Corner Sharpness?

Just started playing with my Canon 10-22mm lens in Ikelite housing with 8" dome, correct stalk etc.

The centre of the image and so on is great and sharp BUT the corners are extremely soft and very noticeably so on every shot ive taken with it.

Am i just going to have to live with this or would a dioptre help at all ? Going on a trip soon and would rather not have several months potentially of very soft corners or having to crop all my images all the time to remove it.

A few examples showing it off fairly badly:

http://farm4.static.flickr.com/3465/337905...c49135b87_b.jpg

http://farm4.static.flickr.com/3571/337905...56a141c19_b.jpg

If a dioptre wont help is anything likely to such as closing down the aperture, zooming in etc ?

A diopter will help corner/edge sharpness. Buy a close-up kit (+1, +2 & +4) & do some testing. You can test in a pool or large tub of water. The dome is all that needs to be wet. Photograph something with small detail in the corners like text or bar code. Check lens at 10mm & 22mm @ f4-5.6. As a reference point, I'm using +4 with my Nikon 12-24 & 6.75" dome. Do you know that the center of curvature of the dome is properly placed at or very near the nodal point of the lens?

Do you know that the center of curvature of the dome is properly placed at or very near the nodal point of the lens?

That i dont know and cant really see any way of finding that out. Its the standard ikelite 8" dome and the stalk they recommend for it (5510.22). When its all fitted the markers on the camera for the point are hidden.

Are there any disadvantages to using a dioptre if one does work? Will i lose the ability to focus further and so on?

(fwiw the ikelite lens/port chart says one isnt needed for my combination of port and stalk).

a quick search brought up this quite usefull post:

http://wetpixel.com/forums/index.php?showtopic=26677

a quick search brought up this quite usefull post:

 

http://wetpixel.com/forums/index.php?showtopic=26677

From there it doesnt look good then. I may just have spent money on something that isn't going to produce decent shots. Resisted getting a fisheye as they're completely useless on land and i dislike the curve on some U/W shots.

From there it doesnt look good then. I may just have spent money on something that isn't going to produce decent shots. Resisted getting a fisheye as they're completely useless on land and i dislike the curve on some U/W shots.

I would disagree that you won't get decent shots but this lens certainly has it's limitations. I too fell into the same trap of thinking that I'd get more use out of this lens because it could be used topside too. I've found a +2 diopter and zooming to around 16mm certainly helps but this equates to about 26mm on a full frame camera so not necessarily as wide as you'd want to go. Stopping down to f8.0 seems to help a bit too but I don't think you'll ever get away from the softness completely. In many shots I don't think it's too bad and in some it's hardly noticeable but in others I've either had to crop it out or delete the pic. Close-up wide angles (like your second pic) tend to be the worst offenders.

I would still do some diopter testing. Sharpness is improved (maybe not enough with this lens). You just have to put up with the CA & pin cushion distortion. Although u/w you don't notice the distortion unless you're shooting straight lines.

I found this Googling--no guarantees, but may be of some help.

"I use this lens on a 30D. The following numbers (location of nodal point) are found by trial and error. The distance is measured from the sensor plane (or at the center from the tripod screw at the camera base). At 10mm setting = 105mm, 12mm =103mm, 14mm = 100mm, 17mm = 100mm, 20mm = 101mm, 22mm = 104mm. I hope these numbers can be used with the 400D"

i got a Tokina 11-16 for my 20D after some disappointment with the 10-22 corners both topside and UW. The Tokina is better topside, but again, disappoints UW -- using the extrnsion ring recommended by Aquatica (the "41mm" which actually provides 28.6mm of extension) and a +2 diopter recommended by Ryan at Reef. According to Ryan, the trick is to get the lens as close as possible to the center of the dome radius as possible without vignetting, so there may some more room to play with extension ring length - however, i haven't yet figured out a convenient way effectively vary the length of the extension tube to determine the vignetting point. Maybe it's easier to order some rings from B&H and send back what doesn't work.

However, after discussing wide angle photography with Mark Strickland on a trip to the Andaman Islands (first time i've had the opportunity to dive with someone who really knows what they're doing) i strongly suspect that a fisheye is the only satisfactory solution if you want decent sharpness across the entire image.

As wide angle is a secondary interest for me, i'm not sure how much time and money i'm going to invest getting it right.

Anyone had experience de-fishing a Tokina 10-17 with PT Lens? UW and topside?

Folks seem to have very good results with the Tokina 10-17 (if you like the fisheye effect), so maybe that's the way to go. Regarding the other lenses, I would rate optimum optics (dome location & diopter) over vignetting. If you get vignetting the dome isn't wide enough. Some domes that look like 180 deg measure less than that. Could this be part of the problem?

Loftus started a thread on correcting the fisheye effect a few weeks ago (See here). Opinion was split on who liked the original and who the corrected, I personally preferred the corrected images. I don't know about how successful topside corrections would be though.

Hi, I've the same problem with the 7-14mm and... was almost solved with a larger port.

You need to have more distance from the lens to the dome.

I'm sure that you problem is only with the more wide focal length.