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Everything posted by Tom_Kline

  1. A lot to respond to, which is posted below in the same order as above. Karl, I do not have an UW photo specific website. However, if you follow this link, there are hypertext links to some UW pix of mine from Prince William Sound. http://www.pwssc.gen.ak.us/shepard/docs/re...dal/diving.html They are small pix, which is good given the relative slow connection between here and the outside world. I frequently tell people that Alaska is on the gravel road of the information superhighway! (we have a lot of gravel roads here). The vis was quite bad at the location, so they look better small. ReefRoamer, CeeDave is quite right, think of it this way: 1:1 means that if you take a picture of a 30mm long nudibranch it will appear 30mm long in the image (film or sensor) plane of your camera. With a 24 x 36 mm (i.e., FF) you will be able to fit it lengthwise with 6 mm to spare. Because the Nikon DX format (for example) is 23.3 x 15.5 mm, a 30 mm will not fit lengthwise into the frame at 1:1. At half life size it would appear 15mm long in the image plane and would be able to fit with room to spare in a DX frame. At one half life size on a FF camera there would be a lot of space around it. To make one print from each camera in such way that the nudibranch is the same size (in the print), you would have to blow up the FF shot by 1.5 times as much compared to the DX shot. The smaller the sensor size the smaller the field covered at the same reproduction ratio. Shoot a coin at 1:1 on 35mm film and it appears large; on 4x5 inch film it appears small (at 1:1). BUT, if you laid the negatives (or transparencies etc.) side by side on a light table the coin images would be the same size and would be the same size as the coin itself. There would be just a lot of wasted film on the 4 x5. James, The Exif info in Nikon View does not show the focused distance on D70 shots (just checked). My guess is that what you are seeing is the same distance that you can read off the lens barrel, which would be the apparent distance. The Rolleimarin housing focusing knob had two scales, one for apparent, and one for actual distance. I gather former was to for guess focusing (they made an external metal frame-finder for the housing) when not using the focusing screen while the later could be used with a measuring tape. Bandit, I gather that the 5050 is a fixed-lens camera. It may zoom to a shorter focal length to achieve macro-range focusing, which means very short working distances. The 1.33 mag means that you do not need to even focus as close as 1:1 as inscribed on a macro lens barrel to achieve 1:1, so would have more WD. Racked out to 1:1 (as on the lens barrel), mag is 1.33:1 at the same WD as 1:1 in air (this WD has to include the space inside the housing in front of the lens as well as the port thickness; so distance from front of the port will be a bit less). Craig, I think I just answered your questions (first question -see reply to Bandit; second, the reply to ReefRoamer). It is still 1:1, just the format (senor size) is smaller!!!!!!
  2. Actually, it is a first order approximation. The full formula from Mertens (1970) p. 148 is as follows: Apparent object distance = 1/RIw x actual distance in water + 1/RIport x (port thickness) + lens-to-port distance RIw = 1.33; RIport ~ 1.5 (glass) Remember to always be consistent with measuring units to avoid the NASA 'problem' I am not sure what you mean by a lens 'thinking'; maybe apparent distance, this is what one perceives behind a diving mask. Things appear closer than what they actually are. A problem for aiming a strobe as you know. T
  3. Remember from your OW training - it looks closer but the distance is the same. The focal length is magnified by the RI water, so the FL is now 60 times 1.33 (almost 80 mm) and the maximum reproduction ratio is now 1.33:1. Cheers! Tom
  4. "I have always been a big Hugy fan." Is this because they designed the first Hassy housing, which formed the basis for the later model that you have? BTW, the port threads of the Huggy are the same as the blue housings (I had both for a while). Also the lens gears are exchangeable across all models, even with the stainless steel EL housing. They different mainly by whether or not they have a 'see-through' slot, which does not affect their coupling functionality. Cheers! Tom Cheers! Tom
  5. I found their definition: "One item of scuba-diving equipment is defined as one scuba tank (empty), one scuba regulator, one tank harness, one tank pressure gauge, one mask, two fins, one snorkel, one knife, one speargun, and one safety vest." Without a tank and speargun then ones equipment does not fall within this definition. BTW, I have flown to Anchorage with just my reg (no other scuba gear) to have its annual inspection there, most recently last month, without any hassles from them. Cheers! Tom
  6. I assumed he was referring to rings that go between a camera body and lens because these are used to focus closer than what a lens can do otherwise. We have two kinds of extension rings in UW photography! Back when macro lenses only went to 1:2 one had to use an extension ring to go to 1:1 for example. Cheers! Tom
  7. I have done informal experiments that convince me that at least some fish respond to ones bubbles. On a trip to Oz where there are many small fish in coral heads it was very obvious that they would withdraw as I approached. Upon stopping I noticed they would go in and out of the coral heads according to my breathing. I purposefully modified my breathing pattern and they changed their in and out pattern accordingly. I have seen UW footage where the fish were exhibiting a similar behavior. I could 'visualize' the breathing of the cameraman by watching the fish in the footage, which followed a normal breathing pattern. I suspect just moving the exhaust to behind the head will be beneficial, especially with a 100mm and longer lens (still photography). The extension hose would probably be better - is this an old trick from the 1960's when 2-hose regs were popular? Cheers! Tom
  8. I don't think one can find an extension tube thin enough for the job. Nikon made a very thin one in the K set but it will not work with modern bodies. Zooming and floating/rear element focusing designs may be a further complication since focus is optical rather than simply a variable physical extension of the lens. Cheers! Tom
  9. My most recent trip on Alaska Airlines with scuba gear was in October - I was not charged anything extra but I did have the scuba and UW photo gear (strobes, trays, and arms) mixed in with the rest so as to spread out the weight to two bags. It was also in-state. There has been a 2- bag - 50 pound limit in effect on Alaska Airlines for some time now. Cheers from Alaska ! Tom
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