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Forum: Pentax News and Rumors 12-07-2014, 10:07 AM  
Is this Pentax's future? Translucent mirror with adjustable transmission rate patent
Posted By hcarvalhoalves
Replies: 78
Views: 11,265
If the mirror can change it's transmittance by electronic means fast enough, the camera doesn't have to *move* the mirror out the way anymore, just switch to 100% when you hit the shutter. That would make a very interesting and durable camera, with less mechanical pieces to fault, without the shortcomings of SLT.
Forum: Pentax SLR Lens Discussion 09-08-2014, 04:31 PM  
How to kill fungus
Posted By hcarvalhoalves
Replies: 11
Views: 1,954
Sun exposure helps to kill fungi, but it can also trap moisture inside the lens. You can use an UV-C lamp (can buy from aquarium supplies, it's used on algae filters) and expose the lenses for some hours to do it in a controlled way.

To completely kill fungi (including spores) the only solution is exposing to X-Ray. This process is used to sterilize hermetic industrial equipment, satellites that go to space, etc. Of course, almost no one has access to this.

None of those methods will remove fungi that have *already* grow on the lenses. The only solution is taking the lens apart and cleaning the affected elements with a water, (4%) ammonia and (2%) hydrogen peroxide solution.
Forum: Welcomes and Introductions 08-25-2014, 12:32 PM  
Alô, de Maceió, Brasil
Posted By hcarvalhoalves
Replies: 2
Views: 329
Alô Maceió!

Welcome to the Pentax Forums Fernando ;)

Existem alguns usuários brasileiros no fórum. Fica a vontade p/ tirar dúvidas.

Forum: Troubleshooting and Beginner Help 08-23-2014, 01:38 PM  
Haze on the rear element, is it much of an issue?
Posted By hcarvalhoalves
Replies: 8
Views: 901
I have a M 50 mm with fungus in the rear elements. It's not the usual web pattern you see in funginous lenses. Only by looking really close I can see tiny semi-transparent spots very tight together, making the element appear foggy.

It takes fine pictures still. This one with a macro tube:

IMGP4127 by hcarvalhoalves, on Flickr

I believe the haziness doesn't affect as much when it's on the rear element since there's no stray light coming in.
Forum: Pentax News and Rumors 08-19-2014, 01:07 PM  
Pentax K-S1!
Posted By hcarvalhoalves
Replies: 1,867
Views: 151,021

I refuse to believe it's not a fake.
Forum: Post Your Photos! 08-10-2014, 07:06 PM  
Night Super Moon.
Posted By hcarvalhoalves
Replies: 4
Views: 625
That's some serious rig!
Forum: Welcomes and Introductions 07-31-2014, 11:17 PM  
Hello from Brazil
Posted By hcarvalhoalves
Replies: 9
Views: 479
For bird watching the 300mm f/4 is more useful, with birds often you're never close enough and the +50mm makes a difference.
Forum: Post Your Photos! 06-21-2014, 12:17 AM  
Misc World War I pistol
Posted By hcarvalhoalves
Replies: 9
Views: 615
It's pretty amazing this design has almost 100 years.
Forum: Pentax Medium Format 06-18-2014, 06:23 PM  
Post your medium format photos!
Posted By hcarvalhoalves
Replies: 11,129
Views: 1,804,064
These are excellent, love the tones. I'm curious whether you retouched it, and if so, how?
Forum: Post Your Photos! 06-12-2014, 12:40 PM  
Macro Some crazy saturation from a CCD sensor
Posted By hcarvalhoalves
Replies: 12
Views: 782
CCDs are still used in high-end applications, like telescopes. CMOS in consumer-grade because it's cheaper and more flexible.
Forum: Post Your Photos! 06-09-2014, 03:41 PM  
Macro Some crazy saturation from a CCD sensor
Posted By hcarvalhoalves
Replies: 12
Views: 782
The CDDs from that generation (K-10D) are still way better than current CMOSes at low ISOs.

