Lens Focusing Issue???????

On Wed, 2 Jun 2010 10:01:34 -0700 (PDT), infiniteMPG
wrote:

I have a Sony A-100 and have had good luck with my Tamron 18-250 and
also with my Tamron 90 (with 2X doubler for tight macro shots). I
have been wanting to occasionally shoot some distant stuff like an
eagle's nest that is not far from my home, so I shopped for something
inexpensive to do this with occasionally. I found a Rokinon 800mm
f8.0 mirror lens with an adapter to my Sony (Minolta) mount. I have
not had much time to play with this but did last night.

It was still sunny out so no problem with light. I had this mounted
on my tripod and noticed that even the slightest motion would cause
the lens to bounce around. I was using shutter only as no adjustment
for f-stop available, fixed f8.0. I would get images locked in thru
the viewfinder and would tweak as to get the focus as crisp as
possible, snap the picture, replay it on the camera and zoom in to see
everything blurry. No matter what I tried or how fast I made my
shutter, same thing.

How fast is fast? Assuming 1.5 crop factor 1/f = 1/(800*1.5) =
1/1200sec. Are you anywhere close to this? If not bump up the iso.

On Wed, 02 Jun 2010 18:07:25 -0400, me wrote:

It was still sunny out so no problem with light. I had this mounted on
my tripod and noticed that even the slightest motion would cause the
lens to bounce around. I was using shutter only as no adjustment for
f-stop available, fixed f8.0. I would get images locked in thru the
viewfinder and would tweak as to get the focus as crisp as possible,
snap the picture, replay it on the camera and zoom in to see everything
blurry. No matter what I tried or how fast I made my shutter, same
thing.

How fast is fast? Assuming 1.5 crop factor 1/f = 1/(800*1.5) =
1/1200sec. Are you anywhere close to this? If not bump up the iso.

That's a rule of thumb for handheld shooting. It doesn't apply to tripods,
beanbags, etc.

--
Regards, Robert http://www.arumes.com

On Thu, 03 Jun 2010 12:16:49 -0400, me wrote:

On Thu, 03 Jun 2010 09:58:59 +0200, in rec.photo.digital.slr-systems
Robert Spanjaard wrote:

On Wed, 02 Jun 2010 18:07:25 -0400, me wrote:

It was still sunny out so no problem with light. I had this mounted
on my tripod and noticed that even the slightest motion would cause
the lens to bounce around. I was using shutter only as no adjustment
for f-stop available, fixed f8.0. I would get images locked in thru
the viewfinder and would tweak as to get the focus as crisp as
possible, snap the picture, replay it on the camera and zoom in to see
everything blurry. No matter what I tried or how fast I made my
shutter, same thing.

How fast is fast? Assuming 1.5 crop factor 1/f = 1/(800*1.5) =
1/1200sec. Are you anywhere close to this? If not bump up the iso.

That's a rule of thumb for handheld shooting. It doesn't apply to
tripods, beanbags, etc.

No kidding sherlock. As to whether or not it applies to a
vibrating/moving tripod...... Another poster has stated he shoots his
mirror better hand held than on his tripod. It is a point of reference,
and the OP hasn't ever stated what shutter speeds he has tried or what
he considers fast.

He hasn't even stated what the blur looks like. It might not be motion
blur at all, dear Watson.

--
Regards, Robert http://www.arumes.com

On Fri, 04 Jun 2010 00:24:45 +0200, Robert Spanjaard
wrote:


He hasn't even stated what the blur looks like. It might not be motion
blur at all, dear Watson.


Which is why I'm trying to rule it out. I shoot 400 X 1.4 x1.5 hand
held all the time. I have much better control hand held than on flimsy
tripods, which the OP admits is an issue.

me wrote:
Robert Spanjaard wrote:

He hasn't even stated what the blur looks like. It might not be motion
blur at all, dear Watson.

Which is why I'm trying to rule it out. I shoot 400 X 1.4 x1.5 hand
held all the time. I have much better control hand held than on flimsy
tripods, which the OP admits is an issue.

Tripods can easily be worse than nothing, even big sturdy ones. Possibly
he could use the tripod like a monopod with the head loose, held steady
by hand... like is done with a gimble head.