Star Trek, I mean Trail

Star trails have become a popular 'right-of-passage' type of photo for new photographers to attempt. They require some know-how and access to an area with minimal light pollution, however. So, living east of San Francisco, I can see about a dozen stars on a dark night. Capturing a star trail at home would not be feasible. Over July 4th, I was in Grass Valley, so I pulled an over-nighter and got 254 30-second images for my digital star trail. I also captured a film star trail. Here's the film image:


This was shot using 100 ISO Agfa film Next time, I'll try this with 400 ISO. The 100 exhibited poor star capture. It managed to capture the hills, though, because this was a four-hour exposure. Also, next time, I'll have a graduated neutral density filter to use to darken the lower landscape.

My camera for this was one of my Pentax K2 cameras with my Sigma 35-80mm, set at 35 and pointed north-ish. One risk of long exposures is light leaking onto the film through the eye piece, so I borrowed the eyepiece cover off my KM or K1000 (I forget which) and taped it in place so I wouldn't lose it. Then I remembered I needed to compose the image, so I took the cover off, composed the image, then re-placed it.

To prevent camera shake, I used a decently sturdy tripod and placed it in a protected area away from wind. This was the third and longest of my film images, taken after the moon set.

Taking a digital star trails image is a slightly different and requires multiple images. Digital sensors, unlike film, heat up and leave 'hot pixels' on the sensors after a while. Ultra-long exposures can also damage sensors, I've read, though I can't verify that empirically.

There are some pieces of gear you'll need:

1- A digital SLR or other digital camera with manual settings.
2- A sturdy tripod
3- An intervalometer (unless your camera has one built in.)

My Pentax K-7 has a built-in intervalometer for up to 99 images. As of this blog's writing, cheap, new intervalometers that allow up to 399 images can be purchased on eBay for $12-$20 (USD). This allows you to take hours of photos to capture things like star trails or experiment with stop motion.

I set my K-7 to 30-second exposures with five seconds in between. I should have left no more than two seconds in between as the five-second delay left gaps between the stars that were difficult to fix.

So this is the star trails image. Once I had the 254 images taken, I loaded them in Photoshop as a stack, auto-aligned them (which took hours and turned out not to be needed, since all the images were taken on a tripod-mounted camera. Then I had Photoshop blend the images. I experimented with various layering and blending methods, and arrived at the image above. Not hard, but time consuming.

Well, it's not 100% accurate to say I arrived at the image above. I had lots of little gaps between the stars, so I had to make a copy of the stars layer and rotate it. In order to rotate it, I had to do some geometry to calculate the rotational axis, which was WAAAAAAAAAAAY off the side of the image. I didn't get it quite right, so I needed up needing two layers (one for the outer rings and one for the inner.) You can see in the top middle where the two layers don't exactly align.

If you don't have Photoshop, there are a few free or inexpensive software options. Basically, if you have a decent tripod and decent DSLR (or entry-level DSLR and an intervalometer), you can make a star trails image. I do suggest Photoshop, though, as it allows you to remove the hot pixels that will show up on your image.

Spanish-American War Memorial

Wednesday sent me down the F line toward Castro and while I was there I decided to stroll into a pre-demolition building to photograph it before it's pulled down. The interior shots were painfully boring, so I'll spare you. However, at that intersection -- Dolores and Market -- is the San Francisco Spanish-American War Memorial. So I took a few shots of it.

On an unrealted side note, the F line toward Castro goes through some seedy areas. So now, when something is heading in a bad direction (such as a mad dog at a child), I refer to it as 'taking the F line toward Castro.)


1/125th, f8. It may not look it here, but this statue is 26 feet tall. It's a 16-foot-tall bronze masterpiece on top of a 10-foot-tall granite slab. Here we see Roman Goddess of War Bellona and one of the two American soldiers depicted in the statue. Bellona rides Pegasus. I read on Wikipedia that it was hard to get Bellona and Pegasus to model for the sculptor since they're both very busy, despite the fact that no one worships the Roman gods anymore.


1/500th, f2.8. OH MY GOODNESS IT'S GOING TO TRAMPLE ME! Not really. It's bronze.


1/125th, f8. Oh, hey someone actually got trampled. Maybe that joke above wasn't so funny.


