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Earl

Atik 490EX

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So here is first light for my 490ex (well first lightish - I did run the camera last night capturing some binned colour data for M100). First impressions are good and it seems almost as sensitive as the 460...

This is just 6 x 300s subs through a Baader luminance filter, on a fairly moony night.

M51 through Celestron Edge HD 11 with Optec Lepus focal reducer (so f/6.2; f/l 1736mm).

post-11821-0-25288700-1366495982_thumb.p

This hasn't been stretched or processed; just stacked in AA5.

Cheers, Ian

Edited by x6gas

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Processed version with 31 x 300s posted here:

Ian

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Not sure if I am being stupid but the 490 really attracts me, I am new to this game and have been imaging (trying) with a D700 but want to go CCD for DSO. I own a Celestron 9.25 on an EQ6, OAG and Lodestar for guiding. i have looked at the relative software to show me the fov and am happy with the results. I was looking at a 383L before the 490 came out, would welcome any view on my way ahead before I spend a lot of money and am "disappointed"!!!!.

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Always good to see another SGL'er over here!!

Anyway, I digress - Have a look on a fov calculator such as CCDCalc (free to download) or http://www.12dstring.me.uk/fov.htm to get a feel for the different field of view you will get with the chip sixe and pixel size when coupled with your scope.

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Thanks swag72, yep I am using CCDCalc and working out a cost effective way ahead, mainly trying to get "best value" per pixel.

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I'd like to go down the ccd route too and have looked at the 490. I know nothing about how to decide which ccd best suits my scopes though. I have a 102mm triplet apo from Explore Scientific. I think it's f6.5 or thereabouts and an Explorer 200 pds which I believe is f5. Would the 490 be of use with both these scopes or could someone suggest a better alternative. Any advice much appreciated. Oh, and would I need a focal reducer for the refractor?

thanks

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I'd like to go down the ccd route too and have looked at the 490. I know nothing about how to decide which ccd best suits my scopes though. I have a 102mm triplet apo from Explore Scientific. I think it's f6.5 or thereabouts and an Explorer 200 pds which I believe is f5. Would the 490 be of use with both these scopes or could someone suggest a better alternative. Any advice much appreciated. Oh, and would I need a focal reducer for the refractor?

thanks

The 490ex will offer 1.07"/ pixel with your ES 102 apo while a 460ex will give 1.31"/ pixel - both of these probably well oversampled in typical UK skies on this scope but to be honest I'm a fan of oversampling.

The longer focal length of your 200p means that either camera will be even more oversampled.

Personally I wouldn't worry too much about that. The 460ex is - by most accounts more sensitive. The Atik 400 series platform of both cameras is excellent and both are so quite that you won't need to take darks - this is probably the biggest advantage for me over the 383L.

In short I think you'll be well pleased with either the 460 or the 490ex with your set-up, but you might be best advised to go for the 460 given it's slightly better sensitivity.

At some point I will be doing a side-by-side comparison of the 460 and 490 to assess their relative sensitivity under real conditions...

HTH, Ian

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Thanks Ian. I look forward to seeing your comparison. I'm in no rush as this is a big outlay for me and I want to explore very option before committing to one camera. Hoping to have a budget of around £3000 but that's ti include a filter wheel and lrgb filters and possibly Ha, O III and SII as well. No doubt there'll be other things like a reducer and various spacers etc. By the time I have the cash there'll probably be even better models out there. Must try and get people to give me money for Christmas rather than socks.

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I'd love to see a shoot out between these two. For very short FLs the tiny pixels would be great. However, sampling rate has a big effect on speed.

Olly

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I've seen some superb images from the 460 used on a wide variety of scopes. Would like to see some from the 490 too. Not ruling out other manufacturers either. What I need is someone who knows what they're doing to put together a comparison website with all the ccd cameras and which scopes they are suited to. Perhaps it could offer a free cuddly Martian for using it.

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What counts as short FL? Also what figures do I look at in manufacturer spec sheets to work out which ccd will best suit my scopes. I know things like QE apply to all scopes, so is it pixel size?

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You can use this to calculate your sampling rate. It's a cracking site. http://www.12dstring.me.uk/fov.htm

I take published QE with a pinch of salt because I've never found a strong 'real world' correlation with use in practice. I've just come down by 5% with my latest CCD but it seems faster to me. It has larger pixels so that's probably the answer. (If you divide a given FOV into smaller pixels then each gets less light.)

Opinion has been changing recently on sampling rate. People used to say that about 2 arcseconds per pixel was the best the UK atmosphere would allow but imagers are demonstrating that a far higher resolution seems to be possible.

Choosing a sampling rate is a bit like choosing a binning rate. Bigger is faster but less resolved. I use both over and undersampled setups and I prefer to get the signal in the can. I'm right over at 3.5 arcseconds per pixel in one rig but how much does it matter? For example; http://ollypenrice.s...11RGBWEB-X3.jpg

That 2-panel only had 8 hours per panel but I think it's fairly deep and that's down to the big pixels. The QE is only 50% in that camera. That's why I'm wary of getting too hung up on the numbers.

Olly

Edit, In common parlance I think most of us would call 500mm short, a metre medium and beyond a metre and a half we probably call it long. It isn't really defined.

Edited by ollypenrice
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Geordie,

To be considering the 490, I would say you'd need to be using a scope with an FL below 450mm. The 694 chip (atik 460) works beautifully with an FSQ85 at it's native focal length, as does the 383. When the baby Q is reduced to 330mm, you can see the pixel structure in the stars when you zoom right in (re-sampling helps). Of course you could use it at 800mm+, but this is certainly not it's intended use.

