A bad attack of the pox

[Ian]

I'm surprised you'd need to explain it to some doctors

The eye has two sorts of receptors, known as rods and cones. The cones have a colour capability, the rods intensity only. However, the cones need a minimum amount of illumination to work, and are *much* less sensitive than the rods. In low light, the cones are completely inactive and so we have no perception of colour.

Interestingly, the one colour that can sometimes be visible is green. In a big scope, like the society lightbridge, bright nebulae like the orion nebula can look green. This may well be due to the green sensitive cones coming "on-line" as it were first making it seem green. Most attempts at true colour images of that nebula are rarely green, although that might be in part due to convention. Of all the colours, green response is the greatest...

[Rick]

For a photographer back in the days of film there's an advantage to having the IR out-of-focus at the film plane. Consider the effects of taking a setting-sun photograph...

[Carole]

Thanks Ian,

I had been showing the doctor's some of the members imaging and mentioned that I had actually seen things like the Dumbell and Ring nebula but they hadn't appeared in colour as they did in the images. 

These are gynaecologists, so although they get a general training, the eyes are not their best specialty.

Carole

[mickw]

Biting tongue.......................

Beer coming out of nose.......................

[Mac]

Puts a new slant on the ring nebula.........................

[Ian]

and I was thinking things are looking up...

[MarkS]

Rick,  it looks like you were correct.  The CLS filter does allow infra-red through.  So a lot of the red around the stars will be long wavelength red and maybe infra-red as well not coming to focus.  I need to get an IR filter to prevent this.

When I imaged the Dumbbell, the main optical elements in the scope were mirrors so there no differential focusing.

Ian, you're right about IR passing through the RGB elements of the Bayer matrix - Christain Buil has some interesting response curves here: http://www.astrosurf.com/~buil/350d/350d.htm   It explains why your DSC IR image is almost monochrome.   

[Ian]

It explains why your DSC IR image is almost monochrome.   

Actually, it doesn't entirely. My D70 has the OEM IR block in place. The interesting palette is mostly down to the fact nearly zero response in blue and green and you really have to be creative with the colour balance (the in-camera colour balance doesn't stand a chance)

I'll probably take the filters down to DSC in August, bright sunlight is best, not least as the IR pass filter cuts more than 4 stops. If you get enough signal in the blue and the green then the most effective colour balance is to make green foliage white (apparently it's as close to a complete reflector of IR you're going to come across in a sheep field in Kent). This PBase photo album is a good example.

What would be fun would be to try my IR pass filter on one of your modded Canons. It would have a much wider response across the who sensor.

[MarkS]

Do a google search for "Boke", there is a view that spherical aberration is good for a camera lens, as long as it's the right way...

Boke - now you risk getting me onto one of my other favorite subjects - point spread functions and deconvolution of de-focused images.  I've written some (buggy) software to do this. 

An example: here's a random picture I found on the internet.  Yes, that's Beckham in the foreground, but who are those England supporters in the background?



Deconvolution provides the answer:



The same technique works remarkably well on planetary images   

[Ian]

that's impressive Mark. So how does your program differ from other methods of deconvolution? (I'm prepared to not understand the answer, but nothing ventured... )