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DSLR
TTL troubles with the Nikon D100 - A user's perspective
By Alexander Mustard
There is no such thing as a free lunch in underwater photography. So while I was fortunate enough to get the first Subal D10 from Ocean Optics at the end of last year, it seems that in return I get the somewhat dubious honour of having to write about the problems I have had trying to use TTL with the D100 underwater.
For other aspects of the camera and housing see my review in Underwater Photography Magazine Issue 11 (www.uwpmag.com)
This subject has now been expanded upon in my article in Issue 13 of Underwater Photography magazine. Check it out. It's a great magazine and it's free! (www.uwpmag.com)
These are my opinions and do not necessarily represent those of Ocean Optics. Digital photography is evolving very rapidly and although all the information on this page is, to my best knowledge, correct – certain things will undoubtedly change. “Nothing endures but change ” Heraclitus (540-480 BC)
The Problem
Simply - there are NO underwater strobes that offer Through-The-Lens (TTL) flash metering with Nikon’s D1 series or D100 cameras.
Why is this?
The problem lies with the cameras. The D1 and D100 cannot perform standard Nikon TTL flash control, so as an alternative Nikon has developed DTTL.
DTTL is NOT the same as TTL and all existing underwater flashes are designed for TTL. The only guns that will do DTTL are Nikon’s land guns – the SB28DX, SB50DX and SB80DX. And these aren’t waterproof!
The SB80DX
Nikon’s standard TTL (with a modern Nikon Speedlight) works by monitoring the light coming in through the lens (TTL) using BOTH pre-flashes in the microseconds between the kill button being pressed and the shutter opening AND during the actual flash exposure once the shutter is open. The pre-flashes are used to predict the amount of light an exposure will require, AND then this is fine tuned while the shutter is open by monitoring the amount of light reflecting back of the film. Once enough light to produce a correct exposure has reached the film the camera quenches the light output from the flash.
Submersible strobes are not as sophisticated as modern Nikon Speedlights and cannot do the pre-flashes. Luckily our film cameras are pretty smart and realize this and revert to TTL without the pre-flashes. Problem solved….
...until the D1 and D100 came along. The problem the D1 and D100 have is that their CCDs do not reflect light in the same way as film. This means that they cannot perform TTL metering while the shutter is open (which relies on monitoring the light reflecting off the film). As a result they have to rely only on the pre-flashes.
In practice this works fine with the SB28DX, SB50DX and SB80DX. But underwater strobes cannot do the pre-flashes. So can’t do DTTL.
At present there are a number of “digital” underwater strobes on the market – but, at the time of writing (03.03) none of these can do DTTL. Despite sometimes confusing naming – such as Sea and Sea’s YS90 DX!
Hopefully things will change on this front. But Nikon so far has been unwilling to tell independent strobe manufacturers how DTTL works. One of the golden rules of diving is “ Don’t hold your breath! ”. That applies now!
Solutions
There are several ways to overcome this problem. The simplest is to stick with manual flash. Housing a DTTL gun is more complex and brings its own set of problems but does work.
A) Shoot Manual Flash Exposures
B) House a Nikon Digital Speedlight
C) Buy a Fuji S2!
A) Shoot Manual Flash Exposures
For those coming from a modern 35mm SLR the idea of giving up TTL seems crazy. But shooting manual flash is very easy with a digital SLR because you can immediately check your exposures (with image review) and change your settings and re-shoot if required. Furthermore with digital pictures it is easy to make small corrections to the exposure of the resulting image with your computer without any significant loss in image quality. (If you shoot in NEF RAW you can correct the exposure of the images to a much greater degree without loss in quality).
Most photographers who have tried digital SLRs underwater are very content shooting with only manual control over their flashguns. Warning: by going over to manual flash you do run the risk of perhaps becoming a better photographer!
Below are two quotes I have stolen from the discussion forums on www.wetpixel.com (these forums are a very good source for digital info at present – while the expertise of users is in many cases exceeding the knowledge of retailers and housing manufacturers):
“Took it out again this weekend in Monterey and got some amazing shots. I am really liking
the lack of TTL on the D100 for underwater shooting...I know that sounds crazy.”
“I see far less advantage to TTL with digital. I can't change the exposure of a slide…
[but with digital] manual strobe control can easily let you get close enough to the proper
exposure that a little digital tweaking can fix.”
So, because of the lack of DTTL UW strobes and because using manual is so easy several D100 housing manufacturers are supplying their housings configured to only fire flashguns in manual. This is good because it means you can plug in your existing Nikonos/Nikon compatible guns, using standard Nikonos connectors, and they WILL WORK ON MANUAL . But they WILL NOT TTL .
An ideal manual gun for digital is one with lots of power settings, such as a Subtronic or the Inon T flash . That way you can easily adjust your flash power to get the correct exposure.
If you don’t already own one of these guns don’t worry! I have been doing most of my camera trials with an old Sea and Sea YS30 which has only one power setting - “ON” ! The amount of flash light recorded by a camera depends on:
i) the power output (or setting) of the flash
ii) the distance from the flash to the subject and back to the camera
iii) the size of the aperture letting light into the camera
So, even though I can’t vary (i) with the YS30 I can still move it closer and further from the camera (ii) and change the aperture in the lens (iii) to get the desired exposure.
