|
Forum: Pentax DSLR Discussion
09-04-2009, 09:56 AM
|
| |
But it's not like the K100D is going to look any better when doing larger prints or extreme crops. *All* cameras will have worse noise at larger print sizes than small ones (ditto for crops). It's not fair to say the K10D is worse than the K100D just because it looks worse at a large print size than the K100D looks at a smaller one. If you want to print big, fine - but then, do that for *both* cameras and then compare. and you'll find they *both* look worse than the K100D did at the smaller size.
The point being, increasing pixel count isn't what makes noise worse - going to a larger print size is. While the higher resolution camera might not give you *better* noise performance at a given print size, it isn't making it worse, either. It's basically a non-factor.
Now, of course you are right to ask yourself if you're just "wasting" those extra pixels if they provide no advantage. Well, they *do* provide an advantage. First, in low ISO shots, no question you'll get more resolution from the camera with more pixels. Second in high ISO, what that extra pixels really give you is the ability to do more aggressive NR and still retain detail. That is, the K10D and K100D might be similar when comparing at the same size but not doing any additional NR. But given tha the K10D starts off with more pxiels, and thus more resolution, you can perform some relatively heavy NR if you want on that original file before resizing and still retain as much detail as the K100D. So that by the time you downsize it, it actually has much detail but *less* noise thn the K100D.
At least, all of this would be true if not for the specific flaw in the K10D design I mentioned (which i just learned about yesterday; until then I had no idea why the K10D always came out anomalously worse in noise comparisons). That is, the K10D is sort of unique case, because it really does have some disadvantages in the noise department due to its extremely unusual signal amplification design - not its pixel count. The K200D uses the same sensor as the K10D but the same type of signal amplification design as the K100D, and thus makes a better point of comparison. And indeed, I've found through countless direct comparisons that what I say holds true.
|
|
Forum: Pentax DSLR Discussion
09-04-2009, 08:36 AM
|
| |
Perhaps - especially regarding the K10D, which is the weakest of the Pentax cameras in high ISO performance. Mostly, it really is just a question of how picky you are about the results. But also, a question of the scene and your exposure - an ISO 1600 picture taken of one scene with one exposure might look much better or much worse than an ISO 1600 picture taken with the same camera but of a different scene and/or at a different exposure.
Are you comparing at 100%? That's not a fair comparison - you're blowing the image (and its noise) up bigger on the K10D. compare both at the same size - and make sure it's the same subject, same exposure - and see if the difference is really *that* great. No question the K10D is not as good as other cameras at high ISO, but aside cases where the "banding" that the K10D is prone too, it shouldn't be a whole stop of difference when performing a fair comparison.
BTW, aside form the fact that having more pixels (and hence higher pixel densities) means you are tempted to blwo the image up bigger, that doens't in itself cause more noise. That's kind of a myth, and see the thread on noise FF versus APS-C for more on this. According to someone (GordonBGood) who has extensively analyzed the RAW data from different Pentax cameras, as well as the design specs of the cameras themselves, what does the K10D in was the decision not to use an analog amplifier to implement higher ISO but to try to take advantage of the 22 bit ADC and do it all digitally. According to Gordon, this would have worked in theory, but the way they actually went about it was flawed.
Actually, it's pretty consistently lauded for this, so I wouldn't call it underrated. but I do think if you perform a more carefully controlled experiment, you might find the gap between it and the K10d not quite as great as you think, and in any case, that's unique to the K10D. The other higher-resolution cameras use a traditional analog amplifier and when comparing image at the same size, differences in noise are practically indiscernible. Or, perhpas more accurately stated, you'd have difficulty reaching any sort of consensus in a blind test which was actually better.
|
|
Forum: Pentax DSLR Discussion
02-22-2009, 06:22 PM
|
| |
I suppose I should should post some K200D ISO 1600 samples here, then :-). And since it seems relevant in this case, here is one taken with a slower lens: the DA50-200 at 200mm, f/5.6, 1/30".
