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Canon XL H Series HDV Camcorders
Canon XL H1S (with SDI), Canon XL H1A (without SDI). Also XL H1.


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Old November 23rd, 2005, 08:19 AM   #1
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Why have video lenses anyway

Quote:
Originally Posted by Chris Hurd
35mm still photo lenses already resolve to higher-than-HD standards, so they're all considered "HD." Just make sure that you're not using the cheap glass like the throw-away lenses given away with inexpensive SLR's like the old 35mm Canon Rebel G. If you stick with Canon "L" series glass (with the red ring around the lens barrel), you'll have more than enough optical quality for HD.
May be a little naive on my part, but if 35mm lenses are better than HD & SD video lenses, why have video lenses at all ? I've never understood why video cameras don't use 35mm lenses, especially whilst there are forums here dedicated to making adapters to do just this.

Take something like the letus35 adapter that takes a standard 35mm lense, projects it onto ground glass, and then the video camera lens focuses on the projected image. The image is upside down, but only because this is external to the cameras video lens which already makes that correction. You get the great shallow DOF and manual lenses as standard !!

In other words, why don't video cameras like the XL2 & XLH1 use a 35mm system, built in ? You would have a hugely vast array of lenses at your disposal. The EF adapter is great but introduces the 7.2X magnification (which is nice for some things).
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Old November 23rd, 2005, 09:34 AM   #2
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(this is a new topic split from another thread)

Hi Declan,

I believe there are two primary reasons at work here. First and foremost, as indicated by the "35mm" nomenclature, a 35mm lens is designed for a 35mm image plane, the size of the film where the image is made. The image plane in a video camera is much, much smaller... about 8.5mm or so for the Canon XL2 and XL H1 for instance. That's the size of the CCD block. So you can see how it requires a lens which makes a smaller image. Otherwise with a 35mm lens you get that 7.2x magnification factor which you mentioned (hence the popularity of the Letus35 and other adapters which attempt to skirt that issue).

The other primary reason is that 35mm still photo lenses don't have motorized zooms, and the ability to pull a zoom during a shot is seemingly one of the most important aspects of video production, at least, it's certainly a popular thing to do anyway. Plus having a motorized zoom means you can control the camcorder remotely without having to touch it. Not touching the camcorder during shooting is the best way to operate it, and this wouldn't be very easy without zoom motors. Hope this helps,
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Old November 23rd, 2005, 10:25 AM   #3
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Chris

I understand what you're saying, but my point is this. If the 35mm format can be "skirted" around by use of an adapter, that's one issue solved. i.e. the difference in image sensor size can be accomodated by such an adpater. Rather than manufacture larger video lenses with motorised zooms etc, why not have manfactured lenses in 35mm format to accomodate the extra features required by videography (if you see what I mean). This would give the user the choice of dedicated 35mm video lenses or existing ranges of SLR lenses.

I believe that there can be a 1 stop loss in light using such an adapter, but there must be some other technical reasons why this route wasn't taken. The adapter could have been built in to the camera body. Like I say, I'm probably missing something fundamental, but in my view of the world people are finding solutions to enable them to use 35mm lenses with good results. I can't see why the camera manufacturers didn't consider this as an option (perhaps cost or quality).

Just posing the question really.
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Old November 23rd, 2005, 11:04 AM   #4
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Quote:
Originally Posted by Declan Smith
The adapter could have been built in to the camera body.... I can't see why the camera manufacturers didn't consider this as an option.
Probably because the overwhelming majority of camcorder owners simply don't need that feature. And if they do need it, there are plenty of affordable third-party solutions to choose from.

I realize there is a lot of discussion about those third-party 35mm adapters here at DV Info Net, but that's because we're the center of the universe for that sort of thing. If you look at the big picture, most videographers have no need for it at all. The 35mm lens adapter is for a very tight niche market, with its nexus thankfully on this site, but the overall demand for it is not compelling enough to build into a camcorder a feature that most videographers aren't going to use.

Video cameras need video lenses, which are very different things from still photo lenses. I think the array of available third-party 35mm adapter solutions will easily and adequately meet the demand for that specialized kind of shooting without the camera manufacturers getting involved. Consider also that it's a lot less expensive to go through the process of an add-on third-party 35mm adapter. If it was built in to the camcorder, you'd pay a higher premium for it in the form of a much more expensive pricetag on that camcorder.
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Old November 23rd, 2005, 11:33 AM   #5
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Quote:
Originally Posted by Chris Hurd
I realize there is a lot of discussion about those third-party 35mm adapters here at DV Info Net, but that's because we're the center of the universe for that sort of thing.
The 35mm lens adapter is for a very tight niche market, with its nexus thankfully on this site.
Quite right ! Long live DVINFO.

