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DOF Comparison

Discussion of Beta Testing.

I want shallower DOF!!!

Poll ended at Fri May 26, 2006 8:45 am

Yes please Dennis!!
5
83%
I like it deep!
1
17%
 
Total votes : 6

DOF Comparison

New postby Andy Gordon on Wed Apr 26, 2006 8:45 am

Here's a quick sample you can freeze frame to see how much deeper the Brevis DOF is than it should be. The difference is huge. My Rode videomic was on the cam as well. Noise is pretty obvious.

http://www.savefile.com/files/1897965

Hope you can see the dramatic difference in bokeh. Much more film like if you ask me with the POC20. The Brevis is nice and sharp, but the DOF is way too deep for an f1.4 lens...

I've nearly got my own adapter working, just need to fix the oscillation so it's circular, the grain is pretty obvious at the mo.

Light loss is the same since you have to stop down the Brevis to f4 to remove the haze.

I'll post some daylight comparisons at the weekend if anyone's interested.
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New postby Steve Strickland on Wed Apr 26, 2006 9:25 am

Andy, I wish you weren't right, but for me, you are. The shorter dof really does it for me. Much more filmlike.
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New postby Francois Poitras on Wed Apr 26, 2006 9:54 am

Is there an opening in your adapter? The loud ticking would let me think there is.

It would also be interesting to post a higher rez clip to show the grain of the POC20.
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New postby Andy Gordon on Wed Apr 26, 2006 10:31 am

No way man I'm trying to hide the grain! Just kidding I'm on dial up. It's more obvious on the last shot.

The noise is the motor wire tapping against the side of the pipe. Haven't managed to get rid of it, or get circular oscillation yet. The wires are affecting the shape of the oscillation. Might try more flexible wires. The oscillating part has a very small clearance to the pipe. If I get the wire clear of the pipe think it'll be silent.
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New postby Joshua Nitschke on Wed Apr 26, 2006 6:29 pm

Steve Strickland wrote:Andy, I wish you weren't right, but for me, you are. The shorter dof really does it for me. Much more filmlike.

Me too.

I really need some very shallow DOF in my movie....and from what I'm seeing the Brevis isn't cutting it. The bokeh was ok for me, but with that deep DOF is not gonna work for me.

If I wasn't shooting in a month I'd wait for some input from Dennis, but with him gone it looks like I'll be ordering another companies adapter soon. :(

Even if he were to come up with a solution for us, it's not so much a matter of me thinking that he wouldn't or can't, it's a problem with time. I don't have time for him to do more research and send us a new GG or whatever, and I don't have the time, money, or knowledge to try to make modifications to this one.

I wish Dennis all the best, and I hope he takes the reactions of the beta groupers to heart and does some modifications.

I'd also like to see some footage from somebody else besides Andy, just to make sure it's not a problem with his Brevis....
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New postby Francois Poitras on Wed Apr 26, 2006 6:55 pm

I don’t think Andy’s diffuser is defective. His short clip is representative. With objects within three feet of one another, the objects in the background will look just like in his clip. The results look better with a background which is farther from the subject in focus, like in Dennis’ sample footage, for example.
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New postby Andy Gordon on Wed Apr 26, 2006 7:02 pm

It's true the difference is exagerrated at close range. I'll do another comparison in daylight at longer range, but the whole point is to get shallow DOF so why would you be happy with something that is not as good as it should be. I'll also compare the DOF on the Breivs to straight cam with zoom. For all the draw backs of using an adapter, if the DOF isn't significantly different to straight cam then there's not much point using it.
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New postby Hrafn Jónsson on Wed Apr 26, 2006 9:28 pm

Funnily enough I'm not really worried...

Offcourse those who really want maximum reduction of depth of field have a point, but for me personally it is kind of a relieve in a strange way. The reduction of DOF is probably more than enough for me at f/1.4. It was one of my main fears that the DOF would be TOO shallow and full open, and that would be a real problem when I needed the full sensitivity. From what I have seen the DOF is plenty shallow in medium and close shots.

