Thu, 12/28/2023 - 17:59
I am using an Astrodon V photometric filter and would like to add a Blue photometric filter to my system. I have been looking at the Blue filter form Chroma(27061) and Badder(29617508).
Is there any significant difference between the two?
Thanks
David
I don't know the answer to your question, but here are a couple of things to consider.
All these filters (Astrodon, Chroma, Baader) are interference filters. except I think the Baaders are kind of highbred using some colored glass. B interference filters tend to have a "red leak" where some red light gets through into the B. This can cause a problem when observing very red stars. The original Astrodons also had this problem. Arne Henden collaborated with Don Goldman, the owner of Astrodon, to fix this problem.
Since then the Astrodons have been the gold standard for Johnson/Cousins photometry. As far as I am aware all subsequent B filters that have become available on the amateur market do have some red leak, including the Baaders. I have not yet seen any reports concerning the Chromas, but this would be an important consideration. In a recent forum post Arne mentioned that he has been testing of all the available J/C filters and may be getting close to reporting his results.
Another minor point: Astrodon J/C filters are 3mm thick. It would be helpful if your new B filter also had a 3mm thickness so they would both come to the same focus. Otherwise if you wanted to use your J/C filters to also make pretty pictures you would have to refocus when you changed filters. This is not so important for photometry since precise focusing is not necessary.
Phil
Hi Phil,
I "jump" on the subject because talking to you about it...
Have you done any studies on Optolong filters?
I've been using them since spring and I'm really happy.
After having made several comparisons, my data is average, in the spring, I want to check them with transformation.
Their light curves are also tighter than the Astrodon and Baaders. Can you tell us more about it?
Thanks in advance!
And happy New Year!
Health and Wisdom (Today, the world needs it so much...)
Hi JB, It's nice to hear from you.
"Have you done any studies on Optolong filters?"
Back in 2020 I did some testing comparing the B,V,I transforms of Astrodons, Chromas, and Optolongs. I wanted to see how close the transforms from each maker got to ideal (Color transforms = 1.000, Mag transforms 0.000). I used a 10 slot filter wheel so all the tests were done with the same camera and telescope (SBIG ST-10 and C5) without the need to remove and replace any of the filters in the wheel.
Of course the Astrodons were best. I'd say the Chromas and the Optolongs were about equal and both would have passed muster if you had submitted those transforms yourself when you took CCD2. What I should have done (but didn't) was to use the three sets of transforms to measure a very red star, the proof of the pudding.
Those Chromas were the flat top, square shoulder version. Now there is a Chroma version which more closely follows the J/C standard passbands. Someday I'd like to do this again with the new version. As far as I know the current Optolongs are unchanged since 2020.
I haven't done this same project with Baaders. I'm hoping soon to see Arne's results.
Phil
I've used both filters and far prefer the Chroma.
The only drawback to the Chroma filters are the price. They like their filters a lot.
Chroma is 3mm thick so will be a better fit with your Astrodon filter in terms of the focus of the telescope.
Baader filters do not have red leak as has been reported with some other filters.
The Baader filter is 2mm thick, so would be a slightly different point of focus.
My main complaint about the Baader (and specifically the blue)...is that they have pretty significant haloes around stars of any brightness at all.
Baaders: "Baader filters do not have red leak as has been reported with some other filters."
"My main complaint about the Baader (and specifically the blue)...is that they have pretty significant haloes around stars of any brightness at all."
Thanks for your comments. They make me think that you may have the older Baaders which I believe were not interference filters, rather made using all colored glass. Filters made only with color glass, as far as I know, do not have problems with red leak. At least a year ago, maybe a bit longer, Baader changed the recipe for the J/C filters and stopped production of the earlier version. If I remember correctly, the marketing information at that time said the change was made specifically to suppress scattered light halos around bright stars.
Phil