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#1 Clive

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Posted 27 August 2010 - 08:10 PM

I was wondering if changing optics from say Amphibico to Gates in a housing (supposing possible with a little modification to the housing) would affect the camera and image. I understand that every lens has its own characteristic and traits. Hence, possible barrel distortion with one and not the other. The reason why I am asking is I am exploring building a housing and buying the lens port separately. And was wondering if the distance between the camera and lens would be VERY critical. Or the camera will be able to compensate for sharpness as long as within a certain range of distance. If so, is that why lens port are not camera specific?

Also in the sticky thread on Close-up diopters, I realised that although there are talks on quality sharp lenses there are no mention of distortion. Why is this so? However, when looking through recommendation for SLR lenses there are always talk on aberration, barrel distortion etc. Are close up diopters not prone to distortion?

#2 Drew

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Posted 27 August 2010 - 08:50 PM

Depends on the lens. For example, the WP80/100 is a fathom designed UOM built lens as OEM for various housing brands. The lens is essentially the same but the mount is obviously different. Same goes for the Gates SWP44 which is also the Sealux Fathom 120, both OEM from Fathom with different mounts. Optimized lens distance is definitely an issue for the housing. It's like adding a wide angle adapter. The optics have to work and they generally do because they function within the same threshold.

Good suggestion for the diopter thread. I wrote that diopter thread as info for people. I figured the only reason to use a diopter on a fixed lens video camera is to shoot something up close. Using a diopter means there'll always be diffraction and CA, goes without saying. I guess it should be clearer.

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#3 Clive

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Posted 28 August 2010 - 07:42 AM

Thanks Drew. As always your replies are helpful and full of depth.

Optimized lens distance is definitely an issue for the housing. It's like adding a wide angle adapter. The optics have to work and they generally do because they function within the same threshold.


I am actually curious as to what happens if the lens distance is not optimised? Will the picture be out of focus? If so, then can we adjust the focus or zoom to compensate. I suppose if this then possible it would be within the threshold as you mentioned. Or will there be distortion which cannot be compensated by the camera?

With many reviews on WA lenses having "full zoom through focus" is this the result of optimised lens distance?

I figured the only reason to use a diopter on a fixed lens video camera is to shoot something up close. Using a diopter means there'll always be diffraction and CA, goes without saying. I guess it should be clearer.


Although I have been shooting UW video for a while I have not gone into the depth that the people here are. I guess you can say that something that "goes without saying" to the knowledgeable "goes without knowledge" to the illiterate :) At least now I know a little more.

#4 Drew

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Posted 30 August 2010 - 02:05 AM

Clive, all that depends on the lens designer and what they are trying to achieve and also what price range they are trying to hit. Just because it's full zoom doesn't mean you'll get a sharp image throughout. Whereas a partial zoom may have a better image in its operating range.

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#5 HDVdiver

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Posted 31 August 2010 - 03:48 AM

Just because it's full zoom doesn't mean you'll get a sharp image throughout. Whereas a partial zoom may have a better image in its operating range.

Clive, all that depends on the lens designer and what they are trying to achieve and also what price range they are trying to hit. Just because it's full zoom doesn't mean you'll get a sharp image throughout. Whereas a partial zoom may have a better image in its operating range.



This is absolutely correct. Full zooms are generally very complex/expensive designs...and physically larger than partial zooms. Sometimes a simpler optical design will perform better (ie better resolution, less flare & ghosting) within the narrower focal length range that it's optimized for than a full zoom lens that tries to do everything. The full zoom results will look OK...until you do a side-by-side comparison with a partial zoom.

As far as modifying/adapting a lens for your own project, I'd suggest that a cheaper, easier and more versatile alternative would be to buy a good glass dome port and simply machine the correct bayonet to your housing front. The new WA converters from the camera manufacturers are excellent...and, importantly, are optimized to work with the wider angle lenses on the new cameras.

For example the Panasonic TM700 fitted with Panasonic's W4607H wide conversion lens is a superb (full zoom) combination that works well with a 6 or 8 inch dome port.


"I am actually curious as to what happens if the lens distance is not optimised?"

The main problem will be vignetting. Bringing the lens closer to the camera lens won't be a problem...moving it further away will.

Edited by HDVdiver, 31 August 2010 - 03:53 AM.


#6 fxvideo

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Posted 31 August 2010 - 08:03 AM

I'm having the same issues with my domeport and wideangle adapter combination.
I modified a older Amphibico housing to fit my Sony HC-1e HDV camera and used the wide angle adapter provided with this housing. I used a stepdown ring to fit it on the camera and found out after the first shot that the centre is sharp but on the edges it looks out of focus.Next thing I like to do is try to move the camera back or forward to see if this will improve the picture.
If this does not help I want to mount a diferent wide angle lens and see if this helps.

#7 Clive

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Posted 01 September 2010 - 06:47 AM

The main problem will be vignetting. Bringing the lens closer to the camera lens won't be a problem...moving it further away will.


I read about the vignetting part from a review from Wagsy as well. If I understand Drew's mail well, I will have a threshold distance to move the camera. Within this threshold too far from the port and I will have vignetting (no problems with focus I am assuming). Too near to the lens I will sacrifice usable wide angle, again I assume the will be not problems with focus. Is this right?

I used a stepdown ring to fit it on the camera and found out after the first shot that the centre is sharp but on the edges it looks out of focus.Next thing I like to do is try to move the camera back or forward to see if this will improve the picture.


I will be interested in your feedback after moving the camera. Please let us know if it improves.

#8 fxvideo

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Posted 05 September 2010 - 05:29 AM

I have just performed a series of test with my Amphibico housing a 2 wide angle lenses, one 0,5 and a 0,7 lens. I have made a speciale structure where I could fix my housing to and placed it opside down in my bath. On the bottom I taped a series of plastic sheets with a grid printed on it.
Distance between the lens and the sheets was 45cm.
I started the test with the 0,5 lens, but whatever I did I couldn't get the edges of the picture sharp.I changed to the 0,7 wide angle lens and performed the same test of moving the camera to improve the focus on the edges.
The result of these test are that moving the camera aft or forward didn't improve the focus on the edges.So I stay with the 0,7 wide angle lens and moved it back as possible inside the housing to get the "biggest"picture without vignetting.


I read about the vignetting part from a review from Wagsy as well. If I understand Drew's mail well, I will have a threshold distance to move the camera. Within this threshold too far from the port and I will have vignetting (no problems with focus I am assuming). Too near to the lens I will sacrifice usable wide angle, again I assume the will be not problems with focus. Is this right?



I will be interested in your feedback after moving the camera. Please let us know if it improves.