Hi Everyone,

I'm trying to determine what lens setup produces the best DOF control on the XL2. Basically, I'm looking for very shallow DOF control. I'm trying to wrap my head around all the information I've read.

I've done a fair bit of reading on the Canon 16x manual servo lens (http://tinyurl.com/8eqx3) and the various available 35mm lens adapters, such as the Letus35, G35, and the ones from RedRock, P+S, etc.

So I have a couple questions:

1) I own the stock Canon 20x OIS lens. From what I understand, the 16x lens is better for rack focus and DOF control. But I have yet been able to figure out why this is true. Is it only because the 16x has markings on the focus ring? Or is the 16x lens capable of producing a shallower DOF? If so, why? (Perhaps my rudimentary knowledge of optics is in the way of my understanding.)

2) With the availability of the 16x lens with rack focus, why are 35mm lens adapters such as the Letus35/micro35/etc are so popular with the XL2 for DOF control? I realize that 35mm lenses have a shallower DOF, hence their popularity on miniDV cameras. However, I've also heard that the 16x lens is capable of great DOF control -- when I asked a respected dealer about 35mm adapters, he recommended using the 16x lens instead. But is that not quite true? Do 35mm lenses on the XL2 still produce a much more shallow DOF than the 16x?

Thanks!
Adam

On the 20x lens, the focus is controlled by a servo motor. When you turn the focus ring, you're actually telling a little motor which way to focus the lens. The result is that its an infinite spinning ring. This makes focusing virtually unrepeatable.

On the other hand, the 16x lens has a true manual focus. When you turn the focus ring, you are directly changing the positions of the lens elements. The focus ring has hard stops and focusing is repeatedable.

I can't imagine why the 16x would be better at DOF control. The DOF of 35mm comes from the fact that the lens is projecting onto a relatively large patch and therefore doesn't have to be very long. In contrast, prosumer minidv cameras, with their tiny 1/3" CCDs, have very long lenses in order to project an image onto such a small receptive patch.

It is true that you can control DOF to a degree by using a larger aperture and zooming in, but no lens alone on a minidv camera will create any where as shallow a field as a 35 adapter.

I have the fujinon 14x manual lens. Whilst this is a great lens for all the manual features, it doesn't come anywhere near the SG35 35mm adapter & canon FD lenses for DOF. With an F1.4 lens attached to the adapter I get something like 3cm DOF on close shots. Check out the alternative imaging forum and view a few sample clips put up by DVINFO members. You won't be able to get these results with the Canon 20x, or 16x video lenses.

There is a tradeoff though, slight light loss and a softer picture, but whether that is a problem all depends on the end result you are looking for.

Without using a ground glass and intermediate for focussing, your depth of field will be best controlled by the largest possible aperture. Therefore a lens that will open to 1.2 or 1.4 will give you a shallower depth of field then one that will open to only 2.x The 16x lens is a bit FASTER than the 20x especially at the long end where the perception of the DOF effect is greatest. Hence the 16x APPEARS to give you a shallower depth of field due to the faster F stop.

Thanks, everyone, for your replies! The answers you have given me are what I thought was true, but was having a hard time pulling it all together.

One more thing, though. As I have always understood it, the term "rack focus" just meant changing focus from a foreground subject to a background subject.

However, one person I talked with described the 16x lens as having a rack focus capability that allows you to specify a near focus point distance (X) and an infinity focus point distance (Y), so that you can focus on only everything at distances between X and Y. For example, you could set X to be 45 feet and Y to be 55 feet, so everything inbetween would be in focus, and everything outside of those bounds would be out of focus.

Is this actually possible with the 16x? Does the 16x have manually adjustable dual focus points? All my reading so far hasn't exposed anything like this.

Thanks again!
Adam

Adam,

What you are describing, only makes sense in respect to the concept of "Depth of Field". The depth of field includes everything that's in focus between the nearpoint and farpoint of the focal range.

"Rack Focus" does in fact, refer to racking, or 'rolling' the focus between two specific points in the frame. For instance, one might 'rack focus' between the end of the gun barrel, and the eyes of the person HOLDING the gun.

The 16x focal ring, is a manual ring. That is, when you turn it, the lens elements actually move, as opposed to an electronic servo moving in the 20x lens.

When "Pulling Focus" using a mechanical focus puller mounted on rails next to the lens, it is easier to get accurate focus adjustments with a manual lens, as it can be repeatable. Not always so with a servo focussing lens. (Not impossible, just not always spot on.)

I don't think I understand your question about DUAL focus points. Just not possible. As I mentioned, when listing a specific Depth of Field, one might mention the near point, and the far point of the field while everything in between those points is in focus.... but that is not to say there are DUAL focus points. THis is true of all lenses with their respective depths of field.

