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Messages - epsiloneri

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286
Lenses / Re: L-fever...
« on: April 26, 2011, 05:58:50 AM »
If you already have the EF 70-200mm f/2.8L IS USM II, it is already close to the ultimate portrait lens. Have you considered using macro extension tubes for it? The 100/2.8L macro is great, but perhaps you would complement your lens collection better with a wide-angle lens. (depends on what you have and are interested in, of course)

287
EOS Bodies / Re: 26.4mp 5D Mark III Mid-year? [CR1]
« on: April 26, 2011, 05:35:58 AM »
Ahhhh...well, then...I hope you don't use a dSLR when you need reach, because it sounds like the Canon PowerShot SX30 IS is the perfect camera for that.
Why are you talking about PS when I'm talking about DSLR?

Perhaps I should let neuroanatomist reply that one to you, but since you don't seem to appreciates each others argument, maybe I can help:

1) You said there are only advantages to having higher pixel densities. That is obviously an exaggeration that you probably did not mean literally.

2) neuroanatomist gave the example of SX30 to show that a higher pixel density is not sufficient. He probably gave the example to make you think and realise why you are wrong in the "high pixel densities always rule" assumption. However, I don't think his example was very successful for that purpose because a) There are many other variables in addition to pixel density that are not kept constant (like sensor size, optics), so it's hard to from this one example to disentangle what the significance of the higher pixel density is. I tried to resolve it in a post above, but perhaps it was too technical to read well. b) He was not very clear with what the example was supposed to demonstrate. c) The tone in his reply was unnecessarily deprecatory, bound to fail an explanatory purpose and trigger the reaction you gave.

To be clear, here is an explicit list of some disadvantages with higher pixel densities (in approximate order of significance):

a) Readout noise increases with number of pixels
b) Slower readout time (limits your images per second rate)
c) More quickly gets limited by diffraction, so needs faster optics to be useful
d) Requires proportionally smaller tolerances for the camera house / optics to make use of the pixels
e) More sensitive to illumination direction (limb darkening)
f) Space/processing requirements increase
g) More expensive to manufacture

Note that I don't list noise as a disadvantage, since the quantum efficiency and collecting area does not change much with pixel density (only in the case where you are read-out noise limited will higher pixel densities produce a noisier image). Also, the dynamic range will not change significantly either, because the storage capacity of pixels is usually determined by their areas, so even if pixels are smaller and have smaller capacities, the number of photons they have to take care of is proportionally smaller.

The list of advantages with higher pixel density I can think of is much shorter, but very significant:

a) Potentially resolves finer detail in an image

I say potentially, because this statement is only true within certain limits. E.g., there is a limit how fine detail the optics will resolve. For small apertures, this limit may well be the diffraction limit (this is a physical limit); in general it is probably more common with imperfect optics. It also assumes that you have sufficient light and short enough exposure time for the pixels to be well exposed without introducing motion blur at the pixel scale.

There is always a balance between the advantages and disadvantages that sets the optimum pixel density. Depending on how much weight you give the different properties, this optimum balance will shift. For FF cameras with current optics, I think a practical upper limit on the number of pixels is around 50 Mpix, approximately the pixel density of 7D. Going beyond that does not make much sense to me, unless there is a revolution in lens manufacturing. I expect higher resolution images will be the domain of larger size sensors, medium or large format, as it is much easier to produce appropriate optics for them. I believe this will be even more true in the future, as sensors will be increasingly better and less expensive, while I don't expect manufacturing of optics to improve at the same pace.

I'll be happy to discuss any items above you may disagree with.

288
EOS Bodies / Re: What do you want from the 5D mk III
« on: April 21, 2011, 05:48:20 PM »
The flash will sync with all speeds (see page 17 in the Manual)

That's pretty cool. I didn't know you could change the flash duration with modern flashes. Thanks for the tip!

Some more background is available in this blog entry.

289
EOS Bodies / Re: 26.4mp 5D Mark III Mid-year? [CR1]
« on: April 21, 2011, 04:48:28 AM »
if you need 800mm - use 800mm L lens with a 5d/1d or whatever you can afford, but promoting a powershot with 150mm in this case... kind a silly, isn't it? :)

If the SX30 can do the job for 2% of the cost, why not? The problem is that it cannot, of course, because its optics is not diffraction limited at 150mm, and the light gathering power is abysmal. That said, if you increased the pixel density of 5D/1D then you would get higher resolution images ("longer reach"), so it does make sense to use a 7D in those cases. Which I think was Tuggen's point.

