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Posts posted by segal3

  1. Underwater photographers like to talk about using flash as fill lighting. But that is not really true. We blast it. Flash is our main lighting! And as such it means we don't have to think much about light. Whatever we aim our camera at - our strobes are pointed at too.


    Mildly off-topic for this thread, but since Alex brough up the idea of fill-flash, which is used a great amount in nature photography (topside), I figured it had some relevance...


    This is one of my few attempts at fill-flash underwater...my strobe batteries were just about dead, so it didn't put out as much power as I initially wanted, but the effect works nonetheless.




    From the Solomons...all I needed was a group of canoes on the surface and it would've been perfect :D


    ~Matt Segal

  2. snake oil I think,  Matt  san!  I notice that this "wonder" lens is not in your line-up;-)


    I'm but a mere student. :D


    Snake oil, hardly - it's proven topside. The one caveat about the lens is that it is not internal focusing, that is, the lens extends as you move towards 5:1 (5x lifesize)...this complicates port selection. I'm working on getting my hands on a copy to try and figure out the logistics.


    ~Matt Segal

  3. You misunderstand the purpose of the pellet.


    When batteries are charged or discharged, they have the means to emit small amounts of hydrogen gas (especially prevalent with lead-acid batteries). Normally it's not an issue, because the area the batteries are charging or discharging is not sealed. In underwater lights, however, that is not the case.


    You do not want gradual buildup of this gas, so the pellet removes the small amount of the hydrogen.


    I'm still confused why this was posted in DIY...


    ~Matt Segal

  4. Given the same f-stop but different lens (60mm vs 105mm) would the DOF be different for each lens?  It seems that my 60mm photos when compared to my 105mm have more of the subject and negative space in focus compared to the  105mm...


    I'll go with a simple 'yes, the DOF can be different' and let Herb elaborate :) Of course, sometimes the DOF can be the same for a given f-stop, if the distance is different.


    You ask this question without providing more specifics. It's hard to quantify beyond that.


    Here are a few semi-in-depth articles on what you're asking about: http://www.waynesthisandthat.com/dof.html , http://www.luminous-landscape.com/tutorial...eries/dof.shtml , and http://www.naturescapes.net/102004/ps1004.htm . Hope this helps.


    ~Matt Segal

  5. Agreed. The batteries are the limiting factor. Unfortunately, I don't think any of the Canon DSLR's can charge the battery thru the camera. I would consider making the mod to the housing to do that and download if it could be recharged.


    On the contrary, for the current line of dSLRs, I hardly consider the battery to be a limiting factor. In P&S cameras, yes, they have to be changed after a dive or two. However, (at least with my 20D) I can get more than a full days worth of shooting (5+ dives) on a single charge. Stated specifications for the 20D battery is something like 700 shots/charge.


    On a liveaboard, I download after every dive. If I continue to shoot with the same lens, I am able to download my photos five times without ever having to open the housing (with the USB modification I made to my housing). Even if I do have to change the lens, I can remove the front port and switch, and not have to deal (additionally), with the main housing seal. I open the main housing seal once a day (at the end of the day) to swap batteries, and then it's sealed for another 24hrs. In terms of increasing reliability and failure protection, this is an ideal solution.


    For reference, here's a page on the modifications: Adding USB Connectivity to your U/W Housing


    ~Matt Segal

  6. I tried to go to Matt's site but got an error that it could not find the default language eng when I was looking at the galleries. Does anyone else have this problem?


    Sorry about that - my host has been working on some of the php/mysql database backbone over the last week or so...everything should be alright now :unsure:


    ~Matt Segal

  7. In that case, the lens and camera are mounted to the housing and the buoyant force from the port can actually be held DOWN by the lens.  Weird, eh?


    True, it is that case with the 100mm macro with my setup. Then, however, you not only have to worry about stressing the port, but putting a lot of force on the lens mount :unsure:


    ~Matt Segal

  8. Because my Seacam uses a very robust thread mounted port, I wasn’t worried about the strong buoyant force popping off my macro port underwater. This may be a concern for others though, so take this into consideration if you decide to put buoyancy onto your rig.


