zwo asi 174

[Luke]

Here's my first ZWO image with my 120mm scope in h-alpha. Conditions were not that fab, I've downsized the image but there's no cropping apart from anything Autostakkert clipped off due to any slight drift.

I think there is more to come from this camera on my setup under better conditions, but I am very happy with the potential it's showing, it's clear to me that this sensor will work very well for h-alpha (well I already knew that from some excellent images from others, but it's nice to see the data myself, wondering how it would feel versus the Grasshopper 3 CCD).

To avoid the vignetting I got from the brief previous session, this time I put a 1.6x Barlow onto the 0.5x reducer, with the 0.5x reducer closest to the camera. I had tried this briefly before with my Grasshopper, to try and get about 0.8x on that cam. There was a bit of a hotspot in the middle, but I think the flat has sorted it so I might get away without having to source a shorter nosepiece. Taking multiple flats during the session sort of worked out okay with the defocus method, whether I need multiple due to shifting Newton's Rings I don't yet know, so I played it safe and took one flat per two images, one either side of taking the flat.

I also took shots with my Grasshopper 3, main issue with the ZWO is that I couldn't seem to adjust the gamma in FireCapture. That made focus tricky, I normally set gamma lowest to boost contrast while focusing then pop it back up.

I mentioned somewhere before that 2xbinning seemed to darken the image. Not sure what happened but this time binning was fine, the image went brighter and I could pull exposure back down and use a faster frame rate, as hoped.

The other issue is that the image is much darker at the same exposure than with the little pixels of my Grasshopper 3 (ICX687). For same brightness, so far it looks like I need about four times or so as long an exposure with the ZWO. This is limiting the speed I can capture at as my Quark is a bit dark and needs about 8ms or longer with the Grasshopper, so that's ending up about 30-ish ms with the ZWO. So I am not getting a hugely faster capture with the Quark so far, unless I find some other buttons to press.

Could be I can get away with darker captures, and there are some interesting looking options like Brightness and Software Gain as well as factoring whether faster frame rate at expense of gain improves things.

Very happy I bought this camera, it is also so that Sarah and I both have access to a camera, we had been looking for a second camera for a while and this chip at this price looks a great contender in the value stakes if it's suitable for your needs.

[michael.h.f.wilkinson]

Try upping the gain on the ASI174. Because of its deep electron wells (big pixels) it can gather far more photons before it saturates. This is reflected in the ADC gain settings: the same number of photons yields a much lower grey level. Upping the gain corrects for that. I could run at fairly short exposures with higher gain without any noise issues.

[Space Cowboy]

Would this laptop be good enough for the 174 cam? http://www.argos.co.uk/m/static/Product/partNumber/3146071.htm

[JamesF]

I'd have thought it would be ok, though it's not exactly blessed with lots of USB ports so you'll probably be needing to use a USB hub as well.  A 13" screen is quite small.  Not too small to be usable, but if you're used to much bigger you might find it a pain.

James

[riklaunim]

Find similar one with quad core Bay Trail instead if dual core. Price difference msy be minimal, but may give sime extra processing power, more usb ports even maybe.

[Space Cowboy]

The screen is actually larger than I'm used to James but even my perky old netbook has 3 USB ports so as you mention an extra USB 3 port would be better but can be got around.

Reading through this thread I see it mentioned that the 174 ROI jumps from full res to only 640x480 which is disappointing as this would mean having to capture Jupiter's moons at full res which would be an insanely large avi!

[JamesF]

I had a feeling that FireCapture would allow you to crop a frame before writing the data to disk.  I've never tried it, but I thought it would.  It's certainly a feature I intend to add to oaCapture at some point.

James

[Space Cowboy]

What's oacapture James?

[JamesF]

What's oacapture James?

It is an open-source (planetary/solar system, mostly) capture application wot I have writ for Linux and OSX: http://www.openastroproject.org/

James

[rwg]

SharpCap gives you a whole range of ROI possibilities for ZWO cameras, including the ability to create your own custom ones.

cheers,

Robin

[JamesF]

Ah, yes, good point Robin.  I'd completely forgotten that.

The ZWO cameras allow you to specify any ROI that is a multiple of 1024 pixels in area (or at least that's the impression I have from Sam@ZWO).  I've certainly tried it on the 174 with "odd" size frames (512x400 say) and it seems to work fine, so you should be fine there Stuart.

Other cameras don't necessarily work the same way.  Some only give you a set list of frame sizes and I think cameras such as the QHY5 can do the vertical part of the ROI on the camera, but then rely on the driver to crop the horizontal to size.

James

[Space Cowboy]

Thats good to know! I've only been able to use EZ capture with the QHY cam to get full frame rate which is one reason I need a new laptop so I can exploit the exotic bells and whistles of Firecapture & Sharpcap! The good thing about this hobby is the amount of clever people that are involved James & Robin

[jimbo747]

Might just be me but I find a backlit keyboard essential on a laptop/tablet when working outside.

An original surface pro can be picked up with the type 2 keyboard for around £250-£300 - will happily charge from a 12v socket on a power pack too.

Failing that a quad core atom will be fine (just be aware alot come with a 32 or 64gb MMC so will be filled rather quickly and you probably won't want to be sharing the USB bus)

[Space Cowboy]

Thats a very good idea Jim. I did deliberately choose a white netbook for that very reason.

