Optimal aperture setting for XH A1
 

I just noticed the following in the manual concerning ND filters: "When recording under bright conditions, the camcorder sets a small aperture value, and the picture may appear blurred..."

I've often filmed at the lens's smallest aperture of f9.5 (which has always seemed to me a relatively large 'smallest' aperture - the XL1 has as its smallest f16) to get maximum depth of field.

Does the above line from the manual suggest that should be avoided? Is there considered to a best aperture on the camera's lens?

Thanks.

John

The trouble you run into with small apertures around f/9 or so is a soft-focus issue called diffraction (same thing can happen at fully open apertures as well). The ideal aperture value, the sweet spot, is f/5.6 or thereabouts.

Wow this is news to me. I'll have to give it a shot. I always shoot wide open even outdoors in bright sunlight. If the NDs don't do it I crank the shutter.

Same with me. I shoot as wide-open as possible. Most of my shoots are indoors, so if I wanted to shoot at f/5.6, I'd either:
1. need a Hollywood-sized lighting setup
2. need to get right up in everyone's face
or
3. pump up the grain...um, I mean "gain".

I'm not a true lens geek. Is there a way of determining what the sharpest aperture will be on a given lens without just shooting and comparing? I'm a math and engineering geek. I need formulas.

This morning I spent three hours sitting on a cliff top watching a family of kestrels. I've just downloaded the clips, and had a look at the results. I was disappointed that they weren't as sharp as usual, and put it down to the hazy light. But then there were a few wide shots that looked as though I'd focussed manually but got it wrong. Strange, as everything was done on auto-focus (because of eye problems, not because I'm too lazy).

Towards the end of the session, I realised the neutral density filter was on 0, usually I have it on at least 1/6, if not on full to keep the depth of field narrow (the last time I used the camera was in poor light, hence the ND was off). If I hadn't had the portabrace body armour on the camera, I'd have realised earlier that the ND switch was in the wrong position.

So I did a few shots using the filter, just before I left. Those last few shots are sharp - at least as sharp as the light allowed. The earlier ones are complete rubbish by comparison. I hadn't realised just how much softer the picture was a small apertures. In fact, I think Canon have it right by calling it "blurred" in the manual!

I saw a video of some XH-A1 lens tests carried out by Dennis from Cinevate, and he determined that the A1's sweet spot for edge to edge sharpness is f4. I now try to keep my lens as close to f4 as possible and am happy with the results. Of course I also use wider apertures as well if I want to reduce DOF or in low light conditions, but I try not to close down beyond f5.6 or so.

I've had similar experiences to Annie's in the past, where the footage was basically unuseable because the aperture was too small. Scenes with fine details are especially bad, you wouldn't think it was the same camera. So even in AE mode, I always try to remember to push Exposure Lock to check aperture.

Richard

Unfortunately that's a promise I made to myself that I seem to have forgotten. I use TV (shutter priortity) mode mostly because when I first got the camera, I was using the AE lock as though it was the button in the same place on my XM2, and ending up with all sorts of wierd shutter speeds. Now at least I'm keeping the shutter speed consistent at 1/50. Perhaps it's time I changed back to AE (my stills cameras are permanently on AE mode).

Annie. I got fed up with screwing up shots because of focusing problems in difficult conditions (low light, through trees, detailed close ups, pulling focus etc) and bought myself a monitor. It's cost me more than I can afford but I think it will be worth it.
It's no good though when you need to move the camera around and get your shots quickly - too cumbersome by far.
I've been shooting more in manual recently too (used to use TV together with exposure lock all the time) and try to keep at around f4 or 5.6 ish and I am sure that has improved the image too.

Hi Richard

I can't use the viewfinder easily because I have "floaters" in my eyes that tend to hang around or drift across the centre of my vision. Using the LCD screen is difficult because I need reading glasses to focus on that properly (the vari-focals are ok for very short periods). So then I can't see my subject if it is in the distance. The kestrels were particularly difficult because they were brown birds against a brownish cliff. There was one the the early clips from that session where I was actually filming some vegetation because I couldn't see that it wasn't a kestrel - the kestrel was on the top edge of the frame. But now I can see that part of the difficulty was that wide open aperture.

