Posts Made By: Larry Citro

Here's a lrgb using some old color data

Larry

hi,

Congratulations on the great image.

Larry Citro

hi Eric,

i read your post on on yahoo groups about the blue halos.
One trick i sometmes use is to median filter the rgb componets before combining them. Look at the realtive star sizes in the r,g& b images and they may be unequal, in your case the blue maye have a larger FWHM of the stars. This could be do to focusing, optics, tracking or atomspheric refraction.

Median filter the offending image(s) until the star sizes are equal ie in Maxim the r may require none, the green a 3x3 matric and the blue a 5x5 matrix. You wont lose any resolution when you do the rgb in Maxim.

clear skies,

Larry

hi,

That is a very nice image. Great jpb processing it.

clear skies,

Larry Citro

hi,

First the technical parts must be right. Good guiding, good focus, a well collimated scope with good baffling and so on.

>>>> Composition is very important to make an beautiful astrophotograph. This may requires the right FL for the object being photographed. M31 looks best with short FL instruments and so do open clusters. A cluster surrounded by a rich star field has a lot of interest, while a close up of a cluster can be quite boring. Globular clusters can be done either wide filed or close up high resolution.

Galaxies and planetary nebula generally look better to me with long FL high resolution images. An exception is galaxy groups such as the Leo Trio or others that have several galaxies close together and these are presented in a more interesting fashion with wide field images.

>>>> Processing the images can make or break an astrophotograph. Too often the images are grainy with a low S/N ratio. Noise reduction software helps but even better are long integration times.

The photo should look "natural" and too often they are over sharpened giving them a "computer" look. Try and balance the amount of detail you pull out of the image with a natural overall appearance.

Color balance is important. Astronomical objects do have natural hues such as the teal green in planetary nebulas, the red of H alpha regions and the blues of reflection nebulas and colors in between where they overlap. Most importantly color saturation of astro objects is subtle and too often we oversaturate the colors in the image. This of course is an artistic processing choice but I tend to favor subtle colors.

>>>> Monochrome images such a H alpha and straight lum images can be most interesting. The key here is to present them with a wide latitude of grays and don't make then too back/white with few grays in between, make sure all the shades of gray are there.

I'm sure there are many other things that come into play , but this is my short list.

clear skies,

Larry Citro

hi,

Very nice for sure

clear skies,

Larry Citro

hi,

very nicely done.

I agree with Roland that resolution is not limited to large
aperture scopes. Most sites in the US have an average seeing of about two
arc seconds. Assuming a ST10 camera and 3 pixels per unit of seeing this can be
achieved with a 8" scope ( a 16" scope for 1 arc sec seeing ).
Beyond that larger aperture means you get achieve a higher s/n ratio per unit
time of image accumulation, assuming sky noise limited exposures.

Larry Citro

hi,

Great optics. Outstanding on axis resolution. Tremendous contrast. Mimimal off axis coma.

Larry