68 replies to this topic

[adamhanlon]

Hi Steve,

Thanks for all this-it is fascinating stuff. I think though that the blue tang image would probably work with a normal dome? If so, I think you will get round all the corner issues. You are absolutely right though, that for fish portraits, I find the 17mm end of the 10-17mm the place to be:



1/60th @ F9 ISO 200

This was with a conventional 8" dome. I think the lighting issue becomes a problem with CFWA, which this image isn't really! If you put a converter in, and then get the dome close, then where to put the strobes is a challenge.

As regards the golden retriever getting the fish-simple, hide it under your stetson!

Adam

[davephdv]

Okay, what gives?

Following this thread I shot the 100 mm dome with the 10-17. A Subal rig with a D300 and 3rd generation mount. Using a 15 mm Subal ext. ring.

All 10 mm images showed significant vignetting. Images shot at 12 mm and longer were fine.

I looked back a the first time I shot this set up, not using an ext. ring.

Only two images were shot a 10 mm. No vignetting is noticeable. The many shot 11 mm and longer were all fine.

Why is the 15 mm ext. ring recomended with this port? It seems not to work.

[PRC]

From a conversation a while back with Ryan the issue may that Subal are not particularly consistent on camera focal plane position housing to housing - so your Subal D300 housing may be different to my Subal D300 housing.

If this is the case then on Subal it will be a 'suck it and see' trial.

If true this is sloppy engineering.

To be fair I guess that this placement is going to become more critical with small radius domes and WA lenses.

Paul C

Edited by PRC, 18 April 2010 - 05:11 AM.

[pmooney]

From a conversation a while back with Ryan the issue may that Subal are not particularly consistent on camera focal plane position housing to housing - so your Subal D300 housing may be different to my Subal D300 housing.

If this is the case then on Subal it will be a 'suck it and see' trial.

If true this is sloppy engineering.

Paul C

If this was the case you would also have control alignment issues.

I think a more likely explanation is that bodies are set back further in the Subal housings.

[PRC]

Can't disagree with your logic Peter but there seems to be some unit to unit variation going on specifically with Subal.

Haven't Subal in the past have been reluctant to supply replacement backs for their housings, taking a "it needs to come back to the factory for fitting" type of position?

I had always assumed that this was just to foster a replace rather than repair type of mentality.



Paul C

[Ryan]

Extension Ring 15 definitely doesn't vignette with the ND300 or ND30 housings (two models have actually be produced for D300), both have been tested pretty thoroughly by us and our customers. My first thought would be to measure your extension ring and make sure you have what you think you have, as both 18 and 20 vignette. They are easy to measure, just the measure the length of the knurled part you'd put your hand on when mounting.

Subal port spacings are not sloppy within a model, but they have moved the port mount to camera lens mount steadily closer to the camera on more recent models, which can make for inconsistent extension ring recommendations.

[davephdv]

This looks like vignetting to me.



This looks like a 15 mm ext. ring.

Has the combo of the 100mm Zen dome and 15 mm Subal ext. ring been test with the 3rd generation Subal mount?

[davephdv]

It is hard to compare due to different settings, but the edges appear sharper on the shots I took without the ext. ring.

Clearly with this dome the edges get sharper starting around F 8 or F 9.

[Ryan]

That definitely is vignetting, and that is a 15mm extension.

We tested the combo with several Subal third generation combos, including D300 (both the ND30 and ND300 models I believe). I've sent a pm asking the housing serial number so we can look into this further.