Sunday, May 19, 2013

Astrophotography: M42 without a Mount or Telescope

this is our starting image, before processing.

You know how they always say gear doesn't matter?  Well, if you've ever tried shooting sports or events, you'll have found out that it does matter, quite a bit.  Deep-space astrophotography is the same way.  To do serious astrophotography of that sort, you need a telescope or a supertele lens, a camera with a good sensor, and most important of all; a tracking mount.  A tracking mount is, essentially, a heavy-duty tripod hooked up to a computer that is aligned to the north or south pole (this is known as polar alignment).  Those babies run around $700 for a cheap one worth its while.  You can build your own Equatorial mount, which is designed to spin the camera/telescope at the same rate of the Earth's rotation, for about $100; however they aren't very good for high-magnification (resolution) shooting because of their inexact nature.  Both of these will let you shoot extremely long exposures; from 30s to several minutes per frame without issue, but the former is expensive and the latter isn't the best (sharpest) there is.

That leaves us with  fixed tripod shooting, which severely limits our shutter speeds.  The rule is 600 / focal length · crop factor to prevent rotational blur, since the earth spins on its axis 24 hours a day, 7 days a week.  This isn't a hard rule, and you can experiment to figure out just how long you can shoot for on a given night, but it holds true most of the time.  Now, astophotography from a fixed tripod is a battle between magnification and exposure time, since to get a higher resolution image, you must use a longer lens.  The above frame (it's not a finished image, we'll call it a frame) was taken at 300mm on a 1.5x crop body.  Now, step one is to break out this awesome program known as stellarium and find what you're after in the night sky.  In my case, that looks like this:

peering out into the night sky at M42 with stellarium.
Using stellarium, we find our object, the nearest cardinal direction, about how high it is above the horizon, and other stars and Deep Sky Objects (DSOs) of note nearby to help us find it at night.  Once we've located it, step two is to make a plan (once you've done this a time or two, this step isn't really necessary).  In our plan, we need to gather every piece of information we can.  Mine looks like this:

  • Ideal shooting time, day/month/time, you can preview any moment of time in stellarium
    • 4/6/13 at about 9:45pm
  • What the weather is like at that time (very important)
    • Clear skies!
  • Equipment:
    • Nikon D5100
    • Tamron 70-300mm f/4-5.6 VC USD
    • Manfrotto 055xprob
    • Manfrotto 410 geared head
  • Location/travel time and level of light pollution:
  • Frame ratios, light/dark/bias, and if you need to reframe the target to finish capturing lights.
    • As many lights as possible (265)
    • A good number of darks: 50
    • Twice as many bias as dark: 100
  • post-processing workflow:
    • Shoot
    • Deep Sky Stacker (DSS)
    • Star Tools
Now, that's a lot of technical jargon, so let me explain some things before we get all confuse and quit.  In order to shoot DSOs from a fixed tripod, we need dark skies.  I'm lucky enough to live in a nice, rural place with dark skies, so I don't have to travel far.  Here is a superb map of dark sky locations across much of the western hemisphere, US readers can use it to figure how far they might have to travel.  Now, to image DSOs like M42 (which is the Orion Nebula, by the way) at a high magnification is going to take your longest lens, unless you have something longer than 300mm on crop (450mm equiv), at which point you can't possibly get long enough exposures.  Ideally, I'd like a 200mm f/2.8 lens (6x as much light can be gathered), or a 200mm f/4 lens (4x as much light), but this is what I have to work with.  Next up, frames.

Stacking is the process we use to reduce noise (and boy does it reduce noise a lot), every time we double our number of light frames, we halve the noise.  That means that with my 265 light frames alone I have already cut the noise down to around 1/16th the level it was already at, but we're not done yet.  Dark frames are used subtractively to cut down on the noise produced by the conditions shot in.  These include: exposure time, sensor heat, sensor model, firmware,and sensor amp noise.  You take them by simply putting on the lens cap and taking exposures just as you would light frames.  Using 50 of these we further cut noise levels, but we're still not done.  Next come bias frames, or frames at the same ISO, with lens cap on, at the fastest shutter speed, and if you're anal about it minimum aperture.  There is no possibility of there being true signal in a bias frame, so everything in it can be subtracted as noise.  We do all of this in DSS, which is free, or Registax, or any other stacking program.  After that we produce an output and edit it in other software, I use StarTools because it's very inexpensive and very powerful.  But first we have to shoot our data...

