Good wide-angle lens for TRV900E

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Christian Lett
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Joined: Apr 26 1999

Hello all!

I wonder if anyone could recommend a good wide-angle converter for my Sony TRV900. It doesn't have to be a Sony but it needs to be good quality and with no vignetting (I've got one already that cost me £10 but vignettes at the widest angle)!

I'm shooting a film soon and the widest zoom setting really isn't wide enough for some of the shots I need to make

Thanks,

Christian.

------------------
Christian J. Lett
[email=christian.lett@nationalexpress.co.uk]christian.lett@nationalexpress.co.uk[/email]

Christian Lett After Effects and Maya Artist www.quarterlightpictures.com

Des
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I have the standard Sony wide angle at 0.7, it is a zoom through and works so well I forget to take it off.

Flare is very common but if you clean the lens very frequently and avoid shooting straight at bright light it is surprising how much you can get away with.

I have not noticed any softening or lessening in contrast but to be fair I have not done tests, just used it in the field.

I believe the price is about £115 - I find I use it 70% of the time and cannot remember when I did not need it on a shoot.

Des

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Christian Lett
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Thanks, Des. I'll probably go for that one.

Christian.

Christian Lett After Effects and Maya Artist www.quarterlightpictures.com

tom hardwick
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I've done some pretty exhaustive tests with the RaynoxHD-6600PRO on my TRV900 and I'm greatly impressed. It's the first zoom through I've tried that doesn't add to the barrel distortion, it's £100 and is available at Jessops. It's 0.66x but they do a more powerful (and more distorting) 0.5x if you need more wide angle (don't we all).

tom.

Christian Lett
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Joined: Apr 26 1999

I popped into my local Jessops yesterday with my TRV900 and tried out the Raynox 6600, which fit the bill perfectly. So I parted with my hard-earned and bought it. Thanks for the advice, Tom.

On the flipside, would it be advantageous to get a telephoto lens as well? I'm thinking that maybe giving the lens a longer focal length will lower the depth-of-field slightly, allowing me to blur subjects in the foreground (in an over-the-shoulder dialogue set-up, for example). I know this is the case with larger format like film but will it work with a tiny CCD? If anyone out there has got a telephoto converter, please let me know what you think of it.

Thanks again,

Christian.

Christian Lett After Effects and Maya Artist www.quarterlightpictures.com

tom hardwick
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Joined: Apr 8 1999

Yes, buying a telephoto converter will allow you greater differential focus as the focal length will be increased but the maximum aperture remains at f2.8.

If you use the digital zoom this is not the case and the differential focus remains the same as that obtained at the longest end of the optical zoom, so buying a telephoto converter is the way to go for quality.

But I've never felt the need to extend the tele end of my 900 and haven't tested any telephoto converters. But I was so impressed ny Raynox's 0.66x that I'd sure like to have a look at one. Don't forget that the Steadyshot won't be
designed to compensate for anything over 51.6mm in length and your microphones will be even further from the subject.

tom.

Des
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Joined: Apr 7 1999

Tom
I'm very interested in differential focus. I thought that minimum depth of field was a product of f stop and your distance from the subject, not the focal length.

I'm constantly trying to hide the 'video look' by differential focus so would very much appreciate your comments, but in simple english please.

Des

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tom hardwick
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OK Des - the greatest differential focus you can get with your camcorder is obtained in the following way. 5 letter words max, OK?

Use the longest (optical) telephoto you can dial in. Use a telephoto converter if you have one.

Use the maximum aperture of the lens. Force the camera to use this by either upping the shutter speed (wrong) or adding ND filters (right).

Film at the closest focus possible. It's a bit restricting I know, but the huge enlargements from a 1/4" chip to a 34" TV can make the differential focus look pretty good even with my max tele of 51mm.

tom

Des
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Joined: Apr 7 1999

Use the longest (optical) telephoto you can dial in.

Does this mean maximum zoom?

Use the maximum aperture of the lens. Force the camera to use this by either upping the shutter speed (wrong)

Why? Surely f3.5 will force the effect whether obtained by an ND filter or a higher shutter speed.

Des

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tom hardwick
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Yes - use maximum zoom if this means telephoto to you. Maximum zoom really only means 12x or 20x or whatever the range of the zoom is. You want the most "telescope" effect.

