I'm going to do a bit more research and reading on this on Saturday during the day.
Just one question - if I'm going to do darks, should I turn off the noise reduction in my camera?
Dave
Yes.
There are couple of reasons for taking separate darks:
- Taking separate darks and stacking them in DSS results in slightly better SNR for the same number of stacked frames.
- LNR takes twice the time (for example, if you are taking 30 sec exposures (lights), camera will take another 30 sec for LNR compensation for each frame).
Please note, you should take the same exposure time for darks. But it can be done later, and you do not have to take as many darks as lights. Some people will say you should take the same number but this is not my experience). They should be taken at same temperature, though.. best immediately after your photo session.
Theoretically each sub should have a dark and a flat taken at the same time, added to each before stacking. This will usually ensure that the camera and chip errors can be cancelled out as accurately as possible leaving only the picture and the noise in the sub. In practice this is usually not necessary as has already been said and described.
Then as the noise is random stacking will increase the picture level much more than the noise thus improving the S/N ratio and consequently allow more latitude in processing the final picture.
It's making sense to this lad. Slowly. I guess, even if I only get 10 second subs due to poor polar alignment, I should be able to take *lots* of subs, darks, flats etc and still get some half decent images. The amount of data is really then going to be up to me, and how prepared I am to get the necessary amount of subs. I'd love 5 min subs, but alas, without a permanent observatory, it's not really feasible imho. Especially since due to either poor weather, or just simply being too tired, my scope time is limited. I love Astronomy, and I really want to do more imaging, hence asking these "silly" questions.
Thanks Barry. It's a pity I never got to sit down and talk to you about it all when I lived with Warren & Ange.
OK, I had a crack at M8 last night - 23 data shots @ 6 secs apiece (to limit star trailing). 5 darks, 1 flat. Better than nothing. The battery on my camera was near dead, so this limited me. I assembled everything in DSS, and it kept 18 files. FWHM was around 3 for most images, which is probably pretty good for manual focus I suspect. The resultant tif (around 35mb) can be found here:
I'm not quite sure how to best approach post processing of this in Photoshop. I tried some work with levels, but whilst it revealed details, it introduced a LOT of noise and colours were not right.
Hmmm
Something is not right here.
I opened your file in DSS, and re-saved it as 16-bit tiff, to be able to process it in DPP.
There are some artefacts present to the right of each brighter star (black dots) and the noise is almost as if the stacking did not take place at all.
Maybe you did not follow the DSS procedure correctly?
To stack, you need to just click on "register checked pictures".
Make sure all is checked, and darks and flats are loaded as such (upper part of the left-side menu).
Otherwise I do not know what went wrong here.. but something did, and badly.
And, yes, do not do any curves in DSS... it is painfully slow so it is very hard to control the process
Actually, when I think of it, the image is pretty good, considering you took 6 sec exposures only.
The noise came from stretching.
You really need longer exposures..
However I can not explain those black artefacts.
The colours may be wrong because of light pollution? Where did you take those pictures from?
Just to give you a reference, the attached image was taken from my backyard last year, with MTO1100-A (1100mm, F11) lens, 30 sec at ISO1600.
It is a stack of 8 exposures.
Thanks guys. You are probably right - not enough data.
Trevor - I'm using a Equinox 100ED + EQ6PRO mount. Since I don't have a permanent setup, nor an ability to have one (long story short my parents property is in about the worst possible shape/position/location possible), I'm having to setup every time. At this point I am not doing an accurate polar align, I'll try this via the drift align method when I get a Reticular eyepiece with about 90x mag. That should hopefully allow some longer subs then.
I'm shooting from suburbia Brissie - Ipswich. So, LP is an issue. The Mark IIn camera is older as well, so noise at ISO 1600 is quite bad, especially when compared to newer cameras like the 5D Mark II.
Bojan - I have a sneaking suspicion that the black artifacts are from DSS trying to remove hotspots from my camera's sensor. Again, I'm very unhappy with Canon in this respect - my Mark IIn has probably 100+ hot pixels even with Six second exposures. It's not normal and is not within spec I believe and is disgraceful QA from Canon.
I'm to the point where after being a Canon user for 20 odd years I'm going to give them the finger and switch to Nikon. Far better cameras imho.
BTW, my image was taken with Canon 400D.
And it was done with the lens mounted on EQ6, no guiding, polar aligned with provided polar scope. I have roughly 70% good frames with 30 sec exposure (the rest show trails due to PE and noise in gears).
As to removal of hot pixels, this is accomplished by darks. So you should un-check the removal of hot pixels feature in DSS.
However, I do not think this is the reason for black artefacts... it is almost as if the negative image was superimposed onto the rest, but shifted (most likely due to a bad polar alignment).
At least to start with, just take longer exposures to get some data to play with. Then you can work on alignment later.
Alternatively, go wider in field, screw your camera onto the top of the OTA and take shots through a normal lense (50-100mm). You could then easily go out to about a minute with out too much alignment error and start capturing some real/better data.
Yes, it could be slight movement of the frame I guess during the period that I took the shots, and then, I guess misalignment in DSS. I've seen similar things using CombineZM for my macro shots.
