L.pro Review

[Allen Yerke]

Thisfilter is less aggressive than all of the other astrophotography filters I use in terms of blocking light. As a side-effect of retaining natural starlight color, each shot will also expose more skyglow than I am used to with the much more aggressive SkyTech CLS-CCD.

The L-Pro is a multi-bandpass filter that suppresses the transmission of select light pollution lines. For example, mercury vapor lamps, sodium vapor lights and even skyglow caused by the oxygen in our atmosphere. The balanced transmission aims to offer great color balance and minimal color cast.

As I and many other amateur astrophotographers have discovered, the L-Pro makes an excellent all-around broadband color filter. Even when shooting emission nebulae projects that benefit from multi-bandpass filters (such as the Optolong L-eNhance), it is beneficial to collect exposures using the L-Pro to capture the natural star colors in the field.

For example, the image of IC 2177 below (part of the Seagull Nebula) was captured using the Optolong L-Pro filter in front of the ZWO ASI533MC Pro camera. This data will be blended with narrowband images of the area (primarily H-Alpha) to achieve a more well-rounded and natural-looking image.

I have chosen to capture an exquisite deep sky object that will showcase the broad spectrum qualities of the Optolong L-Pro filter in a light-polluted area. Pleiades (Messier 45) is a well-photographed open-star in the constellation Taurus. It contains a collection of 7 bright blue stars and plenty of reflection nebulosity. A deep long exposure image will also showcase vast amounts of cosmic dust surrounding this cluster.

The test images were captured using a stock Canon 5D Mk II DLSR and a William Optics Zenithstar 73 Refractor Telescope. Each shot is a 90-second exposure at ISO 800. The RAW images have been converted to jpegs, but have otherwise not been processed.

The camera I am using for Pleiades image is a stock Canon EOS 5D Mk II. This is my full-frame daytime photography camera that should provide an honest example of what you can expect using stock DSLR with this filter. The camera includes the original IR cut filter which reduces the impact of hydrogen-alpha light collected by the sensor. For reflection nebula targets like M45 without any h-alpha light, a stock camera like this is perfectly capable of producing a cracking image.

For large (broad-spectrum) deep-sky targets like the Pleiades star cluster, Andromeda Galaxy, and Triangulum Galaxy, the combination of a stock full-frame DSLR and a telescope like this can create some incredibly wide shots that capture the entire object with room to spare.

The Sky-Watcher HEQ5 Pro SynScan computerized telescope mount performs exceptionally well at this focal length, even without the use of autoguiding. Accurate polar alignment and balance are imperative for successful imaging using an EQ mount without the aid of autoguiding.

The data collected using these settings falls in the middle of the histogram, without clipping any information in the darks or highlights. The images could be shot using longer exposures, but I want to reduce the number of subs that could suffer from the periodic error of the telescope mount.

As you can clearly see from the single image frame comparison image I posted, the Optolong L-Pro filter makes a huge difference in terms of reducing light pollution. This certainly helped me collect data with better contrast and less skyglow for my image of Pleiades.

As always, increasing the overall integrated exposure time is my greatest ally in the battle against city light pollution. To create an image with a signal-to-noise ratio comparable to a dark sky site, I need to collect 4-10X the amount of data. Image processing is still a challenge, but I am used to it.

My final image of The Pleiades includes 4 Hours and 10 minutes of total integrated exposure time. Each 90-second, ISO 1600 light frame was stacked in DeepSkyStacker to improve the signal-to-noise ratio of my final image. Final image processing was done in Adobe Photoshop using a number of plugins (listed here).

For the image comparison below, a modified Canon EOS Rebel T3i was used. The shots were 30-seconds each on a fixed tripod. I intentionally included the light from my back window to showcase the subtle light suppression qualities of the L-Pro filter.

Because the L-Pro creates a rather natural-looking image, this would make a great choice for Milky Way nightscape photography. It could help tame any surrounding light pollution without creating challenging color correction issues to deal with in post-processing.

I am quite pleased with the effectiveness of the Optolong L-Pro filter from a city sky and thrilled with the image of Pleiades I was able to produce. The 2-inch round-mounted version fits neatly inside of my field flattener, allowing me to connect any type of camera I want.

