have you been to an optometrist lately? They can run a TEST on you and your eyes.
have you been to an optometrist lately? They can run a TEST on you and your eyes.
This from Wiki;
Rudi, how do you determine the nodal points for the exact lens/camera combination you happen to be using, and the precise positioning in relation to the dome, in order to extract maximum performance from the lens?The nodal points are widely misunderstood in photography, where it is commonly asserted that the light rays "intersect" at "the nodal point", that the iris diaphragm of the lens is located there, and that this is the correct pivot point for panoramic photography, so as to avoid parallax error. These claims generally arise from confusion about the optics of camera lenses, as well as confusion between the nodal points and the other cardinal points of the system. (A better choice of the point about which to pivot a camera for panoramic photography can be shown to be the centre of the system's entrance pupil. On the other hand, swing-lens cameras with fixed film position rotate the lens about the rear nodal point to stabilize the image on the film.
Thanks Frazier, hence my question regarding aperture, although Pawel indicated it might be something else.Depth of field in Pawel's image Tom, congrats Pawel, the stills look great, will love to see some motion imaging.
You made some claims and comparisons of sharpness of various optical systems. When I questioned the basis of your comparison, you back off and say the sharpness is not relevant and further say that you did not have quantitative method of comparing them. Why do you bother writing about sharpness and comparing one optical system to another, then?
The main reason I use Red Epic is because I do care about image quality, sharpness and distortions and I want my lenses to resolve full image sensor and not introduce image distortions, aberrations or fuzziness.
You are incorrect about people not caring about lens sharpness. Lens manufacturers as well as most professional operators shoot charts and make measurements for very good reasons. If we can't measure it, we can't compare it or improve upon it.
It happens that I projected both and this is not the conclusion that I would make.
Both lenses comfortably out-resolve the Epic sensor on land at f/4.0. Nikon is obviously inferior in that it can not be opened to f/1.2, like Master Prime can. The Master Prime is optimised for maximum sharpness fully opened and outresolves the Epic sensor even at f/1.2 corner to corner and therefore I would conclude that as a land lens it is far superior. However, when placed behind a flat or dome port, things change dramatically. Neither 14-24 nor MP 14 can resolve the Epic sensor across the entire frame. The dome creates curved virtual image inches in front of the lens, which degrades performance to unacceptable (as in limiting) levels.
Nikonos 15 does not suffer from those limitations: it does not suffer from image plane curvature and doesn't distort or produce fuzzy edges at close focus range. It has been specifically designed to achieve maximum performance in water and at close working distances. It is the right tool for the job.
However, what I do find "antiquated" is putting a land lens behind an underwater port and expecting 4k or 5k performance. It just doesn't happen. You can't even achieve SD quality across the entire image frame and claiming it to be "tack-sharp" seems to me greatly exaggerated if not completely incorrect.
I'm looking for a dive mask for underwater work, wondering what you guys are using?
I have been using the "Aqualung Maui Dive Mask (Black)" last summer and today; the mask just seems to hold up. It keeps a clear image, has a decent FOV and tends to fog less than my more expensive Atomic Aquatics Frameless. I bought this single lens frameless mask (double the price) because I thought I needed to see everything and in clear (not black) to add extra peripheral view but the mask is always fogging on me and the nose fills with water too often. I also bought it because it's a super light weight mask, which is nice.
Do any pros dive with clear masks? I thought this would be the way to go, but the dark frame seems to direct my focus forward where the actions is.
I must have a weird upper lip or something because most masks leak at the nose on me, either that or do I need to shave prior to every dive? I could install a nose purge valve but shouldn't I look for a mask that just fits right in the first place?
Most of my work is free diving in rivers, steams. Any recommendations? Thanks
I use the Drager full face mask on my megalodon rebreather and it is amazing very comfortable.
Last edited by Ross Isaacs; 06-17-2012 at 10:45 PM.
I should have know this argument would ensue, but first, let me apologize if I misled you to think that I need you to "believe" anything I say. I don't. A few answers for you.
