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Old February 26th, 2008, 04:04 AM   #1
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JVC GY-HD100-250 35mm Nikon-mount lens adapter comparison

Guys, as promised Mike Tapa of MTF Services came through with a GY-HD100-250 Nikon lens-mount adapter for us to do a little comparison against the Zork adapter that I've had here for a few months now.

I'm no genius but I have been dorking around with the Zork and Nikons for long enough to know some of the issues we face while choosing this path.

1 - fit. The first Zork that I received was a little sloppy at the Nikon/Zork connection. Zork quickly replaced this "rogue" adapter and now we've got no problems. The MTF fit snug right out of the box.
2 - build. You'll see from the images I took. The MTF seems beefier.
3 - design - It's just a simple adapter. No glass, no electronics. Basically it's a spacer. But then you go and use one for a while and you learn the two adapters are actually pretty different. Mike gave a lot of thought to his design. It makes better sense where he put the aperture indicator. You'll see from the photos.
4 - RED FLARE. This I do not have the answer to, yet. But I plan to do some comparison shots this upcoming weekend. Should be interesting.

I put two pages together with some rollover images and some text for anyone who's not quite sure about these things. Please pardon the typos. It's late and my eyes are crossed. Just wanted to get this done tonight.

Here's the comparison http://www.reelsense.net/HD-200/JVC-...terCOMPR.html#
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Old February 26th, 2008, 09:17 AM   #2
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Thanks Eric for the report and ongoing comparison of the Nikon adaptors. I look forward to the "rockets red glare" test and your conclusions. The MTF is looking good so far. I thought one of the differences was that it had more black finish on the interior to theoretically help block reflected light. In the pics they look pretty similar in that department.
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Old February 26th, 2008, 01:04 PM   #3
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You are right Sean, they look the same considering bare aluminum flanges. I am going on what others have said about the red flare and where it comes from. If it is the aluminum ring, I can't see how the MTF will cure it. However if you look at the cylinder type sleeve that protrudes into the JVC you'll notice the MTF sleeve is longer. I don't know. Testing will tell. And I know exactly how to produce the flare..

By the way Mike tells me not one person has ever reported any red flare while using his adapter. While the Zork rep was well aware of it and even suggested the black magic marker solution - which did not work for me.
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Old March 14th, 2008, 02:20 AM   #4
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Red Curse

OK I've chased this red flare problem into a corner. Still don't know how to fix it, but at least now I know a little more about it:

What: Lower 20% of frame turns translucent red.

When: While shooting high contrast subject matter with the whites over exposed. Neither aperture, zoom, or focal range matter much. Once it shows up, it's there.

How much: The more over exposed the image, the worse the flare.

Why: Need a genius here. I am not a genius.

Solution: So far, "Go away from the light"

How to avoid: Use your zebras. Do not overexpose any part of your image.


Unfortunately, as you can see from the frame grabs below, BOTH the Zoerk adapter, and the MTF adapter produce the same red flare. The images were taken of exactly the same subject - the back of 600w flood light with flat black barn doors, aimed at a white wall. Exact same lens/camera/subject/settings for every example shown. Each image is named appropriately - Zoerk_RedFlare-100shtr.tif = Zoerk adapter, Red Flare example, shutter speed used in shot. All shots at f2.8, but you can get this flare at any aperture.

NOTE: The examples shown here are extreme cases. In fact I worked hard to capture this condition at it's worst. Although I definitely have had this show up in usable, and in fact "used" shots, I have never seen it this bad out in the real world. The most consistent conditions where it shows up for me is while shooting surfers in bright sunlight - where you need to let the darks of the water and surfer pour into the lens, but then end up blowing out the white water as the wave suddenly crashes. When the white water over exposes the bottom of your frame turns red.