1.359th, f4. To end on a light note, seeing as how someone got stomped by a horse in the last two photos, let's ponder this establishment, and muse on what they sell. More importantly, let's ask who they sell to. I picture their patrons walking down the street and seeing the sign.
'Liquor and groceries,' the patron may think. 'What was the first one? Well, I don't need groceries, so I'll keep walking.'
Now imagine the same scenario with the above signage:
'Liquor, groceries, and liquor,' the patron may think. 'Hot diggity! I could go for some liquor. What were the first and second ones? Oh well, I should go buy liquor.'
This sign is ridiculous! But at least we know what they really want to sell.

Special Edition: Golden Gate Park

Last Wednesday I did not get to take a camera out, so fortoday's post I'll share what I had originally planned to save for this Saturday as a special post. Instead, you can see these photos today. As is normal for Saturdays, I don't track the lens and film combinations towards the goal of using a unique combination every day this year. Also, this trip had three films: Ilford PANF 50, Agfa 100, and TMax 400. The TMax is still in the camera and I'll finish it this weekend or sometime next week.


Trees at Sunset. Agfa film. The trees appear to be lit up because the sunset was casting them in red light. With a red filter, that light became lighter compared to the rest of the image. I expected this to be blurry as it was hand-held at about 1/15th or 1/8th of a second.


Urban waterfall, a creek at the National AIDS Memorial. When without a tripod, flat rocks will do nicely. Afga film.


Not entirely sure I care for the way the Agfa rendered these rocks. Maybe I should have used the red filter I brought that day, like I did with the other images above.


Another waterfall shot. Super contrasty. Agfa again.


Agfa, red filter, effectively making the forest seem even darker at dusk.


The one Ilford shot that turned out. I brought a roll marked "27" but it only had four exposures. This was shot resting on a fence on a four- or six-second exposure, f22. At 75mm, this may actually have been around f29 or f32. There were kids playing in front of the building, all effectively gone due to the long exposure.

How Filters Work: Part 1

Monochrome photography benefits greatly from filtration. But filters present a problem, too, in that they can increase glare and reduce image quality. Low-end filters, made of plastic or plexiglass, especially reduce image quality. Basically, using cheap filters on a nice lens cripples its performance, like putting a quarterback in a cast. Good filters can be $50 or $75 for a basic ultraviolet filter. Polarizing filters, $200. That said, I don't have any super-nice lenses, nor am I sitting on any $200 filters. I do have a set of filters I bought on eBay for $15 from a seller in China. They are of such poor quality that the dye job on the blue filter is not even consistently dense. That said, the results below are not going to be as dramatic as could be achieved with good filters. Also, the results below are simply for illustration of basic function. That's why they're a fairly boring image repeated over and over.

Firstly, here is the test chart I used for these samples.


It's important to understand how this will look rendered monochrome.

This was taken with Pro Max 100 ISO film. Now, had I known last week what I know today about Pro Max, I would have used something else. Pro Max, apparently, is rebranded Agfa. Agfa stopped making film in 2004, but apparently the company they used to make Agfa brand film still makes the same film for resale as generic brands.

All monochrome films see color. A monochrome film's ability to see color is called the spectral sensitivity. In fact, most films have spectral sensitivity charts posted online somewhere on the manufacturer's websites. Here is a link to a PDF for a film I'm fond of: Ilford PANF 50 ISO. The first page of this PDF has the chart you'll want to at least glance at before reading further.

So let's understand exactly what Ilford tells us here about their film:

I've reproduced (without permission but also hopefully without hurt feelings) Ilford's chart. This chart does not tell the whole story and you should visit Ilford's website and use their guidance when you use this film. That said, the numbers along the bottom are light in wavelength. The levt side, up to about 320 nanometers (nm), is ultraviolet. That's light that we can't see, neither can this film. In fact, UV light can't really penetrate glass. So those UV filter, they provide no additional benefit for your images.

PANF 50 begins seeing light in the dark-blue and violet range. It sees light up to the reds, the 600nm range. Infrared, which humans can't see, begins with near-infrared light at about 680 or 700nm. So this film also cannot see infrared light. The peaks and valleys along the spectral sensitivity line tell you how much each color registers on the film. The higher the peak, the lighter more sensitive the film is to that color, the lighter it will appear on the film. So this curve tells us that if a field of light, from left to right, from 300nm to 800nm were projected at the film, that it would see from dark blue up to red. Further, this tells us that dark blue and dark red would be the darkest shades. Green (500nm) would be the darkest of the middle tones. Orange (600nm) would be the lightest. We see that because the height of the line on the chart correlates to how close to while the film will see a color.