just imagine it's nighttime.
First you put the camera on the tripod, obviously, lens attached, and with hood on to prevent flare and reflections from the moon.  Ideally, the lowest tripod height is most stable, but I'm not about to get crouching down for it if it might not matter.  Once you get your camera all set up on the tripod and everything, and have found the object, you get to spend several minutes focusing.  Infinity marks on autofocus lenses are not accurate, and you will need to use high magnification live view and manual focus to get it just right, remember to disable any image stabilization.  After you focus and have dialed in your settings,

missing SD card, boy oh boy it's like you're right there when it was done!
(By the way, if you don't shoot this in RAW, forget about it), you get to start shooting.  If you camera is a Nikon, you have an intervalometer built in and can just configure it like this:

300 frames, 1sec between each frame.
If you shoot Canon, Pentax, Sony, or anything else you'll have to see if you have an intervalometer, if not use something like EOSUtility or other software to automate capture, or do it manually... in the cold...  You must use a remote to avoid causing shake to do this.  Once we've captured our images we get to stacking:

click to magnify.
Holy crap!  That's not the screen you start with at all!  I've gone ahead and done some stuff and will assume you're smart enough to open your files correctly.  First, after importing light frames I went ahead and checked all of them, DSS doesn't check them all by default because there might be some duds.  Then I used the tool very top right to adjust the gamma curve the preview adheres to to make M42 more visible (it's in there, I promise), and lastly I used the top tool on the right to draw the output box, we don't need the extra black space.  From there, I registered the files, so DSS can find the stars and offset amounts.  However, because my data is very dim, I need to use a more aggressive star threshold:

"register settings" is in the bar on the left.
Once that is done, and it will take a few minutes, we get to stacking parameters:

click stack on the left, then advanced settings.
Because I have so many light frames, I can use the Median Kappa-Sigma method, which essentially rejects what it identifies as error.  It works really well with lots of frames, and like crap with few frames.  I use per-channel background calibration, because I find it to work better.  The dark settings and bias settings are similar:

bias is set up the same way.
You can safely walk away from the computer at this point, the stacking will take a few hours to complete, when you come back you'll see the result.  Use gamma and stuff to "preview," but reset everything before export.  Save it without any modifications as a 16 or 32 bit TIFF, unless you plan to edit in photoshop or lightroom (highly not recommended), in which case adjust gamma and saturation some here.   If you plan to use those, you can stop reading.  If you want to see (roughly) what I did in StarTools, read on.

the very second thing you will see in startools.
Ay yai yai!  We're working backwards, now it's even more faint!

Not quite.  Stacking does appear to have moved the fainter structures of M42 to be darker, but that's fine.  Step one is to bin and perform a small crop, binning to 50% resolution to increase signal quality, and cropping to remove stacking artifacts from the borders.  From there, we move on to the first pass of developing...

developing, pass 1.
Ah, thar she blows!  Because our data is faint, we apply a pretty intense gamma curve; 2.3 in this case, and we use a dark anomaly filter to ignore the background a bit when raising the gamma.  From here, we do a wipe to remove the light pollution and darken the background.  Problem is, it's easy to go overboard...

grab your glasses or view larger.
Well crap.  We tried using another dark anomaly filter, and we did a wicked aggressive wipe.  In the process, we absolutely destroyed M42!

round two, might want bifocals.
We remove the dark anomaly filter and turn down the aggressiveness a bit, effectively un-damaging some structures.  After this we go back to the develop panel and tweak our gamma adjustment (redo the stretch, do not stretch as-is).  From there, fret not, we intend to bring our fainter bits back out to play.  We go into the HDR module...

Remember, HDR doesn't mean clown vomit.
Normally, I would tweak this for a long time, but this is just for example so I didn't bother adjusting much.  As you can see, we brought back a lot of the faint stuff.  What's nice about StarTools is that it doesn't clip data in either direction, so everything can be fixed.  Unfortunately, it is a linear editor and does not work with layers or anything like that, nor can you save part way through an edit, so you should make sure you like what you've done with every tool before moving on.  Moving on, we go to the life module:

a mask should be used here, without one we can only increase contrast on the object itself.
Normally, we use Life for two purposes.  The first, to brighten the core area as you can see, increasing contrast and making it a bit prettier.  The second is to lift the object from noise, but without a mask that part tends not to work.  Making a mask would take far longer, so I haven't in this example.  Before and after using the life module, I run wavelet sharpening.  The first pass is weaker, the second, after life, is the default intensity.  After that I adjust saturation and perform a crop.

