The focal length of a mirror is equal to the focal ratio times the diameter of the mirror. For example, a 1-meter telescope that is f/8 would have a focal length of 8 meters.

Object size and camera format determine magnification. Magnification and working distance determine lens type. Please refer to the lens calculators for fixed focal lengths and the respective charts for zoom systems and Precise Eye systems. See similar questions...

Every lens has a focal length which is a physical property of the lens. Once the lens is made, this cannot be changed. The field of view associated with a lens will be a function of the area projected by the lens that is captured by the camera. For 35mm film photography, this area is 36mm by 24mm. Note that if you change the area captured, the field of view also changes. See similar questions...

Measured TRV900 focal length Jake Socha (jjsocha midway uchicago edu) Sept. 25, 2001 When I assume that the widest angle is at 4.3 mm, the estimate for the max zoom is 48 mm, instead of the [Sony] listed 51.6. When I use the zoom as the reference, the wide point is estimated at 4.6 mm. Both answers are about 7 % off. See similar questions...

The focal length is a basic optical property of any lens, and the most important one to a photographer. The simple way to think of the focal length is to think of it as a numerical value, expressed in millimetres, which represents how much of a given scene (the coverage area) a lens can take in. Focal lengths for Canon SLR lenses range from ultra-wide (14mm) to incredibly long telephoto (600mm and 1200mm). The typical range of an affordable lens or lenses is from 28mm to 105mm or so. See similar questions...

Measure the diameter of your dish and convert this value to inches. Measure the depth of your dish in the middle by placing a flat board across the center of the dish and measuring from the board to the dish. Multiply the diameter of the dish by itself. Multiply the depth of your dish by 16. Divide the depth value into the diamter of your dish (the squared value that you calculated). This is your focal length. See similar questions...

A woman does not need a record of her previous cycles, but we ask a woman to answer a few questions that will help her or her provider to know whether or not she is in this range. These questions include: See similar questions...

You can equate your 35mm format focal length to focal lengths in larger formats with our Lens Conversion Chart. See similar questions...

Focal length is the distance from the bottom of the lens to what you are looking at. The focal length decreases with the stronger lenses. Viewing area is the size of the lens you are looking through, which also decreases with increased strength. See similar questions...

The focal length of a telescope is the distance (usually expressed in millimeters, or mm) from the telescope's main optical element (main lens or primary mirror) to the point where light rays are brought to a focus. Focal length is an important telescope specification because it determines, among other characteristics, the magnifying power of the telescope. See similar questions...

In short, it tells you how much from the scene you will see using that particular lens. It is called Field of View and is expressed in degrees. Example: 4mm 1/3" lens will give you 63 degrees of horizontal field of view while 8mm 1/3" lens will give you 34 degrees a field of view. Click here to find out exact numbers. See similar questions...

The larger the telescope lens or telescope mirror, the fainter the objects a telescope will reveal (the more objects that will be visible), and the greater the telescope magnification it can use and still produce a good image. For example, at 120x, a ten inch telescope will reveal hundreds of objects not visible in a three inch telescope. In addition, at 120x, the 10" inch telescope will produce images that are brighter and sharper than the 3" inch telescope. See similar questions...

I’d sit down with your photos and think about what focal lengths you tend to use most and where there are gaps. Maybe you want an extreme wide angle, for example. If so there’s no point getting another telephoto. See similar questions...

The magnifying power of a telescope will change depending on the focal length of the eyepiece you are using (see question on determining a telescope's magnification below). A more appropriate question may be to ask how much light-gathering power does a telescope have. Light gathering power is a telescope's ability to see faint, distant objects (see question above) and is solely determined by the aperture of the telescope's main mirror or lens. See similar questions...

Prime lenses generally afford higher optical quality than zooms, except in the case of really expensive pro zoom lenses. However prime lenses mean you have to walk around more - you can’t simply adjust the zoom setting to get the framing you need. See similar questions...

The magnification of a telescope changes as the eyepiece is changed. Magnification can be calculated by dividing the focal length of your telescope by the focal length of the eyepiece. Always start with your lowest magnification (longest focal length) eyepiece and work upward from there. A 2x Barlow lens will double the magnification of whatever eyepiece you use with it. For example: using a telescope with a 900mm focal length with a 20mm eyepiece will give you 45x magnification. See similar questions...

The magnification is fixed, so there’s no need to calculate this property. What’s left to calculate is the working distance (WD) that results for a given lens extension or spacer between the lens and the camera. For any of our Double Telecentric lenses, the change in WD is inversely proportional to -(the square of the magnification) times the (spacer length), or: NOTE: If you are using a cs-mount camera without a 5mm c-mount adapter, this is the same as using a negative 5mm spacer. See similar questions...

It doesn't; it is subject distance that affects perspective. However, a longer lens provides more subject magnification at a given distance, so you can get farther from your subject without having the image be too small. By moving back, you make the magnification ratio between the front and back of your subject smaller, because the distance ratio is closer to one. See similar questions...

The fixed f3.5 on all Minoxes except the Plastic ones (5.6 I don't know that this is equal to) is actually the same as a f12.5 on the 35 mm format --- I found this out by trial and error -- It would be a useful piece of information to include as many 35mm buffs may try Minox 8 X 11 thinking that the F3.5 is the same as on 35mm--- I did until I found under exposure on my Minox lll, if you know ahead of time that f12. See similar questions...

With an interior environmental portrait made with a wideangle lens the important factor becomes the lens to subject distance. If the subject is kept central in the image and the head is placed approx. 1.3 (5 feet) from the camera it will be relatively free of distortion. Obviously any limbs nearer the camera will increase in apparent size. This is often seen in fashion shots. See similar questions...