hey, ive been ckecking out this forum for a couple weeks now. I just got an overhead projector(cheapie old 3M). I just found an interesting deal on ebay
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2731142139
this is also for sale from the same seller
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2731122328&category=3698&rd=1
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2731142139
this is also for sale from the same seller
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2731122328&category=3698&rd=1
That's gotta be someone on here!
So who's gonna own up to this one?
I could be way wrong here, but in my experience those OHPs that have the bulb assembly off to the side, and have a plane mirrror to reflect the light up through the fresnel, don't use a condensor lens, and aren't nearly as efficient as OHPs with centre-base mounted bulbs, using a dish reflector and condensor lens.
These are designed to get the most from transparencies - not lcd panels.
So who's gonna own up to this one?
I could be way wrong here, but in my experience those OHPs that have the bulb assembly off to the side, and have a plane mirrror to reflect the light up through the fresnel, don't use a condensor lens, and aren't nearly as efficient as OHPs with centre-base mounted bulbs, using a dish reflector and condensor lens.
These are designed to get the most from transparencies - not lcd panels.
I dunno. The results look pretty good to me.😉
After a few weeks of checking this forum out I can see that sooner or later everybody goes to a metal halide setup. This one has all the work already done.
Also from what i recall this monitor hes selling (Benq FP567s) is one of the easy ones to take apart. Theres no need for a flat cable extension. Which would make a few of our lives easier.🙂
After a few weeks of checking this forum out I can see that sooner or later everybody goes to a metal halide setup. This one has all the work already done.
Also from what i recall this monitor hes selling (Benq FP567s) is one of the easy ones to take apart. Theres no need for a flat cable extension. Which would make a few of our lives easier.🙂
Im not interested who is selling but am interested in the thought that the Mirror reflected OHP are not as good as Center Bottom mounted ones. Anybody clear this up? I have a OHP that looks alot like the one in the E-Bay add (mine is a Dukane 633 that I put a 410 bulb in instead of the 360) Im getting "close" to satisified with my Output, but if a Bottom light OHP with the same bulbs is better, I may switch... anybody with more info on this?
Clok
Clok
My guess is, generally, A mirrored OHP vs A direct light OHP are pretty much the same except for some slight light loss at the mirror. Just how much light loss depends on the mirror and OHP design i guess...
I believe that the mirror actually takes some of the heat off of the fresnel as opposed to the direct light approach.
Surely not - I always thought that heat was only really problematic with halogen lighting -aren't metal halides much cooler running..sure they need cooling, but I've seen centre-bottom MH ohp's that operate with no temp problems at all - in fact, you can leave them running for 30 minutes, then lay the palm of your hand on the stage glass, and it still feels pretty cool.
I always thought the plane mirror design was used as a space-saving measure as it allows the body of the OHP to be a lot lower-profile on a desktop.
Centre-bottom models have to have more height between lamp and fresnel, for optical reasons - hence, bulkier design.
I always thought the plane mirror design was used as a space-saving measure as it allows the body of the OHP to be a lot lower-profile on a desktop.
Centre-bottom models have to have more height between lamp and fresnel, for optical reasons - hence, bulkier design.
Actually, Ive seen side mounted metal halide bulbs that have similar effects on glass. To be more precise, a 250w run for at least an hour and having no effect on stage glass temperature.
OHP Temps
Henrik:
The problem isn't with the OHP stage glass getting hot, it's the LCD panel that can overheat. The polarizer on the bottom of all LCDs only passes 1/2 of the light, the other 1/2 is dispersed as heat into the LCD. The brighter the OHP, the hotter the LCD gets.
With no LCD in place my Elmo 305SD barely gets warm....but add the LCD and temps can get to 135F quick.
Henrik:
The problem isn't with the OHP stage glass getting hot, it's the LCD panel that can overheat. The polarizer on the bottom of all LCDs only passes 1/2 of the light, the other 1/2 is dispersed as heat into the LCD. The brighter the OHP, the hotter the LCD gets.
With no LCD in place my Elmo 305SD barely gets warm....but add the LCD and temps can get to 135F quick.
clok said:
I remember I read it somewhere that the best mirror will still absorb at least 7% light. I would guess with good opticals, it wont matter too much, and you will have a smaller base.
the overall output will be affected by many factors, including point light source, good refelector, condensor and well design projection lens etc. I would bet some side mounted light OHPs have better light than center mounted even though mirror take some light away. I would say stick with the OHP that you can get cheap and easy to modify, and look into upgrading light source (if it is not MH).
To me a non mirror OHP makes more sence, you have less that can go wrong in positioning the bulb so It bounces off the mirror in the center of the fresnel etc, But I do wanna know who this is selling this LOL we have lurkers on this forum it seems.
🙄
🙄
Re: OHP Temps
proto5:
I understand and agree with your point that it is the LCD in place that causes the heat build-up...I was responding to a previous contention that the heat from a MH lamp in an overhead projector could make the fresnel get too hot - my point was simply that in my experience halogens seem to run much hotter than comparable output MH's.
The big question for me is - do these mirror OHP's use a condensor lens, as that seemsto increase LCD performance considerably - the side-mounted MH I had, had like a slightly convex glass cover infront of the bulb, which I don't believe was a true condensor lens - so I got good, but not great performance from it.
proto5 said:
proto5:
I understand and agree with your point that it is the LCD in place that causes the heat build-up...I was responding to a previous contention that the heat from a MH lamp in an overhead projector could make the fresnel get too hot - my point was simply that in my experience halogens seem to run much hotter than comparable output MH's.
The big question for me is - do these mirror OHP's use a condensor lens, as that seemsto increase LCD performance considerably - the side-mounted MH I had, had like a slightly convex glass cover infront of the bulb, which I don't believe was a true condensor lens - so I got good, but not great performance from it.
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