Hotspotting

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e1miran

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Joined 2005
#1
I did a search and cannot find anything that helps me. I have an ASK Impact 24 OHP LCD panel and a Dukane 681 (575w MH bulb).

I'm satisfied with the setup except for the terrible hotspot right at the center. In fact, when you look at the LCD you can clearly see the beam of light transmitting through it that eventually gets projected as the hotspot. I've tried flipping the fresnels with no luck.

I'm assuming this is caused by the second fresnel concentrating the light. Will using a split fresnel configuration solve or at least ease the hotspotting effect? If so, I could buy the lumenlab or DIYPJCO fresnels to replace the one from the OHP. But, I'd like to know if this would help before spending the money.

Thanks.
 
#3
It sounds like you need to adjust the distances of the light engine components , whether it's the bulb, reflector or condenser lens if it has one. Moving the components around may eliminate the hot spot without you having to spend anymore money.

ramkishan said:
Further the arc length of the bulb is also too large......
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Ramkishan, this is the bulb the OHP uses. Please explain why you think the arc length is too large.
http://www.theelectronicsshop.co.uk/Spares/hmi575 lamp.htm

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#4
Mikey p said:
Ramkishan, this is the bulb the OHP uses. Please explain why you think the arc length is too large.
http://www.theelectronicsshop.co.uk/Spares/hmi575 lamp.htm

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The arc length is too large in relation to the point source as in commercial projectors. As a result beam of perfect parallel rays can not be obtained and thus affecting uniformity of brightness and focus corner to corner.
 
#5
ramkishan said:

The arc length is too large in relation to the point source as in commercial projectors. As a result beam of perfect parallel rays can not be obtained and thus affecting uniformity of brightness and focus corner to corner.
Click to expand...

e1miran posted that the problem is a hotspot, which is an issue of optical alignment of the components. It has nothing to do with the arc length of his bulb, which is 7mm, and far superior to the large metal halide bulbs with arcs of 25 to 30mm. Regarding the last part of your statement, "" focus corner to corner "", are you suggesting that corner to corner focus is a function of the light source?
 
#6
Mikey p said:


e1miran posted that the problem is a hotspot, which is an issue of optical alignment of the components. It has nothing to do with the arc length of his bulb, which is 7mm, and far superior to the large metal halide bulbs with arcs of 25 to 30mm. Regarding the last part of your statement, "" focus corner to corner "", are you suggesting that corner to corner focus is a function of the light source?
Click to expand...
All hail the all knowing ramkishan (sarcasm goes in this spot). That is correct, it has to do with alignment. I have tested using a 220 and 330. inwhich was told the hotspot would be worse with the 220mm. It was not. Take the fresnels put them towards a light, and move them around. You will see different aborations which look exactly like a hot spot. When you don't see them, that is when you won't have a hotspot. It has to do with alignment and the alignment of the light distance. Not anything to do with your arc length. I have a 71mm arc, and no hotspot, using a 220mm and a 550mm. The length of your arc will only tell you if the light will get to the wall through your lens.
 
#8
e1miran said:
Truthfully, I have removed the fresnels from their mount which allowed me reposition them and aim the beam on the direct center of the triplet. This greatly reduced the hotspot some, but it's not perfect.
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Do you have any adjustments you can do with your reflector or precondenser lens?
 
#9
e1miran said:
Truthfully, I have removed the fresnels from their mount which allowed me reposition them and aim the beam on the direct center of the triplet. This greatly reduced the hotspot some, but it's not perfect.
Click to expand...
The hotspot is the image of the arc length and the apparent removal by way of adjustment is relocation of the same out of field of vision but that obviously disrupts the uniform spread of light rays as confirmed above. The best option would be vertical mounting of the bulb in the reflector.
 
#10
ramkishan said:

The hotspot is the image of the arc length and the apparent removal by way of adjustment is relocation of the same out of field of vision but that obviously disrupts the uniform spread of light rays as confirmed above. The best option would be vertical mounting of the bulb in the reflector.
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Ramkishan, it's time for you to consult with one of your "experts" that you claim has reviewed your site. You are making no sense at all.
 
#11
My contention is based on well known optical fundamentals as well as practical observations. That is why the best mounting is verical as in commercial projectors and automobiles. I have prepared the design and will report the results in due course of time. It is needless to mention that sound theory should preceed practice if we wish to aim at scientifically correct results.
 
#12
ramkishan said:
My contention is based on well known optical fundamentals as well as practical observations. That is why the best mounting is verical as in commercial projectors and automobiles. I have prepared the design and will report the results in due course of time. It is needless to mention that sound theory should preceed practice if we wish to aim at scientifically correct results.
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I'm looking forward to your prepared design and results that you will report in due course of time. At that time could you please list the "well known optical fundamentals" and " practical observations" that you refer to. Don't forget to consult with your "experts"😀 I'm done.
 
#13
While you are at it, learn your directions. Vertical is up and down, and horizon is sideways. Cars and commercial units go horizontal. Plus, some lights can not be mounted vertical, like mine. It is horizontal only. Thus it's name HOR in the title. But keep up your posts. They are funny and show everyone how intelligent you are.
 
#15
Two things that I saw there. First, the bulb they said they wanted to do with that, can not be put vertical. That is why on the specs, they say horizontal with +- 45degrees. Actually, I think the picture looks vertical, but in reality, the light would still be put horizontal. Also, another thing I saw there, is that it wasn't proven to work. That had nothing to do with hotspoting and arc size making it hotspot. So not sure what that has to do with anything on this particular thread? Has anyone told you, you are weird. Very weird.
 
#16
Miedosoracing said:
Two things that I saw there. First, the bulb they said they wanted to do with that, can not be put vertical. That is why on the specs, they say horizontal with +- 45degrees. Actually, I think the picture looks vertical, but in reality, the light would still be put horizontal. Also, another thing I saw there, is that it wasn't proven to work. That had nothing to do with hotspoting and arc size making it hotspot. So not sure what that has to do with anything on this particular thread? Has anyone told you, you are weird. Very weird.
Click to expand...
 
#17
Miedosoracing said:
That had nothing to do with hotspoting and arc size making it hotspot.
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In all the bulb assemblies of the commercial projectors as well as in automobiles, the bulbs are mounted vertically. BTW I also referred this matter to an expert who replied "if you mount the lamp vertically, then nearly all of your light will be coming from the reflector" Obviously in that case there will be no hot spottig. This is just for your information that I am making such bulb assembly for my DIY projector and will report the results.
 
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