What is focal length? Explanation of basic knowledge ... - define focal distance

 2024-10-27 02:06:09

The image above was taken 2 hours after sunset on a full moon night at a range of 250 m. The visible image was captured using a Canon 5D Mark iii with a 115 mm f/4.5 lens with exposure forced to 1/30 sec and ISO 12800.

The visible image above is taken of an actor wearing artificial facial hair which is virtually undetectable with the visible camera.

Thank you so much, Jen! Jen is a regular contributor here at Shoot It With Film, and you can check out her other articles here, including 3 Great Film Stocks for Winter and 5 Tips for Great Black and White Film Photography.

As mentioned earlier, you will need to let your lab know if you’re exposing for the highlights. They will still process your film as normal, but they will then scan your film for the highlights and not try to bring up any detail in the shadows.

Before you walk out the door with your camera, you will need to decide what film to take with you. Some films are created with higher contrast than other films. If you desire more contrast in your images, no matter what the lighting situation, you’ll want to take films whose emulsion already has some built-in contrast.

A high contrast scene or image will have very bright highlights as well as very dark shadows. A low contrast scene or image will have tones that are all similar and more in the middle of the contrast spectrum —shades of gray, if you will.

3D volumetric rendering of whole OCT volume illustrating the ability of high-speed SD-OCT to map the complete back of the eye in one capture.

Find hidden moisture patterns identifying potential pipe or exteriors leaks before they spread. Our infrared cameras can help you perform building diagnostics and forensic analysis giving you clear images without performing destructive inspections.

If you come from the world of digital, you may think that pushing film in development “adds light” to an underexposed roll of film. That is not accurate. Pushing adds contrast to your roll of film making the brights brighter and the shadows darker. Film is pushed by leaving the film in the developing chemicals longer or changing the temperature of the developing chemicals.

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SWIR image of the same scene using a Sensors Unlimited SWIR camera. SWIR light interacts with objects similar to visible light, therefore producing a familiar image through the glass window. Notice the cars in the parking lot have shadows similar to those produced by visible cameras. Because SWIR light passes through glass, commercial visible lenses can be used to produce SWIR imagery. However, imagery can be enhanced greater using a SWIR optimized lens.

Visible and SWIR image of an apple. SWIR light has high absorption in water, making the bruised section of the apple easily detected in SWIR.

Visible and SWIR image of an apple. SWIR light has high absorption in water, making the bruised section of the apple easily detected in SWIR. Learn more about using Sensors Unlimited SWIR cameras for agriculture inspection

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Contrast is the spectrum from white to black with every tone in between. (Tone is the lightness or darkness of a color.)

The image above was taken 2 hours after sunset on a full moon night at a range of 250 m. The SWIR image above was taken using the high definition 1280x1024 JSX camera. The image was captured using a 50 mm f/1.4 SWIR optimized lens with exposure set to 1/30 sec. Due to ambient irradiance of the night sky, Sensors Unlimited’s high gain SWIR cameras are able to produce clear nighttime imagery over visible imagery.

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SWIR cameras can detect hot temperatures similar to those observed in hot glass inspection. Using a SWIR camera, the hot wine glass is false colored to show the evenness of the heated areas of the glass. Additionally, SWIR light passes through glass, as demonstrated by the business card behind the wine glass. Sensors Unlimited SWIR cameras can be used for industrial inspection of glass manufacturing to detect defects and reduce scrap.

Our short wave infrared (SWIR) cameras can extend vision into wavebands normally invisible to the eye and other types of thermal imaging. These near and shortwave IR images reveal details in clear, lifelike form. Click on an image below to enlarge it.

To control contrast in your images, you will need to know how to create the contrast you desire no matter what the lighting situation you may find yourself in. The challenge when you’re shooting film or using a digital camera is that your film has less dynamic range (the ratio between the darkest and brightest tones in an image, from pure black to pure white) than your eyes, so you will have to choose what to prioritize in the scene and in your image, how to meter, how to compensate, and how to process your film.

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High-speed SD-OCT en-face map of the retinal blood vessel network called the choroid. This illustrates a new level in eye diagnostics called OCT-Angiography where blood flow can be measured to determine tissue health. In the above image the vessels in nerve fiber layer and ganglion cell layer of the retina are in red, those in the inner plexiform layer are in green, and in the outer plexiform layer are in blue.

Generally speaking, many people prefer images with more contrast than images with little contrast. Contrast catches the viewer’s eye and can add a feeling of drama in your image. That isn’t to say that images with less contrast are not good images. You, as the photographer, can use contrast as one of the tools available to you to help convey the message you want in your images.

If you want to make sure that the details in the brighter part of the scene are maintained, meter for the highlights using your spot or incident light meter. Know that when you do this, you may lose details in the darkest part of your scene.

