I was able to A-B test the new Lumicon OIII Gen III filter last night (2-inch) against my earlier version Lumicon OIII and an Orion Ultrablock. I was using my 18-inch Dob. It is definitely a nice filter and performed very well. There is a noticeable, if not remarkable, improvement over the old filter.
NGC 1514 (PN Tau) is an object that really benefits from a filter. I could definitely see an improvement with the Gen III. I first tried it with 87x (35mm Televue Panoptic). The background sky appeared blacker and the nebula’s contrast in the new filter was noticeably better than the old OIII. I couldn’t quite decide my preference between the Gen III and the Ultrablock, but if pushed would award the ribbon to the Gen III. I compared them both by inserting each filter into my TeleVue Paracorr but also did quick comparisons by blinking the filters by hand. At 197x (12mm Type 4 Nagler) I thought the Gen III was the best of the three. My results with NGC 2346 (PN Mon), NGC 2022 (PN Ori) and NGC 2359 (BN CMa) were similar – the Gen III outperformed the original OIII a bit and the Ultrablock slightly. Unfortunately, I did not compare the Gen III to the UHC which has always been my filter of choice for Thor’s Helmet (2359) – but I just might be changing my mind about that. The view in the Gen III was hard to beat.
I also tried all three filters on IC 418 (PN Lep) and M97 (PN UMa) to see what I thought about their performance on objects that don’t need a filter, but that do respond to them. I couldn’t really award a winner (I much prefer the unfiltered view of both).
So, to anyone looking for my recommendation, here it is. If you do not own an OIII filter, now is the time to buy one and I don’t think you could go wrong with the Lumicon Gen III. If you already own an OIII, I think you’ll find a marginal improvement in the new one. Lumicon set out to improve the quality of an already good filter and I think they succeeded. Whether the degree of improvement justifies the expenditure is a personal matter. I’d assign a “nice to have” rather than a “must have” score. I’m happy that I bought mine – I use filters a lot and these old eyes need all the help they can get. Even a few percent improvement was worth the $200 (for the 2-inch – the 1.25 is $100).
P.S. An FYI to those that are unfamiliar: Visual narrowband filters like the OIII (spoken “oh-three”) block most of the visual spectrum and allow only a narrow range of wavelengths through to your eye. This has the effect of making nebulae appear brighter because the contrast is so radically improved. Natural skyglow, artificial light pollution bands and a significant portion of the stellar spectrum are effectively blocked. The OIII passes light in a narrow band about 10-12 nanometers wide centered around 500nm. The two strongest emission lines in planetary nebulae come from the recombination of doubly ionized oxygen atoms which produce light at 496nm and 501nm. According to the test data provided, this new Gen III filter passes 98.6081% of the light emitted at 496nm and 98.5658% of the light emitted at 501nm and transmits significantly less than 1% at all wavelengths outside of its design bandpass.