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Old 15-07-2009, 10:56 AM
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toryglen-boy (Duncan)
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Whats better? CCD imager or cooled, moded DSLR?

Howdy

Whats better for long exposures with lower noise? a dedicated CCD astro imager, or an IR modded, peltier cooled DSLR?

Also, can anyone gimme a guestimate as to comparative exposure times/noise leves between a DSLR and an average CCD? would a 10 mins CCD exposure have the same noise as an average 3 mins DSLR exposure?

i know its a bit vague, please indulge me


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Old 15-07-2009, 11:29 AM
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I suspect this is very much a matter of personal preference, if you are comparing one shot colour CCDs with a cooled spectrum enhanced CCD;

the reason I went from a DSLR to a cooled CCD is simply noise

With a DSLR I had to take 6 to 7 dark frames-for 10 minute subs that's over an hour and when you go to 15 min subs-well that's a lot of time-and in fact people recommend you need to take as many darks as you take lights

my particular CCD is very low noise-many people don't even bother with a dark, I might take one or three depending on the night. This is virtually not possible with a uncooled DSLR

a cooled DSLR is probably on par with a cooled One Shot Colour CCD. Costs about the same too

there are pluses and minuses of course
the CCD is laptop dependent; rough framing can't be done by squinting through a view finder.

A mono CCD is much more sensitive of course but requires other accessories such as a filter wheel

when I bought my QHy8 I think it was actually cheaper to do that compared to buying the cooled modded DSLR.

course you could buy a used 350 D for 400$, take off the filter yourself and build your own peltier cooling using parts from a travel fridge-there are plans available on the internet.

noise profiles also vary depending on the model of the DSLR. My 300D was very noisy; the 350 D is much less; maybe newer models have progressed further in terms of noise reduction
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Old 15-07-2009, 03:06 PM
Alchemy (Clive)
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Whats better for long exposures with lower noise? a dedicated CCD astro imager, or an IR modded, peltier cooled DSLR?

generally a dedicated CCD is less noisy... note some ccd chips are noisier than others. you will find however to get a 10 megapixel chip is much dearer on a CCD ( the QHY8 is 6 megapixels and as noise free as ive ever seen)

Also, can anyone gimme a guestimate as to comparative exposure times/noise leves between a DSLR and an average CCD? would a 10 mins CCD exposure have the same noise as an average 3 mins DSLR exposure?

it depends on the well depth of the pixels at first glance ie, a 20 min exposure on a qhy8 will leave some color still in stars less than mag 8 this wont happen on a 20 min dslr exposure they will be burnt out.

when i get a 10 min exposure its pretty dark but you can stretch it out to reveal all the detail. it would take pages to describe all the ins and outs........

there are a whole bunch of variants to consider , well depth, bit depth, noise of individual chips. Note i think the cannon 40d is a pretty good buy lots of megapixels, pretty good for dslr, if its modded then Ha is good. One further point having used both, the temp makes a HUGE difference, try shooting a cooled CCD and a DSLR on a warm night (25 deg) and the dslr is a poor second.

i had the money to buy a 40d or a QHY8 , i bought the QHY8 and would do so again in heartbeat, note i already have a camera for regular pic taking so that wasnt an issue, its astro only.
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Old 15-07-2009, 04:30 PM
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With CCDs you set a temperature which is regulated by software and usually maintains that temp +/- 1 degree or usually a fraction of a degree.

So you take a library of darks usually about 6 -16 at a particular temperature (one that you can attain in winter and perhaps a 2nd set for the temp you can attain in summer). You don't need to take a fresh
set of darks each night. Even if your camera does not have accurate temperature regulation you can use adaptive darks where software measures the noise and adjusts your dark to match. It works very well and I can see no difference between exact temp/time darks and close but not the same darks set using adaptive darks.

DSLRs are great instruments but they have trouble with capturing star colours very often and also as they are one shot colour they tend to have trouble with colour noise. Their main advantage is they are portable, don't require a computer to operate and are easy to use and give great results without a lot of fuss. No filter wheels etc.
Also easy to use with a variety of lenses and you can use them for daytime work as well.

In addition they seem more affected by light pollution than cooled CCDs again because of the noise factor.

A one shot cooled CCD is more similar to a cooled DSLR except the accurate temperature regulation is an advantage. I am not sure how accurate the temp regulation is on a cooled DSLR.