Image: Visible thunderstorm cloud base near Lebanon, Indiana on 15 June 2016. Researchers at Purdue University’s Earth, Atmospheric, and Planetary Sciences Department conducted a test program to determine the practicality of using Shortwave Infrared (SWIR) imaging to improve detection of poorly-visible tornadoes in supercell thunderstorms. The research concluded that there is a distinct possibility that SWIR video imagery can be beneficial to storm spotters. In particular it found that, “an ambiguous, non-tornadic cloud base lowering was quickly dismissed by a participant viewing the scene in SWIR, while a participant viewing the same scene in VIS light had a more difficult time determining that the feature was non-tornadic. Because SWIR light is less susceptible to scattering by intervening haze, allowing cloud base features to be more easily discerned.”

The SWIR image easily defeats the disguise worn by the actor. Human hair and natural fabrics such as cotton are highly reflective in SWIR. Notice in the SWIR image where the actor’s natural hair meets the artificial facial hair worn in the disguise. Further note the actor’s black suit and shirt appear white in SWIR.

Thermal imagers detect contrasts in temperature. Because the swimmers have similar temperature to the water they easily blend in with the background. This is called thermal crossover.

But if you want to increase the contrast on a roll of underexposed film or a roll of film that has less contrast already built in, you can have your lab push process your film.

High-speed SD-OCT image of the front of the eye from the top of the Cornea to the bottom of the lens. This slice of a 3D image capture assists eye surgeons to assess the cornea and lens before Lasic or lens replacement surgeries and to assess the potential for glaucoma as a result of the angle between the cornea and the iris.

Thermal image of a glass window using a Long Wave Infrared (LWIR) imager. Thermal imagers detect contrasts in temperature, therefore the thermal camera produces an image of the temperature of the glass window and nothing behind the window.

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This works the other way as well. If you’re shooting in fairly flat or soft light like an overcast day and would like to punch up the contrast, bring a high-contrast film. But if you want to accentuate the low contrast or are aiming for the light and airy look, bring a low contrast film.

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Or what if you want to embrace a low contrast scene or decrease the contrast in your image when you’re faced with a high contrast scene?

If you want to make sure that you retain the details and have a little less contrast in the darker part of your scene, meter and expose for the shadows.

If you’re confronted with a lighting situation that has a great deal of contrast, you will need to make some decisions about how you want your final image to look.

SWIR image of the same scene using a SWIR illuminator which is not detectable with the human eye. Sensors Unlimited SWIR cameras can be equipped to vehicle platforms to provide driver vision enhancement in total darkness.

SWIR cameras detect reflected light similar to visible cameras. Due to the high absorption of SWIR light in water, the swimmers shown in the SWIR image exhibit high image contrast making them easier to detect.

With color film, it can make the colors punchier and more saturated. Pushing film in development should not be used to “fix” bad exposures. But it can be used intentionally to add contrast. You don’t necessarily need to underexpose your film before you push it.

For example, Kodak Ektar is a higher contrast color film than Kodak Portra 400. Kodak Tri-X black and white film has more contrast than Ilford Delta 400. But that doesn’t mean that Portra 400 can’t have more contrast; it can if you shoot intentionally to add contrast. The same goes for Delta 400. We’ll talk about that in a bit.

Knowing how to control contrast in your images is an important tool to have in your photography skills toolbox to help your images convey the message you, as the artist, are trying to communicate.

Short wave infrared InGaAs cameras have the ability to take pictures through rain, haze, smog and other obscurants. The visible image above cannot be detected. However, a SWIR camera from Sensors Unlimited, Inc. is able to pentrate through atmospheric obscurants to determine what is behind it. This image was taken in late afternoon before dusk about 150 feet from the ground. The hotel that is shown here is around 1.5 miles away from the camera. Learn more about SWIR cameras.

In vivo 3D CBFv networks on mouse sensorimotor cortex (2.4×2.0mm2) imaged by 800nm µODT vs. 1310nm µODT. (a, b): 3D rendering to illustrate dramatically enhanced image depth by 1310nm µODT; (a’, b’): the corresponding MIP images; (e-f): en-face CBFv images of sub-stack cortex at different depths from 0 -1.4mm; g) capillary CBFv at different depths. CTX: cortex, CC: corpus callosum. Low dose intralipid (0.5mg/kg/h) was given to the animal intravenously (i.v.) as optical contrast agent to enhance capillary flow sensitivity for panels a) and b).

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Depending on how great the contrast is in the scene you are photographing, you may lose all detail in the brightest part of your image. If you’re okay with this, you will have created an image with less contrast in the shadows and over-exposing the highlights. Because most film photographers expose for the shadows, you will not need to give the lab any special instructions.

If you are okay with letting your shadows go to black, you will have created a fairly high contrast image. Be sure to let your lab know that you’ve exposed for the highlights so that when they scan your film, they won’t try to bring up the shadows.

