Tamron SP 70-210mm F/3.5 19AH: won't focus at infinity

On Fri, 4 Sep 2009 08:04:01 -0700 (PDT), TJ wrote:

Advice please

I have a Tamron SP 70-210mm F/3.5 Model 19AH: with the Adaptall 2 for
Canon EOS on a 450D body.

It is wonderfully sharp - but won't focus sharply on infinity - like
the moon.

What to do?

Thanks

TJ

If you don't have access to a precision machine-shop to refigure the faces
of the adapter by making it a couple millimeters thinner, you can also
replace the negative achromat in it with something of slightly higher
negative power. A couple extra negative-mm's focal-length would do it. Or
you could instead add a similar very-low power negative achromat to the
front of any lenses you put on the adapter, effectively achieving the same
effect. The cost of putting the fix on the front of the lens, as opposed to
replacing the achromat in the adapter, would be rather high. Well figured
achromats jump in price astronomically as diameter is increased. Especially
negative achromats of the size needed to put in front of a lens because
that size would most certainly be a specialty low-production-run item.

If it was me? I'd probably disassemble the adapter and see which
internal-facing flanges or collars could be ground thinner, then probably
do this by hand on a flat surface with grinding compounds. A couple
millimeters wouldn't take too long to remove and be the simpler and less
costly solution. Though, I would first dig in all my optics "parts boxes"
to see if I had a negative achromat of just the right diameter and
focal-length to replace the lens element first. It would be extreme pure
luck if I had one just the right specs but stranger things have happened
from my optics "parts boxes".

On second thought, you *might* get away with inserting a very low-power
crown or flint (inexpensive) negative single-element lens (not achromat)
just in front of or behind the internal achromat lens element. Whichever
side has the most available working space. There might be enough
refraction-match where you could get away with this and not impart
excessive CA or softness. I had this happen once on a fish-eye lens that
wasn't quite matching my camera's FOV with a full-frame circle, top and
bottom of the circle ever-so-slightly truncated. By inserting a low-power
negative flint element behind this lens I not only obtained a full-circle
FOV, but it also surprisingly cleaned up a very slight bit of CA that was
inherent in the original design. Win-win just by experimenting with some
"junk lenses" that I had laying around in my surplus parts boxes.

"TJ" wrote in message
...
Many thanks Andy for your detailed suggestions. Amazingly I have
access to a precision machine shop! so will investigate
possibilities.

Alternatively, I'm waiting for another Adaptall 2 for EOS to come from
Hong Kong, to fit a Tamron lens I bought a friend. I will try that
adapter on my 19AH lens and see if the non-factory takeoff 'corrects'
the no-infinity focus defect. If it does, I'll buy another. If not,
I'll try grinding a few mm off.

It probably doesn't need a "few mm" it may only need a polish on all
surfaces (what engine tuners call blueprinting). I think it may be easier to
adjust the infinity stop of the lens. I don't recall if there was an
adjustment screw undre the rubber hand grip on the zoom-focus ring or a cam
in the mechanism, but almost all manual focus lenses had some method to
adjust infinity.

"TJ" wrote in message
...

It probably doesn't need a "few mm" it may only need a polish on all
surfaces (what engine tuners call blueprinting). I think it may be easier
to
adjust the infinity stop of the lens. I don't recall if there was an
adjustment screw undre the rubber hand grip on the zoom-focus ring or a
cam
in the mechanism, but almost all manual focus lenses had some method to
adjust infinity.


Thanks for your advice, Darrell.

'Polishing' sounds like a prudent way to start.

If that fails there probably is an infinity adjust screw somewhere.
But unless I can find photos of the insides, or a plan, so I know
exactly where it is, I really hesitate to open the lens and tinker
around. The lens is a cracker. Would be stupid to ruin it. The moon I
can live without.

In fact, come to think of it. How many times have you ever used a tele
lens (longer than a portrait) lens on subjects at infinity? For long
'scenery' shots there's usually just too much heat haze/pollution to
get a sharp image anyway.

I saw that this fellow rebuilt and adjusted the infinity stop on the same
lens

http://forum.manualfocus.org/viewtopic.php?id=12559

his website is;
http://www.snaar.co.uk/lenses

He may have some tips.

Darrell Larose
Ottawa

On 9/5/2009 11:36 AM TJ spake thus:

I saw that this fellow rebuilt and adjusted the infinity stop on the same
lens

http://forum.manualfocus.org/viewtopic.php?id=12559

his website is;http://www.snaar.co.uk/lenses

He may have some tips.

I'm sure he has. But are my hands steady enough and my eyes sharp
enough to take advantage of it ??? !! That is the question. I'll try
the polishing first, I think.

I wouldn't do that. After all, why take a chance on physically altering
your lens, possibly damaging it, when a simple adjustment might solve
your problem?

Another source of information is Rick Oleson
(http://members.tripod.com/rick_oleson/index-18.html). I don't think he
has specific information on working on your lens (I haven't searched the
site recently, so it's possible he does), but I've contacted him in the
past with repair questions and he's been happy to help. He's quite
knowledgable and can be trusted to give reliable information.



--
Found--the gene that causes belief in genetic determinism

On Sat, 5 Sep 2009 00:45:57 -0700 (PDT), TJ wrote:
:
: It probably doesn't need a "few mm" it may only need a polish on all
: surfaces (what engine tuners call blueprinting). I think it may be easier to
: adjust the infinity stop of the lens. I don't recall if there was an
: adjustment screw undre the rubber hand grip on the zoom-focus ring or a cam
: in the mechanism, but almost all manual focus lenses had some method to
: adjust infinity.
:
:
: Thanks for your advice, Darrell.
:
: 'Polishing' sounds like a prudent way to start.
:
: If that fails there probably is an infinity adjust screw somewhere.
: But unless I can find photos of the insides, or a plan, so I know
: exactly where it is, I really hesitate to open the lens and tinker
: around. The lens is a cracker. Would be stupid to ruin it. The moon I
: can live without.
:
: In fact, come to think of it. How many times have you ever used a tele
: lens (longer than a portrait) lens on subjects at infinity? For long
: 'scenery' shots there's usually just too much heat haze/pollution to
: get a sharp image anyway.

