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I've recently found out about Celestron filters such as this one, which are meant to be used for telescopes, not cameras, but I would love to see examples of photos taken through these filters if anyone has ever tried this.

If you have used it yourself to take pictures, would you say that it is possible to use them for portrait photography or other types of photos than sky photography? (for example, portraits with strong stars in the background sky?)

Otherwise, maybe I'm dead wrong assuming they would be the right equipment, and in this case let me know what better suited filters would work for photography or even filming.

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Size

The description of the item is "OXYGEN III NARROWBAND FILTER - 2 IN".

That '2 IN' is about what you would need to screw it into. These go into the eyepiece of a telescope. A 2" filter is 50.8mm across and you would probably need a special adapter to take it to a photographic lens filter diameter (I don't know of any). Furthermore, unless you are dealing with rather small lenses, the smallest filter size that I use is 52mm. This wouldn't fit.

Narrowband

A narrow band filter is one that has a small bandpass.

The 2" OIII narrowband filter isolates the two doubly-ionized oxygen lines (496 and 501nm lines)

This filter is on the order of 5nm wide (maybe a bit wider) in the blue-green part of the spectrum. Its goal is to capture the light from doubly ionized oxygen.

oxygen transitions

What does this mean? Its used in astrophotography to capture the blue channel in photographs such as:

Eagle nebula

In this, the green is from Hα, and the red from the SII (Sulphur) transition. This isn't the "real" color (Hα is at 656nm which is actually a red) and SII is a deeper red at 672nm.

The true color for the image is actually:

enter image description here

(from http://thinktribally.org/article/coming-life-hubbles-25th-anniversary-honored-new-hi-definition-photo-pillars-creation-eagle-nebula/ )

What would a photograph through one of these filters look like?

An example from a Hα filter that is 3nm wide of NGC 6888 on Wikipedia is:

NGC 6888

Or the horsehide nebula in Hydrogen Alpha here

These images are not in color because there is no color to be seen in the photograph. Its all one very narrow band of the light and is best understood in terms of grayscale.

They are of very limited use for general photography.

What to actually use

It depends on what you want to photograph. There is no way to say what filter one should have. They are tools. Asking this question is like asking "should I get a philips screwdriver of size 2 or size 3 for building a house?" Chances are you will want a few of them - of different types. The same is true of filters. However, as with building a house, there are some that are less useful than others as they are very specialized in their use. Astrophotography filters are very specialized tools.

  • Thanks @MichaelT for your help in understanding this complex concept. Sorry if I sounded like a noob, I definitely know that we need a lot of filters all the time :) What I don't understand is: why would the second photo be B&W but not the first one? Wouldn't a camera be able to reproduce what the eye sees, including colors? Also, my question was, simply, if you used this filter for regular photography (i.e. long pose portraits under a night sky), would it pull out "more" details and colors from the sky than not using a filter? I built adapters & lenses before; so Ø of thread is not important. – MicroMachine Aug 3 '15 at 3:55
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    The color of the first image is a false color composite, as explained in mcwetboy.com/mcwetlog/2010/04/… . The second (now third) image is a gray scale because using color data isn't meaningful when there is such a narrow band of color. I would suggest going and borrowing a R25 filter and shooting a few frames through it (and its not a narrowpass filter - you'll get more 'color' data out of it). The filter is designed for capturing a very particular color of light and taking photographs that have exposures of several minutes. – user13451 Aug 3 '15 at 4:09
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    Imagine taking all your photographs using only the light from a low pressure sodium vapor lamp - i.stack.imgur.com/CvIjo.jpg and that is the type of color you would get with a bandpass filter. Though this one would happen to be in the blue-green part of the spectrum rather than the yellow. Black and white photographers use such filters - but not narrow bandpass. The green filter that a B&W photographer uses (a 58 or 61) has a bandpass of ~150nm. Others tend to be long pass. photo.net/learn/optics/edscott/cf000010.htm - try those instead of a narrow band pass. – user13451 Aug 3 '15 at 4:16
  • I guess what I was trying to ask, underlying in my question, is whether or not it would be possible technically, to take pictures of the sky in which colors that are hard to see with the human eye would appear. Not necessarily zoomed pictures, but landscapes or still life or portraits in which the sky is visible. – MicroMachine Aug 4 '15 at 9:54
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    If you are after night sky photographs to try to get colors we don't see, you may instead want to consider a broad 'sky glow' filter such as telescope.com/Accessories/Telescope-Eyepiece-Filters/… which blocks the frequencies of light that terrestrial sources give (and reflect back). However, I would strongly suggest you read up on astronomy and emission nebulae. Also note that the colors in the photographs are not the ones in nature. – user13451 Aug 4 '15 at 13:21

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