    This has been in the back of my mind since you originally mentioned the buoyancy collar, so I'm glad you at least mentioned it.


    Keep in mind that just about every flat port has a great deal of buoyant force, regardless of whether or not there's a buoyancy collar on it, so I'm not sure what the addition might do. Generally, to minimize chances of ripping the port from its mount, I suggest trying to keep any additional buoyancy as close to the mount as possible (less torque).


    I do like the results however. Nice work.


    ~Matt Segal

  9. Given a perfect optical lens, a camera captures the most resolution (resolving power) when the aperture is wide-open


    Not true

    I have to repeat that this is in fact true. However, given that we don't have perfect optical quality lenses, more times than not the best lenses have a resolving power peak around f4-f5.6 and the worst lenses have a peak around f8-f11. After that, you're on the way to serious diffraction on a cropped-sensor dSLR.

  10. To clear up some ideas being thrown around here...


    Given a perfect optical lens, a camera captures the most resolution (resolving power) when the aperture is wide-open, and the least resolution (losing inherent sharpness and ability to see detail) when stopped down, due to diffraction and the fact that you're taking a picture of a scene through a tiny hole (as compared to a larger one that will allow more light through, etc).


    Now, when given a real-world lens, the same applies, but you are limited by the lens at the widest apertures (look at MTF charts for the variances). This is why it is usually taught to stop down 1 or 2 stops to get the best balanced resolution (resolving power, ability to see detail) from any given lens and camera.


    When shooting at extremely tiny apertures, no matter what you do, even though you gain DOF, the amount of the image in focus will not be as sharp as that taken at a lower aperture.


    On a separate note, in response to Rand's comment about the Woody's diopter, I have seen no reports from any individual that the addition of Woody's diopter leads to any noticeable (real-world) loss of sharpness (resolution).


    ~Matt Segal

  11. Remember too, that the only reason that the entire frame is not blurry is because with those settings (F/29 or whatever translated is, F45?), when the flash fires in 1/400s or 1/500s or whatever it is, that that's where the majority of your light is coming from, 'freezing' the subject.


    But yes, I agree that a higher shutter speed is necessary regardless, and I merely theorize on why it worked period.


    ~Matt Segal

  12. For wideangle, I've used the 10-22 underwater and it's a fabulous lens.  Again, it's an EF-S so if you ever decide to get a full frame camera (like the 5D) then it will have to go.


    I don't know James. When I upgrade in a few years to whatever Canon has out then (FF), I see myself keeping the 20D w/ lenses as either a backup camera underwater, or for topside work. Small and light are two great advantages.


    ~Matt Segal

  13. But why not use the regular mount so it can project onto the 35mm sensor as in the 5D?  It seems that canon is saving itself a few bucks and not passing to the  consumer - can't think of any other reason...


    Because EF-S lenses use less glass (making them smaller and lighter) and project a smaller image circle...retrofitting them with an EF mount would be an exercise in futility, since the captured image would hardly fill the frame of a 35mm sensor...


    While we're at it, let's start using DX lenses on full frame Nikon cameras (guess those would be film though, no?). See my point?


    ~Matt Segal

  14. I have to say, while you captured the sunrays (and your thread should be titled w/ 'sunbursts', not just 'sunballs') well in each of the photos you posted, that especially in the second, third, and fourth examples you should be more than careful with the use of the Shadows/Highlights recovery tool, as they work to introduce the varied grey-cyan circular banding around the sun that is so noticeable. This is a result of the computer trying to interpolate from photosite data that really is not there (overexposed), even though it seems to be.


    The clearest solution for sunbursts (to reduce the possibility of having to make major adjustments that introduce this effect) is in fact to expose for the situation and not have to rely on computer manipulations. Often the banding will still exist in some lessened form, but it will not transition through as many as three different color ranges (each with their own range of banding) before reaching the white middle of the burst.


    Just something to think about...


    ~Matt Segal

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