KnowM2 Focus Screen Issues / Anyone About Glass One?

Neurodancer

Neurodancer

Well-known member
I got my M2 and set it up. It made so much noise and vibration that I had to take it apart to rebalance the spinning ground plastic. I am not impressed at all with the use of plastic in this unit.

First off the spindle hole looks to be deliberately oversized to make adjustments. The need to make adjustments is because the hole in the plastic is either not centered properly or the plastic is not truly round. The fact that even after rebalancing there is vibration on mine and 2 other units that I know of leads me to believe that this is a design flaw.

Secondly, the idea of a ground plastic is not a very brilliant idea. There is no way that plastic can accept as fine a grain as glass can due to hardness. The result is more image degradation. A questions I have is: Why would you put a plastic filter in front of your lens?

I feel that the M2 is a great piece of equipment with this one major flaw. The DOF is great with this unit, but the image is in need of improvement. I am hoping someone knows of, or is working on a true ground glass solution.
 
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I am surprised that the focusing element is plastic. Are we talking about the "cinescreen?"

I have a DIY DVD in the works for building a vibrating/oscillating adapter (Snod35). The design uses optical glass for the GG. In fact the DVD shows you how to grind the GG yourself. The achromat makes up the bulk of the price in building the Snod35, so if you have the redrock achromat already, you might want to give it a shot. Of course, the DVD is not ready yet :) (1-2 months).

We shot our Hero Fest entry with the original version of the adapter. There were some design flaws that have since been corrected. The main one being a more stable solution for preventing the GG from moving along the Z axis. At the time we were using the infamous Nikon D screen, which works well, but is a bit too rough as far as the surface grain of the GG. The new DIY GG makes the D screen look like scotch tape at higher F/stops.

With that being said, the images that I have seen from the M2 sure look great. I agree though that plastic seems less ideal than optical glass.
 
The cinescreen is ground glass, not plastic. Well on mine it most certainly is anyway. Perhaps you should email Redrock or post on the redrock forum. You will get a quicker response there.
 
Steve Shovlar said:
Perhaps you should email Redrock or post on the redrock forum. You will get a quicker response there.
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I agree. They can best explain why they chose the materials for their cinescreen.

The key to eliminating the vibration is in how much you tighten the screw that secures the cinescreen. Too much or too little and there's more vibration. You have to tighten the screw, turn on the motor, see how much vibration, then adjust the screw a little bit, try it again, until you find the sweet spot where it's all "in tune" and the vibration is minimal.

The Redrock guys held a free seminar in Burbank about a month ago, and helped a small group of us new M2 owners with setting up our units. I'm not going to complain about how the unit could've been better out of the box, I'm just thrilled they are making a unit that rivals the P+S in image quality and light loss at 1/10th the cost!

As you know, the M2 is all about proper setup. Tweaking and adjusting it (for proper alignment, for vibration, for backfocus) are all essential to get the best image. I have seen beautiful images from the M2. It just requires effort (and expert guidance) to set it up properly. In my case it involved dropping down the motor a bit, and tightening the screw just so... so the vibration was minimal. This was a lot easier for me, since I was fortunate to have the Redrock guys do it for me at this seminar.

I would've been a bit lost without their assistance in person.

They are happy to assist new owners. I'd contact them.
 
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Steve Shovlar said:
The cinescreen is ground glass, not plastic. Well on mine it most certainly is anyway. Perhaps you should email Redrock or post on the redrock forum. You will get a quicker response there.
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I bought the M2 direct from Redrock about 5 weeks ago. The screen is definitely plastic. I am a technician. I have no problem with balancing the unit. I tip is to click the switch on for a second to get the ground plastic spinning slow enough to see if the rotation is true. You can use a reference point like a piece of red tape. Keep centering disk until is as true as you can get it. Do not hold your breath for it to become vibration free. The plastic is not precise enough for that. Most cheap cooling fans such as those used for cooling a processor on a video card are balanced much truer than the M2.

What would work much better is optical glass about ½ the thickness of the plastic. I am going to talk to someone about making one out of a 4x4 clear filter. If anyone has any info or abilities to make such a ground glass, I would sure like to hear from them.
 
