Digital SLR Class Notes
DSLR
Most professional 35mm cameras have always been single lens reflex cameras. As part of the class we will look at the older cameras and see how they have progressed. Film cameras were called SLRs and when they became digital, they became DSLRs. In an SLR, the photographer sees the image through the same lens as the camera will use when the photo is taken.
When composing the image, a mirror reflects the image from the lens onto a screen which allows you to see it. When you press the shutter button the mirror flips out of the way to allow the light to pass through the lens diaphragm, past the open shutter to the the film, or CCD or CMOS sensor.
Viewing through the lens enables more precise focusing and composition.
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Dust
Unlike a film camera where fresh film is always in there for the image to be captured on a digital camera has the same sensor for every image. Over time, that sensor will get dirty.
Cleaning the Sensor
DSLRs have a "mirror lockup" function that flips the mirror out of the way to expose the sensor for cleaning, and there is a raft of sensor cleaning materials on the market that cost from a few dollars to several hundred. For a comprehensive overview of all cleaning methods, visit www.cleaningdigitalcameras.com.
Megapixels
The number of pixels determines the maximum size of the resulting image and quality of printed and viewed images. The higher the resolution, the better the results. You can always shrink your images, but when you go from low to high the end result is not good. Following is a guide which shows the relationship between megapixels and use:
Usage Minimum Megapixels
Web site images 1 MP
Computer screen 2 MP
3x5 and 4x6 prints 2 MP
8x10 print 4 MP
11x14 print 6 MP
16x20 print 12 MP
Now, lets take this a little further.
Simply put, the more pixels you have, the better. The larger the images that you can print and at a higher quality. For most home printers, you should assume that you'll get the best results when you print about 300 dots per inch. To do the match, simply take the dimensions of your photos and divide them by 300 along both the horizontal and the vertical axis. The answer is the largest print size you can make.
For example: If you have a photo that's 2240 by 1680 pixels the math will tell you that you can get an image size of 7.5 by 5.6 inches. .
So, when you see a camera with a 6 megapixel sensor you would know that at 300 dpi it will produce a nice 6.5 x 10 inch image. Here are some other standard resolutions:
- 2 megapixels = 1200 by 1600 pixels = 4 by 5 inches
- 3 megapixels = 1536 by 2048 pixels = 5 by 7 inches
- 6 megapixels = 2400 by 3000 pixels = 6.5 by 10 inches
- 10 megapixels = 2592 by 3872 pixels = 8.5 by 13 inches
- 12 megapixels = 4368 by 2912 pixels = 9.7 by 14.5 inches
No, it not really that simple and this does not factor in interpolation which can increase resolution.
For example, the list assumes that you're printing at 300 dpi. The reality is that you can print at lower resolutions and still get fantastic prints, especially for larger prints which are viewed at more of a distance. If you're printing a 20-by-30-inch poster, most people will stand back to see the whole image and will not realize that the final image is not as detailed. A great comparison to this is your TV screen. Move in close and observe the lack of detail. (Yes, even hi-def has limitations.)
Another advantage a DSLR person has is that their sensor is much larger than the smaller point and shoot
Your camera's sensor size, for example, affects picture quality. A small point-and-shoot might take the same 8-megapixel images as a more costly digital SLR, but the SLR probably relies on a physically bigger sensor. That adds up to a higher quality image, and the resulting prints will be better. As a result, you might have better results printing your point-and-shoot photos a tad smaller. [Learn More about Megapixels]
Paper Sizes
Now that you understand megapixels you may be looking at your camera settings and noticing that they don't show what is a 4x6. Instead you see a number from the International Standards Organization. If you are on vacation, have a limited number of cards, and know you never print on anything larger than a set size you can shoot for that size. You will find the chart below useful when trying to understand paper sizes in the ISO standard designation and inches.
| Format | A series | B series | C series | Recommended Camera Resolution |
|||
|---|---|---|---|---|---|---|---|
| Size | mm × mm | in × in | mm × mm | in × in | mm × mm | in × in | |
| 2 | 420 × 594 | 16.5 × 23.4 | 500 × 707 | 19.7 × 27.8 | 458 × 648 | 18.0 × 25.5 | 4800 x 6000 |
| 3 | 297 × 420 | 11.7 × 16.5 | 353 × 500 | 13.9 × 19.7 | 324 × 458 | 12.8 × 18.0 | 3300 x 4200 |
| 4 | 210 × 297 | 8.3 × 11.7 | 250 × 353 | 9.8 × 13.9 | 228 × 324 | 9.0 × 12.8 | 2400 x 3000 |
| 5 | 148 × 210 | 5.8 × 8.3 | 176 × 250 | 6.9 × 9.8 | 162 × 229 | 6.4 × 9.0 | 1500 x 2100 |
| 6 | 105 × 148 | 4.1 × 5.8 | 125 × 176 | 4.9 × 6.9 | 114 × 162 | 4.5 × 6.4 | 1200 x 1800 |
| 7 | 74 × 105 | 2.9 × 4.1 | 88 × 125 | 3.5 × 4.9 | 81 × 114.9 | 3.2 × 4.5 | 900 x 1500 |
| 8 | 52 × 74 | 2.0 × 2.9 | 62 × 88 | 2.4 × 3.5 | 57 × 81 | 2.2 × 3.2 | 600 x 900 |
For more information on these paper standards visit (Wikipedia)
The tolerances specified in the standard are
- ±1.5 mm (0.06 in) for dimensions up to 150 mm (5.9 in),
- ±2 mm (0.08 in) for lengths in the range 150 to 600 mm (5.9 to 23.6 in) and
- ±3 mm (0.12 in) for any dimension above 600 mm (23.6 in).
Taking Care of Your Digital Camera Batteries
Nickel cadmium batteries, were the most commonly used rechargeable batteries in electronic devices for many years. These batteries had a limitation called the memory effect. With these batteries keeping them charged caused them to lose its full original capacity. To mitigate the memory effect, manufacturers recommended that you regularly run your battery completely down, then recharge it.
Nickel-metal hydride batteries, which succeeded NiCDs in many applications, were originally thought to be free from memory-related problems. Unfortunately, users have found that NiMH batteries also suffer from memory issues. While engineers will call it voltage depression, most of us will call it memory effect. While basically the same as with NiCD batteries, it is not as severe.
If you really doubt why I am saying this take a look at high-end battery charges or some that come with the high end digital cameras. Many of these charges have a conditioning mode in them which drains and then recharges the battery.
If you camera uses a Lithium ion batteries you will find that those batteries are free of memory-related problems. Another plus to these batteries is that their charged shelf life is much greater than the older NiCD and NiMH batteries who lose their charge rather quickly.
However, your batteries will degrade just as a point of use. To preserve the life of your batteries follow these rules:
- If you have completely drained your battery recharge it ASAP.
- When buying a charger make sure that the charger will allow your batteries to be left in the charger on a trickle.
- Don't drop your batteries. This fracture the internal chemistry.
- Avoid excesses in cold and heat.
- If the battery is cold, let it warm up before using it.
- Don't let the batteries roll around lose in a bag, purse, or pocket. I have actually seen batteries melt because they got shorted against change in a purse. It is actually a fire risk.
