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Posts posted by herbko

  1. Fred. Thanks for taking the time to share your experience. I agree with James. That post is an interesting article in itself.


    I've been using a Canon 100mm + 1.4x teleconverter and a Canon 500D (+2 diopter) in combinations for most of my shots so far. I think I'll get a set of extensions and try them out in the future.



    Starting thoughts. The theory. Any lens is capable of only so high a resolution at a particular magnification. I’ll use some theoretical numbers here to illustrate what I want to convey. Let’s say, for example, you have a Nikon 105mm f2.8. And that at your actual shooting aperture of f16, and at closest focus, 1:1 magnification, the lens is capable of resolving 200 lines per millimeter at the center of the picture. If you extend the lens out farther from the camera body using extension tubes or a bellows attachment to reach a 2:1 (2x) magnification, you are spreading that resolution of 200 lpm over twice the frame length and therefore your actual resolution, everything else being equal, is going to be only 100 lpm.




    It's true that there are optical limits that will limit resolution at high magnification, but I don't think the above is a good example of how that works. Taken to the other extreme your example would imply that a lens focused at 5 meters would only have half the resolution of the same lens focused at 10 meters.


    I came across this extensive test chart for Canon lenses used with diopters and tubes by Bob Atkins at photo.net awhile ago. It's very handy.



  2. That still gives a magnification of ~1.7x. Very good.


    Actual focal length at macro focus is complicated. In practice, it's really the working distance, front of the lens to subject, that's of most interest.


    While you're testing, please check the minimum magnification also i.e. what's the biggest subject that will focus.


    Thanks for checking this out.

  3. Herb, I was in the Similans Dec 05/Jan 06 and there was little damage noticed. There was maybe one minor site that showed some hard coral damage, but the marquee sites were pretty much intact.


    Thanks for the update. That's good news.

  4. Herb, if those are beautiful to you, then that is all that matters. On a personal level I don't find that any digital camera renders sunballs pleasing at all, let alone equal to film. My D2x s a nice camera, but I leave the sun out of almost all wa shots I make. Sometimes a little sunlight is worth the effort, but I always know a shot of a sunball will ruin whatever success I might have otherwise had with that image.



    Perhaps I haven't seen enough good film sunballs shots to be much of a judge. If you think they are inferior to film shots, I really would like to know the details and perhaps have something to work on the next time out. Which cameras have you tried to shoot sunballs with? It seems to me to that before making a statement like "digital can't do sunballs" one should have tried a wide range of cameras and techniques.

  5. Been out of Texas quite a while now Herb.


    Oops. Sorry. I blame it on this age thing.


    I'm talking about the guy that reminds you to take your laptop out of the carry case and tells you you need to take your shoes off. Or are we just overregulated and bossed around excessively here in the People's Republic of Oregon :D


    I do see that guy some of the times. In lots of cases, he's out at the line directing traffic, telling people which of the N lines to go to and not watching the input to the x-ray.

  6. I haven't been through LAX in a long while, (thank $DEITY), but in all the other airports I have been through recently there has been a TSA employee loading things into the xray machines and generally keeping the line moving... are you saying they have stopped doing that?


    Things must be different in Texas. :D


    I can't remember ever having someone else load my stuff into the x-ray machine.

  7. I'm not a fan of the TSA, but I wouldn't even consider this a TSA screw up. They have one staff member watching the metal detector and one watching the x-ray monitor. That should be enough to cover security. I don't think adding another one at the x-ray input to cover the one in a billion case that a baby gets put on justifies the cost.

  8. Hi Herb,


    I'm trying to wrap my brains around your comment above. When not using manual mode, the camera will compensate for a change in ISO by adjusting its shutter and/or aperture settings so that the "image strength" of the RAW file will remain similar. However, I'm pretty sure that on my Canon 20D, changing the ISO setting will impact the RAW file when using identical exposure settings in manual mode. Is the ISO 50 setting on the 5D an exception and if so, what is the point?


    Between ISO 100 and 1600 changing the ISO setting will change the gain in the analog amplifiers between the sensors and the analog-to-digital converter. It's good to set the gain ( choose the ISO ) high enough to use the full range of the analog-to-digital converter but not so high that the highlights get clipped. 100 to 1600 is the full range for the 5D. Both ISO 50 and 3200 just adds a tag to the raw file and changes the exposure. It's useful if you're shooting JPEG.

  9. By now means a brilliant software specialist but my 2 eurocents:


    the raw format of each camera is specially tailored at the brilliancy and idiosyncrasies of that particular sensor. I would say that transforming these data to a DNG would just be an extra computer step (in camera or at home). In my view it is better to convert the raw to enduse, rather then taking an extra step.




    16bit TIFF files are BIG. For example the raw files form my 5D are typically around 10 to 12MB the converted TIFF files are 75MB uncompressed and not that much smaller with LZW compression. That's a huge difference in disc space.


    I don't know this in great detail, but from what I've read, I think it is possible to preserve all essential information in converting to DNG. I think camera makers can adopt DNG without compromising image quality if they choose to.


    I'm keeping my raw files in the native format and not converting to DNG. Converting would limit my raw converter choice to essentially just Adobe, and I happen to like a least a couple of other ones better. I don't loose any sleep over the possibility that I'll not be able to find a converter for my current files in the future. For the worst case I have a copy of the source code for dcraw, but really doubt it'll ever come to that.


    The idea of a standard raw format in a good one, but I don't think that the major camera makers and the other raw converter vendor would trust Adobe enough to go along. Some do. For example the Pentax K10D has a DNG output option.

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