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How to decide what matters with a planetary camera


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As a relative newbie I've been reading through loads of posts and talking to people, but struggling to decide which of the various things matter when trying to pick what planetary camera I should get.

1) CMOS vs CCD - what determines which type is best?

2) chip size - typically 1/4", 1/3" or 1/2 ". Is biggest necessarily best

3) pixel size - is smallest pixel size going to produce the crispest images?

4) resolution - typically anything from 640x480 but up to 2592x1944 - I'm guessing lots of pixels only useful if they're small, but is having too many potentially counterproductive?

5) frame rate - is a fast rate necessary

Then there's the trade off between them because they're all going to inter-relate....

At the moment I've borrowed a Phillips SPC900 and done my first pictures - stills and video - and put the video through Registax (default settings - no idea how to tweek them yet!) but far from impressed with my Saturn images - I mean it's clearly Saturn but little definition or colour. But then the seeing is rarely great here, atmospherics probably poor in the summer, and the street light directly below the planet probably didn't help!

On my possibles list is the NexImage 5, SkyRis 132 or 618, Opticstar PX-75C and Atik GP. But could quite easiuly opt for something completely different. 

But first I just want to understand the parameters, so any guidance much appreciated! Thanks!

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Interesting set of questions, don't know anything specific but may as well give an opinion:

1) CCD seems to be better for long exposures and CMOS for the video side, however it may be that CMOS cost less to produce and for video CMOS may have no real advantage over CCD. So you just see more CMOS for the reason of cost alone. But if no advantage then get a CMOS and save the money if it is video only.

2) Really the bigger the better for the chip size, but they cost more and the cost is not linear. I would say simply it is easier to get the image on the chip if the chip is bigger.

3) The pixel size is more relevant then simply the smaller the better. Seems they need to be matched to the scope and it seem that the match is pixel size is about an angle of 2 arcseconds through the scope. 

So basically Pixel Size = Tan(2")xFocal Length.

However then it is said that for brighter objects (Planets) you can use 1 arcsecond instead.

Seems to be a bit of a grey area, the SBIG site say's 1 arcsecond for deep sky and less for planets. 2 arcseconds however seems about the middle. If you start looking at camera specs and pixel size actuall few are as small as would seem to be suggested.

4) Resolution is related to chip size and pixel size so really comes out from 2 and 3.

5) Frame Rate I suspect depends more on the capabilities of the camera and the processing power available. Too slow and you could not collect enough data as a factor of not geiing enough frames, too fast and you could be too fast to get meaningful frames. So that is likely a suck-it-and-see scenario. I would guess that most cameras have an optimum frame rate.

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I’m by no means an expert and I’m sure some good people may correct me.

Question one is probably personal, some will say CMOS, other CCD and some either.

I myself started out with a SPC900. I modded it myself and even changed the CCD from standard ¼” to ½” (ICX414), but the pixel size also increased to 9.9um.

I was going to use the camera for long exposure so this wasn’t a problem. But on planets I then needed to use a barlow in the region of X3 to X5 to get a decent image size.

This made the focus train very long and not too stable. So in my opinion chip size can be small as long as pixel size is small.

I’m now using a QHY5LII which is CMOS, has a smaller chip and smaller pixels of 3.75. The region of interest can be reduced which makes keeping the object on the chip harder but the frame rate will increase. I now only need a X2 barlow for the same scope.

Frame rate is the biggest improvement from using the SPC900 which could only run at 10fps max. The QHY5LII is running at over 100fps. But the computer has to be up to the job too. But with a higher frame rate you have a better chance of getting those moments when the planet is sharp and focused, even for a microsecond. With the SPC I could only capture a 1000 frames and stack 15% to 20% which is not great. Now I capture 10,000 frames in the same time and with a stack of 15% to 20% the final image is much better.

My best advice is to practice, make detailed notes on sky/weather/temperature conditions, kit used, setting etc. and play with processing. The more you practice the more you will hopefully understand what is working and what is not.

There are so many variables to this question and others I’m sure will add to this thread.

Below are some images taken with the SPC900 showing how with practice alone (and good seeing) how things have improved for me using just a simple webcam.

Lee

post-5674-0-41693000-1402993559_thumb.jp

post-5674-0-50951500-1402993604_thumb.jp

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Blimey Lee, that's amazing! I've never managed to get anything remotely like that with my SPC900. I guess it's the LX modding. How do you do that?

I'm interested in this thread as I want to buy a colour planetary camera. I have two in mind: ZWO ASI 120 MC  or  QHY5L-II.

Alexxx

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1) CCDs used to be far more sensitive than CMOS sensors.  That's not so much the case now.  The gap has narrowed significantly and many people have moved over to CMOS-based cameras.

