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T-Mount adjustment



 
 
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  #1  
Old February 28th 08, 05:05 AM posted to rec.photo.equipment.35mm,rec.photo.digital.slr-systems,alt.photography
Paul Furman
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Posts: 7,367
Default T-Mount adjustment

T-mount is a universal adapter for old 3rd party lenses with an approx.
42mm female thread to recieve the lens. There are 3 set-screws on the
side. Is that for the purpose of adjusting the flange distance or just
the rotation? I don't want to mess it up experimenting. I also don't
want to strip the flat-head screwdriver slot if it's going to require a
real tight twist. It already rotates a little if given a firm twist.

What I've got is an old 500mm f/4 Century Tele-Athenar II lens (not a
mirror lens) and I was doing some tests today against other lenses with
teleconverters which revealed that it is not very sharp at all at
infinity (2 miles away) but pretty darn sharp at 100 feet away. I
noticed some other shots where 2 miles away was decent stopped down but
lights at night 10 miles away appeared to be out of focus: that might
just be the lights at night. Some long lenses allow focus beyond
infinity and now I'm starting to understand why!

I do have a split focusing screen but it's still hard to tell,
particularly because the focus on this lens is soooo gradual: there is a
half inch of turn between 500 feet and infinity.
  #2  
Old February 28th 08, 05:25 AM posted to rec.photo.equipment.35mm,rec.photo.digital.slr-systems,alt.photography
jean
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Posts: 337
Default T-Mount adjustment


"Paul Furman" a écrit dans le message de news:
...
T-mount is a universal adapter for old 3rd party lenses with an approx.
42mm female thread to recieve the lens. There are 3 set-screws on the
side. Is that for the purpose of adjusting the flange distance or just the
rotation? I don't want to mess it up experimenting. I also don't want to
strip the flat-head screwdriver slot if it's going to require a real tight
twist. It already rotates a little if given a firm twist.


Yes, the screws are to line up the lens with the camera, do it once and
forget it.

What I've got is an old 500mm f/4 Century Tele-Athenar II lens (not a
mirror lens) and I was doing some tests today against other lenses with
teleconverters which revealed that it is not very sharp at all at infinity
(2 miles away) but pretty darn sharp at 100 feet away. I noticed some
other shots where 2 miles away was decent stopped down but lights at night
10 miles away appeared to be out of focus: that might just be the lights
at night. Some long lenses allow focus beyond infinity and now I'm
starting to understand why!


At that distance, air currents may blurr and distort the image, no fault
with the lens (prolly)

I do have a split focusing screen but it's still hard to tell,
particularly because the focus on this lens is soooo gradual: there is a
half inch of turn between 500 feet and infinity.


Jean


  #3  
Old February 28th 08, 07:03 AM posted to rec.photo.equipment.35mm,rec.photo.digital.slr-systems,alt.photography
Richard J Kinch
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Posts: 203
Default T-Mount adjustment

Paul Furman writes:

There are 3 set-screws on the
side. Is that for the purpose of adjusting the flange distance or just
the rotation?


Just the rotation. Run the screws well out and remove the insert they're
holding in, and you'll see it's just a dovetail.
  #4  
Old February 28th 08, 02:04 PM posted to rec.photo.equipment.35mm,rec.photo.digital.slr-systems,alt.photography
[email protected]
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Posts: 1,311
Default T-Mount adjustment

Paul Furman wrote:
T-mount is a universal adapter for old 3rd party lenses with an approx.
42mm female thread to recieve the lens. There are 3 set-screws on the
side. Is that for the purpose of adjusting the flange distance or just
the rotation?

What they said - just the angle, normally, but it might be worth just
checking, given your problem... However, if it's old, the screws may
have corroded/self-welded themselves....

What I've got is an old 500mm f/4 Century Tele-Athenar II lens (not a
mirror lens) and I was doing some tests today against other lenses with
teleconverters which revealed that it is not very sharp at all at
infinity (2 miles away) but pretty darn sharp at 100 feet away. I
noticed some other shots where 2 miles away was decent stopped down but
lights at night 10 miles away appeared to be out of focus: that might
just be the lights at night. Some long lenses allow focus beyond
infinity and now I'm starting to understand why!


You should be able to tell if it's short, simply by watching as you
focus - pick your scene carefully, so as to include lost of far detail
at varying distances - you'll see it if it goes beyond infinity, and
should be able to tell if it's coming up slightly short. If it is
short and you are brave and mechanically gifted, it's worth
investigating - some lenses are as easy to adjust as peeling back the
rubber sleeve over the focusing ring, and loosening set screws so you
can rotate the focus sleeve slightly relative to the barrel so that
you can rotate it further than it did.

