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Tom_Kline

Member Since 07 Nov 2004
Offline Last Active Oct 26 2014 11:34 PM
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Posts I've Made

In Topic: Canon 16-35 f4 L

26 October 2014 - 10:17 PM

Thanks for the images Thomas. By the looks of things it seems to be an improvement. How much though over the 17-40mm? Is it worth the upgrade?

My upgrade path was from the close-focusing Sigma 20/1.8 and 28/1.8 lenses. It is worth it thus far for these advantages: one lens instead of two, faster focusing, and weather sealing. The Sigmas work rather well optically when housed for under water use. I have no personal experience with the 17-40.


In Topic: Canon 16-35 f4 L

25 October 2014 - 12:08 PM

Here is another shot. I set up the housing with the smaller (than Superdome) Wideport as I was expecting shallow water. It turned out that I probably could have used the Superdome at this spot ;->>. The curvature of the virtual image is related to the dome radius of curvature. The Wideport has an obvious smaller radius than the Superdome. Seacam does not specify either. I used the same port extension as above, 65mm, and shot at f/8 with flash. One pic is of the whole frame and there are two blow-ups. One shows the eye in focus but not the tip of the snout whereas sediment behind the fish (~ 0.3 to 0.5 m) is sharp. The other blow-up is from the right side. One can see a zone of sharpness running diagonally from lower left to upper right. This is due to effects of the image plane falling behind the concave virtual image - the peripheral parts of the image are back-focused. One can get away with using a smaller dome like this but one must try to have the subject fit the in-focus zones if possible.


In Topic: Canon 16-35 f4 L

25 October 2014 - 11:30 AM

It looks like this lens has the same minimum focusing distance as the 16-35/f2.8 ii and the 17-40/f4, so I'd expect the performance related to the dome to be similar. Image quality of the lens overall does sound better though. Also, for underwater behind a dome f/4 vs f/2.8 doesn't matter much since you're stopped down so much.

Differences in flatness of field can make a difference. The virtual image is concave. If the the lens has a convex field it is problematic. Flat would be better than convex. Also the position of the entrance pupil can vary such that one lens will focus closer (when properly installed behind a dome port) than another in the same dome even if the minimal focus distance is the same.

The new lens incorporates new tech that will improve performance on both the long and short term - see lens rentals blogs on this:

http://www.lensrenta...zoom-comparison

http://www.lensrenta...-took-one-apart


In Topic: Canon 16-35 f4 L

25 October 2014 - 09:48 AM

I have been using this lens for several months, mostly with a Superdome. I have tried different port extensions. I started out with 55mm, the same as the 16-35 II lens. I also tried 60 and 65mm. There seemed to be a slight improvement with 65mm which is what used for the attached shot. I selected this shot for this thread because it has relatively bright Coho Salmon (with well delineated scales) that were near the edge and corner. Shot at 16mm and f/8 @ ISO1600 using aperture priority - available light only. One pic is of the whole frame, other pix are blow-ups of parts. The color fringing is due to the ripples on the surface refracting the sunlight.


In Topic: Wiring an underwater camera to external power?

25 October 2014 - 09:04 AM

This video might give you some ideas. It shows a Nikon D4 underwater housing fitted for external power, remote control, and Ethernet for use in the London Olympics:

It is possible to buy some of the wiring components from http://www.seacamusa.com/, see "prices" in menus.

I have used the SEACAM remote control components which use S6 connectors and cabling. The price lists indicate some new sizes but I have not seen any description of them outside of this video. S6 bulkhead fittings thread into the wall of a housing. I have seen S6 bulkheads with a nut so they possibly can be installed in an Ike housing with a plain hole.  http://reefphoto.com/shop/  also makes and sells some S6 items. FYI S6 cables have 6 conductors.