# Another aspheric lens question



## Raybo (Jul 4, 2010)

I'm not sure about the formula to figure out all the particulars so could someone please tell me how this lens would work out for a thrower?

http://www.surplusshed.com/pages/item/l3788.html

Thanks as always,
Ray


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## saabluster (Jul 5, 2010)

Raybo said:


> I'm not sure about the formula to figure out all the particulars so could someone please tell me how this lens would work out for a thrower?
> 
> http://www.surplusshed.com/pages/item/l3788.html
> 
> ...


It might work quite nicely. You will have a real heard time finding a host for it. In the end there is only one way to know. Buy it! It doesn't cost all that much anyway.


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## Walterk (Jul 5, 2010)

It is a nice lens, would make nice flashlight with strong beam.
For a thrower it has a bit too long focal length, the f-number is 1 (diameter divided by focal length), for a thrower you look for something between 0.5 and 0.7.


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## Dr.Jones (Jul 5, 2010)

Walterk said:


> For a thrower it has a bit too long focal length, the f-number is 1 (diameter divided by focal length), for a thrower you look for something between 0.5 and 0.7.



That does not affect throw itself though. A lower F# lens will give a wider beam, but with same intensity and same throw. However a wider beam with the same intensity contains more total flux (lumen).

Are there actually single aspheric lenses with an F/# as low as 0.5? As far as I know they are more like 0.7 and above, and multi-lens systems can get below that.


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## Walterk (Jul 5, 2010)

I have a Thorlabs 75mm f 0.55 and an Edmunds 75mm f 0.45 but it has worhtless beam and focussing, a lot of distortion. The Thorlabs is fine. 
*A bulky and thick HID-lens f 0.7-0.6 is probably at least as useful and less costly.*

Edit: 
To be more specific: 
Edmundoptics: NT46-244 - Aspheric lens 75mm Diameter x 50mm FL 
Thorlabs: ACL7560 - Aspheric condenser lens, 75mm dia, f=60mm.
I got uncoated, best is anti-reflective coating on both sides.

Mind the difference in focal length and back focal length in the datasheets.
Mind the difference in clear aperture / clear window, with or without rim.

I dont agree with Saabluster, the Thorlabs is fine. 
I have maybe two lenses with better image, but not one with a good image AND this size.
A slightly longer focal length would give you a smaller spot if that is what you are after.


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## saabluster (Jul 5, 2010)

Walterk said:


> I have a Thorlabs 75mm f 0.55 and an Edmunds 75mm f 0.45 but it has worhtless beam and focussing, a lot of distortion. The Thorlabs is fine.
> A bulky and thick HID-lens f 0.7-0.6 is probably at least as useful and less costly.


The Thorlabs 75mm is worthless in my opinion. It's like they went beyond the diffraction limitation of the glass in making the focal length too short. The lens itself looks gorgeous however.


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## Dr.Jones (Jul 5, 2010)

Walterk said:


> I have a Thorlabs 75mm f 0.55 and an Edmunds 75mm f 0.45 but it has worhtless beam and focussing, a lot of distortion. The Thorlabs is fine.


I think I found them. Didn't know there are such high-aperture lenses.
Can you post pictures taken from the side?


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## beam24 (Jul 5, 2010)

not to hi-jack ur thread but i have the same question >>would this work for a good thrower ?? 


http://www.surplusshed.com/pages/item/l10085.html

because im looking to make my own custom host and would like it kinda small in size


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## Raybo (Jul 5, 2010)

saabluster said:


> It might work quite nicely. You will have a real heard time finding a host for it. In the end there is only one way to know. Buy it! It doesn't cost all that much anyway.



I have an "original" FM 3" head that I intend to use, I will need some kind of jig to hold the lens but I know a few people that own a machine shop.

Thanks for the information I think I will purchase the lens, not a big loss if it doesn't work out.

Thanks again,
Ray


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## Th232 (Jul 5, 2010)

Walterk said:


> I have a Thorlabs 75mm f 0.55 and an Edmunds 75mm f 0.45 but it has worhtless beam and focussing, a lot of distortion. The Thorlabs is fine.
> A bulky and thick HID-lens f 0.7-0.6 is probably at least as useful and less costly.





saabluster said:


> The Thorlabs 75mm is worthless in my opinion. It's like they went beyond the diffraction limitation of the glass in making the focal length too short. The lens itself looks gorgeous however.



