Olympus TG4 darkens exposure considerably on zoom

[Wiggsy]

Hello all,
I bought my lovely dive buddy/wife an Olympus TG4 and an Inon s2000 strobe and have just returned from The Maldives with a lot of problems. Using Aperture priority, ISO 100; magnet out and camera flash set to Fill in flash, (EV value -1.0) we found everything underexposed badly as soon as the lens was zoomed at all, getting quite black as telephoto range increased. I understand the principle that a small sensor camera will have smaller relative aperture as lens length increases but this was ridiculous. I did one dive with it and found I'd have to manually increase strobe power and open up aperture as soon as we zoomed even moderately. I finally found a 'solution' but one I'm not happy with. Setting ISO on AUTO means good exposures as the camera compensated for loss of light levels as zoom increased. Anyone else experience this? Suggestions would be most welcome!

 

[divinh]

It's pretty common for lenses to lose brightness when zoomed in. Lenses will have a rating, like 24mm-240mm, f2.8-8, for example. At 240mm, the best aperture you can have is f8. You can either open the shutter longer, which means longer exposure and streaky photos, not ideal for fast moving fish, or allowing the ISO to be auto, which can cause noisy photos. Perhaps read up on camera photography and the interplay between aperture, shutter speed, and ISO?

 

[Chris Ross]

Need some more details on your settings, what apertures were you shooting at? You say magnet out - what mode was the S-2000 on - TTL or manual? EV -1 on ambient exposure or flash exposure?

 

[Wiggsy]

It's pretty common for lenses to lose brightness when zoomed in. Lenses will have a rating, like 24mm-240mm, f2.8-8, for example. At 240mm, the best aperture you can have is f8. You can either open the shutter longer, which means longer exposure and streaky photos, not ideal for fast moving fish, or allowing the ISO to be auto, which can cause noisy photos. Perhaps read up on camera photography and the interplay between aperture, shutter speed, and ISO?

Thanks - compact camera zoom lenses have pros and cons. The Oly TG4 is rated at "4 X optical zoom 4.5 - 18.0 mm and 1.20 - 4.9" from the lens barrel. I'm well aware of lenses losing light as the lens lengthens, but this seems extreme as it drops off from pretty much wide open (f2.8) down to closed off at f.8). I've read elsewhere that that TG cameras don't have mechanical apertures, rather a series of Neutral density filters that control incoming light. I'd just like a solution other than relying on Auto ISO which can mean losing control of grain.

 

[Wiggsy]

Need some more details on your settings, what apertures were you shooting at? You say magnet out - what mode was the S-2000 on - TTL or manual? EV -1 on ambient exposure or flash exposure?

Thanks - this is my wife's camera and I've only done one dive on it (I use an Olympus EPL1 micro 4/3 myself). I was generally at f2.8 for wide angle shots - say clown fish in anemone, on S-TTL, with synch magnet out; with EV on minus 0.7 to darken the background for a richer blue - and this yielded great results at wide angle. But as soon as I zoomed in the aperture visible in the LCD would drop off to f.6.4 or f.8 producing very dark images, both foreground and background. It is as if it sets aperture priority for wide angle only and can't recalcualte as the lens zooms. And I'm talking a huge fall off in light over only a few extra mm of zoom - even trying to get say a 1.5 - 2 X zoom yields darkened images. I have camera internal flash set at 'fill-in' , Inon s2000 at S-TTL (though I tried manual also to see if I could get it all working) So - it is a bit of a mystery. I've read elsewhere that the TG cameras don't have mechanical apertures, rather a series of Neutral density filters that apply to control incoming light. Doesn't appear to work very well from my experience!

