Bad sharpness in the corner, when I use Inon UWL 100 close to subject.

[blacknet]

Dee once bubbled...
Thanks, blacknet and Avatar for the descriptions and examples. I've always seen the coma effect referred to as vignetting.

BN...I totally understand about added elements...you lose a bit of quality with each one. But sometimes for underwater, because of budget and other things, we can't all posess Nikor quality lenses and the camera and housings they require. We do the best with what we have.

Hello,

Yes indeed. There is nothing wrong with using equipment that will yield results like this. The solution is knowledge. Understand how and why it does what it does and you can use it to your benefit.

All to often these 'technical' descriptions get swept under the rug and called 'vignette', or some other catch-all phrase.

Ed

 

[David Evans]

Your mileage may vary....

BUT....

I have had EXCELLENT results when using these types of accessory lenses by leaving my camera in MACRO mode - all the time!

Yes, even when shooting scenics, or wrecks, or big fish.

I don't know why it works, but it does.

Now, I haven't used the Inon lens, but I have used the WA lenses from Light and Motion for both my Tetra and my Titan setup, and the results are the same for both lenses: leave the camera on Macro mode for ALL shots.

And, no, this doesn't change the field of view (aka focal length) of the lens.

Just give it a shot and report back...

-d

 

[TheAvatar]

David:

You mean you use one of those Macro dioptor closeup filters? Those are a bit of a different animal.

 

[James connell]

blacknet once bubbled...
Strobes do not cause vignette! This is NOT an example of vignette or a DOF issue.

What we are seeing here is coma. Since this is an addon lens we may have barrel distortion, wrong curvature of field or a number of other nasties.

at least you recognize that's not vignetted.

when i saw the typo - i went to edit "i'd say > 1/2 stop and that may be caused by the strobe" to "i'd say < 1/2 stop and that effect may be caused by the strobe" but the darn system woudn't let me edit after 30 min.

the EFFECT that was mistaken for vignette by others is a result of the strobe being missaimed - it's high and to the left, a better position in this case would be as close to the lens as possible and slightly right (but may not be a possible with his setup).

the uneven ilumination only makes it harder to determine vignetteing and as i said i(doubt it's >1/2 stop if noticable at all.
All lenses vignette it's a matter of howmuch.

there is coma - in about the amount to be expected in this lens
( all lenses have some amount of coma as well).

there is a focus problem because the rocks under the fish are in good focus ( as is the body/pectral fin) the Dof was not suffient to cover the entire subject ( nor at this angle is it likely to be).
since it's my guess that this camera auto focuses on whatever is in the center of the frame. composition is more difficult, unless there is a focus lock.

i think most of the problem in the corners are curvature. an attemp at a closeup ( looks more like a macro) with a wide angle -

 

[blacknet]

Hello,

It is difficult to say, other than speculation, about the DOF due to the location of the tail and it could be due to the shutter speed and/or from the coma present at the edges. Either way it doesn't matter.

Anyone have an ID for this fish? Closest I can find is Batrachoides manglae Cervignón, which is probably wrong.

Ed

 

[James connell]

blacknet once bubbled...
Hello,

It is difficult to say, other than speculation, about the DOF due to the location of the tail and it could be due to the shutter speed and/or from the coma present at the edges. Either way it doesn't matter.

Anyone have an ID for this fish? Closest I can find is Batrachoides manglae Cervignón, which is probably wrong.

Ed

i can't id the critter, doesn't seem to be in NW pacific waters, it looks a little like some of the stuff we have here but differnt markings.

i doubt that shutter spedd played a part in the tail being blurred - look at the depth of the shadow under the rock! strobe should have froze it. what does interest me is the reduced coma on the bottom of the pix. is this a water contact lens or does it go inside the housing? i had the thought that it's not fitting on its mount square. IF the lens is properly aligned, being cocked with respect to the main lens would explain the 'intermitant' effects reported as well as the assymetrical effects. it's uncommon for a lens to show as much difference in it's distortion.

 

[blacknet]

Hello,

This is a wide angle adapter that screws onto the flat port of the housing. As for the bottom of the image having less coma I would speculate cropping.

Ed

 

[David Evans]

TheAvatar once bubbled...
You mean you use one of those Macro dioptor closeup filters? Those are a bit of a different animal.

Avatar, no, I mean setting the camera in macro mode. My Olympus (and Nikon) digital cameras have a "macro mode" setting - both have a little icon that looks like a flower.

I have found that using that setting dramatically improves the edge sharpness (and overall sharpness) of the add-on wide angle lenses I have used.

Again, your mileage may vary, but that's been my experience in a year and a half of shooting digital with these types of lenses....

-david

 

[TheAvatar]

David.... thats intersting... I'm not sure why that would work off the top of my head... but if it does, more power to you.

 

[David Evans]

Avatar, yeah, I have to admit that I don't understand why it works either. It really doesn't make any sense.

Anyway - I got that tip from Berkely White at Backscatter, and he DEFINITELY knows his stuff.

I just got back from Fiji, where I took my Titan and wide-angle lens, and left the camera in macro mode the whole time.

Here's a photo I took using the wide angle lens with the camera set in macro mode.... not that it's a great photo, but note the depth of field and the corner sharpness (and granted, this was the Light and Motion lens for my Titan - not the Inon lens....)