Altair 130mm Aperture D-ERF MonoBand Ha Solar Pre-Filter - with Cell

Altair 130mm Aperture D-ERF MonoBand Ha Solar Pre-Filter - with Cell

The Altair Dichroic Solar Energy Rejection Filter or D-ERF protects your telescope and solar imaging equipment from excessive heat build-up when solar imaging ...
Manufacturer : Altair Astro
Price: 1116.81 € excl tax
Delivery date : 1-4 weeks
Product description

Altair 130mm Aperture D-ERF MonoBand Ha Solar Pre-Filter - with Cell

The Altair Solar Energy Rejection Filter or D-ERF protects your telescope and solar imaging equipment from excessive heat build-up when solar imaging or observing with your Daystar Ha Quark, or other Etalon filters. Because it has OD3 (0.1%) UVIR blocking and OD4 0.01% of unwanted visual wavelengths. The protection of your solar equipment from heat is a priority.

NOTE: This D-ERF filter cannot be used on it's own. It can ONLY be used in conjunction with a Daystar Quark, or other similar product, which has it's own complete blocking filters built-in. Serious eye damage will result if this product is used on a telescope without a professional Etalon product (such as the Quark) with it's own blocking filters at the eyepiece end of the telescope. If in doubt, contact Altair Astro or your dealer for clarification before ordering.

The Altair Hydrogen Alpha D-ERF filter transmits Hydrogen Alpha or "Ha" light and has an FHWM of 40nm. It has extremely efficient blocking of UV and IR light and OD4 blocking of visible wavelengths outside the desired target. This allows use of ultra narrowband Etalons such as Daystar Quark Chromosphere without overheating.

A 140mm D-ERF filter element is mounted in a special cell with 130mm clear aperture to fit your refractor. The ERF filter holder fits dew-shield diameters of 173mm to 138mm* which is compatible with most 130mm / 5" refractors. The ERF cell is made from lightweight, tough UV resistant cold cast aluminium (50%). The knobs are cold cast brass (50%). The cell is lighter than aluminium and does not distort the optical surface of the filter, allowing for top quality images.

  • Altair 102mm, 110mm, 115mm, 125mm, 130mm refractors
  • Explore Scientific/Meade 102-127mm refractors
  • Skywatcher / Celestron 100mm-120mm refractors
  • Orion EON 100 to 130mm refractors

Altair D-ERF Filter Specifications:

  • ERF Cell fits telescopes with outer dewshield diameters of 173mm to 138mm. See telescope list above.
  • Clear aperture of 130mm / 5" (Contains 140mm D-ERF Filter allowing 5mm edge for mounting)
  • Unique Cold Cast Aluminium / Brass Cell - distortion free, light, and tough!
  • M3 Corp Silicon Rubber Cushions to protect optical tube paint
  • Top quality substrate, parallelism and surface for sharp images
  • Top quality Multilayer coatings with hard SIO2 protective overcoat
  • 40nm FHWM* Bandpass at H-alpha (H) wavelength of 656.28 nm (*Full Width Half Minimum)
  • Transmission: 95.5% T @ 656.28 nm
  • UVIR blocking OD3 0.1% @200-1100nm (remainder is very low and blocked by 3rd party Etalon)
  • Visible light blocking: OD4 0.01% @200-700nm to reduce reflection effects - reduces approx. 95-98% of heat reaching the optics to keep Etalon from drifting off-band.
  • ERF filter element diameter 140mm, thickness 12.0mm required to achieve best surface precision
  • Glass substrate is Russian K8 or German BK7 depending on availability (4x harder and less expansion than the glasses normally used in coloured-glass ERFs)

Benefits of using a D-ERF on scopes of 4" or larger:

  • Reduces heat build-up by approx. 95-98% before it enters the telescope, leading to a sharper image and no heat haze from air currents inside the telescope tube.
  • Reduces the impact of heat on your Etalon, prolonging life of the product.
  • Reducers the impact of heat on your Etalon bandpass, keeping it on-band and allowing longer imaging sessions, as well as longer animation sequences. Example solar Hydrogen Alpha animation with Altair ERF (opens new window).

