Adjustable bokeh with Triotar

[vilva]

While examining the 4/135 Triotar, I noticed that the front cell can be screwed off, e.g. to facilitate access to the aperture blades. The threads are very fine, and the threading is rather long so that the cell can be gradually moved several millimeters forward like in a front cell focusing lens. I began to wonder what optical effect this had and started experimenting. Infinity focus was lost, of course, as the helicoid doesn't offer enough travel to counteract the front cell focusing effect. What about the bokeh? Well, here things get interesting. The bokeh of the Triotar isn't bad to begin with, there is just a slight bright edge. Here is a test shot:



With the cell about 2-3 mm out, the bokeh turned out to be Gaussian:



The change in the OFF verticals is quite interesting. At first it seems they are better in focus despite being further back, but this is just the effect of the Gaussian distribution. The center (i.e. the top of the distribution) is more distinct, especially evident in the light vertical, and the edge is wider. With a normal subject, e.g. flowers or twigs, this would mean that there wouldn't be any distinct edge "bands" anymore, all the linear edges in the OOF region would soften out.

This may explain the good bokeh of my front cell focusing 4.5/105 Radionar. In fact, this means that the Radionar bokeh can perhaps be improved even further if I set the front cell focus at the near limit and use the macro bellows or the variable close-up ring for focusing. As for the Triotar, I have to make a choice between having infinity focus and having an optimal near field bokeh -- no need for bokeh at infinity as there is nothing OOF past infinity.

Veijo

PS. Attila, the problem with your Triotar may be just due to someone cleaning the aperture blades and not properly re-inserting the front cell. This would explain the lack of far field focus.

[Abbazz]

Mmm, very interesting pictures, Veijo. Thanks for sharing. Could you please post some resized full frame pictures?

I have some old 6x6 or 6x9 cameras with front focusing triplet lenses ("Zeiss" Novar, Agfa Apotar, Angénieux U1) and I will try them on a bellows.

Cheers!

Abbazz

[Richard_D]

Fascinating experiment - thanks for sharing.

[vilva]

[Nelson]

i made the same test with pentacon 135.

When i dissambled my pentacon 200 i also noticed a sort of "soft focus" by unsecrewing the front lens.

I tried to do the same on 135mm but failed.

[ChrisLilley]

The gaussian distribution is clearly superior. I suspect that a position that is maybe 3/4 the way to your gaussian position would be even better, reducing the central highlight.

Also, from your experiments and thinking back on photos that I have disliked, the type of busy, squirmy bokeh that I most hate is probably caused by overlapping and reinforcing edges.

I have sometimes wondered about taking two shots, one with and one without an (in-focus) subject; using the two to generate a mask for knocking out the background; convolving in various ways the background image, and then inserting the masked-out foreground subject.

[hacksawbob]

Sounds a little like the Orton effect?
http://pcin.net/update/2006/11/01/the-orton-effect-digital-photography-tip-of-the-week/

[ChrisLilley]

[vilva]

[vilva]

[patrickh]

I wish I understood even some of what you are talking about.


patrickh


PS I agree with Chris about the spiky/busy OOF. Dont like it either.

[ChrisLilley]

[Ballu]

[valli]

I've bought a Triotar very recently and I'm using it on the new D7000 with its APS-C 16MP sensor. Thus, the lens becomes a 202mm lens.

Anyway, the M42 adapter I have had an _awful_ infinity glass inside which I got rid of earlier as it affected a Takumar when wide open (f/1.4).

For those unfamiliar with M42 adapters on Nikons, you lose infinity focus (this Tritoar can focus maybe up to 15-20m - haven't really measured it) but I think it's also affected the depth of field as it's much more shallow.

Check out this example, there is a red glass about 0,5m behind the tap then a green bottle of olive oil 20cm further away (the white/green highlights you see just below the tap)

My point is that the bokeh is already in full effect at such a close distance (0,5m) giving the lens a macro like quality - not that I mind. Wonderful lens that deserves a clean up at the local camera repairman, as it has a bit of a rough focusing ring.

[Attila]

Welcome Valli!

[valli]

Cheers Attila! Awfully quiet here, isn't it

Did a few more tests with the Triotar and I'm very happy with it. Haven't bothered mounting the glass back on the adapter to do a side by side test of the bokeh but I suspect I'm right.

The way it's set up now it's a wonderful macro lens, especially for its price!

[gillbod]

thanks for posting this. looks interesting.

particularly, moving the front element of the triotar looks like it messes around with spherical abberration particularly. as a side effect, it does give a glow to the in-focus subject too.

nikon's dc lenses do similar things (although i'm sure a heck of a lot more sophisticated than unscrewing front elements) but the lenses are also stopped down according to the amount of spherical abberation introduced.

long post cut short: it would be interested at messing around with different amount of unscrewing and stopping the lens down.

i might have to get myself a triotar...

[PaulC]

That's a very nice shot, Valli.

[buggz]

This is the Carl Zeiss Jena Triotar?

[vilva]