Flaws in my (ahorton's) aspheric lenses

ahorton

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This thread may get geeky.

A while ago I had a batch of aspheric lenses made and about 950 have been sold so far, (all through CPF). For those who don't know what I'm talking about, a search for 'ahorton aspheric' will give most of the relevant threads.

Saabluster, (known for creating the DEFT family of high-end throwers) recently brought to my attention his concerns and disappointment at the variation in the 200 lenses he bought.

Rather than repeat what he told me, I've invited him to show his findings here so that anyone who considers buying my lenses has the full story. After that, I expect that others who have bought my lenses can share their experiences (good or bad) and a consensus can be reached about whether or not there is a problem.


My own position is this:

  • I'm aware of some variation since I use a fairly cheap method of moulding to produce these lenses in small quantities.
  • For my own lights I have never cherry-picked the best lenses because the variation didn't bother me enough in my applications. Obviously I weed out any with chips or scratches but that's all I do.
  • I've used a lot of lenses and some do focus better than others, but I never had one bad enough that I wanted to swap it. Of course we know Saabluster to only ever use the very best in everything.
  • I tested 20 lenses last night when I got the email from Saabluster, but I couldn't see any significant variation. Of course I'm open to learning and doing more thorough tests.
I want this thread to stay fairly technical and become a useful resource on testing lenses but here are some possible future actions (more ideas will be welcome when we have enough information) if the variation is declared to be a problem:


  1. I sort the lenses into bins. The best ones will be more expensive. The average price will also go up because the job sounds really boring and this is meant to be a fun hobby.
  2. I continue selling unsorted lenses and everyone acknowledges that there's a bit of variation and risk.
  3. I sort some into bins and others get left unsorted. So buyers can choose either to take a risk or buy the best and the prices will be appropriate.
 
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Packhorse

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Does this only apply to the 27mm lenses or the 30mm ones too?

After using a fair amount of the 30mm's I have never noticed anything.
After using 4 or so 27mm's I have also not noticed anything.
 

trout

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Oh Damn and I have 50 on the way now anxious to hear what Saabluster has found out

any hint as to what to look out for?????
 

saabluster

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Does this only apply to the 27mm lenses or the 30mm ones too?

After using a fair amount of the 30mm's I have never noticed anything.
After using 4 or so 27mm's I have also not noticed anything.

It most likely would apply to both since they both are made using the same process. Understand that I am a picky man so I may notice things others don't. I also don't think ahorton did anything wrong here just to be clear. It is just the nature of the product and methods to produce it. I am going to go get some pictures and data together to help everyone a little better here and will be back with a much more informative post. No since getting too upset at this point. Ash just wanted to be fair and open with everyone here and I think he is a good man for doing so. I need to finish a pot of corn chowder I am working on and then I'll get the info together.
 

Kestrel

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This thread may get geeky.
Nice to have this phrase come up at the beginning (via the 'hovertext' feature). To paraphrase the movie line, "You had me at 'Hello'". :)

But seriously, I'm a materials engineer with a little injection molding experience. There is some slim chance I might have something helpful to say. :shrug:
 

Walterk

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Curious what the fuzz is about.
Optics are fun.
Its only a 10? USD aspheric lens custom made to match certain diameters IIRC.
 

saabluster

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OK I finally got some time to get some pics and data for you. First I want to show you three categories of lenses.

First up is the "best"
9db0db7c.jpg


About 1/4 of the lenses fell into this category with roughly half following close behind in what I called the "good" category. Together this group made up about 3/4 of the lenses.

Next is the "bad" although as you will see maybe it is a bad descriptor.
fb043a67.jpg


Notice that to the outer portion of the lens the lines get badly distorted? That means that part of the lens is not playing along. The real question is how much does that outer portion matter anyhow. We shall get to that.

Next is a really horrible lens and is the worst I found in the bunch with a massive distortion.
79bcf416.jpg

616e188d.jpg


The lens on the right is the one in question and you can clearly see it is way out of whack. But that was only 1 in 200 so it is very unlikely you would receive a lens like that.

Now the actual performance. The "best" and "good" were about 8-10 percent better in lux than the "bad" ones. Not that big a deal really for most people. The edges of the "bad" ones clearly do not play along so what this tells us is that the closer you get to the edge with these lenses the less it is helping anyhow. This effect is due to limits of the glass itself in being able to bend the light but also stems from the fact that at that angle of entry reflection losses are quite large. This is especially the case with this lens since it was designed to have an extremely short focal length.

In the end I believe that it is not something to worry too much about. I am a freak and love to have the best of the best but one has to be reasonable in ones expectations. I only had one lens to look at prior to buying the 200 and as it turns out the one I had happened to be one of the better performers. I was just hoping that the rest would be the same or better and it turned out that there was a bit more variance than I had anticipated.

I don't think we should ask Ash to go through and measure ever single lens as it is not a fun job and will beat him down as well as raise the price of the lenses. They are being offered by him at reasonable prices anyway and instead of buying one you should buy several and expect to have some better than others. I thank him again for even offering these up for us and enabling a new product for me.:thumbsup:
 

ahorton

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Well there's no doubt that the worst one shown is very very bad. I'll have to make it up to Saabluster.

I try to weed the really bad ones like that out but I'm sorry that one slipped through.

For the rest of them, the difference between bad and good is apparently about 8-10% lux. Knowing the cheap price of these lenses, I can live with that amount of variation. It's just a bit more than the variation within my favourite LED bins. Of course if there's 10% variation in lens and 10% variation in LED output, two seemingly identical flashlights might vary by 21% intensity. Probably not enough to be noticeable unless they're right next to each other.

