For dramatic increase in visual and photographic detail in deep-space emission and reflection nebulae. Meade Series 4000 Nebular Filters incorporate the very latest in interference coatings technology. Each filter includes more than 40 coating layers to reject, with precision, unwanted light from urban light pollution while passing critical nebular emissions with minimal reduction. Technical Basis of the Meade Broadband Nebular Filter: As shown in the transmission graph below, the Meade Broadband Nebular Filter strongly rejects the light of sodium- and mercury-vapor lights as well as natural airglow and auroral emissions. Conversely, the strong nebular emission spectral lines, transmitting in the visually sensitive regions primarily at 486nm (Hydrogen Beta, or Hß) and 496 to 501nm (Oxygen-III, or OIII), are passed through the filter with high transmission percentages. The effect of the filter is that nebular light reaching the eye is observed visually in dramatically increased detail, while the effects of unwanted city lights are greatly reduced. The Meade Broadband Filter also passes photographically-important Hydrogen Alpha nebular light at 656nm largely unattenuated, making the filter a valuable aid in the photography of deep-space emission nebulae as well. The contrast between galaxies and the night-sky backdrop is also typically enhanced by the filter, but because galaxies emit light in a much broader range of wavelengths than nebulae, the effect is generally not as dramatic in these cases. Two models of Broadband Nebular Filters are available: #908B: Threads into the barrels of all Meade 1.25" eyepieces, and into the barrels of virtually all other 1.25" eyepiece brands as well. Clear aperture is 26mm. #911B: Threads onto the rear cells of Meade LX-series mirror-lens telescopes and onto Meade ED Apochromatic Refractors (using the Universal Thread Adapter), as well as to the rear cells of other Schmidt-Cassegrain brands. In this way the telescopes are converted into a basic "nebular mode," for visual observing or for photography with the T-Adapter or Off-Axis Guider. Clear aperture is 36mm.
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