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Sooty_1
Sooty_1 Critique Team 41207 forum posts United Kingdom198 Constructive Critique Points
31 Aug 2012 - 3:29 PM


Quote: 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 was considering the lens elements to be a constant, as they will (to all intents and purposes) be the same whether you have a moving mirror or not.

I also disagree about the refraction. Shine a light through glass and there will be refraction. Not much if the light is perpendicular or close to, but the mirror will be at 45 degrees, so the light hits at different parts of it's path. The light striking the mirror will not be at the same angle all over the mirror, as the light 'rays' are unlikely to be parallel, therefore will be refracted by differing amounts, dependent on the angle of incidence. The mirror is not at the plane of focus.
You will also get a small amout of secondary reflection from the internal surfaces of the mirror glass which will not help the situation.

You cannot use the same technology they use in lenses, because they use different elements with different refractive indeces and aspheric elements to 'refocus' red, green and blue light into the same plane (the film or sensor). The pellicle mirror does not have an optical construction like a lens, so it is not possible to 'correct' the different colours of light.

Nick

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31 Aug 2012 - 3:29 PM

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Steppenwolf
31 Aug 2012 - 4:19 PM


Quote: 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?

Read the reviews - you won't find a mention of any image degradation on the current range. AP found that the A77 had the best resolution of any APS-C camera on the market. DPR gives it much higher marks for image quality than, for example, the 7D.

But basically the SLT is just a pragmatic solution to the obvious problem that DSLRs have - i.e. they can't shoot at very fast frame rates and they are not very practical for video. The fixed mirror eliminates both these problems, so the A77 shoots 12fps which is pretty amazing for fast moving subjects, and it shoots video like a dedicated video camera with full functioning AF and EVF - so you can shoot video through your favourite SLR lens. And the focus is more accurate than a DSLR in my experience (and several others). If you don't like video and you favourite shots are of still life or landscapes none of this will be of interest, but if you shoot fast moving targets with long lenses the SLT is a much better tool than any DSLR I've ever had. Maybe a top of the line pro DSLR will match the A77 but these cost a fortune.

Steppenwolf
31 Aug 2012 - 4:48 PM


Quote: I was considering the lens elements to be a constant, as they will (to all intents and purposes) be the same whether you have a moving mirror or not.

Of course, but if you're not worried about light passing through 15 lens elements, why are you suddenly worried about one more plane element? Are you worried about the effects of in-lens image stabilisation on the integrity of the image, for example? Or is it only technology that is not Canon/Nikon that worries you?


Quote: I also disagree about the refraction.

Disagree all you like. The fact is that a piece of plane glass inserted into a light path does not introduce dispersion. They teach this stuff in elementary optical physics at school. Try looking through a window, for example, at any angle you like - you won't see rainbow patterns. The light only gets broken up into its component colours if the exit face is at an angle to the entry face - e.g. a prism. If the two faces are parallel the light is exactly reassembled.

I suggest you look up "dispersion" and read about it.

Carabosse
Carabosse e2 Member 1139444 forum postsCarabosse vcard England269 Constructive Critique Points
31 Aug 2012 - 5:04 PM

It surprising, in a way that it is Sony which has resurrected this quite venerable technology and not Canon........... their first camera of this type was the Pellix (1965).

I guess the only way to be sure there is no image degradation is to do the sort of test similar to the one done, all those years ago, on the Canon RT. I.e. put the camera up against a DSLR of the same make and resolution, and using the same lenses. I have not seen any such reviews personally, but I assume they are out there. Smile

mikehit
mikehit  56457 forum posts United Kingdom9 Constructive Critique Points
31 Aug 2012 - 5:15 PM


Quote: but if you shoot fast moving targets with long lenses the SLT is a much better tool than any DSLR I've ever had.

Again, you seem to disagre with any comparative overview I have read which says that SLT is better at immediate focus but is less efficient than SLR at focus tracking.
And I find 8fps of the 7D perfectly adequate. Your compromises may be different.

Steppenwolf
31 Aug 2012 - 5:26 PM


Quote: It surprising, in a way that it is Sony which has resurrected this quite venerable technology and not Canon........... their first camera of this type was the Pellix (1965).

I guess the only way to be sure there is no image degradation is to do the sort of test similar to the one done, all those years ago, on the Canon RT. I.e. put the camera up against a DSLR of the same make and resolution, and using the same lenses. I have not seen any such reviews personally, but I assume they are out there. Smile

Not so long ago Sony made DSLRs, CB - you may have forgotten. They made so many I can't even remember how many there were - A200, A300, A350, A500, A550, A580, A700, A850, A900 - there were loads of them. The A55 SLT was basically an A580 without the flappy mirror - same sensor, same processing, same lens, etc etc. When they were compared their image quality was the same - the only difference was due to the loss of light (for the AF sensor) which meant that the A55 had slightly inferior noise levels at high ISO.