I have recorded directly to the laptop on occasions - in the garden - and oh, the joy of being about to focus something properly using the big screen . . . . . So I've thought about getting a monitor, but it means extra weight and bulk to carry out in the field, more fussy things to set up, and currently my tripod is inadequate for the job. For future reference, what monitor do you have?

I agree with Richard - if you're shooting in HDV onto tiny 1"/3 chips and are critical of your results, then f/4 is as small an aperture as you want to go. You should call up the NDs way before the silent scream begs for them. If you have ½" chips you can stop down to f/5.6, and of course if you're shooting onto full frame DSLRs then you can safely go to f/8.

When I tell people this they often think I've got it the wrong way round and that 'the smaller the aperture the better'. But these folk invariably come from the old school, where back in the 80s they used film SLRs with zoom lenses that had nowhere near the build quality and assembly tolerances of today's zooms. With those old zooms you needed small apertures to overcome element miss-centering mainly.

My old VX2k was able to film at very small apertures, f/11, 16. 22 and 45 before the aperture blades closed, and this gave a very convincing demonstration as to what diffraction does to sharpness. Wide open at f/1.6 it was a lot better than stopped down to f/8.

tom.

Hi Annie
The viewfinder is pretty hopeless anyway for really accurate focus.
I bought a used Marshall V-R70P-HDA from a nice guy on DV Info. I don't know if it is the best monitor I could have got for the money and it may have been superseded by now. So don't take this as a recommendation (eg with the battery it is very heavy).
However I am really pleased with it. I can see exactly what the camera is seeing and can get the focus spot on.
Even secondhand, with a new V Lock battery and charger, bag and a mounting arm it's cost me over £1,000.
It plugs into the component-out cable from the back of the camera.
If you ever decide to go down this route I can send details of how I fixed the mounting arm to the tripod (it moves with the camera) which works well for me.
BTW I am only using a pretty ordinary Manfrotto tripod and it seems to handle it all OK.
The monitor and battery go into the same bag and probably weigh about 5lbs. I don't know how long the battery will last for yet.

Tom - I usually have the ND filter on full, and only turn it down when the picture is getting too dark.

Richard - thanks for that. My tripod is a Manfrotto 190 with a 50mm levelling column. It's the column that isn't up to the job - so I'm going to purchase a Libec38 when I get paid for the other work I'm doing. (or should be doing - why am I looking at this forum when I'm supposed to be writing reports?)

To those who prefer to shoot at wider apertures, how far up will you run the shutter before compromising on aperture?

Not entirely sure what you mean Doug, but my FX1 and Z1 can be run in the aperture priority mode rather than the more usual shutter priority mode.

Say you wanted to film at f/2.8 so that you got minimal dof. You lock in the w/bal, the gain and that aperture and the camera compensates by varying the shutter speed in infinite steps between 1/50th sec and 1/10,000 th sec.

To lock down the exposure you simply touch the shutter speed button whereupon the v'finder display gives you the figure to the nearest ¼ stop. To go back to auto you touch that button once again and the s/speed display disappears from the screen.

If it gets too dark for f/2.8 and 1/50th sec you have to release the gain, and then that too will vary smoothly between 0 and +18db. The camera doesn't include the slow shutters in its auto mode.

I notice if the shutter speed is about 1/200 th and shorter, when moving objects start to become slightly stuttery.

tom.

Tom to simplify:

You want to shoot at at 2.8

To do so you would need to set shutter at 1/1000

Are you going to shut down the lens or live with the stutter?

I would prefer to add an ND filter (or 2) to cut down the light and try to get the shutter speed to 1/50s or so.

Richard

Stop down the lens. Or screw in an ND filter to add to the in-builts. If your camera allows it, use negative gain.

just to clarify, what is negative gain?

Hi Josh. Gain is used to boost the analogue sensor signal before the A-D conversion stage. Gain values of +3dB, +6dB, +12dB are common on many video cameras. Without any boost the gain is 0dB. If the signal is cut instead of boosted, that is negative gain, for example -3dB. To give you a feel for the numbers, if the signal is cut by half, which is like losing one stop of light, the gain would be -6dB.

Richard