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-   -   Light scatter or something. (https://www.vintage-radio.net/forum/showthread.php?t=160393)

Wendymott 8th Oct 2019 10:01 pm

Light scatter or something.
 
Hi Peeps.
Something occurred that may or may not interest you.. but it left me scratching my head... As i have no degree in Physics or anything else for that matter..... I was wondering if any other members may have a reason for the following..
As a few of you may know.. I make / process my own pcb boards. This is always using pre coated etch resist board.
However after etching.. next comes drilling...I was having difficulty seeing some hole centres, even with a magnifier.
I installed a small LED lamp to illuminate the drill point area. Still it could be hit and miss. I wear varifocal glasses.
Then one day I rotated the board 90 degrees in the horiziontal plane and "VOILA"...I could see the drilling points much easier, and from that day, I rotate the material to give me the best illumination, and thus most accurate drilling.
I would think it is due to light polarization, but I am only guessing.
Over to you

joebog1 8th Oct 2019 10:11 pm

Re: Light scatter or something.
 
You are correct!! Its light polarization. Since I have stopped wearing glasses I dont have that problem anymore. I used wear multifocal ( Varifocal ? ) glasses and when examining something very closely ( bottom of the glasses with maximum magnification ) I quite often "missed" with the soldering iron or screwdriver. I "think" that the glasses themselves sort of prism the light and causes it to bend sufficiently to cause this effect.


Joe

merlinmaxwell 8th Oct 2019 10:55 pm

Re: Light scatter or something.
 
More likely the "grain" (scratching) of the copper layer, I have seen this and never thought it a problem, merrily rotating the board as you have done.

Boulevardier 8th Oct 2019 11:04 pm

Re: Light scatter or something.
 
Interesting stuff! I've been wondering about getting varifocals or bifocals for a while now (might be better than putting on different specs for different distances!). But I've always been worried about how well they'd work - it could be an expensive experiment with something that doesn't work. I'm particularly worried about safety on stairs and steps - we take it for granted that things are where we see them to be, but they can be in different places through different parts of a lens. I anticipate some twisted ankles and serious trips - or worse. Be interesting to hear how others have fared...

Mike

Andrew2 8th Oct 2019 11:29 pm

Re: Light scatter or something.
 
Mike - I recently got varifocals after years of taking my reading glasses on and off (my distant vision is perfect) and I find I feel a little unsure when using stairs or stepping on/off kerbs. It's quite disconcerting sometimes.

Terry_VK5TM 8th Oct 2019 11:43 pm

Re: Light scatter or something.
 
Wendy, do you strip the etch resist before or after drilling?

Might be interesting to experiment with both conditions and see if it makes any difference.

I always (used to) drill before removing the etch resist as the higher contrast made it easier for me.

Varifocals and bifocals don't agree with me, so it is multiple glasses for reading or the computer. At this stage my distance sight is fine (ish).

fetteler 9th Oct 2019 12:09 am

Re: Light scatter or something.
 
Interesting stuff, I can't imagine what you are seeing - is it possible to photograph the effect?

Cheers
Steve.

Argus25 9th Oct 2019 12:18 am

Re: Light scatter or something.
 
It should be understood that bifocal glasses BF or multi focal glasses MF's are a compromise and an attempt to fit a dual lens into a single glasses frame. As a result, compared to separate glasses for separate working distances, there are compromises, and they are different compromises for bifocals, trifocals and multifocal glasses.

Multifocals have no line in the glass above the reading or near segment. The curves in the glass (or plastic) are blended together. As a result there is on optical channel with fairly severe distortions on other side. So if you look downwards and left and right there is distortion and image swim. People like them though because there is no line in the glass and a gradual blend of the focus from far to near with BF's.

Bifocals are better because when you look below the line in the glass the focal power of the segment is the same anywhere, you can look left and right with minimal distortions, that is if it is a large size bifocal segment that is high set with a straight line across the lower 1/3 at least of the whole lens, these sorts of things suit engineers better. These were called "executive " bifocals. Yet some Optoms make glasses with very small semicircular bifocal windows which again, like the MF might improve the cosmetic look, but are less functional. On the other hand there is a sudden jump in the focus from far to near.

