Not all 3 element lens are the same focal length.

[RedCowboy]

Not all 3 element lens are the same focal length, I had noticed this before but never counted the turns, well tonight I was goofing around with a triple 7875 HH just for the fun of it and discovered side by side I could see what I already knew.

The middle lens in the pic is a G7 in a 5mm long holder, I ended up going with 3 G7's in 9mm long holders, but 2 3elements focused onto my wall at 6 feet and the 3 elements were at a different distance from the diode and the lens was not unscrewed/coming apart, the actual number of turns to focus were different and I have noticed this with 3 elements before.

I have noticed AIXIZ 3 elements seem to consistently have a longer FL and a tighter spot, I will try to do a measured turn count each time I buy one at a set distance, but there seems to be 2 different FL 3 elements.

I have not torn apart the lens and measured the lens yet, but I can count turns and this is not the 1st time I have noticed this, either one internal lens or the spacer must be different.

I am using the module thread play to adjust the beams, a fraction of a mm adds up over a distance of several feet......Yes I know it's sloppy but I'm having fun.

Also here are some pics and a quick vid of 3 x 7875's in a HH, this SOB gets hot even in a 2.675' x 2' round aluminum bar heat sink.

 

[GSS]

RedCowboy, thats really good to know. I've been building a nice collection of 1W to 2+W of 445,s and a PLTB450. I want to do some wooden board burn tests like I've seen on your threads. I might just do them on my wooden TV table to give the lived in look. Just a question before I back up and look at your OP again are any of the different lengths 3 elements bottoming out and or the focus ring hitting the heat sink before a good focus?

 

[RedCowboy]

No they don't bottom out it's just some have a longer focal length and as the diodes output expands like a fan that means more of the edges will be clipped, but what gets in will have a tighter focus, it's minimal but noticeable.

Podo's G7 and 3X expander looks like a good combo, but I have not yet tested his expander, the G7 in the 5mm long housing I like.

But as the new diodes are more divergent cylindrical correction seems to be the ticket, but the 3 element, either variant works, and they don't bottom out for normal up close to infinity focusing.

 

[GSS]

Talking about the new diodes, Lifetime hooked me up with the PLTB 450 with a G2 at 2.5W. The beam quality is as good as a 3 element on my M140...Only draw back I see is you cant run the 450 as hard?

 

[Cyparagon]

Are you sure you don't have one backwards? If not, I suspect one or more of the elements are loose.

 

[RedCowboy]

Here are 2 3 elements, both are tight.
One focuses much differently, yet inside all parts are the same, did they not assemble it right at the factory?

I will put them back the same and see, but this is how I got them, I still need to compare an AIXIZ.

On these the large lens is made from 2 bonded lens then the spacer then the single that's concave/convex.

I will reassemble the same and see if that was it, is this a somewhat common factory error?

This is an image I found, did they simply start bonding the large, it looks bonded from 2 lens.

The one may have a defect that's hard to see, but I also wonder if the grind has changed any over time?

 

[Isaac Clarke]

Good find!!! but i've never run into that problem before....

 

[GSS]

Red, ok I was confused why it was called a 3 element an now remember the bonded thing. I wonder if its a cost or optical reason they manufacture it that way?

 

[Pi R Squared]

Good find!!! but i've never run into that problem before....

I doubt if anyone would even notice unless they had a laser like that with 2 or 3 modules.

Alan

 

[RedCowboy]

There are some differences, I just checked 2 brand new perfectly tight lenses one from DTR and one from another seller and from the moment they caught thread one was 7 turns to focus on my wall 7 feet away the other was 6 turns from where it first caught thread.



EDIT:

I did re seat one of these lens several times and finally got it to settle in, Cyparagon you may be right, some of these may just be unsettled, I will have to work with them and see because they can be difficult t get settled in just right, or maybe I'm not very good at it.