Neurodancer said:
... There is no way that plastic can accept as fine a grain as glass can due to hardness. The result is more image degradation. A questions I have is: Why would you put a plastic filter in front of your lens?
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I am not an expert on this, but I think you are mistaken on the groundglass's purpose in the M2 unit. You call it a plastic filter, but despite material, it is not a filter. Some think the M2 directs the light from the lens straight to the CCD, I believe this is not the case. My understanding is the M2 groundglass is like a projector screen. The groundglass is positioned where the film would be in a film camera, meaning the light bends to focus at that point. What your camera does is zoom and focus on this mini-screen. It spins to keep the grain from being stationary. Therefore if you are complaining about how you want a more clear 'glassy' groundglass (you mentioned using a less thick glass filter) you are essentially using a window as a projection screen... which you must see the problem with.

I may have misread what you meant. But this is how I see it.
 
The Redrock guys told me that they experimented with hundreds of different types of materials for their cinescreen, and found that this one is the most effective in terms of minimizing light loss while maintaining image quality.

I'm not an engineer, I'm a filmmaker.

At the end of the day, the people who watch your movie or program don't give a damn whether it was plastic or glass. They'll only care if it looks good.

The M2's image looks GREAT. And the price is within reach. That's good enough for me.
 
Yes Gale! I have to agree. Minimizing light loss while maintianing image quality is probably making the cinescreen as clear as possible (light loss) and still getting best image 'projected' on the 'screen' (quality). I would say again that Nuero's glass filter cinescreen will be to clear to pick-up an image.
 
The image is not formed in the plastic disk but on the thin diffused layer sprayed on the side that faces the 35mm lens.

I think weight played a big role in choosing a plastic disc instead of glass.
The mattescreen in my Canon DSLR isn't glass either...
 
=Prodigy= said:
I am not an expert on this, but I think you are mistaken on the groundglass's purpose in the M2 unit. You call it a plastic filter, but despite material, it is not a filter. Some think the M2 directs the light from the lens straight to the CCD, I believe this is not the case. My understanding is the M2 groundglass is like a projector screen. The groundglass is positioned where the film would be in a film camera, meaning the light bends to focus at that point. What your camera does is zoom and focus on this mini-screen. It spins to keep the grain from being stationary. Therefore if you are complaining about how you want a more clear 'glassy' groundglass (you mentioned using a less thick glass filter) you are essentially using a window as a projection screen... which you must see the problem with.

I may have misread what you meant. But this is how I see it.
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You are correct about the spinning so called ground glass (ground plastic) almost all ground glass is done by sandblasting one side of the glass. There may be other etching methods used. The quality of the image can be somewhat dependant on the thickness of the material. That would be if the material was adding any distortion, the thicker the material the more distortion.

I don’t think this is the case with this particular plastic being used. I am interested in glass for the following reasons:

A- because of the rigidity of the glass you can use a thinner piece. This serves to reduce the mass. The less mass makes it easier to balance. If it is slightly off balance the effects will not be as noticeable

B- Glass can be of a finer optical quality than plastic

C- Glass being harder can accept a finer grain of texture. This serves to make a sharper image. It will still be soft, but not as soft as the plastic. The coarse texture used in the plastic becomes very apparent as soon as you turn off the motor.

I hope that I have made myself clear. Much of this experience comes from 10 years of staring at a ground glass of a view camera or a Hasselblad. As a commercial photographer I was always willing to spend more money on better ground glasses. The payoff was always a better preview image. I cannot see why these same principals would not apply to this. I think it would apply even more so due to this being the image plane.
 
I think they whent with a Non-glass Imager because of Weight. more wieght means slower rotation= you'll see the Grain of the ground glass like in the mini35 adapter. plus when you get the smallest of dirt on the GG of the P S technick you see it. the M2 is really good because it rotates it so quickly. I've never had a problem with the Vibration even handheld and Stedicam.

Are you useing the AC/DC Adatper? because every time we used it in small rooms our sound guy would make us turn it off and use the onboard battery.

also Mine used to make a horiible sound they said it was
because teh motter was dieing. but since yours is brand new I'm shure thats not the case.


try to go to there next get together it was great for them to help us better setup our adapters.


VP
 
Vincent Pascoe said:
I think they whent with a Non-glass Imager because of Weight. more wieght means slower rotation= you'll see the Grain of the ground glass like in the mini35 adapter. plus when you get the smallest of dirt on the GG of the P S technick you see it. the M2 is really good because it rotates it so quickly. I've never had a problem with the Vibration even handheld and Stedicam.

