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STF mode in Maxxum 7 recreated for DSLR's

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photoman View Drop Down
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Post Options Post Options   Quote photoman Quote  Post ReplyReply Direct Link To This Post Topic: STF mode in Maxxum 7 recreated for DSLR's
    Posted: 03 November 2009 at 04:02
I recently was pining over the 135mm STF lens because of the beautifully smooth bokeh that it can produce. It manages to smooth out the bokeh of an image much better than pretty much any lens ever made. For those of you who arent familiar with the amazing bokeh of this lens, here is a website that gives a good comparison:
bokeh comparison

During my longing for this lens, I happened to remember that the Minolta Maxxum 7 had on it an STF emulator mode. This mode was supposed to give you a similar amazingly smooth bokeh on any lens that you owned. I'm pretty sure this was the only camera in the Minolta/Sony line ever to offer this feature. It was a great feature, but I dont think people really understood it well which is probably why it is no longer included in any cameras.

Well, I decided that I was going to make an attempt to manually recreate this feature on my a700. Here is how it worked on the Maxxum 7: The camera would take a sequence of 7 photos in rapid succession while varying the aperture for each shot. All exposures would be made on the exact same frame. The idea was to vary the aperture for each shot and then it would smooth over the circles from the aperture blades in the background.

I tried to recreate this by setting my camera up on a tripod and taking seven individual exposures of the same scene at varying apertures.   I then blended the images in photoshop so that each image composed 1/7th of the final exposure. Interestingly, it actually worked! The background is creamy and smooth smooth in the shots where I tried to recreate the STF mode.

I tested this on two lenses: minolta 50mm f/1.7 and an old Sigma 24mm f/2.8 macro

The aperture sequence for the 50mm was as follows:
f/1.7
f/2
f/2.2
f/2.5
f/2.8
f/3.2
f/3.5

Here are the results:

50mm STF mode recreated


50mm f/1.7


50mm f/2.5


50mm comparison




24mm STF mode recreated


24mm f/2.8


24mm f/4


24mm comparison



I like the results and can definitely notice a difference. I think the results would be even more interesting with lenses such as the 85mm f/1.4 or the CZ 135mm f/1.8.

Let me know what you think of these results.
 



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zk-cessnaguy View Drop Down
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Post Options Post Options   Quote zk-cessnaguy Quote  Post ReplyReply Direct Link To This Post Posted: 03 November 2009 at 04:31
Very interesting. Can you please explain your method for blending the images in Photoshop? I like the results you got with the 50/1.7 especially.


EDIT: just figured out how to do it. In CS4: File/Automate/Photomerge

very cool.

Edited by zk-cessnaguy - 03 November 2009 at 05:40
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wallyb View Drop Down
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Post Options Post Options   Quote wallyb Quote  Post ReplyReply Direct Link To This Post Posted: 03 November 2009 at 04:39
That is VERY cool. I never noticed the STF function for the few months I tried out (and loved) a Maxxum 7. I'm going to have to give that a shot!
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Post Options Post Options   Quote skm.sa100 Quote  Post ReplyReply Direct Link To This Post Posted: 03 November 2009 at 05:12
By 1/7th exposure, do you mean to say that you set the opacity to 1/7th and used overlay mode?
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photoman View Drop Down
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Post Options Post Options   Quote photoman Quote  Post ReplyReply Direct Link To This Post Posted: 03 November 2009 at 05:24
Here is how I did the blending. In one photoshop document, I created a layer for each of the seven images. The blending mode was set to "normal" for each layer. The blending was done by changing the opacity of the layers. The layers were ordered from "Layer 0" through "layer 6" with "layer 6" being the layer on top. Here are the opacity settings for each layer.

Layer          Opacity
Layer 6        14%
Layer 5        17%
Layer 4        20%
Layer 3        25%
Layer 2        33%
Layer 1        50%
Layer 0        100%


This results in each image making up 1/7th of the final image.   It doesn't matter what order you have the actual photos in as long as you arrange them so that the topmost photo has 14% opacity and the second topmost photo has 17% opacity... and so on.
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photoman View Drop Down
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Post Options Post Options   Quote photoman Quote  Post ReplyReply Direct Link To This Post Posted: 03 November 2009 at 05:27
Originally posted by skm.sa100 skm.sa100 wrote:

By 1/7th exposure, do you mean to say that you set the opacity to 1/7th and used overlay mode?


