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Optolong L-eXtreme 7nm Dual Narrowband Filter (H-Alpha and O-III)

In Stock - Ships Today if Ordered by 2pm! (Tues - Fri)
L-eXtreme 1.25"

We will price-match Canadian astronomy dealer pricing


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If you'd like maximum light pollution management while using a one-shot colour camera to image H-Alpha and O-III emission targets, the Optolong L-eXtreme is the best filter for the job.

The L-eXtreme is a 7nm dual bandpass filter which can be used with one-shot color cameras like DSLRs and CCD/CMOS astrophotography cameras. It's most suited for fast systems or long exposures. The convenience and cost effectiveness of this filter allows amateurs to image emission nebulae even in bright, light-polluted or moonlit skies.

The L-eXtreme isolates the H-Alpha and Oxygen III emission lines so that the contrast and signal-to-noise ratio of a nebulae are maximized. For people who are imaging in very light polluted areas or when the moon is out, the L-eXtreme is an excellent choice.

The advantage of the L-eXtreme filter is that there is no light transmission between the H-beta and OIII lines (as there are no nebula emission lines there). This reduction in light pollution maximizes the nebula's signal and makes the sky background darker while imaging.

Unlike the L-eNhance filter, which is a tri-band filter (it transmits H-Alpha, H-Beta, and O-III), the L-eXtreme filter is dual-band, passing just the H-Alpha and O-III emission lines in order to deliver improved light pollution rejection.

The Optolong L-eXtreme filters (apart from the 2-sided 10mm thickness version) have threads on one side to keep them very thin - 1.85mm - they can be used with Filter WheelsFilter Drawer System, focusers with a place to thread focal reducers internally (such as some Moonlite focusers) and camera nose pieces that fit into compression rings, but the 1.85mm filter should not be threaded into the imaging train like an adapter ring with threads on both sides.  The 10mm version with threads on both sides however can be used like an adapter ring and can be threaded directly into your optical train.  The back focus used by the 10mm version and clearance required is 7.6mm.

Note: For imaging galaxies and reflection nebulae, the Optolong L-Pro filter is more appropriate as the L-eXtreme and L-eNhance filters will reject much of the light from those broadband or reflection objects.

 Manufacturing Technology

  • High-precision grinding and polishing to make sure the substrate parallelism is greater than 30" and the surface accuracy is better than λ/4 ;
  • Purified water ultrasonic cleaning is aim to effectively remove impurities and dust from the substrate surface.
  • Electron-beam gun evaporation with Ion-assisted deposition coating technology for durability and resistance to scratching, as well as stability on CWL(central wavelength) no deviation affected by temperature change; IAD not only consolidates membrane compactness, increases film firmness, but also changes vacuum coating material characteristics.
  • Planetary rotation system offers precision and a homogeneous coating ensuring high value on transmission of pass-band and Optical density of off-band;
  • Non-cementing optical substrate coating;
  • Quality Control: each filters is examined by Spectrophotometer for spectrum characteristic, and Laser Interferometer for surface accuracy.


Outer Box: cardboard sleeve box

Inner Plastic Box: Strong PP material

Lining: Imported high pressure white EVA


Returns Policy

You may return most new, unopened items within 30 days of delivery for a full refund. We'll also pay the return shipping costs if the return is a result of our error (you received an incorrect or defective item, etc.).

Items that have been opened, damaged or are otherwise unsaleable will be subject to a minimum 10% restocking fee, to be assessed by Telescopes Canada upon receipt of the returned goods

You should expect to receive your refund within four weeks of giving your package to the return shipper, however, in many cases you will receive a refund more quickly. This time period includes the transit time for us to receive your return from the shipper (5 to 10 business days), the time it takes us to process your return once we receive it (3 to 5 business days), and the time it takes your bank to process our refund request (5 to 10 business days).

If you need to return an item, simply login to your account, view the order using the 'Complete Orders' link under the My Account menu and click the Return Item(s) button. We'll notify you via e-mail of your refund once we've received and processed the returned item.


We can ship to virtually any address in the world. Note that there are restrictions on some products, and some products cannot be shipped to international destinations.

When you place an order, we will estimate shipping and delivery dates for you based on the availability of your items and the shipping options you choose. Depending on the shipping provider you choose, shipping date estimates may appear on the shipping quotes page.

Please also note that the shipping rates for many items we sell are weight-based. The weight of any such item can be found on its detail page. To reflect the policies of the shipping companies we use, all weights will be rounded up to the next full pound.

Typographical Errors and Order Cancellations

Telescopes Canada reserves the right to cancel an order due to an error in pricing by Telescopes Canada or one of our suppliers, equipment being no longer obtainable, or other events which are out of our control.

Client-Initiated Cancellations

Client-initiated order cancellations are accepted prior to delivery of the equipment to the customer, thereafter it is a return.

Substrate: B270
Thickness: 1.85mm
FWHM:  O3 7nm+Ha 7nm
Blocking range: 300-1000nm
Blocking depth: light pollution line blocking >99%
Surface quality: 60/40
Transmitted Wavefront RMS: λ/4
Parallelism: 30s

Questions & Answers

  • Good morning ( optolong L extreme 7nm ) What is the format ( 2”. ? ) to fit my setup ? Skywatcher evostar 80ed, starfield 0.8 flattener/ reducer , Canon Dslr eos 700 d

    Yes for the L-eXtreme you will need to use the 2" filter as there is currently no clip filter available for it (as of June 2021).  We would recommend using a filter drawer, assuming you have the available back focus.  The ZWO filter drawer consumes about 21mm of back focus:

    As far as I know, you cannot install a filter inside this flattener, but good to check this.  If so it would also be the 2" version.

  • When are you expecting the L-eXtreme 7nm 2" to be back in-stock?

    We expect the L-eXtreme 2" filters to be back in stock sometime in the week of October 26th