I think the only way to determine the current focal length would be to shine a flashlight through it on both settings at a constant distance. If the image is bigger, then I believe it is the lower FL and if the image gets smaller, it should be the higher FL. Do you know the FL of the first objective in the lens? Because that is the distance you would want away from the 2nd fresenel (I think, i still haven't finished my proj yet...damn school and work). The best way to determine you distances is to fire up everything and use a piece of paper (guy_grotke went over this once i think) and determine your distances that way. You will see where the light lands on the paper, try to get all the light to focus as close as possible to the center of the paper (where your lens is going to be mounted). Hopefully I helped, but you shouldn't just take my word for it, im still a no0b too 😀 reiterating what i've read
Oh didn't notice you said you have 305mm FL 2nd fresenel. for that lens you want a 330mm so you get everything good (same fl from fresnel to lens makes it a good pair for some reason) I am going to have an extra 317mm fl 2nd fresnel if your intersted. the dimensions are 12 9/16" (319mm) x 9 15/16" (252.4mm) x 2mm. The lens was used once when I held it up to test out the distances but I've decided to go the 15.4" route and this lens is too small. It has a few fingerprints on it, but in great shape.
just a small question
exclusiv online gives the following distances
Reflector + 1mm to HQI + 23.85mm to condensor + 136.15mm to fresnel + 285 to 330mm to objective
as i understand it the 1st fresnel (fl=160mm) should be 160mm from the center of the light source. from the avove distances does that mean the condenser should be 23.85mm from the center of the light?
>about the distance from the second fresnel to the projection lens i've decided to do is make the projection lens 330mm away then shorten everything if i need to.. better that way round than trying to enlarge the box.
exclusiv online gives the following distances
Reflector + 1mm to HQI + 23.85mm to condensor + 136.15mm to fresnel + 285 to 330mm to objective
as i understand it the 1st fresnel (fl=160mm) should be 160mm from the center of the light source. from the avove distances does that mean the condenser should be 23.85mm from the center of the light?
>about the distance from the second fresnel to the projection lens i've decided to do is make the projection lens 330mm away then shorten everything if i need to.. better that way round than trying to enlarge the box.
if by condenser you mean pre-condenser not the fresnel but a glass lens, then you want it only a few mm away from the outer envelope of the light source, depending on the FL of the pre-condenser. Mine has a FL of 305mm and is about .5 inch away from the light and it covers the entire condenser fresnel+ so I can move it a little bit. But you really do not want to put an acrylic fresnel 23mm away from the light source (it could melt/warp). My condenser fresnel (the 1st fresnel in the setup) is going to be about 19-21cm away from the pre-condenser lens.
dismantled the Hami yesterday to get some accurate measurements. to anyone thinking of getting one of these its not too hard to do. only problem was some of the screws were really tight (broke one of my new screwdrivers and had to drill it out). might post some pictures later
argh...my lighting and mirror plans have fallen through..
anyone know of any places i can get a 250w metal halide set up here in the UK for a reasonable amount?
a front surface mirror would be useful too but if i dont get one i'll change the design.
anyone know of any places i can get a 250w metal halide set up here in the UK for a reasonable amount?
a front surface mirror would be useful too but if i dont get one i'll change the design.
This setup has been getting some awesome remarks. http://18wheeler.no-ip.org/ and here is the thread discussing it http://www.diyaudio.com/forums/showthread.php?s=&threadid=59091. The bulb is very small and very powerfull. The bulbs cost I think like 40-50, cheaper then the HQI setup. You should try it because it's only setup for 240v I think. Send the money through paypal and you're covered 🙂.
hmm, i'd rather get one from the UK if possible. Also the UVS feature on the metal halides means i don't need a UV filter
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