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drsteve

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Everything posted by drsteve

  1. You may be right about the fish id. I am certainly no expert. I thought they were skipjack tuna.
  2. One of my favorite dive spots on the planet is Roca Partida, which is part of the Revillagigedo Archipelago (sometimes called the Socorro Islands). When I was there last month we had ripping currents which make photography challenging. The upside is that strong currents sure bring in the sharks. Here is a short video I made while desperately trying to hold position. https://flic.kr/p/nvAqBR Enjoy, ...STeve
  3. One of the things that makes them look strange is their ability to suddenly switch directions and swim backwards. I don't know of any other creature that can do that.
  4. Hi All, I recently got back from a dive trip to Clipperton Island. One of the interesting things about this remote atoll is that Moray eels cover the reef and many are out free swimming during the day. They are completely unafraid and swim right up to divers. I put together this short clip of one of them. [VIDEO] [/VIDEO] Enjoy,
  5. Last month I did a great trip to the Revillagigedos (Socorro Islands) and Clipperton Island aboard the Nautilus Explorer. On a late afternoon dive at Roca Partida it was clearly dinnertime as the big fish started striking the small ones. First the Sharks came in, then the Wahoo, then big Yellowfin tuna, and finally Dolphins. Here is a photo from the beginning of the feeding frenzy with Galapagos and Dusky sharks pursuing a big school of tuna. Awesome. Dinner time at Roca Partida by - drsteve -, on Flickr
  6. Last month I did a great trip to the Revillagigedos (Socorro Islands) and Clipperton Island aboard the Nautilus Explorer. On a late afternoon dive at Roca Partida it was clearly dinnertime as the big fish started striking the small ones. First the Sharks came in, then the Wahoo, then big Yellowfin tuna, and finally Dolphins. Here is a photo from the beginning of the feeding frenzy with Galapagos and Dusky sharks pursuing a big school of tuna. Awesome. Dinner time at Roca Partida by - drsteve -, on Flickr
  7. I have a Lifeline and the thing I like about it is that it allows you to communicate directly with vessels in the vicinity. All satelite based systems alert an operations center that then has to coordinate a rescue. That may work great when you are in a developed country with good search and rescue infrastructre, but I am skeptical about how well that works in many of the remote locations that divers visit. Do you really think that a satellite operations center in Nebraska will be able to communciate with a panga in Indonesia that happens to be a mile from you? The advantage of VHF solution + GPS is that it will work everwhere there are marine radios (i.e. everywhere), even if they are ancient. That being said, I have only used my Lifeline for "radio check.... radio check..." :-)
  8. That is a good question. A few years back I bought the Aquatica service kit and replaced all of the o-rings in my 5D housing. It isn't particularly hard but you have to be meticulous. The buttons use x-rings and I damaged one during the service. Since the kit only gives you the exact number that you need I bought a bunch of spares from Mcmaster-Carr. X-rings only come standard in Buna-N and Viton. I am pretty sure that they use Buna-N but both materials are fine for use with silicone oil. Even so it would be prudent to check them periodically. A safer alternative would be to pack some of the Christolube into a gluing syringe and squirt the outside of the button seal with extra grease.
  9. After every rinse, I use a Rocket air bulb to quickly blow out the water from the buttons. Next to each button is a small access hole to let water in and out during actuation. A quick puff of air gets 90% of the water out. The less water left in the hole, the less residual salt will be deposited when it drys. I also blow water out of the gap between the back plate and the housing. I then towel dry everything. The more water you get out, the less likely you are to drip when you open the housing. If I am not diving for a week, I usually remove the ports and the back plate. I always remove the strobe cables and dry the connectors because they are prone to corrosion. Diggy, thanks for the silicone oil tip. That sounds like a great idea.
