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4.5/105 Radionar / VPK Rapid rectilinear...bokeh test
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PostPosted: Sat Oct 06, 2007 1:41 pm    Post subject: 4.5/105 Radionar / VPK Rapid rectilinear...bokeh test Reply with quote
Having got the bellows for the Cooke I've started remounting some of my old lenses. The 4.5/105 Radionar and the VPK Rapid Rectilinear are ready, the latter one with some difficulty, and the Meniscus is in the queue. The focal length of the RR is so short that I almost couldn't use it with the bellows because it didn't quite reach infinity focus even when mounted with the help of a mere reversal ring. Finally, I found quite an unorthodox solution. The lens assembly, i.e. the shutter box turned out to be so narrow that it fit inside the bellows but just wide enough not to pass inside an M42 extension tube. This gave me an idea, I glued the lens to the back end of an extension tube, which became a short lens hood. Now the lens resides totally inside the bellows when mounted:



After this short introduction, we get to the business of the day. Of course, I had to test this setup and took my usual round, the most of which I'll skip this time. After the round I went to have the usual beer and while sitting there decided to take a look at the bokeh highlight behaviour of the RR. The scene in front of me looked like this:



I took three defocused photos simulating different subject-to-background distances - without any subject:



On the left, I focused rather near the background, and the result was a very distinct bright edge on the highlights. At an intermediate distance, the highlight bokeh was a very good Gaussian one, and finally, focusing rather far from the background, I got an almost neutral bokeh, on the right.

I think this series explains some of the anomalies we have observed with many lenses, i.e. the fact that even the lenses with a reputedly good bokeh will occasionally produce a rather restless one or even a bad one. The quality of the bokeh isn't entirely a function of the lens but also of the exact situation where a photo is taken, the relationship between the lens-to-subject and subject- to-background distances relative to the focal length of the lens.

The RR isn't very sharp, it is also rather slow at f/7.7 and has a low contrast, but the bokeh it produces is quite exemplary, more often than not. Here are a couple of examples:





More photos with the newly remounted RR at http://galactinus.net/vilva/retro/eos350d_rr2.html

Veijo


PostPosted: Sat Oct 06, 2007 2:42 pm    Post subject: Re: An illuminating bokeh test Reply with quote
vilva wrote:
...took my usual round... After the round I went to have the usual beer.. .


Very Happy That sounds great. A nice habit. Wink

Thanks for this interesting report!


PostPosted: Sat Oct 06, 2007 8:44 pm    Post subject: Reply with quote
Yeah, I suspected something like that (that the highlight bokeh may change in function of the distance from focal point), but your test shows it clearly.
It'll be interesting to repeat this test with some contemporary lenses.


PostPosted: Sun Oct 07, 2007 5:44 am    Post subject: Reply with quote
Aperture also plays a significant part?


patrickh


PostPosted: Sun Oct 07, 2007 8:09 am    Post subject: Reply with quote
patrickh wrote:
Aperture also plays a significant part?


Yes, certainly. For the best bokeh, you should stop down, use small apertures. A large aperture has a shallow DOF, and things get soft very quickly behind the subject, but this DOF related softness isn't bokeh, and if there are suitable objects or highlights in the relatively near background, you may get a very prominent restless bokeh, often with rather strong CA. With a small aperture, the critical zone is deeper and the softness further away, but the restlessness usually isn't too conspicuous and the probability of having a disturbing amounts of CA is much lower. The f/7.7 RR has probably the best bokeh among my lenses, the way I usually shoot with them. Of course, its inherent softness also somewhat helps alleviating the very worst bokeh phenomena.

We often use fast lenses in order to get a soft background, to separate the subject from the background, but under some circumstances we must compromise and use a slightly smaller aperture in order to avoid a bad bokeh caused by objects between the subject and the main background, a slightly more distinct background may sometimes be the lesser evil. The absolute separation of the subject and the background many people are striving to achieve is possible only when there is a sufficient physical separation to start with. With a continuum of objects behind the subject, it simply isn't possible, and I think it's better to retain the continuum and strive to have a good bokeh within it .

Veijo


PostPosted: Sun Oct 07, 2007 8:23 am    Post subject: Reply with quote
Orio wrote:
Yeah, I suspected something like that (that the highlight bokeh may change in function of the distance from focal point), but your test shows it clearly.
It'll be interesting to repeat this test with some contemporary lenses.


It isn't merely the highlights, also the bokeh behaviour of other objects in the background depends on the relative distances. There is, e.g., a good example in your very nice Smile autumn photos, Photo #22. The kind of near background bokeh you have there can be very distracting, even to the degree of spoiling a shot. On the other hand, it can sometimes produce aesthetically pleasing results, almost like some slightly stylized painting.

Veijo


PostPosted: Sun Oct 07, 2007 4:03 pm    Post subject: Reply with quote
vilva wrote:

It isn't merely the highlights, also the bokeh behaviour of other objects in the background depends on the relative distances. There is, e.g., a good example in your very nice Smile autumn photos, Photo #22. The kind of near background bokeh you have there can be very distracting, even to the degree of spoiling a shot. On the other hand, it can sometimes produce aesthetically pleasing results, almost like some slightly stylized painting.
Veijo


Thanks. Yes that's also true. One has to understand if the most important factor is the physical distance from the film, or the relative focusing position of the lens. One thing I always noticed with macro lenses, they all have great bokeh, cheap ones and good ones. So my suspicion here is, that more than the distance object-film, what really counts to make bokeh smoother is the relative focusing distance of the lens. In other words: I may have two objects next to each other, a man and a flower, and I may have background objects both placed at, say, 30 meters from the subjects. I would like to test this in fact... what I suspect is that if I photograph the man with a 50mm normal lens at a typical distance for that focal lenght (like 0,50 m), and then I photograph the flower with a 50mm macro lens from a distance of say 0,1 m, (of course using the same aperture value), the distance of the background objects placed at 30 meters will change only slightly (30,5 meters in the first case, 30,1 in the second), but the resulting bokeh may probably be much smoother in the macro shot - I repeat, this is my suspicion, I have not tested it, I only reason from my experience - therefore I suspect that for the quality of bokeh, the relative focusing distance of the lens may be more important than the actual distance of the background objects from the camera.


PostPosted: Mon Oct 08, 2007 1:14 am    Post subject: Reply with quote
I got this lens last week.. need to make the assembly/mount..
Thanks for sharing the results..
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