Leroy's FilterQuest

The filters referenced here are listed in Leroy's Filter Evaluation (link at the bottom of this page).

I use and love 2" oculars (eyepieces), however, they are not routinely produced below 25mm focal length. As a consequence, I also have and use 1.25" oculars as well.

I had only recently read about, and realized the benefits of color filters for Lunar and Planetary observation. Since this is one of my primary interests in astronomy, I thought I should acquire a set which would give me the range of variation I expected, and one also suitable for astro-photography as well. I had seen the sets of 1.25" filters that Meade and Orion sold, and The Backyard Astronomer's Guide even produces sufficient justification for buying them. I ignored their advice that not all of the filters are needed—I want to seriously study each planet as they soon become available again (rationalization, justification, ... :-).

It only made sense that I should try to acquire the filters I wanted for 2" sized oculars, if I could somehow use them for my 1.25" oculars as well. Fortunately for me, I discovered that Lumicon made several adapters for the 48mm filters they carried, both color and specialty (DS, UHC, H-beta, etc.). Lumicon makes a threaded 1.25" insert for 2" star diagonals, a threaded T-adapter for prime focus photography, and of course, all of their other accessories (Giant Easy-Guider, Star Diagonal, etc.) are also threaded for 48mm filters.

Another issue arose at this time—what is a 2" filter? Lumicon's literature really didn't say, just that their 48mm filters fit "most 2-inch eyepieces". Orion had similar wording for their filters. Calling Orion, I discovered that their filters were actually 50.038mm in diameter. Then I started wondering how this 48mm was determined. It wasn't until I asked Cathie Havens at my local telescope shop, that I discovered (finally) a definitive answer—48mm is the 2" standard filter!

I trusted that last piece of advice, and started experimenting. Since Orion's catalog told me that their filters fit "most modern eyepieces", I ordered the three that were available at the time. I figured with their generous and reasonable return policy, I could try them out and return them if they didn't work out for some reason. They didn't work in the two newest 2" oculars of my set (the Tele Vue 55mm Plössl, and University's 25mm MK-70), nor did they completely and properly thread into my Lumicon 1.25" ocular insert. I returned the Orion filters.

I had found ASTROPTX on the web and ordered a pair of replacement legs for my Dynamax 8 telescope. Along with them came their mail-order flyer which mentioned their 2" filters. Scouring their web site, I could only find a specific reference to their Vernonscope filters, but the prices didn't match. I called them. The cheaper 2" filters from their flyer were Celestrons, and they told me that their Vernonscope filters had a different pitch from the industry standard, and were used exclusively for the Brandon oculars. So I ordered a set of four of their 2" Celestron filters.

The Celestron filters arrived. Three worked just fine, though they had the same problem with the Lumicon adapter that the Orion filters had. I had also immediately noticed that the Celestron filters, except for some labeling, were practically identical, including the storage cases, to the Orion filters (I hadn't returned them yet). When I did return the Orion filters, the customer service person I spoke to (interestingly) blamed telescope manufacturers for the rift in filters for 2" oculars.

The fourth Celestron had the exact same threading problems (all of them, not just the Lumicon adapter) as the Orion filters had.

ASTROPTX tends to be a collector of many things. They told me that they bought out all of the Bausch & Lomb telescope gear when they closed that division (the old Criterion company). That is how they came to have legs that I needed for a telescope more than 20 years old and long since out of production! I noticed that the boxes for the Celestron filters had the original factory scotch-tape sealing the filters in. I also noticed that the one Celestron filter that didn't fit differed from the three that did in a single way—its "MADE IN JAPAN" was a stick-on label on the box tops, while the other three were stamped "MADE IN JAPAN" on the box bottoms.

I reasoned that what we had here were two different generations of Celestron filters. I returned the one filter to ASTROPTX and they found a replacement filter with stamping. They could also find only one more filter that I needed which was also stamped and not labeled. Both stamped filters had only the deficit of not working with my Lumicon adapter (like the other three).

My reasoning about two generations of Celestron filters was reinforced by the fact that ASTROPTX had fewer choices of filters in the stamped boxes than in the labeled boxes. Also, the filters I had obtained were those Wratten numbers that there would have been less demand for.

When the Orion filters had fizzled out, I decided to seek more sources of pure 48mm filters. A friend had introduced me to the web site for Hands on Optics. Gary Hand set me up with the set of Hoya 48mm filters that he sells, as well as three Vernonscope filters. But Wait! you say, what about the different thread pitch? Turns out that would only seem to apply to their 1.25" line of filters for Brandon oculars, not their 2"—the Vernonscope filters work perfectly fine with all of my equipment.

Cathie Havens introduced me to the line of fine B+W filters that she carries, however B+W does not carry the wider range of Wratten numbers that I desired. I have bought as many of those filters as possible, though the set of Hoyas from Hands on Optics did give me a #80A. There is one other B+W filter (#82A) that I may or may not buy.

One other item worth mentioning. The Hoya filters use their own labeling scheme, non-Wratten based. Therefore, the Wratten numbers I have for Hoya filters are based strictly upon what Gary Hand told me. My friend had looked through the Hoya literature and came up with different numbers than Gary's. Just this morning as I write this, I noticed that the documentation with the Hoya filters says that their series of Neutral Density filters (only mentioning NDx4 and NDx8) are suffixed with the denominator of the fraction of light reduction—if that is correct, their ND2 is not the Kodak #96ND 0.2 with 63% transmission, but:

ND2 -> 2 -> 1/2 = 50% = Kodak #96ND 0.3! (Sigh - already have in B+W)

I have one (or maybe two) duplicated filter(s) from the Hoyas now, so I'll probably sell it/them. Maybe I'll replace the Celestrons with more Vernonscopes. Maybe the FilterQuest will never end ...

Footnote: March, 2002 — I ended up buying the three Meade filter sets because I have purchased three small telescopes since I wrote this web page. They all use 1.25" accesories, and I will sometimes need to use those without access to the 48mm collection. Ironic isn't it?

Written: 25 June 2000.

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