Thursday, 28 August 2014

the Rabbit Proof Fence

In the early days of the settlement of Australia some idiot released rabbits into the landscape. There was great damage to the environment and indeed great financial losses to the pastoralists and graziers of the day. In an effort to stop the spread (before eventually technology allowed biological methods were employed) a rabbit proof fence was built in many parts of Australia. This one is just near me and passes through the rain forest in the mountains near Killarney

Its a lovely region to go exploring (with the camera too). The mosses which appear on the rocks and branches are actually a lichen.

and grow on everything which they can get onto ... its extraordinarily beautiful in the mists that are common there.

Its right on the edge of the plateau there, and quite rugged terrain. Walking around the edge of the plateau is tough going as is getting up there ... for years there were only a few places up onto the range from the eastern side.

The view to the east (and the Pacific ocean) is spectacular ... and even though the elevation here is about 1000 meters the ocean is still behind a few more mountains yet.

Sunday, 17 August 2014

telephoto by cropping - or why have a telephoto


The question arose of "I have a high quality prime such as a 20mm f1.7, so why would I bother buying a telephoto?", so I thought I'd have a whack at answering it. The asker professed to have some years experience with 35mm and seemed happy with just cropping. I covered this from another angle back in 2010 here, but as my purpose was different I thought I'd redo it entirely.

To some extent you can "increase" the focal length of your lens by cropping - which is exactly why cameras with smaller sensors than the 35mm standard format are called "crop cameras" and exactly why there is the idea of a focal length multiplier (or effective focal length). This is often a bewildering topic for beginners (and even seasoned 35mm photographers who never dealt with 645, 6x7 and large format).

The confusion often comes from the misunderstanding of f-numbers. These (often called f-stops, but that's also confusing) were designed to allow photographers to determine exposure back when a hand held light meter was used to determine exposure and the photographer wanted to change lens (and keep the exposure the same).

Commonly the confusion comes from discussions involving  Depth of Field (DoF)

Its the size of the hole

When it comes to DoF the important factor is the size of the hole (old page of mine but better javascript), not the f-number on the lens (of course magnification is the other important factor), remember that an f-number is just a ratio. It is the focal lengh divided by the aperture size (in whatever units you like, inches or mm). I thought I'd compare two lenses, a 20mm (as I have a 20mm f1.7 Panasonic lens) and a 50mm f1.4 (as I have one of them too). So the iris diameter of the aperture on a 20mm lens at f1.7 is 11.76mm and the aperture needed to make a 11.76mm diameter iris on a 50mm is f4.3 ... such a setting is not available on my 50mm lens so I picked f4.5 which is a little bit bigger at 11.11mm

So if all things were equal then a standard lens could work as a telephoto by just cropping. However, if we use cropping (essentially maths) to make our 20mm into a virtual 50mm then we would just set our apertures to be the same and all will work out the same. Of course all things aren't equal, so I thought I'd explain this with pictures.

Firstly, lets take a shot of my mate with a 20mm f1.7 lens on my GH1

This was taken with the camera on a tripod, using the Panasonic 20mm f1.7 @ f1.7 and focused with face recognition.

Now, lets put on a 50mm lens (which is telephoto for 4/3) and have a look at that.

A quick glance at the image seems to show that DoF is quite similar to the central portion of the image taken with the 20mm ... so, lets crop the guts out of it and have a look.

Well actually its close isn't it, perhaps if I'd stopped the 50mm down to 5 it would be even closer. But you can see the point here (I hope).

Whats different?

Firstly I encourage you to "right click" on the above images and open them up in separate tabs (or windows).  I think you'll see quickly that even at the modest sizes we have that there is much more information (look at hair strands) in the image from the 50mm and not much at all in the image from the 20mm (cropped image). This is because we are essentially concentrating the image to be clearer with the scaled down 50mm image, but dilluting the 20mm image with magnification (and pushing its limits). Essentially we are pixel peeping with the 20mm but giving the 50mm room to breath.