  10. The rule of thumb for static face seals is to design around a nominal 20-30% compression with a worst case including tolerance stackup of >10%. Reciprocating seals on shafts (i.e. buttons) are typically designed around 15% compression with a minimum compression >10%. It varies somewhat for different materials. I measured my 5D housing since it has a traditional rectangular o-ring groove. The vacuum system is on my 5D3 housing which uses a dovetail groove. The calculations are a bit tricker for the dovetail, but I pump my housing down by 10inHg = 4.9psi. The cross sectional area of the rear door is roughly 50 in^2, so the vacuum is applying an additional 250lbs of force. Jean said that they set the latches to apply 45lbs, so an additional 250lb should be safe ;-)
  11. Jean, you inspired me to measure my 5D housing to see how well it conforms to the standard mechanical engineering face seal guidelines. Attached is the face seal design from the Parker o-ring catalog. The first thing to notice is that it assumes sufficient clamping pressure that the surfaces are pressed together so that the two metal surfaces touch and the o-ring is completely trapped within the groove. My 5D housing uses a standard 1/8" ring. The terminology is unfortunate because a 1/8" o-ring has an actual thickness of 0.139 +-0.004. The guidelines specify that the groove should be between 0.101 and 0.107 deep, which would give a compression ratio of 20% to 30%. The width for a standard o-ring should be 0.177 and 0.187 to give room for the o-ring to expand laterally when compressed. The groove in the housing measures 0.100 deep and 0.136 wide. The depth conforms to the standard depth assuming enough clamping force to compress the two halves until they touch. However the cam latches do not provide enough force to do this. When closed, there is a gap of 0.032 so that the o-ring compression is only 0.008 or 5.7% This is seriously under compressed, which is the point I made in the original message. I believe that you test housings to insure that they seal reliably, however since the initial seal is seriously under compressed it will work only if everything is perfectly clean and greased and nothing gets bumped in the rinse tank. Of course everyone everyone should keep their o-rings perfectly clean and greased, but there are plenty of stories of someone getting a stand of hair or a piece of lint under their o-ring causing it to leak. The if o-ring were designed per the guidelines, it would be much more robust. A hair or a spec of lint wouldn't cause it to fail. The good news is that the vacuum system provides enough clamping force to make the seal much more reliable. ORD 5700 Parker_O-Ring_Handbook static seal.pdf
  12. Adam, you are partially right, but you have confused the hardness of the o-ring material (durometer) with the o-ring resiliance, which is the tendency to become permanently deformed. The durometer rating is related to the clamping pressure required to make the seal, whereas the resilience depends primarily on the material used and the percent compression. If you have enough clamping pressure (ie bolts) you don't need to use a soft material. For example Buna-N o-rings are inexpensive and have good resilience, which is why they are so commonly used. A face seal using a 70 durometer Buna-N o-ring with a 15% compression is good for over 3000psi without even trying. If you use bolts, you get plenty of clamping force. You don't need a torque wrench, you can simply tighten the screws until you hit the hard stop of the two surfaces touching. The problem is that the suitcase clamps can't do this, so the housing vendors rely on an incomplete face seal and let the water pressure complete the seal. To me this is a poor trade-off and explains the tendency for housings to flood in the rinse tank. Frankly, the pressures experienced in recreational diving are trivial for a good o-ring design, so unless the o-ring is physically damaged, issues like compression set should be almost irrelevant. If you are interested, there is more than you ever wanted to know about designing seals at http://www.logwell.com/tech/O-ring/Parker_Handbook.pdf I too need to give this thread a rest.
  13. No I didn't have a leak. When you pump it down, you only partially evacuate the housing. I started with a partial vacuum (-10inHg) and ended with the exact same partial vacuum (-10inHg). Voila!
  14. I am often asked by novice divers how do get into underwater photography. I tell them first become a good diver. If you don't, adding the complexity of underwater photography makes you a bad diver and a bad photographer. You can live with being a bad photographer, but not with being a bad diver.
  15. I don't want to be a shill for Backscatter, but I bought one of their systems and am very happy with it. It was a bit pricey but the peace of mind is worth it. Besides no one is suggesting that a vacuum system is a substitute for regular maintenance and careful inspection during assembly. Being able to measure the housing integrity sure beats looking for bubbles in the rinse tank. It also solves one of the things that has bugged me about my housing for years. That is that the main housing o-ring is intentionally under compressed by design. If you go to any o-ring catalog or consult the Machinist's handbook, there are very clear design guidelines that date back nearly a century. Face seal o-rings are supposed to be clamped tightly enough that the two metal surfaces come into contact, with the o-ring trapped in the groove. Every housing I have seen violates this design rule. I believe that it is because the clamping force required for such a large o-ring would require bolts, and housing vendors perceive that this would be too annoying. Instead, for convenience, they use suitcase style cam-latches, which cannot provide enough force to complete the face seal. That is one of the reasons there are so many floods in the rinse tank. An under-compressed o-ring seal can flood when bumped. Most housing vendors explain away this design decision by saying that the water pressure causes the housing to "seal better" when you take it diving. This is certainly true, but it is really an acknowledgment that the seal is marginal at the surface! Perhaps someone can correct me, but I think that only Hugyfot uses bolts instead of suitcase clamps. Another benefit from a real face seal, is that if you shore dive with your housing (which I rarely do), the gap between the two surfaces can allow sand to enter. It doesn't necessarily compromise the seal, because it is outside the o-ring, but as you descend, it gets ground into the surface as they are pressed together under pressure. The vacuum check system solves this problem. The partial vacuum provides the additional pressure to complete the face seal. It also locks the ports. I love it!