From what Saabluster told me in an email, there were about 150 in the 'best' or 'good' category and 50 in the 'bad' category.

So my plan at this point is to leave the price as it is and not do any extra sorting. I'll probably make a comment about the variation in my sales thread.
 

CKOD

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Did the place you had make the lenses normally do government work? That "really bad" one looks like someone dropped it while it was still hot and said "ehh good enough for government work" :nana:

I'll have a peek at mine and see how they look over my LCD since that seems to be a good test pattern. Ive kept them in the wrapper, trying to avoid fingerprints all over them for now :)
 

saabluster

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Well there's no doubt that the worst one shown is very very bad. I'll have to make it up to Saabluster.

I try to weed the really bad ones like that out but I'm sorry that one slipped through.

For the rest of them, the difference between bad and good is apparently about 8-10% lux. Knowing the cheap price of these lenses, I can live with that amount of variation. It's just a bit more than the variation within my favourite LED bins. Of course if there's 10% variation in lens and 10% variation in LED output, two seemingly identical flashlights might vary by 21% intensity. Probably not enough to be noticeable unless they're right next to each other.

From what Saabluster told me in an email, there were about 150 in the 'best' or 'good' category and 50 in the 'bad' category.

So my plan at this point is to leave the price as it is and not do any extra sorting. I'll probably make a comment about the variation in my sales thread.

Seriously Ash there is no reason to make anything up to me. It it what it is. I expected the actual numbers to be worse than they were judging by the way the lenses looked using the screen as a test pattern. In the past with other lenses it would have made a bigger difference but the super close focal distance made it such that the outside edge doesn't contribute much anyway. Keeping the same diameter and increasing the focal distance should improve the performance from a lux standpoint.
 

Kestrel

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Did the place you had make the lenses normally do government work? That "really bad" one looks like someone dropped it while it was still hot and said "ehh good enough for government work" :nana:
Actually, it looks like someone in private industry said; "Well, the more substandard ones we can crank out and get out the door, the more money we'll make."

Seriously, any more OT 'government work' cr@p posting is volunteering for time off from CPF.
 

ahorton

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... Keeping the same diameter and increasing the focal distance should improve the performance from a lux standpoint.

Maybe. Of course then you'd need to make sure the lens was perfect all the way to the edge. I don't think many budget lenses offer this. Also, I have yet to see a 25-30mm lens that gives a higher intensity, though many I tried have smaller images (because of longer focal lengths).

Of course we're comparing to lenses that were designed for some other purpose. I'm sure a better one could be made but it won't be by me. I feel like so much of my life has been lost on this lens that I don't have it in me to come up with another one.
 

saabluster

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Maybe. Of course then you'd need to make sure the lens was perfect all the way to the edge. I don't think many budget lenses offer this. Also, I have yet to see a 25-30mm lens that gives a higher intensity, though many I tried have smaller images (because of longer focal lengths).

Of course we're comparing to lenses that were designed for some other purpose. I'm sure a better one could be made but it won't be by me. I feel like so much of my life has been lost on this lens that I don't have it in me to come up with another one.

That was just me thinking out loud not a suggestion. If the focal length was longer I probably wouldn't want them as it would not fit inside the light without the need for a special bezel. For what these lenses are they are fantastic. Strangely enough even that "elephant" lens was only down in performance by about 35% which considering the shape it was is quite remarkable.
 

Harold_B

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ahorton - Do you have a published specification for the lens? I have cruised through a few of the previous threads but didn't find a spec sheet that would allow me to create a model of what you are supposed to get with that lens. EFL, BFL, radii and conic values, clear apertures, coatings if any, material (I found a reference to BK-7) and allowable distortions. The photos show both pincushion and barrel distortion as well chromatic distortion but it is impossible to draw much of a conclusion beyond one is different than the other. If you are interested I could put one on our optical bench and measure it. Get in touch if you would like to pursue that option.

Harold
 

ahorton

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ahorton - Do you have a published specification for the lens? I have cruised through a few of the previous threads but didn't find a spec sheet that would allow me to create a model of what you are supposed to get with that lens. EFL, BFL, radii and conic values, clear apertures, coatings if any, material (I found a reference to BK-7) and allowable distortions. The photos show both pincushion and barrel distortion as well chromatic distortion but it is impossible to draw much of a conclusion beyond one is different than the other. If you are interested I could put one on our optical bench and measure it. Get in touch if you would like to pursue that option.

Harold

The funny thing is that a lot of those specs don't quite work the way we initially expect them to when putting them in front of an LED. Naturally we think that a shorter focal length is going to capture more light but then we have examples of longer focal lengths giving better beams.

I haven't given many details like that because I didn't want to get drawn into unhelpful comparisons with other lenses.
 

Harold_B

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Understood as far unhelpful comparisons. My thought is to measure the lens against the design specs as a way to assess your product prior to shipping. Application by the customer is always a whole different story!
 

Packhorse

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10points for mentioning problems with the lenses.

But in the end they are budget lenses. If people want 100% accuracy and faultless production then they should be willing to pay 5 times the price. Or just buy 5 of yours and pick out the best.

I have not gone through mine looking for duds. I will one by one as I use them and discard any lemons. I certainly will not be looking for refunds unless I end up with a large number being junk.
 

saabluster

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But in the end they are budget lenses. If people want 100% accuracy and faultless production then they should be willing to pay 5 times the price. Or just buy 5 of yours and pick out the best.
Yes that is the conclusion I came to. Excellent lenses for the price and I am more than willing to run through the lot to pick out the best. :)
 
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