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Old 20-02-2008, 04:55 PM
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Originally Posted by PhotonCollector View Post
Yes i was also wondering why you are doing these comparisons between DSLRs and CCD Cameras ?

What are you trying to prove ?

Peter if you are only trying to highlight that a $10,000 purpose built astronomical CCD camera returns better images than an off the shelf $1,200 Digital SLR camera built for everyday photography, then I think most of us already know that the CCD camera is likely to produce "better" images.

The reality is (IMHO) that not everyone wants too or can afford to spend that much money and so as an alternative we can use something almost 10x cheaper - a DSLR.

Peter if I didn't know better I would think you are a CCD Camera Dealer and what you are doing here on IIS is sales work ?

regards
Paul
Totally agree with you Paul.

Hey one thing straight, a dedicated CCD image can never take daylight photography so us DSLR guys have best of both worlds for 1/10th of the price too.

I must admit, I would love to get my hands on an SBIG, but price vs quality, i can't justify spending 8-10k for a few pretty pictures. not sure how many astro images you have taken peter with your SBIG lets say 10 pretty pictures, thats equivalant to $1,000k for 1 pretty pic!!!! i personally cannot justify that.
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Old 20-02-2008, 04:57 PM
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Hello Peter
Havent had time to peruse all the new comparative data yet.
Would like to ask if you have ever taken a pic of ngc4565?
If so would you post on this forum.
Regards
Steve
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  #43  
Old 20-02-2008, 05:37 PM
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The reason I made the exposures all 30 seconds was based on the following logic....

Object rains down say 900 photons in 30 seconds...and to simplify the argument, evenly spread in R, G and B

Multi-spectral camera gets all 900 photons shining on the sensor.

Mono Camera with R G or B filter in front gets only 300 photons. To get an equivalent "full spectrum dose" three exposures need to be made to get the equivalent 900 photons to the sensor.

Also I could only trip the 5D for a maximum of 30 seconds using a USB cable, and didn't feel like guiding any of the exposures


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Originally Posted by h0ughy View Post

Curiously the rgb the st11 took were 30 seconds each, so thats 90 seconds, yet you only took a 30second shot with the dslr? my maths was never my strong point
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  #44  
Old 20-02-2008, 05:50 PM
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There are lots of much less expensive CCD alternatives that are just as sensitive to the gear I happen to be using at the moment, they just have smaller arrays.

$1k a pic is just a silly throw away remark..... I've taken tens of thousands of CCD frames in the last 20 years....some admittedly quite tragic, some not bad....in any event I'm probably down to 5 cents a frame by now

It's still a cheap hobby compared to yachting!


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Originally Posted by EzyStyles View Post
not sure how many astro images you have taken peter with your SBIG lets say 10 pretty pictures, thats equivalant to $1,000k for 1 pretty pic!!!! i personally cannot justify that.
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Old 20-02-2008, 07:40 PM
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I see your point re the comparision exposure times, but most people would be interested in a same total exposure comparision. i.e 3 x 30 second Canon stack versus a 30 sec RGB. I think thats a comparision people would want to see.

The back illuminated CCD is just amazing....

Terry
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Old 20-02-2008, 08:47 PM
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Originally Posted by Peter Ward View Post
The reason I made the exposures all 30 seconds was based on the following logic....

Object rains down say 900 photons in 30 seconds...and to simplify the argument, evenly spread in R, G and B

Multi-spectral camera gets all 900 photons shining on the sensor.

Mono Camera with R G or B filter in front gets only 300 photons. To get an equivalent "full spectrum dose" three exposures need to be made to get the equivalent 900 photons to the sensor.

Also I could only trip the 5D for a maximum of 30 seconds using a USB cable, and didn't feel like guiding any of the exposures
This is not so..
Mono camera gets 300 photons with each filter... which is 900 for RGB picture (three frames times 300 photons, right?)

But DSLR has 1/3 number of sensors for each colour. So the sensor gets 300 photons for the whole frame... this is 1/3 sensitivity compared with CCD mono.
Not fair comparison,
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  #47  
Old 20-02-2008, 09:18 PM
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Quote:
Originally Posted by Peter Ward View Post

$1k a pic is just a silly throw away remark..... I've taken tens of thousands of CCD frames in the last 20 years....some admittedly quite tragic, some not bad....in any event I'm probably down to 5 cents a frame by now

It's still a cheap hobby compared to yachting!
Was that with the ST11 though?
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  #48  
Old 20-02-2008, 09:34 PM
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Point taken. So where do we draw the line? Flux hitting the sensor? or somewhere before that?

With a non filtered mono sensor how do we proceed?

Do we drop a ND filter in place so the single shot still looks good?

What about using a H-Alpha filter? ( trust me, this is not pretty for the CMOS).

Fair? What has fairness got to do with the sensitivity of a camera?

So many questions

Quote:
Originally Posted by bojan View Post
This is not so..
Mono camera gets 300 photons with each filter... which is 900 for RGB picture (three frames times 300 photons, right?)