Just curious, which lenses are those? The only 75 mm ones from those labs are these:

http://www.edmundoptics.com/onlinecatalog/displayproduct.cfm?productID=2454
http://www.thorlabs.hk/NewGroupPage9.cfm?ObjectGroup_ID=3835


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## saabluster (Jul 5, 2010)

Th232 said:


> Just curious, which lenses are those? The only 75 mm ones from those labs are these:
> 
> http://www.edmundoptics.com/onlinecatalog/displayproduct.cfm?productID=2454
> http://www.thorlabs.hk/NewGroupPage9.cfm?ObjectGroup_ID=3835



That's the ones. Don't waste your money. I will say that the Thorlabs one had the best AR coat I have ever seen in my life. Still the lens didn't work very well.


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## Th232 (Jul 6, 2010)

Thanks for the info.:thumbsup:


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## Walterk (Jul 7, 2010)

Th232 said:


> Just curious, which lenses are those?


 as followed my post 5;

Thorlabs ACL7560
Dia 75
Clear aperture 75
Total thickness 30
Back focal length 40
F number 0.55
Viewingangle 42 degrees

Edmunds NT46-244
Dia 75 
Clear aperture 72
Total thickness 30 
Back focal length 32
F number 0.45 
Viewingangle 49 degrees

Ebay lens
 Dia 66 
Clear aperture 60
Total thickness 24.5 
Back focal length 40
F number 0.66 
Viewingangle 37 degrees








The Thorlabs and 66mm lens work fine, easy to focus and good clean spot. (although always some spill, but will be lost at longer distance.)
The Edmunds gives no neat and clean spot at all..., it works but is messy.
After I shot these photos I realized it may be due to that it is hard to focus. 
Another remark, although it may not show in the photo: Edmunds but especially the 66mm lens gives a small blurry spot in the center (as focussed on paper, in real the 66 shows a fine spot).
And another: The Thorlabs seems almost evenly rounded, the Edmunds is steeper and smaller at the top, and the 66mm lens seems more round then shaped.

I find photographing lenses hard. I focussed them by hand on the underlying paper, and took a photo by hand. Lens foccussed to paper, but distance from the camera to the lens may be different but around 20-30cm. Its a simple camera with bad macro-function.

Wonder what can be analyzed from this ....


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## Dr.Jones (Jul 21, 2010)

Walterk said:


> Wonder what can be analyzed from this ....
> [/FONT]



Most obvious: The Edmund lens is bad, has strong barrel distortion; it has a short focal length at it's center and a longer one at it's edges.

The Thorlabs lens has a slight pincushion distortion.

The DX 66mm looks quite ok, too, except for the center; mine has that, too, but it fortunately affects only a small area.

Thorlabs and DX both have big distortions at their edge (Thorlabs more than DX), reducing the effective diameter (depending on the (virtual) die size).

Such pictures should be taken from as far away as possible (with some zoom) to catch nearly-parallel rays with the camera.


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## Walterk (Jul 22, 2010)

Thx, This is an interesting way of looking at lenses! 
Almost obvious, and making sense for me as a laymen.



Dr.Jones said:


> Thorlabs and DX both have big distortions at their edge (Thorlabs more than DX), reducing the effective diameter (depending on the (virtual) die size).


 
You say 'depending on the (virtual) die size. Dou you mean that it only plays a role when the virtual die covers the clear aperture from a distance? Like in: At a distance the full lens may look enlighted, but their may be big variation in intensity ?



Dr.Jones said:


> Thorlabs and DX both have big distortions at their edge (Thorlabs more than DX), reducing the effective diameter.


This might explain why the 75mm lens is not substantial better then the 66mm lens.



Dr.Jones said:


> Most obvious: The Edmund lens is bad, has strong barrel distortion; it has a short focal length at it's center and a longer one at it's edges.


