Master The Light Webazine

DIY BOOM

The problem with a lot of studio lighting setups is that you really need to use a boom for the top light otherwise you end up with a light stand in front of your lens. Now we don’t all have booms lying around but it’s really easy to make one out of two light stands.

Disclaimer: Please be aware that this is only for use with small light flashes and should never be used with heavier studio lights and although I have used this trick myself on many occasions, by trying this you do so at your own risk and I cannot be held responsibility for any loss, damage or injury that may occur as a result of following these instructions.

What you will need:
1. 2 x Medium weight light stands
2. 5 to 10 Cable ties
3. Gaffer tape
4. Sand bags

Now all you have to do is cable tie the leg from one stand to the upright from the other. Make sure you use a few cable ties and that the stands are solidly joined together.

You need to make sure that the upright stand is weighed down with sand bags or weights and that the cable ties are strong enough and tight enough and if in doubt as to how many to use, err on the side of caution and use more.

It is also a good idea to wrap gaffer tape around the overlapping poles for extra strength.

You can adjust the height by raising the upright stand and you can adjust the angle by adjusting the legs of the stand that is acting as the boom.

So there we go one easy DIY boom.

A lot of people get confused about the difference between PPI and DPI and what PPI setting you should use in Photoshop and how PPI relates to cameras, so I dug up an old article I wrote that will hopefully shed some light on the subject.

The simply answer would be to tell you that the PPI is actually irrelevant when it comes to comparing the resolution of cameras but we are also going to talk about DPI, so it I think it would be more beneficial to take everyone through a detailed description of how this all works and why so much confusion surrounds it.

Your cameras sensor consists of a grid of square, or in very rare cases rectangular blocks, which we call pixels or photosites.

Although the physical size of the pixel may vary between different types of sensors, all digital cameras produce a raw image (no interpolation or processing) with a fixed number of pixels that is dependent on the number of pixels that the sensor has.

At this stage, each pixel has no defined size but simply represents a single square of a particular colour.

The confusion creeps in when it comes to applying a resolution to the image and understanding what it does.

As I have mentioned, pixels do not actually have a size but combine to give an image a pixel dimension (number of pixels across and number of pixels down). If we want to print or display the image at a particular size, we need to assign a size to the pixels and we do this by applying a resolution, which is an output scale factor, that specifies how many pixels there are in an inch or cm and lets us calculate a size for each pixel.

Remember that this is just a factor that affects the output size and it does not in anyway alter the actual size of the original image which has no physical size.

The confusion creeps in because there is no standard for the default resolution that applications like Adobe CameraRaw apply to images, unless you set the default yourself.

What is happening is a situation where on the one hand, a resolution of 180ppi may be applied to one camera’s images and on the other, a resolution of 72ppi may be applied to the another camera’s images.

The relevant part of the scenario is above is the word “applied” as the resolution is applied to the image and is not a component of the image and can simply be changed at your discretion without the actual image’s resolution being altered as this is defined by the pixel area not the output size.

If we look at the Photoshop “Image Size” screen below we can see the Image’s Pixel Dimensions represented by pixel width and height.

It is interesting to note that each 8bit pixel has a size of 3 bytes so for every pixel in your image, the image size increases by 3 bytes.

In the “Document Size” section of the screen you will see the Document width, Document Height and Resolution. The Document Width and Height are calculated by dividing the Pixel Dimensions (width and Height) by the values entered in the Resolution box.

So there are two approaches one can take when it comes to resolution. If you know what you want the output size to be, you can enter the desired output width or height into the relevant box and the resolution will be adjusted accordingly or if you know what resolution you need, you can enter the resolution and you will get the corresponding output size.

We have already mentioned that the resolution simply defines the number of pixels per inch in the printed or displayed image and affects the print size of your photo but it can also affect the quality of the output.
We also know that the resolution defines the number of pixels per inch and therefore the size of each pixel. If there are too few pixels per inch, then the pixels will be very large and you will get a very pixelated image (jagged edges or the individual pixels will be visible).

So what is the correct resolution for and image? A lot of this will depend on the size of the print. This is because you look at large prints from a further distance than a small print, so you can get away with a lower PPI and still have the image look fine.
Seeing that all resolution does is affect the print size of the image there are 2 ways that you can change the print size, and these are by resampling or by not resampling.

Not resampling is what you want to always do if possible as this will only change the size of the print out. Resampling will actually change the number of pixels and thus the file size in order to match the print size (Remember every 8 bit pixel = 3 bytes).
So for instance, if you don’t resample, changing the PPI setting will increase or decrease the print size. It will increase if you drop the PPI setting and it will decrease if you increase the PPI setting.

With resampling, you will lose pixels if you set the PPI setting to a lower value or you will have pixels created if you increase the PPI setting. Creating pixels is always a bad idea as they get generated by the software through a process of interpolation and the results aren’t usually that good. Throwing away pixels is fine as long as you won’t need them later.

