STF mode in Maxxum 7 recreated for DSLR's

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.

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!

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.

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.

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

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.

Oh, that is exactly the point, that the points of light are moving... think out of the box. ;)