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herbko

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Posts posted by herbko

  2. Posted

    Wow - A black frogfish you can actually see! Cool.

     

    Alex

     

     

    Thanks Alex. This is one of my favorite shots from the trip. It was fairly deep and dark. I had to use high ISO and significant contrast adjustment with curves to get it looking this way. This is one where the 5D came in handy.

  6. Posted

    One issue that comes up frequently in discussions is that of diffraction, an issue that gets worse with small photosites (high megapixels, small sensors). Low pixel density FF sensors (such as the 5D, D3, D700) are the best to combat the loss of sharpness due to diffraction at small apertures. And the theoretical limits of systems are often quoted.

     

    For my own camera, an aged D2X (with high pixel density), a diffraction limit of F11 is cited (to quote Thom Hogan "On a D2x it seems to be around f/11. Up to f/11 and the D2x's acuity appears as you'd expect. Beyond f/11 and you'll likely start saying to yourself that the results don't look like you're getting the full impact of more DOF.").

     

    However, this is not what I see in my underwater images. And my only conclusion is that by the time you are shooting through port glass, murky water etc, diffraction is not the biggest of your worries. Even in the lenses sweet spot (F8-F11) you loose acuity for these other factors. So stopping down the issues of diffraction are not so significant?

     

    Yes. If dirty water is the limiting factor, getting closer is only way to improve resolution.

     

    I think the term "limit" in this context refers to the system no longer limited by the resolution of the sensor at F/11 and the lens is more of a limiting factor. The extra megapixels you got from upgrading your D100 is not going to improve your image. Of course if you have a murky medium, that could be the limiting factor rather than the lens.

     

    If stepping down to F/25 does not degrade the image then the sensor is definitely not the limiting factor, and as Craig mentioned you can probably get the same results with a D100 or D2H.

     

    If you know you are diving in these conditions, a wider lens may be a better choice. The image quality will be limited by how close you get to the subject. If the subject is still too small to fill the frame at this distance, you can crop and not lose anything compared to a longer lens that will frame fill the subject. The water is still the limiting factor. I think that's why the film shooter here in northern California used to prefer the 60mm over the 105mm.

     

     

    ... My standard image delivery size is 45x30cm (c. 18"x12") @ 300DPI, which is just under 19 megapixels. With a D2X (12MP) this requires up-rezzing (which is why I want a new camera), which I tend to do in one step in Lightroom, then re-sharpen, lightly in Photoshop (leaving final sharpening to client when image repro size is decided).

     

    I find this hard to understand especially in the context of the rest of the post. Are you saying you are going to buy a new camera, housing, and lenses if you change to FX, just to skip the step of upsizing, with no expectations of increased image quality?

  7. Posted

    I made this point before in the other thread. Within a 24M pixel FX sensor is a 10.7 M pixel DX sensor. If Nikon or Canon comes out with a ~24M pixel FX sensor camera in about the same body as a 12M pixel DX version, I don't see any disadvantage with the FX camera besides the cost.

  8. Posted

    Paul is right that recharging batteries in a small enclosed space is a potential hazard. Doing it inductively does not change that.

     

    Sure. It's a problem that can be overcome with the right set up and done carefully. However the underwater housing market does not have anywhere near the resources of the medical industry, and the end users are not trained technicians.

     

    We are still using electrical cables in a salt water environment to trigger strobes while we've had fiber doing 1 Gigabits/second running around the office for a decade.

  10. Posted

    Was the first octopus taken at night, if so it's probably Octopus luteus, or commonly known as a starry night octopus! They will often go a rather deep red colour too!

     

    Yes. It was a night dive. It didn't like having it's picture taken and reached out for it's hole after the second shot. I got in 4 shots. Here are the other 2. The one above with it's body elongated was the third where it was pulling itself into it's hole in the sand.

     

    IMG_9838.jpg

     

    IMG_9840.jpg

  12. Posted

    anyone know if this is still the camera that echeng uses? or has he moved on to the MKIIIs?

     

    the photos he took with his mkII are just amazing... i think that's the camera i want to get when i saved up enough money.

     

    Or do you guys have any suggestions for any cameras that are of equal quality?

     

    Eric put his mkII up for sale awhile ago and upgraded.

     

    There's a lot more to photography than just a great camera. If you have to wait and save for a 1DsII, you are probably better off getting in the water earlier with a lesser camera.

  14. Posted

    Actually it only goes to 11 :D

     

    I think James is mixing a couple of things we talked about at the Philippines.

