|Home >> Ask Olympus: Digital ISO|
Question: Please explain digital ISO. How does it differ from 35mm film ISO?
Answer: In both film and digital photography, ISO is a standard measurement of the film or sensor response to light—sensitivity. The International Organization for Standardization (based in Geneva, Switzerland) is an organization made up of standardization groups from all over the world.
Film ISO is a fixed sensitivity value resulting from the manufacture of the film. The sensitized material in film consists of microscopic light sensitive crystals whose structure changes when exposed to light, and become images on the film when chemically processed—either as slides or negatives. The ISO varies by the size of the crystals in the film, which are “grown” in manufacture to different sizes to make the different speed film emulsions. Small crystals result in “slow” films. Large crystals result in “fast” films. All film emulsions have a mix of many-sized crystals.
The advertised speed of a film shown on the packaging relates to a speed rating in which the film can be expected to perform predictably under standard lighting conditions, set by the ISO organization. Therefore, an ISO 200 film should perform the same in terms of exposure from different manufacturers and with different cameras. This also means that the exposure systems in the cameras should perform predictably in relation to the film speed.
For the average user, the film ISO is a set value with some exposure latitude. Exposure latitude can be employed by users with advanced photographic skills to alter the performance of film through exposure and processing techniques. However, the ISO cannot be changed from frame to frame while the film is in the camera. You are “stuck” with the ISO of the film until the roll is finished and you reload the camera.
Without a doubt, one of the most attractive aspects of digital photography is that you can change your “film type” from shot to shot using different menu settings. A digital camera uses light-sensitive photodiodes (pixels sites or “pixels”) in the sensor instead of the light-sensitive chemical crystals found in film. The sensitivity of the pixels can be increased or decreased by varying the gain (voltage) on the pixels—much like changing the volume on a stereo.
In the early years of digital photography, ISO values shown on digital camera menus emulated the ISOs of the films available at the time—64, 100, 160, 320, and 400. This was so that people could relate to how their digital cameras performed in relation to their film cameras. Today the ISO values are mostly multiples of 50 and 100.
The photographer has the option of selecting preset ISO settings using the camera menus and different shooting modes. However, since digital cameras are capable of automatic exposure, if you look in the metadata of images shot in auto modes, you may find that the camera is “making up” ISOs for specific situations by creating its own gain values.
As you increase the ISO, the image may become grainier. In this respect, digital photography is no different than film photography. In film photography, if you wanted a higher ISO, the trade-off was larger grain. In digital photography the same thing is true; but, unlike film, the camera and imaging software have tools to diminish the graininess.
Archive - Compact Cameras:
- Playing back photos and movies
- Printing the date on your photos
- Taking better indoor photos
- Changing resolution
- Best image sizes for emailing
- Avoiding blur in low light
- Taking pictures faster
- Evening out exposure for panoramic sequences
- Digital vs. film ISO
- Grainy pictures
- xD-Picture Card Use and Care
- Black and White with your point and shoot
- Shooting for online auctions
- Panoramic photography
- How do I photograph documents?
- Get images off of internal memory?
- Increasing shot-to-shot speed
- Tips for shooting portraits
- Tips for shooting holiday lights outdoors
- Tips about memory card usage
- My videos I'm not getting any sound. Why?
- Tips for shooting panorama photos
- Minimizing shutter lag
- Transferring your photos to a CD
- Macro photography
- Double exposures and xD card questions
- Battery charging guidelines
- Truer color indoors
- Proper settings and exposure for stage photos
- Minimizing glare from glasses
- Adjusting for photos shot into the sun
- Keeping faces sharp
- Why do I get red-rye?
- Steadying camera in NIGHT Scene mode
- Extending my battery charge?
- Shooting in cold weather
- Using the Macro shooting mode
- Save a zoomed playback image
- Printing from Olympus software
- Low Light Sports Photography
- Shooting indoors in the winter
- Using my camera on a telescope or microscope
- Tips for getting better results using the flash
- Tips for controlling sunlight
Submit your question using the form below and we may feature it in our next edition!
Please note: Questions submitted to Olympus will not receive individual responses.
If you have a specific tech support issue for which you need immediate assistance, please contact our technical support group by sending an email to firstname.lastname@example.org, or by calling 1-888-55-DIGITAL.