We're doing a survey to find how many observers are currently looking for either Johnson/Cousin or Sloan photometric filters. If you have recently ordered and/or received filters, what did order and how long did it take to receive them?
At this point, my list of possible filter vendors includes: AstroDon, Baader, Chroma, Custom Scientific, Omega Optical, QHY CCD, and Spectrum Thin Films. If you have ordered either type from another vendor, please let us know. If you know of other vendor who should be added to the list, please let us know.
I thin we are all aware that COVID-19 has created difficulties for manufacturers, suppliers, and vendors. As the pandemic begins to wind down, filter availability may change in unpredictable ways.
This is part of a larger inquiry to determine the level of support AAVSO can offer to Sloan filter users in the future.
I ordered a 1.25" B filter from AstroDon in Nov 2020 with a due date of March 2021. It arrived in May 2021.
My club, ATMoB, ordered a set of unthreaded 50mm UBVRI filters from AstroDon in Nov 2020. The promised delivery was March 2021. Not only have they not arrived, they have not responded to emails or phone calls.
All filters referenced were Astrodon filters sold by Farpoint Astro. I understand that Farpoint purchased the Astrodon product line.
In November of 2020 I made an advance order for a J/C 1.25" B filter. The order was fulfilled seven months later. I was able to order and immediately receive a J/C 1.25" Rc filter, second quality in June 2021. At this time I am in need of a J/C 1.25" Ic Astrodon filter. At Farpoint I was informed to go to their website and get on a preorder list. However their website no longer has any Astrodon J/C photometric filters listed. A subsequent inquiry received a frustrated response informing me to 'just keep looking'.
I spoke some months ago with an Astrodon person on the phone. A long delay in receiving a clear filter to go with my BVRI set that I had ordered and received before the COVID insanity! I was told it was difficult for them to obtain specialty glass from their glass suppliers also that the government was buying all the specialty glass and that glass makers weren't being bothered with small orders. They did not get the glass from China nor Japan. Not a direct quote but the gist of my conversation with Astrodon. I did receive my Clear filter about three months ago.
So I anticipate the need for a new V filter for the ST8.
Also a new set of BVRI for a possible new camera.
The ST8 is fantastic, but aging.
I use Astrodons.
Finding filters has been a challenge...
I recently purchased 2nd quality 50 mm round filters from FarpointAstro where scratches were near the edge for Sloan r', i', and z'. I use these for exoplanet transit observing and transit depth chromaticity dependency tests due to the sharp band wavelength cutoffs. FarpointAstro also has the Exoplanet CBB filter which I also purchased.
I made an order for 1 1/4" round filters for g', r' and i' in Sept 2020 to FarpointAstro. I only received the i' filter as of now.
I also received an J/C Ic 50 mm round filter that was briefly in stock.
I placed a wanted ad for Astrodon Sloan and J/C filters on astromart and only had a response for a 1 1/4" i' filter.
Still need 1 1/4" r' , a 50 mm g' Sloan filter, and a B J/C 50 mm filter to complete the Sloan and J/C filter sets.
The filters from other companies compared to Astrodon seem to have different shaped wavelength bands for photometry filters so there is no standardization, which can be a problem for magnitude measurements comparable to the AAVSO databases.
I had been using a DSLR for a year or two but recently bought a ASI183MM-Pro with a filter wheel intending to get a set of Johnson/Cousins filters but if it’s hard to get hold of those in the US it’s even harder here in the UK. The only European manufacturer was Baader but they have now discontinued production. I did order a Chroma V band filter through a UK dealer but after waiting months and reading in the forums here about doubts over the transmission curves of Chroma filters, I decided to cancel. Instead, I went for LRGB filters, reporting the results as TG, TR, TB. This is disappointing as it partly negates the benefits of the new camera compared to the DSLR. but for now I intend to sit tight and wait for more clarity on 1) the suitability of the Chroma filters, 2) improvement in the supply situation generally 3) whether Sloans are going to replace Johnson/Cousins..
Regarding the list of suppliers, I thought Optolong also offered Johnson/Cousins filters and I think their transmission curves look a bit less square than the Chroma ones.
Soon I will also do the transition from DSLR to CMOS camera with filter wheel.
I have read that transforming form RGB to Johnson .. BVR .. is also possible. ( G-> V) (...and much cheaper?)
But one has to do calibration (of Jonson UBVRI) anyway, or do a transformation (TG to V) in either way...
My question is: How applicable is it to just use a 2" G Filter and transform it to Johnson V-Band?
I assume, that the correction value will be greater, as if one uses an original Johnson V Band?
