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Manual Focus Nikon 16mm fisheye


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#1 volnay1

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Posted 19 November 2007 - 05:32 AM

Nikon N90s with above in Ikelite housing. Trying to stop 'hunting' in AF Mode so setting to Manual. Anyone had experience of above and if it improves etc.?

#2 Dan Schwartz

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Posted 19 November 2007 - 06:49 AM

I'm holding in my hands Right Now an N8008s, an N90s, and F100, so I'll try to answer you as best I can while sailing a desk.

The N90s about doubled the AF speed of the N90; while the F100 doubled it again. (I forget the CAM model numbers of the AF module off the top of my head). Anyway, the n90s has a red AF assist light above the right grip (where the second command dial on the F100 is now located: I mention this because it doesn't look like the F100's controls match up to an N90/N90s housing; so spending $185 on eBay for a used F100 -- with its much better AF -- is not a viable option.

Is either the case, bracket, or your (gloved?) right hand blocking the red AF assist light?

Does your flash have a red or white AF assist light? red AF assist is used because it's less noticeable than the white AF assist on my S2 Pro.

Also, by the very definition of the wide field "fisheye" image presented to the AF sensor, it will require more light to "grab onto" something to focus on.

Nikon N90s with above in Ikelite housing. Trying to stop 'hunting' in AF Mode so setting to Manual. Anyone had experience of above and if it improves etc.?


[By the way, diverging slightly off topic, a handy factoid about the N90s is that it has the smallest "spot" (narrowest angle of view) of any 35mm SLR's spot meter: This is VERY handy when shooting chromes to avoid blown highlights (and for The Zone System for B&W) -- That's why I kept mine, even after I bought my F100 a few months ago.]

Edited by Dan Schwartz, 19 November 2007 - 06:52 AM.

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#3 Cerianthus

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Posted 19 November 2007 - 07:48 AM

why the red red ?

Anyway, these AF assist lights are useless under water. They are blocked even by the clear housings of ikelite and dont travel much in water anyway. If it is just too dark for AF or MF, you'll need a focus light (at least on the focus points you're using)

I have a sigma 15mm with a canon 20d. In ikelite housings can use the housing focus control, so no need for separate mf ports. I generally use AF on servo, but with the start stop function enabled, but I am not yet a wideangle wizard.

MF might be better, because you could use the DOF to your advantage by setting the hyperfocal distance.
http://www.dofmaster...hyperfocal.html

Edited by Cerianthus, 19 November 2007 - 07:50 AM.

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#4 Dan Schwartz

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Posted 19 November 2007 - 08:02 AM

why the red red ?

Anyway, these AF assist lights are useless under water. They are blocked even by the clear housings of ikelite and dont travel much in water anyway. If it is just too dark for AF or MF, you'll need a focus light (at least on the focus points you're using)


My "point," exactly! :wacko:

All kidding aside, given the level of expertise on this BB, I didn't want to be accused of dumbing down my answer to explain the absorbtion curve of water, yada yada yada...

Also, notice I wrote I'll try to answer you as best I can while sailing a desk.

Cheers!
Dan

Edited by Dan Schwartz, 19 November 2007 - 08:03 AM.

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#5 Lionfish43

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Posted 19 November 2007 - 08:06 AM

I do this all the time. Simply focus on a near subject that you can easily lock focus on - I use my outstretched hand - and then turn your focus to manual. This will disable autofocus. If you want to go back to auto focus you can just turn it back on.

I have one of the old manual focus 16mm's and I just set the focus distance on the lens to 1.25 ft before I install it in the housing. as long as you use f8 or better pretty much everything will be in focus.
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#6 Cerianthus

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Posted 19 November 2007 - 09:37 AM

Larry, switching it is probably only possible with nikons (do you use the AF/MF switch on the camera for this), but then, the question is about a nikon.

With canon they're on the lens, with slightly changed positions. My housing doenst give access to these switches, so i have to use the custom functions * button for that.
Gerard

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#7 james

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Posted 19 November 2007 - 09:40 AM

Good info so far from the underwater photographers on these forums.

If the N90s has an M-S-C switch then you can use Larry's technique to great effect. For close focus wideangle, focus on your hand, then flip to M. For normal wideangle, focus on your fin, then flip to M.

Cheers
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#8 dhaas

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Posted 20 November 2007 - 03:05 PM

I had Larry on a boat with me in the Bahamas this year in August and watched him shoot.......

His technique goes back to the days of us dinosaurs depending on the depth of field of fisheye lenses to deliver sharp photos in fast conditions.. But it works very, very well and I've seen his pictures that prove it........

Yes, us old dogs DO know some tricks that are so simple as not to be believed :)

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#9 seagrant

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Posted 20 November 2007 - 07:35 PM

Good info so far from the underwater photographers on these forums.

If the N90s has an M-S-C switch then you can use Larry's technique to great effect. For close focus wide-angle, focus on your hand, then flip to M. For normal wide-angle, focus on your fin, then flip to M.

Cheers
James



I use this technique with the 16mm all the time with manatee and it works great most of the time (Ryan Canon actually turned me on to this technique, thank goodness I got a housing w/MSC switch cause I use it constantly.). Only problem is when they hit right between the "close-focus" and "regular w/a" range - as they are big creatures sometimes I don't get enough DOF if I bargained on a little closer focus.

But it works much better than the 16mm auto focus because there can be lots of light rays dancing around that the AF won't focus on and that change constantly.

Lots of good advice on WP for sure! Carol :)

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#10 Dan Schwartz

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Posted 20 November 2007 - 08:09 PM

Gerard, the article you cite below has some bad info on hyperfocal distance: The strict definition is the closest distance remaining in focus while infinity is also in focus. The last definition (from 2000) is correct when one of the two distances is at infinity.

I normally don't like to quote Wikipedia, at least until I look at the references and the discussion. That being said, the Hyperfocal Distance article looks pretty good.

For a more thorough description, see Harold Merklinger's book The INs and OUTs of Focus, now available in PDF.

MF might be better, because you could use the DOF to your advantage by setting the hyperfocal distance.
http://www.dofmaster...hyperfocal.html


PS: I shoot large format sometimes, bending the bellows into a pretzel! :)
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#11 volnay1

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Posted 22 November 2007 - 02:09 PM

Thanks for response, food for thought!

I have set up via Ultralight clamp a Mini Q40. This activates AF also helps manual focus in poor light.

I have two DS-125's but avoid pointing strobe directly and thus do not have benefit of modelling light, as prefer to point lights out to side to catch subject with edge of strobes.

Will see how I get on..........lots of opportunities as I'm in UK with often poor light and dark nights!

However vis gets better as temp. drops to about 9c too.

Happy Thanksgiving to all you USA guys. :)

Regards