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About DrMark

  • Rank
    Moray Eel

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  • Gender
  • Location
    Austin, TX

Additional Info

  • Show Country Flag:
    United States
  • Camera Model & Brand
    Canon G9 (still) & Sony A1-U (video)
  • Camera Housing
  • Strobe/Lighting Model & Brand
    Ikelite DS-160 x2 & Ikelite Pro-2800 x2
  1. I have this dome port on order, and am looking for the same solution. Can you tell me the deminsions of the port (I know it is 8" in diameter, what is the other dimension)? Thanks, --Mark
  2. My research has also lead me to the Sigma 8-16. --Mark
  3. I went to a local camera store yesterday and played around with the Sony a65 some. I was able to verify that it *is* possible to hold the focus on video when in auto focus mode. In the camera menu, you can map any of a number of functions to the AEL button. One of those features is "focus hold." As long as you depress the button, the auto focus will hold its current focus point. I wish it were a toggle, but this is better than nothing. So, if you see a whale swim by, you can hold down the AEL button and shoot away, not having to worry about the camera focus hunting on you. --Mark
  4. I wasn't so much wondering about switching between auto and manual focus, but rather just being able to force the camera to hold the current focus from within auto focus. So, for example, if I see a whale in the distance, and it happens to be in focus, I want to be able to turn off the auto-focus so that it doesn't continue to focus hunt. I think they call this "focus hold", but from the on-line documentation, it is hard to tell exactly what it does. --Mark
  5. How did you find the focusing with the A65 to work underwater? I have recently learned about some serious limitations with the A65 auto focus in video mode, and I don't think you can both manually focus and zoom in an Ikelite housing. The feature I'm most worried about is the ability to hold focus with video to keep the camera from hunting in poor visibility. I would appreciate any advice you can give on this. Thanks, --Mark
  6. To try to answer the original poster's question, there are tradeoffs with each frame rate you choose. As others have said, if you are shooting for somebody else, then they will dictate the frame rate. If you are shooting for yourself, then you need to be aware of some limitations in the camera. HD-SLR's have an upper limit on the amount of data they record per second (this is where you hear about AVCHD 2.0 28Mbps (28 million bits per second) and AVCHD 1.0 21Mbps). It is the camera's job to compress a 1920x1080x24 bit frame into a frame that can be recorded without exceeding 28 Mbps (which is just 3.5 MB/s). If you look at the raw data rate for 1080p30 (1920x1080 pixels * 24-bits color per pixel * 30 frames per second), we are talking about compressing 178 MB/s into just 3.5 MB/s, which is a little over 50:1 compression! Cameras have very sophisticated compression algorithms. The first thing they do is throw out most of the color information (which is why it is so important to white balance when recording video). After that, they do tricks like encoding only the parts of the picture that change from frame to frame. Keep in mind that in the end, the camera cannot exceed the data limit (28 Mbps, 21 Mbps, or 17 Mbps). If you have ever seen a sporting event on TV, when they show a bunch of fans jumping up and down and waving things in the air, the picture starts to break up into lots of blocks. This is what happens when the compression algorithm can't keep up with the amount of changing data from one frame to the next. Ok, so why did I tell you all of that? The different frame rates you asked about all need to get compressed into one of the bit rates of the standard. Canon uses 44Mbps for both HD modes (1080p and 720p) on their HD DSLR cameras, so the compression rates are the following (by video mode): 1080p24: 26 to 1 1080p30: 32 to 1 720p60: 29 to 1 So, as you can see, the different video modes require different amounts of compression. If the scene you are recording has very little fine detail or motion, then you probably won't see any difference between the formats (as far as loss of detail due to compression), but if you are shooting something with a lot of detail and a lot of motion (say a bait ball), then the higher the compression, the more loss of detail. What you have to do is shoot some scenes in the three video modes and watch the playback to decide if the loss of detail is visible or not. The advantage of 720p60 is that you can slow it down 2 to 1 for nice slow motion shots of that bait ball. Of course, you have much less resolution (1280x720 vs. 1920x1024), but from what I have read, there isn't really more than 720p actual resolution in a 1080p recording from Canon cameras. Again, you need to do some test shots to see what you think based on what you shoot and how you display it. By the way, you cannot compare data rates across cameras because each has their own compression algorithm, and the quality of the compression is different. The current king of compression for consumer grade cameras is the Panasonic GH2 (when hacked). People have been recording at an astounding 190 Mbs, which for 1080p30 is a compression rate of just 7.5 to 1. Also, that camera has a very good compression algorithm, so it does a lot with those 190 Mbs. Of course, whether you need that high of a data rate depends on what you are shooting and what you want to do with the video you shoot. Here are two nice reviews of the video capabilities of the Canon 60D and 7D that I found on the internet. They explain a lot of the differences between video modes: http://www.imaging-resource.com/PRODS/E7D/E7DVIDEO.HTM http://www.imaging-resource.com/PRODS/E60D/E60DVIDEO.HTM I hope this helps. --Mark
