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Current sources of Johnson-Cousins filters

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spp
spp's picture
Current sources of Johnson-Cousins filters

Several photometry course students have been having problems getting J-C filters.

I spoke on the phone with the managing partner of Optical Structures which acquired Astrodon sometime in the last quarter of 2019.  O.S. is in the greater LA area. 

 Astrodon filters are now not being produced as a result of the business shut-downs from the pandemic.  They intend to resume production, but he is not sure when.  It certainly will not be until after the problems associated with the pandemic are cleared up.  Even then it may take some time to get back up and running.    

A number of retailers offer Astrodon filters on their websites as "back ordered".   They will take your order.  Some will also charge your credit card.  Some unfilled orders went back to mid January.  Everyone I have spoken to did get a refund without problem when the order was canceled.

Custom Scientific:  The CS website states that they have discontinued production of J-C filters.

Chroma.:  The B,V,R,I Johnson-Cousins filters are listed on the Chroma website, but each of these is shown to be "discontinued".  That said, Sarah (the proprietor Woodland Hills)  told me that she just spoke with Chroma and was promised the Chroma J-C filters within two weeks.

Baader J-C filters are still available, usually only as sets of U,B,V,R,I.  Highpoint Scientific offers individual J-C filters on the website, but they are not in stock and show  "more on the way" for the individual filter listings.

Woodland Hills offers Baader J-C filter sets on the website, but not individual filters.  They have the sets in stock now (March 31, 2020).  I asked if they would sell individual filters.  The answer was yes, they will break up the sets and sell the individual filters, but you must specifically ask for this.  (I got the impression that this offer is somewhat dependent on how many filters you want.)  That option is not on the website.  You'll have to make the order over the phone.  The quoted price for these in-stock individual Baader filters is the same as the individual filters offered by Highpoint. 

(I have no financial relationship with Woodland Hills.)

Optolong J-C filters:  These seem to be availble, but I don't know anyone who has had experience with them.  See this:  https://www.aavso.org/optolong-filters

If anyone has experience with Optolong J-C, please comment.

Phil

Eric Dose
Eric Dose's picture
The situation is just about

The situation is just about as bad for Sloan and certain other filters including the Astrodon blue-block (500 nm cutoff) filter, now renamed the "exoplanet" filter. This particular out-of-stock problem has nothing to do with the current isolation: I've been on its wait list for many weeks.

Don't forget when considering a different filter supplier from your previous one: in addition to quality, you'll want to consider (optical) thickness, else your focuser will get a workout every time your filter wheel turns. Specifically, Custom Scientific and Astrodon filters have very different thicknesses and thus focus quite differently.

I recently met an established high-end optical flats company in the northern US; they mentioned looking for new supplemental markets. I didn't think of it at the time, but I think I'll write them.

spp
spp's picture
thickness

"...when considering a different filter supplier from your previous one: in addition to quality, you'll want to consider (optical) thickness."

This is an important consideration.  Astrodon's are 3mm thick.  I think the CS's are 4mm.  So are the Baaders. 

My scope is F/10.5.  In my wheel I have four Astrodons (BVIC) and one CS (R).  When the Astrodons are in good focus, the stars in the R image are little donuts until refocused.  This amounts to about 115 tics in the TCFs focuser.   (Fortunately, the Optec software has a "focus offset" tool that allows a quick, one click correction.)

"This particular out-of-stock problem has nothing to do with the current isolation:"

It may not have been the cause of the out-of-stock problem, but it has a lot to do with when the Astrondon filters will again become available, if ever.    

Phil

 

 

 

ldj
ldj's picture
A month or two ago I received

A month or two ago I received, as a customer of Optical Structures, an email where they were making it known that the company was for sale and they were looking for a buyer. This makes me wonder, independent of the pandemic, if they had paused manufacturing of some or all of their products. Many (most?) of the Astrodon products at OptCorp are listed as "more on the way" (and we know they stock just about everything they carry!

Dave

spp
spp's picture
Optical Structures

Dave,

I was also contacted by OS.  I may be wrong about this, but I didn't quite get the message that the company was for sale.  My impression was they were trying to raise money by bringing in new investors.  ...not quite the same thing, but still not encouraging.

They have, unequivocally, stopped manufacturing all their filters.  That much was clear from my conversation. 

