Clouds

Copyright ©Praveen Chamarthi 2006

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Wild Berries

Not wild really

© Praveen Chamarthi 2006

Beauty is simple

© 2006 Praveen Chamarthi

One light on..

Petunias

Petunias

Camera: Canon EOS 300X;

Lens: Sigma 70-300 APO DG (Macro)

Film: Fuji Velvia 100F (Slide)

Aperture: 5.6 (Macro mode)

Green

Rain brings out the best colors of nature. Green is one of them

Camera: Panasonic LUMIX DMC FX-09, 6.0MP

Digital Crop Factor

On Digital SLR’s, when mounted with a lens of given focal length, you would have noticed a considerable change in the Field Of View, when compared to a film camera. This is nothing but the “Crop Factor”.
Let’s consider the prime 50mm lens:

When mounted on a 35mm film camera the focal length of the lens remains the same i.e. 50mm, as the lenses are designed for 35mm films/equivalent sensors.

When mounted on any Digital SLR the focal length remains the same but due to the crop factor the field of view drops considerably, as the sensor sizes of most of the mid-level D-SLR’s are smaller than 35mm.

For Canon EOS 350D the sensor size is 22.2 x 14.8 mm

For Nikon D70S the sensor size is 23.7 x 15.6 mm

So a wide angle lens loses it’s field of view when mounted on a D-SLR (of sensor size less than 35mm)

For instance when a 50mm lens is mounted on a CANON EOS 350D D-SLR, whose sensor size is 22.2 x 14.8mm, the crop factor calculates to
crop factor = 35/(sensor size)

i.e. crop = 35/22.2 = 1.6
so now the field of view, for a 50mm lens, on a D-SLR translates to:

field of view = focal length of the lens X crop factor

i.e. field of view f = 50 x 1.6 = 80mm (i.e field of view is equivalent to a 80mm lens)

wow!! it’s almost become a tele photo lens. Note that the focal length remains the same but the field of view of this lens now becomes the equivalent field of view of a 80mm lens.

If you are a D-SLR (serious amateur level) user and if you are going to buy a lens then don’t forget the crop factor otherwise you end up picking up a 16-35 L series lens for 1,500 USD and when you mount it on your D-SLR you’ll have a field of view equivalent of a 25-56mm lens. So plan your buy keeping the full frame sensor in your mind.

Invest in expensive lenses only if you are going to switch to a full frame sensor in the future.

For Nikon and Fuji D-SLR users the crop factor is approx: 1.5

For Canon D-SLR users the crop factor is approx: 1.6

Pottery

• ISO: 100
• Shutter Speed: 1/25
• Aperture: 7.1
• Focal length: 50mm
• Photographer: Praveen Chamarthi

Crack of dawn

This picture has been featured on the flickr’s interestingness page a long time ago. I thought I would share with you all.

I experienced this beautiful formation during my trip to Singapore.

Anatomical 18% gray card

Any SLR user (advanced) who shoots in “M” mode must have surely come across the term “18% gray”. So what exactly is this 18% gray and how does it affect exposure?

Mostly all cameras have an in-built light meter, which are calibrated for 18% gray i.e. the reference point for a camera’s light-meter to determine exposure are the surfaces that reflect 18% of the light that if falling on them. It is similar to a thermometer: At room temperature the thermometer stay at 94-97 deg i.e. the mercury in the thermometer remains stable during these temperatures. As the temperatures rise above this point the mercury starts reacting and shoots up the meter depending on the temperature it has been subjected to. So a reference point for a thermometer are the points at which it stays stable. Depending on this you can say if a person has a fever or if there is a drop in temperature. Similarly a camera”s light-meter is calibrated for, surfaces that reflect 18% light, or in other words, surfaces with 18% reflectance. So the mid-tones in your frame are rendered as surfaces that reflect 18% gray and deflection from this point results in an over or an under-exposed picture.

For instance if you compose a picture with your SLR camera in such a way that the frame is filled with any black material, the famous example is when you shoot a black cat. Place a black cat on a leather couch which is also black in color and then compose and shoot the picture with the whole frame filled with the black cat and the background, the black couch.

The results will be surprising you will see that the camera will fail to understand the shades of black and your picture will have a noticeable layer of gray on it. This is because of the camera calibration to 18%gray. Since the light-meter cannot find any mid-tones it renders the whole picture as gray. Similarly you can try this with your frame filled with only whites and you’ll see that the results are more or less the same.

So, how do we expose correctly for black cats 🙂 or rather when your frame is filled with same colors? The answer is very simple: “Use an 18% gray card/surface to determine the exposure”.

How do I take the reading for a good exposure? You can place the 18% gray card next to the subject of interest. Zoom in with your lens (or go closer) and now focus the gray card, adjust your shutter speed such that the light meter indicates perfect exposure. Now remove the gray card, zoom out and recompose your frame with your cat or whatever it is, DO NOT CHANGE YOUR EXPOSURE SETTINGS (let the reading be the one that you took off from the gray card) and then shoot et voila you now have a better and most realistic colors and shades of the picture as opposed to the one that the stupid light-meter has decided for you.

So now where do I get a gray card?

You can pick them at any of your local store for a few dollars.

What If I don’t have one or If you forgot one at home?

Most of the camera bag manufacturers (LowePro) provide the adjustable partition strips inside the bags with gray color. you can just strip on these and use it as your gray card. Alternatively an average human palm is supposed to reflect 18% gray so you are never out of options.

Tricky situations can be encountered when you are shooting a landscape with hills, clouds, flowing water, rocks and the green valley. Obviously, one cannot walk up to the hill place your gray card, come back place it on the water and then on the greens, take readings and shoot. The solution for this is quite simple and also complex

keep reading this blog for more on exposure techniques.

Good day people!