Have to keep in mind that CCDs are analog while CMOS is digital - the later send image data as bits to the camera, and you always lose some fidelity when you encode a signal as bits. In audio, it's the difference between vacuum tube vs. digital equipment. In the case of photography, CCDs allow a very saturated output without clipping, while CMOSes have a tendency to clip (more visible on the red channel).

I would take a CCD camera + fast glass any day for still photography, too bad all manufacturers dropped it in favor of CMOS (which is cheaper to manufacture and allows video).
Forum: Photographic Industry and Professionals 04-27-2014, 07:52 PM  
Rare photos of 19th century Brazilian slaves
Posted By hcarvalhoalves
Replies: 25
Views: 2,976
Politics and racial issues is certainly on the topic since I was discussing it and this was originally posted on "General". I don't think anyone (specially someone who is not the thread author nor a moderator) has the right to bully Edgar for expressing his political views, including flaming his own government if he wants to. If one disagrees, he should add some views of his own, not engage personally. If it's too much to stomach, refrain from the discussion altogether. That's how you keep it civil.

Now I hope this thread can continue without turning into an echo chamber.
Forum: Photographic Industry and Professionals 04-25-2014, 08:28 PM  
Rare photos of 19th century Brazilian slaves
Posted By hcarvalhoalves
Replies: 25
Views: 2,976
Racism exists and is a issue in Brazil. That said, it's also silly, because a large portion of the population can trace it's roots back to a slave, and the ones that don't are first or second generation born from European/Asian immigrants of the early 20th century, in which case talking shit about race would cut both ways. All-in-all, race-superiority idiots don't find a fertile ground here, I believe the absolute majority Brazilians take pride on their multi-ethnical background.

A little history for the inclined:

Even though slavery got totally abolished by an imperial decree only in 1888, it was a process. In 1850 human traffic was already prohibited, and during the next years other decrees were made to free special cases (slaves older than 65, newborns, etc.). Members and friends of the royal family went as far as buying slaves from owners to free them. The princess personal counselor was a black civil engineer.

It took long because Brazil was mostly agricultural back then, so the plantation owners had immense political power. So much power in fact that one year after the princess abolished slavery the republican party (mostly plantation owners) articulated a coup-d'etat to turn Brazil into a republic in an attempt to reinstate slavery. They failed at it, but the illegitimate republic was kept, which proved to be the cause of much political instability and power struggles... The result is that Brazil only consolidated it's democracy in 1986 (!!!), and it's still shaky and plagued by corruption.
Forum: Photographic Industry and Professionals 04-25-2014, 07:27 PM  
Rare photos of 19th century Brazilian slaves
Posted By hcarvalhoalves
Replies: 25
Views: 2,976
The first photo seems to have been carefully planned and staged to make the most out of the scene and the equipment. Large format has a quality of it's own.
Forum: Photographic Industry and Professionals 04-24-2014, 09:27 PM  
Rare photos of 19th century Brazilian slaves
Posted By hcarvalhoalves
Replies: 25
Views: 2,976
These recently recovered photos were made between 1860 and 1885, about the time slavery got abolished in Brazil, and depict the soon-to-be-free slaves. The emperor (Dom Pedro II) was a photography enthusiast and sponsored some photographers to depict the daily life of the empire back then.

I'm posting here not only because of the oddity, but I've found the pictures are surprisingly good in terms of artistic and technical quality. It's also close to the heart, as it's my knowledge my grandfather was the first generation to be born not in slavery.

