The reason people disagree about this being an issue or not is that it's a large subjective component. How much can you compromise with color reproduction, it's subjective. I'm of the opinion that if you sell a system you should yourself have an established view on acceptable quality, and if a system does not live up to your standard you don't sell it, even if a customer may have lower standards than you have. Personally I think the Sony backs (and A7r) are past the limit of what's acceptable (too limited and unpredictable performance) and therefore one should not suggest using these with tech lenses wider than say 50-60mm, and in this context the Cambo Actus is an illogical product, but apparently many dealers have a different opinion. As long as customers are well-informed I guess it's okay.
Tech camera users are screaming for live view so I understand now when we have live view backs we want to use them on tech cameras. But I think we're in the space of wishful thinking. Live view is wanted so badly we stretch farther than we should concerning compromising our quality standards. The Cambo Actus is a very sexy product, but the technology is not ready. New sensors (back-illuminated or similar technology) or stronger retrofocus lenses are required to get a compatible package with good performance over the whole range. Stronger retrofocus would be a step in the wrong direction for tech cam land, so I hope better sensor technology comes first.
(As a sidenote, I don't like it when people say "lens limitations" because it's nothing wrong with the lenses -- use a film back and see, there's nothing wrong, no cast no nothing -- the whole term "lens color cast" puts focus on the lenses when it's actually "sensor limitations". What tech camera customers should want from the manufacturers is better sensors rather than "better" lenses. It's unfortunately easier to make lenses that compensate for sensor limitations than make sensors without these limitations though. Oh well, it's probably not too hard to make Kodak-style light shields but those that manufacture sensors optimize for other applications than tech wide optics.)
Andres - I sincerely appreciate your input on this topic - as many do. As I agreed, you are correct, there is not enough widespread information being shared on the topic, and you've helped tremendously for many to better understand the issue.
I also understand your feelings about being technically correct in describing conditions. If we, as a dealer, use the phrase "this lens is limited" we mean it only in the most direct usefulness to the client. In the majority of cases, an existing sensor is already present, and lenses are being considered. In that case, most are sticking with their sensor, and so the focus is on the performance of a given lens with an already existing sensor. We understand that the sensor design is the core culprit, although your comment about film backs working perfectly fine still points to some culpability on the part of lens manufacturers, who are aware that their lenses are being used for digital capture, some of these lenses in a substantial majority of instances. Regardless - as a result of this, we typically describe the performance of individual lenses with one specific sensor to our clients because they usually have one sensor (and have already). They will have multiple lenses, and the lenses will react differently.
From the "solving the problem" perspective at the design end of things, it may be more important to you or manufacturers to think in terms of who or what is responsible. From the usage standpoint of these existing tools, at least in terms of recommending products, at the dealer level we feel it is more important to focus on the performance of the variable components, rather than the cause of the issue from one component that is already in their possession. There's nothing wrong with focusing on that, but our focus is more on what happens with that combination. We find that serves the person who is considering that lens best. It's slightly semantic, but we feel it helps our clients understand what lenses to choose for best results, depending on which sensor they have. "Which digital back are you shooting with" is typically the first question asked when someone asks for information on lenses to be used with tech cameras.
In terms of the subjectivity of color reproduction, or even quality in general, you're absolutely right - it is subjective. We evaluate and assess the performance of the products we sell at least as hard and generally with a harder eye than our clients do. We have extremely conservative views on what is acceptable and what is not. That doesn't mean we won't sell these products, we communicate the restrictions and describe the positive performance potential - and then it is determined if this product(s) is a fit for that particular user. Digital backs have been sold with ISO ranges from 50 - 800 for years. Have we ever recommended to anyone that ISO 800 is usable? Never. Check my post history and you'll see that I commonly refer to legacy digital backs as ISO 50-200 usable range products. When it comes to crosstalk effects and other anomalies with shifting lenses and digital backs, or even straight up lens performance without shifts, we're extremely critical with our assessments. And our clients use these products in many different ways. Ultra wide creates more challenges. Moderate wide may produce perfectly acceptable results. That is part of the conversation as well. These products can work for you, but it depends on what you are using, how you are using it, and what you are trying to accomplish. That's all part of the conversation. So - we don't see that selling these products is a matter of living up to our standards - in general they all exceed our standards, but all products have performance restrictions - it is important for users to understand the restrictions, if for no other reason than choices at the high end are not as abundant as choices at the low end.
All this has to be discussed in detail with a prospective purchaser of these systems. I realize you may be referring to dealers in general and not Capture Integration, but that only underscores how complex these products are in their use and their expected and actual results. Dealers should be better informed by manufacturers, dealers should be more concerned about initiating their own knowledge base regardless, but also, this is not easy or without a requirement of significant resources and commitment to sell these systems, and that certainly limits the availability of good dealers as much as anything. It is nothing like selling a simple Canon (or even Pentax) system.
Sorry for the long winded post.
Steve Hendrix
Capture Integration