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V Filters

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V Filters

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.[url=http://www.ebay.co.uk/itm/151001863309?ssPageName=STRK:MEWAX:IT&_trksid=... cuts from an eBay seller[/url]andAstrodonsDoes 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?

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Re:V Filters

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-fil... 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

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Re:V Filters

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

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Re:V Filters

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?

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Re:V Filters

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

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Re:V Filters

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.

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Re:V Filters

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...