Photography A to Z: C is for Crop Factor

There is quite a lot of hoohah about crop factor but I'm not going to get into all that at the moment - just a brief description of what it is!

Simply, crop factor is the ratio of sensor size to a reference 35mm (or full frame) sensor which measures 36mm x 24mm.

By MarcusGR [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons

So the graphic above shows that the reference full frame sensor is considered to be a crop factor of 1. Any sensor bigger than this will have a crop factor less than one, and any sensor smaller than the full frame reference will have a crop factor greater than one.

There is a bit of math that goes with this but it's not that interesting really so please just look at the picture.

Why is any of this important?

Well, back in the day when 35mm film was a very popular format everyone knew what to expect from a particular focal length of lens - i.e. they knew what to expect in terms of field of view for that lens. This made discussions about what lens to use for a particular type of photography pretty easy as everyone was singing from the same hymn sheet, so to speak.

Then digital sensors hit the scene but were, initially, for economic reasons, smaller than 35mm and this brought its own set of issues. How so? 

A lens is circular and a sensor is rectangular. The image projected by the lens is, very originally, known as the image circle and this lands on the sensor - a full frame sensor is one that covers the full area of the image circle whereas a crop sensor is one which covers a smaller area of the image circle. In effect the rest of the image is thrown away or 'cropped'.

Source: https://commons.wikimedia.org/wiki/File%3ACrop_Factor.JPG

By Self En:User:Ravedave (Self En:User:Ravedave) [GFDL (http://www.gnu.org/copyleft/fdl.html), CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/) or CC BY 2.5 (http://creativecommons.org/licenses/by/2.5)], via Wikimedia Commons

In the picture above, the full frame sensor is in red and the crop sensor is in blue and it can be seen that the crop sensor looks more zoomed in - in other words it has a narrower field of view than the full frame (assuming each version is viewed at the same relative size).

And this is where the confusion begins. A lens on the full frame will render an image differently to a crop sensor even though the lens' focal length remains the same. So going back to the beginning, I said that crop factor was a ratio of sensor size compared to full frame - this means there is more math that I won't bore you with which ultimately leads to a thing called equivalent focal length.

A Canon APS-C (crop sensor) has a crop factor of 1.6 (take my word for it otherwise I have to show you some math!). This means that a 50mm lens on a camera with that sensor has an equivalent focal length of 50 x 1.6 = 80mm as compared to a full frame sensor. Now you can see why it can start getting confusing as to what kind of image you will get with a lens as it will vary dependant on sensor size.

Crop factor cameras are also cheaper to produce and they can have there own lenses too. These lenses will use less glass due to the decreased image circle and are therefore cheaper than full frame equivalents. Another advantage of a crop factor sensor is that apparent 'zooming' effect which can be good for wildlife and sports photography as it allows the use of a cheaper telephoto e.g. a 400mm lens on the Canon crop sensor above will be the equivalent of 400 x 1.6 = 640mm. It would cost an awful lot more to have a Canon 600mm lens than a 400mm!

Like all good things there are a couple of downsides - one of which is that, generally, there is more digital noise from a crop sensor than a full frame one. Technology is moving so quickly that this is becoming less of a problem with every new release of a camera.

So there you have it; a very brief foray into sensor sizes and what it can mean for your photography.

Have fun!

Photography A to Z: B is for Bracketing

Bracketing, in and of itself, is not an exciting subject; however it can produce some excellent results. So what is it? Well, very simply it's when you take the same photograph multiple times with different exposures and then combine them later using software.

Sounds simple, and it is!

The key to good bracketing is to not let the camera move between each exposure. In other words this works best using a tripod. Having said that, a lot of cameras have a setting called Automatic Exposure Bracketing (AEB) which will do the hard work for you - making it easy to take the 3 or more (bracketed) shots in quick succession without having to go to the hassle of using a tripod.

Why on earth would you want to take all these photos and stick them together? If you have a really contrasty scene, say with bright highlights and deep shadows, then this can be a way to bring out more detail in both the highs and lows, making an otherwise unachievable shot, achievable.

The idea is to take 3 or more photos with 3 (or more) different exposures e.g. one exposure is 'normal' and this is the one that the camera thinks is how to expose the scene, one is darker and one is lighter. It might come as a bit of a shock but the camera can, and does, make mistakes when it comes to exposure especially if there are a lot of extremes in the scene i.e. bright and dark.

Something like this.

This is the 'normal' exposure. You may think that this is perfectly acceptable and what's all the fuss about? It is pretty good but I wanted more detail in the shadow area.
So I shot a couple of more frames. This next one is 'lighter'.

It brings up the darker shadow area really well but has blown the highlights somewhat.

Then there's the dark one.

The highlights are much better controlled but the shadows are way to dark.

Now for a little magic in Photoshop to combine these 3 shots into, hopefully, something that is nicely exposed throughout. For those of you interested I used the HDR function in Photoshop.

The end result:

I hope that you can see that there is more detail in the shadow area and the highlights aren't blown making for a much more balanced exposure.

These were all taken using a tripod and wellies and the site is St Nectan's Glen in Cornwall.

Hope this makes sense and can become a useful tool in your photographic arsenal for some of those tricky exposure scenes that your camera can't handle by itself.

