JVC RS4800 lens defect ?? - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 10 Old 06-09-2019, 07:08 PM - Thread Starter
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JVC RS4800 lens defect ??

Hi, i'm new to this hobby and bought this projector a few week ago.
I cannot clean the spots, they are inside the lens.
To see them correctly i use a led flashlight, so there's reflections from it.
Thanks for any advise !
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post #2 of 10 Old 06-09-2019, 07:15 PM
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Is it affecting the projected image?
If so, then yes it's defective.
If not, then nothing to worry about...

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post #3 of 10 Old 06-09-2019, 07:20 PM
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Quote:
Originally Posted by HPRpinball View Post
Hi, i'm new to this hobby and bought this projector a few week ago.
I cannot clean the spots, they are inside the lens.
To see them correctly i use a led flashlight, so there's reflections from it.
Thanks for any advise !
Looking at the picture, I doubt what is shown there, has any effect on the image.
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post #4 of 10 Old 06-09-2019, 07:38 PM - Thread Starter
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Thanks for the fast answers :-)
I cannot see the defect on the image but i didn't install a quality projector screen yet.
I'm using the wall for testing purpose at this moment, it have a yellow tint.
The lens usually should be completely transparent right ?
Someone already saw those inside lenses kind of spots in older projector ?
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post #5 of 10 Old 06-09-2019, 07:40 PM
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Quote:
Originally Posted by HPRpinball View Post
Thanks for the fast answers :-)
I cannot see the defect on the image but i didn't install a quality projector screen yet.
I'm using the wall for testing purpose at this moment, it have a yellow tint.
The lens usually should be completely transparent right ?
Someone already saw those inside lenses kind of spots in older projector ?
You will be hard pressed to find a projector lens that does not have spots or what looks like dust inside.
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post #6 of 10 Old 06-09-2019, 07:41 PM
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Quote:
Originally Posted by HPRpinball View Post
Thanks for the fast answers :-)
I cannot see the defect on the image but i didn't install a quality projector screen yet.
I'm using the wall for testing purpose at this moment, it have a yellow tint.
The lens usually should be completely transparent right ?
Someone already saw those inside lenses kind of spots in older projector ?
Not necessarily, you'll see dust particles and stuff on any projector lens, but it's normal and does not hurt the image. As far as spots, I've seen that before and it usually does not affect the image, but it can if the spots get big enough. It could have been from someone smoking or if someone was cooking and they filled their house with smoke accidentally, but there are other reasons it can happen. What happens is the smoke gets inhaled through the projector's fans and then gets into the internal parts, and some of it drifts into the light path. It could just be completely normal and may be wet spots from previous condensation that dried up...

The lens of a used projector should not look like a cleaned lens, and I would not clean the lens if I were you anyways. It's very risky unless you do it exactly right. Even people that thought they were doing it right ended up damaging their lens trying to clean it sometimes.

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post #7 of 10 Old 06-09-2019, 09:01 PM
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Quote:
Originally Posted by HPRpinball View Post
Thanks for the fast answers :-)
I cannot see the defect on the image but i didn't install a quality projector screen yet.
I'm using the wall for testing purpose at this moment, it have a yellow tint.
The lens usually should be completely transparent right ?
Someone already saw those inside lenses kind of spots in older projector ?
I've bought a few used projectors so far and all of them had a better looking lens than yours, but that doesn't mean there's actually any problem with the image in yours. Marks and spots on the front lens element rarely have any impact at all on the image. Even severe damage to the front surface usually will only cause a very very subtle image defect.

So, find a white surface to project on and test it there. Issues with used projectors are rarely related to the lens, and more often related to the internal optical elements, especially regarding color. You should, however, test focus uniformity, which depends mostly on the lens (but which should not change as the projector gets old). It's the 10th page on this test:

https://www.eizo.be/monitor-test/
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post #8 of 10 Old 06-10-2019, 07:06 AM
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Quote:
Originally Posted by HPRpinball View Post
Hi, i'm new to this hobby and bought this projector a few week ago.
I cannot clean the spots, they are inside the lens.
To see them correctly i use a led flashlight, so there's reflections from it.
Thanks for any advise !
From my experience with camera lenses these spots look like mold on the inside of the lens to me. This can happen if the projector was used in a very high humidity environment, like a basement with minimal humidity control.

If it is actually mold beware as it can completely destroy the lens over time as it naturally spreads. If mold the lens needs to be disassemed and carefully cleaned (or elements replaced) and the projector must be used in a low humidity / low mold environment going forwards. Note this will likely not be cheap to repair if this is indeed the case.

The dots could also be dust (which would be nothing to worry about) if they are very very tiny, but on your picture the dot size and characteristics looks like mold (could just be a bad picture tho). If the lens in person does look exactly like this picture in terms of dot size and shape I would send for repair to have lens evaluated for mold.

Last edited by Ruined; 06-10-2019 at 07:18 AM.
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post #9 of 10 Old 06-10-2019, 03:28 PM
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Quote:
Originally Posted by descalabro View Post
You should, however, test focus uniformity, which depends mostly on the lens (but which should not change as the projector gets old). It's the 10th page on this test:

https://www.eizo.be/monitor-test/
That is interesting.

Slightly off topic, but Sony say their Digital Focus Optimiser feature compensates for the physical degradation of the lens due to age.

But from what you have said, and I agree, age should make no practical difference to the performance of the lens focus.

They really were struggling to justify the difference in price between the 760 and 870 in my view and cranked up Reality Creation even higher with special attention to the corners. Not necessary with such a great lens!

“Remember to look up at the stars and not down at your feet. Be curious. And however difficult life may seem, there is always something you can do and succeed at. It matters that you don’t just give up."
Stephen Hawking.
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post #10 of 10 Old 06-10-2019, 07:44 PM
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Quote:
Originally Posted by Archibald1 View Post
That is interesting.



Slightly off topic, but Sony say their Digital Focus Optimiser feature compensates for the physical degradation of the lens due to age.



But from what you have said, and I agree, age should make no practical difference to the performance of the lens focus.



They really were struggling to justify the difference in price between the 760 and 870 in my view and cranked up Reality Creation even higher with special attention to the corners. Not necessary with such a great lens!


I wasn’t even aware such feature existed. Considering what I’ve seen about projectors, such feature would make more sense to compensate for minor manufacture flaws on lenses, but it still wouldn’t make much sense at this price point where lenses are usually very good. And it’s not as if the focus will be adjusted often, as it does with photo cameras, so I really don’t know what to think about that. In a time when even high-end models get replaced rather quickly, features of this kind seem very unusual to me, as this is too specific a feature to used as a marketing gimmick.


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