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Forum: Flashes, Lighting, and Studio 1 Day Ago  
A New Way To Do Serious Damage With A High Voltage Flash
Posted By photoptimist
Replies: 27
Views: 1,038
Electrolytic capacitors tend to self-discharge (just like rechargeable batteries) with a time constant on the order of 100 to a 1000 seconds.

There's no reason add a bleed resistor to the circuit, it's just extra cost and worse battery life.
Forum: Flashes, Lighting, and Studio 1 Day Ago  
A New Way To Do Serious Damage With A High Voltage Flash
Posted By photoptimist
Replies: 27
Views: 1,038
The discharge from the capacitor through the flash tube does not go through the hot shoe.

Instead, what goes through the hot shoe (or PC cord) and thus through the camera is less than 0.1% of the flash's power. The hot shoe of an old flash does carry the full voltage of the flash but it connected to a high-resistance, tiny-capacitance circuit. (Notice the 7000:1 ratio between the 160F main capacitor and the 0.022F firing circuit capacitor plus the 1 megohm resistor in the firing circuit )



P.S. Switching the flash OFF does not make the hot shoe safe on a lot of old flashes. The on-off switch only controls battery power to the flash-charger circuit, not capacitor power to the hot shoe & flash tube circuit. (Try turning on the 283, letting it fully charge, then switch it off and measure the shoe voltage. The shoe voltage will probably remain quite high for at least several minutes and maybe longer.)
Forum: Flashes, Lighting, and Studio 2 Days Ago  
A New Way To Do Serious Damage With A High Voltage Flash
Posted By photoptimist
Replies: 27
Views: 1,038
Sorry for your loss!

Two minor quibbles:

1) the amount of current in the hotshoe contacts of an old flash is never high even though the voltage is high. The hotshoe circuit essentially connects the high voltage capacitor to an electrode on the OUTSIDE of flash tube which creates a high-voltage field in the tube sufficient to start the breakdown of the xenon inside the tube. The amount of current is negligible and short-lived (just enough to charge the capacitance of the trigger circuit) because that circuit includes the glass envelope of the tube (a near-infinite resistance). That's why accidentally touching bare wires going to or from the hotshoe with your fingers will give a little sting but not create a burn or risk of electrocution.

2) Digital circuits can be killed by voltage alone without much current involved. The junctions of transistors inside chips can be very thin in order to create sensitive, high-speed circuits. Voltages as low a 20 volts can instantly destroy the junction even if the current is small and short lived.
Forum: Pentax SLR Lens Discussion 3 Days Ago  
Half-Step Aperture Value Incorrectly Labeled!
Posted By photoptimist
Replies: 31
Views: 750
The aperture scale is inverse-quadratic (1/x^2) -- if you double the f-stop, it's 1/4 the light, 3X the f-stop is 1/9th the light, etc. The mid-point between f/4 and f/8 uses a square-root of 2 which makes it 5.657 (the label should be 5.7!!!)

It would seem that somewhere in the mists of time, some photographer made the labels of the aperture scale by using the powers of 2 (2, 4, 8, 16, 32, etc.) and then multiplying by 1.4 (not 1.41421...) to get the intermediate stop numbers. The correct label sequence should be: 2, 2.8, 4, 5.7, 8, 11, 16, 23, 32, 45,...)

The LV scale is logarithmic in light level -- doubling the light flux increases the LV by 1.
Forum: General Talk 3 Days Ago  
Coronavirus
Posted By photoptimist
Replies: 4,075
Views: 99,236
LOL!

You should tell her it's too late! If she has a driver's license, social security card, or bank account, she's already registered with the government!
Forum: General Talk 4 Days Ago  
Coronavirus
Posted By photoptimist
Replies: 4,075
Views: 99,236
Distrust in authority is fine when ever the topic is subjective lifestyle issues. But when it involves physics, chemistry, or biology, the effects of distrust can be fatal.

The virus is an authority that brooks no disobedience. The virus does not care about anyone's constitutional rights to assemble, religion, or not wear a mask (not sure which amendment that is).