Shooting charts and putting lenses under demonstrable and repeatable tests is a proven way to measure lenses against one another based on their exhibited sharpness, etc. Nothing wrong with that, it is the way in which many people choose their lenses, especially when testing several of them for a particular use that requires a particular feature of the lens to perform at a certain level. Great. But, there are many other people that do not bother doing this, who will trust the images the lenses produce as all the proof they need. This includes highly successful people in Hollywood who shoot with multi million dollar budgets and whose films gross even more than their budgets.
I arrived at my conclusions by looking at the projected images and then saying: "Oh wow, that looks tack sharp from corner to corner". That's it. Not scientific enough for you? Too bad. I'm entitled to my opinion, which is all I've posted here.
I've seen the Nikon 14-24 projected on a huge screen against the MP 14, two projectors at the same time, same image side by side, in one of the biggest rental houses in Europe, which has those two projectors set up for such tests. To my eyes, the Nikon looked noticeably sharper, especially at the corners, than the MP, from f4 and upwards. It was also the consensus among the rest of the people attending the demonstration. The fact that the Nikon does not open down to 1.2 does not mean that at the same aperture values it could not be sharper than the MP. It appeared sharper to all of us.
The Nikonos 15 is DEFINITELY an antiquated lens, regardless of how good, and I agree it produces outstanding images, it is even by today's standards. But, it was built using technology, methodology and materials that have been since, far surpassed in quality. Several generations of lens making have come and gone since. That is definition of antiquated. Just as a sports car built in the 1970's is still fun to drive and fast, when you compared it to the technologies available today, you realize what antiquated and modern means. Thus, the quality, precision and coatings of the glass used on the Nikon 14-24 is far superior to those employed in the Nikonos 15, as are the precision of the methods used for its fabrication. Fact.
But, how then does the Nikonos lens still look much better than most, if not all, water corrected lenses behind a dome? The simple answer as you pointed out is that it is a system built from the ground up to compensate for, or eliminate, the problems the underwater medium presents. But in so building this system, Nikon simply took a 20 mm air corrected lens and built around it to eliminate the aberrations that water introduces. The solutions to this problem, though ingenious, are simple:
- use a dome that will precisely align with the lens' entrance pupil, so that nodal point is equidistant from dome center and sides. This will produce a a properly aligned image, though with softer edges since the image projected by the dome is still curved.
- Build the dome with variable thickness glass, such that thicker edges provide a magnifying effect and help render the softer corners sharper so they match the center. To that effect, the center of the dome is much thinner.
- Introduce corrective elements in the lens design that will further correct the aberrations and curvature of image so that final result is rectilinear and sharp from edge to edge.
That's it, is not rocket science. I believe, after carefully listening to the engineers working on this project that the most important element of all is the variable thickness dome. Again, as I once told you, open up one of those 15 mm lenses and measure the thickness of the outermost element, a dome, and you will see that the edges are much thicker than the center. That is 90% of the Nikonos' magic. I have done this when I accidentally cracked one of my 15 mm against a reef and took a peek inside. In fact, I have also with me the front element of a Fathom SWP 44C, the one made for the Sony EX-1 that yields about 115 degrees FOV sharp from edge to edge, and I can see the same thing. I don't have calipers with me right now, but the edges of that element have to be at least 15-17 mm thick, while the center cannot be more than 3 mm. I keep that lens around to show customers why we don't rent expensive optics unless one of our operators goes with it (it was, again, cracked by an enthusiastic rental shooter on a wreck dive) but I will be happy to send it to you for perusal if you so desire.
I don't know what else I can tell you, I'm sure you'll have retort, but I won't. I was merely trying to share my excitement for something I've seen that seems to solve the main problem underwater encountered by a lens, the 14-24, that on land is possibly the very best rectilinear wide angle ever made. I know I am enthused with the images I'm seeing, as would be many other people on this forum that, like me, go more on feeling than on numbers.
I want one of those domes ...
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