Old castles in Slovakia

There are 425 castles and 180 forts in Slovakia, more than in most European countries. The castles were built since the twelfth century, originally as defense posts, later as domicils of the upper echelon. The cold and dark fort compounds were not particularly homy and pleasant, so in 16th century the nobility started to build more comfortable castles and mansions below the forts. Most of these structures were attacked, destroyed, reconstructed, repeatedly burnt, but many buildings have survived and prospered till the modern days.

As to the photographing many of these monuments, what lenses should one use? Although a wide angle lens seems to be the most logical choice, it depends very much on the location and surroundings of the castle. When you get close to the massive structures or even inside the castle grounds, you’ll need extreme wide angles. If it is possible to photograph the castle from the grounds below, I find a prime 50mm lens or 17-50mm zoom very handy. Both lenses can be used very effectively also for panorama stitching. If the castle is perched high on a mountain and the visibility is good, I try to photograpraph it on my approach several kilometers away with a long lens. This gives me a totally different perspective than photographing it from just below the castle.

Let’s start with Bratislava castle, the seat of national government. The recently renovated rectangular building with four corner towers stands on a rocky hill above the Danube river. Over the years the city grew around the castle and today the castle is in the middle of the city. It’s an easy walk from the downtown or you can take a ride in a cute tour minibus.

The castle terrace provides an excellent view of Bratislava, and in good weather even views of two neighbouring countries – Austria and Hungary.

Just slightly over 100km northeast of Bratislava lies a completely different castle, in the village of Beckov. This castle was built on a 50m limestone cliff which was formed a long time ago by the river Vah. This view was captured with a 70-300mm lens, at 110mm.

A close-up from just below the castle walls with a 50mm lens produces quite different view. Although presently, there is no access to the castle grounds, you can walk around the castle, and there is a nice view of the surrounding countryside from near the entrance to the castle.

Another hour away to the east, is perhaps the most famous castle in Bojnice, visited by hundreds of thousands of travellers every year and it is also a popular filming stage for fantasy and fairy-tale movies. It is a romantic castle with some original Gothic and Renaissance elements, located in a pleasant town with a nicely restored town square, beautiful gardens, small zoo and other tourist attractions.

Filakovsky hrad is located in the southern Slovakia, just a few kilometeres from Hungary. It was built originally as a defense fort against Turks, but they invaded it and held it briefly in 15th century. Part of the castle is a massive pentagonal bastion that has been re-roofed and exists in a slightly modified form till today.

same ruins, just from a little bit closer:

Going straight up north, in the northern part of Spis near Polish border, is another old castle in the town of Stara Lubovna. This large castle was built originally in the 13th century on a limestone cliff in the 700m elevation with a large tower and a gothic palace. In 1553, the castle was completely burned. In 16th century, a new palace and a chapel were added in baroque style. Inside the walled compound, there are three courtyards and on the grounds there is an old and huge linden tree, about 25 tall with a 4.5m diameter, estimated to be 300-400 years old. The town below is a well known spa resort in a beautiful mountain setting with a skanzen and other tourist attractions. This photo was captured at 180mm from the east side.

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Two more castles in Slovakia, Spišsky Hrad and Šomoška, have been covered and shown in previous posts.

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Effect of lens sharpness on panorama stitching

Recently, as I was culling my latest batch of images, I noticed a focal asymmetry in one of the images photographed by Nikon D300 and Nikkor AF-S 70-300mm VR-G lens. The building in the image with its bricks and windows makes for a very good test subject. I was standing parallel to the building, across a river about 100m from it, and although its corners are technically slightly further from the camera than its middle portion, the DOF at that aperture should still portray everything in the focus.

The EXIF data shows the following info: ISO 200, 110mm, F5.6, 1/1000s. Shot under almost ideal conditions, one would expect a perfect picture. Captured at the minimum/base ISO, the zoom lens was in the middle part of the barrel, aperture close to the lens sweet spot, and the shutter speed more than adequate for this focal length. To my surprise, the left third of the image was badly blurred relative to the middle and right portion of the image (see below – and click on the images to viwe them in full 100% crop size).

Left Image Segment:
notice the blurred bricks and windows, with the blur getting stronger toward the left edge. The building behind, although not that much further, is totally out of focus.

Middle Image Segment – everything sharp

Right Image Segment:
As sharp, if not sharper than the centre portion.
Notice the sharp bricks and windows, and even the buildings behind are still in focus.
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Obviously, there is a problem with the actual lens or alignment of the camera sensor. Very likely, both. Focal microadjustment by LensAlign won’t help in this case, since the center of the image is already sharp. But that is a topic for another article.

As disturbing as this situation is, it is not that uncommon. Many lenses will show a dropoff of the sharpness towards the edges. As a matter of fact, one reason why the rotational panoramic cameras take very sharp pictures even with less than stellar lenses, is the fact that they utilize just a narrow slit in the middle of the lens that is always sharp (unless you use a really bad copy of a lens).

What does all that have to do with panorama stitching?
Let’s assume, you just shot three consecutive segments in horizontal orientation that you plan to stitch. Well, most stitching programs will attempt to use the leftmost image as the left portion and the righmost image as the right portion of the panorama. The middle image will be inserted somewhere in the centre, not necessarily along straight vertical lines. Makes sense, n’est ce pas?

Unfortunately in a situation, as described above (the lens is less sharp in the left third), if you use an automated stitching program, you’ll be dealt an unsharp half of the left image and possibly also an unsharp left part of the middle image. If the lens is sharp on the right, the right side of the panorama should turn out OK. Now, if you take five or seven segments instead of three, you may get slightly better results, but not that much, since that first (leftmost) image will be used almost in its full size anyway.

So what to do if you want a sharp panorama? F8 or F7.1 aperture may yield some improvement when it comes to the optimal lens aperture, slightly greater DOF, and lower diffraction (depending on the format of the camera), and of course, factory calibration of the lens and camera is in order. But nevertheless, most lenses will exhibit less than ideal sharpness on their extreme edges, so the basic problem remains.

One practical solution is to shoot more segments (i.e. 5-10 or even more, rather than just 3-5), overlap them generously at 30-50 percent, and crop all these images on both sides, so that you retain only the sharpest middle portion of each image. Now YOU are in control! Feeding the sharpest portion of the images to the stitching software will result in a much sharper pano. Just be careful not to lose the overlap when cropping.

Another trick is to compose the first (leftmost) segment in such a way, that its left third will be to the left of the planned edge of the panorama and consequently trimmed off (planned throwaway). Coincidentally, we had to do it also in the old days of rotational cameras to allow the motor to ramp up to its proper speed.

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