67 replies to this topic

[Scubysnaps]

oops forgot one, lots of masked clarity etc gone on here 1/1000 at iso 100

who needs a big d800!

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[aquakiwi]

In a previous post I have a few images taken with my 400d using both Samyung and the Tokina with a 1.5 Teleconverter in similar conditions behind a 6" Dome.

[johnjvv]

You are doing a great job at showing the Sony is a good camera...I wish there were some D90 shots!

[Scubysnaps]

Thanks John.

[Scubysnaps]

How can I say it..just a bit disheartened I'm not hearing from guys who I learnt from 3 years ago on here, guys with more posts than me say? Come on chaps

[Yako]

Hi Paul,

Interesting lens this Samyang.

I have read that the lens is fully manual. Then, when you use it UW, which focus distance and F establish?

[Scubysnaps]

Thanks Yako. I've given plenty of examples above at different apertures and focus lengths. All of them work fine. It's just a case of trial and error. You choose your lens before you dive depending on what you plan to shoot, why not your focus and aperture? You can still adjust your shutter speed and further adjust your exposure by ISO, and focus is guided by the peaking. I'm sure the name Tokina got laughed out of the water at some point in the past?

[coroander]

Unfortunately your evaluation doesn't give any idea of this lens' underwater performance.

When underwater focus for objects at any distance will be between about 0.11m and 0.21m behind the Nauticam 4.33" dome port. Lenses behave differently when focusing very close. It makes sense only to evaluate the lens when shooting objects at this distance (or at distances for the virtual image for other housings / dome ports).

The fact that the lens sits too far back in the Nauticam 4.33" dome (and thus vignettes), may also lead to less desirable optics underwater (increased corner softness, for example, although the vignetting may or may not make that a non-issue.)

The image will soften significantly at small apertures (i.e. > f/11). This may not be visible in web-sized images, but it will be visible in full size images (unless the lens is so soft in general it's not visible), and very noticeable at f/22. So while depth of field increases with apertures >f/11 (making it easier to use fixed focus) overall sharpness decreases.

I do think you'll be able to set the focus at about 0.16m (if you're lucky 0.14m) and f/11 and get almost everything in reasonable focus underwater; whether this is as good for large prints as an auto-focus lens remains to be seen...

Edited by coroander, 31 October 2012 - 11:17 AM.

[Scubysnaps]

Thanks for the input, jmauricio's pool examples seemed ok to me, for what it is I also plan to file the dome shade down to eliminate any vignette if i het the nauticam dome port if it hasnt changed, I have just done examples as requested at various settings, all ofr which beat the tokina in many ways

[coroander]

But for underwater use all that matters is close focus performance on a curved field. The Samyang may be better for land use, but its close focus performance or curved field performance may not exceed that of the Tokina because lenses' performance can change massively at close focus. The lenses use very different designs and may respond significantly differently when challenged on close focus, curved field targets.

A better test would be to place objects in two concentric semi-circles of 33cm and 11cm diameter (16.5cm, 5.5cm radius) on a table, then place the front of the lens at the centre of the circle that would be formed by these semicircles and take photos. That'll give you a curved field, close focus target. And it will give you an indication of their performance underwater inside their respective Nauticam 4.33" dome ports. You'll also be able to test depth of field with your 8mm lens (try focus at 0.15m and f/11 and see if objects in both circles are sharp).

Edited by coroander, 31 October 2012 - 02:11 PM.

[Scubysnaps]

ok (whoever you are!?)

the 1st one is the nex-6 & 8mm, it actually only focuses down to just below 0.3m, with settings as you say, excuse the noise, not much light and I didnt want to fiddle iso is 1600 then 2000

next one is the tokina at 10mm with focus of 0.3m to compare with the samyang

the next one tokina focus is at at 0.15m because it can to compareat this close level for fair comparison I should have really used a tripod but the manual focus of 0.15m combined with the f/11 seems to narrow a DOF whereas 0.3m seems ok, with my chain at 5.5cm I dont think I'll ever be that close on fisheye, or what does this equate to underwater?

Edited by Scubysnaps, 31 October 2012 - 11:07 PM.

[Scubysnaps]

not sure if i got the last 2 the right way round :S

corrected

Edited by Scubysnaps, 31 October 2012 - 11:08 PM.

