Seacam SD and nikon 17-35 mm

Hi,

I am a little confused. In the Seacam portchart they advice for the Nikon D300 with the Nikon 17-35mm extensionring 55mm. Stephen Frink tested the nikon 17-35mm with the Nikon D3x and adviced the 45mm extension.

Does somebody use the Seacam SD with a D300 and 17-35mm and with what extension??

Rob

Rob - I have clients using pvl 45 and pvl 55. Truthfully, you won't see much difference on a cropped sensor camera like your D300. With full frame the offending corners would be revealed but the 1.5 crop is a bit more forgiving.

Having said that, it has been a few years since I ran those tests on the D3x, and as I personally shoot Canon have had no reason to revisit the data. But, I did query my teaching associate for my classes and he shoots d300 with superdome and pvl 45. His words: "It works great and is very sharp at all focal lengths"

10mm extra space in a port extension is a fair bit of upward torque with a superdome. Without appreciable resolution difference in the corners I'd personally opt for the shorter extension to enhance ergonomics.

thanks Stephen for answering so quickly

Can I just add in a few comments? The extension required to optimally align the dome port with the entrance pupil of the lens being used lens will vary and this variance will depend on the focal length to which the zoom is set and also its focus setting. Both of these have the ability to shift the entrance pupil's position and although the shift may not be much (a few mms) it can help explain why there may be varied recommendations. So a recommendation based on 'infinity' focus (underwater that is) and the widest zoom setting may well be different from the longest zoom setting and closest focus. Some lenses may not use a linear shift from wide to narrow field of view so may actually need greater or less extension applied at a mid focal length than at either end. So what I am saying is that using any one extension is inevitably a compromise and, depending on how a particular photographer most uses a specific zoom, may need fine tuning - fortunately possible using the 5mm steps in Seacam's Extension Rings, as 5mm probably (usually) represents the most viable step to adjust by in practice. For more info you can read some more here: http://www.underseacameras.com/Underseacam...Dome_Ports.html

Can I just add in a few comments? The extension required to optimally align the dome port with the entrance pupil of the lens being used lens will vary and this variance will depend on the focal length to which the zoom is set and also its focus setting. Both of these have the ability to shift the entrance pupil's position and although the shift may not be much (a few mms) it can help explain why there may be varied recommendations. So a recommendation based on 'infinity' focus (underwater that is) and the widest zoom setting may well be different from the longest zoom setting and closest focus. Some lenses may not use a linear shift from wide to narrow field of view so may actually need greater or less extension applied at a mid focal length than at either end. So what I am saying is that using any one extension is inevitably a compromise and, depending on how a particular photographer most uses a specific zoom, may need fine tuning - fortunately possible using the 5mm steps in Seacam's Extension Rings, as 5mm probably (usually) represents the most viable step to adjust by in practice. For more info you can read some more here: http://www.underseacameras.com/Underseacam...Dome_Ports.html

Thanks Paul. Very nicely stated.