See more photos at:

10 raras fotografias de escravos brasileiros feitas 150 anos atrás | História Ilustrada
Forum: Pentax SLR Lens Discussion 02-05-2014, 08:13 PM  
Why do mm count more at the wide end?
Posted By hcarvalhoalves
Replies: 21
Views: 1,415
Correct, that formula I gave is a linear approximation, just to make a point (linear -> quadratic). It's a good approximation for the normal focal lengths:

Angle of 50mm on APS-C: 35 deg

(2 * arctan (31.7 / (2 * 50))) * (180/pi) - Wolfram|Alpha

Approximation: 36 deg

(180 * 31.7) / (pi * 50) - Wolfram|Alpha
Forum: Pentax SLR Lens Discussion 02-05-2014, 10:42 AM  
Why do mm count more at the wide end?
Posted By hcarvalhoalves
Replies: 21
Views: 1,415
It's like pxpaulx said. If my math isn't wrong, it's as follows:

The angle of view approximates a linear function of the focal length (AoV = 180 × d / π × f, with d = 31.7mm for APS-C), but the area of an image is a quadratic function (A = π × (d/2)²). Since the lenses are designed to project an image of roughly the same size (to cover the sensor), it follows that a linear change in the focal length has an exponential effect on how much/how little information you cram in the same photo. The side effect is that the resolution follows the inverse relation, because the pixels in the sensor are of constant size, so wider AoV -> less resolution.
Forum: Non-Pentax Cameras: Canon, Nikon, etc. 01-31-2014, 07:20 PM  
LensRental: The A7R teardown: A look inside...
Posted By hcarvalhoalves
Replies: 4
Views: 751
It's more like a computer with a shutter than a camera with a sensor.
Forum: Post Your Photos! 01-16-2014, 06:59 AM  
Pets shot through 1/2 inch glass with kit lens
Posted By hcarvalhoalves
Replies: 3
Views: 519
Beautiful angelfish. Did you used a polarizer? I see no reflections.
Forum: Post Your Photos! 11-23-2013, 04:20 PM  
Nature Van Damme Lizard
Posted By hcarvalhoalves
Replies: 1
Views: 376
Found this little fella splitting in the middle of the road, inside the city's park.

IMGP4860 por hcarvalhoalves, no Flickr

IMGP4865 por hcarvalhoalves, no Flickr
Forum: Digital Processing, Software, and Printing 11-16-2013, 01:18 PM  
Lens Sharpness vs Sharpness in PP
Posted By hcarvalhoalves
Replies: 7
Views: 1,054
Good point on not being able to add something that isn't there from the start.

This is a common problem to capturing not only images, but any kind of signal, like audio recordings (you can filter out noise from a good recording, but you can't restore details from a dull recording). This property can even be demonstrated mathematically.

All the sharpening software does is increase our perception of the edges that already exist on the image, not add new edges.
Forum: Troubleshooting and Beginner Help 11-15-2013, 09:10 PM  
Odd question about K30
Posted By hcarvalhoalves
Replies: 34
Views: 2,069
Using the automatic white balance (AWB) will work on 90% of the cases. You might only have to set it manually if you have really weird light conditions (like at night, under orange mercury lamps, or under incandescent light if you don't have a neutral white/grey in the scene).
Forum: Pentax DSLR Discussion 11-14-2013, 05:42 PM  
Do we REALLY need a mag alloy body?
Posted By hcarvalhoalves
Replies: 71
Views: 4,203
The K-50 build quality might be amazing then, since I already find the K-x very well built. Nothing jiggles on the camera to this day.
Forum: Pentax SLR Lens Discussion 11-08-2013, 07:46 PM  
FA/DA comparison
Posted By hcarvalhoalves
Replies: 5
Views: 1,395
Another way to explain:

Your DA 55-300 and the FA 100-300 have exactly the same max focal length (300mm), you're just using the center of the FA 100-300 because it's a full-frame lens with a bigger image circle (that goes wasted because it doesn't hit the sensor on the APS-C digital). In effect, it doesn't give any extra "reach", the size of the image formed on the sensor is the same on both lenses.

It's not a complete waste though. Because you're using only the center of the FA lens, it's potentially sharper, even though the DA version has an ED element.
Forum: Non-Pentax Cameras: Canon, Nikon, etc. 11-06-2013, 04:33 PM  
Who will get the Nikon 'FM2' like FF???
Posted By hcarvalhoalves
Replies: 36
Views: 3,011
This camera looks excellent. Price is steep, but not so much considering FF.
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