Hi all,
Yesterday I took some sample clips to see how the A1 is working. I use TV mode in a bright light sunny day, no ND, speed 1/500. But all the samples were blurried, not so much, but blurried. Later at night I read in Manual´s page 34 (spanish) that smaller f stops can cause loss of sharpness, that´s all.
I believe is not a camcorder problem, because I have used it inside home with no sharpness problems.
My question is: What is the usable maximum f stop number to avoid sharpness problems?
I know that it depends on multiple variables, but as a general rule and based in your experience, can you, please, give me an idea?

PD: Next time I´ll use AV or A modes.

Thanks in advance.

My question is: What is the usable maximum f stop number to avoid sharpness problems?

Look on it this way - all the apertures on the lens are usable, but some compromise the picture quality for various reasons.

Your Canon's zoom is designed to work best wide open, so in answer to your question f1.6 at wide angle and f3.4 at full tele. But shooting at maximum aperture you'll get vignetting - where the corners of the picture receive less light than the centre. Your zebras demonstrate this clearly, and you'll need to close down 2 stops to evenly light the frame.

At wide apertures you'll also get more internal flare, and this will gently cloud the image. The internal barrel of the lens cylinder should be a perfect matt black - and of course it never is.

Once you go smaller than f/4 (f/5.6, f/ 8 etc) then you'll gradually lose sharpness. It's not Canon's fault - it's the laws of optics at work, and diffraction will gradually soften the picture more and more.

If you're shooting HDV then don't stop down below f/4.5 if you want maximum sharpness, and at wide angle (where diffraction is even more of a problem) treat f/2.8 - f/3.4 as your smallest stop.

tom.

Thanks a lot, Tom

A very usefull information from you. Coming from DSLR world my old rule of thumb is f8 for maximum sharpness, maybe f5,6 for fast lens. But, I reallly didn´t know the specific design rules of the Canon A1 zoom lens.

So, in this camcorder, recording in HDV, minimum f stop will be f4, as a rule of thumb.

Thanks again.

Hu Juan.

Tom's advice is very sound, but I think it would not be a good idea just to set the aperture in Av mode and then let the shutter speed take care of itself (in case that's what you are planning to do, based on your first post). If the shutter keeps changing, the feel of the video will change too, so I would recommend you try it out on several shots with movement and various light levels, and then decide that that is the effect you want.

Usually I will set a fixed shutter speed, and then use ND filters to get the aperture into the right range. The A1 has 2 ND filters built-in, and I have a couple of screw-on ND filters that I can also use if necessary.

Of course, it could just be that I'm a control freak. :)

Richard

Thanks a lot, Tom

A very usefull information from you. Coming from DSLR world my old rule of thumb is f8 for maximum sharpness, maybe f5,6 for fast lens. But, I reallly didn´t know the specific design rules of the Canon A1 zoom lens.

So, in this camcorder, recording in HDV, minimum f stop will be f4, as a rule of thumb.

Thanks again.
Diffraction is more of a problem for the XH-A1 and similar video cameras than it is for DSLRs because the image detector is that much smaller. For good old fashioned 35mm film SLRs, it isn't an issue until you get to really quite high f-numbers (F22 perhaps?)

Richard's right - for movies it's very important to lock down the shutter speed and use the camera in the shutter priority mode. I've seen footage shot in the aperture priority mode (PDX10) that showed the aeroplane's propeller coming to a stop and reversing as the Spitfire took off - all because the shutter speed and the engine's crankshaft were varying their speed and getting in and out of sync.

Mark's also right. A 35 mm SLR uses a huge 'chip' of 36 mm x 24 mm - whereas our tiny 1"/3 chips are but 4.8 mm wide. Diffraction affects us all the same of course, but the much longer focal lengths of the 35 mm camera mean you can 'get away with' smaller apertures. But then again, f/22 will be a lot less sharp than f/5.6 all other things being equal (like off centre elements and so on).

tom.

