There is a saying in electronics engineering world: "Every sensor is also a temperature sensor."
What this means is: almost every electronic sensor is affected by it's temperature- from expensive image sensors to cheap MEMS accelerometers and gyroscopes.
That is why many of digital sensors also report their temperature, although that is not their primary purpose- so that current temperature effects on the measured result can be calibrated out either in sensor's logic, or by host software.
You can calibrate out the mean "light level" resulting from Boltzmann noise. You can't calibrate out the variance, but eliminating the mean noise is better than nothing.
Not quite sure why this hits the front page. Most serious astrophotographers have been using similar setups for a while now, or ideally peltier cooled CCDs (like Starlite Express, Atik or QHY cameras). More recently cooled CMOS sensors (like the ZWO1600MM-Cool) have also gained popularity. It's a bit of niche market, but for long exposure photography having a cooled sensor greatly reduces thermal noise. And since the signal is very faint you often do a lot of "histogram stretching", bringing out the signal, but also the noise. In addition to having a low noise camera you also often do things like bias, dark and flat callibration, reducing impurities further. Dark subtraction is often known as "long exposure noise reduction" in consumer cameras, but astrophotographes like to do it manually. There are a lot of details to consider when doing astrophotography, but I'm always happy I can set my CMOS or CCD (own both the QHY10-OSC and ZWO1600MM-Cool) to a deltaT of -40ºC.
However it still isn't exactly that new or revolutionary... CentralDS has been doing this with Canon cameras for a while now and it looks like P.L.L. has just taken the cooler and retrofitted it to a Nikon this time. Still went with the ASI 1600MM-Cool and MC-Cool based on their prices still being lower together than what they're charging.
I know little to nothing of astrophotography, so this article comes as news to me. (I like the article, FWIW.) I wasn't even aware cooling could be used to account for sensor noise. Now my mind is actively aware of the problem and is trying to enumerate other possible means of correction in this, and other, imaging fields.
The article is mildly interesting, but this is not state of the art by any means.
It's a little bit like an article saying "computer engineers use special software that could take human readable source code and convert it into executable binaries for faster execution". A layperson would have their minds blown, but it's a super-yawner for those in the industry.
Also - the article gives the impression that colder is better.
While there's some truth to that, it's not about how cold you get it, it's about how consistent the temperature is, as for a given CCD noise will usually be the same at the same temperature. I take darks only about once a month or if I notice a new hot pixel on an output - I take them at a range of temperatures, so that depending on what the weather is like I can choose a temperature for light frames, and then just use my pre-cooked darks.
Out of interest, unless you live in a desert, how are you setting to -40 delta without the thing freezing?
As to "why is this here?" - Astrophotography is a great hobby that'd likely appeal to the HN crowd. Sitting out under the stars spending hours doing very fine polar alignment, only to get a few dozen exposures, while worrying about everything from dew to wind to beetles climbing your tripod legs, and then days in startools, DSS, and all the rest, seeing just how much information you can squeeze out of your often slightly blurry light frames.
I actually almost enjoy the DSP end of things more - there's something ineffably cool about starting with the same set of input images and getting radically different results depending on how you treat them. I mean - stick a drizzle filter on your image, do a wavelet sharpen, lift your jaw from the floor, as it seems like you've just done some CSI style "ENHANCE" shit. Here's an example of what you can start with, and end up with - I'm really not too good at this and only have limited kit, but it's still exciting. This is the dumbbell nebula, shot on a windy night with a full moon - I shouldn't have bothered almost, but the final is still decent considering the garbage input. http://imgur.com/a/tyZ4j
Anyway, ramble aside, the more folks who are aware of astrophotography the merrier. It's just too much fun.
Oh I can set it to -40º below ambient. But usually I set it to a target of -15ºC (with an ambient temperature of around 10ºC, this winter I might go a bit lower).