[christhebrit]

Amra,

I've notived you have the 2 cameras I'm comparing currently (in order to purchase soonish).

I like the idea of the QHY5L-II Colour, as I'm sure it's good for planetary.

I'm also interested in the ASI174MM, but this camera isn't colour is it?

I use a Nikon D3100 currently for DSOs in my novice stage, so I'm mainly interested in a nice Planetary Imaging Camera.

I have a laptop with i7 and USB3 which I hope will suffice for the next few years at least.

What sets the ASI 174mm that much apart from your QHY5?

[JamesF]

There is a colour version of the ASI174 -- the ASI174MC.

James

[christhebrit]

lol, I am blonde when I let my hair grow, thanks for the heads up on that :-)

It'd be nice to understand what sets the 2 camera apart, considering they are both colour and used for Planetarty Imaginy.

I now know I would need an IR Filter also, but it doesn't seem there is much more of a benefit for the ASI.

Am I missing the point?

[Amra]

Yes, I don't use my QHY5L-IIc much at all since purchasing the ASI174MM.

I realised pretty soon that I would purchase a mono planetary camera at some point after getting the QHY, because they have some benefits which I'll get into.

The ASI has a bigger sensor so I don't have to do mosaics for the Moon/Sun with my heritage 130P and I can happily let the object drift in the sensor and capture over 10000 frames in a short time frame, making a stacked end result much better without any fiddling with mosaics. And when I do want to do mosaics with a barlow, the individual panes are much bigger and you have higher fps, so it's much quicker process to capture a whole mosaic.

The ASI lets me capture at 120+ FPS at full res, while the QHY is limited to 30.

My ASI has no bayer matrix as it's a mono sensor, so will let me capture more details on the white light Sun (and hopefully future Ha solar imaging.) It's also much more sensitive to use as a guide camera, although the QHY5L-IIc has worked just fine for that purpose.

Considering the Sun in whitelight/Ha doesn't need a colour sensor, nor does the Moon (unless you want to play with saturation & colour) there's not much benefit in having a color camera for those purposes.

However, it is handy to have a color camera for the planets, and this is probably the only place where I will be using my QHY in the future. It has 200 FPS at 320x240 which is decent, The ASI can do 577 FPS at 320x240 though, so it's also a champ at planetary.

And if you buy a mono sensor you can at some point get a filter wheel and the appropriate filters and add colour that way, that's of course expensive though & requires a robust focuser that can carry all that stuff.

[michael.h.f.wilkinson]

I sold both my ASI130MM and my DMK21AU618 when I got my ASI174MM. The latter, with its increased gain, larger size, lower noise, and flexible ROI selection really replaces both. I only kept the ASI120MC for colour use, when I do not feel like faffing around with the filter wheel

[christhebrit]

These insight have just about answered all my queries, thanks you for the time.

How do filters change the colour?

I was under the impression that the Mono chip only reads black and white, I can't see how a filter would change what it reads.

Is the ASI174MC not a better option as it reads colour?

[JamesF]

How do filters change the colour?

I was under the impression that the Mono chip only reads black and white, I can't see how a filter would change what it reads.

Is the ASI174MC not a better option as it reads colour?

A monochrome camera has a sensor that is sensitive to all colours all the time.  It doesn't differentiate between them.  A colour camera has a sensor where the individual photosites are only sensitive to red, green or blue parts of the spectrum.  This means that for a mono camera you can only say "some light arrived at this pixel" whereas with a colour camera you can say "some red (or green, or blue) light arrived at this pixel".  In fact, each photosite in a colour sensor has its own filter for the colour it is sensitive to.

A filter doesn't "change" the colour.  It prevents all colours outside it's passband from going through it.  So a red filter will block everything except the red part of the spectrum.  You then know that all the light reaching the camera sensor must have been in the red part of the spectrum.  Similarly with green and blue.  By taking three sets of images, one with each filter, you can then recombine them to get a colour image.

The reason for using the monochrome cameras is that they "lose" fewer photons than similar colour sensors where some fail to make it through the colour masks applied to the sensor, so the monochrome version is more efficient.  Also, only 25% of the photosites in a colour sensor are sensitive to red, 25% to blue and 50% to green, whereas with a monochrome sensor and a separate filter, all the photosites are sensitive to the colour you're sampling.  That means there's a loss of resolution with a colour sensor.

This all makes colour sensors sound fairly undesirable, but that isn't necessarily the case.  Time constraints and the cost of all the additional kit for mono may make a colour camera a more sensible choice for any given individual for example.  Getting three different colour monochrome captures of Jupiter in two or three minutes is something that takes a certain amount of practice for it not to be a bit of panic, whereas it's far less frantic with a colour camera.

James

[christhebrit]

I believe I now understand.

This has been very helpful towards my decision making.

Thanks for the detailed explaination of Monochrome, as until now I was under the impression it was black/ white.

This now makes sense, meaning I will need to rethink my intentions for a camera.

I'd prefer not to buy something, knowing I'll upgrade soon after.

If it takes a bit more saving, I'll do that.

Chris

[Owmuchonomy]

On 26 March 2015 at 14:31, JamesF said:

It is an open-source (planetary/solar system, mostly) capture application wot I have writ for Linux and OSX: http://www.openastroproject.org/

James

..and I have just discovered it.  What joy!