I late December, I pointed my 300mm Camera lens towards Orion, for another shot using the L-Pro filter. This time, I used my crop-sensor (modified) DSLR, t Canon EOS Rebel T3i. Here is what you can expect to achieve using the L-Pro with a full-spectrum modified DSLR from the city:

In March 2019, I tested this filter on a stock Canon EOS 7D Mark II DSLR. The target was the glorious Carina Nebula using a RedCat 51 refractor telescope. This photo contains less than 10 minutes of overall exposure time and was captured during my visit to Costa Rica.

Nice review Trevor! It is a good filter indeed. Just a side note: I have the Optolong L-Pro clip-in for fullframe Nikon and it vignets heavily when used with my telescope (900mm F9). Normal lenses are fine.

I have a quick question. My backyard is a Bortle 5 and am just getting set up to image. I am using a William Optics GT71 with a 0.8 flatner. My camera will be a borrowed T2i but may move to a Zwo 294MC pro. I can only get one filter at this time so my question would be if you had only one filter to choose from starting out, which one would you prefer? Thanks

I like the thorough review. I have been using a L-pro as well on a full spectrum camera, and I wonder if you could give your opinion on the following:

The L-pro also serves as a UV/IR cut according to the spectrum. I have noticed that on long exposure, the large stars can become a little bit bloated, which may indicate that no all the IR is blocked by the L-Pro.

I live near the city with the view of the city skyline in front of my balcony, so severe light pollution. I would like to know if the L-Pro is the right choice or should I go for a CLS, or even a UHC? I use standard unmodified DSLRs (Canon 200D and the Canon 5DS) and my aim is to capture the Milky Way and possibly deep-space objects from my balcony. Would be great to know your thoughts.

I notice that your photos of Hydrogen rich nebulas, always have the characteristic pink color. Mine are always red. Is there a setting in Deep Sky Stacker that needs to be adjusted for this LP filter?

I have the same problem, with L pro, I have reddish stars, and if I correct the star color with Astro Pixel Processor I get white stars but the target (e.g. some red nebula) becomes more pale, less red.

It may have been explained and I missed it but when using the 5dm2 and the WO Zenith are you stacking the L-Pro twice? Is the drop-in filter in the camera and the 2 inch screwed in the flattener simultaneously?

I will be interested to hear any responses. I have a 1.25" unbranded (or an inexpensive brand) LP filter that I very rarely use but I've recently being getting a 2" set up together for use with my refractors and this included a 2" Optolong LPro. I have not had much time with it on the field or tested it back to back with my 1.25" filter but I can say it does noticeably dim the view although I didn't note how much of a magnitude less I could see. Where I am it makes the background darker but it also makes the stars dimmer. I will need some time in the field before being clear on the pros/cons.

I would say it's more applicable to general imaging than visual from light polluted skies where maintaining color balance and shorter exposures is important. Visually, it would have a subtle effect, but would probably be a decent choice for galaxies. For nebula, there are better choices. It just depends on what you want from a filter.

In my experience neodymium filters are good moon filters but useless for DSOs. The Astronomik CLS used to be reasonably effective on certain galaxies and star clusters where you can't use a UHC/OIII filter but that was when street lighting was sodium and the majority of light pollution was in the band that it cuts out. However, now that almost everything is LED the light pollution is across the whole spectrum and the usefulness of the filter decreases every day. Depending on the type of light sources in your area perhaps a CLS might give some improvement for now but I wouldn't expect any advantage to last. I'll have to give mine another go to see if it is still useful on anything but I don't remember using it for a while now. With the additional transmission spike in the middle of the cut out section I would expect the L-pro to be even less effective than the CLS.

The one thing that did make a noticeable difference was my Rsky observing hood, but I assume that recent events mean that we can no longer buy these and so you would have to find another item to block out any light not coming from the eyepiece.

I also found some of these images. On the face of it the Optolong L-Pro comes out well, but I don't think photographs are representative of what is experienced visually, and I'm wanting to compare the L-Pro and CLS with the Baader Neodymium that I currently have.

I would say it's more applicable to general imaging than visual from light polluted skies where maintaining color balance and shorter exposures is important. Visually, it would have a subtle effect, but would probably be a decent choice for galaxies. For nebula, there are better choices.

The L-Pro is certainly listed by FLO under astrophotography filters rather than visual, but I assume that's because the narrow pass bands help with colour balance rather than because of some issue in using it for visual.

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