  7. I love your photos. Excellent macro work and strobe placement. Did you shoot manual or TTL? How does the white balance work with the A65? Does it have "one-push white balance" where you provide a white reference, and push a button to tell the camera that is white? I ask because although I shoot raw for stills, I need a good white balance for video (it is just too hard to recover good color from compressed 8-bit 420 video; you have to nail the white balance in camera before compression). Also, did you have any problems with white balancing at depth? My current video camera is a Sony A1U (which is amazingly still for sale by Sony all these years later), and it can't white balance below 30 feet. If I try to white balance any deeper, the camera just flashes an error symbol. I work around this with a red filter, but that cuts light. Thanks, --Mark
  8. Thanks for posting your impressions. I'm trying to decide between a GH2 and an A65 (in Ike housing). Are there any negatives of the A64 that you think are relevant? --Mark
  9. Did you use a pre-production Olympus housing? I thought the housing for this camera wasn't going to be available until July. --Mark
  10. HDVdiver, In your experience, how much of a problem is this underwater? If it isn't a problem for me with my current (not high-end) video camera, will I not be bothered by it with the GH2 either? --Mark
  11. HDVdiver, Thanks for your reports on the GH2. I hope this question isn't too far off topic... Given your experience with the GH2, which housing would you recommend? I have been looking at the Nauticam and the 10 Bar. The difference in price is very substantial (the Nauticam is almost double the price of the 10 Bar). What makes the Nauticam that much better? Are there any other housings I should be considering? I have a pair of Ikelite 160 strobes with my current camera, if that would change your answer. It is a pity that Ikelite doesn't make a housing for this amazing camera. --Mark
  12. This seems like the ideal solution. If there is some way to limit the focus range to have the close focus limit be just outside of the dome, then the camera wouldn't auto focus on it. One of the appeals of the GH2 for me is the fantastic hack. I wonder if the firmware can be hacked to add this feature. I might have to make adding this feature a personal project (I'm a professional programmer, so I know my way around assembly language programming). What do you experts think? Would limiting the auto focus range resolve this problem? --Mark
  13. Could you please elaborate on this statement? What kinds of shots can you "nail" with a video camera in a good housing that you cannot nail with a video DSLR in a good housing? Thanks, --Mark
  14. Hi HDV Diver, I have been considering going with a hacked GH2 for a while. It is fantastic to get some feedback from someone with real experience with underwater video. Can you say a little more about the white-balance (limitations or abilities)? Also, for macro work, do you think the 45mm macro is any better than the 14-45 with a diopter? BTW, I also dove with those whale sharks in April 2011 from the Damai. It was a fantastic experience (and the Damai had 24 hour power 8-). --Mark.
  15. As blaisedouros correctly stated, white balance tells the camera what color is white. Since the color of light is a function of the amount of water the light has to pass through, you need to be careful of how you white balance. Here are some rules of thumb: Only white balance with your lights on if you will be illuminating the item to be videoed with your lights. During the day, you cannot do this with video lights at more than about 3-5 feet from your subject. The color of an object is a function of the *total* amount of water the light must pass through. So, if you are shooting a reef at a depth of 40 feet, and are 10 feet away from it, the total amount of water is *50* feet. If you are at 40 feet depth, and white balance against a white slate that is 1 foot away from your camera, then you are white balancing for 41 feet of water (40 feet from the surface to your slate, plus one foot from the slate to your camera), not 50 feet. This will leave you with a color cast caused by 9 feet of water. If the water is very green, then you will get a green image. If you white balance in the same situation (you at 40 feet deep, shooting a part of the reef that is 40 feet deep, from 10 feet away), and you white balance with your lights, then you will be white balancing through 2 feet of water (1 foot from your lights to the slate, and 1 foot from your slate to your camera), but when you shoot, the lights (at 10 feet) will not overcome the brightness of the sun, so you will have white balanced at 2 feet, but be shooting through 50 feet of water. What I do to account for the problem of white balancing against a slate at 1 foot, but shooting a reef at 10 feet is to have a slate with white on one side and light blue on the other. I use the white side for close-up work with my lights, and I use the light blue side for distance shooting. By white balancing against a slightly blue reference, I "fool" the camera into adjusting the red/blue mix a little to account for the extra distance the light has to travel from the reef to my camera. There are also green cards available for use in green water. --Mark
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