Ask uncle Ronnie

Resolution in Pixels & Corner DarkeningI have a Panasonic Lumix DMC FZ50 since about 3.5 years (for which I got inspired through SP).

Although the results have been really good, the problem remains that it clicks photos at 72 dpi. Your photo-contests re-quire snaps clicked at a minimum of 300 dpi. a) Could you please help me? How can I click photos at 300 dpi or more or else how can I convert them from 72 to 300 dpi?b) Also, many a times I have noticed that a black halo appears at the corners of the clicked photo. Please help me regarding the cause for this and how to avoid it.

Mayank Goel, via email

a) When we talk of prints, the term is dpi (dots per inch); when we talk of images, the term is ppi (pixels per inch). Hence you should have used ppi instead of dpi.With some cameras, the images open in Photoshop at 72 ppi; with some other camera models, images open at 300ppi (some even open at 240 ppi, or 180 ppi). Just see that there is no tick mark in the ‘Resample Image’ box and put in 300 in the resolution box. As noted the Resolution should be ‘pixels/inch’. Click OK.

b) I think what you are referring to is corner darkening. This is mostly seen with images shot using wide-angle lenses. Many lenses do not provide even illumination across the frame. The corners, being farthest away, receive less light and hence look somewhat darker.

Sometimes this is also due to a fi lter over the lens, especially if the fi lter has a thicker ring.If the problem is due to the illumination of the lens, I am afraid you can do nothing (except getting rid of the corner darkening using Adobe Camera Raw, which has this provision). If the problem is due to the fi lter, try using a fi lter which has a very thin ring.

Effective Focal Length

1) I am a regular a reader of SP for the past few months and in some issues I have come across the term ‘Effective focal length’. Could you please explain how this is calculated? I am having a Nikon D60 with 18-55 kit lens and a prime lens Nikkor 50mm 1:1.8D.

2) In Point and Shoot cameras the zoom is mentioned as 2x, 3x, 10x etc. In D-SLR section, zoom lenses are mentioned as 70-200mm, 18-105mm etc. Can you explain how it is defined? When some of my friends ask me how much is the zoom of my camera I could not explain it to them.

Rakesh James, Kottayam, Kerala

1). First, let’s understand what the term ‘focal length’ means. Focal length (which is measured in millimeters) is the distance between the rear nodal point of the lens ( the point where light rays appear to have originated after passing through the lens) and the film plane, when the lens is focused at infinity. Here’s a simpler explanation: Hold a single element lens (a magnifying glass for example) and let the sun’s rays focus on your hand (when that happens, you’ll say “ouch”). The distance between the center of the magnifying glass and your hand is the focal length. To a photographer, focal length conveys the ‘angle of view’ of the lens.

For example, a 50mm lens on a 35mm format (film frame size 24 x 36mm), covers a diagonal angle of approximately 46 degrees. But focal length also has a relationship with the film format. On a medium format camera (film frame size approx. 56 x 56 mm), a 50mm lens will not give the same angle. It will give something larger.Now coming back to your first question, the Nikon D60 has a smaller-than-35mm size sensor. (It is known as APS-C size and measures approx. 23.6 x 15.8 mm). This means that a 50mm lens when used on the D60 camera body, will have narrower angle of view. But how much smaller? Nikon tells us that the conversion factor is 1.5 times.

This means that a 50mm lens when used on the D60 will cover the same area that a 75mm lens would have covered on the 35mm format. Hence we say that the effective focal length is 75mm! With Canon D-SLR cameras using APS-C size sensors, the conversion factor is 1.6 times; Olympus D-SLRs have a conversion factor of 2 times. As a rule, the same focal length will give a narrower angle of view on a camera with a smaller sensor than on a camera with a larger sensor.With compact digital cameras, the sensor size varies greatly from manufacturer to manufacturer and even with different models from the same manufacturer.

This causes a great confusion about the effective focal length. Thankfully, the manufacturers provide us this information. Please note that two compacts having the same mentioned focal length can have different effective focal lengths (because their sensor sizes could be different).(For further explanation on the above topic, please refer to Smart Photography, February 2009 issue, pages 74-77)2) I think every zoom lens should have the focal length mentioned in millimeters rather than as 2x or 5x or whatever.

