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RTI Imaging – baby steps

My first attempt at RTI, that’s Reflectance Transformation Imaging to you and me 🙂 . I drifted into this type of photography after shooting graffiti at Gloucester cathedral and quickly realised that normal photographic techniques can struggle to bring out all the detail.

Using directional lighting placed at a low angle to throw a strong shadow into the dips and bumps of graffiti craved into stone gives some impression of what is there.

The RTI technique uses a single light source to take multiple photographs, typically 50 or more, with the light source being moved all around the subject during the capture session.

For my 1st attempt at RTI I used a carving in Welsh slate of a Draig, the Welsh Dragon. The sculpture was commissioned for my home several years ago but seemed ideal as a test subject.

I’ve found a webViewer to display RTI imaging which allows the viewer to control all the lighting to see what can be revealed. This webViewer opens in a new window To control the RTI lighting click on the Light Bulb and then click and drag the mouse within the image to see the lighting angles change.

1st Baby steps – for this test I was using:

  1. A Canon 5D4 and 24-70mm lens set at 47mm focal length with the target approximately 500mm from the camera and the diagonal coverage of the target was 400mm.
  2. A Sirui tripod with the camera suspended off an inverted centre column.
  3. For lighting I used a Godox AD200 flash head and a laser range finder mounted on a common bracket which I can mount onto a second tripod.
  4. A Phottix wireless camera trigger.
  5. The X-rite ColorChecker Passport Photo calibration card.
  6. A 10mm Silicon Nitride ball bearing and a 25mm Obsidian ball.

Some initial thoughts on the image capture process:

  1. Never underestimate the shadow being thrown by the light sphere when illuminated at 15 degrees. Check it with a test image to ensure the shadow doesn’t encroach on the subject. 
  2. Don’t frame the subject too tightly, leave room for the light sphere and check the shadow again. For info, the length of the shadow is 4 times the height of the light sphere at 15 degrees, it is long!
  3. The 10mm ball bearing only covered 160 pixels on the image, the recommended diameter should be around 250 pixels. The sequence worked but I suspect it was marginal. This is the blended light sphere image the RTIbuilder software produced and shows the highlights created by each flash position. It’s nowhere near perfect but adequate for this first test.
The blended Light sphere

4. I used the X-rite ColourChecker Passport Photo calibration chart to ensure my colour and exposure are as good as I can make them. The brightest image will always be when the flashgun is nearest to the surface normal so check the exposure at 65 degrees and avoid blowing out the highlights.

The off white square next to the pure white square should be used to set the white balance and to set the optimum exposure in Lightroom. The RGB value for this square should 200,200,200, in Lightroom this is approximately 90%, 90%, 90%

5. The black obsidian spheres are relatively cheap but the surface is fairly soft and easily marked, I would recommend buying the more expensive Silicon Nitride ball bearings which are very hard and the surface finish is excellent.

6. The distance from the flashgun to the subject should be 3-4 times the diagonal of the image. I used a laser rangefinder mounted to the side of the flashgun to set the distance and the angle of the flashgun.

7. It’s important to ensure that the camera does not record any of the subject due to the ambient light, so use a low iso (100) and small aperture (f11) and set the shutter speed to your highest sync speed, I used 1/160 second. It is not recommended  to use a smaller aperture because of diffraction, this optical effect causes the image to be softer even though there is an increase in depth of field.

2nd Baby steps – for this test I was using:

a dull 2 pence coin captured with a Canon 5D4 and Canon 100mm macro lens

The on-line viewer for the coin is here

 

For further information, software and guidance on the capture and image processing the Cultural Heritage Imaging website is well worth a visit.

Work of Heart Garden

The Work of Heart garden art installation at Gloucester cathedral

For the full story please visit the official website

Gloucester Cathedral

Gloucester Cathedral, formally the Cathedral Church of St Peter and the Holy and Indivisible Trinity, stands in the north of the city near the river Severn. It originated in 678 or 679 with the foundation of an abbey dedicated to Saint Peter.

The High Altar and East window – click here for a very high resolution image of the High Altar

Below is a high resolution interactive view of the stained glass  in the West Window, please use the control bar along the bottom of the image to zoom in/out, pan left/right or enter full screen viewing.