The Bokeh is another issue that I have yet to make my mind up on. But like I said, I'm not at all worried...at least nowhere near enough to start thinking about buying another product before extensive testing of my own..
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New postby Dennis Wood on Sun Apr 30, 2006 10:16 pm

Andy, pmail me and I'll get back to you on Wednesday or so. If you want to bail from the beta group, that's cool. Shipping back to me would be at your expense though....at least you'd recover some of the $540.

The bokeh issue is really a subjective one, and I can appreciate that some will have different opinions...that's why I posted test footage.

Are there particular shots that would highlight issues for a potential buyer head's up?

I've been thinking on the posts from you guys and there are a few changes I'll be implementing in the future units. One is to use 24 gauge wire from the motor and route the wires specifically to avoid the rattle issues...like a car's electrical harness. If the unit is unusually loud, shipping may have shaken things up from my tested here. Likely one of the wires is contacting the case.
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New postby Andy Gordon on Sun Apr 30, 2006 10:43 pm

To me bokeh is not a subjective matter. A given lens should produce a given image. Watch any movie and you'll see hard bokeh, background lights are solid discs in the shape of the aperture. It's the compromises in making a useable adapter that are subjective, not the properties of the bokeh. Light loss vs bokeh/shallowness of dof vs grain.

I don't want to bail. I just happen to think there are options that would make the Brevis a lot better.

The shot I posted is where you really see the difference. Out of focus point sources of light.
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New postby Hrafn Jónsson on Mon May 01, 2006 3:07 pm

"Bokeh (from the Japanese boke ぼけ, "blur"[1]) is a photographic term describing the subjective aesthetic qualities of out-of-focus areas in an image produced by a camera lens. For example, causing an out-of-focus background image may reduce distractions and emphasize the primary subject.

Although difficult to quantify, and hence open to debate, some lenses are believed to enhance overall image quality by producing more subjectively pleasing out-of-focus areas (bokeh)."

Snatched from Wikipedia...I mean..there are offcourse methods to analyze bokeh, but these guys sure do use the word "subjective" alot...But hell..this ios wikipedia...they have been wrong..
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New postby Andy Gordon on Mon May 01, 2006 5:52 pm

Ha ha I stand corrected. I think they are talking about the differencees in bokeh appearance between lenses. You should still get a certain image from a certain lens, with a certain dof.
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New postby Hrafn Jónsson on Mon May 01, 2006 5:58 pm

Yeah, they were indeed talking about how different lenses produce different bokeh patterns, especially light disks and how they differ betwean lenses...so the 35mm lense itself should be the first thing to troubleshoot..

But I understand that you want a certain effect from your bokeh. I don't really mind. My main concern is the deep DOF...how deep it's in fact going to be. But I'll find out tomorrow when I'll pick up my beautiful Brevis :)
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New postby Andy Gordon on Mon May 01, 2006 6:49 pm

Dennis Wood wrote:One is to use 24 gauge wire from the motor and route the wires specifically to avoid the rattle issues...like a car's electrical harness. If the unit is unusually loud, shipping may have shaken things up from my tested here. Likely one of the wires is contacting the case.


When I mentioned wires tapping I was referring to my own adapter. I checked my Brevis last night and the wires aren't tapping. The noise level is acceptable on the built in mic (GS400) but my rode videomic is too sensitive, even with the gain turned down. The mic picks up a lot of vibration through the camera body even though the rode has a suspension system. This is a pain as it means mounting the mic on the cam won't work.

EDIT: I did some more testing and I think this may have had something to do with the way the cam was mounted, but the noise on the Rode is also acceptable now.
Last edited by Andy Gordon on Wed May 03, 2006 5:17 am, edited 1 time in total.
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New postby Andy Gordon on Tue May 02, 2006 2:37 am

Just happened to find this today:

"Let’s say I use my 35mm stills camera and shoot with my 50mm Nikkor lens at f/2.8. I focus on a face 5ft (1.52m) from the lens – a normal working distance and image size for a modest CU portrait. This will give me a 27deg field of view and my depth of focus is just 5in (12.7cm)."

