Re: help with manual focus on Rebel XT

Today default commented courteously on the subject at hand

I often limit which point is used also, because sometimes
it switches focus points from a little wiggle of the
camera, and you end up with the wrong thing in focus if you
let it choose.

I should have mentioned, but didn't think of it until now, but
the method(s) one chooses to use for AF are highly dependent
on the subject type. e.g., it is one thing to keep a pet in
focus when they're jumping around, as my daughter's Chiuaua
was last night, and quite another for me shooting cars in
available light or with flash.

Likewise, if one is shooting only scenics at a distance, you
just set the focus to infinity and shoot. Obviously, that
can't work for you with the long lenses you want to use, else
you'd not have posted in the first place.

I only shoot raw, sometimes raw+jpg because I find I often
want to adjust the exposure or white balance a little even
if everything else is good and raw makes it so easy. 2GB
cards are now less than $99 so storage space is hardly an
issue. Raw+JPG is good for when you want to stop at the
photolab for a few prints and not have to go home to use
the computer to convert them.

I can do RAW+JPEG but I'm too new at the DSLR game to have
even loaded the Canon RAW converter. But, I intend to learn
later this spring, after I'm done spending money.

I am suspecting that I might need a negative diopter
eyepiece to get the viewfinder really sharp to be able to
manual focus accurately. I'm going to order one next week
and see if it helps.

A Rebel has what, 6 or so diopter setting built in. I set it 1
or 2 from one end if I'm wearing my reading glasses so I can
see various small text as I change photometrics as I shoot,
and 1 or 2 from the other end if I'm outdoors and don't need
to play with the camera, just shoot.

I tested what I thought I was seeing against the image that
resulted and concluded how to set the diopter so I can at
least try to get the AF right.

Plus, the Rebel's AF/AE system refuses to show me an AE
lock in manual focus mode unless /it/ thinks I've
correctly got the blinking thing in focus. So, if I could
get 100.0% AF lock on auto, why the hell would I try
manual?

Sometimes the autofocus hunts and overshoots and misses the
right spot. If you switch to manual, you can focus more
slowly and get it right. The AF confirmation is nice for
this.

Yes, but that's not what I'm talking about here. The Rebel
wants me to twiddle the focus ring until I see the red dot
come on, then it shows the green dot for AE and AF. If I
believed the AF, why the hell am I even trying manual? Same
for you, I suspect.

And, if /my/ version is
what I want, good, bad, or indifferent, how can I convince
the Rebel to still do an AE lock? Yes, I've tried the 4
ways that AE/AF can be set as a custom function by
reading/re- reading/re-reading - RTFM, right? Also
experimented, also talked to my local camera store
manager, who is at least marginally good at this stuff.

I just tried it with my Rebel XT and it will happily take
an out of focus picture with AE lock. I put it to manual
focus, pointed it at a bright source with the focus way
off, pressed *, (the * indicator lit), recomposed and then
fired off a very out of focus and underexposed shot. This
was in Av mode with all CFn's set to 0 (defaults). Maybe
yours needs a firmware update?

Yes, you can intentionally take it out. I'm talking about the
old-fashioned way to do it - shift the ring out, move it
fairly quickly in the direction it needs to go, and stop when
it looks sharp. On my Canon, the bull*** AF that I can't shut
off overshoots, so I'm toast.

The goofy thing might be expecting a sharp image from an
inexpensive solution. I am coming to the conclusion that
the Quantaray 500mm F/8 mirror may never focus really
sharp. It is light, small, inexpensive, fully coated and
has correction optics, but it just isn't so sharp. I can
get an acceptable picture for viewing on a computer screen
by reducing the 8MP original down to 800x533 or smaller and
then a bit of unsharp mask. I don't think it will make a
decent print at 4x6 at all.

The kit lens is a tad soft for what I do, but I didn't expect
much out of an 18-55 that only costs $100. And, I didn't
expect a razor sharp image from my $380 Sigma 18-125. But,
with my 2 L-glass lenses costing over $2,100, I /do/ expect
sharpness, and I get it. But these things are huge and heavy,
so again, there's always tradeoffs in life.

I generally shoot at the medium 4MP size, but do go to the
full 8MP fairly often. Since I print almost zero beyond 4x6, I
resize down to no more that 1600 by xxx (aspect ratio) and be
very conservative with my JPEG compressions.

With practice now I can get pretty sharp with the Canon EF
70-300mm F4-5.6 with a Quantaray 2x teleconvertor, but
between 500 and 600mm I am getting a somewhat soft image,
not nearly as sharp as without the TC, but I still think
some of the problem is in focussing techique because I
can't get as sharp manual focussing with no TC as the AF
gives. I am using a tripod, remote shutter switch, and
mirror lock-up, but still I am sure I can do better.

I know why you use a converter, but I've never seen one in 40
years that didn't do a 600 grit sandpaper on my images.
Another of those pesty compromise/tradeoffs.

Since I generaly shoot at 4MP, I can get an effective 4X
"digital" zoom at the max telephoto I have by going to 8, and
cropping a 4MP out of the middle.

The eventual solution might be to learn to live with only a
300mm focal distance and crop somewhat for smaller prints.
Even cropping out 4 of the 8 MP still gives a nice 4x6"
print while increasing the apparent focal distance a lot.

Why? First, though, what are your main subjects? And, what PPI
are you shooting for? With 4MP, which is 3456 x 2304, that's
good for up to 17" x 12" at 200 PPI, which is overkill to the
tune of having 3 nukes for every one the Soviets had. Or, the
ages old boys showeroom measurements, after the minimum, the
rest is just bragging.

So, again I'll ask you. How about supplying some details of
what you do and keep the discussion practical, instead of
going into the tall weeds on perceived vs. real requirements?
I'm not disputing anything you've said, I just can't give you
a reliable opine without knowing more.

e.g., I'm assuming you might like to shoot car races or other
sports from a long distance, hence the need/desire for long
lenses, and may also be interested in the real-world burst
rate of the camera, taking into account AF lag, shutter lag,
and time it takes to write both RAW and JPG to your CF. That
don't mean squat to me, all my cars are sitting still.

--
ATM, aka Jerry
.