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Tom_Kline

Member Since 07 Nov 2004
Offline Last Active Today, 11:42 AM
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Posts I've Made

In Topic: Seacam Seaflash 100D, powerful enough? Any experience?

17 May 2018 - 12:00 AM

Seacam did not say what caused the failures. Both were repaired under warranty.


In Topic: Seacam Seaflash 100D, powerful enough? Any experience?

16 May 2018 - 10:03 PM

I do not have the 100D but do have the other D models. I have used the 150Ds the most - mine are in both Canon and Nikon flavors but just one of each. I have used just one strobe with diffuser for many of my shots with no problem. Fisheye lenses used the most. Do not see a problem with the 100D other than that the LED display was left out and this is one of the nicest features of the 150D IMHO.


In Topic: Wetpixel's Nikon FX wide-angle lens review

07 May 2018 - 10:26 AM

The distance to the dome I was referring to is the subject to dome distance. The virtual image surface shape is a function of focused distance, only spherical at infinity. This is probably why small domes work for macro subjects where the dome is very close to the subject so the virtual image is flatter. Note that this thread is > 3 years old whereas FE question is new.

And for a subject at infinity the virtual images lies at a point which is 4 x the radius of the dome from the centre of the dome which is where the principal point of the lens should be positioned. This means that the centre of the mage is at 4R but because the virtual image is spherical, depending on the lens's angle of view, the edge of the image will be somewhere closer - exactly where will depend on its position and the dome's radius (radii) and thickness and refractive index - its complicated. But the camera lens is not much of a factor here because it can only image what it 'sees'. Its ability to do so will be dictated by the virtual image produced by the dome port and subject and any inconsistencies of the camera lens such as field curvature at closer focus. Its all a bit messy.

 

The 'less curved' dome idea is in effect the suggestion of positioning the camera lens closer towards the dome as opposed to ensuring it is aligned at the centre of the dome. You may want to try doing just this (should be easy enough). If I remember correctly, I think that you will find that it results in the trade off of reducing the field of view as opposed to doing what your diagram illustrates so is counter productive.

 

Sadly I suspect the 'filmdays' rule of thumb of 90 degrees being the maximum viably/easily correctable field of view still applies with dome ports though bigger does help .....

 

I still disagree about the unpredictability of lens performance underwater behind dome ports. Its lack of technical information which hampers prediction nothing else.


In Topic: Wetpixel's Nikon FX wide-angle lens review

07 May 2018 - 08:17 AM

The SD will likely be better and you will not need an extension ring.


In Topic: Wetpixel's Nikon FX wide-angle lens review

06 May 2018 - 02:13 PM

I have used the various Seacam dome ports with fisheye lenses, all but the relatively new CP. I have been too chicken or just did not want to waste a shooting opportunity to use the FMP on FF. I currently have my FMP dedicated to to my 1D3-4 housing with a 1D4 in it which is an APSH camera. This to use where it is too shallow to use the WP. In my experience the SD gives the best fisheye results even with just a lousy 12 MP on APSC as in D2X with 10.5 mm lens. I have found the WP to be OK on FF with the 16/2.8 Nikkor fisheye. Here is an example-- https://www.salmonog...arr/i-bm2qCBZ/A

You have a more demanding scenario with the D800 as I used a D3X for the shot.