35mm FILM cameras do not really suffer from diffraction even at the smallest apertures, as film is not as sharp as the sharpest digital sensors. But full frame dSLR:s like Canon EOS-1Ds Mk III start to loose real resolution if stopped down below f11.

Here is a semi-scientific paper about diffraction: Do Sensors “Outresolve” Lenses? (http://www.luminous-landscape.com/tutorials/resolution.shtml)

At the end is a table showing the best possible resolutions at each sensor size and f-stop. Those sensors are for still cameras, but it is easy to extrapolate and realize, that small compact cameras with slow zooms can not resolve 10-12 MPix as promised, and that 1/3" sensor HD video camera is actually impossible to make, unless you have f2 lens throughout the zoom range.

Take the camera out of autofocus, and manually focus it on your subject.
Use ND fileters outside to set an f stop that applies to what you want in focus, and or where you want bokeh to appear. The XHA1 is very responsive. A number of other things. Do a search on "sharpening + SLR" in Google and look at what most shooters understand about in camera sharpening. Use Wolfgang's -3db custom settings and read what he has to say about this.
If you point and shoot this camera at a subject in auto mode you run the risk of your subject, being in the middle of the screen, going in and out of focus because the camera does not know to follow the action. Go manual or suffer.

Wolfgang's hp blog - Presets for Canon XH A1 (http://66.163.168.225/babelfish/translate_url_content?lp=de_en&trurl=http%3A%2F%2Fwww.fxsupport.de%2F02_Canon_XH_A1.html&.intl=us)

C'mon Petri - saying film cameras don't suffer from diffraction is only correct if you don't use lenses on them. Even a pin-hole camera suffers from diffraction (very much so).

It's the iris diaphragm that causes diffraction losses, and the sharpness of the film (K25 anyone?) has no effect on it at all - it's simply the laws of light being brought into play.

Coming also from high end still digital camera/lens background, I'm surprised there are no resolution charts of stills pulled at the various apertures and zoom distances with a fixed optimal shutter speed. The "pixel peepers" in DSLRs would have been all over this for us ;)

If anybody knows if such a thing for the the A1 with its standard 20X lens, I've love to see the link.

C'mon Petri - saying film cameras don't suffer from diffraction is only correct if you don't use lenses on them. Even a pin-hole camera suffers from diffraction (very much so).

It's the iris diaphragm that causes diffraction losses, and the sharpness of the film (K25 anyone?) has no effect on it at all - it's simply the laws of light being brought into play.


Of course the diffraction is a lens thing, but the fact is that the sharpest digital sensors have far surpassed film resolutions. For that reason diffraction was not of much concern in the good old days of film. Now 20+ MPix full frame 35mm sensors are much better than lenses, same with mid format backs approaching 50 MPix resolutions. But the worst are 1/2" sensor 12 MPix compact cameras, where diffraction starts to kick in the moment you touch that zoom rocker.

Only after 39 MPix (sub-)midformat digital backs came to being did major field camera lens makers like Rodenstock and Schneider start making new "diffraction limited" digital lenses, which start to loose resolution already from f5.6, which paradoxically, means they are of best quality. In the times of film there was no need.

Well, I did a test just a moment before. Iris full open (f1,6), then f 2.0 and f 3.2 and sharpness was really fine. more than enough for me. Several zoom positions.

My DSLRs are Nikon D200 and D300 and all my lenses are fast lenses all of them, more than $1000 each, so I know what I am talking about. In DSLR world most of lens sharpness is in the middle of the f stop numbers, so I can imagine, by simple optics laws, that in a different range of f numbers can change the rule. The Canon is f1,6 -9,3, theorecatelly, the middle is about f4, but, of course this is not a scientific theorema.
Sorry but I can´t express myself as well as I would like, my native idiom is spanish.

Thanks all. Really nice forum.