Not stressing the PEC is gentler on the battery too. You have to be slightly careful when doing cooldown and warmup to avoid condensation and thermal shock (or at least, I think I should be), but I've never had any problems with it.
Also great shot! I feel your pain with the wind, dew and bugs... but it's still an awesome hobby.
Meta question: what do you consider spammy about this blog post? It seems like a perfectly fine, digestible narrative of the product without requiring the reader to sift through a product page.
On a more related note, I find it interesting that the product page says there's a 4 year warranty on the camera body. I didn't see anything about the warranty on the mod itself.
Sensor cooling can lead to moisture appearing in the camera, so the D5500a Cooled uses a special anti-dewing system that uses targeted heat to avoid dew drops appearing.
These are often called "dew heaters", and are really quite simple. It's usually nichrome wire (e.g. what you see in a toaster), or sometimes a bunch of resistors. The tiny amount of heat generated by these straps are enough to raise the optical port a degree or two above the dew point.
My QHY8 (a dedicated astro CCD) for example has a poor/old design, where the CCD compartment is not air-tight. This allows humid air to get inside, which can then fog up the optical glass due to the peltier cooling the sensor down.
The fix is a small ring that screws into the port, and raises the temperature just enough to combat dew. You could also wrap a dew heater strap around the part of the optical train at that point for a similar effect.
Dew (and frost) are the astrophotographer's great, persistent enemy and not just on the CCD. You'll also have dew problems on the telescope itself. For example, my newtonian sometimes has dew problems on the secondary mirror, occasionally on the main mirror, and always on my guide scope.
Most people just create some DIY dew heater straps with nichrome wire... it's super simple and effective.
Interesting. So it's a heating element (wire) which serves as a controlled heater to keep the close environment above dew point. If it's controlled, that is. Maybe it works as a dumb heater also?
OTOH, I've never considered somewhat more performant (not to say extreme) cooling of CMOS in order to eliminate noise. I'm surrounded by CMOS and CCDs every day, in film cameras and telecines (both array and linear chips). I knew, and saw, that temperature can influence noise, but apart from staying within 'normal' operating range, I never considered it would eliminate more noise if significantly cooled down. Probably because I knew noise was inherent to the way those things work and not much could be done to eliminate it altogether. Interesting. I'll try to experiment with a bit more extreme cooling on my equipment to see what yield would come out of it. I'm not that concerned about dew, because equipment is in controlled environment (dry and +-2C deg. stable environment), but nice to know.
A major pain point of dew-heaters is if they are too strong, they induce "tube currents". E.g. the heat from the dew-heater causes the air around the heater to start convecting, which causes ripples in the final image. It's not really visible as ripples, but a general blurring of the image. It's essentially recreating astronomical seeing conditions inside the telescope itself, which is obviously not ideal :)
I think some fancier setups will be "active" and regulate themselves based on ambient temperature, but it's a lot more common for people to over-build their heaters and then use a dimmer switch. So you make your dew-heater for the worst winter night you expect, then dim it down for the rest of the year manually.
They're essentially using Peltier elements to cool the elements electronically. They're also using two elements stacked in series for a lower total temp.
Thank god the CCD is small -- a Peltier unit, as a heat pump, is pretty inefficient, topping out a ~15%, at a low t delta. When you stack two on top of each other, the efficiency is now 2.25%, and this only gets worse as the delta increases or more units are added.
Question to those astrophotographers out there. I notice the cooler has a fan on it, is the fan vibration damped somehow?
I shoot a lot of long distance photos (300mm F/2.8 and 600mm F/4 are my main lenses). Any vibration is greatly amplified when I shoot, and this is a much longer range than that.
Good question. I have a peltier cooled ccd (atik 460) and the fan stays on during the entire exposure, but it doesn't affect the final picture at all, touching the camera I can't feel any vibration, but can hear the fan. Quality is much better than in my fanless Canon 400D.
