D70 AF Questions

Greetings all. New member here and new UW digital photographer. Just upgraded from sealife point and shoot to D70 w Subal housing. Using the 17-80mm "kit lens" and a Nikon SB800 strobe in a subal housing. I am using the +2 diopter on the Subal FE2 dome port as called for on this lens

Took the new rig to Saipan a few weeks back as was disapointed with the AF results. The camera would fire, meaning IT thinks it acheived proper focus, but the results were decidedly mixed. I tried continuous mode, single AF mode, tried a modeling light (hand held), AF assist light on, AF assist light off - same inconsistent performance.

Interestingly, some of the sharper shots I actually achieved during my night dives. Exactly the opposite of what I would have expected.

Any ideas or suggestions? I leave for Belize in 6 weeks - I'd like to get this solved before then.

Thanks!

What Extension Ring are you using? The 18-70 DX lens used in the FE-2 Dome Port should be setup with the 20mm Extension Ring and no Diopter is necessary.

I have to go double check - It think its a 10mm extension ring. This was the setup recommended to me by the dealer who sold me the system - SeaOptics down in Adelaide Australia.

Do you shoot this set-up - is this how you shoot it?

Thanks,

Brad

What shutter speed were you using? Just a theory, if you were using aperture priority at night the shutter speed would be shorter as it would be dominated by the strobe but in daylight would be less reliant on strobe power for exposure.

Also, have you had good results with the 18-70 on land? I had a slight backfocus on mine when I got it. I sent it back to Nikon to be re-calibrated and it is much sharper now. Its acceptable but still not my sharpest lens. The 60mm is much sharper.

I had a slight backfocus on mine when I got it. I sent it back to Nikon to be re-calibrated and it is much sharper now. Its acceptable but still not my sharpest lens. The 60mm is much sharper.

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Did you send back the lens or the camera body....I thought backfocus was a problem in the camera?

Karl

Tech Talk:

Backfocus is not a problem, it's an adjustment. In a lens there two typical adjustments, front and rear. The front adjustment is a linear adjustment affecting all focal lenghts fairly equally (with more affect on the tele end) in a zoom lens.

The rear adjustment, sometimes referred to as backfocus is non-linear and is used to bring the lens focus into balance from wide to tele. Rear focus affects the wide end of the range mostly and is adjusted first. Once the balance has been acheived then front focus is adjusted to bring the lens into specs. In most cases the adjustments affect each other and must be repeated a few times to get the lens as close as possible to proper focus.

Many high end video lenses have a user adjustable back focus so a lens can be calibrated to different cameras by the operator.

In the camera the adjustment is body focus or the depth from the image sensor (film plane) to the lens mount. The mirror angle, sub mirror angle, focus screen position & balance and af sensor position & balance also all affect the focus performance.

Sorry, didn't mean to imply that this was a lens problem. The "problem" was with the camera. I sent back both lens and camera just in case. It was adjusted and fixed.

The backfocus was in the camera and effected all lenses, but it didn't effect all lenses equally. It seemed to be worst on the 18-70mm. Even the 60mm was slightly focused to the back.

It wasn't so bad that I threw out my pics but it was noticibly sharper in real photos and appearent in measurbator tests.

The most painful part was parting with the camera for a month. You live your whole life without the camera and then you have to give it up and you find you can't live without it. :-) I'd recommend anyone with an early D70 do the measurbator tests though and send it back if its not right. No reason to shoot with an improperly calibrated camera.

I'm not sure if this is a lens, camera, port or user error. Just throwing out possibilities.

1) Could be motion shake with long shutter speeds. What was shutter speed?

2) Could be AF-C. I tried AF-C on two dives and didn't get sharp pics most of the time. It was fun to shoot machine gun style though.

3) Could be wrong port extension. User says he's using reccommended port extension.

4) Could be improperly calibrated camera. Have you gotten sharp pics topside? How about other lenses below and topside?

Any other ideas?

triggerfish,

you recommend an FE2 dome with a 20mm extension with this lens - no diopter? Is this the subal recommendation? Your personal experience?

Thanks so much for your help!

Brad

triggerfish,

you recommend an FE2 dome with a 20mm extension with this lens - no diopter? Is this the subal recommendation? Your personal experience?

Thanks so much for your help!

Brad

I think "triggerfish" is my current post ranking.

Yes the Subal Nikon Lens Chart lists the EXR20 and No Diopter Lens with the DP-FE2 port for the Nikon 18-70DX Lens.

