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DirkG

Member Since 19 Jan 2009
Offline Last Active Jan 11 2010 02:00 PM
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Posts I've Made

In Topic: Sardine Run 2009

11 January 2010 - 06:01 AM

Phil

Great report and nice photos

In Topic: S&S NX Compact dome port

16 December 2009 - 12:04 AM

This question seem to solicit some ambiguous answers.

One need to calculate the extensions required. The dome diameter at the base is 145mm with a rise of 47.5mm.
The calculated radius of curvature of the dome is thus 79mm. (sorry all calcs were done in metric units Imperial has gone out of fashion in the 60's in SA)

You have to use the lens field of view and front element diameter to calculate the nodal point of the lens.

at 17mm the Canon 17-85 IS EFS lens have a nodal point at 62mm from base (If the Sigma is of the same dimensions the values should be similar)

The calculated extension length for my Housing (S&S DX30/60), Camera (D60 or 30D) and lens combinations ( Canon 17-85 and Sigma 10-20) is 49mm. In our conditions the 10-20 will probably see little use.

In my opinion the nodal point is more important in limiting aberrations at the short end of the zoom but less so at the long end.

I hope you have some better idea.

Reef said to me I wood need the 40 for the 10-20 and the 40+SX extension for the 17-70. I did not get round to get the 17-70 we will see what the outcome will be.

Regards

Dirk

In Topic: My dome fell off

26 November 2009 - 07:47 AM

Paul
If you are still looking for a better option on the silicone sealant give "Sika South Africa" a call I am sure the technical department would be able to help. They provide most of the sealants to the motor industry.

Regards

Dirk

In Topic: Surface zoom/telephoto lens?

12 November 2009 - 08:55 AM

I would go for the 100-400 on the boat.

As far as safari work is concerned you can rent the long canon lenses in SA at reasonable rates.

The best guys I have had dealings with is Outdoor Photo in Pretoria.

http://www.outdoorphoto.co.za

In Topic: Sea&Sea MDX-D300

12 November 2009 - 06:23 AM

Could you get the knob removed without any damage