Thanks Chris. I guess you're right. I suspect I am looking too simplistically at it. It's a good job we have such a great resource here and plenty of enthusiasm from members.
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Old November 23rd, 2005, 01:13 PM   #6
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Chris nailed the focusing thing: a lens designed for 35 mm film focuses the image onto a 35 mm plane. The magnification of the resulting image is a lot smaller, and thus the overall quality of the lens may be reduced.

The CCD manufacturing process makes large CCDs expensive, so CCDs are typically smaller. Hence the lenses must be designed to focus on a smaller area. The situation we're at now is a trade-off between designing lenses for small sesnors (harder than designing lenses for large sensors), and building sensors large enough to have desirable sensitivity.

Adding a virtual imaging plane to the system increases the complexity, and is yet another feature that would have to be designed and tested carefully. It would add significantly to the cost. Fundamentally, you still have to build a lens to focus the image onto the small sensor - so you don't save anything on lens design costs, though this particular lens could have a fixed focal distance and no moving bits.

The other thing worth pointing out is that nice small video CCDs offer an actual advantage in terms of having large depth-of-field. While the filmmakers among us wish to immitate their richer brethren, dealing with shallow DOF makes focus critical and difficult to achieve.

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Old November 23rd, 2005, 05:32 PM   #7
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A 35mm lens is not sharp enough for HD though. That's why Panavision designed their primo-digital lenses as they found that their existing lenses were not sharp enough for 2/3" CCD HD, never mind 1/3" HD.

And yes, there's the issue of zoom, ergonomics for video, and the added complexity of the beam splitting prism.

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Old November 23rd, 2005, 05:59 PM   #8
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You already gave the reason... in part.

35mm lenses have that 7.2x magnification factor because of the size of the image sensors in these "cheap" video cameras. This is because they basically only use the center area of the image from the lenses.

If you look at the Panavision version of the F900 series you'll see that it includes other optical components to "step down" the resulting image size from the lenses. This adversely affects lens performance. (Many prime lenses of the most common, meaning most frequently used, lens focal lengths have pure "HD" versions used for the F900's... but I digress.)

Now, with smaller imagers like the one's on the XL-1 this performance penalty is very great. The smallest focal length 35mm lens I know of is a 14mm. Once mounted on the XL-1 that's equivalent to a 100.8mm zoom on a 35mm camera. Ouch.

Finally, though the EOS/EF-L glass is fantastic, you must realize it is all now limited by the performance of the EF adapter at present. Additionally, if you want to use a 35mm lens for "normal" video work you would need a wide angle converter of at least 3.6x power. That would make the 14mm lens I mentioned above a 28mm equivalent, which is reasonable.

What is the lens performance penalty for that arrangement though ?

It may be possible to build a 6-7 mm 35mm lens but nobody I know of has done it and I gather there are practical issues not covered in first semester optics class.

If Canon included the features of the EF adapter in the XL series camera and used 35mm lenses by default we might get some advantages, but at greatly increased costs overall.

It is simply easier to build lenses with very wide angles for small chips found in video cameras.

That said, it may be to Canon's advantage to build towards a video camera that can use 35mm lenses with full fields of view. They would have only ONE series of lenses that could bridge the gap from amateur photo and video to the most demanding professional work.

The main reason I suspect they have not done this is because a 35mm sized video imager that operates at full video speeds is a VERY expensive beast right now.

The imagers in top end PRO digital SLR cameras have the raw throughput to image full frame 1080p at low video speeds (24-30fps). A 35mm imager with a resolution of 1920x1440, or about 2.75Mpixels, could easily be cropped to 1920x1080p or shot with anamorphic lenses for vertical oversampling.

Check back in five years.
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Old November 23rd, 2005, 07:25 PM   #9
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Quote:
Originally Posted by Graeme Nattress
A 35mm lens is not sharp enough for HD though. That's why Panavision designed their primo-digital lenses as they found that their existing lenses were not sharp enough for 2/3" CCD HD, never mind 1/3" HD.

And yes, there's the issue of zoom, ergonomics for video, and the added complexity of the beam splitting prism.

Graeme

I was under the impression that panavision designed the primo lenses becase at the time there was no real HD option for primes. This then allowed them to use their own 35mm primes with an adapter to a modified f900 mount. Then Zeiss, and canon and Fuji all released there HD glass, and there's not such a need for the primo's except for if you renting from panavision.

What I'm curious about is the use of a pro 35, why through up a diffusion filter (the gg) and also a lens that isn't sharp (a 35mm lens). That wouldn't make since to me. I think maybe 35mm lenses are sharp enough to resolve HD footage, however, due to the other issues you listed, and largely due to the need to be able to back focus, you find that using 35mm lenses would not be practical for HD. (at least full fleged HD)
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Old November 23rd, 2005, 07:31 PM   #10
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Well, they needed to design new lenses for the reduced chip size over 35mm - that's true, but they also had to make them a lot sharper too.