Other lenses are nowhere near that easy... If disassembly required,
work on a large white sheet, mark the alignment of any parts before
moving/removing them (especially sleeves, barrels, helicoids), and be
very afraid of small springs and tiny ball bearings... Work slowly
and carefully, carefully keep any grease you may want to wipe away
(you may need to reapply it), and .. er.. don't get any on the glass
(sorry for stating the obvious!)...

Good luck. (O:
  #5  
Old February 28th 08, 02:37 PM posted to rec.photo.equipment.35mm,rec.photo.digital.slr-systems,alt.photography
tomm42
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Posts: 682
Default T-Mount adjustment

On Feb 27, 11:05 pm, Paul Furman wrote:
T-mount is a universal adapter for old 3rd party lenses with an approx.
42mm female thread to recieve the lens. There are 3 set-screws on the
side. Is that for the purpose of adjusting the flange distance or just
the rotation? I don't want to mess it up experimenting. I also don't
want to strip the flat-head screwdriver slot if it's going to require a
real tight twist. It already rotates a little if given a firm twist.

What I've got is an old 500mm f/4 Century Tele-Athenar II lens (not a
mirror lens) and I was doing some tests today against other lenses with
teleconverters which revealed that it is not very sharp at all at
infinity (2 miles away) but pretty darn sharp at 100 feet away. I
noticed some other shots where 2 miles away was decent stopped down but
lights at night 10 miles away appeared to be out of focus: that might
just be the lights at night. Some long lenses allow focus beyond
infinity and now I'm starting to understand why!

I do have a split focusing screen but it's still hard to tell,
particularly because the focus on this lens is soooo gradual: there is a
half inch of turn between 500 feet and infinity.



I have a 400mm f5.6 Kilar in Leica Visoflex screw mount, founs a
Visoflex to Nikon mount but the lens is so off on the mount it is
difficult to use, doesn't help that the tripod socket on the lens is
fixed. With the Canon mount I bought it with (FD) infinity was a
little off, it is way off with the Nikon mount, luckily infinity is
within the focus range on outside it. I guess it means the mount is
too short. Great old lens but tought to use. Century optics were made
for the movie industry and should be first rate.
No surprise your images at 2miles are worse than the ones closer in
atmospheric haze will degrade almost any image. Can be a bright sunny
day there is still a lot of air and particles between you and the
subject 2 miles away.

Tom
  #6  
Old February 29th 08, 12:38 AM posted to rec.photo.equipment.35mm,rec.photo.digital.slr-systems,alt.photography
Paul Furman
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Posts: 7,367
Default T-Mount adjustment

tomm42 wrote:
Paul Furman wrote:

What I've got is an old 500mm f/4 Century Tele-Athenar II lens (not a
mirror lens) and I was doing some tests today against other lenses...


I have a 400mm f5.6 Kilar in Leica Visoflex screw mount,


Fun. One of very few mounts that can be adapted to Nikon.

found a
Visoflex to Nikon mount but the lens is so off on the mount it is
difficult to use, doesn't help that the tripod socket on the lens is
fixed. With the Canon mount I bought it with (FD) infinity was a
little off, it is way off with the Nikon mount, luckily infinity is
within the focus range on outside it. I guess it means the mount is
too short.



Great old lens but tough to use.


Yes this one is also not easy ack.

Century optics were made
for the movie industry and should be first rate.

  #7  
Old February 29th 08, 12:53 AM posted to rec.photo.equipment.35mm,rec.photo.digital.slr-systems,alt.photography
Paul Furman
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Posts: 7,367
Default T-Mount adjustment

Thanks everyone for comments, I'm just replying once here to similar
questions.

David Ruether wrote:
"Paul Furman" wrote in message news
T-mount is a universal adapter for old 3rd party lenses with an approx. 42mm female thread to recieve the lens. There are 3
set-screws on the side. Is that for the purpose of adjusting the flange distance or just the rotation? I don't want to mess it up
experimenting. I also don't want to strip the flat-head screwdriver slot if it's going to require a real tight twist. It already
rotates a little if given a firm twist.


As others have said, the set screws are just for changing
rotation of the lens relative to the camera body...


Yep. Hmm, one possibility might be to grind off a bit of the T-mount
adapter so it gets closer.