The main advantage of a cooled DSLR would be it does not require a computer to operate (I think).

One shot colour main advantage is cooling and thus lower noise. Cooled DSLRs do not get as cold as a cooled CCD.

I like to get my cameras down to -35C when I can as I see the CCDs even a relatively noisy KAI11002 is pretty clean around that temp.

So yeah it is a matter of noise mainly. A Canon 5D has quite deep wells and relatively high QE and is no slouch in the specification department. But then that is a $5000 camera.

As far as how long an exposure it would be a matter of how dark is your site you are taking it from. In a light polluted area that may be a max of 3-5 minutes. At a dark site maybe 10. A cooled CCD you can go up to 30 minutes or more. Depending on your tracking. I don't see why you couldn't go 15 minutes with a DSLR set at ISO800 on a cold night.

Greg.
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Old 15-07-2009, 05:47 PM
Bolts_Tweed (Mark)
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Gday Duncan

I back up everything said but when I was buying my first camera I had no idea regarding well depth, QE etc etc - It has been explained pretty well by our friends but.

Just my experience is that I have both (a modded 350D (admittedly not cooled) and a peltier cooled CCD). I havent used the Canon in 4 or 5 months (apart from a few test shots after Eric modded it for me). Admittedly the CCD was twice the price of the DSLR but it was worth every cent.

The disadvantage however is widefield photography with lenses. I notice Hutech make adapters now to fit Canon lenses to T ring CCDS but it is more money.

SO if you decide you are primarily interested in prime focus telescope photography I would grab a cooled CCD but if you want to do some wide field as well a DSLR will still give pleasing results and can also be used for prime focus as well. You may however be disappointed as you take more photos and get more critical of your own images.

Who knows another comet McNaught might be just around the corner.

For what it is worth my vote however goes for a cooled CCD

Mark
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Old 15-07-2009, 06:43 PM
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Hi All

Can I just ask a question here. When you are saying "cooled ccd" are you referring to the 2 stage TEC cooling (Peltier with fan and heatsink) like the QHY8? Or are you including the one stage TEC cooling like the QHY6? And do you include the meade-style cooling with no fan, but just a big heatsink like the DSI-III?

Thanks
Darrell
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Old 15-07-2009, 06:55 PM
Bolts_Tweed (Mark)
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Gday Darrel

How are ya mate. Good point you make - I am talking about peltier fan and heatsink.

Mark
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Old 15-07-2009, 07:54 PM
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Hi Mark

If thats the case, do all the comments made so far equally relate to the ccds with the alternate cooling options? Like being less noisy; or being less affected by light pollution than a DSLR?

If we are talking mainly about noise, and the peltier fan and heatsink ccds are at one end of the scale (less noisy) and the DSLRs are at the other end of the scale (more noisy), do the QHY6 and MeadeDSI-III ccds slot in between. If so, are they close to the QHY8 end of the scale; in the middle; or closer to the DSLR end?

Hope all that makes sense.
Darrell
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Old 15-07-2009, 08:17 PM
Bolts_Tweed (Mark)
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Yeah mate - I will have to leave that for others as I have so experience with other CCDs.

Noise but is noise as I understand it - I have found that with advanced cooling and shorter exposures (say up to 5 - 8 minutes) I can get away without darks if I am stacking enough.

I suppose by inference - less cooling = more exposures and more darks to achieve the same result if all things are equal (QE, well depth etc - which they arent I suppose - I am unaware of the performance of the other CCDs). But i await the voice of experience.

Mark
(half time is nearly over - and blues are winning - back to the TV)
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  #10  
Old 15-07-2009, 11:32 PM
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Signal to noise is paramount, and is the main reason DSLR's do not work well at all in light polluted environments. Cooled CCD's generally have higher QE, dynamic range and lower noise.

CCD's also work significantly better than DSLR's with narrow band (eg H-Alpha) filters as all of the pixels are used to capture signal.

If you ever want to do some real science with a camera, (eg photometry) you'd simply not be able to do so with a DSLR.

By the way, while taking an image of M20 a couple of nights back, using 10 minute subs, I checked the data for minor planets...and was delighted to find a mag 20 interloper....try that with a DSLR from the burbs !