saturation goes a little like this for my example, but is never a standard treatment; every file is different.
From here, we're almost done.  This is actually after all my steps (oops, forgot a screenshot), which is also why the button upper right says "after" not before, I'm not showing it re-saturated, those are just the settings I used.  Afer saturating, we turn to bullying noise.  We go to the upper left, and click the green track button and when prompted, stop tracking and do final NR.  From there, we crop and rotate as we wish to get the composition we want, and are pretty much done.  If you want, you can not cap the green channel in saturation, get a way blue result, and then take this output into LR/PS and tweak the color, but I'd rather get it to 95% of what I want here and deal with it.  My data started so faint there was little color anyway. 

this is the part where you save.
Here's my final image after careful processing:

much cleaner.  Masks will get you far.
Total time shooting: 15 minutes

Total time stacking: 6 hours

Total time processing: 1 hour

This result would be impossible to get from photoshop, the algorithms just aren't there.  PixInsight is another piece of great software, but far more expensive than StarTools.  However, it handles stacking and also contains far more tools.  I don't need them, and would rather $60 StarTools than $300 PixInsight.

If you have any questions, there are lots of great people in /r/astrophotography and on the internet that are more knowledgeable than me, but feel free to ask.

Boy, that was a doosey, I think I'll get some hot cocoa now...

Sunday, May 12, 2013

T-stops vs F-stops

Ah, the first technical photo post.  This one's on what a Transmission stop is, vs a Focal (length) stop, why you (shouldn't) care, and why it matters (but only a little bit).  

We'll start with the caring part.  The T-stop scale is derived from the F-stop scale, it still goes f/1.4, f/2, f/2.8, f/4, etc.  However, F-stops are geometric ideals while T-stops are measurements of light passed through the lens.  All lenses have a difference between their maximum F-stop and maximum T-stop.  This means you get slight underexposures with all lenses, but they are usually less than 1/3EV and not significant, unless you're a cinematographer.  In a motion picture, slight changes in exposure would be noticeable between shots, which is why T-stops are used, not F-stops, on cine lenses, f-stops are not perfect, thus the actual exposure of f/5.6 across a variety of lenses will vary just a little bit.  T5.6 is T5.6, all lenses will be equally bright at T5.6, but not at F5.6.

Right, on to the science.  Lens elements absorb light, as everything does.  Uncoated elements will cost between 4% and 6% of the total light, each.  Coatings improve this to anywhere from 99.4% to
99.9%  That doesn't sound like so much light, but remember that's per element.  An f/1.8 50mm, such as the one in the cover photo of this post has around 7 elements in it.  Uncoated, it would only transmit about 65% of the light a T1.8 lens would, placing it around T2.3-T2.4 for F1.8.  This would produce underexposures of about 2/3EV when shooting at f/1.8.  If we change that number to 99.7% transmission per lens surface, we get 98% transmission, or about T1.8 with only a slight underexposure.  A 23-element lens, such as a 24-70/2.8 or 70-200/2.8, with coatings making it have 99.6% efficiency, would transmit 93% of the light for T2.8, making it a T2.9 or so.  At 94% efficiency, it would only transmit 24% of the light it should; making it a T5.6 lens, two stops underexposure at f/2.8.

Some super-bright lenses, such as the canon 50mm f1.2L, isn't near T1.2 at all.  The lens' efficiency is probably about T1.4-T1.5, but something called pixel vignetting comes into play, where the aperture is so wide the microlens array in front of the sensor actually 'misses' some of the light from the lens, the camera is programmed to raise gain on the sensor when shooting faster than 1.4, which results in higher than expected noise.  However, if you remove this gain change, counting pixel shading you get T1.7, a full stop of light.  

Cine lenses aren't necessarily sharper than their photo counterparts, but they're brighter (for instance, the Zeiss 70-200 is T2.9, Canon's is T3.4), tend to have less CA, and have way longer focus throws.  Those factors make cine lenses more expensive.  You can use photo lenses for video, but at the film/cinema level it's all cine lenses for those reasons.  Photographic lenses are not inferior, they're just made to a different set of standards.  

