Re: Ikelite dome is sharp even with 20mm lens

Posted by Rick on June 20, 2002 at 21:55:09:

In Reply to: Re: Ikelite dome is sharp even with 20mm lens posted by john on June 13, 2002 at 06:27:32:

: : : 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?

Yep, that helps but I'll have to use the rubber ring and glue trick to use the zoom knob on my port as a focus knob with the 20mm. By the way, my dome port is not, according to Ikelite, supposed to be able to accommodate a 20mm without vignetting but that's not so. As long as I carefully place the shade cover so that the cutoff corners line up with the corners of the frame, there's no vignetting. I agree with you about Ikelite housings; the pictures I'm getting already with my Canon EOS and Ikelite housing are as sharp and colourful as I get from my Nikonos V with a 28mm, and, of course, I get the subject in the frame and in focus (actually, I always get the focus right with the Nik V too but I'm buggered if I know how!). Thanks!

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Re: Ikelite dome is sharp even with 20mm lens Rick 01:40:25 11/14/02 (0)

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: : : : 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? : Yep, that helps but I'll have to use the rubber ring and glue trick to use the zoom knob on my port as a focus knob with the 20mm. By the way, my dome port is not, according to Ikelite, supposed to be able to accommodate a 20mm without vignetting but that's not so. As long as I carefully place the shade cover so that the cutoff corners line up with the corners of the frame, there's no vignetting. I agree with you about Ikelite housings; the pictures I'm getting already with my Canon EOS and Ikelite housing are as sharp and colourful as I get from my Nikonos V with a 28mm, and, of course, I get the subject in the frame and in focus (actually, I always get the focus right with the Nik V too but I'm buggered if I know how!). Thanks!

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