Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Dec 31, 2014 15:54:45 GMT
Quick question. I have a H-beta filter for visual use, can it also be used for imaging? or do I need a H-a for that? Whats the difference?
Thanks,
Rchard
|
|
|
Post by Rick in NWArk on Dec 31, 2014 17:37:29 GMT
H-alpha and H-beta are two different wavelengths of light. H-alpha is a deep red (656nm) and H-beta is blue-green (486nm) -- obviously both in the visible part of the spectrum. Both wavelengths are named because they are wavelengths that are emitted when an electron in a hydrogen atom transitions between different states. H-alpha is the most common, where the electron goes from the 3rd most stable energy level to the 2nd. H-beta is when the electron goes from the 4th to the 2nd.
The narrowband filters for H-alpha and H-beta are meant to clear out all of the other light so that only those wavelengths (+/- 1/2 the slit size) is transmitted thru to the eyepiece or CCD. Because of this, exposure times will increase to get the same amount of light for your imaging or video exposure. In an eyepiece, objects will generally be dimmer.
The real challenge is making a list of objects to go after if you are going to do a H-alpha or H-beta video session. Not all objects emit these wavelengths or emit them to the same degree. Many more objects are brighter in H-alpha than in H-beta. However, there are details from the H-beta light that will be missing if you just look at H-alpha. Some imagers will do four different exposures: Luminosity for brightness, H-alpha, H-beta, and Oxygen III (some do Sulfur too). Combining those get a lot of detail for nebula.
For video, H-beta is much much much less useful than H-alpha due to the fact that from a chemistry/physics perspective there are so many more interactions causing the H(3)->H(2) transition -or- the recombination of ionized (removed) electrons with a Hydrogen atom nuclei (which gives the same H-alpha wavelength) in nebulae.
I hope this helps!!
--Rick
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Dec 31, 2014 20:40:57 GMT
Thanks Rick. Lots of good info. What about IR-cut filters, are they useful? I see that alot of people take them out of their camera's for DSO imaging, and some use them for planetary?
Richard
|
|
|
Post by Rick in NWArk on Dec 31, 2014 23:47:58 GMT
Yep, so if you dont know, IR is very wide range of wavelengths longer than the deepest red we can see (usually 700nm). CCDs are of course more sensitive than our eyes and can pick up many IR wavelengths. When the CCDs pick up the IR this causes a large saturation of the red end -- and I am making some assumptions here -- that the IR light gets "converted" as visual red in the output from the CCD. Also, different wavelengths of light will refract thru lenses and prisms differently, and so have different focal points. So if you have some glass in the way, the IR can cause some blurriness.
The IR Cut filter eliminates all frequencies longer than the filter's specification.
|
|
|
Post by Dragon Man on Jan 1, 2015 7:28:31 GMT
Thanks Rick. Lots of good info. What about IR-cut filters, are they useful? I see that alot of people take them out of their camera's for DSO imaging, and some use them for planetary? Richard Richard, almost everyone takes out that crappy factory-fitted IR filters. If they don't it's probably because they haven't read about it in one of the many websites and forums that talk about it. The factory-fitted IR filters are absolute rubbish. They are fine for day time security use, but forget about it for astro. They are so dark that they reduce more than 30% of the light getting to the sensor. Unfortunately, some brands that claim to be 'Video Astronomy cameras' also have the terrible factory-fitted filter. And because these filters aren't designed for Astronomy work they 'cut-off' at the wrong place in the spectrum. Astronomical IR cut filters (and IR/UV cut filters) have to cut off at a very precise area in the spectrum, cutting out all IR but leaving behind the H-alpha. It's a sharp fine line between the two, and security camera manufacturers don't worry about it and just blot out anything in or near IR. And they use too much Blue in the colouring to try eliminate more reds as well. If you have a security camera with a factory-fitted blue IR filter, rip that sucker out If you want to use an IR filter (which is a good idea) buy a proper Astronomical IR cut filter. A good quality one, not a cheapie. The cheapies as nearly as bad as the Factory ones. The proper Astro filters can stay on the camera when doing DSO's. But I personally prefer to take mine off when I am searching for very distant very faint galaxy Clusters or the filter will block the IR coming from those galaxies. And the camera needs all the help it can get to see them.
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Jan 2, 2015 17:35:22 GMT
Hi Richard, First, I would like to acknowledge Rick's excellent explanations of what these filters do. I have recently been doing EAA with a narrow band Ha filter and my mono Lodestar and have enjoyed it very much. If you're interested in seeing some captures, here's a link to my gallery. The NB Ha captures are in two of the albums. The latest captures use a 50mm finder scope that I thought I would try to get larger emission nebulae with a large FOV. If you do decide to use a NB Ha filter, mono will give you the best results and your required exposure times will increase. If you have any questions, just post them here and I'll be glad to try and answer them. stargazerslounge.com/gallery/member/36930-hilodon/Don
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Jan 2, 2015 19:41:38 GMT
Hi Don,
Incredible images! Thanks for sharing. On the X2c can you turn off the color for increased resolution? If so, will it equal the mono version?
Richard
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Jan 2, 2015 21:09:18 GMT
Hi Don, Incredible images! Thanks for sharing. On the X2c can you turn off the color for increased resolution? If so, will it equal the mono version? Richard Thanks, Richard. The X2c is the same sensor as the X2, but has a color Bayer mask over it. This reducers it's sensitivity, but resolution should be the same in normal use if you shut off the color. Sensitivity, however, will not improve and will never be as good as the X2. If you're using a NB Ha filter though, my understanding is that only the red channel will pass Ha, so the resolution will be greatly reduced if you use a X2c even if you shut the color off. That's why it's best to use a native mono cam with NB Ha and that is true for probably any cam, not just the Lodestar. Hope this answers your question. Don
|
|
|
Post by Dragon Man on Jan 3, 2015 9:34:42 GMT
Yep, Don is absolutely correct.
Because there is a Bayer matrix over the front of a Colour camera it will never see as good as a Mono sensor. And there is no successful way to remove a Bayer matrix from a Colour sensor.
Even when switching a colour sensor to Mono, the light still has to pass through the microscopic colour filters of the Matrix, so they are slightly fainter and colour affected. Switching to Mono only turns off the colour display of a colour sensor. Whereas a Mono sensor has nothing in front of it to reduce light gathering.
|
|
|
Post by davy on Jan 3, 2015 12:30:35 GMT
Here's one to stick in the mix.. mono video camera with a filter wheel rgb filters just like in astrophotography..and blank for luminance .could they be combined together in video capture software
|
|
|
Post by Dragon Man on Jan 3, 2015 13:50:39 GMT
Here's one to stick in the mix.. mono video camera with a filter wheel rgb filters just like in astrophotography..and blank for luminance .could they be combined together in video capture software I don't see how Davy. The filter wheel would have to spin at 1000 rpm and then how do you get the separate colours to land on separate pixels Someone clever with software could probably write a program that could spin the filter wheel to each colour for 30 seconds or so, then process it all on-the-fly. But why bother when you can just use a colour camera
|
|
|
Post by davy on Jan 3, 2015 14:30:42 GMT
Post processing. .just like a/p take a couple of min video on each filter then combine after in software .we as well doing a/p..lol. idea was get a mono camera..thus gives you a cracking luminance channel. .rotate in a different filcapturecapture each for couple of min..thinking It would be faster than a/p..ok it's cossing the divide a bit but a few stack video capture images
|
|
|
Post by Dragon Man on Jan 3, 2015 15:19:32 GMT
Ahhhhh, yes Davy, that's how planetary imagers get there great images of the planets when using Mono cameras.
No reason it can't work on DSO's too.
|
|