Gina

You can control the power input to the TEC using a power MOSFET driven from one of the PWM outputs of an Arduino - see circuit diagram in my 1100D debayered with added cooling, FW and OAG thread. With such a high power and inefficient TEC you will need a very good cooler to get rid of the heat from the hot side.

Now have cooling added to the test rig though without any thermal insulation so the cold finger is gathering a thick layer of ice. I am obtaining -8C on the CF with ambient temperature of 23C. So that's a delta T of -31C. I'm running 60s exposures using APT and the 1100D sensor is fine. Without the camera being in a box there is considerable light leakage and the image is showing a medium brightness at that exposure. I'll add some plastic foam as thermal insulation and see if I can get down to -10C on the CF. May also add a DS13B20 digital thermometer to the heatsink to see just how well the cooler is working. I using the MCPE-127-10-25 - PELTIER COOLER, 19.6W with 60x60x40mm finned CPU cooler with fan as shown in my 450D cooling thread. I'm running the TEC at 15v and 1.75A - just below it's maximum rating.

I've tested the white light flats and have a working setup with standard Canon zoom lens and tissue held on with elastic band. Using APT to control exposure and capture data. I need to clean the sensor cover glass before using the results as there are several bits of dust on it. Probably the best time to take the calibration data would be after removing the cover glass or after adding the epoxy resin ie. just before attacking the sensor surface.

Thank you - I'll take a look at RawDigger - looks like the very thing I'm not sure about the antireflective layer - depends on how things go. It may turn out that it gets removed in places anyway. But I'll certainly keep it in mind and make a decision later.

I shall be setting up a proper test rig with cooling to test the sensor at each stage of debayering and will post the results. I will post the details of the cooling system in my own 1100D debayering, cooling, FW and OAG thread and keep this thread on topic with debayering info only.

I intend to debayer half the sensor area too - with an 1100D sensor. I will also provide and area where just the micro lenses are removed. Then for testing I will use white light for one test with diffuser over lens to provide a flat. I propose to repeat this test with an Ha filter in the light path and again with SII and OIII filters. I will then see if I can take the various image areas and select a few pixels from each and make a composite image with these adjacent to each other. The comparison of untouched sensor with the CFA and micro lens removed areas will be the most interesting. It would be nice if I could find a way to actually measure the image brightness for these areas. Oh, and flats taken before any debayering to confirm that the sensor area that will be debayered is actually the same sensitivity as the other side.

I was going by figures and graphs posted above but once I get a part debayered 1100D sensor I shall be able to do some tests. Then we shall see Someone else could well beat me to it though

As I said above, if you want to use the camera for RGB only there would be only a small benefit i debayering and not worth the effort. But if you have the actual resolution from the sky and optics you are using then using a debayered camera for luminance will double the resolution in both axes and if this is used to control intensity in the RGB colour image obtained from an (unmodified) OSC camera then the overal perceived resolution is increased. Narrow band is a totally different matter. The sensitivity of the red pixels is increased for Ha by removing micro lens and red CFA filter. The increase is even more for SII and for OIII it is increased slightly due do the wavelength falling on the sides of the G and B spectral responses. Having two green pixels per quad halps with OIII in the OSC version but by my reckoning this doesn't quite make up for the attenuation from the colour filters. The improvement in sensitivity for Ha and SII is considerable - being around 2x. Then on top of this we have four times as many pixels receiving photons giving the aforementioned increase in resolution. If binning were possible with a DSLR we would gain 3 stops for the same resolution by binning 2x2 over the OSC version.

I may be confused but surely you must compare pixel with pixel not the sum of 3 pixels with the value of 1. If we average over the quad, the sum of the OSC version is R + 2xG + B = 38321. Now lets add the mono pixels = 4 x 13363 = 53452. So comparing like with like, before debayering the sum of 4 is 38321 and after debayering it is 53452. This shows an increase in sensitivity of 1.36 times. Of course if we could somehow retain or replace the micro lenses the benefit of debayering would be even greater. Apart that is from the doubling of resolution in both axes.

Yes - this is what I meant

I think I've pretty much settled on a 4 position FW for my debayered 1100D with Ha, OIII, SII and L filters. The L is useful both as high res luminance and for setting up. I could use an 1100D with untouched CFA for RGB simultaneous imaging. This would almost make up for the smaller, less sensitive pixels compared with mono separate RGB subs binned 2x2 if this were possible with a DSLR (which it isn't AFAIK). This is a cheaper option than a single 1100D with 7 filters as I won't need to buy RGB filters.