It's rare to have enough light for a decent exposure at 1/30" if f/5.6 is the best you can do, and of course, 1/30" is borderline, especially at 200mm. Having an f/2.8 lens helps *a lot*. Here's the M100/2.8 at f/2.8, which allowed for 1/90" in this case:
 |
|
Forum: Pentax DSLR Discussion
02-04-2009, 02:39 PM
|
| |
Seems to me it does either or both, depending on where you set your exposure. Youa re right that if the was exposure to a place where the highlights were going to clip, this will prevent that - thus giving you more highlight details. But if your exposure is set to a place where the highlights *don't* clip, then the result should be more shadow detail.
There's another aspect to the meaning of "dynamic range" that makes the phrase "expanded dynamic range" even more ludicrous in one sense, but also more logical in another. The maximum dynamic range of every single digital camera, every single film, every single painting every painted is exactly the same: it goes from black to white. That is, the physical picture itself goes from black to white. No digital camera can produce a black blacker than the darkest ink used in producing the print, nor a white brighter than paper the image is printed on.
And make no mistake, this is *not* a particularly large dynamic range. It is far smaller than the dynamic range of most real world scenes. Take the blackest object you can find and the whitest object you can find. Put them both in the same (medium intensity) light. Now look around the room and find some shadow areas. Any reasonably dark object - not just black objects - in a shadow is going to be *darker* than that blackest-of-black object in the light. Converse, put the objects in a shadow and look around the better lit areas of the room. Now any reasonably light-colored object - not just white objects - is going to be *brighter* than the whiter-than-white object in the shadow.
What this says is that no matter what light you look at your print in, there will be real world objects that are both darker than the darkest black in your print and brighter than the whitest white. And no camera in the world can change that fact. The dynamic range of the print is from black to white, period. Does matter what the scene being represented was or what camera was used to record the image. The print goes from the black of the the ink to the white of the paper, and that's not a very large range.
In order to be "telling it like it is", a camera would have to look at your blackest and white objects in the same light and make them come out pure black and white on the print. That way, a snapshot of your black and white objects would appear just like the objects themselves when viewed in the same light. And a snapshot of that snapshot would be the same. But as far as I know, *no* camera does that. They *all* compress the dynamic range of the scene so that if the white object comes out white, the black object comes out grey, leaving room for objects in the shadow to come out darker. And if you expose to make the black object truly black, the white object will come out grey, leaving room for objects that are in more direct light to come out brighter. Meaning any snapshot of the black and white objects next to either will be compressed relative to that actual objects. And a picture *of* that snapshot will compress the range even more, and so on.
So what changes from one camera to another is how the real world maps to that range of black to white. If we say one camera has higher dynamic range than another, what we *really* mean is that it is able to take a wider range of values from dark to light and squeeze them into that same print range of black to white. Which is to say, it compresses the dynamic range of the real world to make it fit the fixed black-to-white range of a print. I don't care how many bits you have to represent different *gradients* between black and white in that print - you're not going to get blacker than black or whiter than white in a print.
So it's *already* a misnomer to talk in terms of one camera having higher dynamic range than another. They are *all* identical in the dynamic range they *produce*:. black to white, period. What we really mean is that one camera can take a wider dynamic range in the real world and squeeze it into the black-white range on the print. And the D-range feature does this, too.
So if you accept the ridiculousness of claiming that one camera has higher DR than another but understand nonetheless what is really meant by that, the idea of saying that the D-range feature also increases dynamic range is not more ridiculous.
It's only if you choose to interpret "dynamic range" in terms of the number of discrete values that can be *produced* between white and black that bit depth comes into it - and then, that becomes the one and only determining factor.
|
|
Forum: Pentax DSLR Discussion
02-03-2009, 01:03 PM
|
| |
It's almost pointless to talk about high ISO performance if you're just using the kit lens. The noise content of the image is not affected by the lens, of course, but if you're talking about shooting candids in low light, the kit lens just isn't going to give you fast enough shutter speeds at ISO 1600. Doesn't matter how noisy the picture is or isn't if it's blurry. You may get lucky every once in a while, but chances are on average you aren't going to be pleased.