I just tried what you suggested and it gave me ugly results with ugly contrast and ugly color.
 



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photoman View Drop Down
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Post Options Post Options   Quote photoman Quote  Post ReplyReply Direct Link To This Post Posted: 03 November 2009 at 06:24
Open Letter to Sony: If anybody from Sony browses this forum, Why have you decided to not include an STF mode in your cameras? Please reinstate this mode in your cameras (firmware update). It was a wonderful feature that Minolta had and I see no reason to not include it.
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Post Options Post Options   Quote AlexKarasev Quote  Post ReplyReply Direct Link To This Post Posted: 03 November 2009 at 06:34
I also believe the STF mode goes well with Sony's philosophy of adding value to all lenses via the body (e.g. SSS)

I've written on this subject on this forum before. Even a single-shot STF should be possible, enabling it to be used handeld
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zk-cessnaguy View Drop Down
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Post Options Post Options   Quote zk-cessnaguy Quote  Post ReplyReply Direct Link To This Post Posted: 03 November 2009 at 06:38
Just tried a quick and dirty attempt...


50/1.7 wide open


50/1.7 composited STF image.

I'm very impressed how it works, especially how the specular highlights top left are smoothed out.

Well done photoman!

Edited by zk-cessnaguy - 03 November 2009 at 06:40
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Post Options Post Options   Quote wolfdagon Quote  Post ReplyReply Direct Link To This Post Posted: 03 November 2009 at 07:12
I think I tried the STF mode on my Maxxum 7 maybe once, but at the time I didn't really understand it. I now have the 135 STF for my A700, and i love it. It woud be great if they could implement the STF function in the A700 in firmware upgrade.

Great experiment photoman.
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Post Options Post Options   Quote albnok Quote  Post ReplyReply Direct Link To This Post Posted: 03 November 2009 at 08:11
It is easy to see how STF mode works on the Dynax 7 provided there is no film inside - open the film back and shoot while looking through the shutter.

I believe it shoots 7 frames at 1 stop intervals, thus:

F1.4 F2.0 F2.8 F4.0 F5.6 F8.0 F11

It does sound like it slows down considerably once it gets to the darker apertures, much darker than your 2-stop interval. Will record the sound to get an idea of the intervals.

Using the A900 I intentionally shot a closeup using my Minolta 50mm F1.4 Original, and the heptagonal aperture blades show very obviously. What is worse is that the heptagons maintain orientation as they stop down. Pictures are at home though. They didn't turn out as nice.

Probably I should try with 2/3rd stops instead so it's:

F1.4 F1.7 F2.2 F2.8 F3.5 F4.5 F5.6

I like the math you've done for the layer opacities - I'd been previously blending 2 pictures at 50% and guessing which of the pictures will take a higher precedence.

I still have a roll in my Dynax 7, waiting for when I can take it out with a tripod, and I'll do STF on night traffic. I know I've posted this somewhere but I can't find it.
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Post Options Post Options   Quote LetoAtreidesII Quote  Post ReplyReply Direct Link To This Post Posted: 03 November 2009 at 08:23
I can't see it working so well on night traffic since your subject isn't going to hold still while you shoot 7 frames...
a200 | Sony 18-70 | Sony 24-105 | 50/1.7 | Beercan | 5400HS
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albnok View Drop Down
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Post Options Post Options   Quote albnok Quote  Post ReplyReply Direct Link To This Post Posted: 03 November 2009 at 08:28
Oh, that is exactly the point, that the points of light are moving... think out of the box. ;)
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Post Options Post Options   Quote mhohner Quote  Post ReplyReply Direct Link To This Post Posted: 03 November 2009 at 09:32
Also note that with some lenses the focus shifts when stopping down. So the individual frames will not only have different bokeh and DOF, but also a different plane of focus. That's another advantage of a true STF lens.
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