Resolution is also higher with RGB filters and a mono CCD...infact if you were to use the same rationale as CMOS manufacturers an RGB image taken with a KAF11002 mono sensor would be around 33 megapixels...and a KAF16803 weighs in at 48 megapixels..but I digress.

IMHO CCD's are still the gold standard for deep sky imaging, but require quite a bit more work (darks, lights, flats for each filter etc.).

DSLR's are however excellent under dark skies with wide field/bright subjects....and are very handy when the sun comes up!

Last edited by Peter Ward; 16-07-2009 at 02:44 PM. Reason: typo
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Old 16-07-2009, 06:22 AM
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Originally Posted by darrellx View Post
Hi Mark

If thats the case, do all the comments made so far equally relate to the ccds with the alternate cooling options? Like being less noisy; or being less affected by light pollution than a DSLR?

If we are talking mainly about noise, and the peltier fan and heatsink ccds are at one end of the scale (less noisy) and the DSLRs are at the other end of the scale (more noisy), do the QHY6 and MeadeDSI-III ccds slot in between. If so, are they close to the QHY8 end of the scale; in the middle; or closer to the DSLR end?

Hope all that makes sense.
Darrell
Not sure about the noise aspect of the DSI etc but as a general observation to be able to produce an image that is better than that
of a modified 350D or 40D etc you would have to have a pretty reasonable CCD camera like a 6 megapixel chip or beyond. Below that I think the results on the net say you are better off with a DSLR. After all DSLRs are quite large chips and 6 megapixels and beyond with good sensitivity once modified.

Thats why you see the usual progression of DSLR, then a better DSLR then a modified DSLR then a cooled CCD like QHY models, Sbig, FLI or Apogee.

The price of CCDs cameras seems to be falling as the competition heats up. QHY may be the cause of that. Apogee U8300 cameras which would be superb are around US$3500 or so. A lot, but cheaper than where they used to be. 2nd hand cameras can be picked up at www.astromart .com

You could get a decent one for probably about US$2500 or less. A good 2nd hand modded 350D DSLR is what about US$500 or less so it is a quite a jump. Not familiar with the QHY prices but I know they are probably less than that.

Greg.
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Old 16-07-2009, 09:10 AM
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Hmm, I will weigh in.

I reckon a lot of this has to do with experience and skill level. I like using my cooled 40D because it is easy to use and is not overly complicated. It is great to learn imaging with and processing as a starting point. This is a big factor in imaging, learning should be fun and you getting better results makes for easy learning. Jumping in the deep end will be frustrating at best and could lead to fairlure.

However, there comes a time when you need to move on to better equipment. The cost factor is significantly higher, the resolution is much better, the data is better, but the learning curve is very high. Personally going striaght to monochrome seems like a mistake for a learner. There are so many things an astrophotograher must learn and master first that adding this complication just makes for a disaster. The one shot colour CCD would be fine but really the DSLR is nearly the same and is more versatile and will still mean you have to upgrade down the track to get those awesome images.

I am in the process of upgrading and only went further because I want to get better images than I already am. It is a big step.
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Old 16-07-2009, 09:22 AM
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toryglen-boy (Duncan)
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some great answers here, thanks guys. Would anyone care to choose what they think would be a very inexpensive, absolute beginners CCD to get started?

thanks
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Old 16-07-2009, 09:42 AM
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Quote:
Originally Posted by gregbradley View Post
results on the net say you are better off with a DSLR. After all DSLRs are quite large chips and 6 megapixels and beyond with good sensitivity once modified.
I've found image scale seems to be the key to getting decent images from a small sensor camera. This little 1.3 megapixel starlight hx916 mono camera I've been playing with, can give horrible images at the FL of the vc200l, but at 600mm odd from the tak it's showing real detail. It's seems to be way more sensitive than my old canon 40D or my new qhy8. Light pollution is still a problem for me, it appears to screw up the colours as it shows up more in blue and green rather than red.

Check out some of Max's images with a small sensor starlight camera.
http://www.aaq.org.au/cms/index.php/...kilmister.html
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Old 16-07-2009, 09:47 AM
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some great answers here, thanks guys. Would anyone care to choose what they think would be a very inexpensive, absolute beginners CCD to get started?
thanks
You won't find a cheaper cooled one shot colour than the qhy8.
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Old 16-07-2009, 10:11 AM
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You won't find a cheaper cooled one shot colour than the qhy8.

hmmm ... i know its not that expensive, but i dont know if i would call that something for a very begginer, although i have very limited knowledge on the subject.

isnt there anything else? something cheaper?

