Skip to main content

Exposure Ratios for B, V and R Filters

2 posts / 0 new
Last post
YPFA
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
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.

Arne

Log in to post comments
AAVSO 49 Bay State Rd. Cambridge, MA 02138 aavso@aavso.org 617-354-0484