How to use filters (by Ken Rockwell)

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Lumicon filter profiles

The Nii filter (658.4nm) : Astrodon NII -Ha alpha separation

Useful Targets for the H-Beta Filter

Useful Targets For The H-Beta Filter by David Knisely
While the H-Beta is probably one of the less-used nebula filters, the commonly expressed idea that it works only on a handful of objects is not necessarily true. Here is a list of some of the more prominent objects that the H-Beta may be at least somewhat useful on. Some may require larger apertures, but a few have been seen from a dark sky site by just holding the filter up to the unaided eye and looking at the sky. Some of these will also be helped by a narrow-band filter like the Lumicon UHC.

1. IC 434 (HORSEHEAD NEBULA)
2. NGC 1499 (CALIFORNIA NEBULA, naked eye and RFT)
3. M43 (part of the Great Orion Nebula)
4. IC 5146 (COCOON NEBULA in Cygnus)
5. M20 (TRIFID NEBULA, main section)
6. NGC 2327 (diffuse nebula in Monoceros)
7. IC 405 (the FLAMING STAR NEBULA in Auriga)
8. IC 417 (diffuse Nebula in Auriga)
9. IC 1283 (diffuse Nebula in Sagittarius)
10. IC 1318 GAMMA CYGNI NEBULA (diffuse nebula in Cygnus)
11. IC 2177: (Diffuse Nebula, Monoceros)
12. IC 5076 (diffuse nebula, Cygnus)
13. PK64+5.1 "CAMPBELL'S HYDROGEN STAR" Cygnus (PNG 64.7+5.0)
14. Sh2-157a (small round nebula inside larger Sh2-157, Cassiopeia)
15. Sh2-235 (diffuse nebula in Auriga).
16. Sh2-276 "BARNARD'S LOOP" (diffuse nebula in Orion, naked eye)
17. IC 2162 (diffuse nebula in northern Orion)
18 Sh2-254 (diffuse nebula in northern Orion near IC 2162)
19. Sh2-256-7 (diffuse nebula in northern Orion near IC 2162)
20. vdB93 (Gum-1) (diffuse nebula in Monoceros near IC 2177)
21. Lambda Orionis nebular complex (very large, naked-eye)

In addition, a number of the brighter nebulae like NGC 7000 or M42 will respond to H-Beta use for revealing certain specific detail, although other filters may provide a somewhat better view overall.

Baader filter spectrum

Φίλτρα φωτογραφίας στην ψηφιακή εποχή

Η Heliopan  

και η B&W 

παρουσιάζουν τα προϊόντα τους (σε μορφή PDF)

Γιατί επανεστιάζουμε;

όταν τοποθετούμε ένα φίλτρο ή αλλάζουμε κάποιο ήδη υπάρχον ;

Baader Ha 35nm

Baader's new H-alpha CCD passfilter with medium 35nm-wide FWHM bandwidth is ideal for use with interline CCD cameras (although cannot be used on its own for protuberance imaging).
It's an excellent high-contrast deep sky red filter for RGB use, optimised for all interline CCD chips. It allows CCD-contrast images of H II regions (e.g. North America Nebula) and images can be taken even from "light-polluted" areas.
It comes with a non-aging efficient hard coating on a planeoptically polished surface. Ideal for fast optical systems between f/10 and f/2.8.
It will cause NO haloes and NO reflections. According to the spectral analyse (please see the image below) IR is blocked as well.

Star spike

Με φίλτρο μπροστά στον φακό...

Φίλτρα αστερισμών

The Kenko "soften" filter simulates high clouds or light fog, softening the appearance of stars and other bright objects in astronomical photos. By spreading the light of point sources out (see star profile graphs at right), star saturation on a digital imager is reduced, allowing the true colors of the stars to be recorded. 

Many astrophotographers find this aesthetically pleasing as well as useful particularly for wide-field photos where the bright stars of a constellation stand out compared to dimmer stars.
Availability

Transmission Curves of B+W filters

http://www.mediafire.com/?gjnizzlnitt

KOOD INFRARED FILTER

The Kood R72 filter blocks light below 720 nm (hence the name of the filter), and allows near-infrared light through, making it similar to a Kodak Wratten 89B filter.  The R72 filter is very dark, letting only a small amount of visible light through; holding it up to a bright light, you can see a faint deep-red image.
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Τοποθετείται μπροστά στον φακό. 
Διαθέσιμα για κάθε διάμετρο.
72mm διάμετρος/70 ευρώ περίπου στο Ebay

Vs altitude/True color imaging

The influence of Extinction

The term "extinction" means the loss of light in the atmosphere from a beam of starlight. Because the extinction is generally larger at short (blue) wavelengths the effect is much stronger in blue light than in red light. At the zenith the influence is minor but it increases with a decreasing altitude of an object in the sky because at lower altitudes light has to travel through more air (see figure below).

Wavelengths from 400nm to 700nm are transmitted with approximately equal efficiency at the zenith, but as the angle of elevation of an object approaches the horizon, blue transmission is extinguished much more than red. Green extinction is somewhere in between. For "True color" astro imaging this effect have to be taken in account, specially at lower altitudes.


True color imaging

For true color imaging the above mentioned factors have to be taken into account.

Example : We want to make a true color image of an object at 30° altitude.
Example : Which RGB weight is needed for this true color image?

# CCD response is R : G : B = 1,00 : 0,74 : 0,77
# Extinction correction is R : G : B = 1,00 : 1,08 : 1,15 (see graph above)


The total RGB weight for this image will be R : G : B = 1,00 : 0,80 : 0,83

Therefore a set of exposure times could be R : G : B = 60 : 48 : 50 seconds.

81A warming filter

I still use a mild warming filter (81A) on all my NIKON digital cameras since I prefer the look I get, even with the WB adjusted warm.