     

    This Dpreview page

     

    http://www.dpreview.com/lensreviews/canon_...m_c16/page5.asp

     

    gives a good illustration of diffraction limiting image resolution. Slide the aperture bar from 11 to 16 to 22 and watch what happens to the lens resolution. At F/11 the measured MTF-50 is greater than 1500 line-pairs, better than the 5D sensor, it degrades continuously to 1100 at F/22. I typically try to stick to a minimum "real" aperture of F/22.

     

    The 11 and 13 came from a different different discussion. Canon lenses do not adjust aperture values for focus distance as Nikon lenses do. If you dial in F/11 on a Canon lens and focus down to 1:1, the effective aperture is F/22. I think they call it the effective aperture in the instruction that came with the lens, but that is really the real aperture. I think I mentioned that I usually have the lens dialed to F/11 and may go as high as 13 if I'm not focusing down near 1:1.

     

    As far as moving back to get better DOF, you're sacrificing slightly more resolution that way than using a smaller aperture. It's not a big difference and cropping is easier for a moving fish.

  15. Posted

    ... but since the Inon is slightly less powerful, you'll have to use a higher power on the Inon vs the Ike...

     

    The Inons are NOT less powerful. We've had this discussion before. Every test I've ever seen has shown the Inon Z-220/Z-240 to be brighter than the DS125, including the reference in this thread you started.

     

    http://wetpixel.com/forums/index.php?showtopic=20722

     

    The DS125 consume more electrical power but the Inon Z240 is brighter. The key is the light color output. The redder, "warmer" Ikelite source is much less efficient in converting electrical power to light.

     

    Personally, I prefer the Inons. I'd dump the old Ikelite strobes for a new pair of Z240.

  17. Posted

    Hi Guys,

     

    Has anyone heard from Chris (UnderwaterPhotoNewbie) lately?

    I have sent him a few PM's and no reply as yet?

    Seems as if he hasn't been active on the forum for a while either... ;)

     

    Bruce...

     

    Maybe he just upgraded his "Newbie" status. :)

  23. Posted

    But at what point? - I had previously read that the 'race' would stop at 12-15MP due to some of these effects - and here we are at 18-24.

     

    So where does the practical end lie ?

     

    Given the lens issues coming into play I assume that growing the sensor size >FF is not on?

     

    Paul C

     

    There's no disadvantage in having a larger sensor of a given pixel density that uses the same lenses except for the more difficult shutter design. Canon has been selling FF for 5 years so I would consider it "on".

     

    Do something similar to what I suggested for Phil, go to

     

    http://www.dpreview.com/lensreviews/nikon_...r_n15/page5.asp

     

    and bring up the comparison for the same lens shot with the D300 and look at the results at F16 and F22. At larger aperture the 12M pixel D3 is the limiting factor. I wouldn't trust the accuracy of the part of the chart that is at or above Nyquist except that being above it indicates that the sensor is limiting the measurement and the lens is better than that.

  24. Posted

    The reviewers at slrgear explicitly states that the scales on their charts do not give absolute resolution and should not be used to compare different formats.

     

    Dpreview does give measured resolution. This is new and they don't have very many tested, but there are enough to see the effects of diffraction.

     

    For a graphic demo have a look at the Nikon 70-200 FF review resolution chart

     

    http://www.dpreview.com/lensreviews/nikon_...r_n15/page5.asp

     

    and use their "compare" feature and bring up the only high end Olympus lens tested, the 12-60 and watch the resolution fall as you scroll the aperture from F11 to F16 to F22. Adjusting for the 4/3 vs 3/2 form factor, the Olympus lens clearly only has about 1/2 the resolution of the 35mm lens at F22. This Olympus lens cost $900, not cheap glass.

     

    Diffraction is actually fairly simple to explain. No equations needed. Small apertures cause a slight blurring of the image on the sensor that is proportional to the F-stop: the blurring at F22 is twice that at F11 ... etc. If you are trying to get the same resolution from a 35mm sensor and a 4/3 sensor, the spacing of photosites on the 4/3 sensor is 1/2 the distance of the 35 mm photosites. The same blurring width covers twice as many photosites on the 4/3 sensor, and limits the resolution to 1/2 the value.

     

    Phil, I don't think your 50mm will do better than the 12-60 at F22. If you have both lenses do your own resolution test and compare it to what you get at F11 and F8.

  25. Posted

    With the lens set at close focus and using the 500D, you get about 6" working distance from the front of the lens - just about perfect! AF seemed to work pretty well.

     

    James

     

    I just checked the 100mm macro and got 7" working distance for the same magnification. Looks like the internal focus and the diopter shorten the lens to less than the focal length of the 100mm at this magnification.

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