Most Pelletier chilled assemblies use magnetic bearings for fans, so very low shake. I use an Orion star shoot G3 (can't really recommend it), but vibration from quarrying 20 miles away is more of a problem than the fan.
I notice the cooler has a fan on it, is the fan vibration damped somehow?
I'd assume that the fan is simply turned off for the duration of a photo (plus the time it takes for vibrations to decay). The sensor won't heat up instantaneously.
My astro CCD has a (slow) fan attached the peltier. The vibration isn't usually a big deal for two main reasons:
1) If your setup is sophisticated enough that fan vibration may cause an issue, you're likely already using a german-equatorial mount and some kind of guiding correction (secondary guide scope, or off-axis guider). These adjust the scope's positioning in real-time to keep on-target. So that removes any large-scale deviation that may be caused.
2a) Small-scale deviation is generally not a problem, since most setups are likely to be limited by the resolution of your entire optical train. For example, my 800mm newtonian combined with a CCD with 7.2mm pixels means I have a resolution of ~2.01 arc-seconds. Assuming perfect guiding, my scope can tolerate any vibration as long as my target stays within ~2 arc-seconds. *
2b) In reality, most locations are limited by seeing conditions (e.g. how turbulent the air is), which averages 1-3 arc-seconds in non-mountain regions. Also the calibration of your mount (periodic errors, guiding errors, etc) are almost certainly a greater concern than the vibration added from the peltier.
That's from an amateur's perspective. Obviously high-end setups will start to worry about things like the fan's vibration, but for someone with a backyard setup (doubly so for someone using a consumer DSLR instead of dedicated CCD), there are bigger causes of inaccuracy :)
* This is a bit of a simplification, since things get a bit more complicated due to FWHM, wavelength, etc.
Ugh, yeah, backlash on mine too :( I'm actually in the middle of rebuilding my mount to help with periodic errors and backlash. Replacing a bunch of bearings, re-greasing, replacing the direct gear train with a geared-belt system, etc.
Speaking of... I need to finish that up soon before winter season starts in earnest!
Most actual cameras dedicated for astrophotography (the stuff shown in the article is more like a frankenstein improv) have fans. Most of the large dobsonians have fans. Many high-end SCT telescopes (typically used for astrophotography) also have fans. Fans are good, fans are your friend. They fight all sorts of thermal issues.
They're typically fans with high quality bearings that also are spinning slowly. There's essentially zero vibrations coming out of that.
It's very hard to get decent results out of any optical stack, especially for photography, without having any sort of fans, heaters, coolers, and other air flow and temperature management devices in various places.
From one of the links elsewhere, they're claiming it doesn't: "[...] the relative speed of the cooling fan (which does not introduce vibrations) [...]".
Perhaps they use the fan to initially cool the sensor and then switch it off and let the Peltier cooling maintain the temperature or something?
I would be concerned about this as well. I've not done a lot of astrophotography, but when I have, I've had to make my framing/focusing adjustments, then wait anywhere from 10 to 60 seconds for the vibrations that motion introduced to fade away, before I used a wireless remote to trip the shutter. Obviously this is worst with a long lens[1], but I seem to remember it being a factor with any of the telephoto lenses I tried. This was using a Manfrotto tripod and head.
Seems like some sort of liquid cooling system where the radiator/fan assembly was not mechanically coupled to the camera body (except by flexible plastic tubing) would be a better approach.
[1] For example, I have an antique 400mm focal-length lens that really is about 400mm long. With it attached to the tripod near the middle, and the camera at one end, there is a lot of potential for bouncing around.
Part of the idea is that you will need significantly shorter exposures. Shorter than would be needed to introduce artifacts from vibration.
Such cameras (sold by Nikon [1]) are routinely used on high-end microscopes. They usually have a smaller resolution though - 1024x1024 is pretty common. There are a number of technologies used in scientific microscopy that work well for night-time photography, but most are just too expensive. Electron multiplying CCDs, chilled CMOS sensors, etc. They end up being one of the more expensive parts to a half-million dollar scope though.
