One of the most common questions we get asked here at Ogum is about how the aperture affects the final image. While it isn’t a complex topic, it can be counter intuitive - we talk about a lens being wide open but give it a low number, and then when we are using a small aperture we talk about f/22 and the like. However it all makes sense eventually.

This is not an attempt to teach people to suck eggs nor am I going to go into great depth about how the aperture works (circles of confusion - such fun), you can find out much, more on Wikipedia if you are interested. Suffice it to say that the way photographers talk about aperture it makes sense to see that f/2 is wider than f/22.

When we talk in “f” numbers we are using short hand to explain the ratio of focal length to aperture diameter - so f/2 is really wider than f/22. If you still don’t believe me then substitute  50mm for f. We have a lens with a (50mm/2) 25mm aperture or a lens with a (50mm/22) a 2.2mm aperture. The 25mm (f/2) one is obviously larger. Although this seems simple, this is one of the commonest misconceptions - even some photography books jumble up high f numbers and “large apertures” by mistake.

OK, next - we need to think about what aperture we want to use. With a modern DSLR camera, I would advocate shooting in Aperture Priority (AP, Av etc) mode for around 99.5% of your pictures.  People who use and advocate full manual mode often suggest you use the DSLR exposure guide to see if you are under or over the ideal. Why not go to AP mode and let the camera mess around with your shutter speed? Using AP you can still over or under expose for creative effect - manual mode seems like adding effort and creating the possibility of mistakes, for no benefit. There is an exception here for shooting panoramics or specialist work, where you need the aperture and shutter speed to be set to something fixed other than what the camera would want (and cant generate the effect with exposure compensation controls) but this is rare.

The reason I suggest using AP as the default mode is because this allows you to control the depth of field (DOF). Again this is something people initially struggle with but, when they “get it,” it all suddenly makes sense.

When you use a wide aperture (f/low number) you have a very small plane of focus. This is great for picking out a detail and is often used in portrait work (remember to get the eyes pin sharp!).  Conversely using a small aperture renders more and more of the scene in focus, often the goal of landscape work. Although I have used two examples, every photograph is different and there are lots of reasons to take a portrait shot at f/22 and a landscape at f/1.8.

To demonstrate how this effect looks, here are two pictures taken of the same scene, using the same focal point (top of the tripod head):

Taken at f/2 with a 50mm lens

Taken at f/22 with a 50mm lens

As you can see, the wide aperture image picks the tripod head out from the background fantastically. There is no doubt as to the focal point of that image. With the narrow aperture image, however, you can easily see the distant mountains, with the image being in focus from the very near distance to almost infinity.

There are some other issues to consider such as focal length. A 10mm lens at f/8 will have a greater depth of field than a 500mm lens at f/8 - and again this makes sense when we plug the numbers in - the aperture of the 500mm lens is about 50 times wider at the same f-number. Also, the distance plays a key role so when you focus on something very close your DOF is smaller than if you focus on something far away. An easy way to think of this is a one thirds / two thirds: When you focus on something, the focal plane (area where the object is actually in focus) will extend back towards you for about 1/3 and away from you for the other 2/3rds. You can get all technical with an online depth of field calculator.  This means if you focus on something 12″ away, unless you use a very small aperture you are unlikely to get an object more than 3′ (1m) away in good focus. This is crucial with macro work where the plane of focus tends to be a few mm wide and f/64 is the order of the day.

Crucially, however, there are no hard and fast rules that say you need f/16 for landscape or f/8 for sports. You choose your aperture based on the effect you want to achieve. If you want a huge DOF then set your 18mm lens to f/22 and you can be fairly confident everything will be in focus. If you want to blur a background then increase the focal length and drop the aperture.

Just to let people know Ogum Photography will not be blogging between 1 - 28 May 09. Fortunately we will be doing a fairly complex travel photography assignment and clocking up our air miles.

Ogum plans to be back with a new tutorial on 29 May 09.

Flying in the face of the recession, Nikon has launched another new DSLR camera, the Nikon D5000. Coming five months after the wonderful D3x announcement, this camera seems to be targetting a very, very different audience.

While the D3x was very obviously aimed at professionals who could justify the massive price tag in return for huge picture files, the D5000 is aimed squarely at the enthusiast, semi-pro and has lots of features once only found in compact cameras. Priced around £720 (body only), this seems to be going up against the D300 and the EOS 50D type of cameras, but this may change - it seems to fit more with the D90 / EOS 500D range.

