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Forum: Pentax DSLR Discussion
04-16-2008, 12:00 PM
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Gimbal is completely right.
Pressing a button twice is ABSOLUTELY USELESS as a measure of reaction time. You can double-click a mouse in under 0.05s with a little practice.
Reaction time is a measure of your ability to react to an UNPREDICTABLE STIMULUS. With double-clicking, your brain basically sends two immediate, successive signals to tense your finger muscles. Whereas when you react to a stimulus, you first perceive some sensory input, which travels to your brain, which then sends a signal via your nervous system to your finger.
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Forum: Pentax SLR Lens Discussion
04-11-2008, 02:21 PM
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Hey, meerkats :)
I am pretty happy with my 70-300 Di LD too!! I took it to the DC zoo recently, and worked it pretty hard at ISO 1600 in dim light... still got some decent photos. GALLERY HERE
There is quite a bit of PF around in a couple shots, such as this one of the Panda's face:
I've tried some of the conventional "purple fringing" tricks like turning down the saturation for Magenta only, but it doesn't seem to do much. Does anyone have a good workflow for getting rid of the Tamron 70-300's PF/CA? I'm using the GIMP, for what it's worth, so a link to a Photoshop plugin won't help me ;)
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Forum: Pentax SLR Lens Discussion
04-11-2008, 10:34 AM
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A Canadian who doesn't live close enough to the border to go buy one is a fool. Or a Polar Bear ;-)
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Forum: Pentax SLR Lens Discussion
04-11-2008, 10:33 AM
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Correct. Tamron basically makes three families of lenses:
* LD = Full-frame
* Di LD = Full-frame but optimized coatings and optical formula for digital
* Di II LD = APS-C only
The 70-300 only comes in a Di LD version. It's $130 new from Buydig, I have it, and it's great.
The 75-300 only comes in an LD version. It is negligibly cheaper, maybe $10-20.
Save yourself the hassle, and get the 70-300 Di LD.
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Forum: Pentax SLR Lens Discussion
04-10-2008, 10:03 PM
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I have owned my K10D (my first DSLR!) for about 4.5 months... I love it, but am on a tight budget (grad school :p).
I have the kit lens, an A50/1.7, an A70-200/4 beercan MF zoom, a Tamron A70-300 Di LD AF, and recently acquired a Vivitar 500mm mirror lens, a Sigma 28-80 AF standard zoom, and an FA 28-200.
I use the kit lens all the time! I am very impressed with (minus its low-light performance). Sometimes I bust out the A50/1.7 for low-light stuff, but I usually don't have time to. I also love the Tamron 70-300 Di LD. I am planning to sell the Sigma 28-80 AF zoom, and the beercan, and I expect the 28-200 will come in very handy as a "walkaround" lens for outdoor tourism.
Really, the only thing I wish I had was a faster standard zoom. I've been lusting after the Sigma 17-70/2.8-4, the Tamron 17-50/2.8, or the Tamron 28-75/2.8. Can't really decide which one... do I really need that extra stop at the long end, or would I rather have the wide angle? :lol:
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Forum: Pentax SLR Lens Discussion
04-10-2008, 07:34 PM
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Hi Heather, I hope you're not offended by my unsolicited advice but...
Personally I would not pay $85 for that lens, but would go for the Tamron LD Di f/4-5.6 instead (or spring $200 for the Sigma APO, but I assume you're on a fairly tight budget like me :))
I have not seen that specific lens... but from what I can tell the non-APO Sigma long zooms are not so great. The Tamron lens (I paid $130) or the Sigma 70-300 APO DG will give you significant advantages:- more room at the short end
- a half-stop faster (significant when you need it!!)
- optical formula optimized for APS-C sensors (where higher /lens/ resolution is required because you're trying to cram an equally detailed image onto a smaller sensor)
- nice build quality, and a very generous 6 year warranty (for the Tamron at least)
So I think you'll get quite a bit more bang for your buck if you go for one of the newer consumer zooms, which are just an awfully good deal in my opinion. I don't want to get into a holy war over which of them is better, but I have been very pleased with the sharpness of the Tamron, and can live with the occasional chromatic aberration.
Anyway, that's just my 2¢!
