Optolong L-Ultimate Filter Review

Read our review of the Optolong L-Ultimate Filter – a 2-inch Filter designed for Colour CMOS Astronomy Cameras that makes light-polluted, narrowband astrophotography a breeze.

Optolong L-Ultimate Filter - 2-inch
Optolong L’Ultimate Filter

Introduction to the Optolong L-Ultimate 2-inch Filter

The all-new Optolong L-Ultimate 2-inch Filter is a dual-band, 3mn filter. It works wonders to reduce the effects of light pollution in astrophotography. The L-Ultimate also effectively detects Hydrogen Alpha (Ha) and Oxygen (OIII) emissions from deep-sky objects such as nebulae.

While using the L-Ultimate, you can also expect a maximised signal-to-noise ratio, resulting in impressively dark backgrounds. You’ll also notice a reduction in the intensity of halos around bright stars.

Telescope Compatibility

Optolong designed the L-Ultimate Filter for use with telescopes slower than f/4.

But what if you have a telescope that’s much faster, such as a Celestron RASA at f/2? You’ll probably notice considerable band shifting, which will prevent the L-Ultimate from working properly – if at all.

But if you do have a telescope slower than f/4, you’re probably wondering how the L-Ultimate can enhance your photographs.

Effect Against Light Pollution

Firstly, its important to note that the specifications of the Optolong L-Ultimate makes it a great light pollution filter.

The L-Ultimate works wonders against stray light from both Mercury and Sodium vapour lamps and Sky Glow in our atmosphere.

Review of the Transmission Bands of the Optolong L-Ultimate Filter

The Optolong L-Ultimate has two transmission bands with a bandpass of 3nm.

This makes this filter ideal for astrophotographers capturing the fine details of nebulae emissions – especially in outer regions.

For example, this astrophotograph of the Rosette Nebula was captured in my Bortle 8 backyard with an Optolong L-Ultimate Filter. I have a well-lit railway station across the road, so the sky from my backyard is never totally black.

As you can see, the L-Ultimate is able to block light pollution even in highly light-polluted, urban areas. But at the same time, I can capture both the finest of interior details and the faint regions on the edge of the Rosetta Nebula.

To look closer at what the filter actually does, I have extracted the Hydrogen and Oxygen channels from this coloured image to reveal the incredible detail that these emissions give off.

With some tinkering in post-processing and after using Pixinsight to create a ‘Hubble Palette’, you get the sense of how powerful this filter is!

Ha and OIII channels extracted from the Optolong L-Ultimate filter

Incorporated IR/UV-Cut Filter in the Optolong L-Ultimate

The Optolong L-Ultimate Filter also incorporates an IR/UV-Cut filter. This helps reduce star bloating, especially in cameras that are more prone to infrared radiation.

There is a multi-layer anti-reflection coating on the filter. The coatings are deposited on the substrate using electron-beam gun evaporation with ion-assisted deposit coating. This gives the filter substantial durability and resistance to scratching.

Comparison of the Horsehead Nebula (Alnitak) taken with the Optolong L-Extreme Filter (left) and with the Optolong L-Ultimate Filter (right)
Horsehead Nebula (Alnitak)

Star halos! Like them or hate them? In the case of the L-Ultimate, the star halos of every bright star are kept to a minimum. This helps the stars look sharp and detailed.

It contributes to the definition of a Nebula. Lots of bloated stars in your photo tend to hide the intricate details of images you capture.

A good comparison to show you how the Optolong L-Extreme (7nm) compares to the L’-ltimate (3nm) is within the Horsehead Nebula. The bright star, Alnitak, can be a nightmare to control. But the L-Ultimate is able to control this to give the star a definite shape rather than a very bright, irregular shape.

In the photo above, take note of how the bright star is treated with both of the filters used.

Final Review of the Optolong L-Ultimate Filter

Overall, I am extremely happy with the results I achieved with this filter. 3 nanometres is going to get you extreme detail.

But in addition, the coating on the filter is enough for your stars to have a nice round shape. Something that a lot of astrophotographers dream about!

The only downside to this filter is the lack of a 1.25-inch version. However, a 2-inch Optolong L-Ultimate still serves me well with the use of a filter drawer.

Optics Central sells the Optolong L-Ultimate Filter – here is the link.

Leave a Reply

Your email address will not be published. Required fields are marked *