Gina

Oh That quote didn't work - I'll attach the images again here.

- ->

This is the JPEG image scaled to 1024px wide in PS CS5 no other procesing and the histogram from the original JPEG image. The RAW CR2 image produced by the 1100D is not readable by PS.

Here's a quote from my near ambient cooling thread :-

Now have results from last night's darks sequence run. The computer on the Blue cooler camera crashed before the end of the run but I have full results for the Silver one. Here is an image and histogram from the last dark - 10,000s at ISO 6400. That's 2.77 hours or over 2 hours 45 mins. EXIF T showed 8C but I think this is reading about 3C high - ambient estimated at about 2C

- ->

I've been doing some tests with my 1100d with an image analysis app I wrote, and it seems to me that the 1100d applies the ISO gain to the analog signal right up to ISO 6400. Based on my results I'm pretty certain it is not just multiplying the digital signal at any ISO. Another interesting thing I've noticed is that the number of noise pixels stays constant up to ISO 1600, but shoots up drastically at ISO 6400. I think there is a low level of false signal in the chip that is quantized to zero, but over ISO 1600 the background murmer gets quantized to a positive value.

Do you know what the sensor temperature was when you took those figures, Agnes? I've certainly noticed a disproportionately greater noise with ISO 6400 with an uncooled camera in the warmer weather when the EXIF T reached 20 or 30C. But my noise tests at around 2-3C with cooled camera shows a low noise level even at ISO 6400. eg. the noise with a 10,000 second exposure produces the sort of signal I get with a bright DSO at much shorter exposures. I think I'll go through my data and see if I can find some related examples.

I guess it also depends on whether the ISO setting is adjusting the analogue gain BEFORE the ADC or whether it (at some point) the ISO setting is adjusting digital gain (AFTER the ADC). It might be that the analogue gain is adjusted up to a certain ISO setting, then after that it uses digital gain. A bit like they tend to do with optical zoom/digital zoom on some cameras. I don't know.

I don't know either. I've conducted a noise test run, now I need to do a signal test run. Problem is getting a continuous and steady test signal. There is also the problem of different DSOs having different characteristics, particularly different dynamic range, though I think we can say that they all have more dynamic range than any camera can cope with.

So the big question is, does using a high ISO limit the dynamic range? The next question is, how do we find out? A crude test on a familiar object with say 1m at ISO 6400 and 4m at ISO 1600 alternating should give an indication at least. There may not be a big enough difference with only a 2:1 ratio so I'm thinking 4:1 may be more revealing

There is no doubt about it Gina, you will have to run a very controlled test. Same subject, same night. Short subs at 3200 and longer subs at 1600. The processing should reveal the differences if any. If your theory is correct then both pics should look the same with equal processing.

Yes, I could certainly do that - best would be to inlerleave exposures - pairs of alternating short and long subs with associated ISO setting. No problem in APT. The problem is the weather - no telling when we might get a clear night

Do you still have your webcam link Gina so we can see the roof in action?

It's not working at present - a problem with the computer that serves it I think. I'll check again. ATM any time the roof opens or closes it's me pushing it

I'm looking at how to mount the winch currently but the weather isn't helping - it keeps raining.

Yes, but you would only have the same exposure time and surely that's what counts?

The amount of signal depends on sub exposure time and gain so a 5m sub at ISO 3200 becomes 2.5m at ISO 6400 with the same noise if you reduce the temperature by 7C so in a given total time you can get nearly twice as many subs. (Not quite twice as you have to allow for the sensor reading time between subs.) Hope that clears that up

You lose alot of dynamic range when using a very high ISO. You will find you have no star colour left as they all just end up bright white. Does not make a nice astro photo in my view. The best DSLR astro shots i've even seen have been done with lower iso's.

Do you? Unfortunately the weather has not allowed me to test the use of ISO 6400. I know 3200 works well with a cooled camera but to be able to pack nearly twice as many subs into the available time would be nice. Only time and weather will tell if this works or whether It's better for me to stick with 3200.

Gina, the signal is also affected by gain. So in principal you're not gaining anything by changing ISO since the SNR stays the same (but it's not as straight forward as that either). There's a very good discussion on the topic here: http://stargazerslou...1600-v-iso-800/ and the posts by IanL are very informative!

Also, Ags showed that the noise response of the 1100D sensor from ISO 100 to ISO1600 behaves as expected but at ISO6400 it does not and instead of four times more than ISO1600 it's more like 6 or 7 times more (if my math is correct).

That was what I thought but my measurements have disproved it - at least with the sensor at reduced temperature. See my cooling thread (Cooling to near ambient...) for details. Particularly 10,000 secs at ISO 6400 at a degree or two above freezing. Have to say I was very surprised.

Fundamentally bayer colour filter sensors do not sample all colours at all points, with the information interpolated to produce the nominal full resolution output. As a worst case scenario, the resolution is 25% of nominal! If you have a strongly red or blue subject, with little in the other channels, you're only significantly stimulating 25% of the detectors. e.g. using Ha filter on a bayer sensor, you're throwing away 75% of the sensor output. Removing that bayer filter would get you back to 100% again.

Unfortunately mono cameras where available (astronomical ones too) seem more expensive than their colour counterparts, so if we can remove the colour filter from a DSLR it would enable another level of lower cost imaging.

