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Ouroboros

Modded DSLR or Cooled CCD (Colour)?

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I'm considering moving on from my ageing Canon 450D for use with my SkyWatcher 200P. 

I quite enjoy my "one shot" astrophotography. I don't get much sky time so getting an image at one sitting is preferable.

So my choice seems to be between a modded DSLR or a cooled (colour) CCD with a sensor similar in size to the APS-C size I have in my 450D.

The DSLR route is probably the least expensive and most straightforward.  I can be up and running again quickly. I have already climbed the DSLR learning curve. I have the image acquisition software (BackyardEOS), which I am familiar with.

But the cooled colour CCD route seems on paper to offer some advantages, whilst retaining the advantages of the DSLR. I'm particularly attracted by the lower dark signal claimed for cooled CCDs.  Some manufacturers even claim no dark frames are required. Is this true? 

Any thoughts or advice most welcome. 

Edited by Ouroboros

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Yeah. That's why I have posed the question the way I have.  Given a choice between modded DSLR or colour CCD what are the pros and cons? 

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If you're into DIY then no contest, modded  cooled DSLR.

450d perfectly suitable for modding.

Dave

Edited by Davey-T

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I asked myself a similar question some months ago though it was to go down the mono CCD route (with filter wheel and probably narrow-band). But cost was a deterrent for me.

So I've decided to try and squeeze as much out of my DSLR investment as possible. I'd already replaced the stock IR filter and I am now attempting a cold-finger cooling system. I hope to achieve reduced noise levels close to a CCD while retaining all the equipment, software and processes I am familiar with.

I'm sure a cooled OSC CCD will give you what you want but I think a fully-modded DSLR will come close - and at a cheaper price.

John

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I would probably buy a modded DSLR if I went down the DSLR route.

However, regarding taking dark frames I really resent the time spent during an evening imaging.

I am hoping that a cooled CCD allows for darks not to be taken at all or to be taken during the day at the same temperature.

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If you're into DIY then no contest, modded  cooled DSLR.

450d perfectly suitable for modding.

Dave

Not a great DIYer me!

But you sort of touch on what I'm thinking. In many ways a modded, cooled DSLR would seem to fit the bill. But you can't buy them I believe. I rather assume the cooled colour CCD fills that niche. But I'm put off such cameras because there's such a downer on colour CCDs for all sorts of reasons - not least being the mono/colour debate, and that the colour images are difficult to process.

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Coming from DSLR you risk being addicted to OSC which rather defeats the object of mono CCD. Yes, an OSC CCD will usually beat a DSLR but the 8300 CCD chip does not make a great OSC CCD camera from what I've seen.

If you have already decided on OSC then the debate is hobbled. I'd go for a fresh sheet of paper and (you know I'm going to say this!) I'd go for mono CCD.

Davey-T's view is that a modded and cooled DSLR is a no brainer winner over OSC CCD. That isn't my view. I have seen so many dead, dying, dust and gunge-infested cooled and modded DSLRs (from professional outlets) that I can honestly say I never want to see another so long as I live!

My own 'no brainer' view (and it is just mine) is that mono CCD is still miles and miles ahead of all comers, but that is maybe likely to change in the next ten years.

Olly

Edit. Darks for set point cooled CCD need doing no more than once every six months. Honestly, I do mine once a year - though I tend to use a slightly different method. DSLR darks, being of random temperature, are just as likely to do harm as they are to do good.

Edited by ollypenrice

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However, regarding taking dark frames I really resent the time spent during an evening imaging.

I'm with you on that! If you bought a modded DSLR with set-point cooling then you could create a darks library at various temperature, taken at any time of day or night. Of course, same goes for a cooled CCD.

Craig Stark has a lot of interesting articles about Canon cameras, noise and calibtation (e.g., http://www.stark-labs.com/craig/resources/Articles-&-Reviews/CanonLinearity.pdf). His HangOuts videos are good too.

Certainly, once I have my cooled DSLR, I intend to dispense with darks in favour of BPMs (bad pixel maps). In fact, some suggest that dark frames can sometimes inject noise into the processed light frames because of the perculiarities Craig discusses.

John

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I have seen so many dead, dying, dust and gunge-infested cooled and modded DSLRs (from professional outlets) that I can honestly say I never want to see another so long as I live!

My own 'no brainer' view (and it is just mine) is that mono CCD is still miles and miles ahead of all comers, but that is maybe likely to change in the next ten years.

Olly

And when I've destroyed my DSLR with extreme modding I'll invest in a mono CCD... I agree it's the tried and tested better route. :icon_salut:

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Davey-T's view is that a modded and cooled DSLR is a no brainer winner over OSC CCD. That isn't my view. I have seen so many dead, dying, dust and gunge-infested cooled and modded DSLRs (from professional outlets) that I can honestly say I never want to see another so long as I live!

If it's a choice between spending £1400.00  on an Atik 383 OSC or modding a camera already in your possession it's a no brainer, unless you've got money just to try it and see if you like it and then you can buy a mono CCD but probably not one with a sensor approaching the same size as your DSLR unless it's a mono 383 then you need filter wheel and filters 31mm ? another few hundred pounds.