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Old 16-07-2009, 10:34 AM
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I'd go for the QHY8, it will serve you well for a beginner and still be usable when you progress. The do seem to take great images.
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Old 16-07-2009, 10:47 AM
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Duncan there has been a lot of good advice here so far. A very good starting point is any decent DSLR and when you have mastered that then maybe work out what your next step is.

I started off with an unmodded Canon 20D and within minutes was getting better results than I ever got with film. Once I went as far as I could with the 20D I bought a Modded Canon 5D or 5DH as it is now known.

Not many people realise that Hutech only started calling their modded cameras after the shorthand started on IIS by just adding a H to the Canon 5D I had purchased from them to save typing 'Hutech modified'.

As you may know I Have been experimenting with Peltier fridge cooling my 5DH. I want to do wide fields so the full frame Canon is for me the best starting point. I stlll have not exhausted the possibilities with this camera as I am still learning what can be done.


Post processing of the data you collect becomes ever more demanding as you go up the chain of cameras now available.

The chain as I see it is


DSLR
Modded DSLR
Peltier cooled modded DSLR
One shot colour cooled CCD
Dedicated astro cooled Mono CCD


There is no easy answer as all these cameras will give decent results but the quality gets better assuming competence in collecting and processing the data as you go up the chain.

Quality has two components the main one is signal to noise. Once you have very good signal to noise then greater dynamic range can be a decider.


Bert

Last edited by avandonk; 16-07-2009 at 10:59 AM.
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Old 16-07-2009, 12:42 PM
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Originally Posted by avandonk View Post
The chain as I see it is


DSLR
Modded DSLR
Peltier cooled modded DSLR
One shot colour cooled CCD
Dedicated astro cooled Mono CCD


There is no easy answer as all these cameras will give decent results but the quality gets better assuming competence in collecting and processing the data as you go up the chain.

Quality has two components the main one is signal to noise. Once you have very good signal to noise then greater dynamic range can be a decider.


Bert
That's a really long chain, whilst I agree with the sentiment that you may need to creep up on mono cooled CCD's experiencewise, you could easily omit some of those steps if you know that you're going to end up at the ultimate stage anyway.

This will save you money in the long run.

Here's my thoughts on the subject.

If you're interested in imaging you probably already have a DSLR and are frustrated with the lack of sensitivity.

Get a small chip monoCCD first, preferably one with internal guiding (SBig or QSI). The advantages of the internal guiding chip should remove some of the most frustrating parts of imaging. Unless you have a superb mount, you'll need to guide. Internal guiding is preferable to external because of the flexure problems of external guide setups, I class the QSI off-axis as internal guiding, it has the advantage of guiding in front of the filters, but the disadvantage of having to buy another guide camera. This will allow you to do medium focal length imaging of large targets to hone your skills and see how much you like it.

Next stage is a larger chip as not all targets will fit on the smaller chips. Larger chips require a flat field etc, so they aren't so forgiving of optical errors.

Then think about upgrading the scope/mount to work at different focal lengths.

Then look at adaptive optics, unless you've got a PME by this stage, then OAG for the SBig cameras.

By this stage you'll have to have spent (I hate to calculate this) about $9k to $15k depending on the size of camera you get.

If you go through the steps above, you'll spend

DSLR - $1k
Modded DSLR - $2k-$3k
Peltier cooled modded DSLR - +$1k?
OSC CCD - $2k - $3k
Mono CCD - $3k - ????

So that's spending about $7k to get to the same stage as mentioned above, of which you should get about half back from selling the unused equipment.

It really comes down to the question of how serious you are with imaging, if you are only going to dabble then a DSLR is best, if you pine for better, more detailed images then mono CCD is best. The learning curve can be steep, but the images rewarding. If you've got a small local community to learn off that can help greatly.

Cheers
Stuart
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Old 16-07-2009, 01:00 PM
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Stuart this is NOT a how to. It is a simple question of comparative outcomes as far as a hypothetical imaging device is concerned. The original question was which is better.

Bert
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