Colorful stars

Started 2 months ago | Discussions thread
OP hha Contributing Member • Posts: 725
Re: Colorful stars

Tristimulus wrote:

Most older lenses are not very well color corrected.

This lens shows strong red and blue longitudinal chromatic aberration.

The two brightest stars have B-V values around 0.3 and 0.15 so they should be close to white when photographed with a near perfect lens.

The red star at upper right has a B-V value of about 1.6 so this star has a pretty low sufrace temperature and does not emit blue light. Hence no blue fringe.

So the colorful fringes is a result of a poorly corrected lens. Real star colors are subtle and not easy to spot before learning what to look for. Only well corrected optics can reveal the 'true' colors of stars (or produce good spectra).

Your image is more about lens performance than star color.

Tristimulus:

Notice I said "colorful stars" not "star colors". Since we are not doing any science with these pictures, a little color thrown in, even if an artifact of the lens, does not hurt.

You are absolutely right. The brighter stars with a large B-V tend to look red. This is seen not just on this image, but on images with other lenses.

Yes, this 50 year old lens Nikkor 200mm Q f/4 lens, used at f/4. It has only four elements, and was corrected for only two colors, i.e. achromat. With the D7200 APC format is is effectively a 300 mm lens. I have the Nikkor 180mmED f/2.8, and at f/4 it shows similar colors.

The challenge I proposed to the readers is to take a picture of this area, with Vega at the center,  with their own prime lenses in the 180-300 mm range, with enough exposure and stretching  to make V=+15 stars visible, and see the color they are getting. Are any of them apochromats?

Try it, and enjoy the colorful stars.

Cheers,

hha

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Olympus TG-630 iHS Nikon D3200 Nikon D3300 Nikon D7200 Nikon Z6 +4 more
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