Wednesday, 29 May 2013

Improving Camcorder Sound: Micromuff is Worth the Funny Looks

In making ‘prosumer’ camcorders smaller and more streamlined, Sony moved the microphone(s) to a position on the top  — an ideal spot for catching wind noise. Apart from adding an external microphone (not the most convenient thing to do while travelling) there was nothing one could do. I then saw that Micromuff had started to produce one of their stick-on wind mufflers for camcorders as well as DSLRs. I got one immediately and fitted it in time for a passage up the Mekong in northern Laos and in the mountains of Yunnan. And did the Micromuff work? Yes, brilliantly. There was an enormous reduction in wind noise.

The downside: the rude comments from fellow travellers on the lines of ‘his camera needs a haircut’ and ‘is that a toy mouse on his camera’. My advice: ignore the rabble and get a Micromuff.

I must admit I had never heard of Micromuff before reading about the fitting for DSLR. They appear to be based in UK.  Their website is at:

My Sony HDR-XR550 wearing its Micromuff

Wednesday, 22 May 2013

Sony HX-300, Canon SX50 and Fuji HS50 for Birding: A Quick Hands-On

One of the team was at a hands-on display of super-zoom 'bridge' cameras in Hong Kong this week. As a Nikon P510 owner, he was impressed by the Sony HX-300, thought the Canon SX50 'OK' but really did not like the Fuji HS50 - 'horrible' was his exact word.

Friday, 17 May 2013

Lens Fungus

A lot of utter rubbish appears on internet fora — interspersed with accurate information — on the problem of fungus growing on camera lenses. The advice usually falls into three categories: prevention; whether removal is possible; effects on image quality.

In this post I only deal with the last aspect since we read comments that say the lens must be degraded while others assert there is no effect. Very few of those who offer an opinion take the effort to consider whether any tests they have done are valid in relation to where the fungal hyphae were situated on the lens in question.

In most cases, in old lenses, fungal growths start from the edge of the front element. That is because fungal spores present in the air need an organic source of carbon  — plus warmth and humidity — on which to develop. The edge of a lens, under the rim of metal or plastic, is an ideal resting place for bits of cloth, tissue, skin particles and dust that provide a source of carbon. I have also read that some of the paints and balsams used in lens manufacture also provide a nutritious surface for fungal growth. Fungal hyphae — again in warm and damp conditions — then spread out across the surface of the lens in search of more food. They even release chemicals which etch the coating and glass.

So, first of all, we have to distinguish between between fungal growth around the edges and that which has spread to reach the centre. I am only dealing with the former since the image must be degraded if the whole lens is covered. I am also only dealing with fungus on the front element of the lens. The calculations needed for fungus on inner elements, particularly in zoom lenses, are more complex.

What degradation should we expect in a case of fungus around the edges? What testing would be effective in deciding?

I am going to work through an example to demonstrate how decisions on whether image quality would be affected at a particular exposure could be taken. The photograph below shows fungus on the front element of an Exakta Pancolar 50 mm f/2 lens.

Fungal hyphae on the front element of an Exakta Pancolar 50 mm f/2 lens

The diameter of the front element of the lens shown is 29 mm and a quick measurement showed that the central area clear of fungus is 22 mm in diameter.

Whether that outer region of the lens infested by fungus would have any effect on the final image depends on how much of the lens area is used in a particular exposure. At the maximum aperture for this lens of f/2, the whole diameter of the lens, including that part bearing fungus, is used for the exposure. Therefore, at maximum aperture we would expect the image to be degraded by fungus on the lens. But at which aperture would the affected outer region of the lens not be used and become safe to use for an undegraded image— f/2.8, f/4, f5.6...f/22? Clearly, we need to consider what diameter of the front element is used at each aperture setting.

The diameter of the lens aperture (set by a diaphragm between the front and back elements) is easy to calculate. The diameter (in mm) equals the focal length (50 mm in this case) divided by the f/ number. Thus, the diameter of the aperture (not the diameter of the front element) of a 50 mm lens at f/2 is 25 mm, at f/4 12.5 mm etc.

