I have a Celestron NexStar 130 SLT with a 2x Barlow and a 9mm eyepiece, but my planetary photos still appear tiny in my 45MP DSLR camera. Do I need more magnification?

Steve says: "The Celestron NexStar 130 SLT is a Newtonian reflector with a 5-inch aperture, a focal ratio of f/5 and a focal length of 650mm, making it an excellent choice for general astronomy.


With your 9mm eyepiece and 2x Barlow lens, you will achieve a magnification of 145x. The theoretical maximum magnification of your telescope is 250x.

However, the reality is that in typical seeing conditions, the useful magnification is about 150x so you are already at the point where there would be no useful gain for planetary observing.

For deep-sky observing, apart from splitting binary stars, you would almost certainly enjoy better views with less magnification.

From the brief description of your DSLR camera, it appears that your sensor has 4.3µm pixels so the sampling rate is 1.36 arcseconds/pixel without the use of your 2x Barlow lens.

No matter what camera you use, the planetary disk will always be the same physical size on the sensor for a given telescope.

Using a planetary imager – for example the Celestron 93711 NexImage 5 which has 2.2µm pixels – the sampling rate would become 0.7 arcseconds/pixel so this would achieve a considerable improvement in resolution over your DSLR camera.

You could also consider the Orion 52097 StarShoot 5MP Solar System Colour Camera or the Lumenera Lw575C 5MP enclosed colour camera.

Under average seeing conditions you could push your focal ratio to f/15 to increase object size on the sensor and this could be achieved with a 3x Barlow lens."

Some useful guides that might help:


Email Steve your astronomy queries to contactus@skyatnightmagazine.com and they could be answered in a future issue of BBC Sky at Night Magazine.


Astronomer Steve Richards
Steve RichardsAstronomer and author

Steve Richards is a DIY astronomy expert and author of Making Every Photon Count: A Beginner’s Guide to Deep Sky Astrophotography.