As for cost, don't assume you need expensive DA* zooms to get enough speed. There are lots of great f/2.8 choices for under $300. If you think you can't live without AF, your main options are the FA50/1.4, DA40/2.8, and FA35/2, all of which are in the $200-$300 range (the 50 often a bit below $200, even). But be aware that AF isn't so hot in low light; MF is often just as useful. Once you accept this, you get all sorts of option for under $100 and even under $50. You could get *both* a 28/2.8 and 50/1.7 for under $100 combined.
|
|
Forum: Pentax DSLR Discussion
02-03-2009, 09:09 AM
|
| |
The K200D has a custom option to control whether ISO changes by changed only in full stops (100/200/400/800/1600) or whether it can change in half stops or third stops (according to which way you have your camera set up for the other exposure settings). I have mine set for half stops, so I get 140, 280, 560, and 1100.
Right - I underexposed by a full stop, then pushed it 0.75EV in PP and then applied a curve to bring out the light areas more (basically to a full stop) while pulling back the shadows. I applied very little actual NR. That's kind of my standard approach, and I can do that in about five seconds flat and apply it to a whole evening's shots when necessary (and then go back and adjust exposure further for specific shots that need either more or less).
I have a higher tolerance for noise and a lower tolerance for loss of detail than some. That's why I apply very little NR. But what I like about the k200D is that 10MP is enough resolution to allow me to apply more heavy-handed NR (eg, using Neat Image) if I want, and hardly lose any detail at all that would be visible viewed full screen or in a 4x6 print.
|
|
Forum: Pentax DSLR Discussion
01-27-2009, 04:32 PM
|
| |
Right, and I think that's true of ISO settings that are "real" on the camera - that is, if they are implemented by actually amplifying the signal from the sensor before analog-to-digital conversion. For ISO settings that are implemented by first doing to the a-d conversion and then simply doubling the values, there would be no difference whatsoever, assuming your software *also* performed it's push by simply doubling the values, rather than using some other algorithm.
GordonBGood as well as others looked at the actual numeric contents of the RAW files, and this left no doubt: ISO 3200 on the 6MP cameras contained only even numbers. Clearly, it was simply doubling the values after a-d conversion.
But ISO 800 is "real" - done by amplification of the signal - and as such, could presumably do better than pushing ISO 400.
Now, note that if you run the experiment in JPEG, then ISO 3200 *should* win over the ISO 1600 push, because the camera can perform the push on the original RAW data before it converts to JPEG, and hence has a lot more data to work with. It's hard to imagine how that could come out to be a disadvantage.
But for RAW, there *should* be no difference, unless your PP software chooses to do something other than simply double the values when you push exposure 1 stop. Depending on how clever the software is, what it does might turn out to be better than the simple doubling method used by the camera, or not. But in general, I certainly wouldn't expect it to do worse on average. Either it would be the same if it does just double the values, or slightly better if it knows of a better way (maybe something involving fractals, who knows).
The new K-m/K2000, BTW, apparently does have a "real" ISO 3200.
Anyhow, I say this not to invalidate your test your results, but to point out that whatever effect you are seeing might indeed still be, in effect, measurement error.
|
|
Forum: Lens Clubs
09-02-2009, 10:34 PM
|
| |
This hawk just buzzed me while I was out painting this morning:
 |
|
Forum: Lens Clubs
08-31-2009, 11:10 AM
|
| |
Here's a few from my Vivitar 500/8. Definitely *not* considered one of the better mirror lenses out there, but every once in a while it can surprise you.
 |
|
Forum: Pentax DSLR Discussion
01-20-2009, 11:09 PM
|
| |
Because these people are talking about noise at higher ISO (eg, 1600), and not necessarily noise in just the shadows. K20D may be weak in shadows at ISO 400 compared to other cameras, but it does pretty well in the lights and midtones at ISO 1600.
|
|
Forum: Pentax DSLR Discussion
12-03-2008, 09:52 AM
|
| |
There will alwys be variables, so mostly it's about controlling *which* variables you are allowing to vary.