Saturday, May 11, 2013

Review: Cowon Z2 portable DAP

The Z2 is a $300 DAP from Korean company Cowon in the 32GB configuration.  Cowon specializes in high-end portable audio players.  While behind apple in software and shininess of design, they make the best sounding players at a reasonable price.  The Z2 is the flagship Portable Media Player (PMP), or Digital Audio Player (DAP) and is flash storage based.  The Z2 can play just about every single format under the sun, including FLAC and (unofficially) AAC files. This review will cover everything anyone who has heard of Cowon or who is interested in using a dedicated PMP instead of their phone or an iPod (read: audiophiles) will care about, leaving out the fluff content and features.  Sections will be presented in order of relative importance or interest.

size: Z2 vs zHD
The Personals:
I don't have 20 years of experience reviewing products, nor do I have 10+ years experience with high-end audio, but I know what sounds good to me.  I've used three pairs of headphones with the Z2, all IEMs, and used all of those IEMs with a Zune HD (from here on, zHD) as well.  In order of experience with them at the time of review: Shure SE215s ($100), Sennheiser IE80s ($450, paid $340), and Heir Audio 3.Ais.  Curiously, that's also the order of headphone quality there ;)  My desktop equipment is a High Resolution Technologies (HRT) MusicStreamerII (MSII) connected via monoprice premium cables to an Objective2 (O2) headphone amplifier.  Now, on with the show!

The electric castle: on Z2 and on disk
Sound Quality:
The Z2 is the best sounding portable device I've ever heard.  I haven't heard tons of them, and certainly no exotic $700 DAPs, but it smokes the iPod Touch (2nd generation) and beats the zHD.  It's cleaner, clearer, and has  a very black background with very low noise, though obviously not as low as my MSII/O2 combo. It sounds very crisp, with a bit of an emphasis on highs, or reduction in bass to aid clarity.  At 100Hz, it measures -0.5dB, at 50Hz -1dB, at 30Hz -4.5dB.  Significant, yes, but not spoiling.  It prevents sound from getting super muddy, as headphone bass combined with destructive interference gets messy really fast.  It does not make my bass-emphasized IEMs bass shy, but it does make them quite close to neutral.  There are links to great measurements here at ABI, including this graph.

output FR comparison including J3, which has the same pipeline as Z2

Output Characteristics:
The Z2 has output impedance of 0.54Ω, providing ample electrical damping with any headphones; you'll find no signature changes, other than the bass rolloff.  Comparatively, most iPods are 4Ω, the iPhone 5 is 5Ω, iPhone 4S is 2Ω, and the zHD is 4Ω.  The Z2 provides a far greater damping factor than any of them, making it the best candidate for IEMs that require such low output impedance.  For full-sized cans, impedance of 4 or 5Ω doesn't matter. However, the Z2's amp isn't very powerful, and both the zHD and iPod touch I own are louder. The Z2 does sound better though, pretty similar to my desktop setup actually.  Obviously it can't actually match it, but it gets pretty darn close.

Z2 vs MSII + O2 combo, without cables
The Z2 is clunky. The D3 (predecessor to the Z2) seems like it was a beta 0.5, and the Z2 feels like a beta 0.9. The UI has between 1/4 and 1/2 second of delay on first swipe, which dies down to a noticeable, but not infuriating <1/4s delay on subsequent swipes. This "resets" after 7 seconds of not touching the screen. Speaking of seven seconds, that's an important number. The media buttons, play/pause/prev/next stop working after seven seconds of screen inactivity. The volume controls continue to function, however. That's pep peeve #1, if I stop playback to talk to someone or whatever, I need to turn the screen on to restart it. 

The player also is extremely specific about files. It supports every format under the sun, but to get artist/album/genre fields read correctly is random. My library is ~25GB of content at the moment, and at the letter F it stops reading artist stuff correctly, despite the metadata being perfect, and defaults to artist being <unknown>, though it still interprets album art and album/song association correctly. 

The internet browser and wifi work fine for casual use, but are not the greatest for serious stuff. The document app is useless, since it can't make files and can only view specific types (and curiously, it can't open PDFs). Android apps can be sideloaded, but the play store is not supported. 

The UI is good enough, and 90% of the time I'm just using the music app in folder view mode (my folders are artist -> album) for the best browsing, and it works reasonably well for that. The UI is much better on the zHD for music though, especially with on the fly playlist expansion.  The Z2's UI gets the job done, and has most of the speed a touchscreen should provide, but isn't iPod like in responsiveness.  You get used to the little delays, but they're there. 

Z2 vs MSII + O2 #2, guess which I would want to take along?
Playback, JetEffects, & Sound "Enhancement:"
Playback is smooth, but there are no gapless transitions. There is a very small to very large gap between tracks, depending on CBR vs VBR, and filetype. It isn't huge, but it's there. When you resume or begin playback, it makes a little micro-skip, the first 20ms or something stops and starts again. Not a huge deal, but every pause has that on it. Rarely, but sometimes it will refuse to play a file; producing 7 seconds of silence followed by skipping to the next track.  There are never hickups, stops, or any other glitches once playback is underway.