3D cerebrovasculature of mouse sensorimotor cortex (2.0×0.5 ×1.4mm3) acquired by 1310nm contrast-enhanced µODT. Right panel: statistical distribution of microvasculatural density (fill factor) as a function of depth below cortical surface. Arrows: penetrating pial vessels

Longer wavelengths of light pass more easily through atmospheric obscurants such as dust, haze, and smoke. Because the SWIR band has a longer wavelength than visible, Sensors Unlimited SWIR cameras are able to image scenes behind light smoke as seen in the forest fire image above.

Wide field-of-view high-speed SD-OCT image of the retina showing the structural detail of the retina and the choroid (the blood vessel layer under the retina). These images assist in diagnosing, monitoring and treating eye diseases such as glaucoma, macular degeneration and diabetic retinopathy.

Image: SWIR thunderstorm cloud base near Lebanon, Indiana on 15 June 2016, showing the higher dynamic range and enhanced cloud texture details in the SWIR image. Researchers at Purdue University’s Earth, Atmospheric, and Planetary Sciences Department conducted a test program to determine the practicality of using Shortwave Infrared (SWIR) imaging to improve detection of poorly-visible tornadoes in supercell thunderstorms. The research concluded that there is a distinct possibility that SWIR video imagery can be beneficial to storm spotters. In particular it found that, “an ambiguous, non-tornadic cloud base lowering was quickly dismissed by a participant viewing the scene in SWIR, while a participant viewing the same scene in VIS light had a more difficult time determining that the feature was non-tornadic. Because SWIR light is less susceptible to scattering by intervening haze, allowing cloud base features to be more easily discerned.” Read more about the 1280JSX -30 fps and 1280JSX - 60 fps Mini SWIR Camera.

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Enface view of retinal blood vessel network. The vessels in nerve fiber layer and ganglion cell layer are in red, in inner plexiform layer are in green, and in outer plexiform layer are in blue. The large blood vessels which come across different layers.

Nice article. I think that for many people who deal with film it is hard to use push-pull way to control contrast, because they develop in labs and have no control over chemical processing. I see that a lot of people scan their film and do whatever they want in postprocessing of a scan.

Last time we talked about contrast, we discussed balancing contrast in high contrast lighting situations. But what if you want to embrace the high contrast or add contrast to you image when there may not be much contrast in the scene?

Before we begin, let’s review what contrast is. Contrast is the difference between the lightest tones in your scene or image and the darkest tones in your scene or image.

Learn more about Near/Short wave Infrared Sensors for Optical Coherence Tomography (OCT) High Resolution Imaging in Tissue

Jen Golay is a senior portrait and travel film photographer and a regular contributor for Shoot It With Film. Find her other articles here, such as How To Shoot Kodak Gold 200 and Olympus Pen F Half-Frame Film Camera Review.

Conversely, pulling film in processing reduces contrast. It takes some skill and practice to intentionally over-expose a roll of film and then under-process it. During my college darkroom class, we learned that pulling black and white film can enhance the appearance of skin texture.

If you want to prioritize one end of the contrast spectrum over the other because you feel like the details in that part of the image are more important than clipping your highlights or your shadows, you can use your light meter to accomplish this.

SWIR direct image close-ups of the human eye, as shown above, demonstrates the level of detail captured. The transparency of the cornea extends well into the SWIR band and combined with reduced tissue scattering improves the fine detail captured over that of visible based cameras. This fine structure is a unique identifier of the individual so biometric matching algorithms and databases acquired in the visible should be fully applicable to the SWIR images. This opens up new flexibility in capturing iris images. Most importantly, SWIR offers the ability to capture iris images at distance with controlled lighting sources that are eyesafe and essentially undetectable as they don’t even trigger closure of the iris. SWIR offers the unique capability to capture iris images even when the individual wears regular eye glasses or even sunglasses.

If you know that you’re going to be dealing with high-contrast light, but want to tone it down a bit, choose a lower contrast film to take with you. Conversely, if you want to accentuate the high contrast light, bring a higher contrast film.

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SWIR image of the same scene using the high definition 1280x1024 JSX camera. SWIR cameras detect longer wavelength light than visible cameras, making the various layers of paint on the water tower appear in the SWIR image. SWIR cameras can be used to image artwork for authenticity and changes in design.

Maintenance and repair work is costly to residential and commercial building owners. Each interior and exterior wall can contain valuable information below the paint surface. Quickly identify studs and structural elements and detailed information about your electrical, HVAC, water and security systems with IR inspection cameras

Whether you want to add contrast to a low contrast scene or capture the high contrast; whether you want to subtract contrast from a high contrast scene or maintain the low contrast, you can use these techniques to get the job done.

Hi Dmitry! I agree that most of what needs to be done can be done in post with Lightroom or Photoshop, but to be thorough, I included info on processing as well.

Many more recent film cameras have several metering modes: matrix or average, center-weighted, and spot. You’re going to want to use your built-in spot meter or a hand-held spot/incident meter.

Do you want to try to capture the high contrast as you see it (within the limitations of your film and camera), or do you want to try to find a balance between the two so that you have some detail in both the shadows and the highlights?