About 15 years ago I ran some color neg through a Retina Reflex IV that had been a desk decoration at work. In the spirit of "how well does it work?" and "what's it like to handle this 1960s machine?"
It was in perfect working condition. The prints that came back were noticeably low in contrast, with a little more flare than we are used to with modern lenses. There was no visible haze in any of the three lenses I tried yet the "look' was far different than photos from more modern lenses, pastel rather than vibrant. I was not intrigued enough to experiment further, and the camera went back to being a museum piece. I don't know how this relates to what you saw with your R-R, and I'm not making any claims about these Schneider lenses, simply reporting my experience.
You bring up a good point. That is, What is this look (feeling?) in the Retina Reflex IV photos that caught my attention? And how much of that look is actually due to the Schneider-Kreuznach lenses I used?
I did not attempt to describe or illustrate the look that I was seeing, which was probably a mistake on my part. This thread quickly decided it was the Tessar lens design of the Schneider-Kreuznach lenses that created what I was seeing, but I suspect that is only partially true. For example, I assume various Tessar lenses may have different numbers of aperture blades, which may be curved or straight -- and those factors might affect out-of-focus rendering? Mostly, I use black and white film, but maybe the lens coatings are contributing some small part? And I am guessing that not all Tessar lenses are equally sharp in the middle and become less sharp at the edges? So maybe some Tessar lenses would contribute more to to the look I was seeing, and others might contribute less?
As for "modern" I already have a fair number of "modern" (semi-modern?) lenses designed and made by Pentax and Konica in the 1970s and 1980s. To be clear, what I am looking for is lenses that have less modern rendering. I hate the way that sounds, because I roll my eyes everytime someone starts talking about how their lens has "pixie dust," or "3-D pop," or "bokeh," so I am not going to use the word "vintage." But I realize "less modern rendering" is no more precise, and for that, I apologize.
Examples may be more useful than definitions. As an extreme example of what I mean by less modern rendering, the photos of Eugene Atchet come to mind. I expect it would be quite difficult to reproduce what Atchet did using a 35mm camera loaded with modern film -- but I would like to see if I can get photos that look a little bit more Atchet, and a little bit less modern, if that makes any sense? Obviously, the subject matter, composition, lighting, depth-of-field, film stock, developer, and toners all play a much bigger role in how the image feels to the viewer than does the lens.
Here are the photos that started me down this rabbit hole. The first one (lion) was taken with the Schneider-Kreuznach Retina-Curtagon 35mm f/2.8, and the second one (skull) with the
Schneider-Kreuznach Retina-Xenar 50mm f/2.8. Both are from Ilford HP5+ negatives processed in stock D-76. I think what caught my eye is the way the out-of-focus areas are rendered, especially in those areas which are transitioning from sharp to not-sharp. The backgrounds have a little bit of a dreamy look, but perhaps that is due more to my light and depth-of-field than it is to the lenses(?)