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DTR G8 lens

CurtisOliver

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Yep, these sound like a great all rounder. Thanks for the quick test Paul. (y)
 



paul1598419

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My pleasure, Curtis. I am still planning on some power measurements of this lens compared to others like the G2, the 520nm AR coated 2 element and the acrylic lenses. These are the ones that people might want to use this lens in place of.

The input aperture on this lens is larger than the G3 lens too. That was very important to me as it will clip less than the G3 as they have similar focal lengths.
 
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CurtisOliver

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My pleasure, Curtis. I am still planning on some power measurements of this lens compared to others like the G2, the 520nm AR coated 2 element and the acrylic lenses. These are the ones that people might want to use this lens in place of.

The input aperture on this lens is larger than the G3 lens too. That was very important to me as it will clip less than the G7 as they have similar focal lengths.
Excellent, thanks again Paul. :)
 

steve001

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My pleasure, Curtis. I am still planning on some power measurements of this lens compared to others like the G2, the 520nm AR coated 2 element and the acrylic lenses. These are the ones that people might want to use this lens in place of.

The input aperture on this lens is larger than the G3 lens too. That was very important to me as it will clip less than the G7 as they have similar focal lengths.
If I understand you, this G8 lens has a wider diameter than the other G lenses? If it's not to much trouble. What is it in mm or fraction of inches if you don't have a metric rule?
 
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Immo1282

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These sound great - I'll have to remember to get one or two next time I order from Jordan...
 

RedCowboy

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It appears that this G8 is about as long of a focal length as is practical for our high quality copper modules, granted not all diodes have the same divergence and there are always trade offs, but I see increased output numbers even with the nubm44 compared to the 3 element and G3 that produce essentially the same spot size at distance.

Could the lens barrel opening be opened up a fraction of a mm, yes but not by much and pressed in/glued in lenses may not be square as I have seen with the sanwu G2/G7, having a seat and a retainer is important for squaring the lens to the lens barrel as well as being able to service it.

Also there's what Jordan said about special filtering, I have noticed how lenses like to be utilized across the central 80% or so for the cleanest results, now a lens that has a thick edge as if it was cut from the center of a larger lens can solve some of that, but all in all this is my favorite lens yet besides the G2 but the G2 is better suited to desktop work, CNC and pre beam shaping optics use.

If the lens barrel opening were to be any wider then a thick edged lens may be needed and could be used, just how much more we could squeeze from this form factor I don't know but it's likely there's not a great deal left on the table.

uY5SF3.jpg


I really like the way the G8 still grabs enough thread in the copper module that we can use the sanwu beam expander adaptor, yes I also use a threaded mounting plate sometimes but it's also good when using only the 1 lens to collimate as a lens such as the G7 feels like it's about to fall out and practically does depending on where you focus it, in short I think this G8 is about the best long focal length lens for our favorite high quality copper modules because of their threaded pocket depth and width, something we don't want to change until we have larger package diodes worth redesigning everything around.
 
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paul1598419

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If I understand you, this G8 lens has a wider diameter than the other G lenses? If it's not to much trouble. What is it in mm or fraction of inches if you don't have a metric rule?

No, this lens has a larger diameter than the G3 only. That is the other 8 mm FL lens offered by DTR. I wanted to make that point, but there was a typo in that post so the G7 was supposed to be G3. Sorry.
 

steve001

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No, this lens has a larger diameter than the G3 only. That is the other 8 mm FL lens offered by DTR. I wanted to make that point, but there was a typo in that post so the G7 was supposed to be G3. Sorry.
Huh. Then I wonder how this lens gets rid of the box shaped splash?
 

paul1598419

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I just compared the two lenses side by side....the G3 and the G8, and they are not seated the same distance from the input aperture. The G3 is farther in than the G8, so as near as I can tell they DO have the same focal length. You really can't tell anything from the number of turns it takes to get to focus because the two lenses are not seated the same distance from the end of the barrel.
 

paul1598419

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No, I do admit my initial guess of the FL of the G3 lens was 8 mm, but it was confirmed by Jordan later on. That is how I KNOW.
 

RedCowboy

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The opening looks like 5.25 - 5.5mm wide much like the DTR G2 holder, I did not take out the lens to measure just laid my micro on top.
 

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paul1598419

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I am not talking about the diameter of the input aperture of the lens. I am talking about its EFL. I suppose I could take the lenses out of both the housings for the G3 and G8 and reinstall them in an empty housing. Then, it would be very easy to see if their EFLs are the same. But, I won't be doing that today as it will take some time to get it done properly and I don't have that kind of time right now.
 

logsquared

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To find the FL measure the long part of the spot at a decent distance, say 15-20 feet. Then measure the the spot at the same difference with a known FL lens, say a G2 (4mm FL) then just take the ratio to find the unknown. For example if the G2 spot is 20mm wide and the unknown is 10mm then 10/20 = .5. .5 X 4mm = 8mm.
 

paul1598419

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The FL of a G2 is 2.39 mm. Not 4 mm. Also, the illuminated spot is what you are going to see on the wall, which is not the actual diameter of the spot. The actual diameter is some value that is less than the illuminated spot.
 

paul1598419

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That's the back focal length (BFL). 4.02mm is the actual FL. 4mm is close enough.
The 2.39 mm distance is from the center of the back surface of the lens to the laser die, not counting the diode window. This also changes with the WL of the diode. I believe at the design WL of 405nm for the G2 this distance becomes 2.357 mm. Usually the EFL and the BFL of any asphere increase with the WL the farther it is used from the design WL. Conversely, it decreases in the opposite direction.
 
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