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08-28-2010, 06:09 PM   #1
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Pentax K 28mm f3.2 Shift Lens - Slightly Different Approach in Use

A bit over a month ago, I acquired an older Pentax K28mm f3.2 Shift lens. Over the last year or so, I had a couple of other opportunities, but I passed because of the crop factor that just narrows the lens too much for architecture. Anyway, this time I pulled the trigger (the price was right) and picked up the lens - off the marketplace here on the Forum. Perfect condition, looks like it was factory fresh, no wear to note, no brassing- just perfect.

I have been somewhat busy in my spare time using the lens and figuring it out - there is a learning curve associated with it. Normally, you use it for perspective control, and/or panoramas. For panoramas, you take a normal image, shift the lens off to one side, take second image, then rotate the lens 180 degrees, then take a third image. Stitching them all together produces a very nice panorama.

The old Pentax User's Manual explains it to a reasonable degree.
  • The normal field of view of the lens is 43 x 29 degrees (landscape, un-shifted)
  • Shifted (3 image stitch horizontal) is 78 x 31 degrees (an increase of 93% of frame)
  • Shifted (3 image stitch vertical) is 45 x 68 degrees (an increase of 139% of frame)

Now the lens has a 12 position rotation (just like a clock), where by you can rotate the lens 30 degrees per step, so as to get into the opposite position for the horizontal or vertical stitch shots (6 steps from the initial position). But this brings up an interesting process. What if you take an image at each of the 12 positions steps and then stitch them all together?
  • Well the stitched result is an image that is 78 x 68 degrees (K20: 9300 x 7600 pixels)



This also enables you crop in a number of ways. The traditional horizontal crop (red rectangle), vertical crop (purple rectangle), and also a couple of somewhat non traditional crops (green rectangle - solid line or dotted line).

Especially with the non-traditional crops, you are able to bring in additional height and width (all of which can be perspective controlled). This should at least to some extent make up for the loss of wide angle caused by the crop factor.



This can be replicated using a Pano head (like a Nodal Ninja), as essentially a 2x3 or a 3x2 row x column stitch. However, since this is a shift lens and provides perspective control, the extra added attraction is that - especially for the foreground, it is just not the lens rotated pointing down thereby pulling the bottom into the resulting image, but with the lens shifted down vertically (maintaining a unchanged sensor orientation), the foreground is in the proper perspective.

This bring up some additional and very interesting opportunities, especially with landscapes. In particular where the foreground drops away as in the Grand Canyon, Bryce Canyon, Horseshoe Bend, etc. Also, with architecture, you should be able to compensate for the crop factor by stitching in this way, thus getting additional width AND height - as opposed to the traditional width OR height. This 12 image stitch essentially provides a near 35mm full frame result.

I happened across this when I did not have the lens set up properly and I took a horizontal stitch on the diagonal, which started me thinking about the possibilities. Also, here is a very good overview and explanation.

The bottom line is that, it now appears to me, that this lens is a bit more useful that what it might appear. Yes, it takes a bit more work for the additional shots, but it looks like that the crop factor may be factored out in this case.

Now if you sense that there is not something perfect with the image, its not the lens. I just figured out that the sensor in my K20 is going, as its getting very noisy, especially with over 1 second shutter times - and 30 second is bad. I am having to denoise the images to get something that is reasonable at ISO100. So, I am going to have to send it to the Vet's and have it repaired. The additional 2 year warranty from Pentax will come in handy.




Last edited by interested_observer; 08-13-2011 at 04:46 PM.
08-29-2010, 06:46 PM   #2
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Very interesting, I had not thought about such use and basically relegated the lens to the "collection"! Now I better take it out for a spin!
08-29-2010, 10:58 PM   #3
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Hi Ole,

I am finding the lens interesting and challenging to say the least. Interesting in that I can mitigate to at least some extent the crop factor, and getting a much wider and taller image (the resulting additional image real estate is great). But I am also finding that the lens presents a challenge in terms of capturing the lighting. Ben Edict touch on this in a previous thread, where he indicated "Then colour finging is severe, but that doesn't matter as the image will be completely washed out and out of focus apart from the immediate center..."
Shooting directly in to the sun, just is a non starter. Also, a bright sky tends to be washed out to a large extent. I am starting to wonder if a) its a side effect of my K20D sensor (which is going in terms of a great deal of additional noise), or b) its an artifact of the difference between film and an electronic sensor - where by the light is moved around in a slightly different than normal manner.

What I mean by this is with the lens shifted, the light path through the lens barrel is normal until it hits the K bayonet mount area where the shift takes place. This has the effect of having the light hit the majority of the digital sensor's pixels at an off nominal angle. Since this is a film lens, none of this has been engineered for a digital sensor. This is just my own speculation. My last engineering optics class was 40 years ago in college. With the lens shifted, the view through the viewfinder is, well I will not say obscured, but it is something slightly different than what you see when its not shifted. I am speculating that the light will thus have a slightly altered path to the camera's sensor. I have seen some really great images from this lens, so I know what its capable of. I just am trying to figure out how I can use this to achieve something similar. It all comes down to trying to figure out and understand the light and the lens.

I am sending my K20 to the Vet's for repair, so it's back to my K100 and I will see how that sensor handles this - CCD vs CMOS.

The other thing is that this lens, even though its a f3.5 lens, it really needs to be stopped down to f8 to f11. Even the Pentax User's Manual cites this need. I also have been shooting in the evening, so between the reduced ambient light, the sunsets, my apparently ailing K20 sensor, and needing to severely stop down the lens' aperture, then with trying to figure out how the lens handles the lighting situations - its has been an interesting time.