This subject has been debated to death and some are firmly entrenched in one camp and some in the other, myself I have OSC, CCD, DSLR and other assorted cameras so am not committed to one or the other. (Mrs "T" thinks I should be committed but that's another story)

To quote from Steve Richards revered tome on the subject [ sorry Steve ] "There is much debate over the advantages / disadvantages of the two types [mono osc] but from my own point of view, with fickle skies of the UK to contend with, the OSC version is all the camera I need for the vast majority of my deep sky imaging and the complexity of a mono CCD and LRGB filters approach holds little appeal for me, with one caveat-the taking of narrow band images which means that I do need a mono CCD camera as well. However don't just rely on my take on it as there are two distinct 'camps' on this subject and it would make good sense to listen to both and decide for yourself"

Or be more confused  :grin:

Dave

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Yup, I know and respect Steve's point of view, and he and I have discussed this amicably, but I'm not bound to share it in all respects. In the end I sold my OSC because I didn't find it as productive as a second mono and I don't really find mono complex... I like the control. But, as you say, it's been done to death as a topic.

Olly

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I have to set up and tear down every time I get the opportunity to image - maybe once a month if I'm lucky. I don't need anymore complexity on top of setting up, polar aligning, finding the target, getting guiding working, setting up and focusing the camera. This is why I am considering the OSC route .... irrespective of the arguably better performance provided by mono CCDs.

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I'm with you on that! If you bought a modded DSLR with set-point cooling then you could create a darks library at various temperature, taken at any time of day or night. Of course, same goes for a cooled CCD.

Craig Stark has a lot of interesting articles about Canon cameras, noise and calibtation (e.g., http://www.stark-labs.com/craig/resources/Articles-&-Reviews/CanonLinearity.pdf). His HangOuts videos are good too.

Certainly, once I have my cooled DSLR, I intend to dispense with darks in favour of BPMs (bad pixel maps). In fact, some suggest that dark frames can sometimes inject noise into the processed light frames because of the perculiarities Craig discusses.

John

When using darks with a DSLR you really ought to be using optimised dark scaling.  This scales darks at one temperature to lights taken at a different temperature.  This really is essential because the DSLR sensor temperature is constantly changing during an imaging session.  Also, don't rely on EXIF temperature as an indicator of sensor temperature - there's plenty of evidence to show it is not a good predictor.

Optimised dark scaling also deals very neatly with the peculiarities that Craig discusses. It's an issue that keeps coming up and it's a bit of a red herring.

Mark

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"When using darks with a DSLR you really ought to be using optimised dark scaling.  This scales darks at one temperature to lights taken at a different temperature.  This really is essential because the DSLR sensor temperature is constantly changing during an imaging session.  Also, don't rely on EXIF temperature as an indicator of sensor temperature - there's plenty of evidence to show it is not a good predictor.

Optimised dark scaling also deals very neatly with the peculiarities that Craig discusses. It's an issue that keeps coming up and it's a bit of a red herring.

Mark"

Perhaps a tutorial on the subject would be a good idea, if someone was willing...

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I have a self modded DSLR (Canon 1100D) and a OSC (QHY 8). I only used QHY 8 on limited occasions due to my limited time under the stars and my unfamiliarity with Maxim DL (for QHY). I have Backyard EOS which is very easy to use. The only gripe I have about DSLR is the conversion time required for the camera to process the image and then ready itself for the next shot (and if you want a time gap in between each shot to cool the CMOS sensor, then it can be a long night with minimal data collection time).

Now I have a pier set up, I plan to use the QHY a bit more and learn about it in greater detail. It has very fast download time and a cooled sensor means very minimal time lag between each shot.

Hope that helps.

Bo 

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I have to set up and tear down every time I get the opportunity to image - maybe once a month if I'm lucky. I don't need anymore complexity on top of setting up, polar aligning, finding the target, getting guiding working, setting up and focusing the camera. This is why I am considering the OSC route .... irrespective of the arguably better performance provided by mono CCDs.

Yes, the filters and wheel do add another component to the long list along with a couple more cables if it's electric.

Olly

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I have a self modded DSLR (Canon 1100D) and a OSC (QHY 8). I only used QHY 8 on limited occasions due to my limited time under the stars and my unfamiliarity with Maxim DL (for QHY). I have Backyard EOS which is very easy to use. The only gripe I have about DSLR is the conversion time required for the camera to process the image and then ready itself for the next shot (and if you want a time gap in between each shot to cool the CMOS sensor, then it can be a long night with minimal data collection time).

Now I have a pier set up, I plan to use the QHY a bit more and learn about it in greater detail. It has very fast download time and a cooled sensor means very minimal time lag between each shot.

Hope that helps.

Bo 

My understanding is that a DSLR sensor only heats when actually capturing. If your are pausing for cool down and/or settling after dithering 15 seconds should be more than enough time to download a RAW image to a card , flash drive, or laptop HDD. If it takes longer than 10 seconds look at getting a faster card (class A). Flash drives are fast. Don't take images in RAW+JPG, a total waste of time and space. Ordinary laptop HDDs are relatively slow, yet I download to mine in 10 seconds.

