The examples use the following equipment:
• Skywatcher Esprit 80mm Refractor, 400mm focal length, f/5 focal ratio
• Skywatcher HEQ5 – tracking mount
• iPhone camera
Eyepiece projection using a mobile phone
A modern way of capturing the Moon is to place your mobile phone over the eyepiece of the telescope and take a picture. However, it can be quite tricky to manually hold the phone and align the phone camera with the eyepiece image, as any slight movement will affect the quality. It is also essential to ensure that the phone is level, otherwise you will find that the clarity will be uneven and blurred down one side. An easy way to overcome this is to buy a phone holder which allows you to align the phone over the eyepiece. The phone holder clips onto the eyepiece and will clamp the mobile phone into place; the holder can easily be rotated and manipulated to position the camera over the eyepiece and lock it into position.
Capturing Images
The phone clamp sections swivel and slide, allowing you to easily direct the phone camera and position it over the eyepiece exit pupil.
Preferably set up the mobile phone clamp during the day rather than trying to adjust it out in the field when it is dark. In order to set up the position in daylight, focus the telescope on a distant object, attach the holder to the eyepiece and place the camera into the clamp with the camera live view showing. Ensure that the phone is free to move and adjust it until the full image is sharp in the camera view, then lock the clamp into place. This facilitates installing the phone at night, as the position has been previously set.
Mobile phone holder.
When you are ready to image the Moon, set up and visually focus the telescope before attaching the mobile phone. The eyepiece focal length will determine the magnification and the size of the image in the view. The lower the eyepiece focal length, the higher the magnification will be. I find that it is best to use an eyepiece which allows the image to fill the field of view; otherwise, the mobile phone tends to slightly overexpose the Moon if it is too small in the centre.
When the mobile phone has been attached, ensure that the live camera view is showing. You may have to slightly adjust the phone holder to centre the image. The mobile phone should autofocus the image, although if the view is offset slightly, you may have to direct the camera to focus on the Moon by pressing the moon image on the touchscreen. When the image looks sharp, carefully capture the photo. Try different eyepieces to vary the field of view and experiment for a while until frame the image correctly.
Phone holder in position.
Mobile phone in position.
The raw images below were taken with an iPhone through 13mm and 10mm eyepieces using the 80mm refractor. As you would expect, the 10mm eyepiece produces an enlarged image compared to the 13mm eyepiece and the image would be magnified further if you were to use an even smaller focal length eyepiece. A reasonable amount of detail is evident, although you will notice that the image is flipped horizontally due to the optics. However, most photo processing apps can quickly correct this.
A mobile phone is a very convenient tool for imaging the Moon, but the resolution is generally low due to the tiny sensor sizes. To make the most out of any captures, and one of the most critical aspects, is to ensure that you make use of the full field of view. This will guarantee that the image is captured using as many pixels as possible to obtain the best resolution. The following examples show the downside of the tiny sensor, the pixilation and noise on the cropped image. Stacking multiple images would help reduce some of this noise.
13mm eyepiece.
10mm eyepiece.
13mm Eyepiece – slightly cropped.
13mm eyepiece – extensive crop.
The image above shows the 13mm image flipped back to the correct orientation and cropped to give a more pleasing field of view. Even at this crop level the details seem adequate, but when you crop further, the artefacts and pixilation begin to show.
This extensively cropped example clearly shows the pixilation and noise. It reinforces the need to frame the image correctly to achieve the best performance from the equipment and ensure that you do not over rely on cropping.