CONFRONTO CON IL FILTRO H-ALFA BAADER - Skypoint Srl

More documents

Recommendations

Info

SKYPOINT s.r.l. VIA ZORUTTI (S.S.13) 145/11 CAMPOFORMIDO – UDINE – TEL 0432 652609 FAX 0432 663473 www.skypoint.it e-mail: info@skypoint.it Baader 7 nm H-a with ~ 2.5 OD Blocking Mean ADU 10,022 Thus, even blocking nearly all UV and VISIBLE light with the IR filter, the KAF16803 detector in the CCD was saturated with only a flashlight pointed to the ceiling in these tests. The Astrodon 6 nm FWHM H-a filter rejected all but 332 ADU, whereas the Baader 7 nm filter allowed 10,022 ADU. Thus, the Baader allows a factor of 10022/332 = 30.2 times the amout of NIR light through that the Astrodon filter rejects with this camera and broadband incandescent light source. This, of course, is expected from the spectral scans that show considerably more NIR light leakage from the Baader filter. [Note - there was a dark horizontal band in the Astrodon image above in the original posting. One of the three frams showed this for unknown reasons. The above represents a second FITs file take at the same time. The earlier results showed 365 mean ADU and this showed 332 mean ADU. Thus, this small change is likely within experimental error and does not change any conclusion]. So, what does all this mean for imaging? As most of you know or suspect, attractive H-a images can be taken with a variety filtes from the wide 13 nm Astronomik, the 9 nm Astrodon-Schuler, the 7 nm Baader, the 6 nm Astrodon, the 4.5 nm SBIG/Custom Scientific and the special order Custom Scientific 3 nm. There is no right answer because it depends upon your budget and your objectives for H-a imaging. Greater transmission with the same FWHM increases S/N. Narrower filters with the same transmission increase S/N. Thus, with the above optical performance, you will more likely be looking at subtle differences in contrast with lower level, or background features. With this in mind, we will determine the S/N of several areas of the Eagle Nebula, M16 taken on the same night under idential condtions with the U16M on an RCOS 12.5" RC reflector with the Baader 7 nm and Astrodon 6 nm H-a filters. The S/N was determined in MaxIm, using the following formula (ADU was multipled by the camera gain of 1.2 to convert to e-): S/N = [(signal - background) ] / sqrt [ Signal + background standard deviation^2 ]
SKYPOINT s.r.l. VIA ZORUTTI (S.S.13) 145/11 CAMPOFORMIDO – UDINE – TEL 0432 652609 FAX 0432 663473 www.skypoint.it e-mail: info@skypoint.it The regions shown were taken in areas without stars. The same dark background region was used (not shown). The Baader 7nm H-a filter is on the left and the 6 nm Astrodon H-a filter is on the right. A brighter region next to the Eagle Nebula is analyzed first. Baader S/N = 3.69; Astrodon S/N = 4.10 11% improvement with Astrodon A darker region further away is analyzed next: Baader S/N = 0.92; Astrodon S/N = 1.11 21% improvement with Astrodon. A brighter region with ridge structure inside the nebula resulted in an improvement in S/N with the Astrodon filter of only 4%. This is consistent with the expectations described above. Both filters produce a pleasing image of the Eagle Nebula. The advantages of the narrower filter with slightly higher transmission and much better out-of-band blocking show up in fainter areas and are thus more subtle. Again it really depends upon your goals in astrophotography. Astrodon will continue to make the best off-the-shelf narrowband filters possible for astrophotography, even if they are more expensive. We will not sacrifice blocking, transmission, prevention of halos, or manufacturing consistency for a lower narowband price. For some of you, this is overkill. For others who have spent thousands or even tens of thousands of dollars or Euros on scopes, mounts and cameras, we offer you filters wihtout compromise. In short, as in any other aspect of life, there is "no free lunch".
Page 1 and 2: SKYPOINT s.r.l. VIA ZORUTTI (S.S.13
Page 3 and 4: SKYPOINT s.r.l. VIA ZORUTTI (S.S.13
Page 5: SKYPOINT s.r.l. VIA ZORUTTI (S.S.13

CONFRONTO CON IL FILTRO H-ALFA BAADER - Skypoint Srl

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?