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Forum: Pentax SLR Lens Discussion
04-10-2008, 10:25 AM
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Well, remember that it's a geometric progression... so the difference between f/1.2 and f/1.4 is as big as the difference between f/2.8 and f/3.4 or f/1.7 and f/2.0. :)
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Forum: Pentax SLR Lens Discussion
04-09-2008, 09:29 AM
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The only reason focal length affects the desired perspective is... because a longer focal length allows you to stand further away and still fill the frame :)
A portrait lens has a longer focal length so that you can stand further away from your subject and still capture them in detail. The slightly-flattened-face perspective is a function of the distance. Try it with a wide-angle lens from the same distance as you would take a portrait, and if you zoom in you'll see the exact same perspective.
But yeah, I think your basic point is right, although focal length is totally independent of perspective... in practice they are linked by the desire to photograph subjects of certain sizes from certain distances.
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Forum: Pentax SLR Lens Discussion
04-09-2008, 08:38 AM
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The perspective of almost any scene will be altered by the focal lenght, because of the optical qualities of the lens. This is a function of focal lenght. Wide angles tend to expand space and telephotos compress space. This is more noticable as the focal lenght moves away from normal focal lenght for the camera format. Of course the basic perspective of a scene is a product of the scene itself and the photographers point of view. [/QUOTE]
You're talking about barrel and pincushion distortion, right?
If you take a heavily-distorted image (e.g. from a fisheye lens) and correct it for rectilinear projection, you will see that it recovers the EXACT SAME PERSPECTIVE as any other rectilinear image taken from the same point.
So, I guess that a distorted lens gives the appearance of a different perspective, but it doesn't really change anything. If you take a picture an inch away from the left side of my face, my nose will get in the way of seeing the right side ... regardless of how you distort the image :lol:
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Forum: Pentax SLR Lens Discussion
04-06-2008, 05:10 PM
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Hey is that the Paris metro?
EDIT: of course it is, your "Location" says Paris, France. Duh. I was there in November and had a great time... still miss it :)
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Forum: Pentax SLR Lens Discussion
04-05-2008, 04:18 PM
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Boy, oh boy did I get a deal today:
- Pentax MZ-10 body in good working condition (except for the spring that holds up the flash)
- Pentax FA 28-200 f/3.8-5.6 zoom lens with bayonet hood
- Sigma 28-80 f/3.5-5.6 standard zoom lens
- Tokina circ. polarizing and UV filters for the FA 28-200 (72mm... these don't come cheap)
- Unopened Hoya 55mm circ. polarizing filter (with $55 price tag still intact :D)
- Lens caps and manuals for all
- Mid-size Lowepro Nova 2 SLR bag in great shape ($45 new :))
- Random "Imodium" tablet left in bag :p
All that for $60 from a moving sale :)
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Forum: Pentax SLR Lens Discussion
04-04-2008, 09:19 AM
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That's been my impression too... every sample of the Tamron has the same consistent level of PF and sharpness, while the Sigma seems to vary widely in its sharpness.
Also, I'm surprised to hear the Sigma's build quality described as better. The Tamron feels a lot sturdier to me and the caps and hood are better-quality. The Sigma that I tried had a bit of "slop" in its zoom and focus rings.
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Forum: Pentax News and Rumors
04-03-2008, 12:56 PM
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Ah, gotcha. Well, putting a watermark/copyright splotch is certainly more effective in preventing misuse, I think!
People who are likely to steal your images and actually use them for commercial purposes, where you'd have a financial interest in stopping them, are likely to know how to do this.
If it gives you peace of mind, keep it, but...
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Forum: Pentax News and Rumors
04-03-2008, 12:33 PM
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Dude, I hate to tell ya... but your images aren't "protected" in any way. It takes me 5 seconds to disable JavaScript (Tools | Options | Content in Firefox), and then I can copy the images same as always.
Using Flash would be even more annoying, and equally ineffective...
Technical measures to prevent copying/downloading/ripping DO NOT WORK. If a user can see the image, they can make a perfect copy of it. End of story.
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Forum: Pentax SLR Lens Discussion
04-03-2008, 11:10 AM
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Forum: Pentax SLR Lens Discussion
04-03-2008, 10:39 AM
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Okay, so... to you, "reach" simply means "the image projected onto the sensor"???
I gotcha! The thing is, these are almost purely definitional issues... if everyone uses the same definition of the terms, the consequences are straightforward :)
You say "the same view" because you're defining "field of view" as something like "the width and height of the scene in inches/meters/whatever." Whereas, as I said above, the STANDARD definition is in terms of the *angle* subtended by the scene, as in "12 degrees wide by 8 degrees high." If you define FoV in terms of lienar dimension, your conclusion is correct... but that is absolutely not the standard definition, so it will confuse everyone :)
Also, taking a flower at 1:1 will NOT give you the same picture regardless of focal length!! If you do it with a 300mm macro lens, you'll have to put the camera about 5 feet away. If you do it with a 50mm macro lens, you'll have to put it about 1 foot away. The perspective will be completely different... the flower will look "flattened" with the telephoto lens, whereas it will look more 3D with the 50mm lens.
