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Schuler filters

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Ed Wiley_WEY
Ed Wiley_WEY's picture
Schuler filters

I bought a used set of BVR Schuler filters to go with my newly acquired ST8XE. I have been using my ST403ME with BVI, but though a larger ship was worth investigating. I don't know much about filter cleaning and care. The B looks clean, The R has some crud that does not clean off with alcohol. The V looks fairly clean except around the margins, but has some spots that also resisted cleaning. Fact is: I don't know enough to evaluate whether these fliters are useable or can be salvaged with correct cleaning.

Is there anyone on the forum who might inspect these filters? I could send them with return postage for evaluation. I hate to invest in a new set if I can get these to work, but will if necessary.

Thanks, Ed

hambsch's picture
Schuler filters

Hi Ed,

if those are the original Schuler colored glas filters, then with time thy might have degraded especially in a humid environment.

I know from the V filter that between the two glas plates the glue disassembles when getting humid and a greasy view will be left. Maybe yours is like this.

I have not heard about this to happen in the R, I and B filters. I have had Schuler V filters and had this issue.

I hope this helps,


Josch (HMB)

WBY's picture
Degredation of Schuler Filters

The BG39 glass used in the Schuler (and other) B and V glass filters tends to absorb water over time and get "crusty." I an not aware of any particular tendency toward degradattion in the R and I filters but I have experienced degredataion of those as well over time but to a much smaller degree.   If the most susceptible glass is sandwiched between layers of more durable glass as in the B filter, the moisture tends to work in from the edges. I have heard that the Schuler filters are perhaps more susceptible to degredatation over time than some others but I went through two sets of Custom Scientific filters over 6 years in the Texas humidity. The first set only lasted two years because I left the camera on the telescope. The last set lasted about 2x as long becuase I removed the camera from the telescope and stored it inside the house in an air conditioned environment when not in use. The V ilter was always in the worst shape followed by the B. I might have been able to salvage the R and I filters but since I was replacing two I thought it best to start with a completely fresh set.  

To avoid replacing filters on a frequent basis I changed to Astrodon Interference type Johnson/cousins filters when I bought a large format camera that required 2" filters which are significantly more expensive than the 1.25" I used with my old ST7. The interference type are not hydroscopic, have almost 2x as good transmission in U,  much better transmission in B, and when couple with a CCD, much more closely match the and Ic response curve  of Cousins Bessel  R and more importantly I with the RCA 31034-A PMT than glass filters without dialectric coatings. 

Two informative articles are attached and passband curves of the Astrodon Interference filters. I have no affiliation with Astrodon and only provide the information since I have been very satisfied with them so far in the Texas humidity. Baader filters appear to have similar passband shape for Ic but the lower transimission in U and B typical of traditional glass filters. However, I haven't seen them advertised in sizes larger than 1.25". The cusom scientific I filters has curve with a longer red tail similar to the Is curve in the Astrodon paper, which may make transformation of I magnitudes less accurate.

Sorry you ended up with some degraded filters, but I hope if you decide to replace them the attached info is helpful.

Brad Walter

Jerome Hudson
Jerome Hudson's picture
Schuler Filters

Hi -

I learned this on this discussion group, so am merely repeating it.  However, I had good luck with this technique for cleaning crud from my Schuler V filter.  Also, my friend Lew Cook tried it with success:

Carefully avoid getting water near edges of the filters.  Dab your finger in a few drops of water, then dip in some optical rouge (obtainable from Wilmann-Bell ( Gently polish with your finger tip.  Clean with damp lint-free cloth.  Not 100% effective, but helps a great deal.  The edges will probably remain clouded - don't try to polish there, since you might allow moisture into the sandwich.

- Jerry Hudson


Ed Wiley_WEY
Ed Wiley_WEY's picture
Schuler filters

Thanks for the replies, I think I will just buy new filters and be done with it.


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