Photography A to Z: A is for aperture

This is the beginning of an occasional series of blogs on the meanings of various photographic terms. I've wrapped it up in an A to Z format but will no doubt go round the alphabet several times, as there are a few options under each letter.
So what the heck is aperture? Well, it is 'a space through which light passes in an optical or photographic instrument, especially the variable opening by which light enters the camera'. Mmm, much clearer, eh! No, perhaps not.
Aperture is one of photography's trinity of exposure - the other 2 being ISO and shutter speed (these will be covered in a later blog). So if the hole, or aperture, allowing light into the camera is wide, then more light will hit the sensor, and vice versa. In photography the size of the aperture is referred to as the f-number or f-stop. And if you are interested this is the ratio of the lens's focal length and the size of the aperture.
Here is a graphic showing some of the f-numbers:

These would continue from f8 to f11 to f16 to f22 and further if your lens could achieve it.
It can be seen that the smaller the f-number, the larger the aperture and this would seem rather counter-intuitive. It might also be less obvious that for each 'stop' of aperture there is a halving or doubling of the light entering through that aperture. So for example, going from f5.6 to f8 is halving the amount of light reaching the sensor. Conversely, going from f5.6 to f4 will be doubling the amount of available light. Still not convinced?
This next bit is a bit technical and may not 'float your boat' but I think it's worth sticking with as it proves a point...eventually.
The thing to remember from the definition at the start is that f-number is a ratio of focal length and the diameter of the aperture. For example, if we used a 50mm lens then the diameter of the aperture at f2 would be 50/2 = 25mm. So far, so good. It would make more sense to think of the size of the aperture in terms of its total area rather than just a diameter in order for us to understand how much light might be getting through. This means we have to get into calculating the area of a circle. Honestly, it's not as bad as it seems. We would use that old calculation from school days of πr2. π is a constant, call it 3.142, r2 is the radius (half the diameter) of the aperture, squared, i.e. multiplied by itself. Stay with me ... this means in our example above that the area of f2 would be 3.142 x (12.5 x 12.5) = 490 square mm.
So what was the point of that! Well, if you let me finish it will help show why the next f-number will have a half or double sized aperture area. So if we now go to f2.8 the calculations are the same as above i.e. 50/2.8 = 17.8 mm; πr2 = 3.142 x (8.9 x 8.9) = 249 square mm (8.9 being half (radius) of diameter). Therefore 249 is pretty much half of 490 thus proving that each f-stop either halves or doubles the amount of light passing through it depending which way you are moving through the stops.
Phew that wasn't so bad, was it?
This, of course, means that the amount of light entering the camera is the same for any given f-stop irrespective of focal length of the lens.
Well that's about it for aperture for the moment. There are lots of other relationships for aperture, such as its effect on exposure, depth of field etc and these will be covered in later blogs.
One last thing though. A common term used by photographers is that of 'stopping down'. This just means that they are going to a smaller physical aperture which is of course is represented by the larger f-number e.g. going from f5.6 to f8. On the flip side, 'opening up' means the opposite; a wider aperture but smaller f-number e.g. f5.6 to f4.
Hope that makes some sense of it all for you. Until the next time!

Sleeklens 'Through the woods workflow' lightroom presets review

Sleeklens (www.sleeklens.com) is a newish Danish company that started in 2015 with the remit of producing quality products. They make brushes and presets for Lightroom (https://sleeklens.com/product-category/lightroom-presets) as well as Photoshop; they produce lots of different kinds of templates as well as providing an editing service.
Now, I'm a bit of a preset junkie - I love the idea of them and they appeal to the slightly lazy side of my nature! I have loads in my Lightroom and that's part of the problem; they don't get used very often because I get bored wading through hundreds of choices. The other problem is that all the ones that I have aren't stackable which means that each one overrides the previous one. Not very flexible.
However the good people over at Sleeklens offered me to try out a landscape workflow called 'Through the Woods Workflow'. This is made up of 51 presets and 30 brushes and the best thing about the presets is that they are stackable. I can add multiple presets and they will act cumulatively which is awesome. Needless to say that I said yes to the offer.
This is not one of the best photos that I have ever taken but it will serve to illustrate the process of using the new presets. This is the unprocessed version (apart from lens correction in Lightroom).

Generally a bit washed out and certainly doesn't 'pop'!
So the first preset I applied was 'Warm Shadows' (an All in one preset).

 This definitely perked things up a bit - colours are a bit richer but the sky is still very washed out.
Next I chose an Exposure preset called 'Darken' to help, unsurprisingly, darken the image down.

The default for this preset is a -1.00 exposure. I thought this was a bit much so I reduced it manually in Lightroom to -0.80. This is one of the great things with stackable presets; you can adjust each one to suit, as well as have them add to each other overall.
Still not happy with that sky! This time I went for a Colour preset called 'Deep blue sky'. I had to readjust the exposure back to -0.3 because I didn't like the look I had.

Well it's looking a lot better than it did so is there anything else left to do? I think so. This time it was a Polish preset called 'Add contrast'. It may have darkened the mound a bit but that is easily fixed.

Almost there - I used one of the brushes - 'Cloudy sky definition' at about 50% flow just to get the sky back to where I want it and that was it. I thought about some other things but decided against them at this stage.

So there's the final image - well as final as it is going to be at the moment. There are still a lot of presets left to play with :)
And that's the thing about presets, there are lots to play with and if you like using them then it's a lot of fun trying them out on different images. One preset may look rubbish on one type of image but great on another so they can never be discounted.
So what do I think about these Sleeklens Through the Woods presets? I actually like them a lot. I love the fact that they can be stacked and this makes a big difference to how they can be used to build up an image. I think it's rare for a non-stackable preset to give you the exact look you are after in an image but because these can work together and each one is fully adjustable it is much easier to achieve your goal quite quickly. They give you an opportunity to try out different things with your images in a fairly controlled way.