Sigma 10-20 / Subal - Magic filter combo

There has been much talk ( lot's from me ) about which port and extensions are best for this lens.

My first dive was with Subal D2X / FE2 dome/ 20mm extension ring and used no diopter , with the magic 77 fitted using a blank filter ring.

I am reasonably happy at the first results with the lens - it is really wide and will take a bit of getting used too. I am very pleased with the magic filter's results and can see lot's of available light shooting on the horizon.

Visibility was fairly good - about 11 am

This was at about 14 metres

And another at about 12 metres

And at about 8 metres

Great color, but I find them kind of soft. Did you do any sharpening on postprocessing or are these straight out of the camera?

Just a minor adjustment to WB - nothing else.

On the second dive I added a +2 diopter and changed the extension ring to a 50mm - this is the recommendation for the Nikon 12-24 . I thought it would be a good reference to start with.

and another

and finally.

Good work Peter, the turtle does appear sharper, can't wait to hit some blue water and try mine.

BTW, you never got back to me about what model Aquatica you will have in black, just curious since i'm debating what color to go with my D2x housing.

Cheers

Jean,

I had been toying with the idea of black anodised housings for rental units for quite a while - they would seem to be more beautifull after a bit of use.

I had been thinking to have a black ( anodised - not painted ) D2X housing for myself. ( matching SLR's would be flash )

I have 2 on order in the standard silver colour and had thought that I would discuss the colour variation at DEMA should I make it in time from my pending Flores expedition. We are scheduled to fly out of Maumere on the 5th and may be just a tad pushed for time.

Best

Peter

Hope you make it at Dema, but not at the expense of some underwater time

The Aquatica is black anodized as a standard feature, i'll see if I can rig one up for a shot and post it altought I prefer painted housing in general I understand your concern about scratched paint on rental units, as a precaution I would also go with the wide angle dome shade instead of the Fisheye one, unless you plan on renting with the 10.5mm fisheye, the WA shade is a huge protector of dome, I mean, you would have to go out of your way to bang that dome inside the shade.

Cheers

Is the vigneting in corners caused by a thick filter, or this sigma does this with ultra thin filters too? You have been using the 77mm magic filter... is there a possibility to sticks the rear filter in the back? If it does vignete with any kind of filter it might disapear at 11-12mm. But for me it is a bit disapointing - I was gonna buy this combo too and use it at 10mm! Also some images are a bit soft and I would not say it definitely improoved adding the +2 diopter.

Are you happy with the lens?

Martin

Ultra-thin front filter ring may be required. Many companies make these.

Cheers

James

I would guess it's the filter ring causing dark corners because even with the 20mm extension ring they are visible.

Peter, did you try the 50mm ring without dioptre too? Subal FE2 - is this the one with 180mm glass diameter?

Julian

Julian,

I was hoping you would chip in.

I'm sure it is the filter - the blank ring came from a HOYA filter and they are quite tall.

I didn't have time to try it out without the diopter in the water.

My intiatial tests in the office showed a diopter was neccessary otherwise the lense 'saw' the port shade.

Yes the FE2 dome is the 180mm diameter.

My gut tells me that the 33mm ext ring is probally the best option given that the Sigma lens is about 12mm shorter overall than the Nikon 12-24.

Peter

Hi Peter,

then it's the same dome glass as I use with my Sealux housing. Do you have an opportunity to measure the distance from camera bajonett surface to the outer edge (front) of the dome glass (just the dome mounted, no exension ring)?

Julian

Julian,

The measurement from the face of the bayonet mount to the out side of the dome ( assuming the dome is 2.5mm thick ) is 115mm.

when the lens is set at 10mm it extends 36.5mm into the dome and at 20mm it is 41.5mm.

Peter

The 12-24 extends 50mm @ 12mm

OK, thanks Peter. Based on 115mm (camera bayonet <-> outer dome edge), required extension would be ~ 43mm.

assuming the dome is 2.5mm thick

<{POST_SNAPBACK}>

Glass thickness should be 7mm with this dome glass. Does it mean 115mm is still correct although the glass thickness is 7mm or is the distance different then?

Although this would be the right way in terms of optics, there is still a risk of vignetting. As far as I know the FE2 is not designed to enable the full usage of the dome glass’ field of view due to the port shape. I assume the FE2 port shape is like the 180F in the drawing below? If yes (what I assume), you should check if vignetting occurs with an extension ring closest to the above value (if in doubt between two rings next to 43mm, the shorter one will help of course to avoid vignetting).

To check possible vignetting, stop down the lens as far as possible and set focus to infinity. Theoretically you could set the lens to 1m for underwater as the dome’s virtual image won’t be away further than that. But this way you won't assure that split level shots are free of vignetting too.

I would recommend to use the lens with no dioptre. I can focus down to 2cm from the dome glass without any dioptre.

Do you have one or more extension rings in this range?

Hope this helps

Julian

by the way, nice photos with magic colours

I still have to find/buy a thin filter ring for the lens too. I hope there is one that really works as the front lens' element protrudes a bit into the filter mount level. If you find one that works, please let me know so that I can finally order my magic filter (Hope I don't have to use UR Pro instead due to the filter ring issue).

Julian

The measurement should be adjusted to 120mm based on a 7.5mm thickness.

I got a 33mm extension ring today and will give it a tryout next week in Flores.

The dome is designed like your illustration 180F - it would seem that the only way to use the full surface of the dome would be for the "throat" of the port to be made larger.

This probally explains the variation in sharpness of one lens when compared over a few different housing / ports - bring on the Aquatica.

Thanks for the kind words on the test images - there is certainly a long way to go to reach the potential of the magic filter.

Peter