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Forum: Digital Processing, Software, and Printing 04-08-2010, 06:31 PM  
Linux-pkremote new version!
Posted By wcleong
Replies: 51
Views: 20,716
Looks like an interesting project, but correct me if I'm wrong, but I didn't think that gphoto supported pentax cameras?
Forum: Pentax DSLR Discussion 04-06-2010, 09:42 AM  
Curious about Photos OF light from a DSLR
Posted By wcleong
Replies: 8
Views: 2,197
Hello,
The lights probably have a 120Hz frequency (2x the power line). You could check by counting the number of dashes in the line and dividing it by the exposure of the photo.

@ imtheguy,
FYI, If you are going to test this out at home, beware of incandescent bulbs, as the hot filament probably makes the frequency of the power line unobservable.
Forum: Digital Processing, Software, and Printing 12-10-2009, 09:15 AM  
Linux-pkremote new version!
Posted By wcleong
Replies: 51
Views: 20,716
I had a similar problem as kas_27_es, and just wanted to post to add my thoughts.

I would first test if pkremote can connect to the camera when running as root, ie: sudo pkremote

That worked for me, though it's not the best idea to have to run it as root. So I ended up editing the rules file changing "DIGITAL_CAMERA" to "DSC_K20D", and also appending





Code:

, OWNER="your_username_here"



after restarting udev this ended up working for me

I'm not sure why adding my user to the plughw group didn't work, but I am by no means knowledgeable about these things and my solution was sufficient for me.
Forum: Pentax DSLR Discussion 11-18-2008, 02:42 PM  
Higher pixel count produces less noise...?
Posted By wcleong
Replies: 6
Views: 2,951
Well I'm not sure what your understanding about sensors are, but if it's similar to mine I don't think this article would topple it :)

I'm guessing what you've generally come to understand is this: the smaller the size of the pixel on the sensor, the more noise that pixel will have.

This article isn't disputing this, it is arguing on the method to compare noise between sensors that have different resolution/sensor size.

Imagine this hypothetical two camera scenario: you have a 1-megapixel camera and a 4-megapixel camera with identical sensor sizes (APS-C for example). Because of the pixel density (each pixel of the 4-meg sensor is 1/4 the size of the pixel on the 1-meg sensor) you'd expect the 4-meg sensor to have 4x the noise. All this article is saying that it's not fair to say this 4-meg camera is noiser than the 1-meg camera, because you can reduce the resolution of the 4-meg image in PP 4x to reduce the noise by 4x, which gives you the equivalent of the 1-meg camera's. So in this case the noise is essentially the same.

But, lets say because of technological advances the 4-meg pixel camera manages to only be 3x noisier per pixel, you would actually have a overall less noisy sensor in the 4-meg camera compared the the 1-meg camera. Per pixel the 4-meg camera would look noisier, but you'd still get a less noisy output if printing to the same size.
Forum: Pentax DSLR Discussion 10-26-2008, 12:16 AM  
k20d HDR?
Posted By wcleong
Replies: 23
Views: 9,490
I think you might be getting hung up on the film equivalent. For example, when doing a multi-exposure shot with a film, once you blow a highlight it doesn't matter what else you do, that section of film is blown out. So if you were to take two exposures (lets say 0.7 secs for the shadows and 1/45 for the highlights and keeping the aperture constant), it wouldn't matter, your highlights would get destroyed when exposing for the shadows. If there is no motion, this is basically an addition, the equivalent of exposing the film (or a single picture) for a length of 0.7 + 1/45 = 0.722 seconds. So for film, no matter how you pick the exposures, you will not get any increase in dynamic range captured. And Film multi-exposure is an addition of each frame.

But there is a difference between a film camera and the K20D. The K20D has two multi-exposure modes, one that emulates the film version, and a new one that is only possible with digital (AFAIK). The mode is selected by the "auto-EV Adjust" checkbox. If this is not checked, then it is like a film camera, and you get no increase in DR. However, if you do select it, the camera doesn't add the exposures together, it AVERAGES them. So even though one image has the highlights blown out, the second has the highlights well exposed, and the net effect when you average the two is that you maintain highlight detail, but the DR of the highlights are half of what they are in the well-exposed image. Same goes for the shadows. The key is the average, and it's not an addition. So the resultant image will be like this: the portions of the image that are well exposed in both frames maintain the same DR as either frame, and the portions that get over-exposed/underexposed in only one frame will have half the DR compared to the well exposed frame for that highlight or shadow.

You've maintained your detail, you've just compressed the true DR of your scene into the 8-stop range that a JPG allows.

I also took some test shots to demonstrate this. I lit a portion of the frame (my bathroom) so that it metered at 1/45, and lit another portion so it metered 0.7". This range is larger than the DR of the camera (at least for JPGs). So for a single exposure at 1/8, both highs and lows get clipped:

Attachment 21106

Now, for the multi-exposure I used two exposures, 0.7" and 1/45:

Attachment 21107Attachment 21108

The camera combined them with this result:

Attachment 21109

Compare this the the 1/8 image from above. I think you could say that now the dark sections appear up reasonably well exposed compared to the 1/8, and the bright areas (the shower curtain especially) also has more detail that the 1/8 single exposure.