Question to the Instruments Section: Are there other side effects, beneath a possible greater transformation-correction-value? E.g. of different filter spectral response behaviour with the O B A F G K M spectral classes of stars??? ,
Or what is the scientific difference in transforming G -> V instead of using V and doing calibration with standard (Landolt) fields of V ?
So far my main interest has been timing the minima of eclipsing binaries so whether I'm using TG or V is unlikely to be significant. However I would still like to have got hold of J/C filters just so my results were more compararble with others. I haven't got to grips with transformations yet but as far as I can see there are significant differences between TG and V, especially for red stars and I'm not clear about the extent to which transformation corrects for this. With the TR v R and TB v B filters the differences are greater still ( I believe largely because of the different responses of the filters to H alpha and H beta emission lines). Also, I suspect the red filters in an LRGB filter set will be more sensitive to IR from H alpha than those in a DSLR ( which block IR unless they have been modified) so the TR, TB and TG observations may not themselves be standard or comparable with each other. If a switch away from J/C filters to Sloans becomes inevitable, my question to the group would be about the comparability of Sloans with the decades of V band observations and more than a century of visual observations held on databases like the AAVSO and BAAVSS. Will some form of transformation be possible or will there be a discontinuity ?
IMHO when using very different bandpasses (e.g. rectangular ones in the case of "J-C filters"), much of the previous work about photometric systems is under the fire. In the worst case scenario, astrophysical calibrations established using a standard system are not valid anymore. There are some areas of photometric research, where the impact is small or almost negligible - e.g. times of minima of eclipsing variables and exoplanet transits observed with small telescopes.
At the same time, there are tens if not hundreds of photometric systems in the world, so that wouldn't be something unheard. Creating a new photometric system is definitely not a convenient neither easy task to do.
I ordered at 1.25" Ic AstroDon from Farpoint last November and am still waiting. Contacted Farpoint last week and was told they were out of stock with no date when they would be available.
- Patrick Ashmore
I am looking at larger sensors that take either 36mm or 2" filters. I would definately be in the market for a true Johnson/Cousins BVRI or even a Sloan set of 36mm filters.
I'm looking for our observatory three sets of 50 mm round and unmounted Johnson-Cousins (U) B, V, Rc, Ic filters and also one 50mm round and unmounted set of Sloan (u)gri((z)) filters. My constaints are: very close passbands to the photometric system definition (but I would prefer very much maximum transparency at the peak of passband) , 5mm maximum thickness, parfocal, and hard coating to protect from moisture. IMHO more than one manufacturer in the list you gave fail to meet at least one criterion, the worst and the most common issue is very different passband. IMHO Astrodon filters tend to meet all of those criteria.
I want to transition from dslr to Johnson/cousins. Have had my order in for months for 31 mm astrodon through High Point scientific...still waiting
Hi Richard, I’m looking for V and B filters and have been scouring the vendor no avail. Recently my AAVSO mentor suggested the Chroma Bessel filters would be fine. I’ve contacted Chroma in Vermont and they can provide them. I recently sent the spectral information on these with a comparison spectrum for JC and asked AAVSO folks whether they would be accepted as V and B submissions. I believe Sara Be k may be forwarding the question on to you. Currently I’m submitting TG data based on ASI294 mc cmos camera. I have an ASI178MM which I hope to use with the Chroma filters for V and B submissions - if those filters are approved for V and B data. What’s your view on these filters?
I purchased it a few days after an email notifying me the availability of 2nd quality Astrodon filters from Farpoint/Optical Structures on June 16,2021 and received it within a week.
The defect was not obvious to me but I did not examine it with a microscope.
They have photometric filters for sale but I have no other information
I tried to get Johnson Cousins filters last autuum from Astrodon. But as everyone know, nothing is available. So I went another way. My setup: I use an ASI 290 MM camera (monochrome) with a Baader UV / IR cut filter 400..700nm. And then the program ASTAP for photometry (has eDR3 converted V-magnitudes down to 17m). I compared my results in the range 12..17m, they are V compliant. So I don't report anymore as CV.
As part of an observatory upgrade I will be in the market for Sloan griz filters - probably 1.25". I have not placed any order yet so am looking at this thread with interest.
I have placed an order for Custom Scientific g' r' and i' filters, 50 mm unmounted. They have had some delay due essentially to Covid but I am going to receive the filters in a matter of a few days (I think they have already shipped the filters).
I've been looking for BVR filters for months - no one seems to have them in stock. I ordered a V filter from a company that showed it as "in stock" on their website, but then told me they were backordered and refunded my money. Looking again today to see where I can get some, this thread has helped (I hope).