For instance, one useful test would be to test in-camera JPEG from both. That's relevant in at least some way. So do that, although be sure to try a couple of different mdoes (Bright/Natural, high ISO NR off/weak/strong).
Another would be to test RAW, and you might *think* that's eliminating the variable of different in-camera processing. but in reality, it's simply replacing that variable with a different one: differences in how your RAW converter deals with one cameras versus another. Most RAW converters are tweaked to process each camera a little differently. And one converts might happen to favor one camera, while another converter might favor another.
Obviously, you'll want to test the defaults of whatever converters you have - you might find you get different imrpessions of the comaprison depending on which converter you use. At first, you'd want the default K10D conversion from a given processor against the default K20D conversion from the same processor. But if you are not tied to one particular converter, it would also make sense to compare the *best* converter for K10D against the *best* for the K20D (might be two different converters).
Also, it makes perfect sense to see if you can tweak the results from your favorite converter to imporve on the defaults. Who cares if the *default* settings are noisier in one camera than another, if a simple drag of a slider will turn that equation around? What I found comparing my K200D to my DS is that the defaults sometimes at first showed a slight edge to the DS, but a small amount of NR helped the K200D a lot without erasing detail much, while the same amount of NR on the DS would not help as much and would definitely start eating detail. That kind of stuff is worth knowing, too.
|
|
Forum: Troubleshooting and Beginner Help
10-27-2012, 06:41 PM
|
| |
No camera can do everything perfectly, but as e images show very clearly, the problem is not a camera limitatin but the simple fact that you can't stop motion on low light with slow shutter speeds. No camera can. There is no getting around the need for more light and/or hgher ISO to get the shutter speed. The K200D, like any camera, will do better with more light. Sports photography in low light, especially with slow lenses is difficult, and that remain true regardless of what camera you use.
For the OP: you specifically ,entioned getting better results from your P&S, bt I think you will find on cloer examination that any shot that looked better pon your P&S was taken in better light and thus was able to get faster shutter speeds. Or, you used flash. Again, there is absolutely no way any P&S camera is going to do better in the same light. More modern DSLR's will do *slightly* better that the K200D in that you'll be able to get a stop or so less noise for the same shutter speed, but you'll still have to make sure you ahve fast enogh shutter speeds, and you're not even slightly close to having fast enough shutter speeds as it is.
Bottom line: you need more light, not a new camera. A faster lens will help somewhat, but again, you're *way* off of having fast enough shutter speeds, and a faster lens won't make up the difference.
|
|
Forum: Pentax SLR Lens Discussion
07-23-2012, 07:01 PM
|
| |
Not just style of shooting, but subject matter. AF is just not that reliable on many subjects.
|
|
Forum: Lens Clubs
03-08-2010, 12:48 PM
|
| |
It's been a long winter, but the weather's been cooperating lately, so I took my Vivitar (Samyang) 500/8 out for a walk the other day, along with my DA15 (!). I hadn't used the Vivitar since last fall, and looking at the images I got, I keep having mixed feelings on it. It is *not* a great lens; pixel peeping is not kind to it. But it does (barely) beat cropping my 50-200 or 70-300, and for web resolution, it really is just fine.
Sometimes I think the more interesting use of a mirror lens isn't just shoot wildlife from a distance, but to provide a different perspective on a scene than one could have shot from physically close - and to render a visual effect that just wouldn't have happened otherwise. Somehow, looking across the river at this fallen tree, I just knew the mirror lens was the right tool for the job:
 |
|
Forum: Pentax DSLR Discussion
01-29-2010, 04:50 PM
|
| |
That's where I would disagree.
[/quote]
I guess it depends on which people you think are failing to pick up on this "crucial point". I thought this comment was directed at me. If you really mean, there is a point being missed by people who don't "get" equivalence at all, or by people who believe that equivalence somehow proves that there is in fact *no* benefit to FF (as is erroneously claimed in the title of this thread), or perhaps by someone else on this thread who otherwise is confused, then I'd certainly agree with you that a point has been missed.
