Thursday, January 31, 2013

A Large Finger with Modified Base

After testing with the exposed Pentax K10D camera, I wanted to route the finger through a slot in the base plastic. I could have left the camera open to the night air, but quick testing for light leaks showed that this was a bad idea.

With a dremel tool and some cutting and fitting work with a pair of pliers and tin snips, I was able to trim the copper finger and get the whole assembly to fit together better.

Before I put the parts together, I smeared a thin bead of thermal compound on the CCD assembly plate. This should help improve the transfer in the absence of the gel pad.

Seen here is a larger gel pad that I had in place originally to provide some continual connection with the LCD screen. As the original effort cooled this area, I wanted to provide something similar for testing.

I've been testing via a few standard ways:
  1. I do a "drop from room temperature test" where I run the camera for 1 minute exposures with a 10 second gap.  This runs for 60 exposures, or a little over an hour.  After the set runs, I can pull the images and fire off a bat script that pulls the EXIF temperature.  This gives an idea of what the hardware in the camera considers the temperature.  
  2. I run the above test in two environments: in the open on my desk where the ambient temperature is about 15C and in the fridge where the ambient temperature is 6 C.
  3. I also run a set of 20 minute darks in the fridge to give a good idea of how the camera can be kept cool over a longer period of time.  
  4. For consistency, I've been running these tests with the Peltier device at maximum cool setting (-20C on the dial).
What I've learned:
  1. The camera with a closed base and gel pads on the metal work cools better than it did before.  This is not a surprise.  What was surprising was how quickly it settled at thermal equilibrium in the fridge.  Also the thermal equilibrium temperature as reported by EXIF was 8C.  Thermal equilibrium was reached in 70 minutes in the fridge, dropping from 25C to 7C.  When the sequence started, there were a few frames where the temperature went up to 26C before dropping.
  2. With an open base, the thermal equilibrium was reached at about the same rate: 65 minutes from 26C to 7C.  
  3. With the closed base on the finger, the I missed the test in the fridge, however, I did do a test on the desktop.  I compared the final frame for noise profile.
  4. For one final test, I decided to remove the thermal transfer pad on the LCD and replace it with cardboard in an attempt to insulate the finger.  The goal was to help the cooler isolate and pull heat just from the inside of the camera via the copper path.  I also routed the thermal probe from the middle of the heat sink plate to the cold finger just inside the camera body.  Thoughts were that this would help show what a real temperature inside the camera is.  When testing in the fridge, the thermal equilibrium was tested from 18C to 8C.  The test did not start at a warmer temperature.  Final temperature was reached in 45 minutes.  I also added my amp gauge to better identify when the cooling plate reached a target temperature.  
There are some interesting developments that I'm going to add to the way I work with this device.  Up to now, I've just run it wide open all the time.  I thought that letting it pull as much heat as it could all the time would be the best option.  With extensive checking while the camera was in the fridge, I was able to adjust the dial and look at the current draw to identify what the thermal probe was indicating.

I found that the device will not cool much below -5 C.  This was about a 10C drop from the interior of the fridge.  This was determined by adjusting the dial to see when the cooling cycle would start pulling current.  I noticed that getting to 0C was pretty quick and that the final -5C was slow.

In testing on the desktop in 15C ambient temperatures, 5C was reached within 10 minutes.  0C was reached in 20 minutes.  Holding the temperature at 0C results in a draw of 2.65A (vs 3.46 A during full power).  This should give a bit more life to batteries in tough situations.

Next testing to do:
  1. Apply a thermal transfer material between the heat sink and the copper finger.  Now it's just pressed with elastic bands.  I am not convinced that the thermal gel pad has much benefit.  When I ran the device with no thermal load, I could feel coldness on the exposed metal plate faster than through the gel pad.
  2. Try routing the thermistor probe deeper into the camera or give it a secure attachment to the finger.  Challenge is that it should be removable and repositionable.
  3. Possibly disassemble the Peltier device to remove unneeded mass.  I already have a light weight heat sink for the hot side.  If I can figure a way to mount it onto a stiff, insulating material (considering a wood plank now) then that will be the next step.
  4. Do a quick run of 10 minute at 400 ISO darks to compare vs previous library to see if this reduces thermal noise.  My tests up to now indicate that thermal noise is better controlled than before.

Pads in place

Second Testing by S Migol
Second Testing, a photo by S Migol on Flickr.
After a round of testing with the base plate open, I wanted to close up the camera with the finger in place.

