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Messages - neuroanatomist

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EOS Bodies - For Stills / Re: Amazon vs B&H for purchase?
« on: March 03, 2013, 05:37:31 PM »

Doesn't really matter (as long as you're buying direct from Amazon, not a 3rd party even if fulfilled by Amazon). 

Lighting / Re: Super DIY Remote Speedlites
« on: March 02, 2013, 04:52:32 PM »
Makes sense - thanks!

Lighting / Re: Super DIY Remote Speedlites
« on: March 02, 2013, 04:01:32 PM »
I don't understand - how is the volume potentiometer going to control the flash output?

EOS Bodies / Re: On the 5DM3 what is the difference
« on: March 02, 2013, 02:03:21 PM »
When you look through the view finder, the array of focus points is a matrix of small squares.  But each of those small squares also has an even smaller square in the center of it.  When using Single Point AF, you are using the larger, outer square for that point.  When using Single Point Spot AF, you are using the tiny square in the center of each focus point.

Just to be clear, with Spot AF the actual AF point is still slightly larger than outer square.  The area being used for AF isn't nearly as small as the little inner box, that 'double' box is just the indication that Spot AF is being used.

EOS Bodies / Re: On the 5DM3 what is the difference
« on: March 02, 2013, 12:31:57 PM »
Spot AF reduces the effective size of the AF point. With single point 'regular' AF, the actual AF point is quite a bit bigger than the little box in the VF (basically, the real points on the AF sensor almost touch).  Spot AF restricts the AF point size to only very slightly larger than the little box that represents it in the VF. Spot AF is useful for macro shooting, I also use it with small birds in thickets. It's bad for moving subjects.

On the 5DIII, spot metering is always in the center (only 1-series bodies can link spot metering to the selected AF point).

Lenses / Re: Canon 100-400 f/4-5.6L IS II Leaked!!
« on: March 02, 2013, 06:54:03 AM »
Sorry, but the attempt is pretty lame.  If you're going to put up a fake 100-400, your fake should show focal length markings somewhere.  No numbers around the zoom ring?  More importantly, you're showing a non-extending zoom and it's too short to be 400mm (unless it's a DO lens, in which case you've got the wrong color stripe).  Better luck next time.

Software & Accessories / Re: Good GND filter to go with new Lee system
« on: March 01, 2013, 09:35:36 PM »
The 4x6" Lee (100x150mm), the 150x170mm are too big for the holder. That's the right S-R, though.

Software & Accessories / Re: Good GND filter to go with new Lee system
« on: March 01, 2013, 08:08:54 PM »
NA, any suggestions for a soft 3 stop then? I like the idea of Glass of course, resin is find too I guess.

Personally, I plan to get a 4" CPL and 3-stop grad hard and soft from Lee, and a 3-stop reverse grad from Singh-Ray.

Where does that anywhere say a petal hood blocks light better? That picture shows that using a hood helps. Which it does. The ET-60 will give you exactly that protection against flare.


The point is that you should use a hood.  Importantly, you should use a hood designed for the lens.  In some cases (usually zooms with a wide angle or ultrawide zooms), that's a petal hood. In other cases (standard and longer primes, most telezooms especially 'slow' ones), it's a not petal-shaped.  The folks who design the optical formula of the lens also design the hood for optimal light blocking without vignetting, sometimes with practical compromises (like where possible avoiding rounded edges which result in a lens falling over if set down on the front of the hood).

EOS Bodies - For Stills / Re: Obama using Canon!
« on: March 01, 2013, 12:09:47 PM »
Ok, I was just hoping....

Hoping what?  That the President is under an NDA with Canon and is testing a 35L MkII?   :-X

EOS Bodies - For Stills / Re: Obama using Canon!
« on: March 01, 2013, 12:00:31 PM »
Looks like a 35L, as you suggested.

EOS Bodies - For Stills / Re: Obama using Canon!
« on: March 01, 2013, 11:51:40 AM »
He looks uncomfortable, I think he does better in front of the lens.   ;)

Technical Support / Re: Teleconverter and DOF
« on: March 01, 2013, 11:45:29 AM »
Remember when I said the only two important things are actual apparent aperture size and subject magnification?
DOF is dependent on two factors alone, subject reproduction ratio and apparent aperture. The bigger either is the less dof you have.

"A TC does not alter the apparent aperture, it does alter the focal length. For the same distance shot using a TC will reduce dof, for the same framed shot the dof is the same."

So, you are saying that if you frame a shot with a 200mm f/2.8 lens, then put your 2x TC behind that lens and double the distance to the subject so the subject magnification (framing) is identical, you will have the same DoF in both shots?  If that's true, the 2x TC turned a 200mm f2.8 lens into 400mm f/2.8 lens.  Unfortunately, my 2xIII doesn't do that.  Where can I get one of your magical teleconverters?  :P

EDIT:  I was really hoping my 600/4 could be turned into a 1200/4 by adding $300 of glass to the back end.  Damn, foiled again.   ;)

Technical Support / Re: Teleconverter and DOF
« on: March 01, 2013, 11:36:10 AM »
It's a confusing issue, to be sure. Partly, that's because of semantics.  There are lots of statements to the effect that "a TC doesn't affect the DoF."  That's true, if you account for the effects of a TC on both focal length and f/number. In other words, a 200 f/2.8 lens with a 2x TC becomes a 400mm f/5.6 lens.  That 200/2.8+2x combo will have the same framing and DoF as an actual 400mm f/5.6 lens, it will not have the framing of a 400mm lens with the DoF of a an f/2.8 lens (if you want the latter, you've got to pay several thousand $$ more for an actual 400/2.8 lens).

Somebody posted to some other thread an online tool that graphed background blur as a function of focal length, aperture, and distance from subject. Wish I could remember where it was, but the uptake is that a 50mm f/1.0 will have the most blur for things near the subject, and a 400 f/2.8 will have orders of magnitude more blur for things past about ten feet or so. So, if you want the least-recognizable background possible, speed wins for tight spaces but focal length blows it away if you've got the working distance.

True, but as the OP pointed out earlier, DoF isn't an exact conceptual opposite of OOF blur.  DoF defines what is in sharp focus, and that's independent of the distance between the subject and the foreground/background.  OOF blur is critically influenced by distances between the subject and fore-/background.

Technical Support / Re: Teleconverter and DOF
« on: March 01, 2013, 10:55:21 AM »
Look use this simple example.

100mm f 2 @ 20ft has 1.1ft dof.

Put a 2xTC on above for a 200mm f5.6 @ 20ft and you get 0.54ft dof.

The focal length increased but the actual aperture size (not the f number) stayed the same, so you get less dof.

Sorry, but a 100mm f/2 lens with a 2x TC would be a 200mm f/4 lens, not f/5.6.

So, let's repeat your example with correct math (and a specified sensor size, since that does matter):

100mm f/2 on FF at 20 feet, DoF = 1.54 feet
200mm f/4 on FF at 20 feet, DoF = 0.75 feet

Now, back up so the shot with the 2x TC has the same framing as the shot without the TC:

200mm f/4 on FF at 40 feet, DoF = 3.07 feet

Plug those numbers (100/2, 200/4, 20 ft vs. 40 ft) into your DoF calculator of may get slightly different absolute values (different calculators make different assumptions about CoC, print size and viewing distance, which affects the calculated DoF values), but the relative differences will be the same. 

Compared to a bare lens:
  • Adding a TC and shooting at the same distance means shallower DoF (and a smaller FoV
  • Adding a TC and moving back so the FoV is identical means deeper DoF

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