DPR said:

"The DSLR-A580's imaging pipeline is near identical to the translucent mirror model SLT-A55. It appears Sony has only made minor modifications to the sensor and processing and in practice the output of both cameras is therefore pretty much indistinguishable. This is not a bad thing at all, as we were quite impressed with the A55's image quality".

Carabosse
Carabosse e2 Member 1139444 forum postsCarabosse vcard England269 Constructive Critique Points
31 Aug 2012 - 5:31 PM

I merely wondered why, if the technology was so beneficial, didn't the likes of Canon develop it? They have had 47 years to do so since their first pellicle camera. Smile

mikehit
mikehit  56457 forum posts United Kingdom9 Constructive Critique Points
31 Aug 2012 - 5:35 PM


Quote: pretty much indistinguishable.

In other words, there is a difference. Whether it matters to the user is a different matter but as some seem to obsess about details this may be a factor for consideration.

mikehit
mikehit  56457 forum posts United Kingdom9 Constructive Critique Points
31 Aug 2012 - 5:37 PM


Quote: I merely wondered why, if the technology was so beneficial, didn't the likes of Canon develop it? They have had 47 years to do so since their first pellicle camera. Smile

You'd think so....

Sooty_1
Sooty_1 Critique Team 41207 forum posts United Kingdom198 Constructive Critique Points
31 Aug 2012 - 8:46 PM

Before you become so abusive, I suggest you read my post more carefully!

I didn't say dispersion, I said refraction. I didn't say that there would be rainbows, but unsharpness caused by the light path being refracted by different amounts depending on the angle the light is incident, and therefore not necessarily being brought to focus at the same place.
I am perfectly familiar with A level optics, thank you.

I am not considering the lens elements because of 2 things...
1. The lens will be the same used on different bodies and so is not a factor as you are comparing bodies, not lenses. The way particular lenses interact with specific bodies is a whole other subject.
2. The lenses have already been designed to compensate for aberrations. The light path on exit of the lens is (hopefully) as corrected as it can be, but very seldom are they parallel.

Why do you bring the Nikon/Canon aspect into it? It sounds like you just want to be provocative. I mentioned nothing about camera brands.

Maybe you need to realise that there are differing views on this, and that the opinion of one or two sites is not gospel.
I also find it significant that no-one bothered to develop the idea, if it was so unflawed. Is it just a fad that hype is making sound impressive? It would seem to me to be a halfway house between traditional mirrored systems and a mirrorless system that relies on the sensor to provide the eyepiece view, and maybe one that isn't worth pursuing long-term precisely because it is a compromise?

Steppenwolf
1 Sep 2012 - 8:24 AM


Quote:
I didn't say dispersion, I said refraction.

I'm afraid I dismissed your question without really thinking about it, apologies. You're right that a piece of glass at an angle would cause dispersion. I guess that the reason it doesn't in the SLTs is down to design and materials. Firstly it's not made out of glass but from some composite materials - I can't find out exactly what, but I suspect it's some very low dispersion material. It's also very, very thin. The proof of the pudding is in the eating, however, and the test results of the SLTs don't show any deleterious effects from the translucent mirror. It may well be that the reason the pellicle design is now viable is because of the advances in composites, who knows.

My point about IS is simply that in-lens IS relies on moving one of the elements to shift the image. I'm not sure if a new element is added to the lens to perform this function or if one of the existing elements is moved. Either way this is potentially going to degrade the image. Yet no one ever mentions this as a possible problem - and in-camera IS is usually criticised by the usual suspects on this forum. Maybe it's just my perception but it often seems to me that technological innovation is always rubbished unless it's from Canon - hence the posts above where the clear implication is that the pellicle mirror idea must be flawed or Canon would have pursued it.

strawman
strawman  1022006 forum posts United Kingdom16 Constructive Critique Points
1 Sep 2012 - 10:28 AM

Chapter 15 here indicates how Canon has designed its IS system. It would look that they have not added extra optical items but unless you are very into your lens design it will be hard to tell,but what you can say is they designed it with this in mind.


Quote: Maybe it's just my perception

I agree with you. You trot this anti-Canon stuff out, but you are so hung up on a particular new item from Sony you have picked you have lost objectivity. I tell you why I think the A850 and A900 are the best cameras in the Sony range and tell you why I think they are worth defending and you fly off in a rage. And still that is a Canon bias. Really, picking the A850 over the A77 is canon bias? I guess me critiquing the 5D3 and its unrealistic price and praising the D800 is also Canon bias.

You love to quote DPREVIEW so I went to their review and took some of their test images to show the difference between the A77 and the A900 and you flew off the handle because I provided something people could look at. You link the A77 review and yes they praised the high resolution but read the rest of the conclusion as they raised some negatives for image quality. Of note given your interest in AF performance they did not recommend it for sports use over the moving mirror based technology products. You say a dSLR cannot shoot at high frame rates, yet I have seen a 14fps dSLR. I would have to question how many of us need that and is the next step not to just take frames from a video feed. Its not my style but the technology is going that way. We all pick the features we want.

