Custom Scientific Dielectric Johnson V Bandwidth

Affiliation

None

Wed, 02/19/2020 - 23:58

Having been practising for some time with imaging RGB filters, I now want to buy a set of Johnson Cousins filters (BVRI). Unfortunately there is currently a considerable delay in availability of Astrodon filters which would have been my first choice.

I am therefore considering the Custom Scientific dielectric set which they market as well as the glass filter Bessells.

I note that the V filter bandwidth is quite different to the standard Johnson V. See the attached graph of bandwidth which shows a very square V bandwidth from approx 4700 - 5700 Angstroms. AAVSO defines Johnson V as extending well up to 6200, as seen in the Astrodon filter.

Is this an issue? Should I wait for the Astrodons which may be 3 months +?

Thanks

Matthew Lyttelton

File Upload

Cutom Scientific UBVRI interference.pdf321.59 KB

Bikeman

Affiliation

American Association of Variable Star Observers (AAVSO)

Thu, 02/20/2020 - 00:59

I would not recommend those

I would not recommend those filters, for the reasons you mentioned. I've never seen filters that look like this beeing marketet as Johnson/Cousins filters?!

Are filters from Baader-Planetarium an alternative for you?

I just checked at a German online shop and they also have delivery delays, but are supposed to ship by mid March. That is for 1.25" filters, tho.

mlyttelton

Affiliation

None

Thu, 02/20/2020 - 16:56

Baader V are currently

Baader V are currently unavailable. I had also decided against Baader because the V filter has been noted in previous AAVSO posts to extend furtherinto the red, to the extent that v magnitudes are being significantly affected by H alpha emission.

Your response confirms my doubts about the Custom Scientific. I will wait for the Astrodons to become available.

matthew