But DSLR has 1/3 number of sensors for each colour. So the sensor gets 300 photons for the whole frame... this is 1/3 sensitivity compared with CCD mono.
Not fair comparison,
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  #49  
Old 20-02-2008, 09:53 PM
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Adjusted for inflation, 20 years ago, it might as well have been.

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Was that with the ST11 though?
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Old 20-02-2008, 10:00 PM
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I totally agree that generally DSLR will be inferior sensitivity-wise - actually, ANY bayer filtered colour sensor will have 1/3 or less the sensitivity (electrons per photons) compared with mono sensor, if not worse.
The exceptions are Foveon sensors, but they are of completely different architecture.
That is why professionals use only mono CCD's, because it saves time.
When I said it is not fair, I just wanted to point out that we can not really compare apples and pears (somebody said that earlier) :-)
But if we do, then we have to take correction factors into account. After that we end up with the roughly same result: the point is, we have to allow the same number of photons to be collected, and then compare the output.

edit:
NB: DSLR's are not astro cameras.. they just produce acceptable results in astro field, so you (we) can have two bangs for the same money.

Last edited by bojan; 21-02-2008 at 08:22 AM.
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  #51  
Old 21-02-2008, 03:07 PM
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I remember many moons ago when 2415 technical pan film was made. It was originally meant for microscopy, had very high resolution, incredibly fine grain, was photographically slow BUT unusually red sensitive. It also responded very well to gas hypering, and thus become a mainstay for monochrome amateur astro imaging. later, even the professionals started using it
http://en.wikipedia.org/wiki/Technical_Pan

The real amazing thing was tech pan film was as cheap as chips. When it first hit the market it wasnt available in large glass plates and so the professionals didnt use it but the amateurs could, and so for the first and only time in history, we had a BETTER imaging format than the professional astronomers. Sadly that isnt the case with electronic imaging.

To think if electronic imagers never happened, we could still do LRGB with techpan. Shoot a unfiltered luminance, then put in a focal reducer abd shoot through the filters, then use a high resolution film scanner to resize and combine them all.

A cheap 35mm SLR, and a roll of hypered techpan together a few hundred bucks total, could capture many megapixels

Last edited by tornado33; 21-02-2008 at 03:23 PM.
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Old 21-02-2008, 03:48 PM
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What about using a H-Alpha filter? ( trust me, this is not pretty for the CMOS). PW quote

Bert comment
Really? Canon 5DH at only -4C environment. The sensor would have been a few degrees higher than this! To be fair I only gave it 4min exposure at an ISO of 1600 as opposed to a paltry 30 sec. If you can go three times as much in time then eight times has no consequence in any comparison? It is less than thrice as biased!

http://members.optusnet.com.au/~trlee8/hafl.jpg

It is truly sad is it not? The general background shows variation in intensity and this must be due to the lack of sensitivity!

If as you say you cannot take exposures with a 5D longer than 30 sec, you have no hope of doing a fair evaluation. I even doubt your ability as you said yourself you could not be bothered guiding!. Shirly a timer is easily available for the Canon 5D? It is pointless to put this meaningless 'comparison' anywhere until you can do it objectively!
Drivel about a lack of resources smacks of bias or at best incompetence.

I won't waste any more time. I have better things to do.

The sad thing is a fair comparison would be very informative.



Bert

Last edited by avandonk; 21-02-2008 at 05:59 PM.
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  #53  
Old 23-02-2008, 08:06 AM
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I even doubt your ability as you said yourself you could not be bothered guiding!.........

Drivel about a lack of resources smacks of bias or at best incompetence.

I won't waste any more time. I have better things to do.

The sad thing is a fair comparison would be very informative.

Bert
Bert, I find it odd how my small experiment could be turned in to such scathing rant.

I suspect the physics was lost on you.

Think of it this way. We have two rain gauges. One catches a constant amount of rain for 30 seconds. The strength of the rainfall is then reduced by 2/3rd's. To get the same amount of rain we have to collect it for 3x longer i.e total rain, or in the case of a mono sensor in my experiment, total flux is equivalent.

How the sensors (or pavement, roof-top, back of your head...whatever) deal with the incoming flux does not change the amount of energy hitting the sensor.

For the mono cameras I used a CS filter set, so there was little leakage from the I/R or U/V....but do concede there may be an overlap between RG&B filters that may add 20% or so to the actual energy received....but certainly not 300%.

Energy considerations aside, in a practical sense, you can indeed get 90 (or more) seconds of exposure into a DSLR in the same time it takes to get 3 by 30 second exposures from a mono camera....and is probably worth investigation.

As I personally have 2 DSLR's and will be buying a 3rd soon, I have no problem/agenda here. They are great pieces of kit. If you are prepared to put the time into deep exposures you can still get great results.