In astrophotography, this is actually the opposite of what you want to do. Generally you add cooling so that you can let your sensor run for longer, so you can collect more photons without increasing the noise appreciably.
Image stacking can reduce noise afterwards, but there's no substitute for collecting more photons to increase the signal in an image... and the only way to do that is to try and clean up the noise floor (via cooling, better sensors, etc) :)
Peltier cooling or heating does require a fan.
The peltier cell only moves heat from on side to the other side. Then, you still have to remove the heat somehow (heat doesn't simply dissapear) that's why most peltier setups have fans.
The focus is infinity, so as long as the camera is rigidly mounted the vibration that makes it past whatever damping they have won't wobble the field of view a lot.
For $1000+ I imagine the fans actually don't have much impact.
You've missed out the rotational modes, which matter hugely. A fraction of a degree on a long telephoto lens is a huge part of the frame. (If you're focusing at infinity the translational modes theoretically shouldn't matter at all)
Much more sensitive, the motion will be amplified by the zoom factor. It also introduces (minor) blur as soon as the image shifts further than the gap between the sensor pixels.
Only if you have a time resolution higher the shaking. How do active image stabilizers work?
Edit: yes, that's how active systems work: gyro stuff and counteracting by moving the lens or the sensor¹. For astronomy rather a lens, because the sensor would have to move too far for the big shifts the tele causes².
If you can't tell the difference between the chilled and regular frame I have to suggest taking the dust out of your monitor, as in certain conditions the difference might not be visible
I recently ran across this homemade camera mod [1] to reduce astrophotography noise. There's some brief notes on creating it somewhere in the creator's (James Tobin) profile [2] but G+ isn't the happiest place to search.
I was experimenting with visual calibration of my desktop CNC by hooking up one of those cheap USB 1000x cameras. I had done some back of the envelope calculations to figure out that it was about 5 pixels per thousandth of an inch.
After a few hours of getting weird inconsistent results, I finally figured out to my shock and horror that the image was drifting and warping by upwards of 20 pixels after the camera had been one for a while (I think it was 640x480 resolution). My friend and I thought this was due to the CCD heating up and warping.
It looks like they're using the cooling for noise suppression but I bet the CCD also has the same effect I noticed of 'pixel drift/warp'.
No way this will beat a dedicated astronomy CCD camera. And price point is already not so attractive, ST-8300C costs $1995 and while has 30% less sensor area, is light years away in thermal current at given temperature, and quantum efficiency. For me, if a wanted a color camera (bad idea most of the time), picking between ST-8300C and this would be a no brainer in favor of ST-8300C.
Given the fact that (correct me if I'm wrong) camera sensors use the same sensor elements for red, green, and blue, but with a different filter in front, it seems strange to me that blue and green are almost eliminated by the cooling but red remains to a large degree. I would expect this distribution if the camera used different photodiode types sensitive to their respective color range.
Most CMOS sensors are much more sensitive in the red/infrared spectrum, that's why all cameras have a IR cut-out filter.
This filter is removed in astrophotography cameras (you want all the light you can get) giving aprox. 50% more light gathering, but mostly in red/IR colors.
That doesn't explain why the noise image is red, given that the noise excitations are endogenous and don't go through the filter, does it? Unless that noise isn't noise at all but IR from the room.
Quite a bit, actually. It's why high end telescope CCDs do similar things. A high ISO means you're ramping up the gain, so the bits of random noise get amplified too. Cooling it means you're getting rid of one of the more significant sources.
Hobby use would be a pain: LN2 could be used, but it boils off so a dewar would need to be constantly refilled. For sensor applications where cold matters but a Peltier TEC is insufficient, a Stirling/Joule-Thomson/turbo-Brayton/Gifford–McMahon cryocooler can be used to remove heat, but they're expensive (this is how the Hubble Space Telescope does sensor cooling). They often have high-pressure LN2, neon, or helium as the working fluid, with a cold head attached to the sensor and a remote compressor. Cryocoolers are also used to chill superconducting RF filters (of the sort that may be used in cell phone towers). They're also used to cool MWIR sensors, and thus are often ITAR-controlled. Sometimes higher-temp cryocoolers pop up on eBay...