A 50-150mm zoom lens is 3x zoom; 100-400mm is a 4x zoom. An 18-105mm is 5.8x zoom. You take the second number and divide it by the first number to arrive at the ‘number-of-times zoom’. Really, this is not required as the calculation is so very simple. Also remember that you cannot make out the actual focal length from these numbers. A 100-300mm zoom lens and a 50-150mm zoom lens are both 3x!


Where Does One Draw the Line?Now-a-days photography and photo editing software are reciprocating each other. Photographers are alter-ing their photographs with the help of photo editing software to the maximum. As a result, the originality or the authenticity of a photograph is lost sometimes. It is also right that some photographers are creating beau-tiful pictorial photos in this way.To give a touch of surrealism in the photographs, photo editing software are working wonderfully. The altered photographs are accepted in Salon competitions. But sometimes these photos are wining in straight photography competi-tions also because it is not always possible to identify an altered photograph easily. My question is, how far is this altered photography doing good for photography as a whole?

Kartick Das, Kolkata

There are those who consider editing as part and parcel of digital imaging. And there are those who consider partial editing as okay, and mixing images (where the originality is lost) as taboo. There are also those who have no limits to the amount of editing/mixing they do, even if it means if authenticity is lost. Photography is an art form and we need to respect every individual’s views. Here is a long-winded explanation and the reader should make his or her own judgment.Most people who are against manipulations are not aware of how darkroom processing and printing was done in the past (of course darkroom printing is still done but for the sake of this discussion, let’s say ‘in the past’).

This could be because the modern generation of photographers (most of them anyway) have had no training or experience (or very limited experience) in the chemical darkroom. When working in the chemical darkroom, we often controlled fi lm development (and hence its characteristics) by changing the time and/or temperature of the fi lm developer; by using different types of fi lm developers; by using different grades and types of printing papers. We even used different types of enlargers to achieve different lighting contrast. We also picked up the sky from one image and blended the same on to another image (yes, that too was done, but the technique was limited to the advanced workers who seemed to possess magical powers!). We even got rid of electric cables, and smoothed away the acne, facial hair and other blemishes on lady’s portraits. We employed the technique of ‘dodging’ and ‘burning’ to bring out detail in localized areas. Needless to say, not everyone could do all this because it required years of dedicated practice in the darkroom. So, where does one draw the line? Here’s my take on this topic and the reader does not necessarily have to agree with me. Let’s take an example of a plastic surgeon.

His job is to make his client look handsome or pretty. He alters the nose, creates high cheek bones, does away with fl abby skin or whatever else that would make his client look amazingly good. The ‘originality’ is gone. The ‘authenticity’ is altered. Do we have anything against the surgeon who creates such work of art? I am sure your answer is in the negative. So, why penalize the photographer, who has spent months and even years in improving his skills to create something extraordinary? To stop photographers from this creativity is to kill photography.Now let’s come to the salon participation.

I think every salon of photography must have a section called ‘Digital Art’ or something like that where photographers with a vision can participate without fear of being criticized. But the questions are:How much ‘editing’ will you accept in sections which are not supposed to be (heavily) edited? If skillfully done, how will you know what has been edited? Will the participants honestly say that they have edited their images? From this it should be clear that there are no clear-cut answers or solutions (there are software which can identify if the images are altered in any way but every digital image needs some sort of correction for contrast and/or sharpness and/or color balance).

So coming back to your question “how far is this altered photography doing good for photography as a whole?”, the answer is complex. Have you created the image for your own pleasure? If yes, and if you do not claim the edited image as ‘original’, any amount of editing is fi ne.Is your picture a documentary or scientifi c evidence? If yes, then editing is wrong (sports photography, medical photography, and photojournalism would fall under this category). But as long as human nature is what it is, there will be people who will modify their images and still claim that the images are original.

We also posed this question to Jagdish Agarwal, founder of Dinodia Photos. Here is what he had to say:

You cannot alter photographs, if you are a press photographer, wedding photographer, or do any type of photography where factual documentation is required. There are many known cases, where photographers have lost their jobs, and awards have been withdrawn, after it was found that photographs have been altered or even if the photographer shifted the elements in the scene, before taking the photograph.

But, you can do anything to the photograph, if you are an advertising photographer, fi ne art photographer, or do any type of photography where your creative thought is more important than the means to show that idea. So, you can do double exposure, posterization, solarization, or anything which modern technology allows.

By way of comparison, let us look at painters. If they paint a portrait, it will be factually correct. But if they do fi ne art painting, it can be on any surface, by using any medium, of any subject matter, in any composition.Hope this clarifi es the question.