Using the "wrong" extension ring for your lense

Hi !

A question arrise when i have (or we) to choose/use a new lense that needs a new extension ring (sometimes less that 5-6mm) shorter or longer from what we have (or we can affort to buy....).

What is your opinion/experience on this ?

Hi dpoursanidis

It depends! If you are shooting wide-angle, the extension ring (EXR) length is key as it sites the lens in the correct position for the curve of the domeport. So you do need the right length for shooting wide-angle.

It's maybe not so crucial if shooting with a flatport and macro. It would the depend on whether the port/EXR combination creates any sort of vignetting which spoils the image you want to create. Chances are a few millimetres here and there will not make too much of a difference. But.... it might!

Sorry, maybe this is not terribly helpful but it certainly is my experience. In short: wide-angle/domeports: yes EXR is important. Macro/flatport, maybe not.

Hi Tim

Example first > Aquatica mini dome + Canon 8-15 + 18453 EXR =

Center crop

https://copy.com/DxwZqGGdLV8i92L1

Low right crop

https://copy.com/yIZvbHuxUjCd0WIE

How much "better" can these be with the correct ?

Images are from RAW > JPEG. No editing.

Natural light shot @ 2m depth.

Hi dpousaindis

Hmmm, not sure what to say!

"Better" is a pretty subjective word. Certainly you have some pretty serious blurring going on there and I would have thought you should be able to get it much "better" than that! Sometimes though it depends how much you are prepared to pay to make a difference; and then how much the difference is worth the cost.

I'd start by checking Aquatica's recommendations for the setup for their mini dome and Canon 8-15. If you have the wrong EXR then, bingo, you have the start of the problem and the cost of a fix is "relatively" (ha!) low. And does that combination need, for example, a diopter? If both those questions are resolved and you still have blurring, then the issue could be one that the 8-15 doesn't work well with a mini dome and you might need a larger dome and then the cost of a fix increases rapidly - and hence my rather philosophical question as to whether the solution to the problem warrants the cost of the fix.

But, as I said in the first reply, the right EXR is important when using a dome. Start there would be my suggestion.....

Thanks Tim

The fix cost 250 euros (EXR) so just paid for

Diopter for this lense is not something that i have see/read around, so the EXR will solve this.

Bigger dome is also an option but for CFWA staff.

Dimitris

Good call, Dimitris. Fingers crossed the EXR does the trick.

Fingers crossed too you don't need the bigger dome! They aren't much help for sure with CFWA as they make it far more difficult to get the strobes in the right position: almost impossible I've found.