bad results 6nm ha astromik filters

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sytzezwei

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Hello
Four years ago I bought 3 Ha filters; a 12 nm and a 6 nm Ha astromik filter, and a 7 nm Baader Ha filter.
Two years later I bought a 6 Ha nm astromik EOS clipfilter.
Now for the first time I have made images through these filters of a color-chart from a Eizo LCD monitor with a Canon 30D and a 50mm lens.

Here is a mosaïc from the images, except for the color-correct one on the left, all images were made with the same exposure time, (0.3 seconds, F2.2, iso640).

The results are very, very remarkble, the 7 nm Baader Ha filter and the 12 nm Ha astromik filter suppress the unwanted light much and much better then both 6 nm Ha filters from Astromik.
Also light from a green laser pointer is far better suppressed by the 7 nm Baader and 12 nm astromik filters.

The 6 nm Ha filter from Astromik has been checked by Gerd Neumann, according to him this filter is OK!

I have made a few images with the 6 nm ha astromik filters they look allright.
Are these 6 nm Ha astromik filters realy OK???

Gerrit van der veen , Holland
 

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And here the result of the images with the green laser-pointer;
All images were made with same exposure time.
 

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Gerrit,

These filters are interference filters. I do not know the design of their layers but the transmitted bandwidth and intensity of such filters depend on the f-ratio. In your test you used a very fast system with f/2.2 and I assume that you took the celestial images through a telescope with a slower f-ratio. Do you get the same results with a slower f-ratio?

I take images through an Astronomik 6nm H-alpha filter through telescopes at f/5 and f/5.6 and the images look alright to me. However, I did not make such a test as you.

Regards
Manfred
 
Manfred, I have just test the filters with the laserpointer and set the camera lens to F11.0, with the same results: the Baader filter and the 12 nm astromik blocks much more unwanted light.

But I did get good results with the 6 nm Ha clipfilter:
here is a image of ic 1396 taken with a 135mm canon lens set at F/2.2
 

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Hi Gerrit,

I think the test images you made are virtually overexposed. The red parts of these images are saturated and thus You have no idea how much brighter the red patch had been in comparison to the other colors. Furthermore the display you've been using might have far less red transmission around 650 than one might think. It depends on the red elements of the display. As you stated you needed a much shorter exposure time without filter.
The images are still different and one might think a 6nm filter can't possibly deliver more colour different from red than a 12nm. But it can! The value 6nm or 12nm tells us about the full width half measure. Virtually the distance between the two points of the transmission curve that cross the level of 50% of the maximum transmission (say 45% total transmission if maximum/peak transmission is 90%).
However this value doesn't tell us about the optical density far off the desired transmission window.
The Baader Filter is obviously the filter with biggest optical density. It's almost totally blocking undesired wavelengths.
The deepsky image shows that those Astronomik filters are dense enough to produce good pictures. But look at the stars. The brighter ones are still white which might be not totally undesired. The Baader filter should produce a smaller number of white stars. But keep in mind that a star is usually not just tenfolds brighter than a nebula. Think about the exposure time (without filter) that is needed to picture a star and think about the exposure times needed for nebulas. So the density of the filters is big enough to block most of the sky glow and undesired city light. Only the stars are bright enough in such an exposure to produce white, saturated spots.

Clear Skies
Sven
 
Wenn ich mich recht erinnere, dann verwendet Baader als Filtersubstrat rot eingefärbtes Glas, bei Astronomik ist es klar. Das dürfte den Unterschied erklären.

mfg
Torsten
 
Zitat von Sven_Wienstein:
wie die Filterwirkung erzielt wird, ist im Prinzip egal!
Hallo Sven,

theoretisch ja. Aber wie man an den Beispielbildern sieht, ist die Filterwirkung eben nicht die selbe. Der Baader wirkt wie ein Stack aus HA-Interferenzfilter und herkömmlichem Dunkelrotfilter. Im Ergebnis ist der Durchlass außerhalb des Paßbandes deutlich geringer als bei der Variante mit Klarglas.

mfg#
Torsten
 
hi Gerrit and all,

here is a comparison of Astronomik 6nm and 12nm Filters on M42, I used my Canon Eos 450d modified at Iso 400, the two 7min shots were taken in succession so everything is same except the filter:

http://www.teleskop-shop.at/testphotos/Filter_test/M42_Astronomik_H-Alpha12nm.jpg

http://www.teleskop-shop.at/testphotos/Filter_test/M42_Astronomik_H-Alpha_6nm.jpg

My short conclusion: The 12nm filter gives me a signal on the entire background, shows weaker nebula parts, and produces far less noise. The 6nm only shows the brighter parts of the nebula, rest is black, and is more noisy.

If I look through the filters, I do not see any green colour shining through. No idea what causes the effect shown in the initial posting.

Maybe the stars will be brighter through the Astronomik filter, but anyway I do not mix them to the final picture, only the red nebula parts.

cs, Tommy
 
Interessantes befund! Hat Jemand aktuelle Filtern von die Beide Anbietern getestet?

Natürlich die O-III, S-II, H-b wäre für mich auch interessant...
Wenn die Astronomik auf der ganzen LS-bereich (im Post#1 sehe ich Grün und Blau...) 1-2% durchlasst, vermute ich dass die schmalere HWB-Werte (z.B 6nm Astronomik Oiii vs 8.5nm Baader) helfen nicht so viel gegen starke LP (orange oder rote Zone)
 
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