Prawn HA Widefield

[avandonk]

Here is a HA image of the region around NGC6231. It is 6.85 X 4.5 degrees in area.

Exposures 15 X (120s, 240s and 480s) at 1600ISO. 300mm at f/3.6. fridge at -18C. 13nm Astronomik HA filter.

Large red image 9MB

http://d1355990.i49.quadrahosting.co...6/ngc6231r.jpg

Large B&W inverted image 10MB

http://d1355990.i49.quadrahosting.co...ngc6231bwi.jpg

The dark tower even gets a look in at the top to the right of centre.

Melbourne had a sort of clear night but with the Moon only NB was useful.

I used Logmein to control the laptops in the observatory from inside where it was nice and warm. Logmein works over the internet so when I get a robotic mount I can collect data from anywhere. There is a free version that works very well.

Bert

[multiweb (Marc)]

Nice one Bert. This is on my list todo as soon as the clear weather comes back.

[jjjnettie (Jeanette)]

I nabbed this region earlier this month.
Nice to see the difference a Ha filter makes.
Thanks for posting.

[astroboy]

Nice image Bert
So you call something that brings the temp to -18 a fridge there ? around here it would be called a heater
I don't have broadband so can only see the negative image , impressive though.
One question how do you fit a HA filter to the 5D or is it one that goes into the filter draw in the lens.

Thanks
Zane

[strongmanmike (Michael)]

Hmmm that looks decidedly Phallic to me

Great field

Mike

[avandonk]

Originally Posted by astroboy

Nice image Bert
So you call something that brings the temp to -18 a fridge there ? around here it would be called a heater
I don't have broadband so can only see the negative image , impressive though.
One question how do you fit a HA filter to the 5D or is it one that goes into the filter draw in the lens.

Thanks
Zane

Zane the CMOS chip in my humble opinion is far better than any CCD as far as s/n at the same temperature. The chip in the Canon 5DH is actually 17C hotter than the environment of the camera due to self heating. The cold side of the Peltier is -18C the fridge environment is -12.5C and the Canons CMOS sensor while continuously exposing is at 4.5C. With accurate fridge temperature control and dithering I have very low noise on my stacked images.

I have stuck to using the Canon 5DH as the 300mm F2.8L needs to be connected to a live camera for all the electronics to work for focussing.


By extending the lens hood to limit the amout of sky the lens 'sees' and an 82mm Hutech LPR filter immediately in front of the lens which acts as an aperture and the HA filter in a canon 48mm holder at the rear of the lens only the light that produces the image even enters the lens. Guiding with a 1250mm FL Mak also makes even the very faint stars to be well recorded rather than smeared out into the noise floor.

With wide fields I have found that eliminating ANY light that does not contribute to the image BEFORE it enters the lens increases contrast and hence s/n.

The proof is in the image. Very dim HA detail is quite clear and shows no noise. This is quite amazing as only a quarter of the pixels on the chip are used to produce this image.

It would be very interesting to see what a Canon CMOS chip would do without the Bayer filter array at 40C below ambient.

Below is a 100% crop to show the full resolution.

Bert