Ilford SFX200

b&w, filters, tutorials No Responses »
Jul 042011

Ilford SFX200Ilford SFX200

Images: left – SFX200 film with no filter, right – SFX200 film with Cokin P003 Red filter

Not too long ago, inspired by the work of others (and in order to plot another point on the Stages Of A Photographer graph) I picked up a second-hand Canon EOS film camera. I managed to get an EOS 5 from ebay for around £25 including postage – I had been wanting to pick up an EOS 3 but £100 seemed a little too extravagant. I could also have bought something more fashionable, but as a first tentative step into the world of film it seemed a sensible choice – I can use all my lenses and it works pretty much the same as my main camera, the 5D (although there are some inconvenient differences, such as the lack of dedicated Depth of Field preview button)

I put a couple of films through it to see how I got on, and got them developed locally (and cheaply). Unfortunately the results were pretty poor – lots of scratched prints – but it also seemed that how I metered for digital wasn’t appropriate for film. There were some nice images though, so undeterred I decided to try again so I ordered 4 B&W films at random and it just so happened that one of these was a roll of Ilford SFX200.

I hadn’t really read anything about the film when buying it but whilst casually researching the films before they arrived I noticed that it had “extended red sensitivity” and “using a deep red filter skies can be rendered almost black and most green vegetation almost white”. Reading a bit more about the film I couldn’t really find out any solid facts about using it – although had I found the flickr group earlier I could probably have got my questions answered – so I decided to document my limited experimentation with it so far here.

Kit used:
Canon EOS 5
Canon 24mm f/2.8 lens
58mm filter adapter – as the lens has a 58mm filter thread
Cokin P Series Wide Angle Filter Holder (BPW400A) – I could have used the standard 3 slot one but as I was going to be using film and not digital I didn’t want to be relying on the need to crop the edges if the adapter was visible. (Because the viewfinder isn’t 100% there is always the chance that you don’t see the filter holder through the viewfinder but that it is visible in the shots)
Cokin P003 Red Filter

Notes:
I was using the square Cokin P-Series filters because I already had them. Kood also produce the filter accessories (adaptor, holder), which are generally cheaper than the Cokin ones.
A screw-in Red 29 filter will perform the same function. (A Red 25 filter may also be used but the effect will be slightly less strong)

Without filter/With filter comparison:
The images at the top of this page were shot at the same time (well, within less than a minute of each other) in identical lighting conditions – bright sunlight. Ok – the composition is slightly different, which doesn’t make it a 100% accurate comparison, but my slight change of position will have made only minimal difference to the exposure.

TTL metering was used for both images, metering set to Evaluative. The Red filter has a filter factor of 8, meaning that it absorbs 3 stops of light, so bright sunlight really is necessary for taking shots hand-held. Normally when using the red filter with digital I would shoot at ISO400 but as I was using this film for the first time I decided to use it as its rated speed. ISO400 obviously gives a bit of extra leeway with the aperture setting and I found that I was shooting at f/8 and f/5.6 at less than 1/100s here. Even though statistically 1/50s should be fine with the 24mm lens I still like to shoot a bit faster, so I was expecting a few blurred shots from the roll (but was happily surprised when they were all ok)

As you can see from the images above (left, SFX200 film with no filter – right, SFX200 film with Cokin P003 Red filter) there is a marked difference in the tones when using the red filter. It’s not quite true Infrared as a) the red filter still lets a lot of visible light through and b) the film doesn’t record far into the infrared spectrum, but it’s quite a strikingly different look and one which I far prefer to the 650nm digital conversion that I have.

For a more authentic Infrared effect you could use an IR72/R72/Cokin P007 filter – however this is a very dark filter and it’s virtually (if not) impossible to compose and focus with the filter on. For the time being I’ll be sticking with the red filter as the film camera is a relatively inexpensive thing of fun for me – I’m not quite ready to stick it on a tripod and take it seriously.

Posted by Andy at 6:47 pm Tagged with: , , , , ,

Why I love my ND grad filters

filters, tutorials No Responses »
Oct 202009

There, I’ve said it. It’s probably incredibly unfashionable in this age of digital – in fact I often see people on forums etc discussing selling their grad filters because they have abandoned them in favour of exposure blending – but they are currently my preferred method of attempting to balance exposures.

An ND (Neutral Density) grad (Graduated) filter is basically just a piece of plastic that is dark at one end and clear at the other – the dark part of the filter is positioned over the lighter portion of the scene, reducing the light variation (dynamic range) of the scene so that it can be captured without any loss of detail.

Drawbacks

As with other methods used to make your camera faithfully reproduce a scene with a wider dynamic range than it is capable of, ND grads certainly have their drawbacks:-

  • The line between the clear and dark parts of the filter is a straight one (albeit with a slight fade/graduation to make it less noticeable). Rarely will a scene have a simple, straight line transition between dark and light so you end up having to compromise and perhaps hide the transition somewhere you hope the viewer won’t notice it
  • Getting the gradient to start in the correct place takes a bit of practice – if it starts too low some of the foreground with appear slightly darker – if it starts too late the brightness of the sky might appear uneven.
  • Like all lenses and filters they need to be kept clean – and as I swap them around between filter holders I have a tendency to drop them :(

With so many negative points, why use them?

