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lanierb

Member Since 22 Apr 2002
Offline Last Active Sep 28 2010 09:23 AM
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Topics I've Started

Correct diopter formula?

12 January 2007 - 09:22 AM

In the articles section there is an article by Scheunemann that lists the correct diopter formula as:

D = 100cm / 3.03*r

where r is the radius of the dome in centimeters. However, searching through the archives the following formula often comes up:

D = 100cm / 4*r

Which one is strictly correct? (I have a feeling the first one is correct and the second an approximation but I want to verify that.)

Lanier

Using EFS 60mm on FF cameras

06 March 2006 - 01:16 PM

I thought people here might be interested to know that you can use the EFS 60mm/2.8 on full frame Canon's via the EF12II extension tube with essentially no vignetting (that I can see anyway). I found this thread on another site:

http://www.fredmiran.../topic/360672/0

and then tried it myself on my EOS3 (film camera) and it worked great. In air this combination limits you to about two feet max focus distance, but perhaps more underwater? If you put it behind a dome you might even be able to focus to infinity, but that's just a guess. Anyone want to give it a try underwater? (I don't have a housing for my EOS3.)

Lanier

Diopter and image quality on wide angle zoom?

15 January 2006 - 05:28 PM

I've read through the archives and I'm a bit confused on the use of diopters with wide angle zooms. Specifically, I'm thinking of using one on a Canon 16-35 with an Ikelite housing. My reason for wanting to do so is to reduce the minimum focus distance. Here are my questions:

1) According to the formula on the wetpixel dome theory page, I should be using a 4x diopter with the Ike 6" dome. My question is: will using a high quality diopter significantly influence image quality, and will it make it better or worse? Also, would a 4x be better/worse than, say, a 2x?

2) My second question is more technical, and less important. Does using a diopter change the properties of the lens in such a way that a different amount of extension should be used on the dome port?

Thanks for the help!