Its not about being against new technology its about picking the technologies that give good advances. For example you claim I am anti-new technology. When SLT came out I pointed out why in my opinion there are advantages in embedding the AF sensor in the imaging sensor (there are problems too but I think they are worth it) so rather than jumping to the SLT compromise it may be better to hold off and jump when the all in one sensor solution is produced. Sony has now done this so I wait to see with hope how this new technology works. Congratulations to Sony. I expect this to be the winning system and if Sony have done this correctly then the SLT may well be removed in future A series cameras.

I pointed out to you the impact of diffraction and you effectively called me a liar and rubbished the science of optic design. Then Nikon handily put out its D800 guide and mentioned diffraction and provided data points that matched what you were claiming was not true.

Sorry you have a history of not being objective and taking an Anti Canon stance, in fact anti anything other than your camera stance, even if it comes from your beloved Sony.

Technology opens a box of toys and the technologies that are being worked on are interesting. I expect more and more cameras will turn up with EVF, I do not think SLT will replace SLR, rather they will both be replaced I think. And yes pixel count will rise, its a catch, raise it up too fast and you get noise and speed/bandwidth problems on the camera and buffers get too small. But there is a future point where you can use the extra pixels to correct for optical defects so can get even better results from lower cost optics. But the end output product image may not have a massively higher resolution than we have today. But at each stage it is about balance.

The question, as ever, at what point is it the correct time to grasp the new technology? It is not for no reason that many people call the cutting edge technology the bleeding edge technology.As smart users we need to judge when we get value for money. That is not to say that new technology is no use, but rather sometimes the difference is not worth the effort, and sometimes the bit you trade for new technology is significant. I like the optical finder, a lot of what I like is not the biggest thing in technical use of the product but I like it. Just like some musician friends love valve amplifiers. Sometimes it is just because the user likes something. It is not always a measured item. And for most of us cameras are tools or toys, to be used as we like. I like to think I take the picture, not the camera, and the user interface and tactile experience is important. Its why I still use a nearly 60 year old rangefinder from time to time, its the user experience.

On cars its like dual clutch gear boxes, for powertrain designers and getting around emissions its great, and if driving is a chore it is great. But for long term ownership and driver pleasure its not so good. So great technology but watch out for year 5 ownership cost, not bother you because you keep it for less than 3 years, watch out for 2nd hand value fall. Depending on what you want its great or a not a good change.

Last Modified By strawman at 1 Sep 2012 - 10:33 AM
Carabosse
Carabosse e2 Member 1139444 forum postsCarabosse vcard England269 Constructive Critique Points
1 Sep 2012 - 11:49 AM


Quote: You're right that a piece of glass at an angle would cause dispersion. I guess that the reason it doesn't in the SLTs is down to design and materials. Firstly it's not made out of glass but from some composite materials - I can't find out exactly what, but I suspect it's some very low dispersion material. It's also very, very thin. The proof of the pudding is in the eating, however, and the test results of the SLTs don't show any deleterious effects from the translucent mirror. It may well be that the reason the pellicle design is now viable is because of the advances in composites, who knows.

There must be some advance on what is basically 1960s technology, I would have thought. That's what intrigues me: perhaps Sony have some sort of patent?

mikehit
mikehit  56457 forum posts United Kingdom9 Constructive Critique Points
1 Sep 2012 - 12:07 PM


Quote: My point about IS is simply that in-lens IS relies on moving one of the elements to shift the image. I'm not sure if a new element is added to the lens to perform this function or if one of the existing elements is moved. Either way this is potentially going to degrade the image. Yet no one ever mentions this as a possible problem - and in-camera IS is usually criticised by the usual suspects on this forum.

The most cogent explanationI heard was that in-body IS has advantages for lens size (and available legacy lenses) but in-lens IS is superior for telephoto work - this was a few years ago now so how much in-body IS has closed the gap I don't know. But if Canon or Nikon went to in-body IS across their range and their lenses disappeared from high-profile sporting events that would count pretty much as a PR disaster.

But I still can't shake off the feeling that MFTs have pretty much turned the pellicle mirror into a dead-end or at best a niche market.

mdpontin
mdpontin  106016 forum posts Scotland
1 Sep 2012 - 12:08 PM


Quote: and driver pleasure its not so good

Beware of being hoist by your own petard, strawman. Driver pleasure is not subjective, so you can't make that claim for other people. Actually, some find driver pleasure to be enhanced - just bury the throttle pedal in the carpet and enjoy acceleration to the red-line better than most drivers could achieve with a manual gearbox, accompanied (in my case) by the twin whines of supercharger and turbocharger. But...you know what? Let's not get distracted from the nerdishly obsessional argument about which camera technology is marginally better than another! Wink

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