Other methods of exposure balancing (such as exposure blending or HDR) require multiple exposures of the same scene, which realistically means using a tripod. I have a tripod, and I use it a lot, but I don’t always carry it – when I’m out with the family it’s an unnecessary burden – and sometimes I make the decision not to use it at all as constantly relying on it can lead to a lack of invention. A set of grads takes up very little room in my camera bag.

Processing time. Other techniques may only take a matter of minutes when you are skilled at them but if I’m taking an afternoon’s worth of casual shots I want them all to look their best with minimal editing.

An Example

These two shots, taken at sunset in Bradgate Park show the subtle but pleasing effect of using the Cokin P121M (ND4) grad. The first shot was taken without the filter. As you can see, the foreground is quite dark.

Old John, Bradgate Park, Leicestershire

Technical info: ISO100, 18mm, f/22, 0.5s

The second shot (below), with the filter in place produces a much more even result.

Old John, Bradgate Park, Leicestershire

Technical info: ISO100, 18mm, f/22, 0.6s

No further processing has been done to either image. As you can see from the technical info, the second shot was exposed for slightly longer (0.1s) which allowed more light from the foreground to be picked up by the camera sensor, resulting in a more even looking photograph.

Posted by Andy at 12:26 am Tagged with: , , , ,

Barrel Distortion

tutorials No Responses »
Jul 262009

Seaweed covered rocks, St Bees Beach

After taking this shot I was quite looking forward to seeing how it came out. I was using my Hoya Circular Polariser at the time and I’d rotated it to bring out the best of the colour both in the sky and on the rocks – the green of the seaweed was really emphasised by it and it was one of those rare moments when I was really glad I’d bought it.

Sadly, when I viewed the shot on the computer, this is what it looked like…

Seaweed covered rocks, St Bees Beach

Notice the sad face being pulled by the horizon – I’d forgotten that the Sigma 18-200 has really noticeable barrel distortion (where straight lines are bent away from the centre of the image) at the wide (18mm) end. That’s not to say that it’s a bad lens – for the price it’s a pretty good all rounder.

Fortunately it’s possibly to remedy this (with a bit of trial and error) with The GIMP.

Versions prior to 2.4

Open the file and select “Distorts” from the “Filters” menu. Select “Curve Bend” from the sub menu that appears. You should then see something similar to the following:-

The GIMP, Curve Bend Screen

To correct the barrel distortion we need to build a curve which will be used to modify the image. To do this I first placed a straight line roughly where the horizon was in my shot by clicking on the left and right sides of the grid. Then I placed a point (by clicking in the desired place on the grid) in the centre of this line which I then I slowly dragged downwards, changing the straight line into a slight curve. Once the results of the preview looked acceptable I pressed the “Ok” button and waited for The GIMP apply the changes (which took about 15 seconds).

Versions 2.4 and up

A new filter was added in version 2.4 – Lens Distortion. Open the file and select “Distorts” from the “Filters” menu. Select “Lens distortion” from the sub menu that appears. You should then see something similar to the following:-

The GIMP, Lens Distortion Screen

As the distortion on my original image was convex (bulging outwards) I needed to apply some concave distortion. To do this I tweaked the “Main” value and eventually settled on a value of -12.

From the manual…

Main – The amount of spherical correction to introduce. Positive values make the image convex while negative ones make it concave. The whole effect is similar to wrapping the image inside or outside a sphere.

More documentation on this filter can be found here – http://www.mirrorservice.org/sites/docs.gimp.org/en/plug-in-lens-distortion.html

Posted by Andy at 3:45 pm Tagged with: , , , , , ,

Exposure Control - Stops

tutorials No Responses »
May 192009

I found the idea of “stops” the most complicated part of getting to grips with photography – I can still remember now how my face glazed over when it was first explained to me.

Crudely put, a “stop” involves the doubling or halving of the amount of light hitting the sensor (or in the case of ISO, how that light is used). For instance, if we had our shutter speed set to 1 second, changing it to 1/2s would let half as much light in, changing it to 2s would let twice as much light in.

ISO stops works in the same straightforward, linear way as shutter speed – ISO200 is twice as sensitive as ISO100 but only half as much so as ISO400 – but the aperture scale seems to make less sense initially. Changing the aperture size also affects the amount of light hitting the sensor, however rather than changing in multiples or 2 they change in multiples of the square root of 2 (approximately 1.4) as follows f/1, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, f/32 etc.

When the aperture is stopped down (changed to a smaller opening by increasing the f-stop) less light will enter the camera. In order to obtain the same exposure, the amount of light entering the camera will need to be balanced by slowing the shutter speed down (so that the shutter is open for longer), or the sensitivity of the sensor will need increasing (by increasing the ISO).