See, now that I know you define "reach" simply as "the image projected by the lens" ... I agree :)
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Forum: Pentax SLR Lens Discussion
04-03-2008, 10:21 AM
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This is what I have. You can actually get it for $130 shipped at Buydig.com, which is very reputable.
It is well-built and sharp at the long end. AF is a little slow (though that might be improved with the K20D over the K10D). It suffers from noticeable purple fringing and chromatic aberration in backlit conditions. Here's an example of that, which I took:
I have taken a lot of bird shots with it, and it is great. This is from 11 days ago:
And here's another one from the same session, feel free to browse the rest. This one shows quite sharp detail of a robin eating a worm: IMGP4687
This might be a great "do-everything" lens... but unlikely to be as satisfactory for wildlife. Inevitably, these ultra-zooms lose image quality at the wide and long ends. And it's half a stop slower at the long end than the 70-300.
The Sigma APO and Tamron LD Di are the popular choices. The relative merit of these two is endlesssssssly debated... you'll find a zillion threads on it.
Personally, I appreciate the sharpness, build quality, and low price of the Tamron... and don't mind the PF/CA much. So that's what I would recommend.
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Forum: Pentax SLR Lens Discussion
04-03-2008, 09:32 AM
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But... what... does... that... MEAN???? "The subject projection of the film/sensor"? So reach means... the image formed by the lens??
Argghgh :D
So, you're defining FoV as the linear dimensional extent of the scene in object space??? That's not in line with the usual definition at all: Field of view or angle of view is normally defined as the angular extent of the scene's projection onto the sensor. It can vary independently from magnification.
With the standard definition, FoV is uniquely determined by focal length, f, and sensor dimension, d: FoV = 2 arctan (d/2f).
And magnification is uniquely determined by focal length, f, and camera-to-subject distance, do: m = f/(f-do)
What? The actual, optical focal length stays constant when you put the lens on another format size. It is just about the ONLY thing that stays constant. So if "reach" stays constant, then what is reach... is reach the same as focal length????
EDIT: Hey, this is amusing. I googled "definition of reach in photography" and the first thing I got was another thread, on another forum... which degenerated into an argument over what "reach" means, if anything: Crop Body Madness - Page 6 - Canon Digital Photography Forums :p :lol: |
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Forum: Pentax SLR Lens Discussion
04-03-2008, 12:01 AM
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I would put it as "a TC increases magnification and narrows FoV". Reach=magnification, as you put it... but others seem to think of reach as something else so I get confused :)
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Forum: Pentax SLR Lens Discussion
04-02-2008, 11:18 PM
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On the other hand, if the resolution of the *lens* is maxed out, there's no point in adding the TC... since you're just magnifying the aberrations and not getting additional detail from the scene. This is the reason it's often advised not to use TCs with zoom lenses, but only with primes.
And by "extends the reach", you mean "narrows the FOV". PuhLEEZ :D
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Forum: Pentax DSLR Discussion
04-02-2008, 01:37 PM
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Oh... so *that's* what the little battery grip compartment is for. :cool:
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Forum: Pentax DSLR Discussion
04-02-2008, 01:36 PM
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Hehehe... Pentax's new motto: "We make coatings fun."
Here's another virtually incomprehensible sentence from the continuous mode performance data: "The system expansion of the dynamic slightly reduced pace burst."
Indeed. It's really good, some sentences seem perfectly natural... if this keeps up, I'm going to have to lose my smug sense of bilingual superiority, since everyone can just get their computer to do it for them :o :lol:
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Forum: Pentax DSLR Discussion
04-02-2008, 01:06 PM
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:lol: :lol: :lol:
I like how the "Power & storage" section is variously labeled as "Food" or "Food storage."
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Forum: Pentax DSLR Discussion
04-02-2008, 12:52 PM
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Woah... I didn't even realize you could do online subscriptions. Thanks!
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Forum: Pentax DSLR Discussion
04-02-2008, 12:32 PM
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Yeah, but they don't put much of their material online... and it's impossible to find in the USA. Maybe in Quebec? :(
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