 
It shows blurred in real life, with a brighter hotspot.



Dr.Jones said:


> Most obvious: The Edmund lens is bad, has strong barrel distortion; it has a short focal length at it's center and a longer one at it's edges.


 
For a controllable focus and even spot, we want the same focal length I assume. But what does the magnification factor tells us?
It is resulting from the focal length I presume. 
We want the virtual die to be as big as possible? 



Dr.Jones said:


> Such pictures should be taken from as far away as possible (with some zoom) to catch nearly-parallel rays with the camera.


 
Will try that soon, if my camera permits.


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## Ra (Jul 22, 2010)

....Interesting....




Ra.


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## Dr.Jones (Jul 23, 2010)

Walterk said:


> You say 'depending on the (virtual) die size.


I meant the effective die size 'seen' by the lens, the size of the virtual die image created by the dome or a pre-collimator. I didn't mean the virtual image created by the examined lens.

Your goal is a parallel beam. Thinking backwards, all the parallel rays go through the lens and (assuming a perfect lens) meet at the focal point, where the LED should be. Now if the lens has some distortion at some area (i.e. the edge), a parallel ray through that lens spot misses the focal point - but it might still hit the die, and that depends on the die size.
If it doesn't hit the die, that area of the lens is lost and doesn't contribute to throw.
If it still hits the die, everything is ok, since there is a part of the die sending rays through that lens spot which contribute to the parallel beam.
Thus with lens aberrations, a bigger die helps increasing throw.

I just wrote 'die' in the previous paragraphs, but it doesn't matter if that's a real, bare die or actually an 'apparent' virtual die created by a pre-collimator or the LED dome (which is a pre-collimator, too). That pre-collimator creates a magnified virtual image, i.e. a bigger virtual die, and that's why a pre-collimator can help increasing throw if the main lens has aberrations.



> For a controllable focus and even spot, we want the same focal length I assume.


Yes, since that means all parallel rays behind the lens met at the same focal point, where the LED should be. With the Edmund lens, center rays intersect at some point (the focus), while outer rays intersect behind the focus.



> But what does the magnification factor tells us?


Nothing relevant usually: The magnification in shots of that kind depends on the particular distance between lens and paper. A non-uniform magnification (like with the Edmund lens) however tells something about distortions and aberrations.


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## Walterk (Jul 23, 2010)

This are the lenses form a distance:





This is how it looks mounted with Led at the distance at which it projects the die:


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## Dr.Jones (Jul 24, 2010)

Nice shots.

The Edmund lens close-up looks funny... 
I can't really think of a proper use for that lens... Maybe it was thought to be combined with another lens? Or was it designed to be put the other way around? (Improbable, but try it...)
Paper weight?
The picture with LED shows that it performs bad... Those LED shots are quite helpful: If the whole lens area is filled with 'yellow', then it's ok.
In that Edmund LED shot, only a small fraction is yellow, so the bigger fraction of the lens doesn't contribute to throw. You can improve it by putting the lens more away from the LED, even if you won't project a die image then. Maximize the yellow 
But better just don't use that lens.
In the Thorlabs LED shot the light was held skew, so we don't see the LED well.
These shots should ideally be taken from far away, too, btw.


Funny, even the Thorlabs has a small blurry spot in the center, but much weaker than the DX. 

The Thorlabs shows more distortion at the edges than the DX, on the other hand I can't see much in the DX lens anyway, maybe slightly reduce it's distance to the paper. But it looks rather uniform compared to the others.


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## Walterk (Jul 24, 2010)

Is it safe, for a rule of thumb, to judge the lenses to how much grey blur they show from a distance?
I think the grey blur in the shots from a distance, show pretty much an equal image as distance-Led shots would do. 

I looked up the data-sheets: 
The clear aperture of Thorlabs should be 67mm
The clear aperture of Edmunds should be 71mm
The clear aperture of DX 60mm

Another finding: shape doesnt predict me if its suitable for a flashlight. 

The Edmunds was also sold as a condensor, usually used in pairs facing each other I think. Maybe for theater lights..


