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CAVEAT EMPTOR: This is speculation and not proven by actual purchase or implementation. Yet.




An ND2 filter is essential when a high-output PJ (without adjustable iris) is new. It reduces the lumen levels by half and is appropriate when bulbs have typically less than 1000 hours. In time, when the bulb has dimmed enough, you simply take the filter off. But what if you want to gradually reduce the ND filtering as your bulb burns down in the course of its life? This is the first easy to implement, relatively inexpensive solution I've come across. It will not work on all PJs, but the 72xx's lens is not recessed into its body, so a larger filter is no problem.

If anyone has reason to believe it is not viable, please come forth so this information can be squashed.


On to the show ...


Assumption 1: By Tiffen standards, their 0.3 ND filter is equivalent to the much touted Hoya ND2.

Assumption 2: A Tiffen 0.2 ND filter is only 2/3rds as dense as an 0.3 ND filter.

Assumption 3: A Tiffen 0.1 ND filter is only 1/3rd as dense as an 0.3 ND filter.

Assumption 4: There is no 72mm 0.1 or 0.2 ND filter to fit the 72xx.

Assumption 5: The smallest available 0.1 and 0.2 ND filters are 86mm.


Therefore, we need an adapter -- also known as a step up ring -- to fit the 0.1 or 0.2 ND filter to the 72xx's lens.


First, you need an adapter to fit the Tiffen 86mm filter to the 72xx's 72mm lens:

Go to this e-store and select the 72-86 step up ring.


Second, you need the actual ND filter:
This site has the fabled 1/3 f-stop and 2/3 f-stop filters. There are 4 to choose from: 0.1 and 0.2 in both medium and coarse threads. Uh oh ...

Here's the thing I'm not sure about: whether to purchase the medium or coarse thread on the Tiffen filters. Perhaps someone who's more camera savvy could give a definitive answer.


In practice, I would start with either the step up ring and a Tiffen 0.3 filter -or- just a standard 72mm Hoya ND2; switching out to the 0.2 a couple hundred hours later; then 0.1 as the bulb mellows; and finally removing all ND filtering at some point around 1500-2000 hours.


Whadjya think?
 

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Quote:
Originally Posted by acksnay
Whadjya think?
I think you are on the right track looking for filters to step. Just wanted to mention what I have mentioned before about ND2 filters and whether they are essential with a new bulb though. The notion that they can be used to counteract bulb dimming by leaving them on for part of the bulb's life and then taking them off permanantly doesn't work, as doing the math would show. All it does IMO is mislead the person being told that they do work because that person doesn't get to see how dim things will be the day it is taken off. In other words, they can be shown a problem on day one and made to think that an ND2 filter will fix it, when it won't. With an ND2 filter or without, a 2x ftL range still has to be chosen if a person wants just one screen (other than a method like I describe below with the High Power) and to use the bulb until the end of its life. It can be useful for those who want to put it on and take if off at their leisure depending on their mood or what they are watching though.


But what you have described should work. It took me quite a while to get it, but I finally got a .2 filter. I haven't tried it yet. It is much thicker than I thought it would be and just a piece of square glass, so I would have to figure out how to mount it.


This might not really apply to the 7210, but a person could do something somewhat similar with a High Power or GrayWolf screen. Basically, just move the projector from a high shelf to lower shelves overhead with time to maintain close to the same ftL to a viewer (higher gain position when the bulb is dimmer).


While you could go from the .3 to .2 to .1 and then none, most people aren't affected a lot by small changes in ftL, so you could choose to skip one of those filters and still get a smaller range over the life of the bulb. One thing I will say is that if it were me I would look to optimize things early in the life of the bulb instead of near the end. The reason being that the early life of a bulb is more likely to get used statistically by the first owner since bulbs can burn out, the projector could die, or you could decide to sell the projector partway through a bulb.


Good luck,

Darin
 

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Not sure of the operating principle of these filters, but if it's simple transmission losss, how about just tilting it at different angles so that its effective thickness and loss is changed?


It would be klutzy though, you'd need an oversize filter and a tilting stand of some sort.
 

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Quote:
Originally Posted by noah katz
Not sure of the operating principle of these filters, but if it's simple transmission losss, how about just tilting it at different angles so that its effective thickness and loss is changed?


It would be klutzy though, you'd need an oversize filter and a tilting stand of some sort.
I believe that you would loose more ANSI contrast by tilting the filter. I have read that the filter should be kept perpendicular to the light source for that reason.


Glenn
 

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Darin,


You lost me with your statement about the ND2. I am using this method to try and maintain approximately 7-10ftL over the life of my bulb(as I feel a lower ftL is more pleasing to me personally). Since I dont have a light meter, I intend to remove the filter when I feel that the image has grown too dim. When I do remove it, Wont I immediately double my ftL?


As an example, let's assume that I had about 10-11ftL when the bulb was new and the filter in place. Let's then say that after 300 hrs my output has dropped to 7-8ftL(roughly a 30% decline) and remains around that number until 1500 where, perhaps, it has dropped to 5ftL. When I remove the filter I will be back to about 10ftL for maybe 500+ hrs until the bulb finally expires or dims to under 6-7ftL. Then I install and new bulb and use the same method.


Am I making a mistake/bad assumption?


Thanks
 

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Quote:
Originally Posted by csedaniel
As an example, let's assume that I had about 10-11ftL when the bulb was new and the filter in place. Let's then say that after 300 hrs my output has dropped to 7-8ftL(roughly a 30% decline) and remains around that number until 1500 where, perhaps, it has dropped to 5ftL. When I remove the filter I will be back to about 10ftL for maybe 500+ hrs until the bulb finally expires or dims to under 6-7ftL. Then I install and new bulb and use the same method.
There is no big problem with this except that if you can live with a range of 10 ftL to 5 ftL over the life of the bulb then you probably could have just gotten a darker screen and started with 10 and ended with 5 and the filter didn't really do much. Either way you end up with a 2x range and the darker screen would also help the ANSI CR (and on/off CR if you have any lights on), which an ND filter won't. It is true that there are only so many screens you can get unless you make your own and I didn't go into that detail here, but even with the filter you had to choose a screen that gave you some 2x range over the life of the bulb. So, you probably could have chosen a screen that would have given you something close to the range you are getting now, but with some better CR. Now, if you already owned a screen or needed a particular screen you couldn't get a dimmer version of, then the ND2 may help you there.


I probably should have been more clear that because of limited availability of different things for home theater, there are some specific situations where something like this can help once you know all the things somebody is shooting for and what limitations they are dealing with. My point was more against the rule about ND2s that I believe one company was pushing and didn't stand up to the math or scrutiny.


--Darin
 

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"I believe that you would loose more ANSI contrast by tilting the filter. I have read that the filter should be kept perpendicular to the light source for that reason."


Not sure about the ANSI, but it's common to tilt filters to prevent reflections from entering the optical path, to eliminate ghost images and prevent contrast loss.
 

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I'm thinking about the purchase of a ND2 filter for the SP7200 but is it 72mm or 67mm?. I would like to purchase the right size... ;)
 
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