USB Microscope for PCB work

If a variable focal length isn't a "zoom", then what is?

Thanks, Rich

A zoom stays in focus as you vary the focal length. With an autofocus mechanism, it's not as important I guess. Except, of course, that most of the autofocus things suck.

My Sony Cybershot has a 12:1 "zoom" but it seriously defocusses as you go towards the telephoto end. None of my film cameras do that, but their zoom lenses are huge and heavy, like 12 or 14 elements.

John

Thanks; apparently my Fuji uses the autofocus feature to compensate. :-)

Thanks! Rich

Depends on the camera

Funny. I wouldn't call it a "feature" if it is an undesirable item. More toward "inclusion".

I do not like how IPC-A-610 allows for silk screen "ink" to end up in or on a pad or through hole annular ring. I always make sure that any art I layout has edits in the silk screen workup if there are any places that did not account for this.

Yours sounds like a nick in the silk screen or a glitch when they burned the photo-mask for it.

My beef is how the spec allows for it. Actually, thankfully, your situation is still out of spec, and rejectable. They should coupon a tooling cost break to you on your next board to make up for the re-work time you need to spend to make the boards useable (scrape time).

I hate re-work. 1 hour of a tech's time to do the rework is really 3 hrs of lost work to me.

The hour that got spent. The hour that got lost by spending it on this, and the hour needed to make the item that would have been made if the time were not spent doing re-work.

It is far worse the further the failure mode gets before discovery.

Re-work in the field costs 16 times or more, and perhaps even the customer.

Rework... I call it an upside-down pyramid... from a cost POV.

Minimum loss is 3X the actual rework time, plus overhead.

Rich Grise snipped-for-privacy@example.net posted to sci.electronics.design:

I believe the term used is varifocal. The difference lies in how changes in effective focal length control interacts with the focus control. If they are orthogonal (or nearly so) it is a zoom lens, if they interact heavily it is called varifocal.

Not all zoom lenses stay in focus when zooming. Some even have separate zoom and focus "knobs".

Your film cameras have expensive lenses that have nothing like a 12:1 zoom. You're lucky to get 3:1 with a decent lens (70-210mm is sorta normal).

Hard to compare that. My manly 70-200 is almost 12" long with hood and weighs more than 3lb- 21 elements in 15 groups.

Best regards, Spehro Pefhany

No, it's not hard to compare an *expensive* lens that has a 3:1 zoom ratio over a cheap lens that has a 12:1 zoom ratio. There is a reason for both (price and ratio, with quality mixed in for good measure). The only "fly" is the objective size.

OK, yours is bigger than mine.

(Slinks away quietly)

John

They all do. One knob adjusts for object distance, and the other varies the focal length. The more glass that is applied, the less they interact.

John

It takes a lot more expensive optical glass (or plastic) to make a f2.8 lens vs. a f5.6 or whatever. I wonder how far modern CMOS/CCD sensors are from theoretical limits on noise at 300K.

Best regards, Spehro Pefhany

I inherited one almost that big from my Dad, but I sold it to my uncle.

Cheers! Rich

Sez the man with dozens of high-end oscilloscopes. ;-)

Best regards, Spehro Pefhany

You got out of bed?

John

Yes, but that doesn't affect the zoom ratio. You can't get a 12:1 zoom at high enough quality for 35mm at any price. Even zooms for

AIUI, pretty close. If I find an optics guy (I'm designing camera electronics now) I'll ask.

No, often they have one knob that is used for both focus and zoom. Even my forty-year-old Canons (eBay is your fiend) have single "knobs". The more *math* that is applied the less they interact.

How does that work? What happens when the object distance changes?

Do you mean turn/slide? That's really two kbobs.

John

You push/pull the knob.

Yeah, it took me a while to figure out your problem with "one kbob".