LRGB QUADCOLOR COMPOSIT

 

 

*RGB color, Lab color and LRGB composit

*Drastic reduction of Exposure time by LRGB

 

 

 

 

 

 

 

 

 

 

 


 

 

RGB mode and Lab mode

 

 


 

 

LRGB quadcolor composit method is a new technique to make drastic reduction of exposure time possible, as well as high S/N and high resolution.

 

1) Galaxies, Nebulae

Exposure time ; about 1/4 or more

2) Planets

One good monochrome + poor RGB = Best color image

 

 

 

 

 

 


Concept of LRGB composit

 


The most important point is:
The human's eye is very insensitive to the resolution in coloring data. The resolution of color image is determined by the resolution of the L-image only. This is true either for nebulae and planets.


Drastic Reduction of Exposure Time

In Most CCD camera, the 2x2 or 3x3 binning mode, where the sensitibity is improved in stead for deterioration in resolution, is available. By taking advantage of the binning mode in RGB image, the total exposure time can be reduced without any deterioration of the final LRGB image. This is the first merit of LRGB composite.

Example:

RGB system
without binning

LRGB system
RGB with 3x3 binning
L without binning

Red

9 min

1 min (1/9 of R)

Green

18 min

2 min (1/9 of G)

Blue

27 min

3 min (1/9 of B)

Luminosity

6 min (2/3 of R)

Total Exposure

54 min

12 min (1/4.5)


 

In order improve the final S/N and resolution, extending the L-exposure is most effective.

Example: M101 R=G=B=20 min, L=175 min

 

 

 


 

LRGB image

 

 Further reduction of RGB exposure will be possible

Therefore

The exposure time of RGB image is not dominant
among the total exposure time

 

 


 

 

What is the 'Ideal RGB filters'?

 

1) Ideal RGB filters (broad band)

Very good reproduction of the halftone colors

But low transmission, usually

2) Ideal Dichroic RGB (no gap, sharp cut and

high transmission rate)

No hafltones for objects with line radiations (like planetary nebulae). This is a disadvantage of all dichroic types.

However, if c-line is 500nm,

H-alpha >> pure red
OIII >> blue green -----(c-line)
H-beta >> pure blue ---(b-line)

This will be acceptable: My SBIG set is the case.

3) Worst case of dichroic RGB filters, with a large gap

Some low cost dichroic filters may be this case.

 

 

 

 

My Standard filters

TARGET

CCD

Red

Green

Blue

IR-B

Galaxies

HPC-1

SBIG

SBIG

SBIG

SBIG

Clusters

HPC-1

SBIG

SBIG

SBIG

SBIG

Nebulae

HPC-1

SBIG

SBIG

SBIG

SBIG/
Edmund

Planets

ST-5

KenkoR60
(>600nm)

Kenko
PO-1

Edmund

Edmund

ALL

ST-7

SBIG

SBIG

SBIG

Edmund

1)L images of galaxies and clusters are taken without IR-B.
2)L-images of nebulae and planets are taken with IR-B
3)Thickness of Kenko R60, PO1 and Edmund-B is same (2mm)
L-image is taken with Kenko MC-protector (2mm)
4)IR-B is always used for the ST-7 + C8/C5 system

The charts of various filters

 

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