Sigma 105mm macro - technique advice please

Hi - I recently bought a sigma 105mm macro (EX DG). I have not had a chance to take it underwater yet - but have been taking a few shots on land to get a feel for it and what it can do.

While overall it's a very satisfactory piece of kit - particularly considering the price point between it and the Canon alternative, it does have a few limitations and drawbacks.

I was hoping to get some tips from other people who use this lens so that I can get the most from it - particularly Canon/Ikelite users like me.

1. The autofocus is very slow and a bit clunky - it seems to spend a lot of time hunting - sometimes without any success - particularly as you head closer towards 1:1 - on land, manual focus is the way forward here, however my Ikelite housing does not allow manual focus control of this lens as the focusing ring is too far forward for the zoom/focus gear to reach.

- can anyone give me any tips as to how to minimise AF hunting?

2. Image sharpness/aperture - overall my pics have been sharp as a knife however I have noticed that Images stopped up beyond F22 start to get a bit squishy - making what I thought was a very nice feature on paper (stopping down to F44) almost irrelevant

- has anyone experienced the same? any tips on improving sharpness in the smaller aperture range?

3. Camera shake/shutter speed - on land I normally shoot at around 1/30 - 1/60 or sometines even slower due to the small apertures involved - however when I'm shooting at or close to maximum magnification, images seem to suffer from some camera shake - my guess is that this would be relatively easy to combat underwater as the increased light from my strobes would enable me to use a faster shutter speed, plus with the added stability that the larger size of the housing would give me, shake would be reduced -

any thoughts or advice on this?

1. Use a MF port (they are there). Alternative is to use the function setting to use the * button as a AF switch. Then preset the focus on a contrast rich bit that is the same distance as the subject. Or use a focus light !

2. Thats diffraction. Google it for better explanations then I can give. It happens with all macro lenses.

3. use a tripod on land for these kinds of macro shots. I dont have the lens, but in general shooting with 1/200 or 1/250 (maximum sync or just below) should be allright.

1. Use a MF port (they are there). Alternative is to use the function setting to use the * button as a AF switch. Then preset the focus on a contrast rich bit that is the same distance as the subject. Or use a focus light !

I considered getting a manual port - but according to the port chart, there isn't one for this lens - my experience is that the Ike chart isn't comprehensive though so there may be one but they simply haven't listed it - if anyone can reccomend one that they know does work I'd be grateful.

I considered separating the buttons for shutter and AF - haven't tried it yet (lens only arrived 2 days ago) but its good to know that someone else thinks along the same lines as me.

2. Thats diffraction. Google it for better explanations then I can give. It happens with all macro lenses.

so basically you are saying avoid going beyond f22 then?

3. use a tripod on land for these kinds of macro shots. I dont have the lens, but in general shooting with 1/200 or 1/250 (maximum sync or just below) should be allright.

Normally I would use a tripod - however I'm trying to emulate how I would shoot underwater as much as possible (I even considered putting the camera in the housing minus the port to get used to using the port controls ) - so looking for more dynamic subjects like bugs and butterflies etc where using a tripod is often not practical

1. The autofocus is very slow and a bit clunky - it seems to spend a lot of time hunting - sometimes without any success - particularly as you head closer towards 1:1 - on land, manual focus is the way forward here, however my Ikelite housing does not allow manual focus control of this lens as the focusing ring is too far forward for the zoom/focus gear to reach.

- can anyone give me any tips as to how to minimise AF hunting?

Press to focus. Pick something very close to what you are trying to shoot, but brighter. Once the lens gets close to focusing, take finger off shutter and focus again. This will help minimize the lens racking all the way in and out.

2. Image sharpness/aperture - overall my pics have been sharp as a knife however I have noticed that Images stopped up beyond F22 start to get a bit squishy - making what I thought was a very nice feature on paper (stopping down to F44) almost irrelevant

- has anyone experienced the same? any tips on improving sharpness in the smaller aperture range?

As answered, diffraction. I find the image degrades noticeably after f/16. I choose f/22 as the start point to my compromise between depth of field and overall sharpness. But this depends on the distance to subject.

3. Camera shake/shutter speed - on land I normally shoot at around 1/30 - 1/60 or sometines even slower due to the small apertures involved - however when I'm shooting at or close to maximum magnification, images seem to suffer from some camera shake - my guess is that this would be relatively easy to combat underwater as the increased light from my strobes would enable me to use a faster shutter speed, plus with the added stability that the larger size of the housing would give me, shake would be reduced -

any thoughts or advice on this?

Camera shake only exists for the portion of an underwater image who's exposure is not provided by the strobes. It shouldn't be a problem for macro photography, unless you are very shallow with tons (kilos) of available light. In that case you would actually use a faster shutter speed and let the strobe provide more light. This gets rid of motion blur and provides better color.

Press to focus. Pick something very close to what you are trying to shoot, but brighter. Once the lens gets close to focusing, take finger off shutter and focus again. This will help minimize the lens racking all the way in and out.

I take it you have this lens and you've noticed it doing that as well - PITA isn't it - especially with the relatively stoneage AF system used on this lens - good tip though thanks.

I reckon then that if I combine separating AF and shutter buttons with this technique, I'll be pretty close to a complete solution.

As answered, diffraction. I find the image degrades noticeably after f/16. I choose f/22 as the start point to my compromise between depth of field and overall sharpness. But this depends on the distance to subject.

Thanks again - I'll have a play around in that range and do some comparison shots beyond f22 to find a compromise that works for me.

Camera shake only exists for the portion of an underwater image who's exposure is not provided by the strobes. It shouldn't be a problem for macro photography, unless you are very shallow with tons (kilos) of available light. In that case you would actually use a faster shutter speed and let the strobe provide more light. This gets rid of motion blur and provides better color.

Pretty much as I anticipated, but nice to know I'm on the right lines.

My two cents:

On #1, maybe a focus light would help? I see the same thing with the Nikon 105 in AF; I either use a focus light or manual focus.

On #3, to expand on Scorpio's thought: for macro, it's not so much that the increased strobe power lets you use a faster shutter speed, it's more that the primary exposure you get is the strobe, so the rest of the time your shutter is open, you're not exposing much of anything. Imagine you're in a room with zero light; you can jump up and down with your shutter open for 30 seconds, fire a strobe at the last second, and get a very sharp picture, since you didn't expose anything until you fired the strobe. Alternately, you can burn a candle for 30 seconds (i.e. low ambient light) AND fire a strobe, but you're going to get a really blurry pic with different colors if you do that. As Scorpio says, you also get better colors with a strobe, since ambient light has a blue or green cast to it.