Archive for 6 inches refractor

Saturn with a 6 inches refractor

Posted in Astrophotography with tags , , , , , , , , , , on 2010/04/10 by computerphysicslab

This image of Saturn has been obtained after processing a 4 minutes video took with a Casio Exilim digicam. In order to avoid refractor chromatic aberration a Fringe Killer filter was used in combination with a 14mm eyepiece and a Barlow lens.

A 300mm telephoto vs a 6 inches refractor

Posted in Astrophotography with tags , , , , , , , , on 2010/02/22 by computerphysicslab

The Tamron SP 54 is a 300mm telephoto lens, with an aperture of 54mm. I took a 60 seconds of exposition image of M42 in Orion. A few months later I took a 15 seconds image of the same field through a 6 inches Sky-Watcher non-apo refractor.

The comparison throws some interesting conclusions:

1.- A 150mm lens gives more resolution than a 54mm lens. Stars are fainter in the 6 inches refractor picture.

2.- The light captured by a 54mm lens in 60 seconds is nearly equivalent to the one captured by a 150mm lens in 15 seconds. Nebulosity appears practically equal in brightness in the two pictures. The lower image is a full frame, meanwhile the upper one is cropped at 25%.

Both images were taken using an unmodded Canon DSLR camera, EOS 450D (or Rebel XTi) and an EQ6 equatorial mount.