Astronomik OIII 12 nm CCD Clip Filter for Canon EOS M Cameras

Astronomik Clip Filter for mirrorless APS-C Cameras of the Canon EOS M System

This filter is suitable for photographing OIII regions from artificially light polluted areas or outside the city. The contrast between OIII light and the sky background is increased.

The OIII CCD filter increases the contrast between gas nebulae and sky background. The narrow FWHM combined with high transmission in the OIII lines region increases contrast compared to more broadband filters.

The useful application range extends over a focal ratio of 1:3 to 1:15, the filter can be inserted into the camera body in seconds.

An advantage of the 12-nm filter is that it is easier to find a star to focus on. This becomes much more difficult with a 6-nm filter.

How it works

The filter blocks all unwanted light from artifical light-pollution, natural airglow and moonlight. Especially light from high and low pressure sodium and mercury vapor lamps and all lines of natural airglow are 100% blocked. The filter increases the contrast between the sky background and objects glowing at the OIII lines.

Compatibility

The clip filters for EOS M can be used with the models M1, M10, M3, M5, M6, M6MkII and M50.

The transmission curve:

On the horizontal axis, the wavelength is plotted in nanometers. 400 nm corresponds to a deep blue, at 520 nm the human eye sees green, at 600 nm red.

At 656 nm is the known H-alpha emission line of hydrogen, around 500 nm the two [O III] lines of oxygen, at 486 nm the H-beta line of hydrogen, around 672 nm the two [S II] lines of sulfur. The square brackets indicate that these are forbidden lines.

On the vertical axis the transmission is plotted in %.

The cyan line shows the transmission of the filter.

A short guide for selecting the right filter

Lots of customers are overwhelmed by the vast number of filters offered by Astronomik. Due to that they give you a short guide how to select the right filter for your application below:

Astronomik´s normal recommendation for the "First Filter" is the CLS filter. The CLS blocks all unwanted artifical light pollution and natural airglow and gives you a dark background in your images. When using this filter you may expose much longer than without, so you will be able to pick much fainter structures and objects. The filter is designed in such a way that all objects are given in their natural colors - they would look the same if your human eye would be much more sensitive!

The CLS is the fist choice for any applications like night-scape photography and time lapse movies!

Important: The standard CLS has no built-in IR-blocker. In case your camera has been modified for astrophotography, please take the CLS-CCD which has a built-in IR-blocker!

If you have to work under a heavily light polluted sky, the UHC is a good choice too. Its transmission curve is very tight. It gives you the light from the Hß, [O III], Hα and [S II] lines in one single exposure. The reduction of light pollution is much stronger than the CLS/CLS-CCD, but the filter will work for gas nebulas only - any galaxies and open or globular clusters are filtered out! You will get "false colors" with the UHC, not natural colors like with the CLS/CLS-CCD.

The UHC-E has a more broadband light transmission. Here stars are less strongly suppressed, helpful for nebulae with star clusters.

If you want to die deeper into astrophotography, you should think about emission line filters centered on OIII, H-alpha and SII, available either with 12 nm or even 6 nm bandwidth. With these filters you can do ultra-deep images even under the worst sky you can imagine plus the full moon high up in the sky. The emission line filters isolate the light from a very tight range of wavelengths, don´t get any color information. If you want to create color images (false color like images from the HST), you will need all three filters to mix the three channels into a final color image.

When using DSLR cameras without IR cut filter in astronomy, we recommend the UV-IR block filters of the L-1, L-2 and L-3 series to correct chromatic aberrations when using refractive optics (camera lenses, refractors). Depending on the color correction of your scope you may use a wider spectral window for the luminance data. The L1 filter has the widest spectral window, the L2 is about the same as our current L-Filter and the L3 is much narrower.

If you use an optical system that is more or less free of chromatic aberration you should get an L1 filter for your setup. For general use the L2 filter is well suited to most optical systems with a corrector, flattener or reducer in the optical train while the L3 filter is designed for users of refractors with a less-than-perfect color correction.

As protection against dust in DSLR cameras without IR cut filter, the MC clear glass filter is suitable. It blocks neither visible light nor UV or IR, but is parfocal with the other clip filters for Canon EOS R/RP full-frame cameras.

Especially made for planetary imaging are the ProPlanet IR pass filters. The IR light transmitted by them is less sensitive to air turbulence ("seeing"), which makes the images sharper, with increasingly longer wavelengths being increasingly less affected.

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