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Steppenwolf
30 Aug 2012 - 8:37 AM

Well, they're bringing out a new FF SLT in the next few months (the A99) which is intended to compete with the likes of the Canon 5DIII and Nikon D800. It's also rumoured that Sony are working on a professional FF SLT to follow later. They still seem to be releasing Alpha lenses too. Also they've only just, within the last year, released 3 SLTs (A37, A57 and A77). I very much doubt that Sony would make a decision to abandon this technology before they even know what the sales figures are over a reasonable period of time - remember that Sony production was badly affected by the Tsunami and flooding so most of their cameras and sensors were in short supply until March this year. I wouldn't judge the popularity of the SLTs by the reaction they get on this forum - this is the home of the traditional DSLR (preferably Canikon).

Of course, like I said, if Sony stick phase detection AF into the NEX cameras (and they already have a full function Alpha lens adaptor) there's no particular reason why they should make both the Alpha range and NEX. For example, if the NEX-7 had phase detection AF embedded in its sensor it would make the A77 redundant - people would just buy the NEX-7 and an adaptor, so they'd get a full function SLT and also a compact camera all in one.

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30 Aug 2012 - 8:37 AM

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strawman
strawman  1022002 forum posts United Kingdom16 Constructive Critique Points
30 Aug 2012 - 10:31 AM


Quote: DK does get facts wrong sometimes. He says that the new Sonys use f5.6 crosshairs (rather than f2.8) - like Nikon now does. I'm not sure that this is true.

So when he says something you see matching your very specific belief set he is correct and when he says something that does not match your belief set, and provides an experiment that backs up this point you say he gets facts wrong sometimes. Is it possible it is you who is wrong on those occasions? Who would I believe David or you. Well David as he clearly understands the topic while you do not. Go back and read all his stuff, do not cherry pick, if you dismiss his opinion on some topics how can you use him as a voice to be trusted on others.

You have to be more open minded to look at the full situation and comprehend all that is there. The clever products use the best of old and new technology, stop just reading the marketing guff, if you want to talk about the products use them or get into the engineering of the product. Just throwing away all new technology or all existing technology is stupid. The balance is where the best product is, and that balance point moves. Its not a belief system, rather an evaluation at a set time. And depending upon requirements, different solutions will pop up as best.

Let me try and tell you again what Sony knows and you do not. An SLT camera needs calibration. Its AF sensor is in one physical location, the Image sensor another and a mirror is used to split light between the two. Also the AF sensor has a level resolution when it measure how out of focus the lens is. So AF accuracy is made up of how accurately the AF sensor can measure and how well you have compensated (or calibrated) for any differences in light path length between the lens and the respective sensors. Yes an SLR has more moving parts, but if the light path is correctly calibrated and the AF sensor measures the out of focus distance of the lens more precisely the SLR will have greater focusing precision. It is rather basic, you can grasp that can you not. Now tell me, what is the level of un-repeatability in the light path length caused by a moving mirror? Is it in fact significant shot to shot??? If so please give us some data. It will be over life I agree as you have to consider wear but is it shot to shot?

The advantage of SLT is fewer moving parts, should give longer life, as long as the extra parts added, like EVF, have a greater life than the parts they replace. But remember in the real world you are trading things.For example the OLED looses 50% of its brightness in 10,000 hours, so it too has a wear out effect. Its well know by those that use them, have a look at some data sheets. And to compound that the blue wears out quicker so the accuracy of colour projected is an issue that will grow in use. I expect and hope the EVF is more reliable than the mirror mech, bit it does question the WYSIWYG aspects.

In fast phase detect AF systems, the focus is measured only once, at the start of the process. Then information from the lens and the AF sensor is used to calculate how much to move the lens AF motor. Focus is not re-checked, so the accuracy of data received from the lens is also important or it will be another source of error. This is why Canon and Nikon apply their lens calibration function in the camera specific to a lens as you are compensating for errors in both. So even if they stopped using moving mirror systems and went fixed the calibration feature would be retained. Why? speed. Because as the lens is focusing you can stop down the lens (and lift the mirror in an SLR) so when the lens is focused the shutter can fire as soon as possible. If you are going to re-focus then you have a delay while it calculates focus again moves the motor etc. It all depends on what AF strategy your camera is running and the pace it is running at and whether it is using predictive calculations to predict where your subject will be at a point in the future.

So you can see why I do not think SLT removes the need for a calibration of the AF system, because it does not do anything to resolve the lens information accuracy, and it still has a light path length variable that depends upon the specific build of components in the camera. It is a simpler calibration, but still a calibration.

strawman
strawman  1022002 forum posts United Kingdom16 Constructive Critique Points
30 Aug 2012 - 10:34 AM

Oh look Sony have just produced a NEX camera with phase detection elements in the sensor, never predicted that Wink . Wow what a surprise. If that works well they should use that in their next A mount camera and remove the SLT mirror.

Carabosse
Carabosse e2 Member 1139392 forum postsCarabosse vcard England269 Constructive Critique Points
30 Aug 2012 - 11:16 AM

SLT cameras are probably another Betamax for Sony. Very few, these days, are interested these days in a "better" mirror. Getting rid of the mirror altogether whilst matching, or improving upon, performance of mirrored cameras has got to be the goal.

