2 replies to this topic

[AndreSmith]

I have never quite understood how one can judge the compatability of a given lens for a wide angle port. Sure it must physically fit in the port, it must be in the correct plane, it must be able to focus close enough to see the virtual image ( said to be bout twice the diameter of the dome port) and so on. Yet it seems to me that at the end of the day you have to physically test it underwater to find if it works.

Case in point. While I am anxiously awiting my UK Germany housing for my Canon 10D, I am trying to get some wide angle lenses together. I am thinking of getting the Sigma 15mm 2.8 fisheye lens but will it work? I have asked Uwe at UK germany but he is not sure. The larger dome port that I have ordered is known to be compatable with the Canon 20mm USM and the Sigma 14mm 2.8 EX HSM but there is no info on the fisheye. The physical size and specs are very close to the Canon 20mm : Lenght 2.9 vs 3.1 inches, closest focussing 5.9 vs 9.6 inches ( ie even closer than the 20mm) So I would hope that it will work but it could be an expensive mistake if it doesnt!

Any ideas?

[james]

Some things to consider when trying to work a wideangle lens into your system:

What is the minimum focal distance?

If it is too long for your dome, does the lens accept diopters?

Does the front element move forward and back during zooming and focusing?

What is the correct extension ring to yield sharp corners? Will corners be sharp at all zoom settings? Is one ring better for the wide end and one better for the tighter end??

Is the lens too wide to fit a zoom hear in the port you have?

Is a zoom gear available?

Can you do manual focus with the lens? Manual focus AND zoom?

How does the lens handle sun with respect to flare? Does the lens have a built on hood?

Some things to think about - all of which will affect your lens' performance.

I am pretty sure that the fisheye lens you mentioned will work with the UK-Germany 6" dome port.

Cheers
James

[AndreSmith]

Thanks James - I will soon find out!

While we are on the subject of port/lens compatability, let me run this one by you regarding flat ports:

When putting a certain lens in a flat port, apart from physically fitting in and being able to see the entire image, does it matter how much space is between the lens and the inside of the port glass? Does it significantly magnify and degrade the image if this distance is too long? Some lenses extend a considerable distance to get to their closest focussing position. In order to accomodate such a lens in a port there will be a large space when the lens is in the infinity focussing position. I have a Sigma 50mm macro that behaves like that. I am considering using it underwater as it has the ability to 1:1 macro as opposed tp the Canon 50mm whic h can only do half life size.