Note that all films have different spectral sensitivities. That means that the same film camera can shoot the same scene a dozen times in a day, each with a different film, and get a dozen different results. Well, that's one advantage for film over digital -- a film camera is as versatile as the film inside it. A digital camera is bound by it's sensor's parameters.

So how this effect film when used with a filter is thus: A filter cannot add light, but it can block light. A red filter is not a red-adding filter, but an everything-but-red-cutting filter. That means a red filter allows red light through but blocks blue, green, purple, yellow, and orange in varying degrees. The amount of non-red light a red filter cuts depends on filter quality, tone, density, dye composition, and so forth. Lots of factors that are too specific for this general conceptual discussion of filters. For this post's purposes, understand that colored filters allow their color to reach the film but prevent other colors.

How does this affect monochrome photography, though. Looking at the spectral sensitivity chart above, adding a red filter would suppress all the wavelengths left of about 625nm. Therefore their curves would be pushed downward. On film, everything not red would appear darker. The further from red that color is, the darker it would appear. Blues would be near-black. Greens, dark charcoal. Yellows, darker gray. Orange, less effected but still darker. Reverse that and put a blue filter on, you'll have near-black rendition for reds, darker oranges, gray yellows, and less-effected greens and purples.

So let's see this in practice. Here again is the test chart without a filter.


You'll first notice that it appears to have greater contrast. It does. Notice next that the blue and green are much darker than without a filter. The red filter I used is more of a magenta-ish color, so it does not affect blue as greatly as it should. Comparing the two charts, you can see how the color tone is altered between the two images.


Here the blue filter has made the green darker and the cyan near-white. That's because this blue filter is particularly light colored (and generally poorly dyed.)


And here is a green filter test shot. You'll see a variation on a theme here. Also, these represent the three prime colors for light -- red, green, and blue. Other colors, obviously, compose the visual spectrum including yellow, orange, purple, and brown. The next images show the chart rendered through various non-prime colors.


Orange filter


'Tobacco' filter
This filter is actually an 'artistic' filter meant to give a quick and dirty sepia cast to color images. God only knows why it's on a rotating base. Man that makes it hard to get off a lens.


Yellow filter


Purple (FL-W) filter
This filter is actually used to correct color cast in fluorescent light. Basically, daylight color film can't be used in fluorescent light without casting everything in sickly green. Slap an FL-W (fluorescent white) filter on, and outdoor film can be used indoors. It's not really a color-correcting filter for monochrome photography.

So you can see, scrolling through the images above, that filters change how monochrome film sees colors. What does that mean in practical application, though.

For decades during early photography, the sky rendered white and only white on film. Cloud photography was impossible. Then came yellow, orange, and red filters which darkened blue hues in varying degrees. Red, of course, provided the most dramatic effect. This led to images with dark skies that fundamentally changed how photographers approached including the sky in their images.

Colored filters also allowed for early color photography though a process called color separation. We'll look at that tomorrow in Part 2 when we repeat this experiment with a DSLR. Do CCDs see color differently than film? We'll see.

So colored filters narrow the wavelength band reaching the film. By separating a real-life scene into the various wavelength bands, photographers captured the first color images and printers created the first colored prints. The process is not dissimilar from a color laser printer where a sheet of paper passes under four toner drums -- cyan, magenta, yellow, and black. Each drum prints only part of the image, leaving everything that is not the drum's color blank. Color separation photography and printing work the same way. Three photos taken with three filters -- red, green, and blue. Each negative is printed on the same paper with the corresponding color. In fact, tomorrow you'll see a color-separation recreation of the test chart above. If nothing else, it demonstrates how cruddy these filters are.

So with that demonstration, let's conclude for today by looking at what happens when we combine filters. Imagine, first the result. Light encounters a blue filter. Much of the non-blue light bounces away. Then it encounters a red filter, blocking again much of the non-red light. So greens and yellows ought to be dark black. Reds and blues ought to be the same basic tone. Let's see.


That is about what that looks like to me.


A green and a yellow filter


A blue and an orange filter