auto aperture change
 

On the XLh1, i've noticed that:

with the stock 20x lens, under stable lighting, aperture open up as much as possible, when you zoom into a particular object to the max, the aperture seems to bump up to a number such as 3.4 to 4( depending on the lighting).. And when you zoom out, the aperture goes back to the original number, which is around 1.6 or 1.8...

I am shooting manual mode, and am wondering why these shifts are happening? is it beacuse of the lens quality?Is it to be expected Or is there a setting that i'm overlooking?

I don't know why it does this, but with the 16x manual servo lens for the XL2, it has a manual f/ring so you can set your apeture with a ring and no matter how you are zooming, your apeture stays the same.

I dunno if there is a manual servo HD lens for the XLH1, but I do know that the weird apeture changing thing you are experiencing is just the nature of the lense you are using. I don't have a technical reason for why that is though. :(

This is a standard issue when you work with zoom lenses of any kind. Go pick up an old SLR still camera with a zoom lens, you will see the end of the lens marked something like 2.8-4.5 meaning its 2.8 when it is zoomed wide, and 4.5 when zoomed in.

Its a matter of how the light is focused on the glass, and by zooming in, you are reducing the available light entering the lens. I doubt you will find any zoom lens that does not suffer from this, and if it is, it probably isnt reaching its full wide open potential.

according to the xl2 watchdog, the 16x manual lens uses the electronic iris control on the camera body. the 14x uses a manual iris ring.

My recommendation is to light for a 4.5 and shoot at that fstop, that way if you zoom in, you wont notice any aperature racking.

Xl H1 20x lens is not a pro lens
 

Professional zoom lenses for video have constant maximum aperture ie. f 1.8 at 8mm and f 1.8 at 160mm. Thus, when you zoom in manual operation at maximum aperture, you do not have to worry about the image getting darker.

Unfortunately, Canon did not use this standard on the 20x lens and the maximum aperture gets smaller as you zoom. The specs for the XL H1 ignore this unattractive feature.

There are many zoom lenses that offer constant aperture over the entire zoom range.

Best,
Christopher

The Canon 16x manual lens maintains constant aperture over the range. A big reason why I still own it with the H1. However this lens looks sharpest when it is in the middle of the range......f4-f5.6 or so. Then this lens rocks. However even at f1.6 it looks damn good. Just not as sharp as it is further up the scale.

There are many zoom lenses offering constant iris -- and many zoom lenses that do not. For the record, throughout the history of the Canon XL line, the stock lens provided with the camera has never had constant iris. So it should have come as no surprise that the 20x lens on the XL H1 doesn't either.

Christopher and Chris are right, as many film, video and stills camera zoom lenses hold constant apertures throughout the range.

The best way to hold the aperture for a forward creeping or pullback zoom with an XL stock lens is to make sure that your set aperture (iris opening) is at the maximum (or smaller) of the extreme telephoto end of the lens in use (f/3.4 with the 20X lens) and then press the Exposure Lock button prior to zooming.

Your zoom lens could well have been designed to have f/1.6 throughout its zoom range Spike, but you'd have been much more reluctant to pay for it and carry it and buy accessories for it it had been designed in this way.

It would be far more expensive not only because of the much bigger elements needed in its construction, but because of the reduced sales numbers bumping the price still higher.

So you're overlooking nothing (except the instruction book, that is). Very nearly all zooms designed for the amateur and semi-pro market ramp in this way, some a lot more than others.

tom.

with DSLRs f2.8 is the about the fastest zoom lens. How are the video zoom lenses so much faster?

There's nothing to stop DSLR zoom lenses being as fast as DV camcorder zoom lenses, but remember they cover far more real-estate. The full frame DSLR chips are over 100x the surface area of a 1"/4 chips, so the lenses would have to be monstrous, heavy, expensive, impossible.

There's a lot of 'hybrid' fixed lens DSLRs on the market now. Lots sport 10x and even 12x zooms, and they manage this by using tiny chips. Of course the punter only reads the '8megapixel' bit, and the tiny size of the chip is kept very quiet. No wonder they have difficulty getting differential focus.

tom.

Just to illustrate Tom's point, consider the Canon EOS 1200mm prime lens (no longer manufactured). Observe the enormous diameter of the front objective in this set of photos, and consider that its maximum aperture is only f/5.6. Can you imagine how much *larger* that glass would have to be, if it had say an f/4.0 aperture? Or f/3.5? Or f/2.8? You'd need two people to lift it (and about twenty more to help invest in its staggering cost).

Because video sensors (e.g. the XLH1) are considerably smaller than 24 x 36 mm (the area covered by most DSLR lenses).

Best,
Christopher

Even the Nikon Nikkor 1200-1700mm 'Mother of all Zooms' needs a truck or ten Sherpas to carry it around (16kg!)...35mm SLR equivalent equal to (aprox.) a 13,600mm zoom lens on an XL2 or XL-H1 so that you can film the fly on an elephant's butt at 1,000 yards...as long as you had a 50kg tripod to hold it steady for smooth footage. Imagine how much larger this lens would need to be with a fixed f/5.6 aperture:

http://www.mir.com.my/rb/photography...12001700mm.htm

In my experience very few broadcast lenses don't have some fall off at the long end of their zooms. This is much more noticeable in low light situations then brighter ones. Most manufacturers tell you what the fall off is and when it starts. It is much more noticeable on lenses with longer zoom ratios Ie 20X as opposed to a 10x.