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Astrosurf

OIII Filter for Imaging Rosette Nebula?

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Why not go for a second hand canon 350D and mod that like I did? I am rubbish and soldering and wiring but it was not that difficult to do so long as you have good eyesight and just work very carefully and slowly it takes about 3 hours to do it and if its a cheap camera it wont be so bad if anything goes wrong.

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Why not go for a second hand canon 350D and mod that like I did? I am rubbish and soldering and wiring but it was not that difficult to do so long as you have good eyesight and just work very carefully and slowly it takes about 3 hours to do it and if its a cheap camera it wont be so bad if anything goes wrong.

Didn't take me that long this afternoon with my latest 1100D. Mind you, I did managed to break the blue coloured filter yet again - not that it matters as that's scrap anyway. I got the UV/IR outer filter out in one piece and put that one back. I took quite a long time on that one - carefully cutting round the edge of it and then working my way round the edge of it very gently prising it up with a craft knife. I must have gone round it a dozen or more times - I was determined not to break it. That is the third 1100D I've done the mod on so I am a bit experienced, I guess :D I think I took rather longer the first time.

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Thanks guys. There's someone who could mod it for me, but again, it's the lack of dosh! Always the case. :rolleyes:

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Dosh is always a problem :( We are still suffering from a big repair bill for our 4WD pickup - an essential vehicle for the smallholding with a remote field to access, hilly ground and a decidedly damp climate! There's also VET bills and other expenses. The smallholding is great to have but doesn't actually turn a profit. Apart from that we live on our pensions. Fortunately we are capable of maintaining the buildings etc. ourselves and can reduce essential outgoings to a minimum.

Edited by Gina

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I feel your pain. My tumble dryer, oven and car heater have broken down too! We can't repair them until July.

There should be a hardship fund for hard-up astronomers!

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I feel your pain. My tumble dryer, oven and car heater have broken down too! We can't repair them until July.

Oh dear, that's very annoying :( I don't use a tumble dryer nowadays though the washing machine has a tumble dryer - if the weather isn't suitable for outdoor drying I hang the washing on a rack over the bath to dry after they've been spun partly dry. There's only the two of us so not too much washing.
There should be a hardship fund for hard-up astronomers!
Most definitely :)

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Had a few more plays with this Alex, restacking the raws and just applying levels and curves. Tried a bit of cropping but the balancing act of trying to boost the red and limit the noise and banding is beyond my capabilities! I think its only really achieved what you have got yourself with the subs.

I guess its a bit of a tricky one when you are trying to capture what is essentially mostly Ha data on an unmodded camera you compensate for the lack of data coming through by increasing the exposure time, this then increases the noise introduced and inevitably the CMOS warms up. I believe 5 minutes is a fair bit for a DSLR too (correct me if I am wrong) and I am not going to be anywhere close to that sort of exposure time yet to say from my own experiences. I do however give a good period of cooldown time between shots and I think this helps me out a lot - normally I would leave the camera to cool for the same time as the exposure duration (this may well be overkill but I am personally very cautious of adding any extra difficulties to my imaging!) So I was wondering how long you leave your camera between exposures? And whether it would make that little bit of difference extending it?

Anyway heres what I got from playing with a bit of a crop from your RAW files stacked. (looks a little green looking at it again :shocked: )

post-15439-0-59417000-1340645888_thumb.j

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I've gone up to 8 minute exposures on DSLR and the absolute noise isn't much different than on shorter exposures. However, that might be because it's hidden by all the light pollution! Seriously, there are several noise mechanisms, and I'm not sure the temperature dependant part is that significant. While I can't prove it, my gut feeling is taking more subs would give better results than allowing cooling to take place and get fewer subs. I just don't think it can get rid of the heat inside quickly enough to make a big difference, so just keep running it hot anyway.

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Yes its a very enclosed system. I'll give it a try I am working on an alt-az mount so generally my exposure times are limited to ~ 60s so I always felt leaving it the same amount of time wasnt so productive :) The proof is really in the pudding, if similar results come from not allowing a cooling period then its a clear winner :D

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My experiments have shown that the temperature is a major factor in the noise produced in a DSLR CMOS sensor. Noise increases by a factor of two for each 7C rise in temperature. This is why I have produced a cooling system for my 1100D. I have shown that cooling the sensor to -15C reduces the noise by a factor of 32 times compared with 20C without cooling. AP with almost continuous sensor use does cause considerable heating. Adding a pause between exposures helps a bit. eg. using equal exposure and pause halves the heating effect. I've found virtually continuous exposure results in 5C or more rise in temperature, producing almost twice as much noise.

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While some temperature related noise effect is expected, I didn't think it would be as steep as 7C per 2x. Was that based on your tests or other references? Either way, I think I need to read up more there.

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While some temperature related noise effect is expected, I didn't think it would be as steep as 7C per 2x. Was that based on your tests or other references? Either way, I think I need to read up more there.

I read that 2x per 7C rise in temperature but it was also borne out by my expriments. Where 1m exposure at ISO 1600 is just acceptable at 20C, in my experiments I went up to a full hour to show the noise at -15C. That exposure really showed the noise and I'd probably used a half of that in practice. The theory shows that with a difference of 35C (+20C to -15C) ie. 5 x 7, the exposure could be increased by 2^5 (2 to the power 5) times = 32. In other words 32 minutes at -15C gives similar noise to 1 minute at 20C for a given ISO. I'll see if I can find my experimental results - I know I posted them here some time ago.

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