Funny you should ask. Earlier this week my wife and I both used telephoto
lenses to photograph the surf at the New Jersey shore. It was a cool day, and
the wind was blowing fairly hard, so haze was not a factor. The pictures came
out fine.

Bob

On Tue, 8 Sep 2009 10:44:44 -0700 (PDT), TJ wrote:
:
: : In fact, come to think of it. How many times have you ever used a tele
: : lens (longer than a portrait) lens on subjects at infinity? *For long
: : 'scenery' shots there's usually just too much heat haze/pollution to
: : get a sharp image anyway.
:
: Funny you should ask. Earlier this week my wife and I both used telephoto
: lenses to photograph the surf at the New Jersey shore. It was a cool day,
: and the wind was blowing fairly hard, so haze was not a factor. The
: pictures came out fine.
:
: Bob
:
: Bob, I have a feeling that depending on what tele lens you're using
: (and the internal screw setting) , FAILURE to focus on 'infinity' can
: be a long way off !! Landscape territory. Or inner space like the
: moon.

Modern AF lenses don't appear to have an infinity stop, presumably so that the
high-speed focus mechanism won't bang up against it. So you're probably facing
an issue that will become increasingly rare with time.

: The Tamron is sharp to a mile, and maybe, given optimum environmental
: conditions, to a few mo which again is landscape photography.

We were on the beach at Ocean City, and some of our shots included the skyline
of Atlantic City, which is ten or fifteen miles away. That's infinity for any
lens this side of Mt Wilson.

: What I realise I need, is to change the screen on the 450D - to a
: split screen for easier focusing with manual lenses. That will make it
: easier to see when it fails to focus.

Good luck with that. I don't think Canon makes a split image for a 450D.
KatzEye does, I think; but if the 450D uses the same viewfinder as the 400D
(and again I think it does), you won't be able to see the focus points in the
viewfinder. Rachael Katz told me they've tried countless workarounds for that
problem, but without success. I bought a KatzEye screen for my 400D anyway;
but since I also have a 50D, I'm willing to pretty much treat the 400D as a
manual-focus camera.

Incidentally, the greatest value in an aftermarket screen is that you can have
grid lines etched on it. (KatzEye offers about a dozen variations.) For
architecture and seascapes, I couldn't function without a grid.

Bob

"Robert Coe" wrote in message
...
[]
Incidentally, the greatest value in an aftermarket screen is that you
can have
grid lines etched on it. (KatzEye offers about a dozen variations.) For
architecture and seascapes, I couldn't function without a grid.

Bob

One of the delights of the Nikon D5000 - it has gridlines in the
viewfinder you can turn on and off.

Cheers,
David

On 2009-09-08 22:55:09 -0700, "David J Taylor"
said:

"Robert Coe" wrote in message
...
[]
Incidentally, the greatest value in an aftermarket screen is that you can have
grid lines etched on it. (KatzEye offers about a dozen variations.) For
architecture and seascapes, I couldn't function without a grid.

Bob

One of the delights of the Nikon D5000 - it has gridlines in the
viewfinder you can turn on and off.

Cheers,
David

....and you can go back to the D70 and possibly further for the same feature.

--
Regards,

Savageduck

"Savageduck" wrote:
On 2009-09-08 22:55:09 -0700, "David J Taylor":
"Robert Coe" wrote in message
...
[]
Incidentally, the greatest value in an aftermarket screen is that you
can have
grid lines etched on it. (KatzEye offers about a dozen variations.) For
architecture and seascapes, I couldn't function without a grid.

One of the delights of the Nikon D5000 - it has gridlines in the
viewfinder you can turn on and off.

...and you can go back to the D70 and possibly further for the same
feature.

Or forward to the 7D.

Canon seems finally getting their act together: 7 fps, electronic horizon
(level), grid lines, weather sealing, real HD video, new competitive AF
system.

Grumph. I got 3 great years of use out of the 5D, the 5D2 was a fantastic
upgrade (the resolution and manual focus in live view are wonderful), but it
sounds as though the 5D3 will be not much more than a year after the 5D2.

--
David J. Littleboy
Tokyo, Japan

On Wed, 09 Sep 2009 05:55:09 GMT, "David J Taylor"
wrote:

"Robert Coe" wrote in message
.. .
[]
Incidentally, the greatest value in an aftermarket screen is that you
can have
grid lines etched on it. (KatzEye offers about a dozen variations.) For
architecture and seascapes, I couldn't function without a grid.

Bob

One of the delights of the Nikon D5000 - it has gridlines in the
viewfinder you can turn on and off.

Cheers,
David

One of the delights of any CHDK supported camera, it has as many grid-lines
designs as you want, designed by you or others. Grid-lines that you can
turn on or off (with a quick short-cut button press), or interchange, or
combine any time you want. You don't have to send your camera off to a
custom repair service to change your grid pattern. Just load a new one from
a simple to write text-file made of very basic graphic commands. Keep all
of your grids definition files on your memory card and load any one of them
whenever you desire.

A sampling of 34 different user-designed grids and alignment aids that you
can use in any CHDK camera: http://chdk.wikia.com/wiki/Grids If you don't
see one there that you like you can simply write your own.

There's no reason to continue to support crippled camera paradigms of last
century.