Use the widest aperture by using AE-A programme or by setting it manually, soaking up the light with ND filters preferably. If you let the camera up the shutter speed (per frame) you'll get a nasty jerky stacato effect when you watch moving subjects cross the screen or if you pan or zoom.

Avoid shutter speeds higher than 1/50th sec unless you want to analyse the frames later (or print them out).

tom.

Des
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Tom - Sory I'm still baffled.

You say:
OK Des - the greatest differential focus you can get with your camcorder is obtained in the following way. 5 letter words max, OK?
Use the longest (optical) telephoto you can dial in. Use a telephoto converter if you have one.

If I use a wide angle at f3.5 anf fill the frame with a 6 foot person I will have much less depth of field surely than if I go to a zoom also at f3.5 and fill the frame again with that 6 foot person.

Because I am much closer in the wide angle, it is this closeness that contributes to the lesser depth of field (greater differential) the f3.5 being the common element.

Or have I misunderstood you?

Des

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Ned Cordery
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Joined: Nov 7 1999

To achieve differential focus you need shallow depth of field. DoF is that region that is in focus at a focus setting of the lens and is determined by two factors, the focal length of the lens and the aperture. The greater the focal length (telephoto end) the shallower the depth of field, also the larger the aperture the shallower the depth of field. So, at telephoto plus large aperture the depth of field is very shallow, ie there is not much in focus and if the subject moves (or the camera moves) the subject will go out of focus. Old camera operators will remember the depth of field tables we all used to carry around. There is also the circle of confusion but we can pass on that one!

Simply, long telephoto, wide aperture equals shallow depth of field good differential focus. Wide angle, small aperture very deep depth of field, impossible differential focus ie everything in focus (or as an old cameraman I worked with prefered, nothing in focus). Hope this helps.

Ned Cordery

Ned Cordery
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ps The third factor! Yes, the size of the recording device, film or CCD will also affect the DoF. With small film or small CCD's the DoF will be inherently greater. We had different tables for 35 mm and 16 mm film and eventually 8 mm film. Since most prosumer video lenses have no distance markings on the focus ring and no indication of the aperture it all has to be done by eye!
Ned Cordery

Des
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Ned

Thanks for your comments but I don't know quite how to say this.....

You said:
The greater the focal length (telephoto end) the shallower the depth of field,

it's this that I cannot agree with. Focal length does not affect depth of field. Take the same point again that I mentioned. Use a wide angle to shoot a 6 foot high person at f3.5 say - you will probably have to go some 10 feet in front of them and the depth of field might be some 4 feet in front and say 20 feet behind them. Now go onto zoom still at f3.5 and fill the frame with the same 6 foot high person you will see exactly the same depth of field. Try it out!

In this way focal length does not affect depth of field as you are forced to move further away from the subject. This maintains the depth of field.

Des

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tom hardwick
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For the least possible DOF set the camera on it's closest focusing distance at telephoto. It's something like a metre on the TRV900. Open the aperture till it says "open" in the v/f.

It really is as simple as that Des. There's nothing more you can do except this: import every single frame into Photoshop, use the lasoo tool around the subject and select the background, adding Gausian blur. This'll increase the apparant differential focus.

tom.

Des
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Alan Roberts in a note on the Forum on 12 February 2001 seems quite explicit that ''Depth of Field doesn't depend on the focal length of the lens.'' I extract his comment as the following.....

Unless he is also mistaken I am still confused.

Des

CONCLUSION

Depth of field depends on object distance and lens aperture, visual acuity and magnification. It doesn't depend on the focal length of the lens. It's pretty near impossible to get the same depth of field in a small television camera as we get in 35mm still photography because it's impossible to make lenses with very large apertures (f0.5 and bigger). So, if we want to isolate foreground and background using depth of field, we'd better find another way. The usual technique is to distort the perspective by getting in really close with the camera at a wide angle. That's fine for inanimate objects like flowers and insects, but humans tend to get a bit worried when a camera is thrust up to the nose, they feel a little threatened. And they tend not to like having their noses looking very big either.

By the way, there's a clue here about lensless imaging as in the pinhole camera and the camera obscura. Hands up who can tell me the depth of field for them?

[This message has been edited by Alan Roberts at work (edited 12 February 2001).]

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tom hardwick
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The DOF for the pinhole camera is (theoretically) infinite. From here to infinity and beyond.