290
EOS Bodies / Re: 26.4mp 5D Mark III Mid-year? [CR1]
« on: April 21, 2011, 04:40:12 AM »
... it sounds like the Canon PowerShot SX30 IS is the perfect camera ...

With 1.3 µm pixels, a 150 mm lens would produce a pixel scale of 1.8 arcsec/pix, meaning a well-sampled image would have a resolution of 3.6 arcsec. This corresponds to an aperture of 28 mm, or an "f-ratio" of 150/28 = 5.4. The SX30 lens is 5.6 at 150mm, not too far.

Thus, if there was plenty of light, and the optics were diffraction limited (we wish, 35x zoom!), then indeed the SX30 could have been perfect.

The problem is of course that 28 mm is a very small aperture, collecting very little light. Scaling everything up by a factor of 4, we would have a 600mm lens (still ~5.6) with a ~110mm aperture and the same scale per 5.2 µm pixel (for a 14 Mpix sensor), but would now collect 4^2 = 16 times as much light, and be 4 times further from the diffraction limit.

We could also scale up everything with 4x except for the pixel pitch, resulting in a 224 Mpix sensor. Then the light gathering capability per pixel would be the same as for the SX30, but the pixel scale would be 0.5 arcsec/pix.

Conclusion: As long as you have sufficiently many photons and do not over-sample the resolution of the image, higher pixel densities result in higher resolution images.

291
Lenses / Re: Lens filter: step-down adapter ring, or not?
« on: April 20, 2011, 01:36:07 AM »
I have the same "problem" in that I have mostly 77mm lenses, and then this odd 72mm 135/2L. My solution, based on a principal successfully used by many politicians, is to simply ignore the problem and hope it never gets serious. So far I'm doing pretty OK, since I've never really felt the need to mount the CPL filter on the 135mm. Typically I use it for hand-held low-light and portraits. Should I feel the absolute urge to use the CPL with 135mm, I would probably just use my 70-200/2.8L, which takes 77mm filters. Not the same, but close.

My advice: make sure you really want/need a CPL for your 135mm/2.0L before going through the trouble of getting a step-up ring or dedicated filter. If you feel the need to use a protector, it makes no sense at all to share it with your other lenses using a step-up ring. You would probably increase the likelihood of damaging your lenses while exchanging protectors.

292
Canon General / Re: Don't Break Your Gear
« on: April 18, 2011, 09:28:44 AM »
That picture of the smashed EF 200/2.0L really gives me the creeps!

293
Lenses / Re: Canon EF 35 f/1.4L II [CR2]
« on: April 17, 2011, 03:27:23 AM »
I have a question for you guys: why isn't there fast (around 1.4) primes with IS ?
Because prime lenses at 85mm or less don't require IS.  The lenses are very short and can be easily handheld without the need for IS.
Because it isn't particularly needed. [...] If you really need it - use a tripod!

I don't buy this argument. Slower zooms below 85mm have IS, why not primes? A 1/35s exposure is as short on a prime as on a zoom. Aperture is not really relevant, is it? Why should you be able to handhold 1/35s a lens at 50mm for the EF-S 17-55/2.8 IS USM, but not the EF 50/1.4 USM?

No, I think the reason we see no IS on fast short primes is not that it wouldn't be useful. I think it's just plainly much more difficult to implement IS on fast optics. That may also be the reason why we have IS on the EF 24-105/4.0L IS, but  not on the EF 24-70/2.8L (yet). The faster, longer, and smaller image circle required (EF-S), the easier it must be to implement IS; also, the larger the benefits from IS.



294
Lenses / Re: UV filter for 70-200mm f/2.8 IS II?
« on: April 08, 2011, 04:49:32 PM »
Wow, pretty flares! Thanks for checking.

295
Lenses / Re: Canon Extender EF 2x III review - at the bronx zoo
« on: April 04, 2011, 01:56:34 AM »
I have a question. Since I have the 7D and soon the 70-200mm f/2.8L IS USM II, would buying a 2x Extender actually give me an effective focal length of 640mm?