Why choose an Altair "Dichroic" Energy Rejection Filter, or "D-ERF" instead of the coloured glass type? Special Dichroic multilayer coatings on the flat optical glass block Infrared and Ultraviolet light by reflection, as well as most of the unwanted emission spectrum of the sun, delivering only the useful Hydrogen Alpha wavelengths for solar imaging with your 3rd party Etalon. D-ERF is far more efficient than the cheaper ERFs using coloured red dyed glass, because it works by reflecting heat, instead of absorbing it like dye-based or IR blocking glass filters. It therefore remains cool and stable. Additionally, the Altair D-ERF is  made from 12mm thickness optical grade glass. Therefore it has better optical quality than dye filters, and freedom from striae and distortion caused by internal tensions, or surface tension caused by the coating process, to give the sharpest possible results. It is held an a tension-free housing. An Altair D-ERF will not limit your telescope optics.

IMPORTANT SAFETY INFORMATION: An ERF is ONLY to be used for visual observing or imaging with a Daystar Quark, or other professionally made Etalon in place BEFORE the telescope eyepiece. Any Etalon must incorporate full blocking filters. If in doubt, ask a professional. An ERF cannot be used with a standard Hydrogen Alpha filter such as that used for deepsky imaging. Never look at the sun with just the ERF in place - permanent eye injury will result. Never use a camera with just the ERF in place because the camera sensor can be damaged. Remember to cover your finder scope so you don't inadvertently look through it at the sun. We recommend the Altair Solar Finder which is the safest method of aligning your telescope to the sun. Always place the ERF on the scope and make sure all your equipment is installed correctly before pointing the telescope at the sun. If in doubt, consult the manufacturer.

D-ERF glass filter element: 140mm diameter with a clear aperture of 130mm diameter, 12mm thickness, using the periphery for mounting in a holding cell. The glass substrate is Russian K8 or German BK7 depending on availability. Glass blank specification is 8th wave surface accuracy optically polished with 30 arc second parallelism prior to coating. The filter is 12mm thick to maintain surface accuracy during the coating process. The coatings are ion beam dielectric coatings, and the glass annealed therefore free of Striae - internal tensions affecting image quality. Due to this process, there are usually a 2-3 very small bubbles inside the glass, usually about 0.2 to 0.5mm length, which cannot affect the image quality in any detectable way. Cleaning is the standard method. First excess dust is removed by blowing with a bulb (do not use compressed air). Then to remove stubborn greasy deposits or pollen, you can use Zeiss or other professional optical fluid and optical wipes. Wipe gently from centre to edge, while rolling the wipe to capture dust.

About the ERF Holder Cell Design and Construction:

The ERF Holder Cell is made from special "cold-cast" aluminium, and the retaining hand knobs are made from "cold cast" brass with silicon cushions to protect your optical tube. The ERF cell holds the filter glass securely by means of special pads, and is slightly loose in the holder. This is intentional, ensuring freedom from tensions which could distort the optical surface.

The ERF Holder Cell is quite special - a fusion of modern computer aided design, 3D printing technology, and old casting technologies. Cold casting is by Nick Brooks, a local British fine-art moulding expert. The initial production run is limited by the number of castings possible from the original mould, which due to heat build up, eventually disintegrates. We estimate 20-50 Cells can be made before the mould becomes useless.

When casting is complete, the ERF Holder Cell is subject to some machining operations, then hand polished and finished, giving it a unique high tech, yet timeless hand-worked quality. It's also very tough, UV resistant, and lighter than normal aluminium by volume. You can polish the surface more using Autoglym metal polish, or similar mild metal polishes and a soft cloth. We anticipate the Cell to last generations. We also sell the ERF filter itself, so you can construct your own holder if you wish.

Scope of Delivery:
  • D-ERF 130mm
Products specifications
Filter thread / size115mm
Weight2.5 Kg