Look Des, it's quite simple. You stay here and make sure he doesn't leave. You mean if I want to leave he can come with me? No, no. You stay in here, and MAKE SURE he doesn't leave.

Alan is talking about perspective control with the use of the wideangle lens as we have so little in the way of DOF control with our tiny chips and not-very-wide aperture lenses. He's trying to offer alternatives to give you more ideas (aren't you Alan?). Min DOF is obtained as I've stated in previos posts. No more, no less.

tom.

Alan McKeown
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I think we can state for certain that the focal length of the lens does NOT affect the depth of field, all other relevant variables being held constant.

What a longer focal length does allow is an improvement in perspective over using a short focal length lens close up to the subject. (image size kept the same in both cases).

Alan

Ned Cordery
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I must be missing something here since one of the factors asked for when calculating depth of field is the focal length of the lens used. At cs.ucla.edu there is a DoF calculator and it askes for the focal length of the lens. For example on 16 mm film a 10 mm lens, at f2 focused at 8 feet has a DoF of about 5 feet to 30 feet, a 200 mm lens at f2 focused at 8 feet has virtually no DoF. Forgive me but I need guidance here as I feel my grasp on reality slipping away after using DoF tables for all those years, but perhaps I'm just old!

Ned Cordery
Goslands Studio

Des
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Ned - you're confused...

Welcome!

It may be that when you use the longer focal length you have to be say 30 feet away not just 8 in order to have the same image in your viewfinder. At the new distance of 30 feet and of course a new focus position the depth of field will be the same 3 feet in front of the new position and 22 feet behind it.

Thus the depth of field is the same.
Or am I barmy?
I don't know...

Des

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tim.callaghan
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Joined: Apr 4 2001

Listen up fellars, I ain't Alan Roberts, but I do know this. Regardez, the following formula.

DOF at near point = HS/H+(S-F)

DOF at far point = HS/H-(S-F)

Where:
H = Hyperfocal distance
S = Distance set on the focusing ring
F = Focal length of the lens

To work out the Hyperfocal distance it is

Hyperfocal Distance = F*F/CN

Where:
F = Focal Length
C = Circle of Confusion (usually a constant based on shooting format)
N = F Number

So, yes the Focal length of the lens plays a part in the DOF.

Hard and fast rules:

At a given subject distance, the smaller the aperture, the greater the depth of field and conversely, the larger the aperure, the smaller the depth of field.

The longer the focal length, the smaller the depth of field and conversely, the shorter the focal length, the greater the depth of field. Therefore wide-angle lenses have a great depth of field.

The third thing to affect DOF is the focus ring. When focus is shifted to a subject that is nearer to the camera, the DOF contracts, but when focused on further distant objects the DOF will expand.

Case closes

Tim

Alan Roberts at work
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OK chaps, you've drawn my attention. DoF is an interesting topic, so interesting that it was going to be the first of a series of theoretical articles I offered Bob for publication. Sadly though, what I wrote was too technical for the mag so it never got published. Not wishing to throw away good work, however, I got it posted on the web. It's at the URL given in my profile, at Chromehead. It gives all the maths from first principles.

For those of you who don't want to get that involved, Tim's right.

In simplest terms, for a given image magnfication and F stop, the DoF does not depend on focal length of the lens. If you frame an image at full zoom, record it, then move the camera closer and reframe it at full wide so that the image is exactly the same size, the DoF will be the same. The perspective will have changed a lot, but the DoF is the same. The DoF also depends on your eyesight and is limited by the performance of the video system in that it imposes a minimum size on the circle of confusion which may be bigger or smaller than that of the optical system. But that's another problem.

Have a browse through the maths, I found it great fun working it through from first principles, and with a little help from some friends.

Alan McKeown
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It is meaningless to state that "the longer the focal length (of a lens) the smaller the depth of field" without specifying which dependent variables (dependant on focal length) you are permitting to vary.

The question we were supposed to be addressing is whether it is possible to reduce the depth of field FOR A GIVEN SIZED IMAGE by employing a longer focal length lens. It follows that we MUST increase the subject to lens distance in the case of the longer focal length lens to make the image sizes similar.
This is the only meaningful and fair way to compare the depths of fields between the two lenses in this case under discussion. When we do this, there is no practical difference between the depths of field.