After our email exchange a month or two ago and your positive reaction to the Chroma Bessell filters, I went ahead and ordered the 'V' filter version and it arrived a week or so ago. I'll get the 'B' version once I get some time and experience with the 'V' filter and am ready to get into transformations.
Of course, if you're feeling that the J-C/S filters might become available, I'd be interested to know that before investing in another filter.
Be aware that Bessell I filters do *not* have a Cousins passband. Yes, Cousins had a Bessell filter, but he used it in conjunction with a photomultiplier that cut off at about 900nm. I had Chroma custom-make Ic filters for my photometer using Bessell's reverse-engineering of Cousins' total response curve. The transform coefficient is quite small. Before ordering I filters, check the transmission curve.
can you provide a spectral response tabulation and/or spectral response curve illustrating the Cousins Ic passband for the custom filter you got from Chroma?
Thanks for the input you have provide through your questions.
We're currently working behind the scenes to get a handle on the photometric filter situation. In particular, the key issue is:
Are all filter offered as Johnson-Cousins UBVRI filters equivalent? The classic Bessel design is made from dyed glass while interference filters with the same nominal central wavelength and bandpass are also available. Some years ago Arne Hendon wrote software to simulate the passage of light from different stellar type through optic, filters, and finally to your sensor. He is currently updating the software with the aim of resolving this and similar questions.
We will also evaluate the Green (TG) filters from RGB color imaging sets. We are also looking into related issues such as the effective color of the popular one-shot-color cameras used unfiltered and with different filters. Many observing projects that involve timing of event do not have the rigorous filter requirements that precision photometry does. If you are stuck waiting on back-ordered filters, look into an observing program that may be suitable for your current equipment.
I am a beginner, but I have searched high and low for photo metric filters. It seems like nobody is manufacturing them anymore.
I will need a set within the next year or I will just have to continue using a green filter to approximate a V filter.
We are working on the problem of filter scarcity, specifically whether the standard Bessel BVRI dyed glass filters can be effectively replaced by interference filter with the same center wavelength and passbands. You green filter, if you bought it in a RGB filter set, is probably of this type.
What size filter are you looking for? Which vendors have you tried, and what did they tell you?
Is there any chance that AAVSO will put in a bulk order for filters?? Is there a possibility of a grant to manufacture the science filters and then resell to the astronomical community.
Then resell to members??
I would be more than willing to pay full retail or greater just to have a consistent set of filters.
If we could get a commitment from people to buy filters and then place a bulk order will that be enough to get a company to manufacture them??
This option has been explored. At least for one of the larger, well established, manufacturers there was just no interest at all in offering a discount (or reopening a shut down production line) for a large bulk order. You can still buy traditional Bessell filters by special order from one of these manufacturers, but the price is much higher than for the newer versions of the BVRI filters.
The process now is focused on evaluating the new BVRI filters which are available now to provide some guidance for observers making their own purchases.
I ordered an Astrodon V-Filter in May. So far I have received an email every month that the filter will be available next month.
The day before yesterday I received an email that the filter would be available in February 2022 at the earliest. I do not think that Astrodon is still delivering and I am no longer interested in the company.
I use chroma. I have the complete set of them here.
Possibly order an Optolong filter set for comparison. Let's see but Astrodon is out for me.
Thanks for the input.
Recently we heard from Custom Scientific that they offer 1-1/4-inch mounted dyed glass Bessel filters @ $375 each. Chroma seems to have stock, too.
Arne Hendon is developing software to do synthetic photometry comparing different filter profiles and their effects. I hope this will be done some time after the Annual meeting (we are all busy right now preparing for the meeting).
About one month ago I spoke with an officer of the company that now owns Astrodon. He told me that the UBVRI filters were no longer being made, and that there were no current plans to resume production.
Arne has been testing the Optolongs. There is a red leak in the U and B filters making these unsuitable for observing red variables. According to Arne, the VRI filters are fine. There may be an attempt to help Optolong to remedy this problem.
Baader's new Bessel and Sloan photometric filters are now available.
It would be of great help if the most experienced of the forum could offer us their impression from the manufacturer's specifications.
That's exciting news. The transmission curves look pretty reasonable, though the proof will be in getting them onto some scopes and getting transformation coeffs for them.
The prices are pretty reasonable and, given how hard it is to find anyone selling filters today, that's definitely a nice bonus. I couldn't find a "C" (clear) filter anywhere on their site, but perhaps that was an oversight on my part. It's handy to have a clear filter for faint objects to avoid having to refocus.