Obviously if you’re using one of the camera’s creative modes it will take care of some of this for you – for instance if you are in Aperture Priority mode and you change the aperture size the camera will automatically adjust the shutter speed in order to attempt to get what it thinks is the correct exposure.

Stops in action

Let’s say we’re taking a picture in the early evening which requires a short depth of field, such as portrait, and we’ve got our aperture set to f/2.8. Our camera, which is set to ISO100, has decided that a shutter speed of 1/100s is required for the correct exposure. Say we now want to take a picture that requires a greater depth of field, a landscape for instance – we might set the aperture to f/11 for this.

If we do this however we’ve restricted the amount of light available to the sensor by 4 stops – and because there is now going to be less light hitting the sensor the camera knows it needs to adjust the shutter speed to let 4 stops more of light in. If we follow the progression of stops in shutter speed from 1/100s, dividing by 2 each time, we can see that a shutter speed of 1/6s would be selected by the camera – 100/2=50, 50/2=25, 25/2=12.5 (although this will be rounded to 12), 12/2=6.

Unless we’re using a lens with image stabilizing (or a tripod) a shutter speed of 1/6s is going to result in a pretty blurred image – so we need to decide, do we really want f/11? – using a larger aperture, such as f/8 would give us a better shutter speed – or can we sacrifice some quality by changing the ISO to make the sensor more sensitive to the available light. Changing the ISO to 400 adjusts the whole equation by 2 stops again (100×2=200, 200×2=400) and means we’d now have a shutter speed of 1/25s. Still perhaps too slow for a hand held shot, but hopefully by now you get the idea :)

Other examples

The following settings would all produce shots with a the same exposure:-
a) 1/100s, f/11, ISO100
b) 1/200s, f/8, ISO100
c) 1/100s, f/22, ISO400
d) 1/50s, f/22, ISO200

Can you see why?

Posted by Andy at 7:45 pm Tagged with: , ,

Winter Tree and Photomatix

hdr, tutorials 4 Responses »
Apr 022009

The Winter Tree shot was created using 3 bracketed exposures, shown below. Most DSLRs can be set up to take exposures like this – the camera will take 3 shots (or more depending on the camera) each at different exposures. In this instance they were taken at 0, -2EV and +2EV so that I end up with 3 shots that are all 2 stops apart.

I found the idea of “stops” the most complicated part of getting to grips with photography, but basically a stop is the doubling or halving of the amount of light hitting the sensor – so if we had a 1 second exposure, the next stop down from that would be 1/2s and the next stop up would be 2s. ISO and aperture settings also affect the amount of light hitting the sensor and therefore their adjustment can also be measured in stops, however when taking bracketed exposures these two remain constant – only the shutter speed changes. (A more detailed explanation can be found here – http://www.andystafford.co.uk/exposure-control-stops/)

Having set the camera up to take my 3 shots, I pressed the shutter release and this is what I got…


1/125s
1/500s
1/30s

The numbers underneath each shot are the exposure times – see how the second is 4 times the first, and the third is 1/4 of the first (give or take some rounding). This is due to the 2 stops difference between each shot.

You’ll notice that the shots (apart from the final one) look quite dark. There are three reasons for this:-

  • I wanted to keep as much cloud detail as possible so I metered off the brightest part of the sky to make sure I didn’t get any blown highlights.
  • It was slightly windy and I didn’t want too much tree movement in the shot so I tried to keep the shutter speeds as fast as possible. (1/30s is still quite slow really considering there was moving foliage but I got lucky in this instance). Photomatix can align movement but better to try to limit the problems at source.
  • Accident. I would also have taken a brighter set but I was running out of time.

Once home I loaded the images into Photomatix as follows (Note: if you want to try this there is a link to the source images at the bottom of this article):-

These aren’t the default settings – I find that different combinations of alignment methods work better for different shots. I left Align Source Images set to “By correcting horizontal and vertical shifts” just in case the wind blew the tripod at all and turned off “Attempt to reduce ghosting artifacts”. Movement, especially clouds and running water, can cause problems in Photomatix and I’ll often try different options in these instances.

Once Photomatix had finished its initial processing I pressed the Tone Mapping button and tweaked the settings until I got something that I was happy with.

If you’ve not used Photomatix before don’t be alarmed by how the image looks at the moment – what’s on the screen is only a rough guide. The finished product will look much better :)

The settings that made the major difference to the image were those to do with saturation. With the main Colour Saturation slider set to 0 the image was black & white but changing the Saturation Highlights slider re-introduced colour in the the brighter elements of the shot – the clouds.

If you want to have a go yourself, the source images are available – Source images (3.2MB).

I’m afraid they are jpegs rather than the original raw files, due to space and bandwidth considerations, but they are good enough quality for trying out this example.

Visit http://www.hdrsoftwaretutorial.co.uk/ for tutorials and a discount code which will give you 15% off the purchase of Photomatix.

Posted by Andy at 7:08 pm Tagged with: , , , , , ,
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