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08-15-2008, 08:11 AM   #76
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QuoteOriginally posted by falconeye Quote
People are often confused and compare lenses between systems at the same f-stop rating. This is physically incorrect as you have to compare at the same physical aperture in mm (same physical aperture in mm = same noise and depth of field).
Its true. Well, you read my mind. :-)

QuoteQuote:
And anyway, RH said something different. Namely, that there is no advantage to make a tele lenses's image circle artificially small. This statement is physically correct for any focal length >> image circle diameter.
There is no advantage, but a big disadvantage, smaller image circle means less resolution assuming that noise level is kept at the same level!

We do use higher ISO more often with tele to super tele lenses. So?

08-15-2008, 09:26 AM   #77
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QuoteOriginally posted by RiceHigh Quote
smaller image circle means less resolution assuming that noise level is kept at the same level!
This time, I have to disagree with you, RH. You may not have fully thought thru your argument. It is neither advantageous nor disadvantageous.

To explain: A larger image circle, when combined with a larger sensor, gives you a larger FoV, i.e. a different image. With a larger sensor, you gain light, correct. But the light you gain is from outside your original FoV. So, there is no decrease in noise with the larger sensor. If you increase the focal length to compensate for the larger sensor, the exact same amount of light from the same FoV will be projected onto the larger sensor when compared with the smaller sensor/focal situation. As long as you keep constant the physical aperture in mm, i.e., use a "slower" f-stop lens with the larger sensor.

You are right if you keep the f-stop number constant. But then Photomy is right with his argument, too.

In short: A larger sensor can make better images, correct. A larger sensor doesn't need heavier, more expensive lenses, correct. But if it does make better images, then it will be from using heavier, more expensive lenses.

Or even shorter: A larger sensor gives you more options of choice.

Any argument beyond this is physically invalid.
08-18-2008, 01:07 AM   #78
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QuoteOriginally posted by falconeye Quote
Even if we don't always agree to RH, he is right here.
People are often confused and compare lenses between systems at the same f-stop rating. This is physically incorrect as you have to compare at the same physical aperture in mm (same physical aperture in mm = same noise and depth of field)..
I would think a more important comparison between systems is not the physical size of the aperture but what lens will get a particular shot. f4.0 is f.40 for the purposes of the light required regardless of the system, large format, etc.

I meter my shot using ISO 800 (my limit for image quality) and it says 1/30 with f4.0 with my K20d. Do not want to go slower than 1/30. How am I going to get the same exposure with a lens that only goes to f5.6?
08-18-2008, 03:28 AM   #79
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QuoteOriginally posted by Photomy Quote
f4.0 is f.40 for the purposes of the light required regardless of the system, large format, etc.

I meter my shot using ISO 800 (my limit for image quality) and it says 1/30 with f4.0 with my K20d. Do not want to go slower than 1/30. How am I going to get the same exposure with a lens that only goes to f5.6?
Many people run into this trap. I don't want to argue here (wrong thread), so I make it short: 1/30 with f5.6 and ISO 1600.

When you double the sensor surface, you capture twice as much light and you have to double the ISO setting as well to keep constant the point of reference for image quality. The result is as I said: "same physical aperture in mm = same noise and depth of field".

So, when you compare prints from differently sized sensors, the difference you see is, in first order, the difference in physical sizes of apertures used.

08-18-2008, 06:22 AM   #80
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QuoteOriginally posted by Zebooka Quote
The german site provides PDF document with "winter 2008/2009" dates for 60-250/4 and 55/1.4.
(See page 13)
Well, that only makes the 60-250 a year late compared to the original release projection.
Excellent job of "time to market".
08-18-2008, 06:55 AM   #81
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QuoteOriginally posted by Wheatfield Quote
Well, that only makes the 60-250 a year late compared to the original release projection.
Excellent job of "time to market".
A YEAR? Try Over 2 years, maybe 3 or 4...........
.....................
This is from Tekade again regarding the 60-250 :

that lens is posponed to 2007 because the AF-System has to be changed for the new bodies (faster AF)
btw: Details and pictures of some of the news are here:

PENTAX NEWS release 2006 : PENTAX to Exhibit Upcoming Digital SLR Camera Products at PMA 2006 in the U.S.A.

Feb. 25 2006
60-250 postponed: Pentax SLR Talk Forum: Digital Photography Review
http://forums.dpreview.com/forums/read.asp?forum=1036&message=20132597&q=60250&qf=m
http://forums.dpreview.com/forums/read.asp?forum=1036&message=17030163&q=60250&qf=m
now just think about these poor people. Trying to decide if they should buy the 50-200 or WAIT for the 60-250...
in Jan 7, 2006................
http://forums.dpreview.com/forums/read.asp?forum=1036&message=16600264

Last edited by jeffkrol; 08-18-2008 at 07:03 AM.
08-18-2008, 07:56 AM   #82
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Umm.. There's a multiple factor issue..