There are some buildings in the area that I want to go try this out on, in terms of both the perspective corrections and the additional landscape effect from the panorama using the additional real estate. I had intended to try it out this weekend - however, it just did not happen as planned.

08-30-2010, 01:37 AM   #4
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I think you may be on to something with your light path theory. Also, the narrow mirror box could shield some light as well when the lens is shifted one would think. You don't heppen to have an *istD laying around? The *istD has a full frame mirror box.

The lack of contrast could be due to reflections back and forth between sensor and the lens.

08-30-2010, 06:47 AM   #5
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Unfortunately, I do not have an *ist. I went from my old Spotmatic II, I picked up in the Navy to the K100.

The suggestion that the narrower mirror box may be a contributing factor, has merit - I believe. When shooting a panorama, with the lens shifted, the washed out side occurs on the side of the image, that the sun (or light source) is on. So with a narrower mirror box, it would tend to diminish the uniform distribution of light. The opposite side, when the lens is shifted, would get light, just at an increasingly acute angle to the sensor's pixels. The reduced size of the mirror box, I never knew about, nor considered. Essentially, it would be a type of vignetting (with an opposite effect - potentially concentrating the light rather than blocking it, on the side that is shifted), just not uniformly applied, but radically skewed to one side. I have to give this a bit more thought. This would also, tend to indicate as to why stopping down the lens tends to work better.

I might just have to go out looking for an older *ist body to acquire....

Also, this occurred to me last night. Not that a 645 or 67 would need any additional real estate, but Pentax produced a SMC Pentax 67 75mm F4.5 Shift. Using this lens and rotating it through the various step positions, and stitching, would yield the same results, just on a much larger scale, due to the larger film/sensor frame. It would have some interesting results on a 645D (not that I would ever be able to afford such a luxury, myself), with the use of a Pentax 67 Lens to Pentax 645 Body Adapter #38454. Essentially getting 67 results from a 645 without any panning - just lens rotation (while maintaining proper prospective).


Last edited by interested_observer; 08-30-2010 at 07:00 AM.
08-30-2010, 05:22 PM   #6
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I think this lens would be better on a film camera, where the 28mm FL will be useful in architecture and you can benefit from the built-in filters.

Why don’t you pickup and old K-mount film body and try the K28/3.5 shift on it? Shoot a few rolls of B&W film and see what this lens can really accomplish.

Phil.
08-30-2010, 09:30 PM   #7
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Hi Phil,

Thanks for the suggestion, and it had crossed my mind before that maybe an old film body may be something good (other than my old Spotmatic II).

Anyway, I called Pentax today about my K20 body's sensor problem and then dropped the body by CIRS in the afternoon. However, while I was on the phone with Pentax, I asked a question about the light path and this shift lens. They referred one of their optical specialists to me, and their take on this was interesting.

Yes, with the obvious light path shifted, he though that the sensor would act somewhat differently. The digital sensor is much more sensitive that film to straight on light. Since the optical lens center is moved off to the side, the straight on light has been shifted from the sensor center to the extreme edge, the edge nearest the light would probably be overexposed, while the other side with indirect light would be underexposed to some degree - depending upon the lighting situation (thus the lack of contrast). This was somewhat the same as experienced with film. Rather than using spot metering, the use of averaging would be better, however averaging is still somewhat biased to the center of the sensor. He thought that manual shooting would be better, with on the fly adjustments, across a number of exposures to determine the best setup. He was also interested enough (he had also been looking for a shift lens too), that he offered to send the information to Japan, to see what they though about the shift lens on a digital body, in terms of the light's path and unevenness of the exposure. Obviously, with a shift lens - and an old one, everything is in the hands of the photographer - that I know and accept. I was interested in what he was saying about the sensor's sensitivity towards direct vertical light striking the pixels, vs. the more acute angle to the sensor on the other side of the sensor. The mirror box's size would probably play a smaller part in all of this, in that it should not be reflecting that much light.

So, with this additional information, thoughts and suggestions, I have a number of things I would like to try with this lens. One thing I do like is the immediate feed back of digital. I was never any too good in the darkroom.

08-31-2010, 04:50 AM   #8
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That’s great that you were able to talk to someone at Pentax regarding the shift lens, an optical specialist no less.

I guess you will have to play around and see which metering system works best on your K20. I have only used the K28/2.5 Shift on my K2 & KX film bodies, which have centre-weighted metering systems. On film the biggest issue I have with this lens is underexposure, due to metering issues with shooting in the vertical position pointing toward the sky. I usually have to compensate one stop or so. Other than that it works very well in architecture.

I don’t develop my film either, as I have a few photo labs near by. So if you tried the Shift lens on a film camera then get a lab to do the developing and gets scans done at the time of processing.

Anyway good luck and I hope you find a solution, as it’s a fun lens to use.

Phil.

11-29-2010, 08:40 AM   #9
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IO, just purchased the lens from an ebay seller, and found your article. Your last post was in August. Have you discovered anything else in the interim? Mostly interested in using this lens for panoramics and landscapes. I'm in the process of switching from 4x5 film to my Pentax K20d (K-5 soon?). Any reason to think that the lens would behave differently on the K-5 (sensor box size issues, etc.).
11-29-2010, 11:04 AM   #10
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I didn't know it rotates! Damn, should have bought when I had the chance and budget... Oh well
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