This however does not change the fact there is patently a significant difference in raw sensitivity and dynamic range between DSLR's and a dedicated astro-cam....frankly more than I expected, hence the demo.
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  #54  
Old 23-02-2008, 08:35 AM
Alchemy (Clive)
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I find it odd how my small experiment could be turned in to such scathing rant.

not looking for an argument

im happy to simply accept that a dedicated astro camera does a better job than a dslr

i guess all arguments are settled at the time of posting the finished picture as thats where the results are obvious, so if the purchaser feels that extra resolution/depth is worth the extra cost, thats fine with me

unfortunately my budget doesnt stretch that far.
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Old 23-02-2008, 09:41 AM
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actually what would be fun is a shootoff between dslr owners and ccd owners

(im aware of differences in other equipment so dont go there... this is just for a bit of fun!)

Say M83 imaged with your own gear, results to be published sundown at the 2nd full moon from now, limited to the standard post size on IIS (200kb)

any takers to see just how close the dslr shooters could get to the others.

(if i get a couple takers from either side ill post a general challenge , as not everyone will read this thread)..... id be in it.
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  #56  
Old 23-02-2008, 02:51 PM
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Here is a shoot off of sorts.
First image was taken with a 12 inch Ritchey Cretien F9 and SBIG STL11000M 11 MP monochrome cooled CCD camera. Full Autoguiding on Paramount mount. It is a LRGB image 30 secs lum 1x1 bin and 30 secs rgb 2x2 bin, processed with calibration images in Iris.

2nd was with a 22 year old 10 inch f5.6 newtonian and "Sampson" GEM mount with Shyncronous motored RA drive and manually operated drive corrector, with 2x barlow giving f11.2 Hutech modded Canon 350D with uv/ir and Baader UHC-S filters. 2x Drizzle upsampled during processing. Off axis guided with Q guider camera showing guidestar on laptop where I guide by placing an artifical reticle over the star.

The 2nd image took considerably longer and could not be done "hands free" but does show that ancient equipment of what many would call the RA drive in particular low quality and a vastly inexpensive camera can produce images that are reasonably impressive, and unheard of for the time the scope was built. I should mention my scope has a full thickness Pyrex Sutching mirror, I think only Ion Milling could make a better one than that

To be fair I am not sure how good the seeing was when I took the GRAS image on the RC scope, and it is an excellent image in its own right. I could not affort to do an imaging run on it as long as I did on my system last night. Anyway the GRAS image is not grainy, showing Ive got plenty of signal anyway.

The 3rd image is of the Eta carina Nebula, again with the 2x barlow giving F11.2, duration 92 seconds ISO 160 with uv/ir and UHCS filter, hurriedly taken before more cloud came over. It shows that particularily with H alpha emission, the modded DSLR with its 4x more Ha sensitivity then a non modded one can hold its own.

If a Canon Cmos sensor like the one in the soon to be released 450D could be obtained without the colour bayer array and antialiasing filter, with a simple single stage peltier, and say 10 or 20% longer imaging times to account for a slightly lower QE, I believe it could take images better then anything dedicated Astro CCD's could muster. They might have the edge with fancy back illuminated chips (horrendiously expensive to make due to high failure rates during manufacture). But compare a raw frame from a ASTRO CCD camera with one from a Canon DSLR. The CCD might have column defects and a scattering of dead pixels. These are of course mapped out during processing. But the CMOS Canon sensor has (or should have) none to start with. They are designed to produce the best normal photographic images possible without defect. They dont suffer from dust as much as the cover plate is further away from the sensor. Also remember to consider the most sensitive CCDs do not have Anti Blooming Gate (ABC) and bright stars will bleed down the colums. having ABC is well worth the sacrifice of QE!

Sadly as yet there are no monochrome CMOS DSLR sensors from canon. So I propose in the interim a most fair shoot off. Compare the DSLRs to a COLOUR Astro CCD camera. Pit a dedicated astro CCD one shot colour against a cooled DSLR from central DS

This would be my ultimate imaging device. A monochrome version of this with single stage peltier cooling, no IR cut filter , no Bayer filter array or antialiasing filters. 21.1 megapixels.

Thought id mention many moons ago I got to have a play with a then top of the line ST7 on my gear for one night
http://cust.idl.net.au/josiah/SBIG.htm
The ST7 was a nice little unit, easy to use and did not bloom, if only they were not so costly.
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Old 23-02-2008, 04:22 PM
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Thought id mention many moons ago I got to have a play with a then top of the line ST7 on my gear for one night
http://cust.idl.net.au/josiah/SBIG.htm
The ST7 was a nice little unit, easy to use and did not bloom, if only they were not so costly.
You can actually get a ST7 (standard) for about $3k. $5k was probably when the Aussie Peso was around US 57 cents
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Old 23-02-2008, 04:54 PM
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I take it the current model of that camera is this
http://www.sbig.com/sbwhtmls/ST7ME.htm

An interesting side issue, has anyone here tried this? http://www.sbig.com/pdffiles/ST7-9ICameraApps.pdf
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Old 23-02-2008, 05:56 PM
Alchemy (Clive)
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Fantastic effort with the planetary neb, i reckon the cannon on the 22 yr old newt shows more detail than the Ritchley cretin scope andthe st11000, not the result i expected i must admit.

better drop the shootout idea, could be embarrassing if youve spent 100,000 dollars and lost to a cheap camera and 22 yr old newt.
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