BTW a sensor continues to heat during a session. Seconds, even minutes aren't nearly sufficient for total cool down. A major source of camera heat can be the battery. Replace it with a mains supply, or 12v converter.

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Yes, the filters and wheel do add another component to the long list along with a couple more cables if it's electric.

Olly

I think if I had an observatory and the opportunity to image regularly I would certainly add a mono CCD, filter wheel etc to my kit. Edited by Ouroboros

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Do you image in dark skies or light polluted skies?

I started off with a standard 1100D, then moved onto a self modded 450D, then finally moved on to a Mono CCD.

I have a lots of light pollution to deal with and images I got with the 1100D and 450D I thought were pretty good.

The first exposure I got from my Mono CCD and a ha filter blew me away. I haven't touched my DSLR's since, even though I purchased a small sensor CCD camera and have to produce mosaics of most targets.

If you image in light pollution then you really must consider narrowband imaging with a mono CCD if you can afford it.

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I think Ouroboros kind of hits the nail on the head when he talks about lugging the gear into the garden before he can start imaging.

For those of us lucky enough to have an Obsy or dedicated pier arrangement, setting up and starting is much quicker and those valuable hours of darkness can be more productive.

It certainly means I get out more often even for a hour or so, any time spent imaging and learning has to be a bonus. I'm still at that early stage where each time I go out I seem to find something I could do better/ more effectively and as we know practice makes perfect.

Gareth

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When using darks with a DSLR you really ought to be using optimised dark scaling.  This scales darks at one temperature to lights taken at a different temperature.  This really is essential because the DSLR sensor temperature is constantly changing during an imaging session.  Also, don't rely on EXIF temperature as an indicator of sensor temperature - there's plenty of evidence to show it is not a good predictor.

Optimised dark scaling also deals very neatly with the peculiarities that Craig discusses. It's an issue that keeps coming up and it's a bit of a red herring.

Mark

Mark, could you give us some pointers on how to do this? What software has this feature?

You say not to trust EXIF temperature information, so how can dark frame scaling be applied consistently in an un-cooled DSLR context (as EXIF is the only temperature value we have)? My understanding (please correct me if I am wrong) is that dark scaling is more of a convenience to extrapolate for a temperature not covered in darks library. And maintaining a darks library only makes sense for cooled cameras.

John

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Mark, could you give us some pointers on how to do this? What software has this feature?

You say not to trust EXIF temperature information, so how can dark frame scaling be applied consistently in an un-cooled DSLR context (as EXIF is the only temperature value we have)? My understanding (please correct me if I am wrong) is that dark scaling is more of a convenience to extrapolate for a temperature not covered in darks library. And maintaining a darks library only makes sense for cooled cameras.

John

Very good questions!

Of the packages I'm familiar with, PixInsight, DSS and Iris all have this ability.  I think PixInsight is the most robust.  I'm sure that many other packages have the ability - I just haven't used them myself.

Temperature information is not required to perform optimised dark scaling.  The way the optimisation works is to work out what multiplier (i.e. scaling) is required to the master dark in order to provide the maximum noise reduction when it is subtracted from the light frame.  So the optimisation is looking solely at the image noise and needs no temperature information whatsoever.  This optimisation is performed for each individual light frame.  So, for a typical imaging session,  the sensor temperature and therefore the thermal noise will increase during the session.  So the optimised dark frame multiplier will tend to increase from one light frame to the next.

It might still be worth having a few master darks - e.g. one for a hot night, one for a medium night and one for a cold night.  For myself, I just use a single master dark taken on a warm night and I use it for all imaging sessions.  It's now 2 years old or more and still works fine.  No more stressing over taking darks  :)

Hope that makes sense.

Mark

Edited by sharkmelley

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Do you image in dark skies or light polluted skies?

I started off with a standard 1100D, then moved onto a self modded 450D, then finally moved on to a Mono CCD.

I have a lots of light pollution to deal with and images I got with the 1100D and 450D I thought were pretty good.

The first exposure I got from my Mono CCD and a ha filter blew me away. I haven't touched my DSLR's since, even though I purchased a small sensor CCD camera and have to produce mosaics of most targets.

If you image in light pollution then you really must consider narrowband imaging with a mono CCD if you can afford it.

I now do most of my imaging in North Cornwall. It's not quite as dark as Exmoor perhaps but it's certainly pretty dark towards the zenith and the Northern sky. I have some light pollution towards the south. On clear nights my Sky Quality Meter measures between 21 and 21.5 magnitudes per square arcseconds, which translates to between 6 and 6.5 naked eye limiting magnitudes. A common problem though is semi-transparent sea mist which back scatters the street lights from local villages. But when it's clear it's good and I can certainly take exposures of between 5 and 10 minutes without much problem .... unlike here in Oxfordshire where a minute is about the maximum exposure at ISO 800.

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Of the packages I'm familiar with, PixInsight, DSS and Iris all have this ability.  I think PixInsight is the most robust.  I'm sure that many other packages have the ability - I just haven't used them myself. 

Regarding DSS do you know whether the software is doing this automatically or does a setting have to be clicked somewhere?

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