats go I think they are almost not needed with that chip although there is some gain.

As pointed out with a mechanical shutter you need about 3 seconds for a flat exposure.

I use twilight or dawn flats (mostly twilight) with a white T-shirt over the end of the scope and point towards the west. Usually go for 20,000 ADU and around 3 seconds. I take 3 exposures and use average to combine and subtract a bias.

Greg.

Good advice Greg - thanks for that.

[Hagar (Doug)]

Thanks for the advice Greg. I actually stretched the old tea shirt over the scope this evening and put the EL sheet on top of that and managed some 1 sec flats that don't look too bad but again that was at 1 x 1 binning only. 4 x 4 was still blown out at 0.001 sec.
Tonight I am looking at the same capture using 1 x 1 and the same exposure time to see the diference. Should be an interesting exercise.
Looks like I still have a few items to contend with regarding flats but I will get to the bottom of it eventually. It has to wait until night as it is way to hot in the observatory during the day.

[Terry B]

Originally Posted by Hagar

Thanks for the advice Greg. I actually stretched the old tea shirt over the scope this evening and put the EL sheet on top of that and managed some 1 sec flats that don't look too bad but again that was at 1 x 1 binning only. 4 x 4 was still blown out at 0.001 sec.
Tonight I am looking at the same capture using 1 x 1 and the same exposure time to see the diference. Should be an interesting exercise.
Looks like I still have a few items to contend with regarding flats but I will get to the bottom of it eventually. It has to wait until night as it is way to hot in the observatory during the day.

If you can get a reasonable exposure with the 1x1 binning just use that. Divide the image by 16 and then bin the result 4x4. This will give you the 4x4 flat. For flats this works but not for darks.

[Hagar (Doug)]

Thanks Terry, Sounds like an interesting way to achieve the impossible. I will give it a go as soon as I have sorted 1X1 flats.