There's some quantitative numbers to measure against!

From here:

http://www.showreel.org/memberarea/article.php?172
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New postby Dennis Wood on Thu May 04, 2006 11:07 pm

Andy, if I understand your test, you used the Brevis at F4 (on a F1.4) lens. That in itself is not a fair comparison as the DOF at F4 is much, much deeper than at F1.4. I am concerned that some folks are being "scared" by this, without understanding perhaps the conditions of the test.

It's also critical to isolate the 35mm lens from the rest of the test conditions...for example the haze at full open aperture. Also, I've observed with my spinner (mechanically blasted spinning diffusor) that "good" bokeh at F1.4 with my lens, that is, specular highlights showing the blade pattern of of the aperture on a fully open lens is impossible. They're just mush until the lens is stopped down to F8 or so. Remember that's on a high diffusion (2.5 f/stop) diffusor.

I've deliberately shot at F4 on my Minolta F1.4 to get a much larger field of focus, and the difference between F1.4 and F4 is very large.

As far as haze, I honestly have not seen any of this, on any of the cams I tested. It makes me wonder if there is a reflection issue with your adapter. I'm interested to see the same test but at F1.4 with both diffusors.
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New postby Andy Gordon on Thu May 04, 2006 11:59 pm

Andy, if I understand your test, you used the Brevis at F4 (on a F1.4) lens. That in itself is not a fair comparison as the DOF at F4 is much, much deeper than at F1.4. I am concerned that some folks are being "scared" by this, without understanding perhaps the conditions of the test.

I compared the Brevis at f4 and f1.4 against the poc20 at f4 and f1.4, so the only difference was that the cam went to 3db gain on the poc20. With the Brevis when I went from f4 to f1.4 I saw negligible change in the dof, not so with the poc20, it's much more apparent.


It's also critical to isolate the 35mm lens from the rest of the test conditions...for example the haze at full open aperture.

True and I've compared the diffusers on the Nikon lens, it's just that I can't mount the Nikon on my adapter. The difference between the Nikon and the Takumar (both f1.4s) is not visible next to the difference in bokeh caused by the diffuser. I'm not sure how the lens would affect haze at open aperture, I see no difference between them. I thought the haze was entirely down to the diffuser, maybe you've seen something else?


Also, I've observed with my spinner (mechanically blasted spinning diffusor) that "good" bokeh at F1.4 with my lens, that is, specular highlights showing the blade pattern of of the aperture on a fully open lens is impossible. They're just mush until the lens is stopped down to F8 or so. Remember that's on a high diffusion (2.5 f/stop) diffusor.

It depends on the diffusion to light loss ratio of the diffuser. POC20 is pretty good in that respect, maybe your high diffsion spinner had to much light loss and that's what rendered it impossible, I think it is possible with the poc20.

But it's true I've noticed the same thing the circles start turning to mush with the lens open, I think that happens when the light loss overcomes them, but with poc20 you still get virtually solid circles on bright lights, as shown in my demo, they look better at f2. With poc20 you don't need to go to f8 to get them.

I've deliberately shot at F4 on my Minolta F1.4 to get a much larger field of focus, and the difference between F1.4 and F4 is very large.

With the Brevis as I open from f4 to f1.4 I see no change in the dof but I do see the ghost of the disc expand around a highlight. That'swith my Nikon 50mm f1.4.

As far as haze, I honestly have not seen any of this, on any of the cams I tested. It makes me wonder if there is a reflection issue with your adapter. I'm interested to see the same test but at F1.4 with both diffusors.

Ummm the video already includes that comparision, freeze frame and read the text at the bottom. I compared f1.4 against f1.4 and f4 against f2 I think. The second shot Brevis at f1.4 is much hazier than the third shot poc20 at f1.4.