There is no beating separate distance and near glasses for quality and freedom from optical distortions. If there is any issue with potential falls etc I would avoid walking around in MF glasses and be careful with BF's too.

Jolly 7 9th Oct 2019 1:03 am

Re: Light scatter or something.
 
My optician gave me reading glasses last year after I hit 50 and advised me to use them while working with small electronic components. They have helped remove that constant blur I face while trying to read resistor colour codes etc. without them. Interestingly they also help me read my tablet with more clarity, although I was told the glasses are not meant to be used with a monitor.

Peter.N. 9th Oct 2019 10:25 am

Re: Light scatter or something.
 
Many years ago my optician gave me trifocals and I still wear them, even now at 80 I can still see and work on medium sized PCB's, (not very often though), wouldn't be without them.

I initially enquired about bifocals but he didn't think they would be ideal for electronic work and I'm sure he was right.

Peter

Wendymott 9th Oct 2019 10:27 am

Re: Light scatter or something.
 
Hi peeps...... I did not consider the Varifocals as the problem, in fact they are a boon to me as a normal user. However the contrast thing did make me wonder
Terry... I keep the resist on the copper for drilling, as you say it enhances the contrast. And I keep it on afterwards as I found the copper did tarnish.... I dont hold with that anti tarnish spray. So it looks like the grain effect of the copper is to blame. I have a new pcb to drill... so... onward and upward.

ionburn 9th Oct 2019 8:00 pm

Re: Light scatter or something.
 
I am not sure about the issue above, but I would like to point out one safety issue I have found with prescription glasses. I have some sunglasses which I like to wear when driving. When I wear them the displays are difficult to read. I found, turning my head sideways, that things were almost normal. A very clear case of polarisation and something to be aware of when looking toward getting driving prescription sunglasses with modern digital displays.

AndiiT 9th Oct 2019 8:41 pm

Re: Light scatter or something.
 
Hi,
Having an interest in optics as well as electronics I feel I can add to this conversation about spectacles to correct presbyopia, which is a condition that comes to us all around the age of forty years old and is simply the inability to no longer focus on close objects due to the loss of elasticity in the ciliary muscle which allows us to focus on close objects when younger.

Before any of the short sighted folk come along and say "I just remove my specs to see close up" all you are doing is exploiting your inherent short sightedness to allow you to do so. ;)

Anyway, as some of you may already know there are a number of options to allow you to see close up as age progresses so I have broken it down with some other (hopefully) useful information for anyone interested.

If you have distance sight that doesn't need correction all you require are weak magnifying glasses commonly known as reading glasses

Anyone who has worn spectacles to correct a distance vision error whether it be short sight long sight or astigmatism, once they get to their early forties and begin to struggle with close up tasks will have a number of options which are as follows -

Two pairs of specs one for distance and another for close up,
Bifocals which have a segment in the bottom of the lens for close up - these give two distinct fixed focal points one of distance and the other for close up,
Trifocals which are similar to bifocals but have a third focal point for middle distance - these aren't particularly common however,
Varifocals (not to be confused with multifocals which is the term used for "varifocal" contact lenses where the wearer is looking through the distance and close up parts of the lens simultaneously)

The issue with varifocal lenses is that there are a number of different designs, the cheaper ones having a large degree of inherent astigmatism at the edges which cause a blur that the wearer has to learn to ignore.

If you can afford to it's better to go with at the very least mid range or the more expensive "free form" varifocals which are fitted to quite exacting measurements for your own eyes.
Another thing to remember when ordering varifocal lenses is to request a "short corridor" this means that there is less travel between the distance and close up parts of the lens and subsequently less head movement when switching from distance to close up.

Admittedly whilst being practically a full time contact lens wearer there are occasions when I require to see something small in a piece of vintage equipment I will remove my varifocal specs and use a cheap pair of over the counter "ready readers" with an LED headlight for extra help.

Whilst a little dated, a good book to read about optical errors and correction is "The Eye Book" By John Eden

Regards

Andrew

AC/HL 10th Oct 2019 10:45 am

Re: Light scatter or something.
 
Most of the posts have become about medical matters, which are OT for the forum. Eyesight is important, but difficulties should really be referred to an optician.


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