What I've got is an old 500mm f/4 Century Tele-Athenar II lens (not a mirror lens) and I was doing some tests today against other
lenses with teleconverters which revealed that it is not very sharp at all at infinity (2 miles away)


Few long lenses are except under unusual conditions (VERY clear
air, NO heat rising through the air you are shooting through [or any
other air disturbance caused by traffic, water, etc.],


I compared 1.4x & 2.x teleconverters (with without & stacked) on a 300mm
f/2.8 Tokina MF and 70-200/2.8 and the 500 was even beat by the 200 with
stacked converters in some cases so it's not just turbulent air.

So then tried various apertures and that makes a big difference. But I
think that was just because of the increased DOF because then I did
close up tests (100 feet) and it performed very well wide open at that
distance.

and absolute
freedom from movement of the camera./lens, including tripod
resonances [and the sturdiest tripods are sometimes not good
for minimizing these...]).


The lens came with a monstrous heavy tripod:
http://edgehill.net/Misc/photography...thenar/pg3pc17
but yeah it's annoying to see how much bounce there still is in the
viewfinder so I did these tests with the big metal bracket resting on a
table, mirror lockup, etc.

I have done some successful long distance
shooting with 700mm on FF (see numbers 8, 9, and 10 under
"Cornell" at http://www.donferrario.com/ruether/commercial.html,
taken with a 500mm older Nikkor mirror


Wow, that really flattens out the architecture!

+ TC 14 - the one made for long lenses).


Yep, got those.

Notice the times of day when these were taken
(when the air is usually "quietest" - at sunrise and after sunset...;-).


I woke unreasonably early this morning & caught the moon :-) and did a
bunch of bracketed shots (lots of variability depending on bounce, wind
gusts, etc but at least I knew this is close enough to infinity not to
matter :-)
http://edgehill.net/Misc/moon/2-27-08
I forgot tho crank the ISO though for the darker stacked TC stopped down
ones.

but pretty darn sharp at 100 feet away. I noticed some other shots where 2 miles away was decent stopped down but lights at night
10 miles away appeared to be out of focus: that might just be the lights at night.


Did you see them "twinkle"? If so, the air was not still (the air
was likely over surfaces that were warmer than the air, as with
over buildings on cool evenings...).


I didn't notice but good thing to check.

Some long lenses allow focus beyond infinity and now I'm starting to understand why!


No. This is due to the inclusion of glass that changes FL a bit with
temperature change - and your lens is unlikely to have it. If it needs
recalibration for infinity focus (unlikely, if nothing is loose), it should
be easy to do.


It's got what looks like recessed hex nuts all over but I'd hate to mess
it up. I could send it to the manufacturer but heard they charge a lot
for CLA.

I do have a split focusing screen but it's still hard to tell, particularly because the focus on this lens is soooo gradual: there
is a half inch of turn between 500 feet and infinity.


  #8  
Old March 2nd 08, 07:58 PM posted to rec.photo.equipment.35mm,rec.photo.digital.slr-systems,alt.photography
Paul Furman
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Posts: 7,367
Default T-Mount adjustment

Paul Furman wrote:
Thanks everyone ...
David Ruether wrote:
Paul Furman wrote

T-mount is a universal adapter for old 3rd party lenses with an
approx. 42mm female thread to recieve the lens. There are 3
set-screws on the side. Is that for the purpose of adjusting the
flange distance or just the rotation? I don't want to mess it up
experimenting. I also don't want to strip the flat-head screwdriver
slot if it's going to require a real tight twist. It already rotates
a little if given a firm twist.


As others have said, the set screws are just for changing
rotation of the lens relative to the camera body...


Yep. Hmm, one possibility might be to grind off a bit of the T-mount
adapter so it gets closer.


Alright, I was able to file the adapter down and I now have infinity
focus, plus a little beyond. I only moved it less than half a
millimeter. With the set screws loosened it was pretty easy to file the
soft aluminum of the inside part so you don't see it when reassembled. I
suppose I could put a thin washer in there to bring back to infinity but
I'm happy with it like this for now.

It's pretty amazing with stacked teleconverters 2x & 1.4x. Chromatic
aberration is kind of bad but sharpness is good even wide open, stopping
down hardly changes sharpness but does improve the CA considerably. It
looks like this is a 1978 design. It came with a 1991 lens catalog
showing a list price of $2750 and I paid $500 including a heavy duty
Bogen tripod. I'm happy. It's not a $7,000 Nikkor but it's pretty good.

What I've got is an old 500mm f/4 Century Tele-Athenar II lens (not a
mirror lens) and I was doing some tests today against other lenses
with teleconverters which revealed that it is not very sharp at all
at infinity (2 miles away)

 




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