I didn't see an answer on this thread to the question posed quite early on: "is it better to use a chip with native 7um square pixels or a chip with 3.5um square pixels binned 2x2?" This is a really easy one. As long as the native (unbinned) pixel size suits the focal length then Unbinned is better. There are a number of reasons, such as the reduction in dynamic range (due to the usable 'well depth' being limited by the read-out amp - no point filling 4 pixels with photons if one pixels-worth saturates the readout circuits). Also the fact that although the gaps between the charge/photon collecting pits are incredibly small, more pixels means more gaps between pixels, which means less light collecting area on the same die - even with microlenses.

There are occasions where the drawbacks of using a binned mode can be tolerated or ignored, even if it means undersampling; like grabbing more colour/emission line data to go on top of a correctly sampled luminance layer.

For your current scopes, it's 460 all the way. Or maybe consider a 383. Atik or Sx. Just a shame they're so expensive. I thought when some of the QCUAIG gurus set up artemis and then atik, they were going to have a positive effect on astro camera prices, by competing with the likes of SBIG, forcing them to bring down prices. Doesn't seem to have happened. Of course, they are now polished retail products, but Atik camera plus filter wheel plus OAG isn't actually much cheaper than a QSI wsg. I know - this last bit will probably get me in trouble with the mods. Sorry.

Good luck with whatever you buy,

Jack

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I take published QE with a pinch of salt because I've never found a strong 'real world' correlation with use in practice. I've just come down by 5% with my latest CCD but it seems faster to me. It has larger pixels so that's probably the answer. (If you divide a given FOV into smaller pixels then each gets less light.)

It's pretty easy to test the QE between cameras, particularly if you can put different cameras onto the same set-up (telescope + focal reducer + filters). There are a bunch of very well measured 'standard stars' around the sky, which have very well measured and stable brightnesses. All you need to do is measure the brightness of a star with both cameras, and the difference in flux will be entirely down to the difference in QE (assuming you do it on equally clear nights, of course!). Measuring the brightness of the star takes out the effect of different pixel sizes.

Separate from 'real world' speed as there are lots of other factors than QE, but it would be nice to test the headline QE figures. Could be a nice thing to do if you see quite a lot of cameras through your place Olly??

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It's pretty easy to test the QE between cameras, particularly if you can put different cameras onto the same set-up (telescope + focal reducer + filters). There are a bunch of very well measured 'standard stars' around the sky, which have very well measured and stable brightnesses. All you need to do is measure the brightness of a star with both cameras, and the difference in flux will be entirely down to the difference in QE (assuming you do it on equally clear nights, of course!). Measuring the brightness of the star takes out the effect of different pixel sizes.

Separate from 'real world' speed as there are lots of other factors than QE, but it would be nice to test the headline QE figures. Could be a nice thing to do if you see quite a lot of cameras through your place Olly??

I do, but people come to take pictures and that's what I'm about as well. I'd only want to do this on an imperfect night and then it wouldn't work. :BangHead: Curses!! I'll be honest; I do this a lot and I have a decent seat of the pants notion of what half an hour of Ha ought to look like on this or that bit of sky and I tend to trust that. An example of the problem; I've used the 8300 chip in QSI mono and in a one shot colour SBIG. The SBIG was slow, grindingly slow. The QE is the same but maybe the Bayer Matrix does for the chip? Who knows? But the difference between an Atik 4000 OSC and mono was not, I found, that great. So many variables. You have to find something that you like and which seems to agree with your way of working, I reckon.

Olly

Edited by ollypenrice

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Many thanks to all for the advice. Looks like the 460 is at the top of my list but need to check the sbig, qsi ans starlight express stuff too.

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The new SX cameras have some USB ports (hub) built in - which would be useful for running to a lodestar and a filterwheel (the lodestar and SX filterwheel don't need separate power connectors).

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The new SX cameras have some USB ports (hub) built in - which would be useful for running to a lodestar and a filterwheel (the lodestar and SX filterwheel don't need separate power connectors).

Its a very nice new feature.

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Its a very nice new feature.

But before you buy an SX ask if it will work in Bin2. Of course it will!

Don't bank on it. Yves' doesn't. Ian Bird's doesn't.

Olly

Edited by ollypenrice

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Mine does (as did the previous one).

What does Terry have to say about it?

Edited by dmahon

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Got my copy of making every photon count Tuesday. Great book. Now feel I know a lot more and can make better comparisons. SX are uk made aren't they? Would be nice to support them, but if there are issues that would put me off. Anyone else had problems?

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Just read the review of the new sx trius814 in sky at night mag. Looks good with the filter wheel and USB ports. If a sample rate between 1 and 3 is okay according to every photon then my 714mmm focal length refractor should be ok. Any thoughts?

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I recently bought the QHY23, which has the same chip as the Atik 490.  It's my first mono CCD so nothing to compare with.  But I'm very pleased with it.  I've only had clear skies a couple of times so far, but got a couple of pics of M81 and M82.

The advantage to me with the small pixel size and the larger number of pixels was the flexibility of using it 1x1 on short focal lengths and binning 2x2 on my MN190 (1000mm).  In theory I can still get good pixel resolution with a 2x barlow in the MN190 - although I haven't got a 2" barlow to try it!

Jeremy

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Mine does (as did the previous one).

What does Terry have to say about it?

He says adjust the potentiometer inside the camera. I'm sorry, but shouldn't this be done at the factory? We tried but found that a small improvement in Bin 2 came at the expense of sensitivity in Bin1 and still the bin 2 results were artefact-afflicted. Also no dessicant and no chip window heater. Use a hairdrier? Not impressed.

Olly

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