At the beginning of the winter I bought a Optolong L-eNhance dual bandpass narrowband filter. For the uninitiated, a narrowband filter basically means the filter blocks all of the light coming into the telescope except the light from very specific wavelengths. In this filter’s case, that would be the H-alpha and Oxygen III signal. These wavelengths are the most common narrowband filters people use because many of the nebulae in the sky have tons of these gases in them. Notably though, this filter leaves out Sulfur data, but that’s the lesser of the big three gases and I imagine they did this to save on cost.

Above this is the bandpass chart showing where light is blocked and where it is let in. Note the peaks at Ha and OIII, with H-beta sneaking in.

I’ve had this filter for a while now and got a chance to shoot many narrowband targets and for the price, this is a fantastic one shot color filter. If you have a mono camera, don’t use this, go buy individual filters, but for OSC this has been great. Even with wider bandpasses it isn’t letting in anywhere near enough moonshine and light pollution to wash things out like many said it might. My mean value on a 5 minute sub with no moon was around 1300 which, considering the fact that OIII lets in much more light pollution than Ha was very good.

I have the 2 inch version of the filter and paired with my 2 inch nosepiece gave very little to no vignetting on my DSLR. A 1.25 inch version would result in significant vignetting so only get that one if you’re pairing it with small sensor astronomy cameras. Of course a side benefit of using this filter is that because it is letting in a lot less light than with no filter or an LPR filter, stars appear much smaller to begin with in each frame. With broadband, stars look bloated and are generally twice to 3 times the size as in my narrowband images. This not only increases the image quality of your final image, but the stars just generally look a lot sharper and contrast in nebulae is much improved.

The question is not whether this is a good filter, because it is. This is a great filter in fact. What you really need to consider is whether or not it’s worth it to buy this or to buy individual Ha and OIII filters. In terms of value, you really can’t beat the L-eNhance. At $229, this filter is less expensive than Optolong’s own 2 inch OIII filter. Granted, the Optolong OIII will let in less light pollution and increase contrast on nebulae, but most of that can be fixed or recovered in post. If you’re shooting with a DSLR or color camera at all, the L-eNhance is probably a better option than individual filters. With just an Ha and OIII filter, a DSLR just isn’t sensitive enough to take the best advantage of both and you’ll come away with very similar images in the end and I bet the L-eNhance has less noise in the final picture, maybe someone will do a more scientific test on this in the future. I would really recommend individual filters only for mono and definitely not recommend the L-eNhance on a mono camera. You can see some of the images I’ve taken with the filter below. Ignore the stars in the corners of my images, these were taken with an achromat refractor and no field flattener. The amount of signal I was able to pull out with a DSLR and this filter really was astonishing though, and I’m excited to get onto the summer with more big nebulae.