Colour refractions spots using dome port...

[Tbar]

Hi I have a Nauticam housing for a Sony Nex 5N and use the 16mm with Ultra-wide adaptor in a Nauticam 4.33" acrylic dome port. I have two Inon strobes (Z240, D2000), set to sTTL.

I recently scratched the port and have used micromesh polishing kit the make it look like new.

I dived yesterday and took some photos, only to find that some are great and others show colour 'spots' violet, green, blue. I expect this is some type of refraction coming from the acrylic. I have not had this in the past but have taken many hundreds of photos with same lens/port and strobes.

Attached are a couple of images with the issue and one without.

I expect this is caused by the polishing, should I try again?

Thanks for any comment or help.

 

[Nemrod]

I do not believe those refractions are caused by the polishing. I think the strobes are forward of the lens (9107 and 9118) and that you are also shooting into strong light. Those colored refractions, some are inside your lens, the ghost reflections are inside the dome (9135), bad orientation.

N

 

[Plashb199]

have you tried really cleaning the lens and the sensor?

 

[Tbar]

I have spoken with my Nauticam support shop - Scubapix. There view is that the micromesh has caused some small 'flat' spots and those are have caused the refraction. They say that given the size (4.33") and hence tight radius 'polishing' with micromesh can be a problem. There advice is to use "braso" and a very soft/aged cotton cloth.

@Nemrod - having taken hundreds of photos with this set-up I have never seen this effect. What do you mean by 'bad orientation'?

@Plashb199 - the lens and port were cleaned. I don't expect the sensor to be an issues.

I can get a new dome, so that is in the post today

Thanks for tips

 

[mattia_v]

I get this with my Inon wet lens (acrylic dome) if the strobe is too far forward, or shooting into sunlight. Placing it further back and angling it out further will avoid direct light from the strobe entering the dome - you only want the reflected light. On your first photo you can see the hot spot from the strobe in the top right.

Almost all ultrawide lenses (wet or dry) will refract or flare in some circumstances. Strobe and camera positioning are almost invariably the fix.

 

[Nemrod]

Then try their advice as I cannot disprove that your dome might be in part at fault due to reduced optical properties but the primary causes are strobes forward of the lens and shooting into strong light or having a strong light source within the lens FOV that cast a ghost reflection from the lens to the dome or dome reducing contrast and reflections.

N

 

[Tbar]

Thanks all
I am off to the Galapagos in a week, so will change the acrylic as there are no more 'practice' dives. I will then be double aware of the location of the strobes, and keep them back a little more.
TB