Dave,

I am confused. I have seen 2 port charts for Subal from 2 different dealers. One calls for the diopter, one does not. I have not been able to find an official chart on the SUBAL site, though the site does say:

"To compensate for the power of the dome and give you the full focusing range underwater, a screw-on + 2 with DP-FE2 or +4 close-up (dioptre) with DP-SW lens is required for all lenses except full frame fisheye, which have no front filter threads!"

So of course during my next trip I will experiement with and without.

Thanks!

Brad

Yes the Subal Nikon Lens Chart lists the EXR20 and No Diopter Lens with the DP-FE2 port for the Nikon 18-70DX Lens.

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Could you or someone give me a link to subal lens chart for Nikon?

I could not find it on Subal site and when I did google search, I found one from 2002 and it did not have some of the more recent lenses listed.

Thanks

I am confused.  I have seen 2 port charts for Subal from 2 different dealers.  One calls for the diopter, one does not.  I have not been able to find an official chart on the SUBAL site, though the site does say:

 

"To compensate for the power of the dome and give you the full focusing range underwater, a screw-on + 2 with DP-FE2 or +4 close-up (dioptre) with DP-SW lens is required for all lenses except full frame fisheye, which have no front filter threads!"

 

So of course during my next trip I will experiement with and without.

 

Thanks!

 

Brad

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It cerainly can get confusing, I've seen changes from chart to chart. You are correct Subal generally recommends the +2 Diopter with the DP-FE2. But this is just a recommendation, we suggest that you try the setup with and without the diopter lens and make your own decision. So I agree that you should experiment.

The same is true for the Extension Ring, my Subal chart (Fall '04) lists the EXR-20 with the DP-FE2, once again this is a recommendation. I know many folks using the EXR-33 with the DP-FE2 and the 18-70 lens.

I'd love to hear the results of your tests.

Dave, this "recommendation" business bugs me! Seem to hear this a lot. Aren't there optical "specifics" that could "tell" us what to use for a specific lens and dome combinations?

I know, too lazy to study the optics, I am looking for easy answers... but I can't believe there are not enough of us to be able to "confirm" what works and what doesn't. I hate the idea of diopter use if it can be avoided.

btw, this is in no way a flame of your statement! Just inquiring minds and all that!

Dave, this "recommendation" business bugs me!  Seem to hear this a lot.  Aren't there  optical "specifics" that could "tell" us what to use for a specific lens and dome combinations?

 

I know, too lazy to study the optics, I am looking for easy answers...  but I can't believe there are not enough of us to be able to "confirm" what works and what doesn't.  I hate the idea of diopter use if it can be avoided.

 

btw, this is in no way a flame of your statement!  Just inquiring minds and all that!

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Richard, Thanks for the reminder, there's a great post on Proper Dome Size and Placement by Jean Bruneau & Chis White located here:

Wow that was quick! and of course it was there all along.

Thanks, that is rather helpful!

Looks like a bit of manufacturer info is needed for the lens you wish to use under a particular dome.

Another quick question. Is the Aquatica 8" consider a hemispherical dome?

Is the Aquatica 8" consider a hemispherical dome?

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This is another one of those confusing terms. By definition a hemisphere is 1/2 of a sphere but with dome ports this seams to be a misused term. For instance I found this on the British Society of Underwater Photographers site, in reference to Hemispherical Dome Ports: "Usually the more complete a hemisphere the better the optical quality...".

The Aquatica 8" Dome Port does not appear to me to be a complete hemisphere, in fact it looks to be quite similar to Jean's illustration in the link I posted above.

Are there domes where the radius in not consistent? If so, could it be that a "consistent" radius is what is considered optimum?

It seems to me that a "true" hemisphere would cause problems with the position of the dome...

Brad

I'm using the identical setup to your own, including the housed SB800 strobe. According to the Subal Lens Chart I have, the 18-70mm kit lens should be used with the FE2 dome port and a 20mm extension ring, with NO diopter.

This setup works very well, but the focus needs to be set to AF-C (the AF-S setting results in most shots being out of focus).

Hope this helps.

Jean.

Surely you've got that the wrong way round. AF-C allows the shutter to fire regardless of if the camera has achieved focus. I tried this setting and my inability to reliably depress the shutter half way to focus and then press it all the way down when focus was achieved resulted in a lot of out of focus shots. With AF-S even if you press the shutter release all the way down it won't fire until the subject is in focus.