Gases & Debris

[Gliese 581g]

Newbie Q:

How do you guys achieve the hubble style images? by this I mean capture all the gases and cosmic debris etc, take a nebula for instance as Im sure the images just look B&W to begin with or close to that? Is it software or advanced camera settings, just wondering really.

[rowan46]

I don't image, but I gather its some kind of witchcraft. here is one of the best books around on imaging Books - Making Every Photon Count - Steve Richards I can honestly say that after reading this book I had some idea of whats going on and if a duffer like me can understand it you will have no problem. Its not written for idiots but even so I can understand it.

[rowan46]

sorry wasn't overly helpful. the images are taken by a combination of 3 things money time and skill. the money determines the equipment, then hours are spent taking the photo's and then theres the skill and knowledge required in processing and artistry involved in its composition. techniques in processing are learned from experience and of cours the equipment used deyermines how the pics are taken. Some imagers use 1 shot colour photo''s some use black and white and colour filters then combine, some use narrow band filters to highlight certain areas of a nebula

[ollypenrice]

Except with narrowband images the colours are real and are what the cameras record. Monochrome and colour digital cameras are really the same in that each shoots through red, green and blue filters and from this data a true colour image is calculated by the software. The difference lies in where the filters are placed. In a daytme camera they go over each pixel, one red, one green, another green and a blue in a pattern across the chip. In a mono camera the imager shoots through each full chip filter in turn and then combines the three images (red, green and blue) in the same kind of software that is built into your daytime digital camera. Some astro cameras are also one shot colour.

The secret lies in the exposure time. We use exposures usually between five minutes and twenty and we take many of them and average the results. This greatly enhances the fidelity of what is recorded because many errors are random but the true signal is consistent, so the true signal builds and the errors cancel out. The signal to noise ratio improves dramatically. In order to allow for these long exposures the cameras are usually cooled.

We also measure the errors in our optics and cameras and use instant-ish software to adjust the final picture in the light of the measured defects. These come from camera noise and uneven lighting due to muck and optical defects in our lenses or mirrors.

Sometimes we may apply an extra layer or two from narrowband filters, notably H alpha, to pick up more of the deep red emission spectrum of nebulae.

When we have done all this we meet in threes on the Scottish Highlands and dance round a pot chanting, 'When shall we three meet again, in thunder lightning or in rain...' and that is where the real progress is made.

Olly

[rowan46]

Ha! I knew it be witchcraft