You might go dig up a reference on basic photography, to come to a thourough understand of Depth of Field and how it is controlled and determined by TARGET SIZE, FOCAL LENGTH, and APERTURE. Changing any of these three elements, will affect the depth of field.

Thanks Richard. Like you, when I heard "dual focus points" in the description this other person sent me, I scratched my head, as it sounded impossible to focus on more than one area. I've asked them what they mean by that. Very odd indeed.

Adam,

Reading your post on what you heard (focus on X, then focus on Y, etc), brought to mind one nice feature of the 20X lens. You can prefocus on point Y, program it in, then set the focus to point X. Begin shooting (point X is in focus), then hit the focus preset button and the lens automatically refocuses to point Y. So you get an automated rack focus feature which I've found to be pretty precise. This can also be set up for zoom instead of focus. I'm wondering if this is what you heard, and the speaker confused the 16X and 20X prefocus abilities?

The only drawback that I have with this is that the rate of change in focus is not adjustable. It's pretty quick and most times I'd like a slower change for a little more dramatic effect. The only solution I've found is to adjust the speed in post, but this only works well for stationary subjects or if a slow-motion effect is also desired. Has anyone found a way to modify the rate of focus on the camera?

Pat

Hi Pat,

I've used the feature you're referring to on the 20x lens before, it is quite nice. You can change the focus speed for the preset, but you only have a choice between "Low", "Middle", and "High", and I find "Low" to still be too fast!

To change the speed, use the menu button on the XL2, go to "Camera Setup", then go to "F Speed Pset". You can choose the speed there.

Adam

Patrick,

Thanks for pointing that out. Yeah, I'd say the previous speaker was referring to racking focus or zoom BETWEEN two points, that could be pre-set. Perhaps he mis-spoke, or Adam misunderstood, but that is no doubt what they meant.

This is not available obviously on the manual 16x. That becomes the job of the focus puller!

Ahh. Thanks Adam. I'll try that out on my next shoot.

Pat

By the way, has anyone tried using the EF mount adapter for the XL2 (or one of the mount adapters from Quyen Le at http://www.letus35.com/XL.html) with either a very wide angle lens, or a wide angle lens and a wide angle adapter on top of that? This is described here: http://www.dvinfo.net/canonxl2/articles/article04.php#ceos

The goal of that would be to get close to what a 50mm lens would looke like on a 35mm camera -- since you get a 7.8 magnification in the focal length with the EF (or other) adapters, you need to go really wide so that the magnification results in a "normal human" field of view.

If anyone has tried that out, let me know. Theoretically you should be able to get shallow 35mm-like DOF with this approach, but you loose some light due to the fact that you have to use a slower wide angle lens.

Thanks!
Adam

Adam,

I've tried the EF/XL adapter on my XL2 with some of my EOS zooms that I have for a 35mm SLR. After much experimentation, I've realized that the cropping (7.8X) factor makes most EOS lenses unusuable for practical shooting, unless you do nature or surveillance work. I don't think you can find a 6.4mm SLR lens, which is what you need for a 50mm (SLR) field of view. Besides that, a 6.4mm (ultra-ultra wide) lens will not have the shallow DOF that we're looking for.

I've now picked up a Redrock adapter, which projects the SLR-lens image circle onto ground glass, and uses the 20X lens as a relay lens that captures the entire image (with shallow depth of field, and full field of view). I'm still working on it, but now have settled on using a SLR prime lens (with the EF/XL adapter) as my relay lens, instead of the 20X. I haven't had a lot of time to work on this, so I don't have any captures yet. I'll post to this board when I have some results to share.

Here's a photo of the current setup. Note that the SLR lens is not attached at the front. The 50mm prime in this photo is a placeholder until I've purchased a wider 20mm prime lens which will capture the full image circle of the SLR lens.

http://static.flickr.com/37/87599587_d298149141_o.jpg

Pat
ps: BTW, there's a few more details on my setup and reasons why I've set it up this way in this thread:
http://www.dvinfo.net/conf/showthread.php?t=57789

Pat,

Thanks for the info from your own experiences, very helpful!

How are you attaching the Redrock to the 20mm relay lens -- is there another adapter in the middle that attaches the Redrock to the threads on the 20mm lens?

I've been looking at this and other 35mm adapters for a little bit now, such as the Letus35 and the G35. The G35 looks really interesting, and I'm really looking forward to seeing their press release on the product announcement this week. I *think* that the G35 might have it's own relay lens that can attach directly to the XL2, and I *think* the G35 has no motor. I read that on the cinemek.com forum, but I'll wait until the press release to see what the real deal is.

How much noise does the motor on the Redrock produce?

