Tag Archives: Refraction

Snowflakes – a source of mystery and wonder

Snowflakes are intricate and beautiful.

• Snowflake crystal •
Snowflakes are intricate and beautiful. They are a source of interest to scientist – but photographers can make amazing pictures with them.
Image taken from SnowCrystals.com External link - opens new tab/page

Snowflakes are amazing!

Close up pictures of snowflakes show how intricate and beautiful they can be. And there are an infinite variety of them too. Here are a few ideas…

Some history about snowflakes

The perfect six-sided snowflake exists, but is not the only sort. Early snowflake pictures were taken by farmers’ son, Wilson “snowflake” Bentley  External link - opens new tab/page (February 9, 1865 – December 23, 1931) from Vermont. Aged 15 he was captivated by snowflakes. It started with looking down a microscope. But in 1885 he began experiments with a camera too. After struggling with the early camera technology he began to make some progress. During his life he made thousands of photos of snowflakes. His work still dominate our ideas today. In particular he was the first to claim snowflakes are unique and six sided. His pictures are also some of the best too.

Snowflake photographs by Wilson "snowflake" Bentley

• Snowflake Photographs by Wilson “Snowflake” Bentley •
Wilson “Snowflake” Bentley was famous for his snowflake photographs. Nearly a century after his death we are still using the images.

Research has shown how diverse snowflakes can be. They are not all perfect, regular shapes either. In fact according to “New Scientist  External link - opens new tab/page” (a weekly publication, UK) there are many types. The various forms are created under different conditions…

  • -2°C = Simple hexagons and star shapes
  • -5°C to -10°C columns
  • -15°C Six sided crystals (dendrites) form again
  • -22°C onward… complex plates and columns form again

Here is detailed morphology diagram for snowflakes Morphology Diagram for snowflakes - External link - opens new tab/page. It shows the relationship between the snowflakes’ type and temperature/humidity.

Snowflakes go through a range of temperature, humidity and other changes while falling. They have a unique and sometimes violent history. They clash together. They may ball-up with other flakes. It’s common for them to have multiple crystals joined in one flake. They may circulate in the clouds for long periods. They may also melt and refreeze before descending to the ground. It is not a surprise they are all so different. There is a great infographic on SnowCrystals.com External link - opens new tab/page showing snow crystal growth and the no-two-alike idea.

Capturing snowflakes on camera

You can’t easily photograph snowflakes on the ground. The overall white in a snow mass makes it difficult to distinguish individual flakes. The small size makes them a challenge too. The best approach to snowflakes is two-fold.

  • Use a macro lens or macro extension tubes.
  • Use a clean (new) long hair artists paint brush. Sable hair is best. Use a small black velvet cloth (about 500mm x 500mm) to see the snowflakes.

The aim with these is simple. Tease out individual snowflakes onto a black background. Then get in close with the lens. If you are working with a macro lens help yourself out and use a tripod.

The snowflakes themselves are easily destroyed. The trick is to use the artists brush to lift snowflakes onto the velvet. The brush and velvet have hairs that support the snowflake without damage. Be as gentle as you can to preserve its delicate nature of the crystal.

Sadly tiny ice crystals tend to go grey when on a black background surface. When shot on a dark background they are best converted to monochrome. This helps to increase the contrast and definition of the crystal.

To show the beauty of the refracted light use a well-lit background. If you can, place the snowflake onto a glass slide delicately lifting it off the velvet. You can buy Blank Slides – Microscope accessories External link - opens new tab/pageBuy microscope slides for your snowflake photos. from various places. Make sure you have left the slides to cool down to the snow temperature or the snow will melt on it.

Be sure to keep your cloth, brush and slides cold and dry. Make sure your breath is not directed at the snowflake. Even slightly raised temperature or humidity will affect the snowflake while you are trying to photograph it. More than once I have had them dissolve in front of my eyes.

If you are using an actual microscope, or if you are using a glass slide try to get some backlighting. To get the best refractive results try light at different angles on the snowflake. The best results are not necessarily when the light is directly from below. The angled light tends to create contrasts on the snowflakes. This brings out light and dark as well as some aesthetic colourations from refraction through the crystal.

For your interest here is an amazing camera-microscope…

Celestron Dual Purpose Amoeba Digital Microscope – Blue External link - opens new tab/page
This an affordable and well reviewed digital microscope. It will do detailed images direct from your computer. It’s a photography tool which provides an opportunity to develop your macro skills. Hours of fun too!

Masterful shots

One of the acknowledged masters of the art of shooting snowflakes is Kenneth G. Libbrecht External link - opens new tab/page. He’s a professor of physics who researches crystal growth. He also runs the SnowCrystals.com External link - opens new tab/page website. There are wonderful resources on the site including a “how to guide” External link - opens new tab/page and many hints about photography and equipment. There are some wonderful galleries of images External link - opens new tab/page. There is also a section on how to grow your own snowflakes. Although, the latter was a bit more complex than I think I would go… but who knows. People in this field seem to get obsessive about it. Snowflakes are extraordinarily beautiful.

