How does the 47.4 mm FCCT Clearglass filter help when imaging the Pelican Nebula (IC 5070) with a 3nm Ha filter?
Imaging the Pelican Nebula (IC 5070) with a 3nm H-alpha filter results in a very dim image, making focusing difficult. You would use the Baader FCCT Clearglass filter first to focus on a nearby bright star. Once sharp focus is achieved, you switch to the 3nm Ha filter. Because they are parfocal, your focus will be perfect, and you can begin imaging immediately without struggling with the dim nebula view.
What does "parfocal" mean for this Baader Clearglass filter?
Parfocal means that this filter has the same optical thickness as other filters in Baader's CMOS-optimized line. This ensures that the focal point of your telescope does not shift when you switch between this clear filter and, for example, a Baader narrowband or LRGB filter. This eliminates the need to refocus with every filter change, which is a major time-saver during an imaging session.
Is the FCCT Clearglass filter just a plain piece of glass?
No, it is an optical-grade window with advanced, multi-layer anti-reflection coatings. Unlike a simple piece of glass, the "CMOS-optimized" coatings are designed to maximize light transmission and prevent halos, reflections, and other artifacts common with sensitive CMOS sensors. However, note that this is a clearglass filter; it is not a UV/IR cut filter and should not be used as a luminance filter with refractors or other scopes that are not corrected outside the visual spectrum.
If I'm using a monochrome camera and a filter wheel, where would I install the 2" FCCT Clearglass filter?
You would typically install the Baader 2" FCCT Clearglass filter in an empty slot in your filter wheel, often designated as the "Luminance" or "Focus" position. This allows your software to automatically rotate to the clear filter for focusing routines (like a V-curve analysis) before switching to your R, G, B, or narrowband filters to capture data.
Why is this filter unmounted with a 47.4 mm diameter?
The 47.4 mm diameter and unmounted format are specifically for systems like the Baader FCCT (Filter Changer Camera Tilter) and other custom filter holders that require unmounted filters of this size. It provides a larger clear aperture than standard mounted 2" filters, helping to prevent vignetting with larger sensors and fast optical systems.
Can I use this Baader Clearglass filter for visual observing?
While its primary design is for imaging, you could use it as a high-quality dust plug for your diagonal or eyepiece barrel. However, it offers no filtration or image enhancement for visual use. Its main value is realized in an astrophotography setup as a parfocal focusing tool.
