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herbko

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Posts posted by herbko


  1. I think David Hass mentioned though he uses it all the time and never really has a major concern with no seperate dials.

     

    It's certainly doable, but a hassle. How much hassle depends on the housing. I don't know how Dave's Ike housing handles it. It's a screw in, lock button in my Aquatica A300. To me, it's not easy to tell if it's in or out, and I usually end up having to turn the dial and see if it's the Aperture or shutter I'm changing and go on from there. It was a much bigger hassle in cold water where I have 3mm gloves on.


  2. Probably not soon since the 40D is so new. The next round will implement these things, seems to be Canon's trend with putting out the __D then shortly therefater bumping the Rebel up with some real new cool features which then wind their way back to the next __D about a year later. I think one of the big things is the body itself, I much prefer the layout of the larger body and being able to access things a bit more without menus. Though this new xSI is tempting. Wish it used CF Cards though

     

    Memory cost is so low, 8GB goes for well under $100, that changing formats is no big deal. You'll probably want a bigger card for the increase in pixels and 14 bits.

     

    For underwater use, smaller is good. The one thing about the all the Rebels control that's a pain is not having separate shutter and aperture dials. It's annoying above water and a real pain underwater.


  3. i'm not going to buy any of them so my input is moot. :)

     

    Of course what we say here is probably moot. It's a business and product decisions are driven by perceived demand.

     

    I think the reason DSLR housings are less refine is the product life cycle is much shorter than film cameras. There's a big premium in getting it out quickly as people rush to buy the new models, and sales will probably go to zero in a couple of years as that model gets replaced. There's just not enough time.

     

    People will have their favorite camera for their own reasons and ask for housings for it, but I don't think we'll see much support for most of the 25.


  4. Yes sorry was wrong it will give you 2x maginfication. Using Tele-extenders for macro are not an Ideal way to get true macro shots due to the way it magnifies flaws in the lens. Extension tubes are designed to preserve the optical integrity of the lens. However underwater the rules are a little different. Sorry for the confusion.

     

     

    I don't think you can generalize. I've seen reviews that claim the TCs are better.

     

    It's true that teleconverters can degrade the image, but extensions are not ideal either. Keep in mind that extensions moves the focus plane out of the range that the lens was designed for. The designers may or may not have paid any attention to the behavior of the lens at the extended focus distance. If you're really picky, you need to evaluate this case-by-case.

     

    In practice, macro shots are often stopped down to the point where the image is diffraction limited. In this case the limiting optical element is the hole in the diaphragm, and neither the TC nor the extension will further degrade the image.


  5. I'm siding with George on this one. The strobe manufacturers control one end of the connection and the housing makers the other. The two are different. You can't plug the strobe end of the cable into the housing. Although I've been careful and lucky enough to not have any failures to date, I find the housing end much more trouble to use and keep clean than the strobe end.

     

    There's no reason a housing maker can't come up with a reliable, easy to maintain connector on their housings and sell cables to connect it and Nikonos strobes. To me, it looks perfectly feasible for a housing maker to offer this as an option. I'd take a more reliable connector at the cost of replacing a couple of cables. In fact Ikelite offers this option.


  6. The biggest difference in going with a DSLR is that you're limited to one lens on a dive. There aren't any good zooms that'll let you shoot both wide and macro with one setup. You have to make a choice before jumping in. That's also the source of much of the increased camera maintenance. Battery life and memory capacity are usually enough for three to four dives. It's changing lenses that takes work. When I was at Lembeh and only shot with the 100mm lens, I usually only open the housing once a day.

     

    I think cameras have reached a point that the motivation for upgrades is much less than a couple of years ago. I've been shooting with my Canon 5D for a couple of years, and I have no plans for upgrading. I really doubt that Canon can tempt me with it's replacement.


  7. I think it would be very difficult to light a subject at 1:1 magnification on a 35mm lens. I found it not practical even with a 50mm lens. A 35mm lens was used in an old Nikonos 1:1 framer setup. Those who has seen this, imagine fitting a housing and port between the camera and framer and still get light on the subject. It'll be hard even with a custom port and ring flash.

     

    Consider instead the Sigma 24mm F/1.8 macro. I have one and really like it. It'll focus down to 1:2.7 magnification. I've toyed with the idea of using it with a 1.4x teleconverter behind a flat port. The combination will be the equivalent of a 34mm F/2.5 1:2 lens.


  8. Thanks for the info. I'll look up what Aquatica recommends for the 10.5mm and start there. I agree about the Auto/Manual focus selection. I plan on leaving it on Auto. In practice, for a lens this wide there isn't anything I can do in Manual that I can't do in Auto.

     

    So far I've been happy with the few top side shots I've taken with it. I got it used from the seller that James posted for about 260 songs, so it's not a big deal if it does fall apart.


  9. I appreciate that you have taken the time to learn all these formulas to explain the merits of a 35 mm sensor but I am a show me kind of guy and I have found that added DOF in macro and wide angle for underwater photography is a good thing not a bad thing. It is in fact the reason that medium format has limited use for underwater photography.

     

    I've never used medium format, but from what I've read, the problem of using it underwater is that the lens selection does not give it advantages vs 35mm. In my view, the same is not true of 35mm vs 4/3. I'll state my basic claim here again. If in the 35mm system you increase the focal length, f-stop and ISO by 2 you get the same image as the 4/3 if the sensor technology is comparable. For example, the 4/3 system would require an F/1.4 50mm macro to match the range of a 100mm F/2.8 in the 35mm.

     

    Yes. Usually more DOF is a good thing in macro. Because the diffraction of light though a small aperture limits the resolution, there's a trade-off between DOF and resolution. 35mm has better DOF than 4/3 at a given resolution. It's acheived at 2 stops smaller aperture. The misunderstanding in this debate is that it's not DOF at a give aperture that's important but what's achievable at a give resolution. Have you seen world beating DOF and resolution from the point-and-shoots with a much smaller sensor?

     

    The fact is that Canon, Nikon and Olympus don't all use the same sensor or the same sensor design. It appears from your comments that you would expect that if we both shot an image at F/8 1/125th at ISO 100 with cameras of the same MP count that your image would be four times better and could be enlarged four times larger without less of quality because your sensor is appox. four times larger. That is just not the case.

     

    No. That's not what I wrote. In this case, if the resolution is not limited by the optics, the resolution should be the same. However, the noise in the 35mm sensor will be lowered in proportion to area (4x) if the sensor technology is the same. There are no direct data available for any of current sensors. We can only estimate from the camera output after much signal processing. You can look at the noise and detail and see if there's noise reduction that destroys details has been applied and so on.... So it's possible to argue that Olympus has found someone to make a sensor for them that perform better than the one that Canon has developed. In my opinion, that's not the case.


  10. according to the DofMaster, at 2' and f2, I have a DoF of .03', 1.99 to 2.01 (must be some round off). At 2' and f22, I have a DoF of .31', 1.86 to 2.16.

     

    http://www.dofmaster.com/dofjs.html

     

    I posted something about this long ago starting with the Lens Tutorial in photo.net.

     

    http://wetpixel.com/forums/index.php?showt...amp;#entry80286

     

    Skipping to the bottom line it boils down to

     

    DOF = ( c N / M ) * ( 1 + 1/M )

     

    where c is the circle of confusion (about 0.03mm for FF), N is the F-stop, and M is the magnification ( Image size / Subject size ).

     

    If we only consider non-macro cases where M is much smaller than 1 then DOF is simply c N / M^2. The most confusing part of this equation is of course c, the circle of confusion. That's roughly the distance on the sensor over which the image can blur and still be consider in focus, and should scale with the width of the sensor. That is a sensor twice as wide should have c twice as big for the same image resolution, and also for that sensor M is twice as big which implies that N must be a factor of 2 bigger also for this sensor.

