Survey: Who Needs/Received Johnson/Cousin or Sloan Photometric Filters?

American Association of Variable Star Observers (AAVSO)
Sun, 07/25/2021 - 19:02

Hello photometrists--

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.


American Association of Variable Star Observers (AAVSO)

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.



Variable Stars South (VSS)
DSLR TG, TB and TR should not be condemned

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.


American Association of Variable Star Observers (AAVSO)
Tom said..."Furthermore, as…

Tom said..."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."

That is because the collection of photometry data is based on the "GRADUATE STUDENT MODEL". 

There is nothing wrong with this model for collecting data, if you can afford it.  Astronomy has been fortunate because they have been able to use graduate students for data collection!!!  Cheap labor that is really, really smart.  A great combination for collecting good data.

The rest of the professions are not so lucky. 

As a Forester, our data collection, is generally done with people that have on-the job training.  The data collection is overseen by professionals, with standards for data collection and error checking to reduce and correct data correction errors quickly.

Photometry is a hobby for me. 

It is a follow-up to making observations visually.  I am in awe of the intelligence and competence of the folks that collect the data compared to me.  Quite frankly, to me I just enjoy following variables.  I don't want to be a professional astronomer.  I don't want to go back and relearn the math to better understand what I am doing.  I just want to watch variables change night after night.

In Forestry, we called them "best management practices" to communicate the "standard" methods that would in "most" cases be the best choices for resource management and inventory.

In photometry, there is a great need for a simple best management practice manual for gathering photometry data. 

You really don't need to be a graduate student in a field to collect good data, but you do need to be consistent.  And to get back on topic, a standard set of filters, would really help with data consistency!!! 

More importantly, those measurement factors that result in consistent data management need to be identified, encouraged, and monitored for compliance. 

In photometry, we have LOTS and LOTS of "graduate student" level documents on the theory and background for good photometry.

What we do lack, is a simple guide....follow this process and your data results will be acceptable for scientific data needs.

The talent level of folks submitting data to AAVSO is really, really impressive.  However, there are thousands of folks out there that would be interested in collecting good data but are intimidated by the "nebulous" processes for good photometry.




American Association of Variable Star Observers (AAVSO)
Filters for SSP3a

Tom  with all the trouble of suppliers to obtain filters will any of them even consider handling 12.7 mm for the SSP Optic photometers ? I would like to get a Ic & Rc for my photometer. According to Jerry Persha the Johnson I can be used for the Ic. 


Ken Sikes

American Association of Variable Star Observers (AAVSO)
I have to take issue

Hi Tom,

I came across your post while reading through some AAVSO threads yesterday. As an AAVSO mentor specializing in bringing newcomers into photometry, I find your comments troubling. While I agree that some folks seem reluctant to undertake transforms, I have to take issue with your other points. The AAVSO has already embraced tri-color photometry. Results from RGB-based systems can be submitted untransformed as TG, TB, TR, or transformed into BVR, noting these come from a tri-color system. Arguably, the DSLR Observing Manual needs rewriting to accommodate all tri-color systems, much as the CCD Observing Manual has recently been rewritten to accommodate both CCD and CMOS monochrome cameras.

Bad data can be entered into the AID if measurements are done incorrectly, no matter whether folks are using photometric or tri-color filters or, for that matter, doing visual observations. However, a properly trained observer using any of these methods can provide data of considerable use to the scientific community. For example, I am part of the Red Dwarf Flare Star Monitoring project, and one of the advantages I have in submitting RGB-based data is that I can provide three-band measurements without sacrificing measurement cadence on a flare profile with a rapid initial ramp. This tri-band data can then be used with appropriate calibration to determine changes in apparent star temperature.

Further, many photometric newcomers come from an EAA or astrophotography background. Using their existing tri-color equipment makes perfect sense while they are determining if photometry is right for them. Further, continuing to use this equipment is acceptable if they are well trained, report results correctly, and/or are characterizing targets where timing and, to a lesser extent, relative magnitude change are more important than absolute values.

Finally, IMHO the AAVSO should be doing everything possible to encourage a new generation of photometrists. When I joined, I was surprised at the small number of AAVSO members - I was expecting tens of thousands, not a couple of thousand. I currently mentor ten students, and one thing that discourages them is the notion that tri-color data does not have value and cannot be used for good science.  

Best regards,


American Association of Variable Star Observers (AAVSO)
Quantification of Red Leak in FIlters

It came up at the meeting in Boston that it would be worthwhile to quantify the red leaks.

I can measure a few filters sent to me with OD 6 from 220-1100nm (or as needed to 3000nm) on my UV/VIS for those who think they would like to know about the red leak.

Let me know and you can just send 'em and we'll see how it goes. I will then send you or post the data.


American Association of Variable Star Observers (AAVSO)
Quantification of Red Leak in Filters Shipping Address


Please send them to 

Professor James Hamilton
Department of Chemistry
1 University Plaza, Platteville, Wisconsin 53818

I intend to make a compilation of such data and publish it in the AAVSO Journal



American Association of Variable Star Observers (AAVSO)
Quantification of Red Leak in FIlters

Yes, it seems like the complete set would be ideal for the study.

I will try and return them to you within a week(or two) depending on when they arrive with turkey day upon us..


American Association of Variable Star Observers (AAVSO)
Quantification of Red Leak in FIlters - received filters


Just so you know, we received the filters and did some initial scans. Doing calibration first and we are also scanning a new Optolong LPro filter I had.


I will let you know as soon as we have something.


American Association of Variable Star Observers (AAVSO)
Picked up mine before covid

I have the 1-1/4" mounted V, B, I, and Exoplanet filters from Astrodon for my ST8.  I had problems getting them threaded through the filter wheel and have to buy diamond grit polishing gel to work out the extremely small differences in pitch to get the filters into the filter wheel (I used a blank filter mount and didn't risk scratching my photometric filters BTW).

I also used it on an old Celestron C8 orange tube to get the coma corrector on it.