Sorry Petri and with respect, but what you're saying just isn't true. Diffraction was certainly of GREAT concern in the good old days of film, as anyone shooting Standard-8 or Super-8 film (5.4 x 4.1 mm frame) found out to their cost.

Then you say that, 'diffraction starts to kick in the moment you touch that zoom rocker', and of course this is nonsense. The focal length of a lens doesn't cause diffraction on its own, it's small apertures that cause diffraction. The shorter the focal length the more diffraction affects the sharpness, but it's still aperture dependant.

It's the reason the Z1 allows you to limit how far the diaphragm blades stop down - Sony knows what shooting at small apertures will do to their reputation.

tom.

Same with the Canon XH and XL H series... f/9.5 is about as small as you're allowed to go in most program modes. You can force it into f/11 to f/22, but at those apertures diffraction is indeed a serious problem affecting focus.

The fact that he shot at a much faster than normal shutter speed also probably affected the footage.

This may be a dumb question but isn't this the point of the ND warning ikon ie to prevent exposures that will be small enough to affect focus?

Well you have to use the ND when shooting outdoors under bright sun or you'll be way overexposed, so yeah, I guess you're right. Unless you use a really fast shutter speed, but that's going to mess with the image. It's also a good idea to have an ND .3 filter to stick on the lens if you want to open up wider under those conditions.

Sorry Petri and with respect, but what you're saying just isn't true. Diffraction was certainly of GREAT concern in the good old days of film, as anyone shooting Standard-8 or Super-8 film (5.4 x 4.1 mm frame) found out to their cost.

Sorry, I forgot about really small format film. Never shot hardly any.


Then you say that, 'diffraction starts to kick in the moment you touch that zoom rocker', and of course this is nonsense. The focal length of a lens doesn't cause diffraction on its own, it's small apertures that cause diffraction. The shorter the focal length the more diffraction affects the sharpness, but it's still aperture dependant.

It's the reason the Z1 allows you to limit how far the diaphragm blades stop down - Sony knows what shooting at small apertures will do to their reputation.

tom.

What I meant by"diffraction starts to kick in the moment you touch that zoom rocker" was that cheap long zoom lenses start to loose maximum aperture when you zoom in even a bit. That causes aperture to close and diffraction starts to affect the image. We all (?) know that diffraction is tied only to relative aperture (F-stop), focal length or film/sensor size plays no role in this. It is just that when sensors have too much resolution relative to their size we are faced with this phenomenon. And with super-8...

What I meant by"diffraction starts to kick in the moment you touch that zoom rocker" was that cheap long zoom lenses start to loose maximum aperture when you zoom in even a bit. That causes aperture to close and diffraction starts to affect the image.

I can see how you think this but again it ain't so. Very nearly all zoom lenses lose speed as you zoom, but that's simply a design requirement to keep size and weight down. The 14x Fujinon supplied with Sony's EX1 isn't particularly cheap, yet loses speed like all the rest.

You're correct that they 'start to loose maximum aperture' but that's all they do - they have smaller maximum apertures than they do at wide-angle yet their diffraction losses are still in the small aperture range. Although max apertures are wider at wide-angle, it's these short focal lengths that are worst affected by diffraction.

tom.

Well you have to use the ND when shooting outdoors under bright sun or you'll be way overexposed, so yeah, I guess you're right. Unless you use a really fast shutter speed, but that's going to mess with the image. It's also a good idea to have an ND .3 filter to stick on the lens if you want to open up wider under those conditions.
Thanks Bill
What I meant specifically is that on page 37 of the XH A1 manual it says

'When recording in bright surroundings, the camcorder will set a small aperture and the picture may appear blurred. Turn the ND filter on/off according to the screen display'.

I suppose the question to everyone is therefore can you rely on using the ND filter when the warning icon appears ie is that sufficient to keep you within the exposure range needed to avoid blurring. To put it bluntly, does the ND filter warning icon do the job?