Two other sources of snowflake inspiration…

Official Snowflake Bentley Web Site. This site houses the Wilson “Snowflake” Bentley photographic collection.
For a huge range of inspiring snowflakes images check out this search page on Google: Snowflakes photography  External link - opens new tab/page

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Damon Guy - Netkonnexion

Damon Guy (Netkonnexion)

Damon is a writer-photographer and editor of this site. He has run some major websites, a computing department and a digital image library. He started out as a trained teacher and now runs training for digital photogs.
See also: Editors ‘Bio’.
By Damon Guy see his profile on Google+.

What good is a lens hood?

Five Types Of Lens Hood

• Five Types Of Lens Hood •
Attribution: Photo of five lens hoods for a mix of lenses; March 2013; Author: Geni; Permission: GFDL CC-BY-SA

Using a lens hood is important.

It is not always clear why we need a lens hood. Why do we need them and what are they for? Actually they are pretty important and can help prevent some nasty visual artefacts.

What is going on in the lens

Normally photographic lenses perform really well. They receive light reflected from your subject as parallel beams. These are focused by the lens into an image formed on the digital image sensor.

When light hits the lens from the side the situation is slightly different. Some of the light is refracted through the lens correctly. Some of the light however, is reflected off the surface and lost. But there is a percentage of light that goes astray in the lens. It can be bounced around in the lens – reflecting around from the surfaces of different lens elements internally. If it does so, on each reflection some of the light will get through to the sensor. Each time that happens there will be a slightly side-shifted ghost image. All sorts of light aberrations can be created by this internal reflection in the lens. It is these that cause the artefacts you see in the image.

Light is also scattered by inconsistencies in the lens glass. Chemical, and structural variations in the glass can impact on the way the light travels through the lens. This scatter contributes to the problem. These artefacts, and often an associated haze, are called lens flare and can be worse the further to the side that the light enters the lens. Flare and haze will not only form a distraction but also act to wash out the colours in your shot and reduce contrasts. These will make your picture look flat and lifeless. Unintended flare can simply kill the effectiveness of the shot.

A sharp angle of side-light can therefore cause all sorts of visual image ghosts which are not there in the scene. You can see a range of different types of flare in this Google image search…
Google images: Example lens flare images  External link - opens new tab/page

In general, poor quality glass and multiple elements in the photographic lens will tend to create more flare. Of course better lenses (read: “more expensive”) can help to reduce the problem. Higher quality lenses will incorporate a range of ways to reduce the problem. These include optimised lens-element design, surface coatings and non-reflective surfaces/parts internally as well as high quality glass. Despite that no lens is immune to flare.

What does a lens hood do?

The most common reason we use a lens hood is to reduce the incidence of a bright light source hitting the lens from the side. This will act to reduce the chance that the lens will suffer from the flare problem. In other words, the hood will help to keep the light coming in from the front of the lens in parallel rays.

It is simple really. Put up a wall at the side and the side light is cut out. However, it is not so simple to design a lens hood that will do that without obstructing the lens. The field of view of the lens cannot be allowed to catch the hood sides. If it does it will leave its mark on the image. So all sorts of hood shapes and sizes are required to match the visual characteristics of the lens. Lens hoods are quirky shapes because they have been designed to optimally reduce the side incidence of light and not interfere with the field of view.

Common design elements include “petal” shaped edges. These allow the corners of the sensor a wide field of view without interference in the corners from the hood. The long petal shape must be along the long side of the sensor (landscape view). If you put it on the other way the side of the picture will show the edge of the hood and light will also get in from the top (or bottom) because the cover is insufficient there.

There are conical shapes and cylindrical shapes too. When these don’t have petals they are designed to accommodate the full field of view of the lens from any angle. You may find that these types of hoods are common on lenses where the front of the lens extends when changing focal length. As the extension of the lens will change the field of view the hood shape must be wide enough for the widest angle of view. But it cannot have petals because they would rotate with the lens and at some focal lengths would interfere in the picture.

Lens hoods do more…

As you can see you should buy a hood for your lens that has specially been designed for it. If you don’t, you risk the hood intruding in your shot, or not providing sufficient protection against flare.

Hoods can help in other ways too. When you have a lens hood on the lens it acts as a primary protection for your vulnerable front element. Once, when I was panning to follow a bird with a heavy/expensive pro-zoom lens I whacked the lens hood off the glass of my car window. I am convinced I would have broken the window and damaged the front lens element if I had not had a lens hood on. It harmlessly bounced. Phew! I use hoods whenever I can these days.

Lens hoods also help to reduce over exposure generally from incident reflected light on bright days. There may be no direct bright light source shining into your lens. But it helps to reduce the high levels of brightness from the side regardless. That helps to reduce the overall high light levels and especially the contrast.

Lens hoods are worth the effort

Lots of learner photographers forget the lens hood. Yet it can have quite a significant impact. Even if it is not significant, when you are trying to get a sharp image and reduce the colour wash-out in bright light every little detail counts. Great images come from the attention to detail.

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By Damon Guy (author and Photokonnexion editor)

Damon Guy - Netkonnexion

Damon Guy (Netkonnexion)

Damon is a writer-photog and editor of this site. He has run some major websites, a computing department and a digital image library. He started out as a trained teacher and now runs training for digital photogs.
See also: Editors ‘Bio’.
By Damon Guy see his profile on Google+.