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[test] extension tubes on magnification of macro lenses



 
 
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  #11  
Old July 24th 08, 05:09 AM posted to rec.photo.digital.slr-systems,rec.photo.equipment.35mm
Troy Piggins[_15_]
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Posts: 142
Default extension tubes on magnification of macro lenses

* Annika1980 wrote :
On Jul 23, 8:04*pm, Troy Piggins wrote:

Lately I've been shooting with full set of extension tubes on,
and I realise you lose infinity focus, but I've been wondering
what the minimum magnification really is.


I was out trying to shoot eagles one day and I had the trusty old
Vivitar 2x on the 400 f/5.6. But for some stupid reason I couldn't
get the damn lens to focus, even manually. My 400 f/5.6 has some
focus problems anyway (it slips when focusing manually so using TCs
becomes quite a challenge), but all I was getting was a blurry
screen. I checked every setting I could think of and couldn't figure
out what the hell happened.
I even went through all the Custom Functions to see if I might have
set something screwy. Then I finally noticed that the 2x wasn't the
2x at all, but was actually my Kenko 36mm extension tube that is the
same size and color as the 2x.

Oops!


Haven't heard that one before! I've got the Canon TCs.
They're white, metal, and much heavier than the Kenko black
plastic tubes.

--
Troy Piggins
I always appreciate critique.
  #12  
Old July 24th 08, 05:10 AM posted to rec.photo.digital.slr-systems,rec.photo.equipment.35mm
Peter Irwin
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Posts: 352
Default [test] extension tubes on magnification of macro lenses

David J. Littleboy wrote:

Overheard (really!) in a Navy ROTC course* at a well-know institute of
higher education in the US.

Professor: We will now compute the density of sea water in slugs per cubic
yard.
Cadet: Sir! Excuse me, sir! But, sir! Are you serious or making a joke, sir?
Professor: I'm terribly sorry, but I'm serious.

*: Air, Water, and Interface Vehicles. A seriously great course for anyone
even vaguely interested in boats.


If he allows for a slight approximation then this is actually
a pretty good question for remembering useful facts.

- density of seawater is 64 pounds per cubic foot
- acceleration due to gravity is a little over 32 feet/second^2
- Therefore very nearly 2 slugs per cubic foot of seawater
- 27 cubic feet in a cubic yard
- Therefore nearly 54 slugs per cubic yard of seawater

Now if he insisted on a more exact answer of 53.7something,
the simplicity of the question would be lost, but if "nearly 54"
is a good enough answer then it is good practice for quick mental
calculations and remembering acceleration due to gravity and
the density of seawater.

Peter.
--




  #13  
Old July 24th 08, 01:17 PM posted to rec.photo.digital.slr-systems,rec.photo.equipment.35mm
jimkramer
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Posts: 428
Default [test] extension tubes on magnification of macro lenses

"Blinky the Shark" wrote in message
news
Big ol' Snip


Thank God for the new rails.


New focusing rails? If so, what did you wind up with? My Novaflex set just
doesn't cut it most of the time. :-(

-Jim


  #14  
Old July 24th 08, 06:39 PM posted to rec.photo.digital.slr-systems,rec.photo.equipment.35mm
Blinky the Shark
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Posts: 827
Default [test] extension tubes on magnification of macro lenses

jimkramer wrote:

"Blinky the Shark" wrote in message
news
Big ol' Snip


Thank God for the new rails.


New focusing rails? If so, what did you wind up with? My Novaflex set just
doesn't cut it most of the time. :-(


Something undoubtedly inferior to your Novaflex rig, but the price was
right.

http://www.bhphotovideo.com/c/produc...ag_Slider.html

= http://tinyurl.com/69mqml


--
Blinky
Killing all posts from Google Groups
The Usenet Improvement Project: http://improve-usenet.org
Need a new news feed? http://blinkynet.net/comp/newfeed.html

  #15  
Old July 24th 08, 10:55 PM posted to rec.photo.digital.slr-systems,rec.photo.equipment.35mm
bino
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Posts: 82
Default [test] extension tubes on magnification of macro lenses

"Troy Piggins" wrote in message
...
I've been meaning to do this for months. Finally took the
opportunity. Wanted to take shots of a measurable subject at
different magnifications to:


They all look good to me!

 




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