Baader has C filters. I have Just received one in a package of LRGB imaging filters.
Take a look at their site under clearglass filter
I dont have BVRI filters from them though.
Somewhere on the Baader home page announcing the new filters there was a remark that now all the Baader filters would have the same thickness. This probably means that the Clear filter used with the RCB filters would work.
Of course this should be confirmed by Baader.
To me these look like they have the typical J/C passbands. Baader has experience with hybrid colored glass/interference coating filters. The previous (now discontinued) Baader UBVRI filters were hybrids. Baader has a good reputation for producing quality goods, including filters.
These may be what we have all been waiting for, but they are not actually "available" yet, at least in the US. I have a friend who contacted Alpine Astro yesterday (Nov.2). He ordered a set of the new Baaders and was told that Alpine expected the filters to arrive in December. I plan to order a B,V,I set for testing, but I'll wait until they are in stock.
I have a 7 position filter wheel with LRGB filters. I plan to add 3 photometric Baader filters when they become available. Would you recommend BVI over BVR?
I was all ready to order the new Baader's but then saw forum reports of severe halos for some of the new astrophotography filters, so now I'm a bit gun-shy. Both my Chroma V filters (older versions with J/C passbands) have become unusable with coating degradation (including a replacement from Chroma last summer, new old stock).
Is anybody ordering from anywhere right now? I had a dialogue awhile back with Omega, so might be time to revisit. However their sizes are a bit non-standard, so maybe some creative 3D printing of adapters for my 1.25" filter wheel might be an option.
If you look on the Baader home page it discusses the problem of halos in the prior versions of its filters. There, it states that new filters have been redesigned specifically to correct this problem.
I recently bought a set of Optolong filters from High Point Scientific after looking for a year. Delivery was fast from stock. I haven’t installed them yet but was disappointed to hear at the aavso convention that the B and U filters have red leaks.
You would probably never use the U filter for photometry. I have been told that astrophotographers like the U filters for Venus, so you might be able to sell it on CN or Astromart. A red leak for photography may not be a big problem.
You might be able to substitute a Baader B for the Optolong B. Check the thickness on both the Baader and the Optolong. If they are the same there might not be much of a focus offset. Baader will sell individual filters.
I will note that many satellites, surveys and science programs create their own filter sets.. In addition to Johnson/Cousins and Sloan, there is Tycho, Gaia......
For integrating data from these varied sources into research studies, transformations between the systems have been developed. The literature abounds with them.
Additionally, regardless of the filter "standard" you choose. The passband you actually measure is the convolution of the responses of you optics, atmospheric conditions, and camera. Thus, even observations with "standard" filters need transformation for comparison with other observers data.
Given these conditions, I am going to suggest that we move on add a new standard to the pile!
Why not adopt standard color separation interference filters to the mix?
- They have a mass market
- They are readily available from many sources
- They are relatively cheap
- They are not going away
- Their pass bands are relatively close to J/C B,V,R
- Most every amateur has a set of the them, so AAVSO has a HUGE pool of potential new observers.
I am current working on software that transforms these onto J/C and am have very promising results.
Similarly, One shot color cameras have built in R,G,B filters. Though, they too have passband shapes similar to J/C.
Developing similar transformation software for these devices is yet another new "standard" possible. These devices (when properly sampled) provide simultaneous color measurements. That makes handling extinction and zero point simpler.
The above suggestion does require that photometric measurements of a target must be made in at least two colors to allow for transformation. The OSC cameras make this implicit. For external filters this does require interleaving observations between two filters for time series work, but the cadence ratio, (e.g G/R) ratio can be relatively high.
Getting observers to perform transformation even on standard filters is like pulling teeth. People won't do it. It's bad enough that DSLR observers are pumping untransformed B and R into the AID. Embracing tri-color photometry with CCDs will result in a flood of non-standard data.
Furthermore, as things stand we don't have enough training and mentoring resources to help everyone do good photometry. We could not possibly accommodate a burst of new observers.
There is nothing inherently bad about these non--transformed data. They can be very accurate, with appropriate comp stars.
The issue is that the colour index of the comp star should be as close as possible to the colour index of the variable.
A test with my DSLR showed that for a 0.1 mag unit difference between the target and comp star B-V values, the errors for TB, TG and TR are 0.048, 0.012 and 0.028 mag respectively for measurements on photometric standard stars.
The error relationships are linear. Thus if the B-V colour index target-comp difference is 0.5, the errors will be 5 times greater.