The physical next and last buttons can have anywhere from zero to five seconds of delay on them, depending on track length, position, bitrate, and whether the file being read is CBR or VBR, that is annoying as hell. The UI buttons have a consistent delay of somewhere between 1/4 and 1/2 second.

JetEffects is a built in package of stuff run through the music app, it has an EQ, a reverb effect, and some bass and stereo modifications. The EQ is really, really nice, and behaves very much like a hardware EQ. You get 3 programmable frequencies per band, wide/normal/narrow band, 5 bands, and +/- 12 units (not dBFS) per band to adjust with. The EQ works very well, it's only JetEffects feature I would use. There's also "Mach3Bass,"(guess what that does?) and "BBE+," an artificial stereo widener that I would never use.

A mobile match made in heaven: Heir Audio 3.Ai + Z2
Build Quality:
Build is nice, but it is not the little tank my zHD is. The device must be mostly plastics, because it is very, very light for its size. The screen is covered in gorilla glass, and the rubberization of the whole backside makes it feel good in the hands. I've dropped it 4ft into a thin layer of snow with ground beneath it and got some "chewed pencil" (but shallower) dings on the corner, nothing else.
I've gotten it wet, rather wet, from rain and snow, but not submerged or subjected to pressurized water and it just chugged along. Cowon makes no claims to it being waterproof, but it has not shorted out in the rain.

Battery life:
Battery life is ok, it runs about 20 hours without using jeteffects. With jeteffects in use, it gets about 14 hours. 

However, it cannot sleep. The device is completely incapable of truly sleeping. The sleep function merely turns the screen off, it won't even stop playback. In sleep, it still eats the battery, dropping 14% overnight if you forget to turn it off. If you turn it off, the meter will still say you lost 2-3% overnight. It really can't hold a charge that well...  I charge it nightly, so it's not that big an issue, but the lack of ability to sleep is annoying and will probably bite owners like me in the ass every once in a while.

The Bottom Line:
The Z2 is a hell of a playback device. Most of its operation is flaky, but it sounds exceptionally good, and has a touchscreen for speed of navigation. The lag times and lack of snappiness suck, hard, the battery life isn't great, and the lack of working sleep sucks, bad, but it has no competition. There's the iPod, offering 423423414134 other functions in the same package, but worse sound output. There's sony's players, which don't sound as good, have no microSD card slot, and don't have the file support. There's the zHD, which is decapitated and doesn't sound as good.  The firmware is also in active development, with updates rolling out improving speed, the last of which was put out 19 April, 2013 at the time of this review. 

It's unique in the touchscreen+fidelity+microSD combo, and if that's what you want, you are getting a Z2. The X9 exists as well, but it is very sluggish (resistive, not capacitive touch) and bulky.
The Z2 is... worth it if you can afford it, and the only better sounding players are usually bigger, heavier, have worse battery life, and have godawful UIs while costing over 2x as much . There is no way to get straight DAC output (unless you could get audio over USB working in the newest android, but I am not sure the firmware can be updated to that, Cowon doesn't have a DL for it), but the SQ and low impedance make that a nonissue, unless you need to drive some hungry cans.  For that I would probably start looking at an iPod + line out -> DAC -> AMP, but then you're transportable, not portable.

Friday, May 10, 2013


We won't operate under the false premise that people read About Me's or any of that nonsense (and why should they, that requires a click!), so we'll explain who I am and why I've started this blog. 

I've spent quite some time (hundreds of hours) learning just about everything there is to know about photography and have a vast archive of knowledge.  I often post in /r/photography answering people's questions, though less than I used to.  Typically, they're fairly low-effort and can be answered using the subreddit's search to find thousands of replies, or are answered by a quick google search.  From time to time, a nice juicy question comes along that I can't help but answer in-depth.  Problem is, there are some...difficulties built into reddit formatting.  The lack of ability to post inline images and format them is crippling, I won't reply on RES being used for that.  However, the worst thing is how easily lost those posts are.  I can make a 5,000+ character comment, giving a nice answer, and then poof, it's gone after that unless I save a link to it.  I'd like to stop spending forever and a half typing out answers, so I'll be making a repository of high-quality ones here. 

Right, that's the long and short of the photo stuff.  But what about the other two?  Well, over time I've been accruing a bunch of audio equipment and knowledge, so I can do posts similar to my photo ones, but not to the same depth on audio as well.  There will be gear reviews, too. 

Lastly, I've toyed with the idea of doing album reviews for quite a long time, but never had "space" to do them in, so I'll do those from time to time here as well.