"of the sort that may be used in cell phone towers" - I had no idea this was a thing, so I looked it up. Here's a really good overview of the state of the art in 2004, which is already pretty amazing, and obviously things have advanced a lot since then. There's some serious science and engineering involved:
"An advantage of superconductors is that their low-loss properties enable the fabrication of a variety of microwave components in a far more compact geometry than is practical using conventional materials. ... bulky cavity resonators and dielectric resonator structures can be replaced with compact microstrip designs fabricated on wafer substrates."
"The difficult requirements for successful growth of epitaxial YBCO films are the need for high substrate temperature (typically 700–800 C) and high oxygen ambient pressure. To simultaneously achieve these conditions during a thermal evaporation process, a unique heater concept was developed ... a rotating substrate platter that serves as a partial vacuum seal for a heated chamber held at elevated oxygen pressure. The platter fills the open end of the chamber, leaving only a very narrow (less than 0.5 mm) slit. This arrangement results in a pressure drop of three orders of magnitude between the oxygen-rich chamber and the rest of the vacuum system. Substrates spend the bulk of their time in the chamber, where they are heated and exposed to oxygen. As the platter rotates, the substrates exit the chamber and are exposed to the flux from evaporation sources for the three metallic constituents of YBCO. As long as oxygen is supplied to the deposited metal atoms within a few tenths of a second, they can form the correct phase of the material. Rotating the platter at a few hundred revolutions per minute accomplishes this in the system."
"...wireless customers expect (and require) long, maintenance-free lifetimes. Thus, one does not have the luxury of routine maintenance such as periodically evacuating dewars or recharging helium in coolers that might be acceptable in other application areas. The cryocooler and dewar, as well as all mechanical parts, must be designed to last for more than 40 000 h of operation, or approximately five years. ... Reducing the possibility of leakage requires that the dewar be permanently welded shut .. all feedthroughs must have leak rates of less than 1^10 cm /s He. This far exceeds the levels of hermeticity typically defined for the electronics industry and, thus, often requires custom solutions."
Page 8: photo of a 2002 high-temperature-semiconductor filter, including cryocooler and coolant dewar, showing that it's not that much bigger than a regular rackmount server!
"The practical benefits of HTS filter systems are regularly seen in field trials. Trials usually involve two weeks of network statistics, before and after installing a SuperFilter... Typically the base station receiver
noise figure is lowered by 3 dB by the installation of the HTS filter system. ... Dropped calls were reduced from an average of 3.0% to 1.7% overall. The range observed was 18.7% to 63.6% reduction over all channels and sectors. The adjacent sectors, without SuperFilters, went from an average of 2.0% to 1.7% dropped call rate. Ineffective attempts went from 3.3% to 2.5%, a 26% average reduction."
A lot of commercial cameras for astrophotography get a 40 Celsius temperature drop (compared to ambient) on the sensor - just with Peltier elements. That's a pretty big decrease. You're getting diminishing returns after that (and a bunch of new issues with super-cooled components that you then have to manage).
Not that I know of. CCDs don't generate a lot of heat, so the cooling only has to be relative to ambient, which peltier can do fine. I'd worry more about things like thermal shock when pouring liquid nitrogen over a CCD than the gains in Signal-to-Noise ratio. Although, there are scientific instruments that get cooled way further into super conducting state.
What this means is: almost every electronic sensor is affected by it's temperature- from expensive image sensors to cheap MEMS accelerometers and gyroscopes.
That is why many of digital sensors also report their temperature, although that is not their primary purpose- so that current temperature effects on the measured result can be calibrated out either in sensor's logic, or by host software.