Some examples of using a lens adapter

On January 16, Derek pointed to some interesting links. One of them relates to lens adapters. As Derek has mentioned in a previous blog, I used to be a studio photographer many years ago, and I have a 35mm film camera among my "collection" of things optical. That camera uses Pentax screw-mount type lenses, so it is about 40 years old. Derek's article prompted me to order a lens adapter for my Canon EOS XT Rebel digital SLR camera. At left, you see the adapter (bottom), and the three screw-mount lenses which I used in the photographic experiment described in more detail below. Not shown is a 2x "teleconverter" - an additional screw-mount lens which can be attached to any of the lenses shown, it "doubles" the focal length of all the lenses. The largest lens is a 200mm, f3.5 Bausch and Lomb lens, the smaller one is a 135mm f2.8 Bausch and Lomb, and the smallest a 55mm f1.8 Asahi Pentax lens.

The pictures below show is the effect of using the "full frame" screw-mount lenses have on the scale of the pictures generated in the Rebel XT, which has a "crop-factor" (APS-C dimensions are 25.1 × 16.7 mm and have an aspect ratio 3:2) type of CCD (it plays the role of the film in film cameras, see Derek's post on Aug 16, 2008). In general, the full-frame lenses act as lenses which appear to have a larger focal lengths, when used with a crop-factor cameras. The effect of a crop-type CCD is equal to "cropping" a 16x25mm section of a full (24x36mm) frame, seemingly "enlarging" a section of the full-frame image. Here are some examples:

This is picture taken with a 18-200 Sigma zoom lens at 200mm and f6.3 - the "upper limit" of what this crop-frame lens is designed for. This lens has optical stabilization features, which makes hand held, longer exposure less like to be blurred by camera motion caused by my hand.

For comparison, this is the image from the full-frame 135 mm Bausch and Lomb lens, also set to f6.3 (nowhere near its "upper limit" of f2.8). The scale of the image is almost identical to that of the 200mm Sigma lens, above (just a tiny amount smaller). This lens has no image stabilization. Exposures are calculated and made just like I used to do in the days of "non-electronic" film cameras. There is no electrical connection to the automatic features of the EOS Digital Rebel. There is no automatic focus - it's done through the viewfinder.

Here we have the image from the 200mm full-frame Bausch and Lomb lens, again at f6.3 (also not the limit of f3.5). You can see the image is larger than the 200mm Sigma image. The "cropping" effect shows - the 200mm Bausch and Lomb lens acts more like a 300mm crop-factor lens..

Here we have a picture taken with the 200mm Bausch and Lomb lens to which the 2x teleconverter has been attached. This makes it 400mm full-frame lens, which acts like 600mm crop-frame lens. Of course, the use of the teleconverter makes the f-stop markings on the lens incorrect. The doubling of the focal length requires a fourfold increase in exposure. In this case, to achieve the approximate equivalent of f6.3, I set the lens itself to f3.5 (its upper limit).

This is a picture taken with the 55mm Asahi lens, again at f6.3 (the upper limit if f1.8). This is a reasonably scaled standard image, with a reasonable angle-of-view. The effect is that of a 80mm crop factor lens. Derek presented me with a 50mm f1.8 Canon EF lens a couple of years ago, which gives a wider view angle, at the same speed (f1.8) as this lens.

The conclusion I draw from all this is that for the price of the lens adapter (about $75.00 after shipping and exchange rates are factored in), I have gained the ability to use my high-quality full frame lenses on my Digital Rebel. The equivalent Canon lenses would cost many hundreds of dollars. It's true that the "old" lenses do not have any of the interactive features of the lenses designed for use with EOS cameras, but this only means that I have to fall back on the techniques which I had to use in the the days of mechanical film cameras (calculating light levels, depth of field, exposure times, etc. in my head), before taking the picture. One advantage of the digital camera is the ability to display the picture just taken on the view screen, in the days of film, you had to wait until the film was developed and printed. In many ways, mentally calculating the required parameters prevents the "mental laziness" to which I succumb too readily when using the automatic features on my digital camera.

The use of the teleconverter effectively doubles the number of focal length capabilites, but there is a fair overlap with my crop-factor lenses, so that some of the combinations are essentially available twice. In any case I now have a fair number of possibilities. Generally, fixed focal length lenses tend to have a better optical quality, and much lower f-ratios - i.e. they are "faster", than the zoom lenses that commonly come with digital cameras of the Digital Rebel level, so if a given picture has to have critical definition, or is taken in low-light conditions, the use of the full-frame lenses may be a better option.

A Planetary Perspective

As I mentioned yesterday, we spent a few days in Mexico (Puerto Vallarta) recently. During that time, and considering my interest in things astronomical, I took a picture of a loose alignment of three planets, and the Moon, visible for a short period after sunset. The planets were Jupiter, Mercury, and Venus (in order of increasing distance from the horizon).

To see the details better, click on each picture.

Jupiter, the largest planet is closest to the horizon, actually seen through a light cloud. Mercury is slightly to the left of, and a little higher than Jupiter. The bright spot to the left of the Moon at the top of the picture, and somewhat lower, is Venus. The leftmost picture shows the actual scene; the right picture is the annotated version.

This is an interesting demonstration in planetary perspective. In this picture, Jupiter, the Solar System's largest planet (it has a mass equal to 318 times Earth's mass), is six times farther away from us than Mercury. Mercury is the planet closest to the Sun, Venus is next closest (our Earth is third) and Jupiter is the fifth of the major planets orbiting the Sun. Jupiter orbits five times farther out from the Sun than Earth. As shown in the picture, even that far away (we're talking about 900 Million km - 560 Million miles), Jupiter shows up brighter than Mercury. Mercury is around 160 Million km - 100 Million miles away. Venus (almost equal in size to Earth) is at this time about 110 Million km - 70 Million miles away. The closest is the Moon, "only" about 380 thousand km - 236 thousand miles away.


