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adamhanlon

What are the advantages of small domes?

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9 hours ago, adamhanlon said:

Responding to this thread, @Alex_Mustard and @adamhanlon chat through small dome ports' pros and cons. These offer some unique creative possibilities, reduced cost, and portability advantages, and have limitations that should also be considered.

 

Is anyone else having problems getting this to play? 

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It's working for me...but I would be interested in hearing from others...

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51 minutes ago, adamhanlon said:

It's working for me...but I would be interested in hearing from others...

Also working here.

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It’s working here.

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Hmmm, my problem then. I'll play around!

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1 hour ago, TimG said:

Hmmm, my problem then. I'll play around!

Got it now!

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It seems to me that fisheye lenses in large domes are a problem, because most big domes are not hemispherical but truncated hemispheres. The Nauticam 230mm is about 70% of a hemisphere. So if you place the front entrance pupil at the centre of curvature, the dome mounting plate will vignette the lens. (I realise that with fisheye lenses the "front entrance pupil" is slightly arbitrary.) I made an 8" hemisphere once but it was so buoyant I never used it. I also made a 14" hemispherical dome for only over/under shots so buoyancy didn't matter, but it needed a rotating lead weight to persuade it to float in the right place. I was measuring the Nauticam 8.5" dome and the Aquatica 8" this morning and if you place a fisheye where it should be, both vignette a lot. So the lens needs to be positioned far enough into the dome so it doesn't vignette. Fisheyes seem very forgiving about this. I also have a 6" hemispherical dome I made and I can place the front entrance pupil of the 10-17 in the right place. I am not convinced that optically this will be better than the Nauticam 8.5" in the wrong place. I liked this 6" dome for travel with the D800 because the centre of curvature was perfect for both the Sigma 15 fisheye and the Nikkor 18mm. Has anyone compared results with a small hemispherical dome in the right place with a larger dome in the wrong place?

PeteAtkinson-3(1).jpg

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2 hours ago, PeteAtkinson said:

It seems to me that fisheye lenses in large domes are a problem, because most big domes are not hemispherical but truncated hemispheres. The Nauticam 230mm is about 70% of a hemisphere. So if you place the front entrance pupil at the centre of curvature, the dome mounting plate will vignette the lens. (I realise that with fisheye lenses the "front entrance pupil" is slightly arbitrary.) I made an 8" hemisphere once but it was so buoyant I never used it. I also made a 14" hemispherical dome for only over/under shots so buoyancy didn't matter, but it needed a rotating lead weight to persuade it to float in the right place. I was measuring the Nauticam 8.5" dome and the Aquatica 8" this morning and if you place a fisheye where it should be, both vignette a lot. So the lens needs to be positioned far enough into the dome so it doesn't vignette. Fisheyes seem very forgiving about this. I also have a 6" hemispherical dome I made and I can place the front entrance pupil of the 10-17 in the right place. I am not convinced that optically this will be better than the Nauticam 8.5" in the wrong place. I liked this 6" dome for travel with the D800 because the centre of curvature was perfect for both the Sigma 15 fisheye and the Nikkor 18mm. Has anyone compared results with a small hemispherical dome in the right place with a larger dome in the wrong place?

PeteAtkinson-3(1).jpg

Great dome that you show on the photo (how much cm?)... :good:

 

I have compared, but only on the small MFT sensor (Oly EM1II and EM5II):

Both Canon 8-15mm and Tokina 10-17mm perform at least equal with respect to corner sharpness, if not slightly better, when placed incorrectly behind the Zen DP170 (=11cm radius) compared to placement behind Nauticam 140 hemisphere (=7cm) the correct way. It seems that the bigger radius (and hence bigger virtual image that is further away) makes a greater effect compared to the wrong placement...

 

Wolfgang

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Thanks Wolfgang for that info! That dome was about 18cm radius. I no longer own it.

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10 hours ago, PeteAtkinson said:

. Has anyone compared results with a small hemispherical dome in the right place with a larger dome in the wrong place?

 

I have shot the 10.5 mm Nikkor fisheye lens "properly" mounted behind the hemispherical Seacam Fisheye Macro Port and Seacam Fisheye Port as well as "improperly" mounted segment-dome Seacam Superdome SD. The SD is far better even with just 12 megapixels (D2X).

Edited by Tom_Kline

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These are the tests on a rectilinear lens (modelled) from this article (by myself and Edward Lai):
https://wetpixel.com/articles/review-nauticam-wide-angle-corrector-port/P1
comparing dome port size on image quality
 
MUSTARD_WACP_012.jpg
The impact on image quality across the frame when using different sized dome ports compared with a lens in air (this graph plots RMS GEO radius against FOV of a lens, data source: Zeemax spot diagram analysis, Edward Lai, 2017). Results are discussed in the text below. 

 

Before moving on, I want to add more data to the graph from the previous section, which is very valuable for improving our understanding of using dome ports. As far as I know, this is the first time anyone has probably collected and certainly presented test data of this kind for different domes.

The 100mm (4”) dome port performs slightly worse than the 200mm (8”), while the 230 mm (9”) performs considerably better. However, do note the data for a 230 mm dome that was not placed correctly, using a port extension just 3.8cm or 1.5” too short — something I see lots of people doing. Like this, the expensive 230 mm dome now drops as much image quality at the 100 mm. The graph shows that big, expensive domes deliver on image quality, however, they must be correctly positioned to do so. (Also note that all domes give good sharpness in the center of the picture, the advantage of bigger domes comes towards the edge of the frame.)

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Alex, it would be interesting to see a similar analysis and graph done for a fisheye lens.

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