Canon 20D

I have found that the Canon 20D is not very good in low light conditions underwater. I use it in the Aquatica A20 housing and doing dusk dives I find I have to have use a focus light each time, when my friend using his D100 doesn't have any problems at all. I have tried all kinds of settings for AF but none really do any good. In daylight conditions it's great but when getting dark.... It's not been a problem as I use a focus light and hardly ever miss a shot using it but was wondering has anyone else found the same?

Hi Patrick, I moved your post to the DSLR forums where it will get more attention. I think that you raise a very interesting and important point that a lot of people don't appreciate. That some cameras have AF better suited to underwater (low contrast, low light) shooting than others.

I noted a similar instance in a D70 vs 20D thread recently, when I tried Giles's D60, which has better than D100 AF above water and worse than D100 AF in low light dusk dives.

While I was in Cayman I had a play with Giles's D60 - and the AF on that was clearly better than the D100/D70. On land that is. The D60 is surprisingly fast an accurate in good light, with Giles saying that even his friend who photographs Formula 1 with a 1D Mk2 was impressed with it. But Giles was not so impressed with it at dusk UW. And certainly he was struggling to get images (when we were working in low light) that I had never really had a problem with when using a D100.

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Obviously not everyone shoots at dusk, so this aspect of AF performance will not effect all. But I think that the important message for UW photographers is that UW places different demands on the AF. And just because DPreview or your camera shop tells you that camera A has better AF than camera B it may not be the case UW.

That's where Wetpixel comes in...

Alex

p.s. I must say from your results you don't seem to be struggling too much!

Lens choice is also a factor in AF performance. One of my dive buddies tried the Sigma 28-80 zooms in his 10D and no matter what he tried, the AF wouldn't lock on, he put on the EF50mm Macro, no problem. This was in the darker waters here in BC. I've always shot with a small focus light on my housing (UK SL4) but the only times I've used it during the day was for pygmy seahorses or under overhangs. For dusk dives (Mandarin Fish) I put on a wide beam UK D4R and it helps A LOT.

s.

Good advice Stu,

Anyone else got any good tips for helping AF performance?

Alex

although I tested with a p&s Oly, this information may translate to dSLR rigs......

while experimenting with red focus lights on night dives it occurred to me that the narrow beam of my solitary mini Q 40 was also controlling where the camera was receiving it's AF target data. Consequently I was able to dictate to the AF system what I thought was the most important feature in the composition. Of course spot focus also addresses this, but it still is one more tool available.....

ymmv,

b

In general, I always have found that the center focus spot is the most accurate, and fastest. If you turn off the AI focus, it works better and faster.

Just getting a line or boundary of contrast across the focus spot, and you are good to go.

Hi Don,

On most DSLR cameras, the center sensor is a cross type sensor, meaning it can and will AF on vertical and horizontal contrasts.

On the less expensive cameras, this is the ONLY cross type sensor and all the other sensors only AF on vertical detail (if memory serves, it may be horizontal).

Cheers

James

The Canon's switch to cross type sensors with lenses that are F2.8 or faster...

Not the 1D bodies - just the 20D. I don't have the manual in front of me, but the 1D's will still use the cross type with slower lenses. Still a valid point - fast glass will autofocus better.

Cheers

James

I find if I use "One Shot" then I have to shoot quick. With the 100MM and may be with other lens, once the "one shot" locks you have to release the shutter quick as it will not continue to focus if you move, so I set myself up for the shot and when happy half press to auto focus and once obtained instantly shoot. AI Servo is great for moving targets as it will continue to focus when you move the camera but I feel it's not as fast on locking on in lower light.

As far as the camera, it performs great and I'm very happy with it. I've done about 20 dives with it so far and get shots that were much harder than my Oly.

PS thanks Alex.

Well I had the chance to try the 17-85MM in low light this evening and it was excellent! the 100MM in low light was not that good, but the 17-85MM rocked. Here's a pic

Hi,

I love the 20D performance with low light conditions, but I've got the same problem related with some lenses, Canon 100mm macro and 28-105mm with low light conditions with 20D. I sent my camera/lenses to authorized repair center and they found a problem with focus calibration, for $40,00 my lenses back to me working fine again.

Regards

Fabio Amorim

In regards to Fabio's post and what Alex mentioned earlier with my camera .. it only seems to be a problem with the 100mm macro on my D60 .. it is perfectly ok with the 28 - 70 (just test runned it the other day after work .. was crammed in extension rings and i couldn't zoom .. but...) that lense is a much nicer lense and even though i got no "nice photos" it has potential and would be lovely if i could use the zoom.

i have still not bought the extension rings as I couldn't fully zoom back to 28mm with the ones we had available (lense sticks out) but it should be possible to do ... However I would really like to get a zoom ring on it as well .. this lense would be perfect for wall dives on the north side in the summer if you could zoom ... some nice wall shots .. maybe silhoueettes .. and if a hammerhead cruises by .. zoom .... BLAT BLAT BLAT ... nice

either way ... the more expensive lense was noticeably faster (at 50mm) and was faster in daylight as well as as it got dimmer (wasn't dusk but was very cloudy and similar to dusk

As several people have noted, the Canon 100mm macro lens struggles to focus in low light. I've used that lens with both a 1DMkII and 1DsMkII, and in both cases had so much trouble with it at dusk and at night that I just don't use it on those dives anymore.

IOW, it's not the camera (20D or otherwise); it's the lens. I LOVE the 100mm macro lens during the day, and plan to use it with my 20D in daytime, but I find the 50mm macro far more versatile (i.e., can take fish, octopus, etc. as well as macro) and FAR easier to focus in low light and at night (attached photo of Spanish Dancer gills taken at night in Komodo with 1DMkII using 50mm, 1/50, f16).

As I work in murky temperate conditions, my equipment often struggles to achieve focus too. The 100 usm macro Canon lens is a stunner but I sometimes wonder if its speed of autofocus works against in in lowlight, low contrast conditions - it seems to pass the point of focus very quickly, even before it has had a chance to lock on!

On the other hand using a 24mm f/1.4 lens is a joy, with its very bright viewfinder image, and fast accurate autofocus even in dull conditions. The slower all-encompassing wide-zooms available today perhaps cloud our thinking, a bright viewfinder image will appear brighter to the AF sensors too. I anticipate adding some more fast lenses to my collection as I am so impressed with the 24/1.4. Now if only someone would produce a 90mm f/1.4 Macro.........

Undoubtedly lens choice affects autofocusing ability of the cameras we use. It would be intereting to build up a listing of the most popular lenses and camera models for underwater use. My own favourite remains the 60mm micro-Nikkor which could have been designed for underwater photographers. Its very well made, performs superbly and can even tolerate some flooding. I have one which has been full of sea water at 20 and after repair still works 7~8 years on. Not bad!