[ If you do not believe this check it agaist a depth of field table. Remember, the focussed distances from lenses to subject MUST be proportionate to the focal lengths to ensure that the image sizes remain constant].( eg. a 50 mm lens at 2 m is equivalent to a 200 mm lens at 8 m).

We must conclude that there is no point whatsoever in buying a telephoto convertor in an attempt to reduce depth of field. It will only change perspective.

Alan

Alan Roberts at work
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Yep, spot on. DoF does not depend on focal length. However, focal length comes into the calculations when you're working out the F stop from the linear dimension of the aperture, but it disappears again without trace.

The maths isn't too hard, take a look at my written piece to see it worked through.

Des
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Thank you everyone for a robust, interesting and in cameraman terms a very useful discussion.

Alan Robert for coming to the rescue and in particular Alan McKeown for his last incisive paragraph....I quote...

''We must conclude that there is no point whatsoever in buying a telephoto convertor in an attempt to reduce depth of field. It will only change perspective.''

Des

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tom hardwick
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I disagree. Adding a telephoto converter will not affect the closest focus or the maximum aperture of the camcorder, such that (if you can live with the more close-up viewpoint) you'll get less d.o.f.

tom.

Christian Lett
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Joined: Apr 26 1999

Phew!

I might have known that mentioning the three little letters D, O and F would end up sparking a big technical debate. Not being very good at maths, I only know what I see when it comes to this kind of thing.

Thanks for all the input. After some testing, however, I've come to the conclusion that I'm not going to get a telephoto converter for my camera, as the telephoto end of the standard zoom will suffice for my needs.

L8r,

Christian.

Christian Lett After Effects and Maya Artist www.quarterlightpictures.com

Alan Roberts at work
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Tele-converters magnify the centre part of the image. That's all they do, it's the same as zooming into the existing image. So the DoF doesn't change but objects in the picture get bigger. They also "lose light" because they see only the centre part. A 1.4 times converter will lose one stop, a 2 times 2 stops, and 2.8 times 3 stops etc. (square root relationship because it's the area of the output port that matters). While giving you all these benefits, they make the pictures soft as well (because they only use the middle bit, blah blah).

Got the message yet

Alan McKeown
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Alan & Tom,

If "objects in the picture get bigger" (by the use of a tele-convertor lens or by zooming in) it is because you have kept the subject to lens distance constant. In that case the depth of field will indeed decrease.

But the whole point of this discussion was to keep the images of the subject as near as possible the same size. It is colloquially termed "comparing apples with apples".

Comparing apples with oranges is not always a fruitful exercise.

Alan

Alan Roberts at work
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Alan, I think you'll find that both Tom and I specifically said that, to keep DoF constant when zooming, you have to move the camera such that the image is kept the same size. Certainly I've said so many times.

For a given F stop, the DoF is not a function of the focal length. Read my written piece to find your way through the maths.

Alan McKeown
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Alan,

Thank you for your reply. I have read through your Depth of Field (DoF) paper and have no serious problems with that.

And I think we both agree (with Des) that there is independence between DoF and lens focal length. So no problem there.

However, I feel that, to the casual and even not so casual, reader; statements like your:
"For a given F stop, the DoF is not a function of the focal length"
and Tim's:
"The longer the focal length, the smaller the depth of field"
are not helpful.
For a start these statements contradict each other, yet you have said "For those of you who don't want to get that involved, Tim's right".
I find that very confusing.

From a strictly mathematical point of view, there is no gainsaying the fact that DoF IS a function of focal length. I do not see how that can be denied.

Only in the particular case of constant image size does the DoF become independent of focal length.
HOWEVER, that is the overwhelmingly important case for comparitive purposes.

So from a philosophical, as well as a practical, viewpoint we can justifiably state that the choice of lens focal length does not affect the depth of field of any given picture image.
QED

Alan

Alan Roberts at work
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Your final statement directly contradicts all the maths. But I'm no longer interested in following this argument.

Bye.

tom hardwick
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Please don't go. What you say for the tele-converter holds good for tele-converters that fit between the prime (or the zoom) and the camera body Alan, as in 35mm cameras. Then - as you say, they "zoom in" on the image as seen by the prime and at the same time loose light.

But the A-focal converters we're talking about don't do that.

tom.