Sony are howver, sensibly, putting resources behind their mirrorless range.

Steppenwolf
30 Aug 2012 - 4:32 PM


Quote: DK does get facts wrong sometimes. Blah blah blah

ZZZZzzzz.....

You must be fun to live with Strawman. Sorry, I've stopped reading your posts because they're ridiculous.

Last Modified By Steppenwolf at 30 Aug 2012 - 4:37 PM
Steppenwolf
30 Aug 2012 - 4:35 PM


Quote:
Sony are howver, sensibly, putting resources behind their mirrorless range.

Care to provide a link backing that up?

strawman
strawman  1022002 forum posts United Kingdom16 Constructive Critique Points
30 Aug 2012 - 7:37 PM

Love you Smile

Its the way you accept being wrong so well that makes you so lovable. You can tell as you insult the person when they have you beaten.

Sooty_1
Sooty_1 Critique Team 41181 forum posts United Kingdom196 Constructive Critique Points
31 Aug 2012 - 1:21 AM

Just a quick question for you optical gurus....

If the mirror doesn't move out of the way, it is effectively a piece of glass at an angle to the light path. Therefore, the light will be subject to the laws of refraction. Surely this will affect the critical sharpness, as light striking the air/glass surfaces will be refracted at different angles, dependent on the angle of incidence? Doesn't this hold true for the different wavelengths of light too, else there would be no need for apochromatic lenses? In which case, isn't the critical focus determined by the mechanical construction of the camera rather than by the accuracy of the AF?
At least with an SLR there is nothing in the path during the exposure.

Nick

mikehit
mikehit  46179 forum posts United Kingdom9 Constructive Critique Points
31 Aug 2012 - 9:01 AM

As you say, they have found a way round this with the apochromatic lenses so I guess they have applied the same sort of knowledge for the Sony mirrorless.

Carabosse
Carabosse e2 Member 1139392 forum postsCarabosse vcard England269 Constructive Critique Points
31 Aug 2012 - 10:50 AM


Quote: I guess they have applied the same sort of knowledge for the Sony mirrorless.

We are talking here of SLT cameras not mirrorless. Smile

There's nothing particularly new about SLT technology. The Canon EOS RT had a similar mirror.

AlanWillis
31 Aug 2012 - 11:01 AM

Sony lens range stop at 400mm so its not a priority for Sony either.
[/quote]

Not true 500mm F4 but cost lots of bucks.

I owned a A850 and a A77. I have used the A77 since last September and it is far superior to the A850.
I have now sold my A850 waiting for the A99 FF SLT.

The NEX 5R has WI FI and an interesting focusing system, But will not replace the SLT.
IMO At ISO100 the light makes no difference. 12FPS and refocusing between each frame is awesome.

mikehit
mikehit  46179 forum posts United Kingdom9 Constructive Critique Points
31 Aug 2012 - 11:02 AM


Quote:
We are talking here of SLT cameras not mirrorless. Smile

.

By 'mirror' I meant the flippy thing that moves out of the way as opposed to the pellicle.

Carabosse
Carabosse e2 Member 1139392 forum postsCarabosse vcard England269 Constructive Critique Points
31 Aug 2012 - 11:05 AM

The pellicle is a type of mirror, so it rather confuses the issue if some don't regard it as such! Wink

The pellicle has never caught on in the past and there's no reason to think it will now.

Steppenwolf
31 Aug 2012 - 2:01 PM


Quote: Just a quick question for you optical gurus....

If the mirror doesn't move out of the way, it is effectively a piece of glass at an angle to the light path. Therefore, the light will be subject to the laws of refraction. Surely this will affect the critical sharpness, as light striking the air/glass surfaces will be refracted at different angles, dependent on the angle of incidence? Doesn't this hold true for the different wavelengths of light too, else there would be no need for apochromatic lenses? In which case, isn't the critical focus determined by the mechanical construction of the camera rather than by the accuracy of the AF?
At least with an SLR there is nothing in the path during the exposure.

Nick

If you shine light through a flat piece of glass there isn't any dispersion. Or to be more accurate, there is dispersion going through the first surface but it's perfectly reversed after passing out of the back of the translucent mirror. You only get problems with dispersion when the surfaces of the medium are not parallel, e.g. a lens or a prism. It's obviously a massive problem on glass lenses and requires a lot of clever design and accurate manufacture to try to reassemble all the different colours. Of course the advantage of mirror lenses is that all colours of light are reflected at the same angle so there's no chromatic aberration.

As for there being "nothing in the path of the light during exposure" with a DSLR, I guess you're excluding all the lens elements (from about 4 to 15 elements depending on the lens type). I'd worry more about these than the plane translucent mirror.

Last Modified By Steppenwolf at 31 Aug 2012 - 2:03 PM
Carabosse
Carabosse e2 Member 1139392 forum postsCarabosse vcard England269 Constructive Critique Points
31 Aug 2012 - 2:16 PM

There a comment in the article about the Canon RT:

"Finally, the pellicle mirror does degrade lens resolution, as early tests performed in Modern Photography magazine have shown that the Canon film counterparts produce sharper images than those Canon camera bodies that have a pellicle mirror."

Has these been resolved with SLTs?

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