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Old 21-06-2019, 10:26 PM
Paullus (Paul)
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Talking A Successful Astro Mod

Well I *think* it was. Haven't actually tested it against the night sky yet.

Earlier this week I undertook the daunting task of open heart surgery on my Canon 50D DSLR to replace the LPF2 filter with a Baader BCF filter. It seems that not many people mod their cameras these days but for me it was much cheaper than a dedicated camera. Given the age of the camera and the cost of the filter I wasn't too concerned if I bricked it, but thankfully I did not. I'd never been so happy to see a camera turn on! Once it was finished the task didn't seem too bad after all. There are a number of guides on the internet that step through the conversion process, but I thought I'd document a few key learnings from my experience.

- Create a clean space and barricade the door to keep out significant others/ankle biters/pets. Set aside a couple of hours.
- Work carefully and slowly, even when moving tools to/from the camera/circuit boards. You don't want to accidentally damage any PCB components with a pointy pair of tweezers.
- Steady hands and patience are absolulely necessary.
- Good quality screwdrivers are needed. Some of those little screws are deceptively tight!
- A small Torx driver is also needed for the sensor unit.
- The ribbon connectors weren't too hard. Again just work slowly and don't apply too much force too quickly. Ensure they are re-seated properly. Initially one cable wasn't in far enough and the camera couldn't auto expose properly.
- The guide I followed didn't mention anything about noting the sensor calibration screws. I was expecing to lose autofocus before starting the mod but it wasn't until afterwards that I realised that I should have noted the position of the screws to at least get close to the original position during reassembly. Some people recommend using a dial gauge to measure the height, or marking the screw positions and then counting the number of turns to tighten the screw as far as possible. As I didn't do either of these, I tightened the screws as far as possible, relying on the posts to be all the same height so that at least the sensor unit is reasonably square to the entering light. As the sensor unit is spring loaded, I pushed down the sensor unit as I tightened the screws as I didn't want to run the risk of damaging the presumably weak threads by screwing against the force of the springs.
- Following on from above, the resulting auto focus wasn't too far off the money. Fortunately for the 50D there is a setting to adjust the microfocus (front/back focus) and doing this gave satisfactory auto focus. I wouldn't go shooting action sports for a magazine or super models but for general non-astro duties it'll do just fine. And of course the white balance will also need adjusting to remove the red tint caused by the new filter.
- The most dangerous part of this operation was removing the old LPF2 filter. It was held in place by a rectangular adhesive seal as well as some glue in the corners. I had to break the glass into several pieces to remove it. It was a delicate task to get under and lift the filter with a scapel and not slip and gouge the sensor.
- The new filter had to be held in place with some glue. I used Selley's Roof and Gutter Sealant, 100% silicone and neutral cure. Small amounts were applied using a toothpick, moving along and away from the filter. The last thing I wanted to do was accidentally drag a "tail" of glue on the filter. The filter was left open for a couple of days for the glue to curer. A drinking glass was used to shield the sensor unit from dust.
- Unfortunately the filters aren't as clean as they were before opening the camera, despite my best efforts to create a clean environment and using a lens blower regularly. I cleaned what I could with some isopropyl alcohol. I suspect some of the dust has come from the filter initially moving around slightly before I realised I had to glue it in place. I foolishly applied the glue without lifting up the filter and giving it a blow. Lesson learned. Once glued in place I couldn't remove the plastic frame that holds the filter from the rest of the sensor unit. The dust isn't visible to the naked eye without magnification, but it's definitely there in a f/22 test. Fingers crossed flat frames can resolve this.



So there you have it, my take on astro modding a camera. Not scary as first thought!
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  #2  
Old 22-06-2019, 01:00 PM
Sunfish (Ray)
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Wow. Well done. Sounds complex.

Great job. Maybe a jury rigged flow hood would be best or gloves in plastic box with a glass lid like the mushroomers use if I attempt it.

I was looking also at this. The simplest Nikon to remove the filter off seems to be the d5500 according to the instructions. No desolder even, but they are still expensive . The best would be the D5100 as it has large pixels as used in several astro cameras.

I did see one with a cracked screen for $75 but missed that.
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Old 13-07-2019, 06:31 PM
hamishbarker
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I did my lumix gx1 a couple of weeks ago. my choice was also one of cost, not wanting to splash on a dedicated astro camera before getting a proper mount.


I went for a fused silica filter replacement for full passing of uv and ir as I am into spectroscopy and want every damn photon, and have an all-reflective optical train (newtonian and no focal reducer or barlow) so no worries about achromatism.


removing one of the filters (the one closest to the sensor) on the lumix also requires scary scalpel work on the glue. but all good, works great and spectral range is now circa 365nm to past 740nm (1st and 2nd spectral orders are overlapping after 730nm so it's hard to tell how far it goes. i need to use a low pass filter to see how far into the IR it does go.
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Old 22-07-2019, 07:58 AM
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bojan
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Good job! And definitely worth the effort.

Couple of years back I modified 2 cameras (400d and 450D), obtained on ebay for couple of $$ as faulty (I repaired them first.. 400D had broken CF connector, 450D had a splash of some liquid into memory card slot, so some of the tracks on PCB were eaten out by electrolysis - I replaced them with thin wires).

I simply removed the filter (and ultrasonic "shaker").

Now I am looking for faulty 60D.... or I will simply modify the one I already have (I am not using it much for everyday photography)
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