Adam

Adam,

Sorry for the delay in replying. The 20mm relay lens attaches directly to the EF-side of the EF/XL adapter, which I still have to order. To be totally honest, what is shown in the photo is a 50mm Nikon prime as a relay lens, with a Nikon f-mount to EF adapter (which is simply a machined aluminum ring). I didn't have an EF prime on hand to try out in its place.

The motor in the RR adapter does make a very soft whirring noise. I think I've read that it comes from a CD player, so perhaps you can listen to a portable CD or DVD player, and use that as a rough guideline. I don't think it'll be an issue for most shooting, particularly if you use a shotgun mike on your XL2. I'll try to quantify the noise level, when calibrated to a person speaking about 3 - 5 ft. from the mike. Can't do this for a few weeks, though.

One other thing you might want to consider in your comparison is the efficiency of the ground glass. RR claims that their ground glass is nearly lossless, meaning that very little light is scattered away from capture by the relay lens. Given the fact that you are already losing about 2-3 stops due to the use of a relay lens, you might find that a low-efficiency GG will mean that you need a lot of light in order to film. The tradeoff to the high-efficiency RR GG is that it will not work well for the combination of dim subjects in focus + bright backgrounds that should be out of focus. They do include a second GG in the package for these situations.

For an example of bright-background effects w/ the RR adapter, see
http://www.redrockmicro.com/zen_and_m2.htm
And scroll down to the section on "ghost image"

Pat

Hi Patrick,

How does the 20mm lens attach to the Redrock adapter itself? I see that the 20mm lens attaches to the XL2 via the EF adapter, but I'm curious to know what you used to attached the Redrock to the 20mm. Or am I misunderstanding something?

Cheers!
Adam

Ahh, sorry I misunderstood your question.

The RR adapter includes an achromat (close up lens) with a 72mm thread mount, which screws onto the filter mount of the 20mm lens. Since the sigma lens I'm interested in is a 82mm thread mount, I have to get a 82 - 72mm step down ring. The achromat then slips into a fitted rubber hood on the RR adapter. There is no rigid mechanical connection between achromat and RR adapter, just the rubber hood which sits snugly on the achromat. The rails give the overall rigidity to the entire rig.

In my photo, you can see the rubber hood, just to the right of the RR adapter, the achromat, and then the 50mm relay lens. The 50mm lens does not have the requisite 72mm filter thread mount, so I just pushed up the achromat until it just touches the lens barrel (not the lens glass).

Pat

However, one person I talked with described the 16x lens as having a rack focus capability that allows you to specify a near focus point distance (X) and an infinity focus point distance (Y), so that you can focus on only everything at distances between X and Y.

What he was referring to is the "hyperfocal distance". If a lens is set to the hyperfocal distance everything beyond that distance will be in focus. It is simply calculated by taking the square of the focal length and dividing it by the F stop and then the diameter of the "circle of confusion" which is the size of the blur in the image of a point which is large enough for you to consider it out of focus. If, to make the math easy, you assume the CCD is about 3 mm long and has about 1000 pixels then a pixel is .003mm and blur of 1 pixel should look pretty sharp. Lets say you set the 16x for 12 mm focal length and set the aperture to F/12. The hyperfocal distance is then 12*12/12/.003 = 4000mm or 4 meters. If you set the focus ring to 4 meters everything from 4 meters to infinity will be in focus as will some things a bit closer than 4 meters. This is equally so for any lens. With the manual lenses you have a distance scale you can read and thus compose using knowledge of hyperfocal distance.

For each focal length, focus distance and aperture there is a range within which any point will be focused to a circle of less than B (the Blur radius). These distances are f*D*(f/F - B)/(f*f/F +D*B) and f*D*(f/F + B)/(f*f/F -D*B) with f being the focal length, D the focus distance, F the F number and B the diameter of the blur circle. All these are in mm and the result is in mm.

It used to be common practice on 35 mm still cameras to label the various F stops with numbers of different colors and then have a pair of index marks of the same colors on the focus scale corresponding to the near and far focus limits for the aperture selected. If you use an old 35 mm lens with the XL series cameras those marks will not be useable because B is different for the CCD and film.

I'm still working on it, but now have settled on using a SLR prime lens (with the EF/XL adapter) as my relay lens, instead of the 20X.
Patrick,
Any particular reason why you chose the EF/XL adaptor?
Wouldn't it be easier and "optically better" if you used a straight adapter like this one: http://www.letus35.com/XL.html and simply used a 20mm Nikon AI or Canon FD lens instead?

Also, you mentioned you are looking for a 20mm instead of the 50mm that you already have. Why come? The 50mm is not good enough?

