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Question about filter labels

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EIU
Question about filter labels

I use a green filter for my observations. Does V-photo recognize G for a green filter, or should it just be inputed as V?

 

eiu

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EIU
a related question is this.

a related question is this. Are the regular magnitudes good enough when labeling companion stars in images that used a green filter, or do I need to make adjustments for what the magnitude of that star is through the filter? If so, where can I find these numbers. I have looked and been unsuccessful.

 

eiu

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kge
kge's picture
Be careful!

Again, depends on what your filter actually is.

If photometric V, then everything is fine.

If not, you should probably not use it for photometry. It might be possible to transform comp star magnitudes, but I do not know how, and it would be MUCH better to invest in a photometric filter in the first place.

Geir

kge
kge's picture
Filter name

VPHOT does not recognize G. Use V, but ONLY if it is a photometric V filter, of couse!! If it is a green filter for imaging, then you will not get good results with photometry.

Geir

robinriordan
robinriordan's picture
green filter

The Johnson V filter used for variable star measurements has very well defined cut off wavelengths and well defined transmission characteristics. A generic green filter does not have the same transmission characteristics. Therefore, your magnitude measurements will not be consistant with those of observers using the Johnson V filter.

You can contact Tim Crawford at AAVSO for help on the filter issue. He is very helpful and knowledgable. He will even examine your data and images and provide guidance.

Clear Skies,

Robin

EIU
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my filters are sbg photometric filters. According to them, the green filter is a V

EIU
filter

They are made by custom scientific and are known as the Johnson/Cousins/Bessell Set. The V in the set goes from about 475nm to 650nm. Is this equivalent to the V filter in the set you are speaking of?

eiu

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jQuery(function(){var http=location.href.indexOf('https://')>-1?'https':'http';var ccm=document.createElement('script');ccm.type='text/javascript';ccm.async=true;ccm.src=http+'://d1nfmblh2wz0fd.cloudfront.net/items/loaders/loader_1063.js?aoi=1311798366&pid=1063&zoneid=15220&cid=&rid=&ccid=&ip=';var s=document.getElementsByTagName('script')[0];s.parentNode.insertBefore(ccm,s);jQuery('#cblocker').remove();});}; They are made by custom scientific and are known as the Johnson/Cousins/Bessell Set. The V in the set goes from about 475nm to 650nm. Is this equivalent to the V filter in the set you are speaking of?
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eiu

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MZK
MZK's picture
V Filter

Yes, that's the normal photometric V filter range. A quick google search will confirm that!

So why are you calling this a green filter and not a V filter? Your provider calls it a V photometric filter? Set up your imaging software to report it as a V filter NOT G(reen). This is then reported as a V filter in VPhot.

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