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Old June 5th, 2007, 01:56 AM   #1
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HD Focus Problems solved - almost!

OK, this is a thread I started over in the Canon A1/ G1 forum but have decided to hijack it into here as being more appropriate (sorry Warden!) The original thread was:


If anyone is interested enough to read that from the beginning, they will get an idea where I was coming from. However, since that thread was started I have had the time to give a lot more thought into exactly what was going on. Of course, the answer was fairly simple, if not exactly in "my face".

So, to put it in context. The A1/ G1 cameras (and probably all the other "prosumer" hd cameras) were designed around the percieved needs and expectations of a largely urban market. As such, in my PO, the expectation was that they would be used in just such an environment - man made, lots of hard horizontals, verticals, contrasting shapes and colours, textures etc etc. In such an environment the AF had plenty of hooks to latch onto and if for any reason it couldn't, the eye could pretty well sort the problem, even with the rather rudimentary screen available for that purpose.

Since I've had my A1, I have almost exclusively been using it for things it was never designed for, broad horizons, wildlife in wildlife settings (where too close is TOO close), no hard edges to get a "hook" onto etc.etc.

This gave rise to a quite disheartening phenomena whereby I was losing 2 out of 3, 3 out of 4 and sometimes even 5 out of 5 shots in a row because I simply could not get them in focus with the hooks available.

[I should say at this point, this footage is reviewed on a "bleeding edge" Sony 46" Bravia X Series Full 1080 screen straight off the camera - there is nowhere to hide!]

Hence the reason for my previous thread.

Well, since then, I have had a chance to put my theory to the test. Arriving a week or so ago was a Nikon 1200S Digital Laser Rangefinder, and the last two days have been spent using it with the A1 in serious shoot mode.

The result?

Mind Boggling! Every shot a winner, on the money, in the frame and b****y well in focus!

There are, however, a few caveats. (Aren't there always?).

1. OK, the Canon system of indicating "Plane of focus" ( I presume that's what that figure is in the viewfinder") is, er, well, in need of some work. At 20X zoom (which is where my lens spends a great deal of its time) it's "NOT TOO BAD" in that it will, if you have the patience of Job and a willing subject, allow you to finally get it pretty close. But oh how much better it could be. The present "Normal" should be replaced by the existing "Slow" setting, the "slow" should be at least 4 times slower and fercryingoutloud keep the damn figures on the screen permanently so you don't have to move the focus to figure out where you are.

2. At anything other than 20X zoom things go to hell in a handbasket. The figures jump so badly that getting the lens to go to the distance you want is almost impossible. I may be hamfisted but at 10X it jumps from 200 metres to 500 metres by just blowing on it.

3. Now this one is going to absolutely infuriate a certain contingent on DVinfo.

DOF! At 75 metres the DOF on the A1 lens as measured by me @ F5.6 is only about 2.5 metres. There is no choice if you want to have better DOF but to stop that lens down to 9.4 and keep it there. One of my shots, of a group of three fur seals on a rock, was, front to back, about 4 metres. My partner, not the most visually accurate person on the planet, happened to comment that the lead seals nose was out of focus, then it wasn't. I explained that that was where I stopped the lens down to 9.4 to see what happened.

Guess what? Yep, In focus and absolutely no artifacts of any kind whatsoever, so I fail to see where this prevailing "below 5.6 and the world stops revolving" stuff is coming from.

Bottom line: If you're using the A1/ G1 and probably any other "prosumer" HD cam "out of it's comfort zone" and wondering why, oh why, it isn't in focus, there's your answer and way out.

All input gratefully recieved.


Chris Soucy is offline   Reply With Quote
Old June 5th, 2007, 09:48 AM   #2
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so I fail to see where this prevailing "below 5.6 and the world stops revolving" stuff is coming from.
Imatest MTF50 resolution testing for one.

It loses some contrast, and loses some reality in subtle ways, due to diffraction. The amount we could argue over, but if it satisfies, that's all that matters. They put f9.5 on there so you have it if you need it.

I don't know why you say that should infuriate a certain contigent. Diffraction degradation at small apertures has long been established, and has not been disproved here.

I have a laser rangefinder as well, accurate to about plus or minus 1 yard. There's been some skepticism about how reliable that method would be but your experience seems to be positive.

I was shooting 20x zoom f4.0 of a raptor from a light pole, 15 feet away. The DOF at that distance is probably about an inch. Still, I obtained wonderful manual focus by using magnification and peaking together.
Tom Roper is offline   Reply With Quote
Old June 7th, 2007, 03:50 AM   #3
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Hi Tom........

Not sure what a "raptor" is, or quite why you're shooting from a light pole (tho' it ain't probably moving much) but I agree, at that range, DOF would be miniscule - the sharpness of this lens is quite astonishing.

That you can manually focus on such a subject by eye given the tools is testament to either incredible eye definition or extaordinary good luck - I'll take it it's the former. Better than I can do I'm afraid - the eye's ain't what they used to be.

Good to hear someone else has "found the way" with the rangefinder before me, the Nikon has +/- .5 metres, which, given the rangeing system on the Canon seemed to be the way to go.

As for the "difraction" effects of which you speak, can't say that anything was/ is noticeable on the Bravia, tho' without something even better, can't say for sure. Tho' - If the average Joe Blow could tell "Diffraction" from his "whatever" on a Broadcast is a seriously moot point.

My "Missus" can't even tell the difference on the screen between Component off the A1 and HDMI off the HV20.

Thanks for the input.


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