The ND filter v'finder warning is triggered (in all my Sony cams) by the diaphragm blades hitting their end stops - i.e. max or min aperture, so I'm guessing Canon use the same triggers.

So - flip those NDs into the light path way before the camera silently screams for them. Keep your apertures wide if you want the sharpest pictures.

tom.

The answer is, of course, yes, it does the job.

Do I consider the entire mindset of this thread to be a bit OTT, is also a yes.

Of course, everybody is, strictly, correct.

Now, I might notice it, you may notice it, and I have no doubt whatsoever that the distinguished posters to this thread would notice it.

BUT!

Yer average Joe Blogs in the street who might, just, be on the receiving end of a particularly bad example of lens diffraction (courtesy of the good 'ol Beeb) wouldn't know squat diddly from a bit of bad focus (of which there is a great deal).

Personaly, hey, I've shut my A1 down to near blackout with the ND's maxed and it's still been too bright, but, hey, the footage passed with flying colours and not a murmur of "diffraction" to be heard from the assembled herds of "experts".

Once your head gets so far up your rear end this sort of discussion can get as carried away as it has, it's time to take a step back and ask yourself - what am I trying to achieve here?

Who's gonna watch this?

What's important - the medium or the message?

Yer average Joe is more than happy if it's relatively in focus and has slightly better colour than the 'LSD freak show" phase of CSI Miami (you'd be suprised at how many didn't even notice the latter!).

Absolutely no disrespect to any of the other posters here, I've read their post carefully and there's been some pretty comprehensively good stuff here, no question.

At the end of the day, the guidlines are just that, shoot what you can with what you have and leave it at that.

Concentrate on the message and not the medium (all other things considered, of course).

My 2 cents.


CS


PS. Nice to be back.

"Concentrate on the message, not the medium." Very nice, sir. Very nice.

I actually have some first-hand experience in using the A1 with a very closed iris. I was shooting an outdoors auto show and I was experimenting with "Deep focus," the idea being that closing down your aperture widens your depth of field.

I wanted muscle cars close to me, and ones far from me, to all be in perfect focus. Plus it was super bright, so I closed the iris way down, to like 9.5 (if memory serves) for most of the day.

The A1 takes stunning images and most of the footage was just great. But some footage was very dissapointing - looking washed out and slightly blurry. I've got another custom truck show this weekend and I will certainly be using ND filters to cut the sunlight instead of using the aperture.

If you want more info, and a longer-winded explaination, check out my blog posts about the subject (and how I fixed some of my footage) at XR.

Will Mahoney's Blogs - Color Correcting, Deep Focus, Bright Sunlight and Classic Cruisers! (http://exposureroom.com/members/WillMahoney.aspx/blogs/post/206)

I agree this kind of thing can get totally out of hand (I've witnessed it) but as long as it doesn't take over your thoughts as you shoot, the info is a good tool to have in your box for the overall product.

Besides, the way things are going, who knows what will or won't be acceptable in the future? If I happen to get some really compelling footage, I'd sure like to have shot it in a way that might hold up down the road. That's why I got this A1. It's not the best but its the best I can get for now. And I want to use it at its best. That's all.

But your point is well taken.

JMHO.

I wanted muscle cars close to me, and ones far from me, to all be in perfect focus. Plus it was super bright, so I closed the iris way down, to like 9.5 (if memory serves) for most of the day.

The A1 takes stunning images and most of the footage was just great. But some footage was very dissapointing - looking washed out and slightly blurry. I've got another custom truck show this weekend and I will certainly be using ND filters to cut the sunlight instead of using the aperture.



Will:

If your "very dissapointing" footage was so bad it was unusable, I think I know what you mean. Did the white balance look off too (brownish)?

One of my A1s used to do that every once in a while in bright light when capturing a clip. Usually the next clip was fine even though I didn't change anything. It was something you couldn't see on/in the viewfinder, but on a monitor it was awful.

I sent that A1 back.

Jeff

May I guess the Canon XH A1 is a changeable mood camcorder?