Jump to content

GetClose

Member
  • Content Count

    12
  • Joined

  • Last visited

Everything posted by GetClose

  1. After some time I have got an update from mantamatcher saying that one of "my" mantas has been identified. Now there is a documentation that this manta has been seen at Nusa Penida, Bali from 2013 till 2016: http://mantamatcher.org:80/individuals.jsp?number=INNLP0195A
  2. Due to my knowledge the non HSM version is a much older model with a closed focus distance of 50cm. So you need a diopter which will reduce your angle of view. This lens might have been cheep but it would not have been my choice (except here is another better non HSM version which I do not know).
  3. BS-Kinetics (www.bskinetics.com) offers external monitor housings. But I have no idea, how the connection to the camera works. See Accessory -> Housing Accessories.
  4. That's not easy to answer since I did not use any extension but a dome with specific length. I did try to measure the distance from the bayonet of the camera to the tip of the dome glass and got 145mm. The dome should have a radius of 80mm. So if the dome is exactly adjusted for the lens (no guaranty for that, but the results have been ok) the pupil point of the lens should be at 65mm from the bayonet of the camera. With this information your housing manufacturer should be able to provide a solution. In general you can say: R = Radius of the dome glass E = distance of the pupil point from the bayonet of the camera G = Distance bayonet of the camera to the bayonet of the housing L = Length of the port from bayonet of the housing till the the tip of the dome glass V = Length of the extension You have R + E = G + V + L and V = R + E - G - L Hope my English is good enough to describe it in an understandable way.
  5. Hi, I did use the HSM Version in the good old times with my F80 and I was pretty happy with this lens. You can avoid a diopter even with a small dome because of the close focus capabilities. But the zoom gear is a problem. You will not get anything from stock but you need a custom solution. My solution was this one: http://www.uwpix.org/viewtopic.php?f=56&t=2890 Today you will more look for someone who offers custom made solutions with a 3D printer. (like this one: http://www.uwpix.org/viewtopic.php?f=53&t=6184&start=34 ) But the diameter of this lens is pretty big, so you have to make sure that there is enough room for the zoom gear in your housing. Juergen
  6. Hello, I am not so super active here since I prefer a German forum, but here is something which might be worth your attention: During my last vacation I did attend a presentation on Mantas and current research activities to spread and migration of these animals. There is also a project and an associated website, for which I would like to make some publicity here: www.mantamatcher.org Each manta has a pattern of black spots on its belly, with which it can be uniquely identified. Matamatcher collects relevant photos of Mantas (Belly Shots) with the information when and where this photo was taken. Can you identify the same Manta on several photos , so you can say something about his movement in the sea. The more you know about Mantas generally, the better you can protect them, and know how to protect them best. It is, of course, the more pictures, the better. And now we come into the game. The mostly volunteer researchers can take of course only a limited number of pictures. But where will be much more images of mantas on the hard drives of various underwater photographers. So, if somebody here has suitable images, please feel free to upload them to Manta Matcher. No prize winning images are required. Just the belly should be clearly visible. I think this is a really useful contribution underwater photographers can make to explore and to protect the manta rays. Best regards, Juergen
  7. In Germany I am not aware of any housing manufacturer how offers a port for the Sigma 17-70 and if you have a look on the Ikelite webpage you find a prove that this lens is either wrongly positioned behind the dome or can not be used in its full zoom range [remark (18) in the port list]. The Sigma 18-50 is less extreme and offers the shortest focus distance of all lenses in consideration. And getting close is pretty important in under water photography . Cheers, Juergen
  8. Go for the camera with the biggest viewfinder. Since Olympus offers only a small sensor, the viewfinder will be to small. If you want to do real macro, it is useful to be able to focus manually. Beside a big viewfinder you need a lens for which Ikelite can provide manual focus gear. If you choose a port which is 12mm longer than required by the lens you can combine your lens with an achromatic diopter later on to get even more macro. This makes sense if you chose a lens with a focal length of 105mm or more. HTH, Juergen
  9. I am pretty aware of the difference between a diopter and a teleconverter. I am using both (seperate and in combination). Though this might not be the intention when using a diopter also a diopter changes the focal length . A formula like New FL = 1 / (1 / FL of the lens + 1 / FL of the diopter) is often quoted, but this formula is over simplified (it is indicating a diopter is always shortening the focal length). A more precise formula needs the knowledge about the position of the primary planes of the lens as well as of the diopter. Since these data usually are not available, just go for a practical test. My practical experience is, that the angle of view becomes smaler, if you combine a short focal length with a diopter. Cheers, Juergen
  10. A diopter also changes the focal length and the angle of view. In your case the focal length with dioptre becomes longer and the angle of view more narrow. If you remove the dioptre the angle of view becomes wider and the port or its sunshade might cause vignetting. Cheers, Juergen
  11. Hello, Beside my SLR I am using a digital compact camera (Olympus C4000). It’s a nice thing to play around with, but I am not so happy with the closest focus distance at the long end. Since I use this equipment as a second camera only I do not want to invest in close up lens which is designed for underwater use. So I consider to use a “land based†diopter lens. I am aware, the effect of this lens will be weaker by a factor between 3 and 4 underwater. I am more interested in the durability of this kind of lens in (salt) water. I have found some short information here from people using these kind of lenses, but nothing about the durability. The lens will consist of glass and metal (probably more aluminum than brass). Both should stand also sea water, especially if you do not save the grease for the winding. Does anybody here has experience with using land based diopters or also filters underwater and can share some experience about that? Greetings from Germany, Juergen
×
×
  • Create New...