The Astronomik L-1 UV-IR Block Clip-Filter Nikon XL:
This Nikon XL Clip Filter is designed for the full-frame bodies from Nikon:
The filters sit securely and tension-free in the camera.Assembly and disassembly are easy with your finger, without tools!No changes to the camera are required to use the filters.
It fits: 
It doesn't fit: 
It looks like this: 
The clip filters are optimized for use with normal camera lenses and for use on a telescope.Because of the narrow bayonet and light well, the filters cause minimal additional shading for some optics, which unfortunately cannot be avoided.
Compatibility:
- The XL clip filters for Nikon have been tested with the models D750, D800, D810 and D850
- For the D850, you can only use manual focus lenses or a T-adapter (with a telescope). With AF lenses you will get an error message and the camera will not work.
(Workaround for this: With AF lenses on the D850 you can apply some tape over the lens contacts and the camera will work fine with the XL-Clip Filter installed.)
- Other bodies have not been tested yet.
- The Nikon XL-Clip will not work with cameras with APS-C sized sensors and not with the new mirrorless body. Clip-Filter for the APS-C sized models will be released in the near future.
When it comes to getting a fantastic final image, the Luminance channel is probably the most important. Since we always want as much signal as possible, the filter should then have the highest transmission possible with a wide spectral bandpass. Combining these two properties yields the greatest possible sensitivity and gives the highest photon counts on our pixels.
While the high transmission level is a great aspect of the Astronomik Luminance filters, not all optical instruments or additional optical elements like correctors, field-flatteners or reducers, have perfect color correction, so the width of the spectral Luminance bandpass can cause problems. Having too wide of a bandpass allows the transmission if poorly focused light (chromatic aberrations), which will make stars appear soft or bloated. This will make the process of image processing much more difficult, so it’s best to narrow the spectral window as best as possible in the Luminance filter.
Depending on the color correction of your scope, you may want to use a wider spectral window for the Luminance data. The L1 filter has the widest spectral window, the L2 is about the same as current generations, and the L3 is much narrower.
When using an optical system that is completely free of any chromatic aberration, an L1 filter would be best for your setup. The L2 is best suited for general use with most optical systems using a corrector, flattener, or reducer in the optical train. And finally, the L3 filter is designed for those who use refractors without perfect color correction and potentially in conjunction with deep-sky RGB filters. The L3 will minimize the problem of bluish halos around stars.
The transmission curve characteristics and coatings on these Luminance filters have been engineered in such a way that no halos or reflections will be visible. Even with bright stars in your FoV you will be able to reveal the faintest structures in nebulae and galaxies.
Like all Astronomik Filters, the Luminance filters are made using an extremely durable and scratch resistant coating, deposited on the finest polished optical substrate which is free of any striae or internal strains. All substrates are made to exactly the same thickness, so all Astronomik filters are parfocal.
Additional note for those under light-polluted skies:
If your observing site suffers from light pollution, try using the CLS-CCD filter as a replacement for the Luminance filter. The transmission curve of the CLS-CCD will give approximately the same amount of energy in all three-color channels while blocking nearly all unwanted artificial light pollution.