See how there are two pads visible now.  There's one that is flat against the base with a large area of blue skin visible.  This pad does two functions: it helps protect from shorting on the copper finger and it is another source of cooling near the critical area.  Not sure what the assembly does here, but it can't hurt to have this area cooled.

Deeper inside the camera I've slipped a thin ribbon of pad.  This ribbon goes along the left side of the CCD.  It is not attached to the CCD assembly, rather it is on the main board.  This might help the temperature in this space.  Not sure if it has made much of a difference in testing.

I may remove it or even add more on other areas.  The fit is very tight so it's unlikely that I can get more inside this area.  I also don't want to have the pad touch the CCD assembly that floats because the shake reduction system is still functional.  I don't normally have it turned on, but I want to be able to use the camera as a normal IR camera in the studio or on travel.  Thus everything I do must be somewhat reversible.

Opening the Base

Opening the Base by S Migol
Opening the Base, a photo by S Migol on Flickr.
This is how the base of the Pentax K10D camera looks when it was opened up. Note how you can see into the gap between the CCD block and the main board. This gap is not very wide - about 4 mm.

Also note the v-shaped cut made near the lens side when Spencer's did the modification. I think this allowed them to remove the IR cut filter without taking the whole camera apart.

Camera Modifications

I've been interested in Astrophotography for some time.  I got an extra body of the same series DSLR that I use and had it modified for full-spectrum use to get better images of the night sky.

I even added a peltier device cooler to try to chill the entire camera to get better noise characteristics.

Recently, I've decided to take some down time and improve the performance of this cooler.

I'm not terribly happy with the power requirements of this setup and wanted to get better results.  So, I started looking at what could be done to improve the heat transfer out of the camera.

Here's how it looked when I first started using the cooler:

Peltier Device for Cooling

Shortly after I started with this configuration, I wrapped the gap between heat sink and camera with an old wool sock to give insulation.  This has helped stop the formation of rime ice at the edge which is an indication of wasted energy.

9 months later and I'm getting back into it again.

I looked at the way that the heat is transferred around to the bottom of the camera as seen originally in this photo:

Flexure fixing

This strip of aluminum allowed the cooling to get to the base plate. Of course, this is still outside of the camera with the hopes that some of the heat will still leak out through the plastic.

When I saw this picture in the Pentax K10D service manual, it got me thinking about what was going on inside the box.

The metal plate that has the yellow box is holding the CCD plate.  It also holds the magnets for the shake reduction system so there is limited direct contact with the CCD.  You can see this separation better in this next shot:

There is a gap between the CCD assembly and the metal box.  Still, it got me thinking about what I could do to help assist the cooling of the critical components.

I opened my camera, breaking the seal that had been put in place when the IR modification was done.  It was long enough and Spencer's hasn't been responsive to my questions, so it was up to me to make the changes.  It also didn't require any de/re-soldering of wires, so I felt comfortable with making the effort.

How it starts

Some backstory for reference:

I've been using the internet for quite some time, have owned the domain since 1997.  It's been on a managed box for a long time and then it moved over to Amazon's cloud and now it's living on Google Apps.  Things change as required.

My thoughts on online practices and social media have changed over the years as well.  Originally, I was open about sharing my information and even posted a resume directly on the web.  This was before web crawlers scraped sites for contact information.  Soon after I did this, spam became an issue and I found my resume details showing up in databases that I didn't authorize.

Thus I locked down.  It became a case of the cobbler's children wear no shoes.  Even as I was furthering a career using the tools of the internet, my public online presence became a bit of a cobweb in the corner.

It was only with my participation on Flickr that I started to break the silence.  It's a great resource for getting inspiration and growth of my photography.  I have used it as a touchstone for trends as well as showcasing some of the better work that I do.

Shortly afterwards, I finally signed up to LinkedIn and have kept that profile going.  It's mostly used as a milestone marker in my career and a tool to gather information on best practices in web marketing.

Later, my family and friends used Facebook extensively and I slowly opened up to using that tool. I primarily use it as a tool to share with my circle and not as a promotion device. 

In the crash of the Amazon host and subsequent move to Google I've decided to dip another toe into the social media world with this blog. 

What to expect:
Background on photo-oriented projects beyond what I want to discuss on flickr.
Tracking of my trends.
Details on milestones, projects, and plans.

~ Stephen