I know I am teaching my grandmother to suck eggs, when I draw attention to the fact that the change in diameter is not linear with changing f/number. The change in diameter is much greater between f/2 and f2.8 (a halving of exposure) than it is between, say f/8 and f/11 (also a halving of exposure). The following diagram shows how the diameter of the aperture changes with f/number for a 50 mm lens.

Diameter of the diaphragm at different f/numbers

Because light rays are still converging after they pass the front element on their way to the diaphragm, the diameter of the front element is larger than the aperture. I have measured a number of lenses including the Pancolar and the maximum diameter of the front element is about 1.1 times the diameter of the maximum aperture, that is 29 mm compared with 25 mm. So, we need to multiply the diameter of the aperture at each f/ number by 1.1 to map onto the front of the lens the actual diameter of the front element used at each f/ number setting.

This I have done in the following diagram. It shows how much of the front element of this lens is used at each f/number, from f/2 to f/16.

Diagram showing the area of the front element of the lens used as different f/numbers.
Also shown is the diameter of the fungus-free central area compared
with the diameter of the area used at f/2 and f/2.8

The take-home message is completely clear: there can be no effect of the fungus from f/numbers larger (i.e. apertures smaller) than f/2.8. In other words, even though the lens appears visually to be badly affected, it can be used as a lens with a maximum aperture of f2.8 without fear of degradation of the image.

The same approach can be used for other lenses, although it is easier with those of fixed focal length. All you need to measure is: the maximum diameter of the front element compared with the calculated diameter of the diaphragm at maximum aperture (calculated from focal length and f/number); the diameter of the lens unaffected by fungus.

Finally, returning to this 50 mm Pancolar lens, I would need to test it at f/2 to see if the theoretical degradation caused by light scattering in and under the fungal hyphae was actually discernible in practice. Testing at any other f/number other than within the range f/2-f/2.8 would be pointless.

Wednesday, 8 May 2013

Old Advice on Exposure Compensation - No Wonder We Were Confused

We all now know that exposure meters for reflected light give a misleading reading for snow scenes and that we have to give about two stops more than is indicated by the meter. This is because meters are calibrated for a mid-grey balance between shadows and highlights. The meter interprets the very bright light coming from snow as mid-grey and therefore suggests a lower exposure than in necessary for the nearly all white content. The converse applies to scenes in which dark shadow predominates.

I knew at some time in the past I had read the opposite — and completely wrong — interpretation. Then while researching an article on Alex Pearlman for Club Rollei User Magazine, I came across the following in his Rollei Manual (5th edition, 1971):

Almost all such meters in use today, including those fitted to the Rolleiflex, are known as ‘integrating meters’, that is, in manufacture and calibration, an equal amount of high-light and shadow area is catered for, as this holds good for the vast majority of scenes...From this it will be seen that if the light reflected by a certain subject is all of a light tone, and there are practically no dark areas of tone or of shadow, then approximately fifty per cent less exposure should be given than that indicated by the meter, as this is still thinking for us in terms of equal quantities of high-light and shadow area. Similarly, if a dark subject is being photographed, in which there are very few light accents — and shadow predominates, it will be necessary to give approximately fifty per cent more exposure than that which is indicated by the meter, for exactly the same reason.

Oh dear. I wonder how many people followed his advice and got even worse exposures in snow or deep shadow. But the older readers of this blog will remember that Pearlman was well know for his snow scenes, some of which appear in the Rollei Manual. Well, by chance, I came across an article of his in Amateur Photographer of 1 December 1954 entitled To the Mountains in Winter. What did he have to say about exposure? He was successful in achieving the correct exposure as the photographs illustrating the article demonstrate. This is what he wrote:

Technicalities should present no problems, as there is always more than adequate illumination. The exposure meter should be left at home! Even incident light meters rarely give the correct reading and all types indicate too short an exposure under snow conditions.

So, he was right about the direction of error in 1954 (even if he did not know its magnitude) but not in the Rollei Manual. Very strange.