V Filters

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    Posted by Eliot Hall at 12:06 on 2013 Jul 28

    I am trying to get hold of V photometric filter. All I can seam to find are these two options below.Off cuts from an eBay sellerandAstrodonsDoes anyone else know of any other options that are in the amateurs budget. Also there appears to be different systems which should I opt for?


    Posted by Richard Miles at 18:11 on 2013 Jul 29

    Hi Eliot,Good to meet you at the BAA Exhibition in Manchester.There is only one V passband – that corresponding to the Johnson-V one. It is sometimes called the Vj passband.Nowadays you have the choice of having either the coloured glass one, which is a sandwich of discrete elements originally put forward my Mike Bessell, which are cemented together and mimics the original Johnson filter or a ‘dichroic’ version which comprises an optically flat piece of glass onto which very thin films of various thickness/composition are evaporated which then transmits the Johnson passband range.The coloured glass version should be coated to protect it from oxidising/hydrolysing in moist air, or sandwiched between plates of silica glass or the equivalent. As well as Astrodon, I see a company called Horiba Scientific do these:http://www.horiba.com/uk/scientific/products/optical-filters/optical-filters-by-application/optical-filters-astronomy/?gclid=CKnTw96V1bgCFYOWtAod6ngAmwbut careful – they are not protected and the BG12 component will degrade after a few years unless kept dry.US-based Optec Inc. do various V filters but are pricey:http://www.optecinc.com/astronomy/prices/astronomy_price_list.pdfRichard


    Posted by Nick Atkinson at 18:51 on 2013 Jul 29

    I use a V filter provided by Stargazer made by Norman Walker tel 01323833753 Email enw@stargazer.fsbusiness.co.uk. His filter screws into the back of my H9 camera. However as far as I know they will not fit into a filter wheel.1.25 filters such as those provided by Astrodon are another option and might be cheaper in the long term if you move on to I and R band. This is dependent on the size of your sensor; the larger chips now more widely available would require the larger filters anyway.I have a starlight Xpress 7 position filter wheel that I use for Red Green and Blue colour imaging. Later on should I move on to I band & R band variable star work I might consider buying from Astrodon. My colour filters are made by Baader. They might be another source to consider but I don’t know if they make any suitable for photometry


    Posted by Eliot Hall at 22:21 on 2013 Jul 30

    Thanks for the information.I also have a set of Baader LRGB which I’m very happy with, however unfortunately they don’t do photometric filters. I’m using a Starlight Xpress MX916 which has quite a large chip so I will have to use a 1.25 inch filter.So it’s looking like it’s going to be the Astrodons, and be careful not to get dew on the filter. If I were to use a UV/IR cut filter infront the filter – that should help to protect from moisture and not effect the result or am I being naive?


    Posted by Callum Potter at 12:17 on 2013 Jul 31

    Hello Eliot,i’m not an expert on filters for photometry, but I thought that Baader did supply a UBVRI set, and individual filters.You might need to order direct from Germany, but they are listed here:http://www.baader-planetarium.de/sektion/s44/s44.htmpriced EURO 145Hope this helps,Callum


    Posted by Richard Miles at 17:47 on 2013 Jul 31

    Eliot – Don’t put any other filter like an IR cut-off in front of your V filter.The Astrodon dichroic V filter shouldn’t suffer in damp atmospheres – the problem lies with the Bessell coloured glass version as the BG12 element is hydrolytically unstable. The V filter Norman Walker makes (Nick has referred to this) is an excellent one in that it comprises the standard coloured glass elements sandwiched between 1mm silica plates. I too have one of these as well as the Astrodon dichroic which I have mounted in a Canon 52mm filter holder which drops into a long lens.When I looked on the Baader webpage I couldn’t find the V filter either – Callum’s right though as I have checked out the url he quotes although they are only the 1.25" ones.


    Posted by Eliot Hall at 18:16 on 2013 Aug 01

    Thanks Callum – I couldn’t find that page either.Thanks Richard – I had a feeling you would say that.I’d quite like to stay with Baaders’ if only for the reason that I’m adding to the set I already have.I suppose now all I have to do is save my pennies…

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