This 31mm round, unmounted Baader 3.5nm H-Alpha CMOS Filter 31mm Unmountedfrom Baader 3.5nm H-Alpha CMOS Filter 31mm Unmountedis recommended for extremely fast optical systems from f/3.4 to 1.8, and is designed for the special filter requirements of fast optics like Celestron RASA astrographs. The filter features a Reflex-Blocker hard coating, which has been planoptically polished, and has Life-Coat sealed edges. It is equally suitable for modern CMOS sensors as well as for older CCD camera technologies.

Optimized for CMOS, Suitable for CCD    Reflex-Blocker Hard Coated    Life-Coat Sealed Coating Edges

• 4nm FWHM, recommended for extremely fast optical systems from f/3.4 to 1.8
• Specially designed for the special filter requirements when used with fast optics like the Celestron RASA astrographs
• Reflex-Blocker hard coated and planoptically polished with sealed coating edges (Life-Coat)
• Blackened edges all around, with filter-lead-side indicator in the form of a black frontside outer rim
• Optimized for modern CMOS cameras, but excellent for CCD camera technologies

Related Questions and Answers

Q: 1. it works on pentax K-1...is this a full frame lens?

A: Yes, this is a full frame Pentax lens and will be compatible with the Pentax K1.

Q: 2. Does the new HD FA31mm F1.8 use a SDM motor?

A: The HD Pentax-FA 31mm f/1.8 Limited uses Body AF drive--the camera body supplies the autofocus motor. It does not use an SDM motor.

Q: 3. Can you use the CPL from the Nisi v5 pro kit with the newer v7 filter holder?

A: No, the older CPL for the V5 holder does not fit the new V7 holder.

Q: 4. Baader sells this part packaged also with an M48 ring insert (only in the case of the Sony adapter). Do you include this extra ring?

A: Here is a list of the Baader rings B&H sells for Sony https://www.bhphotovideo.com/c/products/astrophotography-adapter-rings-extension-tubes/ci/48682?filters=fct_brand_name%3Aalpine-astronomical&searchWithin=sony

Q: 5. how to adapt this to a camera lens with a 62mm thread (yes, this will result in some vignetting which I will have to tolerate)?

A: Currently B&H does not stock an adapter allowing the Alpine Astronomical H-Alpha 20nm Bandpass Filter (2") to a camera lens with a 62mm thread.

Q: 6. Can I insert a 4x4 filter, a 4x6 filter, and a NiSi True Color CPL Filter all into this holder?

A: You can insert 4x4 filters, 4x6 filters, and the NiSi True Color CPL Filter in the NiSi V7 Alpha 100mm Aluminum Filter Holder.

Q: 7. Is the 82mm mounting ring compatible with the NiSi V5 circular polarizing filter?

A: No, the 82mm adapter ring is for a lens not the V5 polarizing filter.

Q: 8. This 31mm or the 35mm 1.4? Preference?

A: Selecting what is best depends on the job to be done. These lenses are not in the same class, the choice will be made on how high a quality of image and working experience is required. If the photographs are for personal use as well as experimentation in gathering different looks for an art piece, the Samyang 35mm f/1.4 AS UMC is as good as anything. If the photograph is for commercial paid work, then no question you want the rugged reliability and top level image quality of the Pentax smcP FA 31mm f/1.8. Clients will not be impressed with how much you saved buying the lower price lens if the image is not perfect or if the lens fails mechanically during the shoot.

Q: 9. Does this holder accept the True Color CPL?

A: Yes the NiSi V7 Alpha 100mm Aluminum Filter Holder can hold this NiSi True Color CPL Filter: https://bhpho.to/3KMNA9Q

Q: 10. will this lens mount and work perfectly with a pentax k1000?

A: K1000 has no autofocus motor to run the screw drive. FA-31 ltd otherwise acts like an A lens with an automatic aperture setting but you'll be manual focusing it.