The Nikon D5000 uses a 12.3 Megapixel CMOS sensor (which I assume is the same as in the D300 / D90), giving a 1.5 lens crop, and producing pictures more than suitable for most uses. Twinned with a good lens, this sensor is capable of producing pictures that are sharp enough to be blown up quite a bit before any problems appear. It has the almost standard ISO range of 100 (lo-1) to 6400 (hi-1), which should suit most needs, but isnt great for taking pictures in the dark. All this is pretty much the minimum specifications for a camera now and can be found (and bettered in some instances) on pretty much every camera currently available in that price range.

The new bits:

2.7″ vari angle LCD monitor. Just like you get on compacts. This allows the viewing screen to pop out and be repositioned. This is great for taking pictures in awkward angles but has come at the cost of some screen real-estate (3″ monitor would be better ). If you want to take shots over the crowd or at floor level this can become essential, but in normal circumstances it seems to be a bit of a gimmick.

HD Video. Called “D-Movie” by Nikon, this lets you record high-definition (HD) movie clips with sound. Coupled with a DX sensor and the DSLR range of lenses this means you can produce some spectacular footage. This was first introduced with the Nikon D90 and now appears in lots of cameras (Canon EOS5D MkII being the “biggest”), but is of limited value. If you want the ability to take pictures, interspersed with video clips, then this could be great. If you want to take video footages, I suspect a video camera would be a better idea. One thing which may cause problems here is that the D5000 uses SD memory - this can be slow and may limit the functionality of the system.

Face priority AF. Another one from the world of the compact camera. I suspect this only works with the live-view (using the monitor not the viewfinder) working and it helps ensure that any pictures you take of people “doing things” is focused on the person not the things. This isnt something I have used very much, so I dont really know how much benefit it is. It is likely to appeal to a compact user “upgrading” more than a DSLR user looking for a new camera.

Extensive Retouch Menu. Here Nikon have taken onboard an idea from Olympus and given a variety of special effects you can apply in-camera. If you shoot raw (.NEF), these will modify your image and save it as a JPEG, so the original .NEF file is still available. Most Nikons already cater for Warm Filter, Black and White, Sepia and Cyanotypes, but now the D5000 adds: “Perspective Control, Soft Focus and Color Outline, which transforms your photo into a line drawing.” (From the Nikon site). Perspective control seems very interesting but I have never been a fan of soft focus, and colour outline seems more gimmicky than I’d be happy with. If you dont have a computer (or hate using one) then this could be good - although personally I’d like to see options for pinhole or lomo style effects - but most of the time you would really be better doing this at a computer where you have much greater control over the effects.

Summary:

Overall then, this seems like an interesting enough camera and one that should be aimed at new DSLR owners, ideally those upgrading from compacts, but there isn’t really anything new here. If you already have a D90 / D300 then this really isnt worth buying (unless the price plummets). If you have a Nikon D60 it may be worth it, but really think about if you need the few extra benefits - a D90 is £100 cheaper. If you have a Nikon D40 and want a new camera, then take your pick, although I’d go for a D90 and spend the extra on lenses.

Once it was believed that the advances in DSLR technology would filter down to compact users, and to an extent this was very true. It now seems like the reverse is the case. DSLRs are sporting more and more features once associated with compacts. Some have been very good (VR for example, but for some reason Nikon wont build it into the camera of their DSLRs…), some strike me as pointless gimmicks - in-camera editing and HDvideo clips for example. Still, your milage may vary…

For those of you who are heavily into the Canon system, there is an interesting new camera out - now available for pre-order from most good retailers (such as Warehouse Express).

The EOD500D provides the photographer with a 15 megapixel resolution and an excellent sensitivity range from ISO 100 to ISO 12800. It is an APS-C camera so you will get the Canon 1.6 crop factor (so an 50mm lens performs like a 80mm on a traditional 35mm film camera).Looking at the price and initial specifications, this camera seems to be marketed against the Nikon D300.

Hopefully I will be able to provide a review of sorts in the near future, but until then I would appreciate any feedback from Canon users out there.

Still Lake

This image is available for purchase as a print, canvas or digital file from Ogum Photography.

