Violet Filter W47

Violet Filter W47
Check your spectral charts for the W47 filter as they vary from various filter manufacturers.

A W47 filter allows violet light to pass but also allows a small amount of Infrared light right at the other end of the spectrum to pass. It is most useful in observing Venus because of its ability to reveal dark shading in the upper atmosphere. Its low transmittance makes it suitable (in general) for larger telescopes above 8" of aperture.

A W47 filter allows violet light to pass but also allows a small amount of Infrared light right at the other end of the spectrum to pass. 

The spectral transmission curve for the Wratten 47 deep blue filter.

This is a representative Wratten transmission curve in a general article on color filters. It is not an actual transmission curve for any specific product that we sell. AgenaAstro. The chart stops at 700nm. The #47 near-IR leak starts at about 700nm, so the leak is apparently just off that chart.

Here are imaging examples with a Nexstar 6SE. (Nexstar 6se, ASI1600mm, UVenus filter, no Barlow. Used 1291 out of 4400 frames. Second out of five consecutive attempts. Others were a bit worse, mainly tracking pushing Venus out of the small capture window I was using to maximize framerate at about 80/second.)

https://www.cloudynights.com/topic/562488-small-bore-challenge-venus-w-6-or-less/page-2