Using a 7 nm filter

[JAMES STEWART]

I am new to the site.  I purchased an H-a 7 nm filter in 1.25" in a project to develop a pinhole solar telescope.  A 1 mm aperture worked fine with a 12% Lunar filter and the 7 nm.   I was able to verify that the Sun is round and visible in H-a.  The bizarre images were explained by a physicist friend.  See attached.  So, my solar telescope made up of segments of  3" black sewer pipe, brass pinholes, rack-and pinion focus,  and adapters was a bust.  Fortunately, the H-a filter only cost $24 used.

Now I understand the 7 nm is used for deep sky.  I am using a 6" Newtonian GoTo, so I wonder if I can use my 3mp camera to any good effect?  Now I find it is called a Baader filter.  I met Salter Baader in 1959 and he didn't mention anything about filters.  But then I didn't really know who he was at the time, other than an astronomer from Palomar Observatory.

What say you?

0109151529.bmp

[Merlin66]

The Baader Solar filter has no connection to the US.

Thomas Baader and the Baader company are German.

[rickwayne]

You  might do well with it, but there are, as the Genie says in Aladdin, "a few exceptions, a  few  provisos, and  a couple of quid pro quos".

Hydrogen-alpha photography is mostly done of emission nebulae, where the gas is excited by starlight and glows with its characteristic deep-reddish hue. Other objects (reflection nebula, some galaxies) don't emit much and so aren't suitable.

The  7nm filter lets through only a small slice of the photon flux (as I'm sure you know) so the sensor accumulates much more slowly. For my particular rig, for example, with an f/5.5 scope and a dedicated astro cam  running at full-tilt gain, 10 minutes is a good sub-exposure time, and for a nice Ha picture I'll accumulate 2-4 hours of total integration.

So depending on your optics and mount, you might not be able  to run sub-exposures long  enough to dig your  signal out of the sensor's read noise.

But heck, it's a hoot when it works!

Edited March 3, 2021 by rickwayne