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Exposure Ratios for B, V and R Filters

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Exposure Ratios for B, V and R Filters

A simple question (I think) ...

Obviously, B, V and R filters have different light transmission properties and a given star will appear brighter or dimmer through different filters.

I am wondering about the following: When imaging a star field such as NGC 3532 with a view to calculating transformation coefficients for my telescope and camera (a ZWO 1600 MM Pro CMOS camera, coupled to a Celestron Edge HD 8"), should exposures of equal length be made in the 3 different filters, or should B:V:R be something more like 60:30:20?

Does it matter in the end? I guess the important thing is to ensure that an SNR > 100 or so is achieved through all filters for the stars of interest in the field?

Regards: Paul

HQA's picture
exposure ratios

Hi Paul,

The ratios you mention (60:30:20) are about right for a typical star.  You'd start with that and then adjust accordingly after getting your first set of images of a new target.  In the case of a "standard cluster", there is no perfect ratio, as some stars will be red and others blue.


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