An Example

If you take a 100 x 100 pixel image, it could be printed at many different sizes. If you set the resolution to 10ppi, then you’d have a 10″ x 10″ image.

If you set the resolution to 100ppi, you’d have a 1″ x 1″ image.

Remember that adjusting this value doesn’t affect the number of pixels in the image; it just changes how big the print will be.
Take your 100 x 100 pixel image again. Suppose its resolution is set at 100ppi (producing the same 1″ x 1″ printed image).

With re-sampling off, when you adjust the resolution the dimensions also change. This is how things worked in the example above. With re-sampling on, the dimensions won’t change so if you changed the resolution to 10ppi with re-sampling on, you would still keep a 1″ x 1″ image and the computer would throw out pixels to keep the that size. So in this case, you’d end up with a 10 x 10 pixel image in the end.

If you went the other way, and changed the resolution to 300ppi, then the computer would generate pixels to make a 300 x 300 pixel image that’s still 1″ x 1″ when printed.

If possible, the only reason you want to use re-sampling is for reducing the size of your image for the reasons mentioned above.

DPI and LPI
Seeing we have covered PPI let’s talk about DPI.

The difference between PPI (pixels per inch), DPI (dots per inch) and LPI (lines per inch) can be really confusing seeing that they are all measurements per inch and can be interchanged by really shouldn’t be as dots are dots and pixels are pixels.
The big differences between PPI and the others is that our original images are in a format that is know as continuous tone and consists of a series of coloured pixels with no gaps between them. If we look at a grey scale or colour images on our screen, each pixel can display a shade of grey or colour and are arranged pixel to pixels with no gaps between them. This is known as continuous tone.

Printers on the other hand cannot print shades grey or colour as they limited to a derivative of CMYK inks so the can only print ink or not print ink. In order to simulate shades of grey the printer uses round dots of differing sizes that, when places beside on another at high resolution, trick the eyes into assuming that the area is grey or a shade of colour. This is called halftone screening.

If used in the right context, DPI is only applicable when we are referring to a printer’s resolution and has absolutely nothing to do with any setting in Photoshop’s “Image Size” screen.
So let’s get even more confusing because it seems from questions that I regularly get asked and from my 17 years in the printing industry that even a lot of printers get confused with this.

A halftone image has two components, a DPI and a LPI component.
DPI is used as a measurement of the printer’s resolution and is basically a count of the number of dots per inch that a printer can produce. The higher the dots per inch count, the smaller the dots will be and the smoother and sharper a printed image will look. Unfortunately the DPI setting will not determine the final size of the dots that get output. This is determined by the LPI setting which is a measurement of how many lines of halftone dots get printed on the paper.

What happens is that no matter how high the printers resolution is (DPI setting), bunches of tiny dots get bundled together to make up halftone dots the size of which is governed by the LPI setting. Where DPI does play a big role is that the smaller the dot a printer can produce (higher the DPI setting) the more dots will get used to make up the halftone dot, resulting in a smoother printed image.

The part of this that is relevant to us is the LPI setting that will be used to print the image. Inkjets work in a similar manner to the lithographic printing process but instead of using a normal halftone screening process they use what is know as an error diffusion screening system which is a bit more complicated, but the basic principals still apply.
When a printer comes to you and says they need your image to be 300dpi, they actually mean that it should be 300ppi but they more than likely have no clue why and have probably just been told that that is what all images should be which is not the case.

Even worse, a printer will often try impressing the client with the incredible resolution of their image setter, which the client will not really understand and will then phone you asking for an A3 image at 4000 DPI, in which case you will probably phone someone like me who will fall off their chair laughing.
Boy would I love to see the camera that could take and image that would print out A3 at 4000ppi. It would have about a 2816 mp sensor if my calculations are correct.

There is actually a really easy way to figure out what the resolution of your image needs to be and that is to multiply the LPI setting that will be used by 2.

An example would be a job that will be output at 150lpi which is a very common resolution used by printers. If we stick to the guide lines and multiply the LPI setting of 150 by 2, we get 300 which is the PPI setting we should use for our image.

When the screen ruling gets up into the 175, 200 and even 250lpi ranges, we start to hit a real problem as the resolution that we need to supply the image at starts to seriously impact the size that we can scale the image to without resampling it.

Fortunately the 2 x guideline is a recommendation if you want to get the absolutely best printed result and in practise you can safely use 240ppi for LPI settings as high as 175 and 300ppi for LPI settings 200 and above but the closer you can get to the desired 2 x factor, the better.

The important things to remember from this are:

• Applying a resolution or changing a resolution only affects the output size of the image.
• Resizing the output with resampling off will not change the number of pixels.
• Resizing the output with resampling on will lose or create pixels.
• A printer’s DPI setting is irrelevant to us.
• Ideally the PPI setting for our image should be 2 x the LPI setting that the printer will use to print the job.