Some lenses are more prone to this than others, with wide angle and the more entry level lenses suffering the most. Most people will never notice it, but when you do it can become the most irritating thing in the world.

Chromatic abberation is the result of the lens failing to focus all the colours onto the same point of the sensor. It often manifests as a blue or red glow, or fringe, around details in the picture - depending on the situation though, you can get other colours including green and yellow fringing, but these hide well in landscape shots. Sometimes it can be an almost trivial effect, but on occasion - such as an ultra wide angle lens shooting in difficult light, you can get very pronounced effects that ruin an otherwise great picture. However, all is not lost.

There are several ways to get rid of chromatic abberation - the most effective is to prevent it happening in the first place. While methods such as increasing the focal length or purchasing “pro-spec” lenses aren’t always an option, keeping the lens clean is a great first line of defence. Not only will this cut the risk of chromatic abberation (a little) but it will help with lens flare, focusing and the overal quality of the image.

Sadly, even when you do your best chromatic abberation can still occur. When this happens, software is our friend. I use Adobe Photoshop, so I am not sure about the exact measures in other packages but with trial and error I am sure you can find something similar. With photoshop there are two simple methods you can use, try each one and see which you prefer and which gives you the best results.

Method 1 - the software default method. Using either Adobe Camera Raw (ACR) or the Filter->Distort->Lens Correction option within Photoshop. This is a pretty brute force approach and involves moving the pixels to realign the colours, so you may end up with excess pixels that need cropping. While there is little you can do to control the ACR version, you can get some control over the lens correction approach by duplicating the background layer and using a layer mask / opacity to select areas of greater or less effect.

For most people this is the simplest and most effective method - it is certainly the one I used every time I saw the dreaded red / blue glow.

Method 2 - I came across an article in Digital SLR Photography which offered a second option. I have tried it on a few of my back catalogue and it actually works really well. First off process your picture as normal. When it is finished, flatten it and duplicate the background layer. Next go to filter -> Blur -> Gaussian Blur and enter a low number around 4 pixels is a good starting point. This should nicely defocus your picture. Now change this layer’s blending mode to “color” and you should see the original sharp picture return without the chromatic abberation. The magazine mentions this can cause problems for large areas of red, although I never noticed this myself, but if so, you can use a layer mask to paint out the effect over these areas.

Since trying this, I have become a big fan of the second method and I am pleased enough with Digital SLR Photography magazine I may even consider subscribing now.

Please try these effects out and let me know what your results are like. If you have any other suggestions I would love to hear them.

This picture is available to purchase from Ogum Photography.

A common debate in photography magazines (well, the digital ones at least) and around the internet is around how much work should be done in-camera and how much post shot editing in photoshop (or similar) is acceptable. The majority of this debate centres on High Dynamic Range (HDR) photography but it also applies to the plethora of retouching tools available in photo editing suites  (some HDR examples on Flickr - here, here, here and here among countless other places).

With photoshop, especially CS4, and a raw image from a digital camera, it is possible to massively push the original image. Perspective can change, colours can change, exposure can change, focal plane can even change (within limits). If you add in HDR software (Photomatix for example) then the options of what can be done to an image multiply beyond belief. For some people this moves it away from photography into the realms of digital imaging. The writers of photography magazines add to the confusion, frequently saying how important it is to get it “right in the camera” rather than afterwards.

I sort of sit on the fence over this. Some HDR looks awful, some photoshop edits are terrible, but then some straight photos are abysmal. It is not the process of how the picture that is created that defines if it is good or not, it is the end result. Sad though it is, no one (other than photographers) cares about the hours you spend in the cold, in the wet, in the mud waiting for the right light to get a stunning landscape. Or the hours you spend trying to get a great focused macro shot. They just care about the picture you show them. Its really up to you how you get this - do what ever you enjoy.

There are purists who will object to this. These are the people who proudly send their pictures into magazines with comments like “straight out of the camera” or “only sharpened in photoshop” etc. These are the people who object to the “unreal” nature of HDR and condemn photoshop edits as being something other than the original scene. Purists often demand the picture shows exactly what the eye saw at the time of the shot. The odd thing is that these purists have no issues with filters, flashguns or black and white film…

This picture is available to purchase from Ogum Photography.

Meerkat On Guard Duty...

This is available for purchase, as print or canvas, from Ogum Photography.