To put it as clearly as I can: there is *no doubt whatsoever* that a shot at 135mm and f/2.8 on APS-C is "equivalent" to one at 200mm and f/4 on FF - meaning same DOF and noise for the same shutter speed. Nothing crucial is being "missed" by this statement. But leaping from this to saying there is no benefit to FF is indeed missing something.
I missed all that drama, sorry to say. Well, they crucified Jesus and shot JFK and MLK; sounds like James got off easy :-)
Anyhow, I'm uncomfortable with the idea of my closing a thread in which I have been an active participant - particularly after putting in what would otherwise become the last word. If another moderator wants to do so, that's fine. Or I can do it if we manage to go another few days without any further activity at some point. But of course, that still leaves the door open for someone to start a new thread on the same topic; it's not like closing the thread will end controversy, unfortunately.
|
|
Forum: Pentax DSLR Discussion
01-29-2010, 09:15 AM
|
| |
Equivalence isn't a "test", and as such cannot possibly be "unfair" to any sensor. It's simply a physical law: a method for ascertaining what focal length and aperture you need on one camera in order to match shots between cameras in terms of FOV, DOF, and noise for a given shutter speed. As such, it is no more or less "fair" than the idea of the crop factor itself (which is just a subset of the idea of equivalence). That is, do we say it is "unfair" to a FF camera to observe that you need a 200mm lens to capture the same FOV as a 135mm lens o APS-C? No, it's just a simple fact - neither fair nor unfair. Similarly, saying you need to shoot that 135mm lens at f/2.8 on APS-C to capture the same amount of light you would have capture at f/4 with the 200mm lens on FF is neither fair nor unfair - it simply *is*.
There is nothing "missing", and there is no "curcial point" that anyone is failing "to pick up on". The whole *point* of equivalence is to determine what focal length nd aperture are necessary to make the total amount of light constant. Of course it is "rigged" - that's the purpose. We 8want* the shots to come out the same, so we "rig" the focal length and aperture to make it come out that way. That way, we know what focal length and aperture are needed on one system to compete with the capabilities of the other.
Arguing against the idea of equivalence is liking arguing against the idea of gravity. It's a simple statement about physical reality; it is a not a judgement call that is a matter of opinion.
|
|
Forum: Pentax DSLR Discussion
01-23-2010, 12:28 PM
|
| |
Glad you posted your experience. Like I said, old myths die hard, but perhaps your post will help convince those who have heard and believed the myth but have no way of testing for themselves.
Actually, what would really be interesting is if you could sift through all the discussion on equivalence for the info on DOF, and see if you can reproduce the effect described: shooting the 18mm on APS-C should produce not just the same FOV and perspective as the 28 on FF, but also the same DOF *if* you shoot at one stop larger aperture on APS-C (eg, 18mm at f/4 on APS-C, 28mm at f/5.6 on FF). You'd have to set up a shot where it was reasonably easy to check this. Of course, the 28mm shot at f/5.6 would also require you to be one stop higher in ISO in order to get the same shutter speed.
|
|
Forum: Pentax DSLR Discussion
01-21-2010, 02:57 PM
|
| |
False. If you stand in the same spot and shoot 33mm on APS-C and 50mm on FF, you get *exactly* the same perspective. The notion that perspective has anything whatsoever to do with focal length is a myth that apparently will take a long time to die, but it is a myth nonetheless. Perspective is a function of position and position only. Changing FOV might cause you to want to change position, which is how the myth started ("oooh, this wide angle lens made me come in closer to my subject, and now it's distorted - must be the lens that it did it!" - no, it was the fact that you changed position to accomodate the change in FOV). But as long as you maintain the same position, you have the same perspective. So as long as you achieve the same FOV with two different lens/camera combos, they will have *exactly* the same perspective. Physics does not allow otherwise, I'm afraid, unless you install a black hole somewhere between you and your subject to bend the light. But here on earth, light travels in straight lines between your subject and your lens.
BTW, I could close this thread as Falk suggests, but might as well let this play out - I'd hate to be accused of closing it just to have the last word. And even then, I'm not sure closing it is warranted.