Zoerk adapter Red Flare sample images:

Zoerk_RedFlare-10,000Shtr.tif
Zoerk_RedFlare-4,000Shtr.tif
Zoerk_RedFlare-2,000Shtr.tif
Zoerk_RedFlare-1,000Shtr.tif
Zoerk_RedFlare-500Shtr.tif
Zoerk_RedFlare-250Shtr.tif
Zoerk_RedFlare-100Shtr.tif




MTF Services adapter Red Flare sampel images:

MTF_RedFlare-10,000shtr.tif
MTF_RedFlare-4,000shtr.tif
MTF_RedFlare-2,000shtr.tif
MTF_RedFlare-1,000shtr.tif
MTF_RedFlare-500shtr.tif
MTF_RedFlare-250shtr.tif
MTF_RedFlare-100shtr.tif


Real world shooting problem/example: Challenging exposure to set. Dark water, dark surfer. Everything was going well, until the wave broke..
Zoerk_RedFlare-Surfer.tif


In addition to the Red Flare problem which occurs mainly on the bottom of the frame, sometimes, when you get the light just wrong, there are other red flaring problems that randomly, rarely occur. Follow this link to a short clip showing one of these outer body experiences first hand.
Rack_Focus_FlareClip

Last edited by Eric Gulbransen; March 14th, 2008 at 02:54 AM.
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Old March 14th, 2008, 02:56 AM   #5
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Red Curse

Uh, oh, smoke coming from keyboard
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Old March 14th, 2008, 03:01 AM   #6
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drrr

.sorry, this mac is on crack
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Old March 14th, 2008, 10:21 AM   #7
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Eric,

I was experimenting with a couple of 35mm lenses a nikon and a tamron and tried it directly on the jvc. I havent made a zork like adapter yet just a plastic ring that acts as a spacer to maintain flange distance. And somehow while tweaking the lenses, lo and behold, a bright reddish/ orange flare showed up similar to the images you posted.

So i guess its neither of your lens mounts but more to do with the lens aligned in a certain way and hitting the ccd or it protective glass, that i believe has a special coating, that produces this.

Ted,

ps. how much is the mtf adapter ? can you help me acquire one?
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Old March 14th, 2008, 10:36 AM   #8
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No problem Ted, they are listed here: http://www.mtfservices.com/products/...sadaptors.html

Mike's a pretty cool guy. You can email him directly at: mike@mtfservices.com


That'll really stink if this is unavoidable. Let's hope it's not true.
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Old March 14th, 2008, 10:59 AM   #9
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Hi Eric, Thanks for the sterling work you are doing to pin this problem down.

I have had a look at your images, and to me it looks like something I have seen before in my time at Optex.

I really dont think its an adaptor issue but more to do with the beam splitter in the camera.
The effect I have seen in the past was a common problem with all three chip cameras where top and bottom of the image had a different hue.(slightly blue and slightly pink) cant remember off the top of my head which colour was bottom though.

We used to deal with a lot of Toshiba Mini cams (TU48 or TU63) and our electronics guy could get into the engineering menu to compensate for this.

Point a camera at a white wall with no lens, see if you can spot it.

In the meantime, I will make some calls and let you know if I discover anything.
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Old March 14th, 2008, 11:09 AM   #10
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Thanks Eric for the links,

Mike, I sent you an email regarding your adapter. I plan to mounta 17mm nikon compatible lens on my jvc to replace the fujinon as relay for a lens adapter i made.
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Old March 14th, 2008, 11:46 AM   #11
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Cool Mike. Sounds very interesting.

I have a strange feeling/memory that I actually might NOT have seen this flare while using the 300mm 2.8. I have a few Nikon lenses other than the 80-200 2.8ED which I used for the shots in last night's tests. Tonight I will test them all, in the same exact shot. This should tell us more, I hope.

