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Old May 6, 2005, 2:16 AM   #11
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Like NHL says that's a false comparison. You need to compare lenses with the same "35mm equivalent" focal length to get a true comparison, then you'll begin to see the difference. I don't accept that there would be no gain in making telephoto small sensor lenses. The advantage ofan EF-S telephoto would be in the lens size and it's handling, and the advantage would be sigificant. Look at how small the telephoto zooms are on prosumer cameras. TheNikon 8800 zoom goes to about 350mm (35mm equivalent) and packs down into under 2" long.

On the subject of lens quality I would have thought, contrary to what peripatetic says, that the advantages would be with the 35mm lenses, for the reason that the glass is sometimes the limiting factor and the larger you make a lens the better you can make its resolution in theory.However the relevant question for the mainstream form of dSLR is where the best compromise lies between cost, handling and quality.IMO thebest compromise is with smaller than 35mm sensors, and I think it's significant that the only newly designed lens system (the 4/3 system) has been designed for 18mm sensors. I'm absolutely sure that the boffins at Olympus thought long and hard before settling on this size and selected it because they are sure that the eventual quality they can achieve (taking into account future sensor development) will be good enough for even professionals.The 18mm sensor is certainly good enough, even now, for serious amateurs.

In fact I have an A2 with an 8.8mm sensor and the only reason I'm considering buying an SLR is because I need to use longer lenses than you can get on a fixed lens camera.The reason I haven't bought one yet is that I'm reluctant to buy one of the hybrid systems and the Olympus system doesn't have image stabilisation. Also I don't like the flapping mirror which should have been consigned to the dustbin years ago. I'm hoping that Panasonic bring out a fully electronic body for the 4/3 system next year and that they either license the KM AStechnology orthey start making a few 4/3 IS lenses.


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Old May 6, 2005, 3:44 AM   #12
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Technophile wrote:
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Like NHL says that's a false comparison. You need to compare lenses with the same "35mm equivalent" focal length to get a true comparison, then you'll begin to see the difference.
Apples and oranges. Certainly by using a higher crop factor a given focal length gives you a longer telephoto view. But that's quite different to saying that it's possible to reduce the size and weight of a lens with an actual focal length of 300mm by designing it for a smaller sensor. Of course we know it to be true that it IS possible to do exactly that for a 15mm lens say, or even a 60mm lens. I read from a source I find credible that the design constraints for longer focal lengths are different to those for shorter. Specifically that the limiting factor with the longer focal length is in the larger front elements and therefore is not susceptible to any gain from a smaller sensor. This would seem to be vindicated by the comparison between the 300mm Canon and the 300mm (digital only) Olympus. They have been able to make smaller, higher quality lenses at the wide-angle end, but apparently not at the telephoto end. Perhaps they're still trying to figure out how, but that seems unlikely to me.

I am quite happy to admit however that I am not an optical engineer and may be completely wrong.

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I don't accept that there would be no gain in making telephoto small sensor lenses. The advantage of an EF-S telephoto would be in the lens size and it's handling, and the advantage would be sigificant. Look at how small the telephoto zooms are on prosumer cameras. The Nikon 8800 zoom goes to about 350mm (35mm equivalent) and packs down into under 2" long.
Apples and oranges again; that comparison only works if you're talking about lenses of different focal lengths. Why move up from a 1/2.8 sensor at all then?

Given the engineering provisos I mention above it is certainly true that a 100mm f2.8 lens giving an effective focal length of 200mm is bound to be cheaper and lighter than a 200mm f2.8 lens on a full frame camera. It's one of the reasons I have no particular intention of ever moving to a full-frame 1 series Canon. At the telephoto end of things we get much better value for our money when using a smaller sensor.

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On the subject of lens quality I would have thought, contrary to what peripatetic says, that the advantages would be with the 35mm lenses, for the reason that the glass is sometimes the limiting factor and the larger you make a lens the better you can make its resolution in theory.
Hmm, that doesn't seem particularly obvious to me. Bigger glass = better resolution? Perhaps you are correct, but even so there are other design constraints on lenses that can actually be fitted to a 35mm mount that will still project their image onto a sensor in a usable fashion. Perhaps Canon could design a 16-35mm lens that 2,3,4 ?? times the size of their current model and get fantastic resolution. I honestly don't know, but I'm not sure how usable such a large lens would be.