2) For imaging, small chip sizes usually make for an easier life, up to a point.  There's no real benefit to a large sensor with a high pixel count as the images you're capturing are actually quite small.

3) Pixel size needs to be considered in combination with the scope you'll be using.  The pixel size of the camera determines the optical focal ratio for capture.  Choose too large a pixel size and you need a huge focal ratio (and therefore focal length) to get good detail.  Too small a pixel size and you suffer from lack of sensitivity because the photosites are so small.  I'd say there's little wrong with the 5.6um of the SPC900 nor the 3.75um of the ASI120 though.

4) Total pixel count doesn't need to be high.  The image will not be covering a lot of pixels anyhow and having ones that you're effectively not using just slows down the capture process and generates larger files.  It's not at all uncommon with, say, the ASI120 (which is 1280x960 in total) to only capture an area on the order of 400x400.

5) Fast frame rates are good if the sensor is sensitive enough, though with the SPC900 going above 10fps will suffer badly because of the data compression that takes place as a result (so that it's possible to get that much data over the USB1 connection).

I'm personally unconvinced by the Neximage 5 generally and I think the Skyris cameras are a very high price for what they are.  My recollection is that the Opticstar has had a bit of a slating because of its firmware, too.  I believe, though no-one who would know for certain has said this, that the Atik GP is just a re-branded and re-housed Point Grey Chameleon, which does seem to have a good reputation.  ASI also do a lower-end planetary imaging camera that looks interesting on paper though I've seen no images from it yet.

I'm not sure how much useful planetary imaging can be done from the northern hemisphere (and particularly the UK) now, at least until Jupiter is back in the sky.  I've not seen a clear sky for so long that I've forgotten where everything is :(  If you can wait for a while however, I'd not be entirely surprised if there were a few ASI120MC (and MM) cameras making their way onto the second hand market over the latter half of this year.

These though are some of my Jupiter and Saturn images with the SPC900 and a 127 Mak, so it's quite a capable camera it its own right:

jupiter-2012-10-14.png

saturn-2_03_2012-00_52_11-2.png

Remember though that Saturn is a very tough target from the UK this apparition and things won't improve for a few years.

James

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Thanks everyone! This is just what a newcomer needs to know - it may all be basic stuff but as someone once said, if you don't know it, you don't know it.

My images of Saturn over the past few weeks have been very unremarkable and looking at other people's, my feeling is that I ought to be able to get a lot better considering the scopes and cameras at my disposal. I've had a few cloudless nights although hazy which doesn't help, but still... When I work out how to embed an image or two here, I will... (tips, anyone?) then tell me what you think, please.

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Hi

My 2 penneth for what its worth

I spent nearly 5 years with a Phillips Toucam getting basically no-where. My images paled into insignificance against other peoples efforts with the same equipement.

I think it really came down to lack of practice due to available skies and planetary positions in the UK when seeing was good. I just didn't learn and retain the necessary techniques so almost every time I was re-learning skills.

This year I made a real leap of faith and decided that I wanted to have a real go at planetary imaging and as Jupiter was so wonderfully placed I invested in a ZWO120mm Mono Camera and manual filterwheel with ZWO Filters.

At the same time I had my EQ6 Pro upgraded and modded with ba belt drive conversion.

So straight out of the box I got the images on the computer screen that quite simply blew me away, and they weren't jumping around or swimming in and out like with the Toucam.

The learning curve was pretty straight forward and almost instantly I was getting final images far superior to those I had ever obtained.

Practise, practise, practise and retain as much info as you can. It will get better although I think with the Toucam unless you have the time and patience to spend with it you could become frustrated quite quickly.

The ZWO is a game changer for me, but obviously not for everyone and there are plenty of other cameras out there that produce fantastic images.

Cheers

Nick

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I think the move from colour to mono makes a huge difference, to be honest.  I'd say there was as big a difference for me in going from ASI120MC to ASI120MM as there was in going from SPC900 to ASI120MC, if not in fact an even larger difference.

The SPC900 is a very competent camera for what it is.  Practice and patience (and a bit of luck with the seeing) can turn out some respectable results.  Where the 120MC made life easier for me was in getting more frames and not having to work at such a stupendous ideal focal length.  There is a learning curve however and you can't necessarily expect the results to outdo what you have achieved with the SPC900 immediately.  What works for one camera may not work for the other and vice-versa and you need to find new settings that work with your setup.

James

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More useful stuff, thanks again! I don't want to just throw money at it, BUT I'd rather buy something decent and be a lot less frustrated even if it costs a bit. The SPC900 is borrowed so as yet I haven't wasted any money. I've learnt lessons with camera lenses when I've bought something that sort-of did what I wanted, but knew it could be better so sold them and ended up with what i should have got in the first place, having overall spent a lot more via the resale...