Thanks for jumping in Mike.
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Old March 14th, 2008, 09:09 PM   #12
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I'm having the exact same problem with my 80-200mm Nikon on an HD100, using a self-made adapter (that looks, necessarily, very much like the MTF and Zoerk). I actually thought, for a while, that it was some problem with my adapter, until I came across this thread. So I emailed Eric yesterday; turns out he just was about to go ahead with his tests (thanks for the quick reply, btw).
In my case, the problem is not exclusively related to overexposure, although it seems to be more apparent then. Same as in Eric's experience, zoom, focus and iris setting do not have a big influence. I have pretty much ruled out stray light hitting the lens as a culprit.
Here are some frames that show the effect in rather low key exposures:

http://www.flickr.com/photos/2467297...n/photostream/

Also, it's not always just an out-of-focus flare but often what seems like a sharply rendered secondary image. In this example you can clearly make out twigs and leafs in the 'flare' (note that the extreme blue fringing is an unrelated issue):

http://www.youtube.com/watch?v=zunxmDUHfH4

(sorry for the youtube thing, it's just that my internet connection is pretty pathetic right now, I'll post some higher res examples later)

So, I've been thinking long and hard about this and ,frankly, I'm drawing a blank here. However, I think it's safe to discard the 'reflection from the bare metal flange' theory. The flange (at least in my adapter) isn't even exposed to the light path. l would agree with Mike that this is an issue to do with the camera internal optics. Maybe a reflection within the beamsplitter that occurs at such angles that only the 'red CCD' is hit. (The color of the flare is exactly the same every time and seems to me very close to a spectral red)

Will be very interesting to find out if this only occurs with telephotos.
Ted, what kind of lenses did produce that flare for you ?

I also have a few tests in mind that might shed a little more light on this, but it'll have to wait a little , as my camera needs some surgery right now.

On other threads I've seen posts by a guy who seems to be very knowledgeable about optics. His name is Ryan Damm. Maybe it'd be a good idea to invite him to give his 2 cents to our problem. I'm not a regular forum user and wouldn't know how to do this.
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Old March 15th, 2008, 12:25 AM   #13
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OK I've tested every Nikon lens that I have here. They all produce the exact same red flare - with either adapter being used. So I agree, maybe this isn't an adapter situation after all. However tonight's findings are far from discouraging.

Following Mario's clue about the red leaves in his image, I became curious about identifying exactly what part of the image it was that was being reproduced, or split. It took a bit of dorking around but finally I discovered it's not anything "IN" the frame that is getting reproduced at all. The reflection is actually coming from just BELOW what's visible in the frame. I stuck tiny pieces of gum eraser to the edge of the flood light's barn doors, then panned upward from below until they were out of frame for a bit. As you will see in the linked .mov file, an upside down phantom barn door suddenly appears within the red flare - long after that same edge went out of the frame being shot..

You wanna' know why? Well, don't ask me. It took me six months to memorize my paper route when I was a kid and there were only nine houses on my block...

Here's the Phantom Barn Door video


With all the fumbling around with this red flare chasing and lens switching I have learned a bit more about how to work with it, and even how to avoid it. Turns out it actually IS avoidable, by stopping down the lens and compensating with shutter. I know I said before that aperture doesn't matter, but let me remind you please about the paper route...

At 2.8 with both ND filters on and shutter speed ranging from 1/2000 and below, shooting this extremely bright white wall with a flat black barn door in front of it, this red flare situation is in it's element. You just can't avoid it. BUT as you stop the 80-200 down, and then compensate by removing ND and slowing shutter to equal the exposure you just had, the red flare DOES drastically reduce (in both size into the frame, and brightness). With both NDs off, the shutter set at 1/60 and the aperture at f16, I couldn't get the red flare to occur anymore. Now of course we'll have to test the 80-200 at f16 because that's got to be way past it's sweet spot, but perhaps only this extreme case would force you to go that far down. I did notice the red flare had been reduced by about 65% once stopped down to f8 from f2.8. I bet in real world conditions you wouldn't get flare past f8, in average exposure ranges.

Lastly, Mike, your idea about eliminating any hue seen while shooting a white wall, via the menu settings, is actually a suggestion I have heard before - from our NY friend Sean Adair. He's probably reading your suggestion while reaching for a baseball bat to come gently remind me that I should have done this months ago. Sorry Sean. I dropped that ball. I'll check it tonight..