Yes, you are correct. 7D with a 2x teleconverter and 200mm lens gives a field of view equivalent to a 640mm lens on a full frame camera (e.g. 5D). This combination would likely outresolve the lens, however, resulting in a somewhat softer image at the scale of pixels.

296
Lenses / Re: Focal length limits
« on: April 03, 2011, 03:50:26 PM »
Depends on the application, of course. Amateur astronomers regularly use 500mm-2000mm lenses (telescopes) at typically f/4-f/11. No AF, rarely IS, and never hand held - a rigid mount, sometimes motorised, is required.

There is an upper useful focal length limit, but it depends on the pixel pitch of the detector. The limit is set by the resolution deterioration from the atmosphere and depends greatly on local conditions. For astronomical applications at good sites (e.g. nothing extreme like Antarctica or remote locations in the Andes) you are usually limited to a resolution of ~ 1 arcsecond (1/3600 degree), which means that there is little point in having smaller pixels than 0.5 arcsec/pixel. For terrestrial daytime applications this limit is generally much higher, as the air close to the ground is denser and more affected by turbulence than if you look straight up.

For a 7D with 232 pix/mm, a resolution limit of 0.5 arcsec/pix corresponds to a focal length of 1780 mm, while for a 5D2 you have 156 pix/mm and thus can increase the focal length to 2640 mm before getting resolution-limited by the atmosphere. The opening aperture also needs to be larger than ~10 cm to not limit the image resolution by diffraction.

The record-braking 120 MP APS-C sensor Canon showed off a while ago has 455 pix/mm, which would result in a maximal useful focal length of 900 mm. It would put very severe constraints on tolerances and the quality of the optics, however. In principle one could go even further with even higher MP detectors, but tolerances and dynamic range per pixel would likely be limiting factors. With "perfect" detectors the resolution would be completely determined by the optics. Still, I don't think it would be practically possible to get 1 arcsec resolution on anything shorter than 200mm, because already that would require an f/2 lens (to not be diffraction limited).

Looking at distant objects on the ground limits useful focal lengths to much shorter than the above estimates.


297
EOS Bodies / Re: Odds and Ends
« on: March 07, 2011, 05:44:39 PM »
Note that the portion of the picture on the left has 16-35mm on the lens

Just to clarify... the article is about recommended lenses for portraits, and goes all the way from the wide EF 16-35mm f/2.8L II USM to EF 135mm f/2L USM. The magazine layout is two columns, and the part of the 16-35mm lens seen in the image to the left belongs to the other column describing that lens. A picture of the EF 24-70mm f/2.8L USM lens (sans "II") is shown below the text displayed in the image.

298
EOS Bodies / Re: Odds and Ends
« on: March 06, 2011, 12:56:56 PM »
The same English issue of the CPN magazine doesn't have the "II" typo.

299
Lenses / Re: What ones best?
« on: March 06, 2011, 02:58:49 AM »
Apart from focal length the 24mm's biggest advantage over the 17mm is the ability to accept filters e.g. polarizers for landscape

Isn't 24mm a bit wide for a polarizer? Just asking. ND filters can be useful for flowing water etc, other than that (and polarizer/protector) I don't know what filters are used for.

Regarding the 17mm/4.0L, it is very wide on FF. Also, the depth of focus is not very narrow, making the "tilt"-part difficult to fully exploit. The "shift" parts works as advertised, but you can do almost as well in postprocessing (at the price of some resolution), so I'm not terribly excited over that feature. Mostly good for indoors architecture, where space is limited.

In all, I think the TS-E 24mm/3.5L II is more interesting (less wide and faster -> more evident "tilt" effects), and wide enough for landscapes. The "II" ability to freely rotate the relative angle between tilt and shift directions is a nice feature over "I" (apart from the increase in resolution). For macro, I would recommend the TS-E 90/2.8 instead (+extension tube).

If you have an APS-C camera, however, 24mm might be too long for landscapes. Thus, it depends a bit on your camera choice in addition to your shooting preferences (like scaleusa said).

300
Lenses / Re: Your lenses wishlist for 2011 - RESULTS
« on: February 21, 2011, 02:14:42 AM »
However, I think it's worth bearing in mind that both these stats largely reflect the readership of this forum, particularly those who would respond to posts and have the knowledge and experience to come up with a wishlist. In fact, I wonder what percentage of DSLR owners regularly read up on forums?

Let's make a poll and check: How many of you DSLR owners are reading this forum?

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