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## Dr.Jones (Jul 25, 2010)

Walterk said:


> Is it safe, for a rule of thumb, to judge the lenses to how much grey blur they show from a distance?
> I think the grey blur in the shots from a distance, show pretty much an equal image as distance-Led shots would do.


I'm not completely sure if I understand you.
Generally speaking, you want to see a rather uniform image when looking through the lens.
The distance-LED-shots have the advantage that you can judge if the distortions are small enough (so that even distorted rays hit the LED) or if the rays miss the LED. You could simulate that by drawing a dot with the apparent die size on the paper and focus on that.




> Another finding: shape doesnt predict me if its suitable for a flashlight.


Actually you can see the the edmund lens can't work well when comparing their shots taken from the side as in post #13: Compared th the others, the edmund lens has a higher curvature at the center (indicating a short focal length) but a lower slope at the edges (longer focal length). I can only see that in direct comparison to a 'good' lens, but an experienced lens designer can probably see that at a first glance.




> The Edmunds was also sold as a condensor, usually used in pairs facing each other I think. Maybe for theater lights..


Condensor pairs usually work in a way that the first lens converts the divergent beam from the small light source into a parallel beam, while the second lens focuses that one again into a small point. That Edmund lens fails at both... Two-lens-systems may be tricky though, and may be designed in a way that aberrations cancel each other out; but when trying a little raytracing in my head I don't think that's the case for those.


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## Ra (Jul 25, 2010)

The way I test lenses:

Set up a led with the desired die size and power it at 0.05-0.2 milliAmps (faintly glowing)
Move the led in the focus of the lens, and look through the lens at a distance of at least 7 meters. Then you can see if the entire surface plays along..

You can also do this with a lux meter: Set up a lux meter at 7 meters (or more) and try to focus the lens till the highest lux reading. Look at the lens from the position of the lux meter (use a filter when the led is too bright, or decrease the power) And see how much of the surface plays along.

I don't have to tell you that a perfect aspheric lens is evenly lit by the led over it's entire surface..

Strikes me that there are so much differences between lenses... It explaines the gain in throw in some cases, when using a pre-collimator.. (maybe even in most cases..)


Regards,

Ra.


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## saabluster (Jul 26, 2010)

Dr.Jones said:


> Actually you can see the the edmund lens can't work well when comparing their shots taken from the side as in post #13: Compared th the others, the edmund lens has a higher curvature at the center (indicating a short focal length) but a lower slope at the edges (longer focal length). I can only see that in direct comparison to a 'good' lens, but an experienced lens designer can probably see that at a first glance.


What you are seeing in that profile shot is just showing the asphericness of the edmunds lens. There is nothing amiss there. In fact for flashlight purposes that is a much more desirable profile than the Thorlabs part. The problem I had with my edmunds 75mm aspheric was the glass itself. It was of such poor quality it had swirls all through it that made for a nasty beam projection.


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## Dr.Jones (Jul 26, 2010)

saabluster said:


> What you are seeing in that profile shot is just showing the asphericness of the edmunds lens. There is nothing amiss there. In fact for flashlight purposes that is a much more desirable profile than the Thorlabs part. The problem I had with my edmunds 75mm aspheric was the glass itself. It was of such poor quality it had swirls all through it that made for a nasty beam projection.



Hm... I have difficulties believing that the Edmund lens (I can only refer to the one shown in the pictures) has an ideal profile for collimating. The pictures show that clearly. I think both the Thorlabs and the DX lens have a better profile. 
Of course an aspheric has less slope at the edges than a spheric lens, but the Edmund lens exaggerates that, it's more like an "anti-spheric" than an aspheric, it produces the contrary of a spheric lens' aberration.


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## saabluster (Jul 26, 2010)

Dr.Jones said:


> Hm... I have difficulties believing that the Edmund lens (I can only refer to the one shown in the pictures) has an ideal profile for collimating. The pictures show that clearly. I think both the Thorlabs and the DX lens have a better profile.
> Of course an aspheric has less slope at the edges than a spheric lens, but the Edmund lens exaggerates that, it's more like an "anti-spheric" than an aspheric, it produces the contrary of a spheric lens' aberration.





