Celestron NexImage 5 Solar System Imager review

The Celestron NexImage 5 is a versatile entry-level planetary camera, capable of taking high-resolution colour video of the Moon and planets.

This video is then split into separate frames and the sharpest are stacked together for the final image.

Apart from a computer and a driven telescope, the camera has everything you need to image the Solar System for the first time.

With the supplied iCap2.2 camera control software installed on our computer and the camera connected via the USB cable, we were ready to get started. Opening iCap for the first time presented a faint image on the preview screen.

We couldn’t access the exposure controls or see the recording toolbar that were shown in the manual until we turned on these controls via the menu.

With the image brightened and using the full chip area of 2,592x1,944, the camera gave nice smooth video images and when operating in full-colour mode it gave well rendered colours, especially with the ‘Enhance colours’ option ticked.

iCap is not the most elegant camera control program we’ve used.

The way you set the video output format is rather confusing and is not discussed in the manual.

We found the best video quality was given by recording in an uncompressed format, by first setting the codec value in the recording toolbar to ‘Unspecified’ and then setting the correct value in the device toolbar.

You can record in colour or monochrome by specifying ‘RGB32’ or ‘Y800’ here; it is also here that you can specify the chip area you want to use.

Note that Y800 mono video files are four times smaller than RGB32 colour ones, allowing faster frame rates, and that you can recreate the colour later using RegiStax.

Size matters

For planetary imaging it is best to use the smallest chip area that completely covers the planet: this reduces the video file size and potentially allowsthe fastest data transfer rates.

Using our short focal ratio 8.75-inch Newtonian reflector with a 2x Barlow lens, we successfully recorded a video of Saturn at a resolution of 640x480.

However, the frame rate was only 10 frames per second (fps) due to the long exposure times needed.

We then tried to record both Saturn and its largest moon Titan in the same frame, by using the full chip area and removing the Barlow.

To record Titan, however, we’d have needed exposure times longer than 0.25 seconds, even with the gain close to maximum, and at these longer exposures the background pixels start to pick up unwanted noise.

Our own Moon, being a much brighter target, allowed us to drop both the exposure time and the gain right down, so we were able to record a 640x480 video at the highest frame rate of 52fps.

When we selected the whole chip area we were able to record an area of the Moon 16 times larger than before with the same resolution.

However, the increased data load dropped the frame rate of the capture down to 6 fps, and we ended up with a 1,000-frame Y800 file that was nearly 5GB in size, while the corresponding RGB32 colour file was a whopping 20GB.

End results

We processed the videos in RegiStax 6 and were able to produce some nicely detailed final images, especially considering the low altitude of both Saturn and the gibbous Moon.

Our shots of Saturn showed the Cassini Division and several belts on its disc, while those of the Moon showed a wealth of craters and other details.

The images nicely illustrate the versatility of this new camera.

It enables you to pick your imaging area to match your intended target, and get high resolution over areas large and small.

Imaging chip

The imaging chip in the NexImage 5is very different from the 0.25-inch, 640x480-pixel CCD chip that most entry-level digital video cameras have.

Instead it is has a CMOS sensor, a chip with 2.4 times the area and 16 times as many pixels (2,952x1,944).

The iCap2.2 camera control software allows you to select the whole of this five megapixel imaging chip, or pick a smaller portion to use.

Picking a smaller region reduces the area that is imaged, but improves the frame rate at which you can capture videos and also reduces file size.

You can pick one of nine possible sizes, from the maximum down to the more regular 640x480 pixels.

This flexibility in the size of the imaging area allows you to pick your area to suit your target – a small area and a fast frame rate will suit many planets, but a larger area and lower frame rate are more suitable for imaging the Moon.

Whatever region size you pick, your videos will all be recorded at the same high resolution.

USB connector

There is a USB 2.0 Mini-A data port on the rear of the camera that provides fast data transfer, ideal for using high frame rates to capture moments of sharp seeing.

Once connected to a computer it also supplies power to the camera.

iCap2.2

iCap2.2 is the program used to control your camera settings, such as the recording format and the gain and exposure time.

A useful feature of this program is that you can set the filename to include the date and time as well as a file ID that increases by one each time.

Body

The plastic body of the camera is robust, well made and very lightweight compared to some other popular planetary video cameras on the market.

Being compact and light means you can attach it to your telescope without having to worry about adjusting counterweights to maintain balance.

Pixel size

Digital video cameras usually have pixels that are around 6µm across.

The NexImage 5’s pixels, however, are only 2.2µm wide.

This means that on a lot of telescopes you won’t need to use a Barlow lens when imaging as these smaller pixels boost the final image size by nearly three times compared to a standard camera.

Adaptor

The camera is supplied with a C-mount to 1.25-inch adaptor that screws into the front of the camera, allowing you to slide it into a standard 1.25-inch eyepiece holder.

No filters need to be attached – the camera has an infrared filter for planetary imaging built in.

This review originally appeared in the September 2013 issue of BBC Sky at Night Magazine.