The following information will help you get the most from your lighted-polluted environment.

Single Unprocessed Frame

4,600 Unprocessed Stacked Frames

(removes most noise)

Stacked and Processed Frames

(detail now appears)

Here's a set of performance examples of the 1000 Oaks mild light-pollution filter model LP-1

NO filter, 5 seconds exposure.

NO filter, 7.6 minutes exposure.

WITH filter, same 5 seconds exposure.

WITH filter, same 7.6 minutes exposure.

Here's The Effect Of Stacking Multiple Same Frames.

Full gain, 2.5 seconds exposure - 1 frame.

Full gain, 2.5 seconds exposure - 50 frames.

Full gain, 2.5 seconds exposure - 11 frames.

Full gain, 2.5 seconds exposure - 100 frames.

Below is an example of how to shoot long-exposures and go deep even in heavy light pollution.  The photos were done without any celestial tracking using just a camera on a stationary tripod.  The secret is to shoot multiple short exposures and then "stack" them together.

The stacked photo on the right was shot at an ISO of 3,200 but it actually has significantly less noise than the left photo shot at an ISO of 800.  Despite the right photo having an integrated exposure of 5.3 minutes on a stationary tripod using a 400mm lens, there are no star trails.

The limiting magnitude in the ISO 800 photo reached 14.8 and the ISO 3,200 photo reached 15.5 both for the same 5.3-minute exposure.  The skies had a limiting magnitude of just 3.5 and all photos used the same DSLR camera and 400mm lens (though with a different F-stop to balance the different ISOs).  There was no photo processing other than stacking.

ISO = 800, exposure = 1 x 320 secs, 400mm lens.

ISO = 3,200, exposure = 32 x 10 secs, 400mm lens.

Below is a 100% crop of each photo.  Because of stacking the ISO 3,200 multiple exposure photo has...,

  • only 3% of the original digital noise

  • reduced chromatic aberration

  • no chroma noise

  • no hot pixels

  • no star trailing

  • fainter stars

The ISO 800 single-shot photo has none of that.

100% crop of the single-frame ISO 800 photo showing several hundred hot-pixels due to the long single exposure.

100% crop of the stacked ISO 3,200 photo.

The chart shows how to get the same limiting magnitude with your city telescope as with your same dark-sky telescope, by increasing your magnification.  A star is a point so it will not dim with magnification but the field's background darkens as its light spreads out.

The White Zone

An Urban Astronomer's Light Pollution Guide to Balcony Imaging

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