From the graphs the KAF8300 mono is actually more sensitive at Ha and SII wavelengths and the same at OIII But as has been said this is a CCD sensor and not CMOS - whether they're the same or different in this respect I have no idea.

Very little then.

40% increase in sensitivity is about half a stop - not a lot Though "every little helps" I guess. I'm not losing any sleep over losing a 40% sensitivity increase

Thank you for that -= I'll look through the links with interest and reply later

Yes, I have. I don't think this blocks much light though and variations in the amount of this layer removed should be able to be compensated by using flats.

450D example - there is a strip on the RHS where the sensor is untouched which may be compared with the centre region with CFA and micro lenses removed. This is a flat using white light in greyscale. CR2 image converted to TIFF and then resized in Ps and saved as PNG. (I'm still looking for representative examples among my dozens of debayering images in various folders ).

Here's some images image taken when I was debayering 1000D and 1100D sensors. These are standard capture using the SD card. When I get going onto debayering an 1100D sensor again I'll provide a better example. 3 1000D examples and 2 1100D. I think the first 1100D image (annotated) shows that the area with CFA removed is lighter than that with normal sensor but with the colour change it's difficult to tell just how much.

I really don't think it's as much as 3 times. When I was debayering and testing the results with side-by-side areas of untouched sensor, micro lenses removed and both removed and while the difference between micro lenses removed and not with CFA intact was noticeable, the improvement in sensitivity due to CFA removal seemed more to me. I'll dig out some sample photos... The effect is subjective and I have not actually measured it - I didn't know how to. You really need to do measurements with a narrow spectrum and compare single pixels at the different wavelengths. With a standard scene it is difficult to tell.

I hope someone understands all that about the BARC layer because I sure don't!

I may have those comparisons one day

I haven't got round to trying the buffing tool dry as yet and I have no idea how to remove that layer below the CFA. I shall endeavour to get the sensor as flat as I can, hoping not to go too far. I think that if I can remove all the CFA over most of the image area, I shall make do with that and use flats to clean up the final image. I've been trying to get my dreaded 3D printer to produce usable prints! I'm up to the 17th attempt at a reasonable frame for holding the sensor for drying and replacing the cover glass and the 4th attempt at the lever that holds the glass and applies it to the sensor frame I'm daft really - in the time I've spent on it I could have made one from sheet plastic or wood with hand tools and hot melt glue! And in fact, thinking about it, I may give up and make it by hand! I'm sure it would be far less frustrating.

That's radical I think it would be difficult to get a clean changeover and also half sensor size partly negates the benefit of a DSLR with it's relatively large image sensor.

I'm still of two minds regarding using a debayered DSLR for LRGB. I'm definitely going for NB as the main reason for CFA removal but I'm weighing up what I would image. My experience with the transparency (or lack of it) and seeing we have in this country, the image resolution is limited by the sky and there is no point in going for small pixels for longer focal lengths. OK the DSLR image size will cover a greater FOV but AFAICT there are few DSOs warranting this frame size and LRGB. In fact the only DSOs I use LRGB for are galaxies and maybe adding star colour to NB. In view of the number of 1100Ds I seem to have I'm thinking I might keep one for use as an OSC camera (assuming I don't destroy all the 1100D sensors I have in total). This would save me buying a set of 36mm unmounted LRGB filters and at the same time mean I would need only a 4 position filter wheel on the debayered camera. The result would be a smaller and sturdier all singing, all dancing camera for narrow band imaging.

The sensitivity to Ha is definitely increased, presumably because the spectral response of CFA red pixels falls off in the deep red. Likewise the sensitivity to OIII is increased because the spectral line of OIII falls between the green and blue responses. SII is even deeper in the red than Ha. So a debayered DSLR achieves better sensitivity for NB as well as having twice the resolution in both axes. For RGB the sensitivity may be slightly lower but the resolution is still doubled. This is definitely a very worthwhile mod for astro use. I have yet to compare a debayered 1100D directly with a mono CCD astro camera but would still expect the CCD camera to win, particularly with regard to noise. But the cost of a 12mp astro camera is considerable. Even with the cost of all the DSLRs I've bought for this project it is still only a small proportion of the cost of a 12mp astro CCD camera. But also, of course, I enjoy the experimenting