Quite apart from these scientific aspects, it was a pretty picture in its own right - certainly quite different from our wintery scene; the temperature at the time I took these pictures was about 22 degrees Celsius (72 F). On the left, you see a wider-angle view. Both Jupiter and Mercury are located to the left of the topmost dark cloud in the lower right (which seems to point straight to them).

We were staying with close friends, one block away from the beach, a couple of minutes' walk to this beautiful scene on Banderas Bay.

^

Away from the snow

I haven't posted anything since Christmas - we were away until yesterday, in Puerto Vallarta, Mexico. To our surprise, on our return, we still found nearly as much snow near our driveway as the day we left. Highly unusual for this city.

Derek had shovelled the snow out of our driveway, so it was easier to get back into the house. He said it was good exercise, and we certainly appreciated his efforts.

Derek had seen no reason for us not to go on this trip - he said that he felt well enough, and also took a little trip to Victoria while we were away. While he didn't enjoy the same kind of weather we had, it is nice to see that he can take some "time off", too.

Common sense?

I haven't written a "letter-to-the-editor" type of note to the media in a very long time, but today I wrote one to the "opinion page" of our local newspaper. It concerns the meteor seen in the sky over Alberta and Saskatchewan on November 20 of this year. Here's the gist of my (expanded for this blog) note:

On Tuesday, Dec.23, page B2 - "Metorite fall could yield scientific gold" - the article regarding the Nov. 20 meteor seen in Alberta/Saskatchewan (picture at left), I read with great interest, and a sense of sad dismay, that the more than 100 meteorites collected are all "...part of a 10-tonne, 10-kilometre-wide meteorite that broke up on impact with the atmosphere, spawning brilliant flashes of light that caught many eyes" (from the 9th paragraph in that article).

To begin with, a meteorite is defined as that part of a meteoroid which is found on the ground after travelling through the atmosphere. A meteoroid is the solid, original body before it encounters the atmosphere. The process by which this body disintegrates when it travels through atmosphere and which results in the 'brilliant flashes of light', and other associated phenomena (heat, ionization, occasionally sound) is called a meteor.

If the meteoroid (taken as a cube to make the basic calculations easy) had indeed been 10 km (about 6.2 miles) diagonally across, it would have had a mass of millions of tons (around 500 million - roughly equivalent to 1 trillion pounds); it would have struck the Earth almost totally intact, and caused a conflagration similar to what many scientists think happened on the Yucatan peninsula 64 million years ago, with the subsequent extinction of many species. If the 10-ton mass (about 20,000 pounds - i.e. about three GM Hummers) is taken as approximately correct, then the meteoroid that hit us, again taken as cube, would have been about 1.6 metres along each side. The meteorites shown in the newspaper's picture with Dr. Hildebrand appear to be of a "stony" nature - approximately 2.5 times the density of water. 10 tonnes of water is equal to 10 cubic metres of water, by definition - 1 cubic metre of water is equal to 1 ton. A 10-ton cube of water would measure about 2.15 metres along each edge. The "stony" equivalent cube of stone would therefore be 1/2.5th of 10 cubic metres, i.e. about 4 cubic metres. This would be a cube measuring about 1.6 metres on each side. How can one equate 500 million tons with 10 tons, or a cube of approximately 5.8 kilometers (5,800 meters) along one edge to 1.6 meters along the edge, or a trillion pounds to twenty thousand?

In reality, of course, the meteroid would not be a cube, but of some irregular shape. That makes calculations like these far more complex, but there is no getting away from the masses of material and the orders of magnitude involved.

What dismays me is the apparent incomprehension of and lack of innate feeling for the relationships between size, mass, weight and other physical characteristics and properties of the things that surround us, perhaps mixed in with lack of understanding regarding the metric system. It is as though common sense has left the authors and/or editors involved in the kind of published nonsense seen in the media far too often.

I gain little consolation from knowing that this kind of "innumeracy" is all too common. Not a month goes by in which I don't see such misrepresentation and misunderstanding in the newspapers or other media. Is this due to a lack of teaching in school?

This whole thing may be of no interest to anyone, but I had to vent my spleen here.

Merry Christmas

This year, we used only the top two/thirds of our artificial Christmas tree (Derek opted for a natural tree this year). We think it looks just as nice this year, and we did not need to move a lot of furniture to accommodate it. The heirloom decorations (many handmade) make it beautiful.

Merry Christmas, and a Happy and Healthy New Year to all of you!

The "full" Christmas tree

The tree this year



















A hand-made decoration. This one came from Erlyne's mother. Erlyne was a bridesmaid at our wedding, 44 years ago, and my wife and she are still in almost daily contact. She's family.

A quick year

It seems that each year goes by faster. It seems like last week that the previous winter was here. Right now, the snow is falling and I'll have to shovel some of it to clear the sidewalk. The grandchildren went off to school, taking along their snow slider board - they'll have a great time at school, where there is a small hill.

I have a theory why the years appear to go faster as you get older: each minute that goes by is a larger percentage of the rest of your life. So, enjoy what you can, you may not have the chance again.

the "meme"

Derek's post of yesterday asks to show a "meme", a picture on the 6th page of my flickr photostream, on this blog. Here is mine. I have no idea what the name means, or why it's called that. The closest word I can think of is the French word for "same" - même. So, perhaps it means something like "copied", but why the 6th picture on the 6th page?

This picture was taken during the "Symphonie of Fire" from the apartment balcony of our close, and longtime friend (she's part of the family) in West Vancouver, looking over English Bay, towards the False Creek area.