 

[Chris Ross]

The TG-4 has f2 and f2.8 as actual apertures, f8 is a ND filter at the wide end. It seems like it is running out of flash power as your aperture gets smaller. When you zoom in it should stop down to f4.9 or f6.3. One thought is what did your shutter speed do? On fill flash it bottoms out at 1/30 so if for example 1/30 @ f2.8 is the correct -1EV exposure on your wide shot then stopping down as you zoom will underexpose the BG - the fact that auto ISO fixes it makes this seem likely. Maybe go back and have a look at the shutter speeds selected. I would also check you are getting proper flash exposure maybe try in a darkened room at similar distances to see if 100% flash shots are properly exposed.

 

[Wiggsy]

The TG-4 has f2 and f2.8 as actual apertures, f8 is a ND filter at the wide end. It seems like it is running out of flash power as your aperture gets smaller. When you zoom in it should stop down to f4.9 or f6.3. One thought is what did your shutter speed do? On fill flash it bottoms out at 1/30 so if for example 1/30 @ f2.8 is the correct -1EV exposure on your wide shot then stopping down as you zoom will underexpose the BG - the fact that auto ISO fixes it makes this seem likely. Maybe go back and have a look at the shutter speeds selected. I would also check you are getting proper flash exposure maybe try in a darkened room at similar distances to see if 100% flash shots are properly exposed.

Thanks Chris - yes I did notice shutter speed dropping off to 1/30th (which is way too slow to freeze fish and moving subjects) but such is the limitations of the unit I guess. I tried exactly as you suggested (on the dive boat in The Maldives no less) and did some topside testing exposures. The fall off in light was noticeable straight away as I moved away from wide towards to the telephoto range....but as soon as I selected Auto ISO exposures were consistent and brilliant despite zooming. It will be a trade off I guess. I tried also using manual flash to compensate but then ended up with yukky very dark blue to black backgrounds. I'm used to using full manual on my rig but was after the convenience of S-TTL for my less experienced other half. The whole situation was possibly exacerbated by the conditions we experienced in The Maldives - with very heavy overcast and early morning dives meaning often low ambient light conditions. We used Aperture priority to get away from using underwater modes which can blow out ISO but it didn't work out as well as we'd hoped. A learning curve - some times full manual (which I use exclusively) is actually easier! Thanks!

 

[Wiggsy]

The TG-4 has f2 and f2.8 as actual apertures, f8 is a ND filter at the wide end. It seems like it is running out of flash power as your aperture gets smaller. When you zoom in it should stop down to f4.9 or f6.3. One thought is what did your shutter speed do? On fill flash it bottoms out at 1/30 so if for example 1/30 @ f2.8 is the correct -1EV exposure on your wide shot then stopping down as you zoom will underexpose the BG - the fact that auto ISO fixes it makes this seem likely. Maybe go back and have a look at the shutter speeds selected. I would also check you are getting proper flash exposure maybe try in a darkened room at similar distances to see if 100% flash shots are properly exposed.

Actually Chris, looking at it again, as one zooms in towards telephoto range, shutter speed actually increases to around 1/100th (I guess this is a built in feature to avoid shutter shake blur with longer lens length) as aperture shrinks to f8. So a faster shutter speed combined with a smaller aperture obviously means light levels will fall off and they do! Quite dramatically. Exposure pretty much falls off a cliff once you get to around 1.5X to 2x zoom. Seems a huge limitation. It just seems weird than noone else seems to have experienced this problem.

 

[Chris Ross]

You shouldn't be seeing f8 at full zoom the apertures are f4.9 and f6.3. Anything higher would mean the ND filter is in use?? Is the camera in auto ISO at that point?

 

[Wiggsy]

Chris - apologies - you are correct. I just checked again and on ISO 100 it only seems to go to f6.3. In fact it goes from 1/30th f2.8 a 1X zoom; to 1/50th f4.5 at 2 x zoom; to 1/80th f5.6 at 3 x zoom; to 1/100th f6.3. I ran identical simulation on AUTO ISO and got exactly the same shutter speeds and apertures. But on AUTO ISO the shots come out fine whereas in ISO 100 they get progressively much much darker. AUTO ISO fixes this but is not ideal I guess.