Hints & tips

Contributions welcome (for this and other pages)!

Do you have a tip that may help other members? Or perhaps a question that we could usefully answer here? Contact the web master.

So far we have only guessed at things that people may like to know.

 Square brackets in Photoshop

Several of the tools in Photoshop involve a small circular patch for applying to a local area. The clone tool and the healing brush are examples. Did you know that you can adjust the size of the patch very conveniently by using the square bracket keys? [ makes it smaller, ] larger.

 Sizing photos for competitions

The size required for images to be projected in competitions is gradually increasing. Currently the common standard is that such images must fit within 1400 pixels (px) wide by 1050 pixels high and be saved in the JPEG format in a file no bigger than 800 kilobytes (kb).

 Width and height

In Photoshop (CS4 shown here, in Windows 10) there are several ways to achieve the pixel size but we will describe the simplest.

On the File menu select Automate and then Fit Image... which opens this dialogue:

Type 1400 into the Width field and 1050 into the Height field and click OK. For the case shown here the result is an image 1400 x 933 pixels because the original was not in the required proportion 4:3. That satisfies the requirement but you may decide to go back and crop the image first so you could use the full 1400 x 1050.

 File size

Again there is more than one way to do this but the best, for several reasons, is the following.

It is important to have first scaled the image as in the previous section. On the File menu select Save for Web & Devices.... This results in a large dialogue filling the screen. The top right corner of the dialogue is like this:

You will want to set the fields just like that, except for the quality field, which we must discuss. Near the bottom left of the dialogue, under a view of your image, you will see information about the file which will be created, looking like this:

Here you check that you are indeed about to save as JPEG and then the size of the file which will be created (here 359 kilobytes). Go back to the top right and adjust the Quality field until the file size is just under 800 kb. The Quality field has a slider to help, or, having put your cursor in the field, you can use up and down arrow keys.

At the bottom right of the dialogue is the Save button, where you can select directory and file name as usual:

The small yellow warning triangle here, as you can find out by hovering over it, is because we set the Metadata field (upper right) to "None". So copyright information, photographer's name, etc will not be saved in the file. And that is a good thing for competitions, so the judge will be unable to see your name.

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 Windows 10 slideshow problem

If you are showing JPEG files, which is usual, Windows 10 has a new program called Photos. The old Windows Photo Viewer is no longer available.

The new Photos has a button for starting a slideshow but it has a very annoying feature. In the old program we used to pause and then step through one a slide at a time. In the new program as soon as you step to the next slide it resumes the automatic slideshow. So you have to pause again after every step. For the way we show PDIs in our club meetings this is impractical.

 Tiffs can help

There is a work-around. If you make a TIFF version of your first slide (or even if you make a new empty file and give it .tif as the extension), right-clicking on it and selecting Open with... makes the old Windows Photo Viewer available again. Whether Microsoft will close this loophole remains to be seen.

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 Stops and EVs

In these digital days when anyone can take decent photos, traditional photographer's terminology is becoming superceded by neologisms. A case in point is the photographic stop. Nowadays people refer to EVs, short for Exposure Values. They are essentially the same. Adjusting the camera by 1 unit in either scale means doubling the amount of exposure (or halving if it is minus one unit). There are 3 ways to increase exposure by 1 stop (or EV) on a digital camera:

Doing all three things increases by 3 stops (or EV) of course, which means 8 times the exposure (2 cubed).

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 f-numbers

What are those f-numbers quoted for lenses? Why are they not whole numbers? And why are the smallest values considered desireable? Here we aim to dispel some of the mystery.

f stands for the focal length of the lens. Camera lenses contain many pieces of glass but if you consider a simple magnifying glass, the focal length is the distance you would hold the lens from a piece of paper in order to sharply focus an object that is very distant. For example, it would give the best chance of burning a hole in the paper by imaging the sun on it.

Lenses having smaller focal lengths give a wider field of view, with less magnification. Longer focal lengths give a narrower, magnified, telescopic view.

If we are setting a digital camera manually, rather than relying on its automatic mode, there are three things which can be adjusted:

The aperture is varied by adjusting an iris diaphragm which changes the size of the opening that allows light in through the lens, rather like the irises in our eyes. The amount of light allowed in is determined by the area of the opening, but the diameter is what photographers specify. If we want to halve the amount of light, reducing the area of the circular aperture by 2, the diameter is reduced by a factor of the square root of 2. Hence we are not dealing with whole numbers.

Furthermore, the diameter is not measured in inches or centimetres but as a fraction of the focal length, f. If the aperture has a diameter which is a quarter of the focal length of the lens we say it is set to f/4. So the f-number in this case is 4.

This may seem awkward but it has the great merit that if we set the same f-number on different lenses maybe with very different focal lengths, we will get the same amount of exposure, other settings also being equal (T and ISO).

A diagram and summary may help:

Do not be confused by a diameter in mm printed on the rim of the lens. That has nothing to do with the aperture but is the diameter of the threaded ring for attaching filters.

 Depth of field

Varying the f-number affects more than just the amount of light entering. Setting a small aperture (large f-number, such as f/22) makes a greater depth of field. In other words the range of distances that are all in focus is greater. Sometimes this is desireable, sometimes not. To make a bird stand out from the background we might want a very shallow depth of field, so only the bird is in focus and the background is blurred out. In that case a larger aperture (smaller f-number, such as f/2.8 if the lens is capable of it) would do the job.

This is exactly why we sometimes need to use the manual settings. In automatic mode the camera cannot guess whether you want the background in focus.

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