     

    Just checking with the DOF calculator you cited I get

     

    for the Canon 5D

    100mm lens

    f/16

    10ft

    DOF = 2.89 ft

     

    for the Olympus E-500

    50mm lens

    f/8

    10ft

    DOF = 2.94 ft

     

    The difference from complete agreement, I suspect, is due to the author of this site scaling by number of pixels instead of sensor width.

     

    Partly diffraction, as you say, but also partly that the lenses were cheap and hit confusion before diffraction, and partly that they are small and at some point a tiny hole is hard to make, even if with the rest of the lens geometry, it's only f8. And why go to f22 when they sync at 1/4000 and can compensate with fast shutter speeds for most of their users (with shaky hands).

     

    Actually, if you ignore diffraction a smaller aperture would mask the imperfections of lousy lenses more than a larger aperture. Also, if you look back, maximum f-stop( minimum aperture ) has gone from ~f/8 -> f/5 as they put more pixels into the same size sensor, so I think it's unlikely it's f/5 because they can't make smaller holes.


  11. I'm not going to debate the merits of choosing lenses on the basis of popphoto subjective tests.

     

    You are correct that proper exposure depends only on f-stop, shutter speed and ISO, and the FOV of the 50mm on the Olympus is the same as 100mm on a full frame. And yes, at the same f-stop the DOF of the 50mm is NOT the same as the DOF of the 100mm. The 100mm at F2.8 has a more shallow DOF, the 50 will have to be stop down to F1.4 to match that. Also, if the two cameras has the same number of pixels, the full frame can be shot at 2 f-stops higher before becoming diffraction limited in resolution. Ever wondered why the point-and-shoots have f-stops that only goes up to f5?

     

    As I mentioned in my responses to Roger's post. For the same FOV, DOF and light captured by the sensor. The full frame should have 2x lens focal length, 2 f-stops higher (smaller aperture), and shot at 2-stops higher ISO.

     

     

    Herb and James,

     

    Your to smart for me, all I know is that at F/2.8 with my 50 mm at ISO 100 I get the same proper exposure as a 105 mm on a 35 mm sensor at F/2.8 at ISO 100. I also get the depth of field of a 50 mm lens with the same angle of view of a 100 mm lens.

     

    The big diffrence and you are welcome to school me on this if you want is that the image quality from the Olympus lens seems to be better than from some other lenses.

     

    Example, These subjective Quality factor charts are from Popphoto, a magazine that takes 20+ times the ad dollars from Nikon and Canon as they do from Olympus. They bench test all lenses with the same type of sensor and run the results through the same processing, which means that all things being equal the results should give an idea of lens quality.

     

    The first chart is the Olympus 50 mm F/2 macro,$425. B&H, 24 degree angle of view.

    The second chart is the Nikon 105 mm F/2.8 VR macro, $740 B&H, 23 degree angle of view.

     

    Phil Rudin


  12. I'm going to stick to my guns and say that it is fair to compare a 300mm oly to a 600mm film lens, and in this case, it's not like adding a teleconverter: you double the mm only to get into the same nomenclature, you aren't really doubling the mm or halving the FoV, and you don't double the f stop in this case. A 300mm oly f2.8 is like a 600mm f2.8 for 35mm film.

     

    Of course your selection criteria is entirely up to you, and it's true that a 300mm oly will have the same FOV of a 600mm on a full frame. I'm just pointing out that at f2.8 it will have the DOF of a 600mm on a full frame at f5.6 and also the same is true of the total light captured at a given shutter speed. So, 600mm f5.6 on a full frame will match a 300mm f2.8 on an oly at any given shot. The full frame will have to be shot at 2 stops higher ISO. The net result is the same amout of light on the sensor, and if the sensor technology is the same so too will be the signal-to-noise at the sensor. Also the oly will reach diffraction limit 2-stops before the full frame for the same final output resolution.


  13. Correct scaling for the sensor size should be a factor 2 in focal length and 2 f-stops between the Olympus and the Nikon and Canon full frames. That will give the same DOF range and total light captured, which at the sensor level determines image quality. So an Olympus 300mm f2.8 should be compared to a full frame 600mm f5.6 which as far as I know does not exits.

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