Can someone tell me how I get an image on here to show you what I'm getting? Thanks!

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When you reply, click the More Reply Options bottom right. Under Attach Files below the text box click Browse and find your image. Double click on the image name then click Attach This File. Then post the message. Hope that works!

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Thanks - as ever it's obvious when you know how. Loads of nice little icons readily on offer for things I rarely need, but not the one obvious thing!

Here's the best of Saturn to date (jpg so it loads fast, but the bmp is no better)... Please tell me I should hope for better, even in the UK!

post-36712-0-83789400-1403187943_thumb.j

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No, not using a barlow or tele=extender at the moment. I've varied the brightness a fair bit - brighter ones were less distinct. So as there's plenty of light intensity a barlow/extender isn't going to diminish it too much, I know. It's on the shopping list - I need to work out what will work best with both this camera and any future one I buy. Thanks.

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If you have achieved that with the default settings in registax then you probably have a great image if you take some time to learn how best to process the raw data.

Even the most fantastic images you see would look very plain if it wasn't for the time spent processing them.

Incidentally a tele extender is for eye piece projection, is that what you are doing or are you at prime focus?

Sent from my iPhone using Tapatalk

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I know a number of people who rate the NexImage5 and I've seen great results from it posted online. This, the QHY5L II and the ZWO ASI120 seem to be the three getting most votes... first two roughly same price, the ZWO a little more. Decisions, decisions...!

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Reading back through these thoughts, I'm sure mono will be the way to go eventually, but I may do best learning the tricks of imaging and processing in colour first. When I've mastered that, I've little doubt I'll want better so will add a new complicating factor! Incidentally, am I right to understand the NexImage5 handles colour and mono anyway? (not that that's a reason on it's own to go that route).

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As a relative newbie I've been reading through loads of posts and talking to people, but struggling to decide which of the various things matter when trying to pick what planetary camera I should get.

1) CMOS vs CCD - what determines which type is best?

2) chip size - typically 1/4", 1/3" or 1/2 ". Is biggest necessarily best

3) pixel size - is smallest pixel size going to produce the crispest images?

4) resolution - typically anything from 640x480 but up to 2592x1944 - I'm guessing lots of pixels only useful if they're small, but is having too many potentially counterproductive?

5) frame rate - is a fast rate necessary

Then there's the trade off between them because they're all going to inter-relate....

At the moment I've borrowed a Phillips SPC900 and done my first pictures - stills and video - and put the video through Registax (default settings - no idea how to tweek them yet!) but far from impressed with my Saturn images - I mean it's clearly Saturn but little definition or colour. But then the seeing is rarely great here, atmospherics probably poor in the summer, and the street light directly below the planet probably didn't help!

On my possibles list is the NexImage 5, SkyRis 132 or 618, Opticstar PX-75C and Atik GP. But could quite easiuly opt for something completely different. 

But first I just want to understand the parameters, so any guidance much appreciated! Thanks!

1) CMOS vs CCD - what determines which type is best?

CCD used to offer the most sensitivity, though the latest CMOS sensors are excellent. The only thing to be aware of is that soem CMOS senors can have issues with bright subjerct (many ZWO cameras seem to show interference patterns when imaging the Sun, for example)

2) chip size - typically 1/4", 1/3" or 1/2 ". Is biggest necessarily best

No, not for planetary as the planets image on the chip is very small. For Lunar and Solar work a larger chip can be advantageous as these objects cover a large apparent diameter.

3) pixel size - is smallest pixel size going to produce the crispest images?

Not really.  Small pixels are less sensitive, so the framerate is lower. Stacking software takes many frames and selects the sharpest, so are better off with a high framerate to gather the most frames in a given period of time.

4) resolution - typically anything from 640x480 but up to 2592x1944 - I'm guessing lots of pixels only useful if they're small, but is having too many potentially counterproductive?

Larger sensors means much more data. Which can mean gobbling up gthe bus bandwidth (which is why some cameras use Firewire and Gigabit Ethernet). There's no point having a huge sensor if the planet's image is only sitting on 1/4 of the chip.

5) frame rate - is a fast rate necessary

For planetary, yes. A higher framerate means more frames in a given period. When imaging fast rotating objects like Jupiter, then you want as many frames in as short a time as possible. For static objects like the moon less so.

Mono is really the way to go....the difference is like chalk and cheese. However...for a complete noob there are a lot of steps to master first. if you have some experience with planetary imaging then OSC webcam is a good start.

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  • 2 months later...

Still not decided but think I'm down to three... Neximage 5, QHY5L-IIc or ZWO ASI120MC. I did at least do something about a barlow so now have a Televue Powermate 2.5x - that is useful for viewing too... when the skies become usable again, which they may be for the next few days!! :-)

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