The virus, not human law, is the actual judge, jury, and executioner here and it metes out capital punishment to transgressors with no opportunity for appeal, mercy, bargaining, or legal motions to dismiss.

With the virus, the only votes that count are the ones that avoid it or prevent its spread.

People might distrust authority, they may not believe in science, but science really is the only way to understand the real laws that actually govern our lives.
Forum: Pentax SLR Lens Discussion 4 Days Ago  
Half-Step Aperture Value Incorrectly Labeled!
Posted By photoptimist
Replies: 31
Views: 750
Interesting! Yes, in theory, the half steps should be 4, 4.8, & 5.6 and the 1/3 steps should be 4, 4.5, 5.0, & 5.6.

This is not unlike the issue that the labeled "15" second shutter time is really 16 seconds long (and "30" is really 32).

It seems clear that the text of the exposure-value labels is stored in some firmware file, not numerically calculated.
Forum: General Photography 4 Days Ago  
At Long Last...Sunny 16
Posted By photoptimist
Replies: 39
Views: 1,089
To summarize, we have:
  • Sunny f-16 rule

  • Hazy f-11 rule

  • Moony f-8 rule

  • and then there's the Rainy f-the-weather rule ;)


Note: f = "forget" in the case of Pentax, which can take a bit 'o inclemency!
Forum: Non-Pentax Cameras: Canon, Nikon, etc. 5 Days Ago  
Panasonic is still ALIVE,even though Olympus is wounded.G100/110 arrives.
Posted By photoptimist
Replies: 19
Views: 577
Everyone has their own personal gear-weight versus image quality trade-offs.

For me, the weight of the K-1 and 5-7 lenses that I usually carry on hikes and trips is forgotten within a few days of my return but the quality of the FF images is remembered and appreciated forever.
Forum: General Photography 5 Days Ago  
At Long Last...Sunny 16
Posted By photoptimist
Replies: 39
Views: 1,089
Indeed!

And yet the moon is in full sunlight so it should be "correctly" exposed with sunny f/16, too. The material of the moon's surface is very dark (about 1/2 stop darker than middle gray) but the human eye is fooled by the dark moon being the brightest thing in the night sky.


Here's a NASA photo taken from space with both the moon and earth, both in full sun, both with the same exposure, and showing the true darkness of the moon surface:

Forum: Product Suggestions and Feedback 6 Days Ago  
Multi Spot Metering
Posted By photoptimist
Replies: 13
Views: 526
If the metering system of the OM-4 got bad reviews it was probably from people who wanted the camera to choose the exposure for them rather than having the photographer choose the exposure. At the time, camera makers were coming out with increasingly sophisticated multi-segment or matrix metering systems that did a better job of picking a middle-gray-objects-are-middle-gray-on-film exposures. These metering systems were less likely to be fooled by strange scenes dominated by large bright areas (e.g., lots of bright sky) or by large dark areas (e.g., theatre spotlighting).

Spot metering has always created problems for novices who don't understand the discrepancy between what the photographer is seeing (e.g., a brightly-lit black cat on a black sofa) and what the camera's meter is seeing (e.g. a very dimly-lit gray cat on a gray sofa). (Even the best matrix/AI automagical exposure system gets fooled by that). The OM-3 and OM-4 were wonderful, convenient metering solutions that let the photographer measure the tones and control exposure relative to those measurements. In many ways multi-spot is superior the today's histogram-based methods because it provides direct control and knowledge over exactly which spot in the image has which brightness in the final image.

TL;DNR: multi-spot metering was for photographers who want control, not automation.
Forum: General Talk 06-24-2020, 10:56 AM  
Coronavirus
Posted By photoptimist
Replies: 4,075
Views: 99,236
Quite true!

We also need more round tuits.

Lerts can spot problems quickly but they won't fix them until they get a round tuit! ;)
Forum: General Talk 06-23-2020, 03:13 PM  
Your latest acquisition
Posted By photoptimist
Replies: 20,035
Views: 1,415,040
LOL!

