Re: Ikelite dome is sharp even with 20mm lens

Posted by john on June 13, 2002 at 06:27:32:

In Reply to: Re: Ikelite dome is sharp even with 20mm lens posted by Rick on June 13, 2002 at 04:11:37:

: : There has been some ongoing threads about lack of sharpness in corners with 20mm lenses in the ikelite dome due to its small (6 inch) size.

: : Some folks have stated that the edges will always be out of focus due to bending of the virtual image.

: : I just returned from Caymans and shot a 20mm lens and got tack sharp images corner to corner. The secret is to manually focus (focus closer than the center of the viewfinder to improve corner sharpness) and use a small aperture (f/8-11) to gain enuf DOF to keep center in focus.

: : The ikelite system is a bargain.

:
: Hi John, a couple of questions - which dome port are you using? How have you rigged the port so that you can manually focus? The clamp I have with my 5503.50 is too bulky for me to use with my 20mm lens so I'm going to make up a rubber ring to go around the focus ring of the lens and glue a couple of ribs on it to fit into the geared sleeve that goes with the port. But if you have a better idea, I'd love to know about it. By the way, Ikelite told me that the 5503.50 would give `vignetting' with the 20mm but it doesn't seem to to me. I just have to be careful how I place the shade cover.

Hi- i use the regular dome, not the superwide one....not sure the numbers, as i bought it in the 70s (and it has taken me this long to figure out the best resutls!)

I manually focus- i think that's the key- the beautg of the 20mm with dome is that you can get real close, but you have to mannually focus- this is really not a big deal. ALso, use fast film (i shoot only black and white) to get to at least f/8-

in fact, if you focus on the center image, then pull the camera away a little bit, you will get better focus on the edges, but have enough DOF to keep the center sharp. I use the old focus gears that came with the ports. Does that help?

Follow Ups:

Re: Ikelite dome is sharp even with 20mm lens Rick 21:55:09 06/20/02 (0)

Name:
E-Mail:

Subject:

Comments:
: : : There has been some ongoing threads about lack of sharpness in corners with 20mm lenses in the ikelite dome due to its small (6 inch) size. : : : Some folks have stated that the edges will always be out of focus due to bending of the virtual image. : : : I just returned from Caymans and shot a 20mm lens and got tack sharp images corner to corner. The secret is to manually focus (focus closer than the center of the viewfinder to improve corner sharpness) and use a small aperture (f/8-11) to gain enuf DOF to keep center in focus. : : : The ikelite system is a bargain. : : : : Hi John, a couple of questions - which dome port are you using? How have you rigged the port so that you can manually focus? The clamp I have with my 5503.50 is too bulky for me to use with my 20mm lens so I'm going to make up a rubber ring to go around the focus ring of the lens and glue a couple of ribs on it to fit into the geared sleeve that goes with the port. But if you have a better idea, I'd love to know about it. By the way, Ikelite told me that the 5503.50 would give `vignetting' with the 20mm but it doesn't seem to to me. I just have to be careful how I place the shade cover. : : Hi- i use the regular dome, not the superwide one....not sure the numbers, as i bought it in the 70s (and it has taken me this long to figure out the best resutls!) : I manually focus- i think that's the key- the beautg of the 20mm with dome is that you can get real close, but you have to mannually focus- this is really not a big deal. ALso, use fast film (i shoot only black and white) to get to at least f/8- : in fact, if you focus on the center image, then pull the camera away a little bit, you will get better focus on the edges, but have enough DOF to keep the center sharp. I use the old focus gears that came with the ports. Does that help?

Optional Link URL:
Link Title:
Optional Image URL: