About this product
Part Number: CT-27002-1.25M
Premium quality 5nm Ha Filter
Chroma 5nm H-alpha filters are essential for imaging nebulae and other objects which are rich in ionised hydrogen. At 656.3nm, a narrow-band emission filter is required to separate H-alpha from the SII doublet (671.6nm and 673.1nm).
Chroma Technology is an employee-owned company based in Vermont, USA. Chroma manufacture the highest quality astronomy filters with durable, sputtered hard coatings using single substrates of the best glass, eliminating the need for laminations. All primary filter coatings are applied on the front surface and anti-reflection coatings on the rear surface to prevent ghosting and to maximise transmission. Chroma astronomical filters are used worldwide in research and amateur applications.
Highly precise and accurate, the passbands of these filters remain spectrally stable and do not drift in response to extreme temperature fluctuations or changes in humidity.
All filters may be used with focal ratios of f/4 or slower. For optics faster than f/4 then due to the spectral shift we recommend using the 5nm filters instead.
- CWL: 656nm, Bandwidth: 5nm
- Durable sputter coatings
- Parallelism: <30 arcsec
- Thickness: 3.0 +/-0.05mm
- Filters designed for use with CCD and for f/4.0 or slower
- Transmitted wavefront better than 0.25 waves/inch
- No reflections leading to image distortions or ‘back reflections’
Cleaning and Handling
Handle coated pieces by the edges only. Clean gently only if necessary. Loose particles should be removed with a bulb puffer or filtered, pressurised air cleaner. If necessary, gently wipe surface using anhydrous alcohol and lint-free lab towels. Use new surface of towel with each wipe.
- AVOID TOUCHING OR WIPING A/R COATED OR METAL MIRROR SURFACES
- AVOID HANDLING EXPOSED COATINGS WITH BARE FINGERS
Proper orientation of the filter is necessary in order to minimise autofluorescence and maximise performance. There is a caret (arrow) located on the edge of each filter in order to aid orientation. Excitation (x) filters should be positioned with the arrow pointing toward the specimen, toward the inside of the cube, and away from the light source. Emission (m) filters should be placed with the arrow pointing toward the specimen, toward the inside of the cube, and away from the detector/eye. Dichroic mirrors should be mounted with the coated surface toward the light source, excitation filters, and the specimen. The dichroics either have an arrow on the side pointing to the coated side, or they are beveled on the coated side. The beveled side is the smaller surface.
|Average Rating (1 Review): |Chroma 5nm versus Baader 7nm
Monday, 31 August 2020 | Tom
As expected / hoped there's a noticeable difference in contrast between the Baader 7nm and the Chroma 5nm Ha filter. In the Ha the Baader 7nm is pretty good and relatively good value. Is the Chroma 5nm worth the upgrade? It's a tough call and I think it's more a financial decision. The OIII is a different story. It's night and day between the Baader 8.5nm and the Chroma 3nm. In light pollution that's a no-brainer. The OIII is primarily why I upgraded the Ha as I wanted consistency across my filters. If you can afford it and you don't already have a good Ha then I'd highly recommend this filter. If you can't afford it then for the Ha something like the Baader will get you 70% (total finger in the air) of the way there for 1/3 the price.
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