And to round things out, here are the histograms for the images:

Attachment 21110

I apologize, the middle plot on the left is mislabeled, it should say 1/8 (instead of 1/20). I didn't feel like re-generating that plot. You can see that there isn't a single exposure frame that can cover the DR of the scene, and that the 1/8 exposure clips both highs and lows. But the multi-exposure image has a nice looking histogram, with very little clipping. The color of the wall behind the shower curtain does look like it's changed, perhaps I should have manually set the white balance, maybe thats what makes it look funny.

Anyways, hopefully that helps.
Forum: Pentax DSLR Discussion 10-23-2008, 07:15 AM  
Strange focusing behaviour on K100D
Posted By wcleong
Replies: 7
Views: 2,407
That's good to hear. Good luck with adjusting the shim. I have in the past used clear tape (like scotch tape) applied to the metal "U" shim that already is in the camera to make some very fine adjustments. It probably will take several layers but I found it easier than making a shim. I don't know how durable this method would be, I only had it in temporarily.
Forum: Pentax DSLR Discussion 10-22-2008, 08:51 AM  
Strange focusing behaviour on K100D
Posted By wcleong
Replies: 7
Views: 2,407
I see it as two separate problems, one with the AF indicator being wrong, and the other being that the viewfinder and actual captured image is different.

As for the AF, I'm not really familiar with the physics behind it so I'm not sure what affects it. konraDarnok may be right saying that it is just an aberrant lens.

Manually focusing in the viewfinder and comparing focus in the captured image image for different lenses might be a good place to start (disregarding the AF indicator), though as you stated you have to keep in mind that the original focus screen can't handle the shallow DOF.

What confuses me is that one of your lenses (disregarding the AF indicator) shows that the viewfinder and CCD in agreement, and that the other lens shows it way off. That doesn't make sense to me, though it wouldn't be the first time :)
Forum: Pentax DSLR Discussion 10-22-2008, 08:17 AM  
k20d HDR?
Posted By wcleong
Replies: 23
Views: 9,490
The difference from the single shot comes by changing the exposure settings between shots. From what I've read (I haven't tried the multi exposure mode yet), the difference is this:

Lets say the scene you are taking a photo of has a DR of 10 stops. And lets say the camera sensor can record 8-stops of DR. And lets assume a single exposure that clips a stop at the bottom and one stop at the top.

If you are doing a two-shot exposure, and you don't change the camera settings (aperture, shutter, etc) for both captures, then pixels that are overexposed in the first image are overexposed in the second image, and when you put them together the are still overexposed. So in this case you don't have any difference compared to a single shot (other than motion being blurred and noise being reduced). Same goes for underexposure.

However, if you are taking two exposures with different exposures, lets say at -1EV and +1EV, things change. The first shot will capture all the shadow details, but overexposes the upper two-stops of DR. The second shot captures all the highlights, but clips the lower two stops of shadow detail. However, when you add them together, the composite image will contain both shadow data from the first shot and highlight data from the second shot, covering the full 10-stop DR of the scene. But, because the highlight detail and shadow detail aren't present in both shots, they can get compressed. In this case, the top and bottom 2 stops of image are compressed, and the middle 6 stops are equivalent as the single exposure.

Check out this post from the linked thread for an illustration:
I can illustrate what Richard described: Pentax SLR Talk Forum: Digital Photography Review
Forum: Pentax DSLR Discussion 10-22-2008, 07:32 AM  
Strange focusing behaviour on K100D
Posted By wcleong
Replies: 7
Views: 2,407
There's the potential that you didn't see any problems with the kit lenses because they are slower (smaller apertures) and have larger DOF, so if there is a little BF/FF it still may be within it's DOF.

Now, if you see a discrepancy between the focus screen and the CCD, ie. when the viewfinder is in focus the recorded CCD image is not, and vice versa, then it would indicate that the lens distance to the focus screen/CCD are not the same (they should be for the image to be in focus at the same time for both). And AFAIK this shouldn't matter what lens is attached. If the distance is the same, what you see should be what you capture (except for the stopping down of the aperture).

At least this is my understanding of how these cameras work.

It might be a long shot, but I've read that some split focus screens come with shims, is it possible you didn't install this? (or potentially put it on the wrong side of the screen?)
Forum: Pentax DSLR Discussion 10-21-2008, 08:58 PM  
RE: K10D few Qs
Posted By wcleong
Replies: 12
Views: 1,526
Also, if you don't plan on using the batteries for a prolonged time, it's best to store them about half charged.
Forum: Pentax DSLR Discussion 10-19-2008, 09:22 PM  
Problem?
Posted By wcleong
Replies: 3
Views: 2,229
I have a k100d, but my camera doesn't ask for focal length of a lens if the shake reduction switch is off. Although I can still enter it in via the menu (it's not grayed out for me). The only time I've seen the SR menu greyed out is when I have one of my DA lenses on, ie. the camera knows the focal length from the lens contacts.

So perhaps try turning on the camera with the SR on? If that doesn't work you can also try it without any lens (just be careful of dust and such) -- with no lens mounted the camera will have to ask what focal length you're using when you turn the camera on (with SR on of course). At least thats how it works with my K100D.
Forum: Pentax DSLR Discussion 10-13-2008, 08:23 PM  
K10D vs K100D AF
Posted By wcleong
Replies: 5
Views: 1,894
Actually, doesn't the focus screen only affect exposure? I believe the auto-focusing mechanism works by redirecting light using an auxiliary mirror, and bypasses the focus screen.

Pentax Auto Focus Systems
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