Finding your own ghosts
This article deals on photography, how to create and find your own ghost.
Ghost is the reflection of light source on the lens, therefore their shape usually resemble the shape of the light source. This is how ghost occurs:
Finding ghosts is easy and not risky. It just need to be done right!
Under fluorescent light, usually ghost from filter will cast greenish image, while ghost from lens will cast other colours such as red or blue.
Ghost will appear regardless the strength of the light source. The stronger the light source, the more visible the ghost will be. The weaker the light source, the less visible the ghost will be. That's because ghost is caused by reflection of light source on the lens, and it existence has little or nothing to do with light source's strength. Ghosts visibility is more closely related to issues on lens design, lens material and coatings.
Therefore, to create ghost, one can experiment using household light, such as table light, instead of sun. Table lights rated 14-20 watts are not bright enough to burn our retinas, they will only hurt your eyes lightly, but no damage is permanent, unless you are abusing yourself or have problems with your eyes.
Please follow the procedure carefully and only with small light source! I don't want someone appears on my door, asking for any damage caused by this procedure! Moreover, following my procedure means, you'll agree to follow it at your own risk.
Please refer to the image below.
There are several ghosts on the image, all caused by the lens, Canon 50 mm f/1.8. Probably due to it's older optic design (1960's design), then ghosts appears. Although the lens is ghostly, this lens is one of my favourite lens and most of the time, no ghosts appears on my photographs, unless I'm deliberately creating and finding them.
If you still can't find any ghosts, you can use your worst and ghostly lens to find the ghosts. Finding ghosts requires training, and it's better for you to train with bad lens or filter so you can easily figure that the ghost is there, and which angle did reproduce more ghosts. After that, feel free to use better lens in finding their ghost eliminating performance.
PS. You'll also need sharp eyes, to notice a very faint ghosts.
Ghost caused by filters
To check filter's ghost eliminating performance, you'll need to know your lens's ghost characteristic and colour. Don't worry, ghost stays the same shape and colour with a same light source. They just move away.
The procedure for searching ghost induced from filter is the same for creating ghost from lens, however here you'll need to put your filter on. Once you got your image and saw ghost, then you can distinguish whether the ghost is from lens or filter from ghost's colour and shape.
Please refer to the image below to see the difference between ghost caused by filter and ghost caused by lens. The blue things is the ghost from the lens, and the greenish things is the ghost from the filter. I use Hoya SHMC filter, which is excellent in combating ghosts, and the ghost is almost invisible. If I didn't tell you about the ghost from the filter, you won't even notice it, I guess you won't even notice that the ghost is there.
My observation shows that under florescent energy saving light, ghost induced from filter will be greenish, while ghost induced from lens will be bluish.
Please refer the image below, those are ghosts induced by a very bad filter.
Please note that ghosts appears just below the light source and on the bottom right corner of the image. The ghosts also have similar shape to the light source, and I believe that's the reason why they are called ghosts.
FYI, when my bad filter was used - although ghost appears on this test - on normal photography no ghost appears on 99.9% of my images. My statistic shows that I shot 10.000 images, and ghosts only appears on 5-6 images with that filter.
When will a ghost be a real problem?
Ghost will be a real problem when you works as a photographer that covers bush fire, pre wedding photographer who photograph sunset everyday, or photographing where the light is extreme.
However, with clever tricks and hand covers, the ghosts usually goes away. Since ghosts are visible, you can then check your image before taking picture. If the ghosts are there, just shield your lens with your hand, and everything is going to be fine.