Oh, and Jewelltrail: "These go to eleven"!
|
|
Forum: Pentax DSLR Discussion
10-09-2009, 11:45 AM
|
| |
Agreed. I don't doubt that you are seeing what what you seeing. I'm just saying whatever it is is specific to the cameras, lenses, and meter you happened to use for the test; it isn't an APS-C versus FF issue. Some camera expose brighter than others given the same settings - and in general, digital cameras might expose a bit more conservatively than film cameras to protect highlights (yes, even for the same settings). But it is just not the case that sensor size plays any role in this.
|
|
Forum: Pentax DSLR Discussion
09-25-2009, 09:34 AM
|
| |
That's sensible, but you have to realize - not everyone cares about emulating the shallow DOF and wide angle capability of FF more than they care about low noise. The discussion is about the noise differences, and hence is relevant for people who care about that. If you're not among them, then this discussion is not for you. That doesn't make it stupid, though - plenty of people *do* care about noise, more than they care about shallow DOF.
|
|
Forum: Pentax DSLR Discussion
09-24-2009, 08:18 AM
|
| |
Actually, this is a good starting point to illustrate the confusion here. What Falconeye is saying, and what most of this thread has been about, is the fact that while that lens collects the same total amount of light whether used on FF or APS-C, the APS-C csmera is not *using* all of that light. Meaning the camera is quite simply collecting less light. Not less light *per square inch*, but less light total, because there are fewer fewer square inches of sensor to do the collecting. The fact that there is less light in total collected for APS-C is why *for the same aperture, shutter speed, and ISO*, the APS-C camera will show more noise. And it's also why using an f/2.8 lens for APS-C will allow it to collect the same amount of light at a given shutter speed. It will be more light *per square inch*, so you'll need a lower ISO to avoid overexposure. And by lowering the ISO, you get noise similar to what you started with on FF. Furthermore - and this part *does* seem like magic to me - it also works out the DOF for f/2.8 on APS-C and f/4 is the same, if you also change focal length to achieve the same FOV.
Anyhow, all that is just restating what has been discussed in the thread previously. The error being made by 24x36 is in thinking that "collecting less light in total" for APS-C at the same aperture, and shutter speed means you'll get a darker exposure at the same ISO. As I said above, less light above, but not less light *per square inch of sensor*. And exposure is all about light per square inch.
|
|
Forum: Pentax DSLR Discussion
09-24-2009, 08:08 AM
|
| |
Very possibly, depending on what your expectations are for exposure. What I'm saying is that an FF digital camera would *also* appear underexposed. You're seeing a difference of opinion on metering between you and your meter here (or a difference of opinion on actual sensitivity between the camera and ISO0, not a difference between APS-C and FF.
If a given amount of light strikes a given spot on an APS-C sensor, replacing that sensor with a larger sensor is not magically going to make more light fall on the original spot. This is simple common sense.
 Quote: Marc, a teleconverter does not change the focal length of the lens; this is an inaccurate oversimplification. Without a good working definition of "focal length" in this context, I cannot discuss the finer points points of what the difference might be betwene chaging focal length and magnifying an image, but in any case, the point being, magnifying an image optically (what the TC does) is different than cropping.
Quote: it would not be possible for a teleconverter of a fixed size with fixed lens elements to alter the focal length of any lens you put it behind, as it would have to be a different size for each different lens to physically alter the focal length of each lens. I doubt that's true - if it were, internal zoom lenses would be impossible. Physical length of lens is not necessarily directly related to focal length in this way; that's the whole essence of what the word "telephoto" implies (a lens whose focal length is greater than its physical length). But again, given that none of this is actually relevant, and I'm not sure I can define what exactly it would mean to say a TC does or does not change FL, I'll just take a pass on this aspect of the discussion.
|
|
Forum: Pentax DSLR Discussion
09-23-2009, 06:01 PM
|
| |
This is 100% in opposition to what any book on photography will tell you, what any experienced photographer will tell you, as well as what what physics and logic predict. There might be slight variations in how close cameras come to their specified ISO, but it is just ordinary variation between cameras, not a 1-stop advantage to FF. If you shoot f/4 on one camera and f/5.6 on another at the same shutter speed and ISO, the f/4 picture will be one stop brighter than the f/5.6 picture, and it doesn't matter whether you use f/4 on APS-C and f/5.6 on FF or vice versa. The same is true if you're comparing FF against 4/3, or medium format against a P&S. A given f-stop, shutter speed, and ISO generates exactly the same exposure regardless of sensor size.
