6" or 8" dome port

Hi guys,

I have finaly decieded to buy the Nikon 10,5mm fisheye. I use Ike housing. I have old version of the Ike 8" dome port ( for 12-24mm) which can't use the extensions rings.

Here is my question:

Is the 8" dome port so much better compare to the 6" dome port? The 6" is around 140 USD and the 8" is around 350 USD. I'm not sure if I should buy the 8..... if it realy perform so much better I should spent more.......

Thanks for opinions.

Petr

I don't own the 8'' only the 6'' but from my experience it's good with the 10.5 fisheye lens.

For the zoom lens like the 12-24 the 8" is probably much better but the fisheye works well also with the small one.

One problem with the 6'' is with split images, it's too small for that, its not that is impossible but harder then with a bigger domes.

Hi!

Dome theory in a nutshell:

1) The dome diameter is responsible for the position of UW-infinity. The larger, the further.

2) The usable angle of a dome has to be at least as wide as the maximum diagonal angle of the lens.

3) The center of the dome sphere has to be placed in the perspective center of the lense.

The above items are vital for a good image quality when using a WA lens. There may be a few changes to the rules above for FE lenses without causing too much loss in image quality.

For a true 180° diagonal FE lens you'd need a hemispheric dome. It works in most cases to use a misplaced dome with a narrow angle (e.g. a 120° dome that is placed closer to avoid vignetting).

The dome diameter determines the distance of UW-infinity. A txpicl value is between 30 an d 50 cm for most common ports. Depending on the focal length and the position of UW-infinity you get different areas of DOF. This is espexially important when doing half-half shots. It is also important for corner sharpness as DOF is the only way to compensate the bent image plain caused by the dome. A larger dome diameter extends the focus range anf the DOF. You'll recognize an increase in corner sharpness.

Having to make a decision between a smaller well placed dome and a larger misplaced one (wrong set of extension rings e.g.) I'd take the smaller well placed post in most cases for WA but maybe the larger one for FE (becaue if it isn't a hemisphere it's misplaced anyway). FE lenses tolerate misplacement of a dome far better than WA lenses do. Thsi is caused by the different way they're projecting an image.

You'll find a more detailled explanation here on Wetpixel when searching for the essay on Dome Theory written by Julian (also contains sample calculations and illlustrations).

Helge ;-)=)

I haven't used the 10.5mm with the 6" dome, but the 10.5mm was not the impetus that drove the 8" dome. The 8" dome was needed to improve corner sharpness on the zoom lens. Fisheye lenses perform very well in small domes. If all you care about is good optical performance with the 10.5mm there is no reason to get the 8" dome.

Now there still may be some reasons you want the 8" dome anyway. For me the top 3 reasons I got rid of all my 4 6" domes are these:

1) Simplify my travel gear. I used to have 4 domes for 4 lenses. With the 8" dome I carry the dome and 2 extensions.

2) Easier split levels. The 10.5mm is a terrific lens for split levels. Its so wide its easy to get a lot of subject in the frame above and below. This is a fantastic lens for split levels. And the 8" dome makes this MUCH easier.

3) Better performance with the 12-24mm.