[coroander]

This is certainly one of the reasons why the Tokina is so well-respected underwater, certainly there's no advantage to the Samyang in these images, but more importantly with the Tokina's close focus ability you could focus the Tokina directly on the outer circle of objects, whereas the Samyang can only focus beyond them. So for comparison, a shot of the Tokina focussed on the outer objects would certainly show the Tokina's true potential.

With the Samyang's minimum focus at 0.3m, it's only depth of field that allows you to get down to focusing on the virtual image which will extend out to a maximum of about 0.21m (3.03 times the dome's optical radius + the distance from the sensor to dome centre). The minimum focus distance is from the sensor to the front of the dome, or about 0.11m (or 1.0 times the dome's optical radius + the distance from the sensor to the dome centre). The two concentric circles in this experiment represent the minimum and maximum focus fields underwater and are 1.0 times and 3.03 times the radius of the dome. Note that the focus distance for the Tokina/D90 combo will be greater than for the Sony/Samyang because of the increased distance from the lens to the sensor plane for the Tokina/D90.

Anyway, objects at infinity will be at about 0.21m for the Sony, and objects touching the dome at about 0.11m. You'll probably find that you'll seldom get close enough to anything for it to be outside a range from about 0.17m to 0.21m. For the Samyang, i guess the question now becomes, does the Samyang at it's minimum focus of about 0.3m and at f/11 produce enough DoF that things at 0.17m to 0.21m are sharp? Or if we are comparing, as sharp as the Tokina focused on the objects themselves.

PS: The 0.15m f/11 DoF test won't work with the D90 because of the increased distance from the sensor plane to the front of the lens (or entrance pupil), which is why that image is so out of focus. It's not really worth repeating at a revised distance because the lens is autofocus...

Edited by coroander, 31 October 2012 - 04:50 PM.

[Scubysnaps]

Thanks again, I will respond to your email better later when work allows.

Meanwhile could I ask anyone out there who is able to go underwater to try their DX and tokina 10-17 at 10mm on manual focus at 0.3m and f/11 and try and come up with some varied examples to aid this test?

Quick question, why does Nauticam only do a dome that only allows CFWA? What about a 6" dome port for normal fisheye vista/wreck shots reducing any curvature and also enabling easier split shots?

Edited by Scubysnaps, 01 November 2012 - 01:12 AM.

[johnjvv]

Meanwhile could I ask anyone out there who is able to go underwater to try their DX and tokina 10-17 at 10mm on manual focus at 0.3m and f/11 and try and come up with some varied examples to aid this test?

Would love to help but the vis here at the moment does not help using a WA, I will try to though....why do you want the test on manual focus?

[Scubysnaps]

Would love to help but the vis here at the moment does not help using a WA, I will try to though....why do you want the test on manual focus?

becasue this 8mm is manual focus and currently that is the closest option to buying a new DX set up with fisheye with a new housing

[coroander]

Problem is this won't tell you much. The depth of field for a fisheye is dependent on the lens design. The Samyang fisheye's are quite different to the Canon and Nikon primes, and certainly even more different in design to any of the fisheye zooms.

On top of that distance is measured to the sensor plane, so if you had a Samyang on a DSLR it could work, but you'd have to use a different distance (maybe 0.33 or 0.34m.) On top of that you'd have to find someone using the same 4.33" dome and there'd be some differences in where the lens sat within the dome...

Certainly a larger dome would fix the problem, a 8" dome would help.

You could get the Samyang to focus closer using an extension tube, but for such a wide-angle lens the extension tube needs to be very small (a 10mm extension would move the focus so much closer that the maximum focus distance would almost certainly still be inside the lens itself.) So ideally you'd try a 2mm extension tube, except such things don't exist. If you could find a 4mm extension tube it might be worth a try, i suspect the 6mm tubes that are available would be just too long to allow you to focus out to .21m...

[Scubysnaps]

coroander, is your math(s) from web research or do you work in a related field? Despite this, I remain optimistic and obviously the best test is in the proof of the pudding, I have only paid £250 for this lens and happy with it even tho it may be just a very good VFM land lens, but we shall see, it may be both

[johnjvv]

becasue this 8mm is manual focus and currently that is the closest option to buying a new DX set up with fisheye with a new housing

Really....no auto focus on this cutting edge setup???

[Scubysnaps]

not with that particular lens no....but I am sure to find the focus peaking feature a great help, of course I have my 16-50 already and who know what else by 7 weeks time

Edited by Scubysnaps, 02 November 2012 - 01:51 AM.