As to Nikon, photography is a major hobby of mine (terrestial). Astro imaging with a DSLR is only a minor interest for me, if I'm going to get serious with astro imaging I'll need a permanent mount setup, accurate polar align, better mount, dedicated imaging camera. Nikon's D3 is far better than anything Canon offers at the moment. And truth be told, I'm rather jaded with Canon over a variety of issues, and exceptionally poor customer service that I've received in the past. I won't go into it in detail, since I'll be labelled a "Canon basher" like I have on POTN.
I do NOT believe in giving praise to a bad manufacturer.
Thanks guys. You are probably right - not enough data.
Trevor - I'm using a Equinox 100ED + EQ6PRO mount. Since I don't have a permanent setup, nor an ability to have one (long story short my parents property is in about the worst possible shape/position/location possible), I'm having to setup every time. At this point I am not doing an accurate polar align, I'll try this via the drift align method when I get a Reticular eyepiece with about 90x mag. That should hopefully allow some longer subs then.
I'm shooting from suburbia Brissie - Ipswich. So, LP is an issue. The Mark IIn camera is older as well, so noise at ISO 1600 is quite bad, especially when compared to newer cameras like the 5D Mark II.
Bojan - I have a sneaking suspicion that the black artifacts are from DSS trying to remove hotspots from my camera's sensor. Again, I'm very unhappy with Canon in this respect - my Mark IIn has probably 100+ hot pixels even with Six second exposures. It's not normal and is not within spec I believe and is disgraceful QA from Canon.
I'm to the point where after being a Canon user for 20 odd years I'm going to give them the finger and switch to Nikon. Far better cameras imho.
Dave
Hi Dave
i used to get subs of about 2 mins tops, before i was autoguiding, so getting a more percise alignment will allow you to get some good shots, and 10 or so 2min subs stacked with DSS will produce a nice image.
While stacking images will improve the SNR and make detail easier to see, at the end of the day, there is no real substitute for exposure, and you shoul do some tests to see how far you can push your subs.
I have one of the first cameras to land in the country and do not suffer from the black dot problem or banding or anything else. I haven't even upgraded my firmware.
I have not received a single complaint from any of my clients that I've photographed at weddings or portrait sessions. Look at the landscape work I have posted. Do the images suffer from noise or image degradation? The A3+ prints are staggering in detail and quality. This comment is not leveled at David (as I know he knows how to take a photograph and process it, his macro work is a testament to that), or anyone in particular, but, you have to draw the line somewhere - stop pixel peeping and get back to the art. A lot of people who do nothing but pixel peep can't take a photo to save themselves. I see it all the time on DP Review. What good is it b*tching about the technology if you can't even photograph properly?
Dave, if Nikon makes you happy, go for it. I'm sorry you feel the way you feel about your gear. Do remember, though, that technology improves drastically with time. Your camera is getting on a bit now. Despite it being professional gear, let's not kid ourselves, it will pale in SNR performance of the newer cameras. I love my Canon gear as it performs flawlessly for me. If you have L-series glass for sale, I'm interested.
No, I'm using an older 1D Mark IIn ;-) the black dot syndrome not only affected the 5D mark II, but also older cameras as well. dpreview.com had countless threads on the subject!
What good is it b*tching about the technology if you can't even photograph properly?
Mate, it is not about b*itching here, it is about correct data record.
I personally do not care about art.. For me the camera is a photometric equipment, and all I care is whether my astro images contain real data I can measure and not artefacts, which are not data.
Of course, if I were in art, I would not mind black dot here and there.. it may even be regarded as an expression of "artistic freedom"
Thanks Duncan - at the moment I'm limited to between 5 and 10 second subs without any drift alignment it seems. Frustrating to say the least. I eventually will get a reticular eyepiece and will learn drift alignment to get better subs, I know it's the best way of approaching this, I'm just trying to hack things "as is" for the moment! Thanks for the encouragement.
Humayun - I know newer Canons are better in noise etc, but my problems require a bit of background history to see where I'm coming from.
1. A very bad experience with Canon Australia re: 1D batteries and a 430ex flash unit and offshoe adaptor. Worst customer service I've encountered in 30 years of being a consumer.
2. I seem to have bought a "dud" 1D Mark IIn, at least in many ways. Far too many hot pixels for a 6 second exposure imho, firewire port died too. True, I bought it 2nd hand, but unit was only 9 months old when I bought it, one owner. I'd expect a 6k pro camera to be made better, and have better QA.
3. Canon refuse to provide 64 bit drivers for FireWire connectibility for the Mark II/n. I'm tempting to take legal action over this, as I believe that they are in breach of several areas of the Trade Practices Act 1974, or at least it's legally open to interpretation. Whilst the Act states that manufacturers are legally obliged to provide spare parts and support for a product for 5 years from date of cessation of the product being part of the current range, I believe that drivers, especially in todays modern products, should be included in this. With things like a camera, the driver is CRITICAL for the product to interface with the computer.
True, I can use a memory card reader, but each time I use that, I run the potential risk of either damaging the card, or the pins in the camera's card slot. As you can appreciate, using a firewire cable from camera to PC is far less risky from that perspective.
Canon simply is being lazy, and tighta$$es by not producing drivers. I'm not saying Nikon is any better in this respect btw. I don't believe in rewarding manufacturers for bad support.
