In article , Eric Miller
writes
Kennedy McEwen wrote:
In article , Eric Miller
writes
Kennedy McEwen wrote:

If it is just about the math then you need to quantify the lens
quality contribution as well

No, the question posed in the original post had nothing to do with that.

I suggest you read what you wrote in your question again and, in
future ask what you mean or mean what you ask! You specifically
refer to resolution and that is a lot more than just pixel density!

- your math is less than half the story, dealing only with pixel
geometry.

That would actually be the whole story, since the original question
strictly concerned the pixels.

No, you stated: "if there is a way to think of resolution as
effective focal length versus the 10D".


Which is a selective quote designed to explain your need to pontificate
about something other than what was really asked

No it is an exact quote of your question, excluding the waffle that put
it in context as that was already clear from the preceding thread.

"So, for example, if I were to get a 7D at 18 megapixels how would that
compare to 10D resolution wise in terms of what focal length lens would
I have had to put on the 10D to get a 5 inch tall bird at 20 meters (or
any distance) to be rendered by the same number of pixels (one
dimension only or my head will hurt too much) on the 10D that it would
be rendered on the 7D using the 400mm lens."

Context. The answer is NOT simply scaling pixel size of the 10D to the
7D, which is what you were given. Without taking optical resolution
into account the equivalent focal length you would need on the 10D
compared to the 7D could be close to 50% higher than is in fact the
case! Optics, even perfect optics, don't have infinite resolution! When
the optical resolution is close to the pixel resolution then they MUST
be taken into account to answer your question, or you end up with
meaningless unresolved pixels. You seem to have a major problem
understanding that.

It isn't surprising that, on the usenet, posters will feel the
necessity to take every question as an opportunity to educate those
lesser minds about what they really should have asked.

When you were 5 and asked your Mom where you came from, you were
probably happy with her reply that a stork brought you. By the time you
were 10 you would expect a better, more complete answer, to exactly the
same question. By the time you were 15 you ought to know the full
answer yourself. Stop behaving like a 5 year old - there is no Santa
Claus, even if some of your friends still believe there is!

Oh wait, let me mimic that little voice you just heard, "Remember, this
post is an opportunity to tell them more of what we know about what
they should have been asking, but were too ignorant to, hee hee hee . .
. God we are smart."

Smart enough to know that any question I ask may well have an answer
which is more complex than I expected and with enough common decency not
to criticise those who make the effort to explain that.

Carry on living in ignorance: the x1.7 scale factor given by the partial
answer is at least 50% too high. A 400mm lens on the 7D would NOT give
equivalent resolution to a 680mm lens on a 10D: you will be lucky to
achieve half of that 280mm effective focal length extension depending on
the optical resolution of the 400mm lens in question. In other words
540mm, or less, equivalence in terms of what is actually RESOLVED.
--
Kennedy
Yes, Socrates himself is particularly missed;
A lovely little thinker, but a bugger when he's ****ed.
Python Philosophers (replace 'nospam' with 'kennedym' when replying)