There are some effects that can be done by both technologies.
Multiple exposure, according to Wikipedia, multiple exposure is two or more individual exposures are made to create a single photograph.
Multiple exposure can be done by letting the film exposed more then twice, which means, shooting different images in same film. Take the photo which is done by NASA as an example, because the crescent phase, it was impossible to shoot the moon next to the rocket, so the photographer has taken two images, the rocket and the moon, into same film.
|NASA Apollo 8 lunch, 1968|
Photos can be joint together by using photo editing software such as Photoshop. Users can control the opacity of photos, and stack them together, or put them into different layers and choose the multiply option to stack them into same photo.
Filter, photographer can use filter to create different effects, for example, adding or reducing colors.
|David Ball Lunar Eclipse, 2004|
Users can insert a filter on the len, so all the light must pass through the filter and be captured by the film.Free Transform
2) What are the photographic techniques which can be only done by digital photography?
Users can make some interesting effects by using different filters, take the photo below as an example, the photographer use the star filter to turn the light source into star shape.
Filter effects can be done by Adobe photoshop, by using it, users can create different effects, such as color subtraction. Take the photo below as an example, the photographer used plugin of photoshop to create star filter's effect.
|Maciej Star Filter, September 2010|
By using photo editing software (Adobe photoshop), users can transform the image and the subjects in the image easily. For example, I have used the puppet warp option to create the second image, and it is cannot be done by traditional photography.
|After the puppet warp|
3) What are the differences between traditional and digital photography?
In terms of cost, digital photography is way cheaper then traditional one. For digital photography, photographer may only need a camera and one computer with photo editing software, and they can do most of the effects. For traditional photography, users have to buy the films, different filters for different effects. In my opinion, lower cost can let more people to use photograph to record their life, or making artworks.
Digital photography is easier to distribute, as the photos are saved in digit, users can email their works to others, or upload it to websites such as Flickr, everyone can see their works in front of their computers, users can show their talents easily. If it is in the past, photographers may only share their works on newspaper, magazine or in gallery, and it is very hard to achieve.
|People talking about Lbrahim Lujiaz's work|
I think it is one of the points that traditional photography is better or different from digital one, photographers can make some experiment with their cameras/ film, for example, they can try some new materials as filters. Or doing tone control with different chemicals. People may invent some techniques which is new and interesting.
There are many differences between traditional and digital photography, but I think the important difference is digital photography can allow more people to use photography for their artworks, as it is low cost, and easy to distribute.