Baader Semi Apo Filter against violet fringes of refractors - 2" cell

Baader Semi Apo Filter against violet fringes of refractors - 2" cell

By selective out-filtration of those parts of the spectrum where the false color of achromatic refractores is significant, this disturbing effect is reduced. Contrast and image definition are improved. In addition, neodymium-containing glass provides a more neutral color tone.

The combination:

Time and time again Baader has been made aware of customers who were combining the Neodymium Moon and Skyglow filter with the Fringe Killers to deliver amazingly colour-corrected images to achromatic refractors. This combination however did produce reflections.

After analysing these reports Baader developed their Baader Semi-APO filter with IR blocker, a reflection-free combination of the Moon & Skyglow with a stronger coating of the Fringe killer. This result was a virtually colour-neutral image without the blue and red halos (violet fringing) and an increase to image contrast.

Differences to Fringe Killer and Contrast Booster:

These two filters have a similar effect. They reduce false colour, but the image also gets a yellowish touch. In some cases, for example for planetary observation, this is wanted.

The Semi Apo filter causes significantly less yellow tinting. The image has only a slightly warmer touch with a light yellow-green tone. It also has more transmission compared with a standard minus violet filter. It can also be used for deep-sky and double star observation.

The Semi Apo filter is a good addition to the Fringe Killer and the Contrast Booster. It can replace a normal minus violet filter and gives less colour shift.

For which telescopes is this filter recommended?

The Semi Apo filter is for all refractors with obvious false colour. The effect is best at fast rich-field achromats but even at ED refractors an improvement is visisble at bright objects.

For reducing the false colour of a fast rich-field achromat to almost non-existing, we recommend the Contrast Booster.

♦ Filter in cell
♦ Protectiv plastic box

Question:
What are the differences to Fringe Killer and Contrast Booster?

Answer from Teleskop-Service:
These two filters have a similar effect. They reduce false colour, but the image also gets a yellowish touch. In some cases, for example for planetary observation, this is wanted.

The Semi Apo filter causes significantly less yellow tinting. The image has only a slightly warmer touch with a light yellow-green tone. It also has more transmission compared with a standard minus violet filter. It can also be used for deep-sky and double star observation.

The Semi Apo filter is a good addition to the Fringe Killer and the Contrast Booster. It can replace a normal minus violet filter and gives less colour shift.