- ShannonRawls.com

When I picked up the EF/XL adapter a couple of years ago, I was more interested in utilizing my EF-L lenses that I have for my Canon SLR. I'm not sure what decision I would make today, given this new application. For me, the EF/XL adapter still has the advantages of aperature control on EF lenses, and use of my EF-L lenses (w/o RR adapter) for occasional long shots, with full aperature control. If I were starting from the ground up, buying with the Redrock solution in mind and with no current SLR equipment to consider, the Letus + Nikon (with manual aperature control) would be an attractive choice.

One additional thing to consider is that with the EF/XL adapter, I don't get a "check lens" flashing warning indicator in the viewfinder of the XL2. With a Nikon lens, or an adapter without electrical connection, the warning appears. If anyone can suggest a way to make this go away, please post.

I will be using a 20mm relay lens because with the 50mm prime I'm cropping out a significant amount of the image circle that appears on the ground glass. This reduces the advantage of the RR adapter and moves us back in the direction of just using a straight lens adapter (though definitely not as severe). The grain of the glass is also visibly magnified, and although it is spinning, I feel it will degrade the overall image. I believe that it also throws away light, because some of the image photons on the ground glass don't make their way to the 1/3" XL2 sensor, and the resulting setup is then less sensitive, or efficient. I haven't throught this through, and realize I may be wrong on this point. Regardless, though, the crop factor is enough for me to pick up a 20mm relay lens.

Pat

understood.

Well, GOOD LUCK! You'll be hard pressed finding a 20mm Canon EF or manual FD lens any faster then f2.8. I've looked all over, but no dice.

- ShannonRawls.com

Shannon,

I wasn't planning on ordering Canon glass. I'm looking at a Sigma 20mm f/1.8, shown here:
http://www.bhphotovideo.com/bnh/controller/home?O=productlist&A=details&Q=&sku=217794&is=USA&addedTroughType=search

I've read comments on this lens that it's soft wide open, but I figure on a 0.35MP (720X480) DV camera, it should be okay.

Pat

PS: I have not yet verified that there isn't a falloff problem with a 20mm prime lens. I've arrived at the 20mm figure using a 16-35L Canon zoom lens. Once I've received the 20mm lens, I'll capture some footage and look at the corners of the image to make sure that 20mm is the correct length. (I've only looked through the viewfinder right now). If there is significant falloff near the corners, I'll probably go with a 24mm focal length.

I'd be glad to report my results in a few weeks. I'm completely swamped right now with work.

What's the widest ange I can go for xl2? Is it 20mm? Or, are there wider angle lenses I could use for xl2 video shooting?

"...One additional thing to consider is that with the EF/XL adapter, I don't get a "check lens" flashing warning indicator in the viewfinder of the XL2. With a Nikon lens, or an adapter without electrical connection, the warning appears. If anyone can suggest a way to make this go away, please post..."

Patrick - This is certainly not true.

With a Nikon Nikkor adapter (made by Les Bosher) mounted on the XL camera body, the viewfinder warning only flashes for about two seconds when you first turn on the camera, and then immediately clears from the viewfinder screen. This is with any Nikkor lens mounted.

http://www.lesbosher.co.uk/

I'd like to add, that the Les Bosher adapters are made from solid metal, and not plastic like the ones shown on Letus35.com (I wouldn't want to fit my heavy and expensive Nikkor lenses on a plastic mount...).

Tony,
How much is Les' mounts? the PL and the Nikon?

- ShannonRawls.com

Tony,

You are right, I was incorrect about the "Check the Lens" warning. When powering up without the XL Lens or EF+EF/XL adapter in place, the camera does display "CHECK THE LENS" for about two seconds, then goes to shooting mode. It does continue to flash "LENS" in red in the upper right part of the field, below the timecode display. Does an XL2 with the Les Bosher adapter + Nikon lens also exhibit the flashing "LENS" warning? I'm not implying that this is anything to hinder shooting, just curious if Les Bosher has found a way to disable the continuous warning.

Pat

Patrick - All Nikkor to Canon XL ( or Canon FD to XL) adapters are similar in that they do not relay electrical signals to the XL body, and also have no extra glass (except the Canon EOS adapter).

The large red "CHECK THE LENS" disappears almost immediately after connecting the lens to the XL body. A tiny white "lens" warning then flashes on the lower right side of the viewfinder (but does not affect shooting, and is easily ignored).
If the tiny flashing "lens" sign is bothering me during shooting, I simply press the EV Display button on the side of the XL body, and this extinguishes the flashing "lens" sign, to give a clear viewfinder frame with no distractions.

I've had my Nikkor to XL adapter for quite a while, and buying direct from Les was cheaper than a similar model sold through Optex. Just give Les Bosher a call, or Email and he will let you know the present price for the adapter.