Well, I think f-number represent the light intensity projected to the sensor *per area unit*. So, we get the following with the same FoV and DoF as well (i.e., in your term: same aperture diameter):

400mm on 135 FF, f/4;

266mm on 1.5X APS-C, f/2.66;

200mm on 4/3 system, f/2

Thus, to keep the *same* shutter speed and assuming the pixel count within the image circle is the same, the ISO need to be varied to adapt, that say:

FF: ISO 400; APS-C: less than ISO 200; 4/3: ISO 100,

However, the noise level depend on two things: pixel pitch size / pixel density and the ISO speed number. The lower the ISO number, the lower noise is. And, the higher the pixel density, the higher the noise will be.

As the pixel density seems to be a prevailing factor more than the ISO speed number from what I have seen from lab test results so far in general, it is therefore the limiting factor here should be the sensor size here, if we have to keep the pixel count here. The higher background noise level of a smaller sensor by itself should be the limiting factor here.

Reversely, if we keep the noise level (so that a larger pixel pitch size is made), the resolution will be scarified, i.e., the pixel count have to be decreased.


QuoteOriginally posted by falconeye Quote
This time, I have to disagree with you, RH. You may not have fully thought thru your argument. It is neither advantageous nor disadvantageous.

To explain: A larger image circle, when combined with a larger sensor, gives you a larger FoV, i.e. a different image. With a larger sensor, you gain light, correct. But the light you gain is from outside your original FoV. So, there is no decrease in noise with the larger sensor. If you increase the focal length to compensate for the larger sensor, the exact same amount of light from the same FoV will be projected onto the larger sensor when compared with the smaller sensor/focal situation. As long as you keep constant the physical aperture in mm, i.e., use a "slower" f-stop lens with the larger sensor.

You are right if you keep the f-stop number constant. But then Photomy is right with his argument, too.

In short: A larger sensor can make better images, correct. A larger sensor doesn't need heavier, more expensive lenses, correct. But if it does make better images, then it will be from using heavier, more expensive lenses.

Or even shorter: A larger sensor gives you more options of choice.

Any argument beyond this is physically invalid.
08-18-2008, 08:33 AM   #83
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QuoteOriginally posted by RiceHigh Quote
[...]The higher background noise level of a smaller sensor by itself should be the limiting factor here.
RH, we agree on first order effects (and normally, only those are discussed).

The difference in read-out noise, dark current etc. are second order effects dominated by technological progress and also the photon noise at all but the darkest areas of an image.

I fear that a thread about the DA*60-250 isn't a good place to continue a discussion about second order effects of sensor size variations.

08-18-2008, 01:37 PM   #84
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Why do all of you want a FF dSLR? Are all of you pro-photographers?

I rather see a digital medium format from Pentax long before a Full frame format dSLR.
A low cost 645D for the "average Joe Pentaxian" with 25-35Mpix resolution. And include many of the same quality that the K10D/K20D have. They can use the same charger and batterys, let it have weather sealing and shake reduction and more.

It's better to compete against Hasselblad and Mamiya with an affordable 645D than compete against CaNikon with a FF that's in the same price range as 5D and D700.
08-19-2008, 10:27 PM   #85
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Personally I'm looking forward to seeing how the new Pentax 55mm compares to new Sigma 50 F1.4 which seems to be getting pretty good reviews...
08-20-2008, 07:10 AM   #86
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QuoteOriginally posted by falconeye Quote

I fear that a thread about the DA*60-250 isn't a good place to continue a discussion about second order effects of sensor size variations.
Especially since it's really supposed to be a thread about the DA★ 30mm and the DA★ 55mm.
08-23-2008, 05:45 PM   #87
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08-23-2008, 06:48 PM   #88
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QuoteOriginally posted by Richard Quote
..........
happens everytime the FFword is used
08-24-2008, 01:04 PM   #89
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FF has drawbacks other than price

It is generally easier to make a diffraction limited optic (or so I have been told) for the smaller sensors. I read a long and interesting piece on this I think from luminous landscape. I agreed with most of the analysis. (Do Sensors “Outresolve” Lenses?) Yes FF does have a higher resolution limit but making a diffraction limited lens that covers FF is harder than one that covers APS-C.

Now I used to shoot a Canon 300D. I have some pretty good lenses. Everything looked great at almost any aperture. Now I have a 400D (and a K10D). And the truth is not everything looks great. You hit the diffraction limit pretty easily.

The item that FF brings to the table is not more headroom for low noise high ISO shots, but rather greater ease to produce DOF driven shots.

The truth is I'd rather see improvements in color resolution (full color sensors rather than array sensors), or dynamic range. HD TVs are only 2 MP, they look very nice at the appropriate distance. People's obsession with looking at the pixel level is crazy. Dpreview points out that the best glass is needed for the newest FF Canon.

When I go out to shoot I find myself worrying well if I shoot at that setting I won't be in the sweat spot of my lens anymore, when I shouldn't be thinking about anything but the art of the situation. Being gear obsessed is a sickness.

The truth is cameras today are so capable that we hardly need anything more. I'd much rather have a camera that I love to shoot than a camera that takes slightly better quality pictures. Which I why I tried Pentax with the K10D.

If you want to obsess about image quality only then I think Pentax is not the best brand to be in. My problems with fully switching to Pentax are complex, but I'll leave that to another post. I think at 10-14 MP I have reached my, it is good enough level.
08-24-2008, 01:20 PM   #90
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Anyone know what the 30mm DA* widest f/# will be yet?
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