NOTE, it has been my finding at least, that the flare problem does not occur by simply aiming the lens at a high contrast, brighter than hell surface. At least with my rig, the flare only kicks up when you happen to aim the lens at just the wrong angle to the source. I'd guess 80% of the time shooting that same light source you won't see the flare. It's just those times that you do see it, that we are talking about here. I would hate to discourage someone from using these lenses on their JVC because we are discussing it in such detail here. Believe me, and like Mike told me in an email a few months ago - not one user of his adapters for this JVC camera has ever even mentioned red flare. So by all means, "Go long..."
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Old March 15th, 2008, 01:54 AM   #14
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having put a canon 50mm 1.8 onto my camera I've also seen a flare, but usually on the top of the frame. so I'm going to say this is about a reflection between the rear of the lens and the front of the CCD block. since the 35mm lens wasn't designed to deal with a reflection from glass, its coatings are absorbing the reflection. I would also suggest that with the greatest of care, perhaps painting flat black into the silver interior of the lens mount might help a little, but if its glass to glass.. your stuck. perhaps a slight shift in the lens to make it NOT parrellel with the CCD would push the reflection out of frame. I've done this with some filters in front of the lens when I saw the lens in the filter. tilt the filter to force the reflection away. while this could cause problems, it would be interesting to try if there was a way to figure out shimming the lens a thousand or 2 one way or the other to make it go away.
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Old March 15th, 2008, 01:01 PM   #15
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Interesting findings, and I think you guys are zeroing in on the problem.
Why not invite MTF and Zoerk to comment on the examples and discussion so far? The Optics guy on the forum can be sent a personal message through the forum by finding him on the members list (menu above), and copying a link to the thread.

The shape offscreen that Eric documented so vividly with the tiltup eliminates a lot of possibilities (including the chromatic shading adjustment mentioned that the 200 series cameras can do). I still think that running that calibration IS likely to reveal some room for improvement overall though.

I think it's pretty conclusive that there is some sort of internal reflection taking place between the rear element of lens and the camera ccd.

Changing the alignment of the lens seems to me could cause other issues (like losing sharpness on one side). Also, it seems it might just move the problem, picking up flare from another place. But with the ghost image coming from OUT of frame, it seems likely to be some other element than the ccd (which should just have the main image hitting it). This could be something in the camera as well - in fact that might be even more likely. Ready to take that sharpie into the flanges INSIDE your camera?

This is also likely (that it isn't the ccd reflecting), when you think about it, since the lens is bringing in a much larger image than the imaging ccd. There is light for a 35mm frame hitting all around the sides of the ccd, that a lens for a 1/3" ccd won't produce. Could this larger area be masked at the adapter stage? It will be a softer edge further from the ccd, but more predictable than trying to mask in front of lens, which will change with zooms, and is likely to be even softer (recipe for some vignetting). I suppose you could experiment with a hole in black construction paper to create a mask mounted temporarily inside to limit the image area before it goes into the camera (or it may sit better right inside the camera...). I notice that there are several filters before the ccd. The ND wheels off, still has a clear element, and there is a clear element in front of that.

Recognizing the problem, and avoiding it in the field, as well as minimizing it when it can't be eliminated possibly will be the only approach. There are already many situations simply unacceptable for the best images, and a pro cinematographer builds up quite a library of problem scenarios to avoid.

The prior knowledge is really important though, since finding out the problem after the fact if you aren't monitoring carefully, could be pretty inconvenient.

It makes sense that stopping down the lens helps - less light bouncing around in that area - the electronic shutter only works AFTER the fact.
Keeping the exposure down with ND filters instead of shutter might help in some cases too.

It seems like this is pretty limited in actual scenarios. If hot spots are essential for your subject, like the white breaking waves, you could try underexposing (with a setting to minimize contrast in gamma and avoiding deep blacks). Then bring up dark/mid areas in post. The details in waves would be an added bonus. A low contrast filter would probably help in these situations as well. For several of the examples, I think this would help the overall shot.

There's also post correction of the red with a software mask and CC, but that would be pretty annoying work given the way the effect can change, move and take on shapes....
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