It's not the sharpness of the lens, per se, but how sharp the lens has to be for the pitch of the pixels in the CCD. The smaller the pixels, the greater their resolution in lp/mm, and hence the lens has to be sharper too. 35mm is a lot bigger than 2/3" and hence can get away with less sharpness for the same amount of resolution in the final image.

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Old November 23rd, 2005, 11:20 PM   #11
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Wouldn't the problem of those high-end lenses for the smaller consumer DV cams with 1/3 " CCD's be solved if the industrie would establish priorities now on scaling the sensor sizes on, let's say 1 Inch, and the professionals even to 35 mm? This step is what I'm looking forward to. It's maybe already off-topic but are there maybe rumours about future steps in this direction? In technical view it would include the step to a single CMOS sensor like in the still photography section.
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Old November 24th, 2005, 01:08 AM   #12
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Quote:
Originally Posted by Dario Meier
Wouldn't the problem of those high-end lenses for the smaller consumer DV cams with 1/3 " CCD's be solved if the industrie would establish priorities now on scaling the sensor sizes on, let's say 1 Inch, and the professionals even to 35 mm? This step is what I'm looking forward to. It's maybe already off-topic but are there maybe rumours about future steps in this direction? In technical view it would include the step to a single CMOS sensor like in the still photography section.
Well, this is what I meant in my post on the topic.

The technology just isn't ready yet, but within five years it will be.

Companies like Canon, well *especially* Canon, would really benefit from being able to sell just one size imager and a single lens system.

Its all about getting the technology down in price though. Well, not all this type of technology doesn't quite exist, but its clear from what does that it could be made.

Its just engineering. Nothing new has to be invented and there is no new physics.

Now, we just have to make sure video camera manufacturers know this is interesting to us... over and over and over and over and over etc.

Of course- we have to ask ourselves first- is this a solution in search of a problem ?

Is it even a solution ?

Still photography lenses have different technical requirements from video and film. Do you really want to do your day to day shooting with a lens designed for 35mm still photography ?

OK, lets say you don't mind that... why is it a problem?

What failing of existing video lenses do you think using a 35mm lens will solve?

What about consequent effects- do we really want an HD imager the size of a 35mm film frame in any dimension ? How does that affect imager performance ?

There are VERY few areas where the trade off is worth it as a user.

I do believe that in the future we will see this feature- but I strongly doubt it will be driven by consumer demand, but rather by cost cutting at a company like Canon.

If Canon make "EOS-V" video lenses and cameras that use the EF mount standard with an imager the same size of the film frame, then they could drop manufacturing for the XL lens lineup- and might even be able to drop it for many of their lower end camcorders as prices come down.

Then you have a situation where Canon sells a range of video cameras for HD, very much like what already exists in the still photo world.

So, yeah it COULD benefit Canon, but I don't get how it would benefit ME.

Unless it means they sell camcorder systems at a lower price... that's a benefit I'd dig.<shrug>
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Old November 24th, 2005, 09:39 AM   #13
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Originally Posted by Alexander Ibrahim
What about consequent effects- do we really want an HD imager the size of a 35mm film frame in any dimension ? How does that affect imager performance ?
A good point. Yes, not everybody would be happy about such a new dimensions. To see a possible solution in the future you can take again a look at Canon's line-up in the still photography section. There you have very small consumer cameras, then professional looking "pro's" - they all still use small CMOS's (up to 2/3"). Semi-professional cameras like the 350D, 20D have a special lens series for their smaller CMOS (around 22.5 x 15.0 mm - smaller compared to 1D's). In the high-end area canon produces still two different kind of sensor cameras, the D1 (speedy camera for ENG's) and the D1s (28.7 x 19.1 mm and 36 x 24 mm). Though - i think the last two's are just a matter of the price and will be full-size only in future. The latest camera in this area is the 5D, a product between the 20D and the 1D's, with a full-size CMOS, but some professional features left. It shows that we might see a comparable solution in the video section in the future. In my opinion, a smart line-up.
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Old November 24th, 2005, 10:04 AM   #14
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Quote:
Originally Posted by Dario Meier
There you have very small consumer cameras, then professional looking "pro's" - they all still use small CMOS's (up to 2/3").
Actually the small PowerShot point-and-shoot digicams use CCD image sensors. The larger EOS Digital SLR series use CMOS chips.
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Old November 25th, 2005, 10:43 AM   #15
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you might also have a look at the prices of 35mm lenses.
http://www.zgc.com/zgc.nsf/0/a7b4102...9?OpenDocument

When you shoot 35mm, almost everyone shoots on rented equipment. And you pay alot pr day in rent. Is that a situation you want?
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