The Thorlabs lens is horrible. When you get the die in focus there is a huge amount of light still outside of the die area. The DX lens is the best out of that bunch. How funny that the cheap Chinese lens is better than the "quality" expensive lenses. Of course from what I've read the DX is hit-or-miss as some people get bad ones. Mine is a very good one.


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## Walterk (Jul 26, 2010)

Ra said:


> The way I test lenses:
> Set up a led with the desired die size and power it at 0.05-0.2 milliAmps (faintly glowing) Move the led in the focus of the lens, and look through the lens at a distance of at least 7 meters. .... a perfect aspheric lens is evenly lit by the led over it's entire surface..



I found my way: my digital multi meter has a function to check for contact with a 'beep' . When doing this, the Led faintly glows, not hurting eyes.








Thorlabs 75mm - Clear aperture specs 67; experienced 50mm
Edmunds 75mm - Clear aperture specs 71mm; experienced 40mm 
Ebay67/DX66mm - Clear aperture 60mm; experienced 46mm

Edit: Updated. The result seems to be very similar from a distance of 6meter compared to the photo's from 1 meter.
Edit2: For the record: Thorlabs _F_# 0.55 - Edmunds _F_# 0.45 - Ebay67mm _F_# 0.66


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## Dr.Jones (Jul 26, 2010)

saabluster said:


> The Thorlabs lens is horrible. When you get the die in focus there is a huge amount of light still outside of the die area.


Yep, that's from the distortion at the edges...



Walterk said:


> On a quick glance:
> Thorlabs 75mm - Clear aperture specs 67; experienced 55mm
> Edmunds 75mm - Clear aperture specs 71mm; experienced 45mm
> Ebay67/DX66mm - Clear aperture 60mm; experienced 60mm
> Will update this list later with experiences from longer distance, as these results seem horrible.


Now that is a nice find. I had that suspicion, but was unsure...
I guess we found out that it's actually true what it's said: Single aspherics with f/# < ~0.7 (35° half aperture angle, NA ~0.6) are not really reasonable.


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## ma_sha1 (Jul 26, 2010)

Walterk said:


> Thorlabs 75mm - Clear aperture specs 67; experienced 50mm
> Edmunds 75mm - Clear aperture specs 71mm; experienced 40mm
> Ebay67/DX66mm - Clear aperture 60mm; experienced 46mm



Nice job! Looks like convincing evidence that too short EFL will hurt performance.


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## Walterk (Jul 26, 2010)

I've been in the archive, look what I've found:

Old CPF-member 'Newbie' learned CPF the aspheric in 2004, this was his favorite lens: 









The specs: (post 41) Diameter 2.5585", height ~1.092" focal length roughly ~1 1/4", giving F# 0.49.
But he also mentions (in post 9) bfl to be 1.4inch. giving F# 0.55.
The shape looks a lot like the Thorlabs if you ask me. 

Other references:
The typical Maglite-aspheric dia50 bfl 32mm is F# 0.64.
The first Deft Subaru SVX '92 Hid Headlight lens - 79mm dia, bfl 54mm is F# 0.71.
(Hence most people didn't got their narrow beam as their F# was to small to fit the Maglite. ) 

So, until more data/lenses on hand; F# 0.5 works, F# 0.6 is safe, F# 0.7 gives narrow beam.


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## Raybo (Jul 31, 2010)

No lens for me!!!
You people must of sucked up all my lenses! 

No soup for me!


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## Walterk (Aug 9, 2010)

Really ...?

I am thinking of buying a HID-Headlight projector lens, 'for the experience'.
Interested in a group-buy?


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## Dr.Jones (Aug 11, 2010)

Walterk said:


> I am thinking of buying a HID-Headlight projector lens, 'for the experience'.
> Interested in a group-buy?



I'm interested, depending on diameter and price... :thinking:


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## Walterk (Aug 11, 2010)

The trick is to find a reasonable priced shop...
Any suggestions anyone ?


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## Nos (Aug 12, 2010)

DX just got two new lenses in SKU 43044 75mm and SKU 43043 99mm.

When you grind of the edge at from the 75mm it will surely fit the DEFT showerhead host 

*order placed :tinfoil:


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## Walterk (Aug 12, 2010)

Awesome find !