  16. Yesterday was Coastal Cleanup day, and the Paradise Dive Club cleaned up Tajiguas beach near Gaviota. Afterwards we had a shore dive at Refugio State Beach. I don't bring my big camera on shore dives because it is too easy to drop it in the sand. Instead I dusted off my trusty old Oly5050, which hasn't been in the water for around 8 years and brought it along. I was glad I did. I found this cute octopus munching down on a clam that he had recently caught. The octo seemed to pose for my camera. I love the way his siphon looks like a third eye. Enjoy. Octopus on a Half Shell by - drsteve -, on Flickr
  17. I think I used two packs of 4 segments. I put three on each of the 12" strobe arm segments and one on the 8" segments. I have been very happy with them and as far as I can tell they haven't degraded at all. BTW, I found a photo of my rig showing the Stix. Enjoy. Me at San Clemente by - drsteve -, on Flickr
  18. I used to use a DIY PVC tube system. It worked fine but they didn't give that much buoyancy given the extra bulk Me and my camera by - drsteve -, on Flickr but I switched to Stix floats and have been much happier. Since they are Divinycell foam, they are slightly soft and don't bang around as much as the PVC versions. Sorry, I don't have a current pic of my camera. The Stix floats work great and are pretty inexpensive, but if you want to DIY, you can always buy your own Divinycell foam
  19. Nice Wolfie. I'm glad you had a good trip. I have done this trip twice, once on the Nautilus Explorer and once on the Swell, and I wouldn't mind doing it again. People look at me strange when I talk about going to Alaska to go diving, but it really is a special place to dive.
  20. I am happy to report that the vacuum system worked as expected. I pumped the housing down the night before the dive. When I got home the housing was still under partial vacuum. The dive itself was fun, although it was dark and the vis was pretty low. You can check out the images at: BTW, I tried out the Magic Lantern dual-iso imaging. It is AWESOME. Here is a sample. http://www.flickr.com/photos/drsteve/9558840145/ Enjoy,
  21. I just bought the new Backscatter vacuum check system for my Aquatica 5D3 housing. It was trivial to install and I feel a lot better knowing that my ports won't fall off in the rinse tank (which happened with my original 5D housing). When the system is pumped down, not only do you KNOW that the system is sealed, you CAN NOT remove the port or the back panel until you crack the vacuum. I will take the newly installed vacuum system for its maiden dive this weekend on the Yukon in San Diego.
  22. I only post low resolution images (800x600) and watermark the upper left corner. It detracts from the images, but at least it means that if stolen, they can only get the low res versions. I recently had one of my more popular non dive related photos scraped from Flickr and used as advertising for a for-profit Facebook page. They didn't even bother photo-shopping out the copyright notice. On Flickr it has around 10k hits. Facebook doesn't share hit counts, only "likes" and "shares". The for-profit site had over 22k "likes" and 2.5k "shares" of the page with my image. If you assume that only 1 in 10 hits on Facebook results in a "like", then this image has 200k+ hits, possibly more. I sent Facebook a take-down notice which they complied with, but the for-profit site had no penalty other than they got to use my image for free for as long as it took me to notice the violation. I recommend using a tool like TinEye to look for copyright infringement. I was a little surprised at how many of my images have been scraped and used without my permission. You might be surprised too.
  23. Just be glad that you weren't distracted by the camera and missed a latch on the rebreather. That could have made for a much worse day.
  24. I have a similar problem. Not only could I see the reflection of the front of the lens, I could read the text engraved on the front black face. I used a Sharpe marker to blacken the text, which helped a lot. I also plan on taping a small donut piece of black velvet to the front to further darken the surface.
  25. Sorry, since I am not a Nikon shooter, I don't know which tele would work best with the Tokina, but be careful with teles under a dome. They move the nodal point outwards and unless you have the right extension ring you will get soft corners.
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