H-system Autofocus

[Chris Gahran]

I work with fellow photographer on his location seamless furniture shoots. He owns Canon gear but I bring CF-22MS backs on 555ELDs and he and his clients really appreciate the images produced by using a 4-shot camera.

He wants to buy into a 4-shot system but his poor eyesight has him thinking he needs an autofocus H-system. I am not sure the H-sytem autofocus will work for him.

I usually shoot at ƒ16-16.5 but if I need to stop down to ƒ22 there is no diffraction softening of the image. (I can stop down to ƒ22.5 without diffraction degrading the image.)

Using a 100mm lens (V-system) when shooting a dining table with six chairs, the nearest chair is at 15ft (~5m) and farthest chair is about 23ft (~7m). I shoot a few Previews (1-shots actually) to reach a compromise focus point so the entire image is sharp.

I am guessing an autofocus system will latch onto the nearest dining chair and not carry the DOF to the farthest chair. Additionally he will not be able to stop down more than ƒ8-11 using a 50MS back.

Also a HTS will not help because with a tall subject in the foreground (a dining chair), you can't tilt the lens. (My comment is based on 20 years of shooting 8x10 and 4x5 film.)

So, will an auto focus H-ysytem really work for him?

Chris

[NickT]

Hi Chris
Pretty much every H user that I know has the AF set to manual but assigns the user button (or true focus button on more recent models) to AF drive. You put the centre brackets where you want focus, press the user button then recompose and shoot. With the image you have posted I'd place something in the on the table to focus on (Assuming the AF couldn't get a fix on the wood grain. I don't know what aperture he'd be happy with diffraction wise, I think that's a personal preference and need to be tested. If I was shooting this with a 50MS and having trouble getting enough DOF at say f11 I'd just back off a bit as there's a ton of resolution to play with.

Hope that makes sense.
Nick-T

[Chris Gahran]

Thanks Nick. Carry a focus target, put it on the table, twist the camera to center the focus target for the AF, lock the focus and recompose the image. BTW, the better solution to get extra DOF would be to change to an 80mm to maintain the perspective.

My friend wants the subjects totally sharp. He will not accept, for example, the back chairs being being slightly soft.

Are the H series zoom lenses as good as primes? Can a 50-110 be set to 100mm then zoomed out to 80mm?

Chris

[NickT]

Yes I should have said back off and raise camera

I have the 50-110 and would say it is very very close to the primes for sharpness.

[Miller]

I have no experience with multishot backs, but isn't it necessary to tether the camera and operate it from Phocus?
If so, in live view mode you have complete control over where to focus the camera from the software.
I don't want to start an endless discussion on what is totally sharp.
Your friend should try the H multishot in order to see if he can achieve his objectives.

[NickT]

Yes multi-shot must always be tethered.

[Alex]

Hi Chris,

Re zooms: I occasionally use a HCD35-90 and have to say it is very impressive and as sharp in middle as the HC80 and HC120II, however at the edges it more softer up and doesn't really sharpen up until diffraction starts kicking in at around F14 - so if you're shooting F16+ it should be fine.

Re Focusing: for critical focusing whether it be for all encompassing small aperture single capture or multiple stacks, a laser measure (with a continuos measure function), mounted on the same plane as the sensor is indispensable for finding the near/far depths and hence locating the focus point position (for introducing a focus targe into the scenet), after dialling the figures into a decent DoF app. I have the camera and laser mounted onto an RRS 18" rail to help keep it all together.