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10-27-2010, 03:47 PM   #1
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Open letter to the Major Camera Manufacturers by Lumionus Landscape

An Open Letter To The Major Camera Manufacturers

interesting read ... no pentax cameras were mentioned here, but can this be one of the reasons why pentax doesnt makes FAST glass anymore?

10-27-2010, 04:17 PM   #2
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Pentax was mentioned on the last part of the column together with other camera makers.
10-27-2010, 04:39 PM   #3
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This is a very interesting letter which merits further thought regarding the purchase of fast glass.

dankoBanana you have raised an excellent question re Pentax no longer making Fast Glass.

Perhaps Pentax is not guilty of the same sins as Canon and Nikon who have been caught by DXO Labs of fudging the ISO automatically on wide apertures and not identifying the adjustment in the EXIF Data.
10-27-2010, 05:41 PM   #4
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QuoteOriginally posted by dankoBanana Quote
but can this be one of the reasons why pentax doesnt makes FAST glass anymore?
so the DA*55mm f/1.4 isn't fast enough?

10-27-2010, 06:42 PM   #5
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What's the T-Stop of a sensor's microlenses?

Seriously, the amount of ISO gain appears to be negligible, and f-stop is primarily for DOF, not just a function of amount of light. These are known tradeoffs that it appears all manufacturers accept due to the continuous evolution of sensor and lens design.
10-27-2010, 07:20 PM   #6
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Does this light-loss thing only apply to lenses with very big apertures? I'm wondering what practical difference there will be between a 77mm f/1.8 and a 70mm f/2.4 lens in terms of t-stop loss at the sensor-level. Probably none significant, right?
10-27-2010, 08:57 PM   #7
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QuoteOriginally posted by jms698 Quote
Does this light-loss thing only apply to lenses with very big apertures? I'm wondering what practical difference there will be between a 77mm f/1.8 and a 70mm f/2.4 lens in terms of t-stop loss at the sensor-level. Probably none significant, right?
I don't think it will have much effect at all, the SMC coatings enhance light transmission significantly. However,I do recall people saying that the FA77 transmits more light at f/2.4 than the DA70mm f/2.4 does. besides, no one here knows whether pentax DSLR cameras are bumping the ISO values or not, but I personally think that it is unlikely that they are.

QuoteOriginally posted by Aristophanes Quote
What's the T-Stop of a sensor's microlenses?
It would make sense that the size of the microlenses are the same as the pixel elements on the sensor. But that isn't the problem here, what the problem is that the sensor wells are deep and angular rays are simply hitting the walls and not reaching the pixel.

Last edited by Digitalis; 10-27-2010 at 09:02 PM.
10-27-2010, 09:18 PM   #8
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QuoteOriginally posted by Digitalis Quote
so the DA*55mm f/1.4 isn't fast enough?
I'd say it is fast enough and moreover, it was designed for digital cameras so I would assume that the light rays are directed so that we get the full benefit of the f/1.4 on a digital camera.

It could be interesting to compare the DA* 55/1.4 with a K 55/1.4! I don't have either so I can't do it

10-27-2010, 09:19 PM   #9
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Interesting article. I wonder if this is a factor in why Pentax seems to favor slower glass in their recent releases (eg. the 35mm f2.4 instead of a direct revamp of the 35mm f2). Maybe the change is partly to help straighten out those rays.
10-27-2010, 10:57 PM   #10
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QuoteOriginally posted by Ole Quote
It could be interesting to compare the DA* 55/1.4 with a K 55/1.4! I don't have either so I can't do it
Oh, yes, that would be interesting to see.
10-27-2010, 11:30 PM   #11
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I sincerely wonder how much influence all this has on real life picture taking (also known as photography). My lens of choice is A 50/1.2 and I don't give a damn about the specifics of my K-7 sensor gain depending on the aperture I choose. I just take pictures. Do you?

To make things clear, the above paragraph is not devoid of sarcasm...
10-27-2010, 11:38 PM   #12
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10-28-2010, 12:32 AM   #13
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The article doesn't take into consideration the reason why people desire wide aperture lenses: they're often built better with more exacting specifications, and perhaps a more pleasing number of aperture blades.
10-28-2010, 01:17 AM   #14
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Excuse my ignorance, but doesn't this suggests a point in favour of smaller "pancake style" lenses that have a lower number of glass elements, hence letting more light through?
10-28-2010, 03:57 AM   #15
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QuoteOriginally posted by Christine Tham Quote
Excuse my ignorance, but doesn't this suggests a point in favour of smaller "pancake style" lenses that have a lower number of glass elements, hence letting more light through?
Well, some of the light loss is coming on the sensor, not in the glass, from what I read in the article. Also, the pancake style lenses are quite a bit slower than the f1.2 apertured lens cited in the article.

It probably does make a difference. It is like Sony's translucent mirror on the A55. They admit up front that it reduces light transmission to the sensor and so the sensor will need to increase gain to compensate. It would just be nice if the camera companies were honest about iso.

It is already well know that most of the camera companies (Pentax included), fudge a little bit on high iso. So, iso 6400 on a 7D ends up being measured by Dxo to be iso 4500. Not a huge difference, but a difference none the less that can make their camera look a little bit better at high iso.
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