This picture was taken with my D100 and 17-35mm lens, ISO 200, YS30 on Full power, f20 @ 1/125th.
Manual flash exposure is easily contolled with digital SLRs
A final word of warning! When using a manual strobe in this way with the D1 and D100, the camera is not aware that it has a flash attached to it. This is because you are only connecting 2 of the 5 flash contacts and are stopping the flash from telling the camera that it is there. This means that it is up to you to ensure that you keep the shutter speed below the synchronization speed (1/180th on the D100 and 1/500th on the D1). For practical reasons it is better to shoot in Manual rather than Aperture Priority mode.
B) House a Nikon Digital Speedlight
If, like me, you far too lazy to get into manual flash or just can’t face the idea of going down without TTL then you only have one option. You have to house a SB28DX, SB50DX or SB80DX. In my opinion the SB80DX is the best of the DTTL compatible guns and has the bonus of fitting in the old tubular plastic SB24/26/28 housing. These housings are reasonably common on the second market (at the moment)! Try Ocean Optics or Paul Kay
To make the housed SB80DX work you need to have the D100 housing fully wired up with all 5 wires of the flash circuitry connected. Peter Rowlands did mine - again speak to Ocean Optics.
With this setup everything works well. DTTL is pretty good on most subjects and I have been very impressed with it in the pool. I was able to get reliable DTTL metered flash over 7 stops without moving strobe or camera. Excellent.
The picture (right) shows a series of pool test shots taken with the D100 on DTTL with SB80DX. Lens Sigma 28-70mm f2.8 zoom at 44mm. ISO 200. Exposures were all at 1/160th @ apertures: f32, f22, f16, f11, f8, f5.6, f4 & f2.8. DTTL has controlled these flash dominated exposures very well at all apertures apart from f2.8 where the camera was not able to quench the light quickly enough.
Problems
Unfortunately, that’s not the end of the story. Not by a long shot.
P1) DTTL meters the exposure during the pre-flashes and from then on the exposure is fixed. If the reflectivity of the subject changes during between the pre-flash and the exposure then DTTL will get it wrong. It cannot react. OK we are only talking about a few hundred milliseconds but there are certain situations that will be problematic. Understanding these will help you get the most reliable performance from DTTL.
First rapidly moving subjects may well change their reflectance on these timescales. The same goes for shots where you are panning the camera. The biggest problem comes with rear curtain shooting because the gap between the pre-flashes and the main flash is now long – as long as the exposure. In fact this is the only time that we can see the pre-flashes the usual gap between them and the main flash is too short to discern.
This rear curtain shot was taken with my 35mm F100 and twin subtronic Alphas on TTL. DTTL would struggle with such an exposure. P2) We can’t fire slave guns. Slave guns will react to the pre-flash and not the main flash and will preempt the exposure. The only way to get them to flash with the SB80DX on DTTL is to use a long exposure on rear curtain synch, which gives the slave long enough to recycle after the pre-flash and for the slave to sense a second flash to respond to. In any case you will run into the problem of very poor DTTL metering in long rear curtain exposures. I have no experience of trying two SB80DXs. But I suspect that it will not be straightforward.
This is another post I have copied from Wetpixel.com :
"From what I understand, D-TTL has big problems when used with two flashes. The software logic for D-TTL assumes that you are using one flash and that it is in the plane of the CCD. D-TTL measures and takes into consideration the distance from the flash to the subject. When one flash is closer than another the preflashes do not return to the camera at the same time and "confuse" it."
P3) The SB80DX does not have sufficient coverage for use with the Fisheye, 14mm or the new 12-24mm Nikkors. So we have to go back to manual strobes.
P4) Problem is we can’t. With the D100 housing wired up for DTTL the camera WILL NOT fire most (probably all - certainly all the ones I have tested) existing UW strobes, even with them set to manual. This is because with full communication down all 5 flash wires, the camera detects it is not a proper Nikon flash and refuses to play ball. On the D100 you can’t even take a picture.
The way that I have found to solve this problem is to block off the three small connectors on the cameras hotshoe (see left). This just leaves the manual Trigger and Ground connected and gets you back to way the wiring was set up for manual flashes. I have found that I was able to make an effective mask for the connectors using a very thin piece of plastic with a hole in the middle for the trigger contact. I made this hole with a hole-punch!
Hopefully in the future housing manufacturers might make alternative hotshoes or a switch on the hotshoe cable that lets you disconnect these three wires and go between a DTTL and a manual setup.
C) Buy an Fuji S2! At present the Fuji S2 Pro is the only digital SLR that works with standard TTL. The S2 is based on the same F80 body as the D100 and takes Nikon lenses. The clever people at Fuji have solved the problem of reading the light off the CCD during the exposure and are thus able to quench flashes using standard Nikon TTL. Amazing. But it does beg the question why didn’t Nikon sort this on their own cameras?
The problem with the S2 is getting it housed. It is an amusing indication of how this area of the market is still developing. This camera seems much more suitable for underwater photography but has been generally ignored by housing manufacturers that have committed to the D100 instead!
The bottom line
When we take digital SLRs underwater we are using developing technology. While this means that you can be among the first few people to try out their unique features underwater, the technology is not tried and tested in the same way as 35mm SLRs. So be prepared for some headaches on the road to success!
Alexander Mustard (12.03.03)
YUP member .BSoUP member .