Anyway, you don't need to take my word for it, have a look at the MTF charts for the EF-S lenses compared to their full-frame equivalents then tell me how I'm wrong. Also have a look at some of the pro forums and tell me that the Nikon digital lenses aren't superior to their Canon full-frame equivalents at the wide angle end. There really isn't much general disagreement about this.

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However the relevant question for the mainstream form of dSLR is where the best compromise lies between cost, handling and quality. IMO the best compromise is with smaller than 35mm sensors, and I think it's significant that the only newly designed lens system (the 4/3 system) has been designed for 18mm sensors. I'm absolutely sure that the boffins at Olympus thought long and hard before settling on this size and selected it because they are sure that the eventual quality they can achieve (taking into account future sensor development) will be good enough for even professionals. The 18mm sensor is certainly good enough, even now, for serious amateurs.
No argument from me there.

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I'm considering buying an SLR ..... (but) I don't like the flapping mirror which should have been consigned to the dustbin years ago.
I'm not sure that you can really put those two things together very well. It's a bit like saying "I'm considering buying a motorcycle but the whole 2-wheel thing is a problem for me." If you get rid of the mirror then you haven't got a SLR any more.

There are a whole range of reasons why a SLR design is to be preferred for some purposes to an EVF. I myself would love to see a reasonably priced digital rangefinder, which is another alternative to the flapping mirror issue.
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Old May 6, 2005, 5:08 AM   #13
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You are 'thinking' in term of 35mm which is OK, but we have a format change here - Remember theses were the same arguments the medium format vs 35mm folks fought about... Take off your mm centric hat for a moment:

-> an 80mm is a standard lens in medium format whereas its a tele in 35mm, hence a fast 85mm tele in 35mm is a lot cheaper and lighter than a standard slower lens in medium format - It's what a lens is used for and not its focal dimension!

An Oly 300mm f/2.8 is only a 300mm in 35mm land, but that's an oxymoron in Oly term since you can't use as a 300mm - When you put it on the camera you're effectively getting a 600mm f/2.8 FOV - Same as a slower EF-600 f/4 at twice the cost and weight. This is the biggest selling point of the 4/3 format (and the same advantage the 35mm folks had over the medium format)

- Oh and BTW we all lost a little of 'Bokeh' along the way and gain more DOF which each format change! :-)
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Old May 6, 2005, 6:07 AM   #14
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peripatetic wrote:
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Apples and oranges. Certainly by using a higher crop factor a given focal length gives you a longer telephoto view. But that's quite different to saying that it's possible to reduce the size and weight of a lens with an actual focal length of 300mm by designing it for a smaller sensor.

I accept that point. Your comparison between the Oly 300mm and the 35mm 300m is actually a valid one, and that doescast things in a slightly different light.

On the subject of the SLR without a mirror I was being a bit careless with my terminology, like when manufacturers refer to cameras like the A2 as "SLR type". The Olympus C2500 I used to have was actually called an SLR, but it obviously has no mirror. I should have said a camera with an interchangeable lens system. Someone will have to invent a new term for these cameras when they arrive - which they will. The main gripe I have about dSLRs is that they are basically a film SLR with a sensor instead of the film. Compared with an A2 a dSLR loses valuable features, like the in viewfinder information and histogram, the ability to use the LCD as a viewfinder (which can occasionally be useful), the ability to actually see what the sensor is recording and detect if it's over-exposed or under-exposed as you can with an EVF, etc. It also seems stupid to continue with the 3:2 format when the lens is projecting a circular image. Why discard part of the image, just because that was the format for rolls of film. The 4/3 system is a bit more sensible in that respect.


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Old May 6, 2005, 7:10 AM   #15
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NHL wrote:
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peripatetic

You are 'thinking' in term of 35mm which is OK, but we have a format change here - Remember theses were the same arguments the medium format vs 35mm folks fought about... Take off your mm centric hat for a moment:

-> an 80mm is a standard lens in medium format whereas its a tele in 35mm, hence a fast 85mm tele in 35mm is a lot cheaper and lighter than a standard slower lens in medium format - It's what a lens is used for and not its focal dimension!