After I ordered the Brevis I went back and looked at your demo footage. It looks hazy to me. The HVX squeeze dolly shot on the watering can looks very hazy to me. When I say haze I mean on out of focus areas. Would probably look better with some colour correction, and the light looked pretty flat as well. But I can definitely see a difference in apparent haze between poc20 and Brevis, just look at the example I posted.

Francois - not to put words in your mouth, but you're seeing the same differences I'm seeing between straight Brevis and extra diffusion in your own tests?
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New postby Andy Gordon on Fri May 05, 2006 12:39 am

And another thing I've noticed - the more diffusion you have (i.e. higher diffusion angle of the gg) the larger the diameter of the discs of light. For the same shot, when I add the gg to the Brevis the diameter of the discs dramatically increases.
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New postby Dennis Wood on Fri May 05, 2006 11:34 am

I hear what you're saying Andy. What I've been thinking is that what is missing here is a reference. In other words, comparing one diffusor to another is one thing, but what really needs to be done is to compare the diffusors to the same lens/aperture recorded on film. I'm going to do this test using my Minolta SLR. and F1.4 lens to compare what is seen on film, vs what is seen with the adapter.

This is why the whole bokeh issue is so subjective (and probably over-analyzed as Steve Dinkins loves to point out). The whole act of recording an image through a diffusor vs. that image terminated on a fixed surface of film, is what is really in question here. And the question remains...what is the real reference? I guess I just don't see an immediate solution to the bokeh issue that would retain light transmission, maintain suitable sharpness for HD, and so on.

The dilema for the POC solution is that grain that is "hideable" is found in the POC30 and up samples, however the light loss is very significant in the higher diffusion angles...as Dan D. has already demonstrated. So again we're at the crux. Coarser diffusion grain cannot be hidden (at least by me), while giving less than 2 or so f/stops of light loss, and maintining HD quality sharpness. It's basic physics..and there's no free ride.

The Brevis GG optics are aspheric in nature, and I've been assured by the optical engineer responsible that barrel distortion from this system is zero. What I have observed is that barrel distortion is very much affected by condenser lenses, and can be in essence corrected for a given lens by varying condenser distance from the GG. I posted up screen grabs from three lenses all set at 50mm on the dvx site to show barrel distortion was negligible with two of the lens, and quite noticeable on my 50mm prime on the Brevis.

Hopefully the rest of you beta guys will look at the footage, do your own tests and come to your own conclusion...because it's a very subjective one. Light loss is a complaint I've heard on every adapter out there. Carefully weigh the advantages, then consider how your audience will actually perceive the footage. They are not bokeh experts, nor do many of them care....what they will see right away is very sharp footage with a much more selective DOF. What you will have is an adapter that requires very little added light, and provides very sharp images where your audience's attention should be focussed...the in-focus part !

Once you start shooting, I think most of you will find that what I'm speaking about makes very good sense. The technical director of the local film school ( a highly respected film shooter with a very large resume) actually asked me to explain the term "bokeh" which helps to put into perspective how deeply the adapter crowd is immersed in the subject.
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New postby Andy Gordon on Fri May 05, 2006 1:56 pm

I would love to see a direct comparison between an slr picture and various diffusers. I don't think anyone has done that yet. Please include the poc20!

The end user being the lay audience is never going to see the difference. They probably wouldn't even notice the difference between straight cam and shallow dof adapter, they're more likely to notice things like content, acting, script, story etc etc. Doesn't mean we shouldn't aspire to achieve what we're aiming for - the most film like look.

And maybe I'm getting hung up on the bokeh that no audience is ever going to notice, but my reference is just what I see in the movies, and pretty much any tv series with a decent budget now that is shot on film. Lost is a prime example, shot with very shallow dof through out, lots of diffusion circles.

Anyways as I've said and demonstrated, the results I saw with poc20 I preferred, seemed to have shallower dof and nicer bokeh with a quite acceptable level of light loss.
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