Phil

BGW
BGW's picture
Me too

I received that email too.  I thought it was pretty odd.  It looked like they were looking for private placement of part ownership of the company.  That would require a ton of "due diligence" !

Gary Billings

Eric Dose
Eric Dose's picture
Whither filters?

Maybe they suspended Astrodon production, but suspending production is not exactly a brilliant strategy to sell one's company, either in whole or in part.

But in more strategic terms, with the way I see things going with *all* the new astronomical catalogs (on which astro photometry depends): in the uber-unlikely event that an astronomical filter company ended up in my care, I would probably set a sunset date on Johnson-Cousins production in favor of Sloans and narrowbands. J-C photometry seems destined to share the fate of glass plates and manual guiding.

 

BGW
BGW's picture
Omega

Omegafilters.com  still lists Bessell prescription Johnson-Cousins filters on their website.  I ordered from them 15-20 years ago.  They've never been a common name in AAVSO circles, but they are there.  You have to enquire for info like prices.  

Gary Billings

spp
spp's picture
Omega

Gary,

Thanks for your comment.  I'm in contact with Omega now.

When you got your Omega filters, were they mounted or unmounted?  Did you have problems with hazing of the V and B filters?

Phil

BGW
BGW's picture
my omega filters...

... are mounted, 1.25".  I haven't had a problem with hazing, but I live in a very dry place.  I think they are AR coated, and I think there has been a problem with the coating on one of the filters, perhaps due to bad cleaning method on my part.  Part of the filter surface looks different (bright) when I look at reflected light off the surface, and I think that perhaps the coating is now absent in that area.  I haven't tested to see if would affect photometry (I don't have that filter installed) but it looks fine in transmission.

Gary Billings

spp
spp's picture
Omega filters

I got a quick response and  good information from Omega.  Omega manufactures their filters in Vermont.  They produce all the Bessells in 1.25" (actually 32mm) and 50mm, unmounted. The transmission curves shown in the website seem to have the standard Bessell shapes and central wave lengths. 

They now have most of the 1.25" J/C filters in stock, but not the B.  There would be a 2 or 3 week delay to get the B.  The price for the unmounted 1.25 inch filter  is $125 each.  The Omega filters are 5mm thick.

They also make Sloan filters to order, but don't keep them in stock.

Phil

 

HQA
HQA's picture
filter sources

For Johnson/Cousins, there are a number of possible vendors, as was mentioned earlier.  Most of these are colored-glass filters that work fine (and probably better in very fast f/ratio systems), but with lower throughput.  Watch out for the U-band filter, as proper red-blocking for this bandpass is difficult with the current available IR blocking glass filters.  One of my favorite test targets for checking red blocking is R Leo, but any cool star works well.  Both U and B can exhibit a red leak in dielectric filters, so test them to be sure they give the right photometry.

For Sloan filters (often the preferred bandpasses for professionals), the situation is much worse.  Basically, Astrodon was the only commercial vendor for these, and without stock to satisfy demand, we're pretty much stuck.  This is particularly worrisome for me, as I barely had enough filters to populate a 3rd APASS system being configured by Wayne Rosing, and cannot get any 50mm round filters for upgrades to AAVSOnet.  That is one of the main reasons we are still using the ZWO ASI183 CMOS cameras, as we had existing J/C and Sloan filters that would work with this small format sensor.  We'd much rather be using the IMX455 sensor (ZWO ASI6200 and QHY600 as examples), but without filters, it is foolish to order cameras.  Like others, I have a backorder in place at Optical Structures.

I've made inquiries with some of the Chinese vendors, with no success.  Perhaps someone else can get better results.  As some have found with some non-Astrodon dielectric filters, both bandpass shape and out-of-band blocking are crucial to good filter performance.  I worked with Don Goldman to get the Astrodon filters as good as they were, and would be happy to work with any other vendor for testing.

Arne

msheald
Filter Sources

Hello! I'm a bit discouraged. I've been thinking how to combine my ATM interest with photometry interest and make an f3 imaging Newtonian with coma corrector. I'd need 2" photometry filters for that in order to cover a full format chip, so I'll have to keep an eye on this. Best regards.

Mike

spp
spp's picture
2 inch filters

Mike,

Look for the 2 inch Baaders or other Bessell filters.  I think the Baaders may be available now.   ...possibly, also the Chromas.  Try Highpoint and Woodland Hills, maybe OPT. 

Phil

msheald
2 Inch Filters

Thank you!

Mike

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