Ngc613

[gregbradley]

Carrying on with imaging the available southern galaxies I turned to NGC613. A small object although fairly bright.

This is more a target for a large RC type scope but it turned out OK considering the TEC180mm APO is more suited to wider field type work.

LRGB 50 50 40 50 FLI Microline 8300, Baader filters. From my dark site near Crookwell NSW, taken last week on Friday night.

http://upload.pbase.com/image/118696944

Greg.

[jase (Jason)]

Greg, something is not right with the TEC180/ML8300 combo. Stars look quite bloated. Is the sampling ideal with 5.4u pixels? I think you missed the colour balance on this one, but I do like the details you've obtained in the galaxy. Sorry to sound harsh and don't be offended, but when you've got the goods and not banging out killer work, it best someone tell you how it is instead of quoting great image. Does binning alter the situation? Perhaps to much resulting in undersampled work I suspect. Would like to understand your thoughts behind this as your M20 image posted a while back exhibited the same traits.

Cheers

[gregbradley]

Now you say that looking at the image again they are quite bloated aren't they?

As I mentioned with the Tak TOA extender star sizes were smaller. Perhaps it has something to do with the small wells of the 8300 chip (20,000 electrons whereas the 16803 is 100,000). Some images using the 8300 though have very tight star sizes but I think the small well depth gets overwhelmed easily in a 10 minute sub if there are bright stars in the image. That is probably the key- are there bright stars in the field.

I have a 47 Tuc taken with a FLI Proline form this same trip I will be posting soon. Lets check the difference out with that. Fro what I ahve seen from that shot the stars are very tight. Also with the extender shot the stars were very tight which is good as that means its not the scope!

I did notice star sizes reduced using the Proline compared to the Apogee U16M but I put that down to using the Baaders instead of the Astronomiks. Perhaps not. Different antirefelction coatings on the CCD windows perhaps.

[multiweb (Marc)]

Great shot Greg! Real nice colors and the galaxy details are awesome. Very cool.

[jase (Jason)]

Greg,
Yes, the 8300 does have a small well depth. On your raw fits what are the ADU counts on the stars? Are they indeed reaching this limit resulting in the gate bleeding? I suspect you'd get a much cleaner image with the U16M. The sampling would perhaps be more practical, though there is nothing wrong with oversampled data.

Cheers

[gregbradley]

Originally Posted by multiweb

Great shot Greg! Real nice colors and the galaxy details are awesome. Very cool.

Thanks Marc.

Originally Posted by jase

Greg,
Yes, the 8300 does have a small well depth. On your raw fits what are the ADU counts on the stars? Are they indeed reaching this limit resulting in the gate bleeding? I suspect you'd get a much cleaner image with the U16M. The sampling would perhaps be more practical, though there is nothing wrong with oversampled data.

Cheers

On the brighter stars the ADU is the limit at 65535. I swapped my U16M and now have a brand new Proline 16803. The cameras give 2 different image scales much like having 2 scopes one long focal length and one shorter. The smaller chip is better for close ups and the 16803 for wider field. The 8300 does max out at 65535 more easily and bleeds harder hence the bloated brighter stars. Perhaps shorter subexposures is in order then. Maybe I should use 5 minutes instead of 10 minutes.

[spearo (Frank)]

You're a machine Greg!
look at the number of images you've produced recently and this is a fine example as are all the others
i like the colors in this one
frank

[gregbradley]

Originally Posted by spearo

You're a machine Greg!
look at the number of images you've produced recently and this is a fine example as are all the others
i like the colors in this one
frank

Thanks Frank. I got back to back 3 clear nights last week which is nice and something I haven't gotten for a while.

[Bassnut (Fred)]

I like your image Greg, but this thread has bought up and demonstrated the very interesting topic of well depth. Ive seen excellent images from the 8300 chip (including this one), but ive been wondering about the growing popularity of this chip, given is has a raw dynamic range of some 14 bits (at 20K e), and probably less if its (albiet low) noise is factored in, say 12-13 bit. I see antibloom factors quoted on ABG chips of 100-1000 and the 8300 has the 1000 spec, but Jase mentions the "bleed" of ABG chips that is not often mentioned and this is the 1st time ive seen an analysed example of ABG cam "bleed".

Goes to show one must be carefull in chip selection, and that all is not what it seems based just on price.

I now think this well depth limitation might be quite severe imaging dim nebulae.

[gregbradley]

Originally Posted by Bassnut

I like your image Greg, but this thread has bought up and demonstrated the very interesting topic of well depth. Ive seen excellent images from the 8300 chip (including this one), but ive been wondering about the growing popularity of this chip, given is has a raw dynamic range of some 14 bits (at 20K e), and probably less if its (albiet low) noise is factored in, say 12-13 bit. I see antibloom factors quoted on ABG chips of 100-1000 and the 8300 has the 1000 spec, but Jase mentions the "bleed" of ABG chips that is not often mentioned and this is the 1st time ive seen an analysed example of ABG cam "bleed".

Goes to show one must be carefull in chip selection, and that all is not what it seems based just on price.

I now think this well depth limitation might be quite severe imaging dim nebulae.

Yes it is an interesting factor and one I was aware of when I bought the camera although I wasn't 100% sure what the effect would be. I did assume that only the very brightest stars may bloat and bleed over which is what is happening. But even less than very bright still tend to bloat. I think it may be ok with 5 minute exposures.

I looked through the Kodak catalogue of chips the other day and a lot of their new offerings and ones that have been around for a while have well depths of 20,000. Quite common. The ones with 100,000 plus are only a handful.

It is another factor to take into account when choosing a chip.

It is still a good chip but as you say you have to be aware of its limitations and work around them.

There are some superb images using one with an ASA 16 by Wolfgang that actually show tiny individual stars in the Andromeda Galaxy.
So matching the scope to it also is a must. I imagine large aperture shorter focal length scopes with short exposures (probably suits the ASA with its flexure issues) is the ideal for it.