dome port - pupil entrance

Hi,

I have been a dslr user for a short time and there are couple things I need ask.

I read articles about the "correct" position of the lens behind the dome.

1. Does the pupil of a zoom lens move when the focal length changes? If it does (I think so) the length between port surface and pupil entrance can only be set for one focal lenght... right? Is there a right port for such a lens, when e.g. this length is set for 18mm (12-24mm)? How big is the pupil shift by 12-24mm. Am I right when saying that only a prime lens can be set correctly behind a port? By any case the port can not be perfect for zoom and its different focal lengths.. right? This is the main reason for the corner softeness and blur.. by 12-24mm right? This is just a speculation whether to buy a prime or a zoom lens for WA shots? I have not used a real WA lens yet so I would apreciate help.

thank you for advice

Martin

The pupil's position indeed shift from one end to the other, wether that is dramatic depend on the lens optical formula, the 10-22mm will likely have less shift than say a 28-300mm, you are right about prime lens, they are eazy to align, but you could optimize a zoom lens a one specific position of its range, if you are patient enough. Normally manufacturer strive to get the wide portion of the lens, this were the positionning is most critical.

Bluring on the edge can be a combination of to small a dome and improper positionning, in any case wider lens will benefit from a larger dome.

As far as aligning the sweet spot there is two school of thinking,

1) extension ring inserted between the port and housing, this usually require a single dome port and you just add extension ring as you add lens to your collection

or

2) get a fixed port for each lens you plan on getting.

Being a veteran user of prime lens, I recently went over to the dark side of zoom, damm well more practical and using a large dome doesn't penalize me that much.

Cheers

Viz'art,

thank you for advice. As I see there is no doubt about what kind of lens would you recommend... prime by any case... Just little zoom atracts me a bit.

Although I have an idea about the image quality and do not want to get rid of it, zoom helps to frame the objects what in fact improoves quality too...

What WA lens do you use the most? I mainly want to shoot sharks, scenary and wrecks :-))) which is quite broad range for one lens... But I think the 12mm (18 on 35mm) by 12-24 zoom would suit me. All I wanna know is if it worths to loose some quality (and how much it really is) and have more versatille lens or go straight for the prime one as I really want quality.

thanks ones more

Martin

My two favorite WA are the 10.5mm fisheye and the 14mm, I recently indulged myself in a 10-20mm Sigma lens, quite inexpensive but slow aperture, I want flexibillity of the zoom but I miss the 104 degrees that I had with the 14mm and 35mm film and the 10mm portion of the zoom is just that 103 degrees. Now I have to run some test and see if that lens is good or just one of my too many ultra wide (weitwinkel) paper weight initial top side shots seems OK, in any case Iwill follow up on this subject later...

BTW: I didn't get the 12-24mm mainly because of how close the 14mm is in coverage.

Anyone else crave a Nikon 9.5mm/2.8 DX AF ED rectilinear? Nikon has an edge (I think) in wide glass and this'd nail it! Under a grand, please...

(edited to change FE->rectilinear ... oops)

I'm waiting for my 12 mm DX 2.0. The equivalent of the 18 mm for film cameras. I always thought that was the best wide angle lens for Nikon underwater.

Maybe a 11 mm DX 2.0 if it would be optically and financially feasible.

Thank you, guys, for advice.

Davephdv: I know it would be much easier to decide what lens to buy if I tried them... I think the 12mm (18 on 35mm) would be fine. 10.5 mm seems to be little to wide for shark and bigger animals shots but great for scenery. 15 mm is not wide enough for scenery and coral shots, but would be good for sharks.. Hard decesion for me as I have not used any WA lens yet.

What would be your recommendation ?

Martin

Me, I'll take a slower lens (2.8) if it can be a bit wider (9.5-10.5). Heck, there is a 10mm zoom out there!

I'm waiting for my 12 mm DX 2.0. The equivalent of the 18 mm for film cameras. I always thought that was the best wide angle lens for Nikon underwater.

 

Maybe a 11 mm DX 2.0 if it would be optically and financially feasible.

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