Quote: APS-C loses a stop of light gathering ability for the same reason that you lose a stop of light gathering ability when you use a 1.4X teleconverter (though by a slightly different path). Since the image circle is much bigger (yes, before you say it, even APS-C lenses often cover FF, and if they don't, still have an image circle much bigger than the APS-C sensor diagonal covers) than the sensor, the light collected is reduced. At the end of the day, there's no free lunch - the 1.5x "multiplier" gets multiplied not only by the focal length, but also the aperture. That's an interesting and almost plausible analogy, but it just isn't so. A TC does indeed multiply focal length as well as aperture. Cropping the sensor doesn't actually alter either focal length or aperture - all it alters is field of view. It is no different than simple taking the picture on a FF sensor and then cropping the result in Photoshop or with a pair of scissors on the print. Exposure doesn't change if you crop with Photoshop or scissors, and it doesn't change is you crop by using a smaller sensor.
|
|
Forum: Pentax DSLR Discussion
09-21-2009, 09:00 PM
|
| |
You might want to think that one through again. Not sure what you meant by "exposure" or "equivalent" in the above, but the sense in which an exposure of f/2.8 on APS-C is equivalent to an exposure of f/4 on FF is that it collects the same actual amount of light for the same shutter speed, and the fact that you are shooting f/2.8 instead of f/4 means you shoot at an ISO setting *less* for APS-C than FF in order to get tha same shutter speed. That's why it works out to be about the same level of noise, because indeed, if you had shot at the *same* ISO, the FF shot would have had *less* noise.
Quote: This is easy enough to test; take some "Sunny 16" images with your APS-C dSLR of a front-lit subject on a bright sunny day at the appropriate aperture/shutter/ISO combination (e.g., ISO 200, 1/250 @ f 16 or 1/500 @ f 11 or 1/1000 @ f 8; ISO 400, 1/500 @ f 16, 1/1000 @ f 11, 1/2000 @ f 8). Your pictures will be dark. Increase exposure by one stop, and they'll be exposed spot-on as they would be on slide film (or, assuming accurate ISO values, on a FF dSLR). This simply isn't true. I mean, any particular APS-C camera might happen to overstate it's sensitivity ratings, meaning it will shoot a bit darker than it should for a given ISO/aperture/shutter speed combo, but it's not an inherent feature of APS-C, but it's not an inherent feature of APS-C. And if it's overstating its sensitivity (so setting ISO 800 really gives you only ISO 700, say), then it's also giving you the slightly less *noise* of ISO 700. Meaning you really aren't paying any particular penalty here. Chances are, any given FF camera will be just as likely to somewhat overstate its sensitivity. You aren't really going to see a difference between APS-C and FF in terms of the exposure you get at a given ISO, aperture, and shutter speed.
So your argument here is based on a flawed assumption. A given ISO, aperture, and shutter speed really 8does* produce the same exposure on both APS-C and FF. With that in mind, I'd suggest reading through the entire thread. You'll find quite a lot of useful information was hashed out there. Not "proving" conclusively that one format is "better" or "worse" than the other, but providing new and more accurate perspectives on just what the differences really entail. Fascinating stuff, really.
|
|
Forum: Pentax DSLR Discussion
09-10-2009, 10:01 AM
|
| |
I've always assumed that a shorter registration distance is "good" for wide angle. But the M9 announcement and dpreview preview mentioned the flip side disadvantage that hadn't occured to me: a "simple" (not sure of the technical term, but not retrofocus or reverse/inverted telephoto or whatever one calls a typical DSLR wide angle) wide angle lens will have the light striking the sensor at pretty steep angles as you move away from the center, which complicates the design of the sensor. Wondering how that will play out in practice.
|
