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Nikon F601 & Subal Miniflex Focus Problems


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#1 FishyPix

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Posted 18 May 2005 - 11:15 PM

Greetings all,

I am a long term Nikonos user and have just tried to switch to housed
SLR cameras.

My gear is a Nikon F601 with either a 20mm wide angle or a 105mm micro
lens housed in a Subal Miniflex N6B with either the DP 54B dome port for wide angle or the
FP 117B flat port for macro.

Does anyone have this setup ?

Right. Here are my problems:

Wide Angle:

I was told to get diopters for use with the 20mm & dome port so as to have
all the shots sharp due to focal plane shifting via the dome. Fair enough.

Using either a +1 or +2 diopter all the Wide Angle photos are STILL out of focus.
Im using F22 with a big strobe to get maximum depth of field.
Softness occurs from 20cm to 20metres.

With a +1 diopter, closest object can be about 40cm from the lens but only the
centre is in focus. Long distance objects are rapidly brought into focus by just a small
turn of the focus knob but again it seems only the centre is sharp.

With a +2 diopter, closest object can be about 20cm from the lens and the edges
seem to be close to being in focus but not quite. Long distance objects take a bit
more of a turn of the knob to come into focus and its difficult to tell if the edges
of long distance scenes are actually sharp or not.

Just for fun, I put the +1 on top of the +2 to see what would happen. Interestingly
enough, I can get the corners in focus but not the centre and when I turn the knob
to get the centre in focus, the corners go soft.

Should I be using a +4 diopter ?
If so, wouldnt that mean my wide angle is no longer wide ?
Which diopter strength can I use to get sharp underwater but also sharp above
water (although very close) for use in promotional shots ?
Am I just not using the camera right ? Im staying in Pm Mode for simplicity.

Macro:

I was told that I could shoot straight through the flat port with the 105mm Micro
without any problems BUT I just cant get a sharp shot !

It focuses great on land straight through the flat port but the shots underwater are
all soft, accross the image, and often with a weird haze/fog effect.

Again, Im setting the lens to F22 and using a big strobe.

Am I doing something wrong with the camera ?

Does anyone else have this setup who can tell me how stupid I am ?

#2 Alex_Mustard

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Posted 19 May 2005 - 03:19 AM

I'll start with the macro. If the lens will focus in the housing on land then it will underwater. Ok the F601 doesn't have the world's greatest AF (its the same as the Nikonos RS) but it does work.

Please can you post some examples of these images.

Alex

Alexander Mustard - www.amustard.com - www.magic-filters.com
Nikon D4 (Subal housing). Nikon D7100 (Subal housing). Olympus EPL-5 (Nauticam housing).


#3 anthp

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Posted 19 May 2005 - 04:28 PM

Ok the F601 doesn't have the world's greatest AF (its the same as the Nikonos RS) but it does work.

<{POST_SNAPBACK}>

The F601 shares a lot in common with the Nikonos RS. They both have a similar Matrix meter and the same AF module (the Nikon Advanced AM200). The AM200 was actually used in the F4, F601, F801/s, n6006, n8008, F50, F60, Fuji S1 and Nikonos RS - pretty good return on investment! It's not that bad, but it only recognises vertical lines/contrast. It obviously not quite as good as the current Nikon CAM900 - particularly for tracking moving subjects, but I did find that it was pretty good in low light. May I suggest trying it in AF-S mode (ie. single shot rather than continuous). In this mode the camera will only release if it thinks the shot is in focus. That might help us diagnose whether or not it is a camera fault.

I'm sure you're not stupid mate, maybe we might be able to help a bit better if you show us some shots to help us figure out the problem together. Alex is spot on with the macro stuff (ok topside should be ok UW). The WA is a little harder to figure out (I found the bathtub quite useful when figuring out a combo a few years back :blink:)
Anthony Plummer
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"It's much better down there... It's a better place..." Enzo, Le Grand Bleu.

#4 FishyPix

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Posted 20 May 2005 - 05:09 PM

G'day again,

Thanks so much for your interest in my problems, I'll try to explain
things a bit better.

Before that however, I think I have figured out the Wide Angle problem
to a BIG extent.... I need a +4 diopter. Doh !

Spoke to Subal and they said that with the following combination, I should
be using a +4 diopter and not a +2 or anything else:

Body: Nikon F601
Lens: Nikon 20mm f2.8 AF
Housing: Subal Miniflex N6B
Port : Dome Port 54B
Strobe: Ikelite Substrobe 150

So, apart from some weird things Im doing, the +4 diopter should make a
great improvement on my focus using Wide Angle.

Now, to the Macro:

As with the wide angle, I am doing a few weird things which may be part
of the problem:

1. Either no diffuser on strobe or using a white hankercheif (dont have proper diffuser).
2. Leaving the F601 on "Pm" - only because it seems to be close to "Auto".

As you can see from the second weird thing, the F601 has befuddled me with its cryptic
mode nomenclature and may be important.
At the same time, I dont think the lack of a proper diffuser can have that much effect on
focus.

Which brings me to the example shots. Trying to upload them just causes the forum
to give an error message about the size - I have reduced them by 80% in Photoshop
so they are quite small but it seems still too big.

OK, reduced one by a further 50% so is now only 10% of original size.

From the picture you can see both how the topic is out of focus and how it is
"foggy" or has "haze".

All the shots are out of focus - like the F601 cant get a fix. Should I be using SPOT
METERING ?
The shots that are taken in sunlight are also foggy (like this one) so is that because
Im trying to shoot too large a topic, that is therefore too far away, thus bringing
between the lens and the topic too much water for the 105mm micro to doits best ?

I'll stop here !

Thanks heaps.Macro2.jpg Macro2.jpg

#5 Alex_Mustard

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Posted 21 May 2005 - 12:35 AM

Right, that makes it a lot easier. The Pm and strobe diffuser wil make no difference to this issue.

As you have suggested - the problem that you are having is that you are shooting through too much seawater. Even the clearest seawater is much murkier than air and you need to get much closer to the subject. In underwater photography we generally shoot everything from less than 2 feet away (60cm) and ideally less than 1 foot (30cm). If we have a bigger subject we either change to a wider lens (which means another dive) or we choose to shoot only part of it.

Koran angelfish are pretty big and for a shot framed as you have you would be better using the 20mm than the 105mm.

Getting closer will solve 90% of the problems you are having. First the pictures will be sharp. They will also be colourful because more light from your strobe can reach the subject. Water also scatters light - and reducing the light path will increase contrast and clarity in your images.

As the old adage goes "the key to successful underwater photography is getting rid of the water".

Alex

Alexander Mustard - www.amustard.com - www.magic-filters.com
Nikon D4 (Subal housing). Nikon D7100 (Subal housing). Olympus EPL-5 (Nauticam housing).