I can confirm that the resolution fo Ha is only a quarter of the stated resolution. The 12Mpx 1100D becomes 3Mpx without the advantage of the larger sensor you would expect at that resolution and sensor size. Astro imaging is very different from terrestrial photography. With the latter the lower colour resolution of the human eye compared with luminance can be exploited to make what's really a 3Mpx from the colour point of view appear higher definition.

In other words - YES. The specified resolution is the actual photocells for the whole sensor - and that includes an area round the edge that isn't used for the picture as well.

Ags did some tests on the 1100D and found the noise at 6400 compared to 1600 is over 50% greater. Forgive my ignorance, but what are you hoping to gain from using these high gain settings?

The noise at ISO 6400 should be four times that at 1600 as the gain is 4x (not just 50%). OTOH the noise is temperature dependent, doubling for every 7C rise in temperature so reducing the temperature by 14C makes the noise at 6400 the same as the noise of an uncooled camera at ISO1600.

Its a bit of a [removed word] they changed so much about the way they made the later sensor. Atleast you can say you tried really hard.

True.

Don't get too rapped up with the higher ISO levels of the 1100d over the 1000d, its only a gain and will do nothing to add photons, if i had one i would still be using iso400-1600 at most. The noise is only a little better but in the scheme of things makes little difference when both are cooled and you stack images. The best thing about the 1100d is its increase in bits from 12-14. I have been very happy with the performance of my 1000d's.

I do most of my imaging at ISO 3200 but recent noise tests have shown that with cooling using ISO 6400 is well on.

I notice the firm doing mono Canon DSLRs don't include the 1100D (Rebel T3) :- http://www.maxmax.com/monochrome_camera_order.asp

Now have 44AH car battery (sealed) and appropriate terminals. And this afternoon connected the battery cables from the winch control to the battery terminals and the other two cables from control to winch motor. Then tried it out - yes, it's noisy so I'll mount the winch on rubber mountings. The winch drum does seem to rotate at a reasonable speed though

Been trying to clean up my other spare sensor. That's the one I covered in electrically insulating thermal grease - a right mess. However, even after making really sure the connector for the ribbon cable was thoroughly clean, this sensor is giving Err 70. All I know is that it used to work but now it doesn't. So I haven't got a spare working sensor to use for testing. It's no use doing anything with a non-working sensor other than what I've already done with the other one. If I were to attack a sensor from a working camera the chances of getting into the sensor without destroying it in the process are pretty poor - certainly far worse than 50:50.

I am highly reluctant to give up but with the way the cover glass is fixed onto the sensor of the 1100D I think I have met my match There would be no point in getting a 1000D as this camera is already 2 stops less sensitive than the 1100D in addition to having a higher noise level. The other mods to the 1100D have been very successful so I guess I'll have to be satisfied with that. Debayering an 1100D sensor is simply an extreme mod too far - at least for me. Oh well, I put my best efforts into it.

It was an accident - honest gov

R.I.P.

I'm sure we are all on your side Gina, and praying that the sensor still works. I haven't had such a laugh in ages. When I think back to the Canon forums and how much folks stress about being ever so careful with their sensors when cleaning them, I just LOL.

Oh I know everyone is with me on this And I agree with you about the great care people take. The sensor is practically indestructible

I've tried a 20mm buffing wheel and paste on the sensor covering most of the area. This was very quick. However, although all the green has been removed the next layer is softish and I've taken what appears to be a varying amount off - it's giving diffraction patterns. Here's a photo.

I'm thinking that if this stage went well I might have a go with the other spare sensor. However, I have to say that the problem with the cover glass makes this tend towards being a bit too extreme and hazardous unless I find the next trial run goes a lot better. It's absolutely essential to be able to remove the cover glass safely, let alone further risking damage when buffing.

I've been doing a bit of research on the application of the CFA layer to sensors and I think it is applied using a Photolithography technique http://en.wikipedia....hotolithography and that the Microlens over each pixel is above the CFA layer http://www.maxmax.co..._conversion.htm

Yes, I know what photolithography is and it is very likely that this technique was used. As for the microlenses, as long as the result is improved sensitivity and resolution I'm not that bothered if they go.

I've tried using a small amount of buffing paste on the sensor using a cotton bud. Within a few tens of seconds I had removed the green layer leaving a smooth gold layer underneath. Here's a photo of the result.

I've got a high power magnifier and been examining all the fine gold wires and their connections and they all seem fine. However, where I ground down the glass cover plate and then prised it off there's damage to the sensor itself - it looks like broken glass.

I've done a couple of tests with IPA and paint stripper - absolutely no effect. It actually looks like another glass layer

Been watching this thread with interest.

Gutted for Gina however I would reccomend maybe trying it once more in case it was a dodgy connection maybe? Err 70 is reported as being "shooting not possible due to an error, turn camera off/on" and "Malfunctions related to the image have been detected".

I have been caught out many times with poorly seated connectors, worth a shot I guess.

Keith

I'm going to try the same test sensor again on the camera - I've had Err 70 from bad connections before.

Just tuned into this thread and it gave me a real good chuckle at some of the antics, you guys have great big cojones to contemplate trying this.

I don't know about extreme mods but I think Gina needs some extreme counselling, jeez man you is one looney character

:D Oh I is looney alright Mad as the proverbial hatter A true mad sciemtist But it's mad scientists who make breakthroughs

I can't see very well from the photos, but is there any way you could prise off the black plastic frame holding the glass from the rest of the assembly?

No. The black frame is what holds all connections and is NOT plastic I think it's some kind of glass - it's very hard.