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Posts posted by segal3

  1. In less than a week's time, two significant tanker-based oil spills have been reported to authorities. The first news came Friday after a sinking in the Philippines, and on Monday, Japan's media stated that the tanker Bright Artemis had spilled oil after a collision with another vessel.

    A Japanese tanker spilled about 1.4 million gallons of crude oil in the eastern Indian Ocean following a collision with a cargo ship, the tanker's operator said Tuesday. Japan's Kyodo news service said the spill — which would be about 4,500 tons — may have been the largest ever involving a Japanese tanker.


    In a separate oil spill, the Philippines said that a tanker had sunk in rough seas Friday off the coast of Guimaras Island, about 312 miles southeast of Manila. About 528,000 gallons of industrial fuel was leaking from the accident, officials said.


    A central Philippine island province declared a "state of calamity" following what authorities called the country's worst spill.

    It is hoped that the nations affected move swiftly to contain the respective spills and attempt to minimize the damage to the environment.


    Related links:

    Large oil spill occurs in Indian Ocean

    Oil spill threatens Philippines

  2. Typical whip coral shrimp shot. I mean he was just resting after his afternoon snack. Sure was tiny though...




    I can't help but think that the underside of Pterois volitans' mouth is one of its least photographed areas. Then again, they didn't seem much inclined to show that side to me...




    Is it just me, or does the pattern look like a stylized question mark?


    Comments, critiques, whatever - I want to hear it :guiness:

  3. Magnification calculations are being based on the 22.5mm horizontal sensor size of the Canon 20D. Text follows images.




    Standard 100mm lens. Maximum magnification is 1:1. Focus distance at 1:1 is approximately 5.5" from front of lens.




    100mm lens with Canon 500D. Maximum magnification is ~1.32:1. Focus distance at maximum magnification is approximately 4" from front of assembly.




    100mm lens with 1.4x TC. Maximum magnification is 1.4:1. Focus distance at maximum magnification is approximately 5.5" (same as lens alone, standard property of TCs) from front of assembly.




    100mm lens with Canon 500D and 1.4x TC. Maximum magnification is ~1.88:1. Focus distance at maximum magnification is approximately 4" from front of assembly. The determined magnification does seem to show that the diopter magnification and teleconverter magnification are associative (~1.32:1 * 1.4:1 = ~1.85:1).


    What would be more interesting is performing this same exercise underwater to determine what changes - magnification or focus distances. Hope this helps slightly.

  4. The 500D is (I believe) an equivalent +2 diopter, and limits infinity focus to ~19" from the sensor plane.


    Topside, the 100mm+1.4xTC+500D diopter magnifies around 2:1, but with only a one stop loss of light. I'll try to check the closest focus distances for both setups (100+1.4x+500D and 100+500D) tomorrow. I've yet to try to measure how either the magnfication or focus distances changes underwater, if they do.

  5. Wikipedia has a somewhat helpful (well, assuming you know or can determine a few variables) formula for dew point (relating to condensation).


    Source: http://en.wikipedia.org/wiki/Dew_point


    Here is a formula to calculate the dew point in degrees Celsius to within ±0.4 °C. It is valid for


    0 °C


    0 °C




    T = temperature in degrees Celsius

    RH = is the relative humidity as a fraction (not percent)

    Td = the dew point temperature to be calculated


    The formula is:








    a = 17.27

    b = 237.7 °C

    ln is the natural logarithm.


    Current temperature when you seal the housing wouldn't be difficult to determine, but relative humidity could be depending on where you are.

  6. I am not sure what the air guide number is for a DS125, but I had guessed around 60. With two strobes that should have given me a decent exposure at f22.


    Many issues here. First is the guessing - I'll let that be :lol:. Second - were the diffusers on (lower power reaching subject)? Third - adding guide numbers is not as simple as GN#1 + GN#2. The formula is NewGN=SQRT(GN#1^2+GN#2^2+...). Even if the air GN of the DS-125 was 60 (ft), the GN of both of the strobes would be ~85 (ft), and at 6ft and f/22, would not provide a correct exposure.


    Hope this helps :D

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