The best I could find was theretrofitsource.com, two lenses shipped to Europe 53 Dollar.

Edit: ordered


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## ma_sha1 (Aug 12, 2010)

Looks awsome


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## Walterk (Sep 14, 2010)

I got my 75mm DX aspheric. 

Measured:
Diameter 77,25mm
Diameter bulb 74mm
Thickness rim 5.5mm
Total thickness 30mm

Backfocal length 44.5mm to top of dome using Cree XRE-R2.

Its not imaging quality; it is a little blurry, but the light is spread out quite even. It is better to use then the Edmunds 75mm, but less clean image compared to Thorlabs 75mm.

For aspheric flashlight it is a very, very good investment.


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## Essexman (Sep 14, 2010)

DX have another 50mm lens new in SKU44653 the product details say 

Angle: 8~120 degree
- Diameter: 50mm
- Material: optical glass
- Light transmittance: 98%
- Compatible for LED spot light, flashlight, DIY LED light etc.

I'd like to know how it compares to SKU 12834 the first 50mm they sold:

2~80-Degree 
50mm*18mm 
Glass Optics 

??


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## IsaacHayes (Sep 22, 2010)

I got 2 of the Jarhead/newbie lenses before he told everyone and they sold out. I should have got more. He told me first. 

Anyway it's got good AR coating and needs a soak in acetone to loose the thread locker around the ring that holds it. I'll leave the lens in the holder though.. The aluminum holder would make a good heatsink to put another LED with less power for up close or flood.

I also have a RGB CRT rear projection assembly, that has like 3 or so lenses inside it and it makes a super small tight and bright and clear spot with a cree.

With an SST-90 it should be about right size. I'll use a huge pentium heatsink so it performs like it should rather than a 3D mag...

Not sure which I'll use but I want to build a SST-90 thrower/scorcher...

I think I'll still assemble my 5 XR-E 3C HA natural light cause I still want a powerful light up everything light, and at 5 amps will run for 1 hour on NIMH C. Plus the heat will be more spread out with 5 LEDs. If I did an SST-90 Mag I'd want the full 9 amps and that's just going to be a compromise. 

So for "Big" white lights I'll have my general use long running 3C black thrower (seoul), 3C HA nat flood (5 Cree), then a laser beam SST-90 asperhic light. Now I just need time to complete the last 2.... LOL


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## MikeAusC (Sep 23, 2010)

I've checked my house for spy cameras - how else could you be copying my current project







IsaacHayes said:


> . . . I also have a RGB CRT rear projection assembly, that has like 3 or so lenses inside it and it makes a super small tight and bright and clear spot with a cree.


 
I bought a CRT rearprojection lens on ebay years ago and am now finalising the design for using the 140mm biconvex lens in it for a Bush Search and Rescue Searchlight.




IsaacHayes said:


> . . . With an SST-90 it should be about right size.


Yes, an XR-E might produce a brighter spot, but I need spot size AND brightness, so I'll be using an SST90.




IsaacHayes said:


> . . . I'll use a huge pentium heatsink


Yesterday my Zerotherm Atom 30H mini low-profile cooler with copper base and two Heatpipes arrived. They're selling for half-list price because they're rated for 65 watts, but most processors now need more. Under $30 Aus.

I've got to have it working for a Search Exercise on Oct 17th, and I'll post photos on my progress.

Hopefully RS components will keep to their promised delivery date for the LDO10C driver !!!


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## bshanahan14rulz (Sep 24, 2010)

Walterk, what did you think of the ZKW replicas?


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## Walterk (Sep 24, 2010)

I didn't got to that, I settled for the 75mm DX, reviewed here:
*75mm aspheric lens source. *
See post 23 for lens specs and 24 for sloppy beamshots.


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## nikosb (Mar 23, 2015)

saabluster said:


> The Thorlabs 75mm is worthless in my opinion. It's like they went beyond the diffraction limitation of the glass in making the focal length too short. The lens itself looks gorgeous however.



Why? Can you still get a nice projection of the LED die or is the die image distorted?


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