Next the 50mm is able to stop down to further, to .4 ... so lets look at that

Which  I'm sure you can see is even more shallow DoF with the focus being drawn to the eyes and the background is just a diffuse background. Personally I prefer the look of this lens at f1.8 or f2, which is still more shallow DoF than f4 yet has a higher contrast.

Then there is the point that the image from the 20mm started out at 4000x3000 pixels and just by cropping alone wound up at 1512 x 1181  pixels .. which is a paltry 1.8 MPixels and really only good for a 4x5 postcard print (or the web).

In a tight corner that may be enough ... but should you shoot for that? Well that's up to you.


Lastly there is the amount of clarity available. The 20mm is a sharp lens, but it has a maximum of about 7Perceptual Megapixels, while the Olympus 45mm has more like 9 ... by cropping you end up with 2 and given that the Panasonic had less to start with you may end up with less Perceptual Megapixels.

I'm really pleased with my legacy FD 50mm f1.4 lens(well and for that matter even more pleased with my legacy OM 50mm f1.8 which is just as sharp (see post here) and cost so little (like $18) its ridiculous. Indeed for folks now (such wasn't available to me when I got into micro43) the Olympus 45mm f1.8 is available in good condition used from around $300 or the Sigma 60mm f2.8 even less ... great optics well within grasp of many and if not then the legacy option is IMO fantastic value. Hell this portrait was taken with my Pentax 110 50mm f2.8 in another mates garage.

and that lens is ultra compact and light (and cheap too).

So, why have a telephoto? 

I guess I've answered that now.

Saturday, 16 August 2014

Cycling and Safety - and confusing sinage

In a world of occupational health and safety and duty of care one wonders about sinage like this:

...and what it means.

  • Is this an acknowledgment that  riding across these tracks will rip your wheel off (therefore don't) and just about tantamount to an admission of a problem?
  • or is it advice to get off and walk it across? Strange that this is signed at a place where you cross at 90 degrees not at a tangent (note the cycle path painted on the road) it shouldn't rip your wheel off
  • just where is that wheel?

So far it hasn't ripped my wheel off, but then I think the vulnerable cycles are those with the really skinny tyres (and mine's a Hybrid MTB) and crossing at a tangent.

Unlike normal trams (street cars) this one is designed to prohibit "mixed" traffic, so it all seems incongruous to me.

Friday, 15 August 2014

eBay feedback policy - Epic Fail

I buy and sell a few things on eBay, have done since before what I then used became eBay (it used to be, which was bought out by ebay more than a decade ago now).

Lately the whole eBay thing has been (in my view) circling the drain, with more and more unscrupulous buyers and sellers alike. To me the main thing which keeps things requiring the minimum of moderation is the feedback system and the strike system. Both are apparently broken now with recent policy changes.

The problem that first presents itself to me is that as a seller I can not leave negative feedback to wankers who buy and then just sit back laughing, never intending to pay. Its just a game to them.

Some cretin at eBay clearly decided that the policy to not allow negative feedback on customers was a good idea.

Well, in a world where everyone has good ethics and a decent moral outlook, perhaps this would work.

{looks left, looks right} ... nope I don't see that round my parts either.

Instead this process allows wankers like this guy to have "fun" at my expense and get away with it.

I'm not the only one with a problem like this it seems, as when I clicked on his (gosh all postive) feedback I see the most recent feeback item (not mine yet) is a "false positive" (meaning they wanted to pan him but the system stops that).

This seller is more 'discrete' than I'd be.

In fact this policy circumvents sellers being able to apply rules to their auctions to prevent wankers from making bids.

A quick search shows that its also a wide spread problem out there with Google giving 7 million hits on this question of why can't I leave negative feedback to non payers on eBay:

I think a worthwhile read on this topic can be had on eBay's own community page here.

This situation will clearly make eBay a place for high volume sellers of rubbish which of course if they don't get paid don't care, won't post it and move on.

One more knife in the back of the 'free market'.

Its interesting that in Japan eBay has not yet taken hold and instead Yahoo Auctions predominate. I used that system for 3 years when I was in Japan and really liked it. It operates under subtly different rules to eBay and it makes quite a difference too.