Are you useing the AC/DC Adatper? because every time we used it in small rooms our sound guy would make us turn it off and use the onboard battery.

also Mine used to make a horiible sound they said it was
because teh motter was dieing. but since yours is brand new I'm shure thats not the case.


try to go to there next get together it was great for them to help us better setup our adapters.


VP
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A thinner glass would be same weight or lighter. The reason for noise, vibration, and dying motors is the factory seems to be shipping many these units with badly balanced ground plastic. I was very surprised to see mine and someone elses vibrating badly and I have read of a few more instances of off balance ground plastic.

I think this is an area that is greatly in need of improvement.
 
Neurodancer said:
A thinner glass would be same weight or lighter. The reason for noise, vibration, and dying motors is the factory seems to be shipping many these units with badly balanced ground plastic. I was very surprised to see mine and someone elses vibrating badly and I have read of a few more instances of off balance ground plastic.

I think this is an area that is greatly in need of improvement.
Click to expand...

You should also post this at the redrock site. I'm surprised one of the redrock guys didn't jump in.

http://www.redrockmicro.com/forum/
 
I don't know about your vibration issues, but my M2 is so damn smooth and quiet I keep forgetting to turn it off! Until I get a rechargable exterior battery it's gonna piss me off.
 
Your experience with noise and vibrations sounds very strange to me. I've had the Cinescreen off and on the spindle a couple of dozen times without it needing that kind of balancing or creating the vibration and noise you describe. Mine is always whisper quiet. I've heard of vibration problems before, but not too often.

With respect to the material and construction of the Cinescreen, mine is solid, maybe 1/8th inch thick, and has the weight and feel in the hand of prehaps the plastic used in eyeglasses. It is etched on one side. I wasn't sure from your description whether your cinescreen is of the same construction. If not, you need to check with redrock.

I've been following the discusion on DVXuser and on DVinfo for the last couple of years on the creation of 35mm lens adapters. There was a lot of experimentation. But because film grain is molecular in size and varies from frame to frame, it was very difficult to create a screen that resulted in a film look. The grain from sandblasting glass was enormous in size compared to grain molecules on film, and in a static screen adapter, the grain is unchanging from frame to frame and becomes immediately noticeable and distracting. People tried plastic, etching glass with various kinds of chemicals (rather than sand), various depositions on glass, even melting strange mixtures of parafins and chemicals onto filters. Also, there was a great issue with light loss. It was a needle-in-a-haystack search. And perhaps it continues today. But the M2 seems to provide a practical solution, in that the moving screen creates changing grain from frame to frame, and the character of the simulated-grain that the M2 produces looks pretty good, and the M2 doesn't give a 3 or 4 stop loss of light like some other designs that were tried.

I'm not an expert or an engineer or a DIY either. Just reporting my expereince with the M2 and what I've read. You might want to search at DVinfo and DVXuser before trying your GG technique, as it may have already been attempted.

Hope it is of some service.
 
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Hi everyone,

Sorry for the delay - we normally handle support requests through the redrock customer support forums (which we encourage you to use as you'll get a faster response).


Clearing up a couple things. regarding noise and vibration, it sounds like it just needs to be balanced. There are two screws that hold the motor - these are designed to provide this adjustment. You can drop us a line (or me, bvalente@redrockmicro.com) and we can give you the instructions. It is also posted on our customer support forums.

Regarding the CineScreen - it is a specially formulated acrylic polymer. Yes, technically it's "plastic" but likes like saying parts of the space shuttle are plastic, or lenses on today's eyeglasses are plastic. It creates an inaccurate impression.

The CineScreen is not 'blasted' but rather goes through a process we developed that creates a high quality intermediate screen - it is good enough we thought to patent it. The image quality is great, in our opinion and the opinion of many of our users. It is true we tried hundreds of combinations (including everything we've seen in the DIY sections of various forums) and we've found this to be the best approach. It also affords other advantages listed below.

The second reason we chose the polymer route is weight. you get two benefits from that: first it allows you to stop down past f5.6 without seeing any grain. You won't see that on other solutions. Second, you get great battery life. We've run it continuously on a 9v battery for 2.5 days.

Third is the low light loss. The polymer and process we use results in about 1 stop of light loss.

If folks come up with 'tuner versions' of image elements - great! We already have folks who develop flip eyepieces, battery packs, etc. so anything that helps filmmakers we're all in favor of!


Thanks


Brian
 
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