It's not surprising, though. If us Pentaxians don't want to buy a "normal" Canikony camera, why would be buy a "normal" lens?
Forum: Pentax DSLR Discussion 06-23-2020, 01:53 PM  
File size comparison
Posted By photoptimist
Replies: 23
Views: 836
"Several digits of accuracy" is impossible and meaningless. Files sizes vary a lot from scene-to-scene, lens-to-lens, and shot-to-shot. Two different photographers are likely to experience very different averages.

Any and all of the following factors can make the image files at the larger end of the size spectrum:
  • more detailed scenes

  • high dynamic-range scenes

  • sharper lenses

  • more in-focus scenes

  • sweet-spot apertures

  • scenes with no motion blur

  • higher ISO settings

  • weird color balance lighting

  • higher sensor temperatures


The best gauge of the relative size is to be found in the back of the K-1 manual which gives the "Approximate Image Storage Capacity" for an 8 GB card and the various combinations of settings you mentioned. You can easily get copies of the various Pentax camera models off Ricoh's site and have nicely comparable data across camera models.
Forum: General Talk 06-22-2020, 12:13 PM  
Coronavirus
Posted By photoptimist
Replies: 4,075
Views: 99,236
Agreed! Water can be a huge issue in drier places.

I live in a town where, until a few years ago, household rain barrels were illegal. The average home owner did not own any rights to the water that fell on their own roof and could not impede the flow of runoff. That seems insane and yet if water is a scarce resource, then it requires some means of controlling exactly who gets to use whatever rain fails on the land.

It's the same with minerals here. Most people don't own the rights to the minerals under their property, either. All the various "property rights' are severable and are be owned by different entities.
Forum: General Talk 06-22-2020, 09:01 AM  
Coronavirus
Posted By photoptimist
Replies: 4,075
Views: 99,236
"Excessive" water use isn't a problem in many cases and places for two reasons:

First, most "uses" of water in urban areas don't really consume any water, they only borrow the water for a few minutes. Washing machines, toilets, sinks, showers, bath tubs, etc. borrow water and return it for treatment. That borrowed water could get used dozens of times between when it fell as rain and when it washed down a river back to the ocean. (Rural septic systems probably return most of the water to the ground unless water-loving plants are growing in or around the leach field.) The biggest true users of water (and the larger problem both as a cause of dropping ground water levels and a downside effect) is agriculture. Too many people are trying to grow huge quantities of the wrong crops in the wrong places. That also includes gardens and lawns with plants ill-suited to the local climate. Also, evaporative cooling for power plants, buildings, and homes also "uses" water in the sense of evaporating it into the air rather than returning it (of course, evaporative cooling has a much lower carbon footprint than regular AC!)

Second, the other huge fact is that water is a local commodity (although the scale of "local" can span hundreds or thousands of miles because it is defined by watersheds). Excessive water use in one location really only affects that location and others downstream. There's no global shortage of water. The point is that no amount of "saving water" in the US or Europe is going to help India.
Forum: Pentax Film SLR Discussion 06-21-2020, 08:17 AM  
Post your B&W Film shots
Posted By photoptimist
Replies: 9,263
Views: 1,039,967
Personally, I'd crop out the "2" because it totally dominates the picture and made me think that everything was stationary until I looked elsewhere.*

The result might be a little unbalanced and cramped but that's actually good! A lack of balance foreshadows future motion and cramping helps convey the packed intensity of the event. Balance and spread-out compositions are for more serene subject matter. A bit of confusing clutter can add to the sense of activity.


*Note: One huge challenge for photographers is to forget what they know about the scene and look at the image with fresh/ignorant eyes. You know this is an image from a boat race, but your viewers do not. I had no clue this was a boat race when I first looked at it. I saw the huge white "2" first and it looked stationary. The wall of the boat looked stationary like maybe this was a picture of a boat dock or floating walkway with the waves hitting it. Then I saw the seated woman & drum -- maybe she was sitting on dock playing for people. Then I saw the rowers digging into the water and realized what was happening. Thus, that "2" really mislead me.
Forum: Pentax SLR Lens Discussion 06-21-2020, 06:31 AM  
3+1 limited / star lens combo
Posted By photoptimist
Replies: 30
Views: 1,416
Based your descriptions, all seven lenses are keepers! LOL!

