From: Paul Furman on
nospam wrote:
> In article <ivvtu5pct712ku0n9h6npe8j37ik5tbkke(a)>, Bruce
> <docnews2011(a)> wrote:
>>>> In macro work, a smaller sensor offers genuine advantages because of
>>>> the greater of field that is available.
>>> The only advantage is smaller size and cost. The DSLR can always stop
>>> down for the same DOF. If you always want to be stopped down like that,
>>> no need for the larger camera.
>> Yes, but stopping down with a DSLR has the consequences of a slow
>> shutter speed that makes a tripod more essential. With a small sensor
>> camera you can still hand hold it.
> raise the iso so that the shutter speed remains the same. the dslr has
> less noise since it has a larger sensor, and by raising the iso, you
> end up with the same image quality as the smaller sensor, with the same
> depth of field.

Yep, no difference so if you only want lots of DOF, get the P&S & save

Paul Furman

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From: Paul Furman on
Bruce wrote:
> Paul Furman wrote:
>> Bruce wrote:
>>> The same guy also had a useful contribution to make recently when we
>>> were discussing cleaning DSLR sensors. Putting aside his perfectly
>>> valid point that compact P&S and bridge cameras don't need their
>>> sensors cleaned, he pointed out that some methods of cleaning DSLR
>>> sensors could induce a static charge on the sensor causing it to
>>> attract dust.
>> That was BS.
> I phoned a materials scientist friend who confirmed it.

Confirmed that it's possible?

> He's a
> university professor at a Russell Group research university - the
> nearest equivalent to your Ivy League. He thought it would make a
> good final year project for an undergraduate student.
>> It's probably possible some combination of materials could
>> create troublesome static but I tried the masking tape idea the other
>> day and it worked fine.
> On a sensor?

Yes. Just one quick test. It was awkward, the tape had to be cut thinner
and hard to lay it down all the way to the edge, so I did two strips and
a test shot showed that I left a dirty stripe down the middle so three
strips and I still missed some of the edges & corners. It didn't get all
the dust, some still glued on, I think from cigarette smoke :-(

>>> I found his contribution useful and constructive.
>> The intent was destructive, as usual. That would be fine to say: "watch
>> out, tape might cause static" but he said: "it won't work, you're an idiot".
> Quite a few people posting here have a similar mentality, including
> some who accuse him of being a troll.

OK but that doesn't change anything.

>>> It caused me to consider different methods of sensor cleaning for the
>>> Kodak DCS Pro 14n I recently bought, whose sensor is a dust magnet.
>> What methods?
> I tried the paint-on goo we discussed a couple of weeks ago. It
> seemed to work reasonably well on the rear LCD, so I tried it on the
> sensor. To be honest, using it on the sensor was pretty terrifying. I
> am clumsy at the best of times but I was particularly nervous because
> of the risk of getting the liquid where it shouldn't go. So I didn't
> cover the whole sensor.
> It wasn't much fun and I won't be using it again. For someone more
> confident, more skilled and less clumsy, it might be OK, but I
> wouldn't recommend it to anyone I like. ;-)

Thanks for the report!

Paul Furman

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From: DanP on
On 15 May, 14:59, DanP <> wrote:
> On 15 May, 12:41, Bruce <docnews2...(a)> wrote:
> > On Fri, 14 May 2010 14:16:34 -0700 (PDT), DanP <>
> > wrote:
> > >I am still scratching my head and thinking smaller lens diameter means
> > >less light captured.
> > >So the FF sensor has to struggle and compensate for the small lens.
> > The trouble is, your mindset is based around retrofocus lens designs
> > that need to clear the reflex mirror in a DSLR.
> No, I do not think of camera design at all.
> Instead I think of binoculars and telescopes where the bigger lens
> diameter gives a better IQ.

To close the subject, after some reading and thinking lens diameter
does not affect the amount of light captured.
But a smaller lens needs to be polished more precise than a big one to
have the same IQ.
In real life better quality lenses have a bigger diameter.

From: Paul Furman on
Bruce wrote:
>> This is why diffraction-limited quality lenses are made regularly for P&S
>> cameras. That much resolution is required or they wouldn't be able to
>> resolve details down to their ~2um size photosite levels.
> Fascinating! Thanks for taking the time to reply.

A sensor with 2 micron pixels would need an f/1.4 lens to operate
without diffraction losses. At f/5.6 the smallest detail resolvable
would be more than 3x the pixel density.

A lens designed for 15x zoom isn't going to perform all that well at
most focal lengths and distances. Surely you know this.

Paul Furman

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From: Wilba on
Bruce wrote:
> Wilba wrote:
>> Bruce wrote:
>>> Some AF systems are even worse; Canon's being a
>>> case in point, with fundamental errors built in to the system.
>> Where can I find out more about this?
> There have been many discussions on Usenet. Search in Google Groups
> for contributions by David Kilpatrick, who gave the clearest possible
> explanation of Canon's AF problems. You will find them either in
> or
> The problem is caused by Canon's choice of site for the AF sensors.
> Nikon chose a different site and, as a result, their AF system has far
> fewer problems than Canon's. But David Kilpatrick's explanation is
> far clearer and more concise than anything I could manage.

I asked David and he said that all he can recall saying is that the AF
points are too close to the edges of the frame on the 7D, which means that
the wrong thing gets the focus when all points are active.

I was interested in the idea I've heard here that the configuration of
Canon's AF sensors is fundamentally different to how other manufacturers do
it, and that that explains some problems. David only mentioned something
like that with the 5D II, and how the 7D seems to be tuned for speed rather
than accuracy. He's not aware of any systemic issue across the brand that
means that single AF point focus is any more erratic or inaccurate than for
any other brand.

Maybe we're thinking of two different things...