An Oly 300mm f/2.8 is only a 300mm in 35mm land, but that's an oxymoron in Oly term since you can't use as a 300mm - When you put it on the camera you're effectively getting a 600mm f/2.8 FOV - Same as a slower EF-600 f/4 at twice the cost and weight. This is the biggest selling point of the 4/3 format (and the same advantage the 35mm folks had over the medium format)

- Oh and BTW we all lost a little of 'Bokeh' along the way and gain more DOF which each format change! :-)
I'm not at all confused about focal length, but I may have been expressing myself badly.

A lens of 300mm focal lenth can be used (with appropriate mount or adapter) on a variety of different sensors. The canon can be used on a 35mm sensor or APS, or smaller if an adapter could be found. For a given focal length the smaller sensor has a smaller FOV.

I personally wish that we'd stop quoting everything i.t.o. 35mm equivalent focal length when we're actually talking about FOV. I move for a switch in terminology so that we quote FOV when that's what we're concerned about. And that is most of the time.

The fact that smaller sensors have a cost advantage when it comes to telephoto work is very clear, after all they need shorter actual focal lengths to get the same FOV.

However I was under the impression that some believed that it would be possible to make a 300mm actual focal length lens cheaper/better/lighter for the smaller sensor and I queried this. To be clear - I believe it has been conclusively demonstrated that it IS possible to make a 10-22mm (for example) actual focal length lens cheaper/better/lighter for a smaller sensor. This seems very apparent when you look at the Nikkor DX lens range. They have nothing at the telephoto end of the range. Why? Because there is little to gain by making a DX lens at longer actual focal lengths, you might as well cover the full frame because covering the smaller area gains you nothing i.t.o. cost/size/performance.

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Old May 6, 2005, 7:18 AM   #16
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Technophile wrote:

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On the subject of the SLR without a mirror I was being a bit careless with my terminology, like when manufacturers refer to cameras like the A2 as "SLR type". The Olympus C2500 I used to have was actually called an SLR, but it obviously has no mirror. I should have said a camera with an interchangeable lens system. Someone will have to invent a new term for these cameras when they arrive - which they will. The main gripe I have about dSLRs is that they are basically a film SLR with a sensor instead of the film. Compared with an A2 a dSLR loses valuable features, like the in viewfinder information and histogram, the ability to use the LCD as a viewfinder (which can occasionally be useful), the ability to actually see what the sensor is recording and detect if it's over-exposed or under-exposed as you can with an EVF, etc. It also seems stupid to continue with the 3:2 format when the lens is projecting a circular image. Why discard part of the image, just because that was the format for rolls of film. The 4/3 system is a bit more sensible in that respect.

All good points.

Of course the SLR & mirror arrangements has its own advantages too, chiefly i.t.o. the bright viewfinder that operates at the speed of light rather than the speed of electrons in your cpu and lcd.

EVFs still have some distance to go before they can compete in that respect; consider the reviews of the Leica Digilux 2 for example.

But you may well be right that the future is in a SLR-like system with EVF and interchangeable lenses, quite probably with backwards compatibility to our current crop of SLR lenses.

I also very much like your idea of changing the format of the sensor. On the Canons for example we could get extra resolution (I mean higher pixel count) from the same lenses by simply increasing the height of the chip to match the width. 4/3 is certainly better than 3/2, but why not make it square I wonder? Surely that would be even better still? After all, we could crop the image back to 3/2 and have lost nothing, but where we actually want a square crop (and I personally find I often do) we would have a photo with increased resolution.
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Old May 6, 2005, 7:47 AM   #17
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peripatetic

Just check the dimension below for a 300mm zoom when it's optimized for APS sensor for comparison:
http://www.tamron.com/lenses/prod/28300_di.asp
http://www.canon.com.hk/En/Product/P...oduct_id=10037


We both can't say anything at this time because such a 300mm f/2.8 'digital' lens doesn't exist - but why can't it be done when one scales the lens to a smaller image circle when all indication show otherwise - Isn't this fast lens smaller and lighter than its full-frame counterpart as well? http://www.sigmaphoto.com/lenses/len...64&navigator=2
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Old May 6, 2005, 8:09 AM   #18
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But peripatetic is pointing out thatthe digital 300mmdoes exist. The Oly 300mm is the same as the Canon except that it's projecting a smaller image, and it isn't actually any smaller than the Canon, which is a veryinteresting observation and one that I'd missed.

BTW, in your comparison isn't the Tamron a 35mm lens, but just "optimised for digital" whatever that means?


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