Why get rid of three lenses? How will you be better off without them?

I can understand not wanting to carry every lens on every outing. But it seems clear that if you make a 3+1 set for each type of outing: landscape, portrait, street, astro, etc., then you'll end up keeping every lens even if some lenses stay home on some outings.
Forum: Troubleshooting and Beginner Help 06-19-2020, 02:35 PM  
Element oranging
Posted By photoptimist
Replies: 6
Views: 545
These lenses (and some others of that era) used glass that contain radioactive Thorium oxide. Over the years, the radiation inside the lens tends to turn the glass a pale orangish-amber. It could affect color balance somewhat but not sharpness.

The coloration can be reduced by exposing the lens to UV light. UV doesn't reduce the radiation (the lens will turn amber afters some additional years) but it clears the color cast for a while.

It's easy to spot a lens with this issue -- just hold the lens in front of a well-lit white piece of paper. If the paper looks somewhat amber or orange through the lens, it has the issue.
Forum: Pentax KP 06-19-2020, 08:55 AM  
Battery life.
Posted By photoptimist
Replies: 17
Views: 616
LV is the worst -- the sensor, CPU, and screen are running full blast.

Turn the camera on for the minimum of time and then turn it off the instant after you take the shot.

Don't use the rear screen for anything.

Don't use SR.

Don't use AF.

Don't use the built-in flash.

Don't use WiFi.

Don't use digital filters, lens corrections, or other fancy imaging processing settings.

Don't save RAW+ or RAW -- JPGs-only reduces total time & energy spent writing data.


The magic formula for maximizing battery life is to not use the camera! ;)


P.S. There are ways to charge a LiIon battery to higher capacity but they increase the risk of fire and reduce the total longevity of the battery. Also, getting the most out of a single charge means running the battery down into the red which is hard on the battery and means the battery will have less shot-life in the future.
Forum: General Photography 06-18-2020, 02:36 PM  
The worst of Craigslist/Shopgoodwill/eBay etc.
Posted By photoptimist
Replies: 1,533
Views: 61,131
Very nice. Those are known as Non-oculars. Very rare! And from what I can't see, they are in mint condition!

(Non-oculars are used for watching birds of "pray". ;) )
Forum: Product Suggestions and Feedback 06-18-2020, 06:44 AM  
Multi Spot Metering
Posted By photoptimist
Replies: 13
Views: 526
I strongly second this recommendation!!!!!!

Multi-spot is nothing like matrix or multi-segment because in multi-spot, the photographer picks exactly which spots to average.

Not only did the OM-4 system let you average selected spots together (up to 8 measurements just like the EOS), it showed the individual measurements as pips on a spectrum so it was easy to see the number of zones between parts of the scene.

The OM-4 multi-spot system was extremely powerful both for getting the right exposure and for understanding the dynamic range / zones of the scene.
Forum: General Talk 06-17-2020, 06:07 PM  
Coronavirus
Posted By photoptimist
Replies: 4,075
Views: 99,236
Such as:

Forum: General Talk 06-17-2020, 12:29 PM  
Coronavirus
Posted By photoptimist
Replies: 4,075
Views: 99,236
Alas, COVID infection rates and deaths are proportional to the fraction of stupidity in the population & leadership. The "brains" have little control over the "bubbas" that think they don't need masks.
Forum: General Talk 06-17-2020, 05:45 AM  
Coronavirus
Posted By photoptimist
Replies: 4,075
Views: 99,236
No it won't be gone, COVID probably will never be gone. It's been allowed to spread too far and deep across the world.

And it won't be "safe" because this world can never be "safe."

But the case count will be low, the death rate will be low, the hospitals won't be fighting so hard, and the economy will be open to all but a small percentage of infected and recent contacts of the infected.
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