The current stained glass was installed in 1859 as a memorial to Dr J. H. Monk, Bishop of Gloucester from 1830 to 1856. It was made by the large Newcastle firm of William Wailes, and is signed and dated in the red strip in the bottom left-hand corner of the window.

The Cloister contains some stunning architecture including fan vaulted ceilings and is famous in recent times for being one location for the Harry Potter films.

The St Andrew’s chapel, adjacent to the South Transept, was re-decorated in the Victorian era and the frescoes are very vibrant.

A large part of the photography at Gloucester Cathedral has taken place to produce a high resolution virtual tour of the cathedral which can be seen below (full screen viewing is highly recommended). Each 360 virtual reality scene has been created from 120 raw images taken on a Canon 5D4 camera and Canon 24mm lens which, when processed, produce 5Gb master images which are 30,000 pixels wide.

Gloucester Cathedral 360 Virtual Tour
Gloucester Cathedral 360 Virtual Tour

Shown below are the Thomas Denny stained glass memorial windows for Ivor Gurney and Gerald Finzi which are installed in the North Chantry in the Lady Chapel. The windows can be viewed in high resolution by zooming into each section.

The official Gloucester Cathedral website can be found here

An on-line reference to the Cathedral church of Gloucester is also available


Painswick Rococo Gardens

Eagle house 360

To visit the Painswick Rococo Gardens website please click here

Trackday at Trac Mon

Clear skies and a drying track greeted the participants at the Track day at the Trac Mon circuit, Anglesey on the 4th February 2018.

My bonus for the day was a track session with Riccardo Losselli in a stunning Alfa 4C, a beautiful car driven by a real character. Many thanks Ricky 🙂

This page has images from the day which are freely available to anyone who wishes to keep a memory of the event or make a print. The on-line images are sized and optimised for use on social media (right click the image and select save image as..), if they are used I would ask that a credit be given.

If you would like a print file then please e-mail me at kevin@photosbykev.com quoting the number of the image(s) and I will send you the image files that you can print locally. No catch, no charge, just my way of supporting the track event. If you wish to give a small donation to support Help for Heroes then please use Mission Motorsport.

Norway deLights

A trip to Norway in January was the perfect way to start 2018. It was cold, it was covered in snow, it was very odd not to see the sun rise (or set) but the Aurora Borealis didn’t disappoint us.

We stayed in a beautiful location on the Malangen fjord and travelled out to Steinfjord, Tennes, Malselv and numerous other quaint locations including an excursion into Finland. The dancing lady was seen five nights out of seven and photographed on four of those nights.

Some thoughts on personal and camera equipment when the temperatures are below -10C:

Down and merino are your friend, a good down jacket and insulated over trousers make life very comfortable when you spend hours doing very little except looking upwards at the sky.

Merino base layers are also a must, if you want to retain your body heat.

On my feet I wore Sorel Caribou boots and Norwegian military socks, a great investment 🙂

A pair of ‘HotHands’ hand warmers in your jacket pockets are also a good idea to keep batteries and your hands warm.

I went to Norway fully prepared to use lens heaters to keep the lenses clear but even at below -10C the lenses didn’t mist up. I guess it was due to the very cold but dry atmosphere. I did have some modified socks that were wrapped around the lenses and I could of slipped a hand warmer into them but they weren’t needed.

Cameras used included Canon 5D4 and 5D3 bodies with Canon and Samyang wide angle lenses and a Samsung Gear360 was used for the fun stuff but it isn’t suitable for aurora photography or video.

Race of Remembrance 2017

The 2017 Race of Remembrance event (#RoR2017) takes place over the weekend of the 10-12th November on the #Tracmon #Anglesey circuit and is hosted by Mission Motorsport

This page has images from the event which are freely available to anyone who wishes to keep a memory of the event or make a print. The on-line images are sized and optimised for use on social media (right click the image and select save image as..), if they are used I would ask that a credit be given.

There are many images (over 1000 !) from the Race of Remembrance weekend so grab a coffee, or three, and get comfy 🙂 #RoR2017.

If you would like a print file then please e-mail me at kevin@photosbykev.com quoting the number of the image(s) and I will send you the image files that you can print locally. No catch, no charge, just my way of supporting the event. If you wish to give a small donation to support Help for Heroes then please use Mission Motorsport.


Friday 10th – practise sessions (440 images)


Saturday 11th – morning qualifying sessions (249 images)


Saturday 11th – Super cars (216 images)