Doug64

14 minutes ago, MarkAR said:

Extension will work.

These should be good quality

https://www.lindy.co.uk/usb-c4/usb-extension-c222/15m-49-70ft-t53

 

Thanks for the reply.

The Lindy 15m USB 3.0 cable is the one I was looking at,as I currently use the Lindy 5m active USB cable and have had no problems, I was just a little worried about the additional 10m cable length and data transfer.

Doug

Hi,

I wonder if anyone can offer me some advice.

I used to set my telescope and imagingbrig up from time to time and was running the imaging rig etc with a Startech 7 port 12v dc powered hub and a 5m Lindy active cable which ran to my computer.

I had no problems running this set up however the good old council have recently replaced the sodium lights with LED lights and now my back garden looks like Blackpool illuminations.  As a result of this I am having  to move my scope and imaging rig further down the garden and will need to run a 15m cable back to the house and my computer.

I will be using my Asi 1600 mono cooled camera and from time to time a DSLR.

Can I just buy a 15 m USB 3 active cable and run this from the USB hub on the scope back to my computer or can I buy a USB 3.0 to ethernet converter and run Cat5 or Cat6 cable back to my computer (would this work).

Any advice greatly appreciated.

Thanks

Doug

Thanks for all the replies, problem now solved.

Doug

7 hours ago, vlaiv said:

You can make one, but it is really up to how you use it.

Bad pixel map is "contained" inside master dark, or rather based on set of darks you can identify all the pixels that are bad and treat them accordingly (usually you can either mark them as bad so when alignment of subs is performed, these values are not used and are interpolated instead, or you can do it prior to alignment - in calibration phase).

It is up to software to handle this, and bad pixel map is basically the same thing as dark lib, except you are not interested in dark current signal - only pixels behaving badly - like those that are dead (returning 0 value), hot (returning clipping max value) or stuck pixels - always returning same value regardless of signal capture. All of these can be inferred from set of dark and pixel statistics and it's up to software that you use to make appropriate action.

Thanks for the reply

Doug

Hi,

I hope someone can help me, I'm writing this whilst banging head on the table as I've waisted 8 hours taking Darks..

I've recently bought a Zwo 1600MM Cool And I have been learning APT as I've never used it before.

I have been making a Darks Library, over the past 24 hours I've created one set of Darks at Gain 139, this morning I set up APT to do a sequence of Darks at Gain 200.  In order to set the Gain to 200 I opened up Settings under Camera in APT and adjusted the slider to Gain to 200 and pressed OK.  Everything appeared to be working correctly.

Having set up the imaging plan I went out and have just returned to find that every Dark taken today has a Gain of 139 and not 200. 

I've run a check and each time I set the Gain to 200 and run a sequence for Darks the images taken have a gain of 139 and in the camera settings the gain has gone from 200 to 139.

I've checked that the Manage Gain box in Settings is ticked.

I know I'm doing something wrong in APT but I can't figure out what it is.

Can anyone help so I don't waste anymore time.

Thanks

Doug

Hi,

Just setting up my Zwo 1600MM Cool.

I've done a darks library and was wondering if you use Bad Pixel Maps with Cmos cameras, I used to use one with my DSLR.

I have read about someone making a Bad Pixel Map with Darks and Dark Flats but other people don't mention it.

I'm wondering what the consensus of opinion is

Thanks

Doug

Thanks for the information.

I always thought plugging any USB 2 device into a USB 3 hub makes everything on the hub run at USB 2 speed that's why I asked the question and I'm glad I was wrong.

You live and learn.

Thanks again.

Doug

Hi,

I currently have a Startech USB 3 powered hub and a gaming computer that runs USB as well as Cat 5/6.

Having just purchased a Zwo 1600MM Cool which has USB 3 and a  USB 2 hub I was wondering what is the best way to set everything up.

My guide camera is USB 3 so that can be plugged into the Startech USB 3 powered hub.

My Zwo 1600 is USB 3 so that can go into the hub.

Now I have two other devices which are USB 2, a Starlight xpress filter wheel and the mount. 

If I connect the filterwheel into the USB 2 hub on the back  of the ZWO 1600 with 0.5m cable will this then reduce the camera down to operating at USB 2?.

Likewise if I put the mount USB 2 into the Startech hub does this then reduce everything plugged into the hub to USB 2 instead of USB 3.

Am I best using two separate hubs one for USB 3 and another for USB 2 or would it be best to use a mini PC or something like ASIair at the mount then wi-fi or Cat 5/6 back to computer.

Everything will be on my mount which is outside as I don't have an observatory.

Thanks for any advice on this is I'm not very good with IT.

Doug

2 hours ago, symmetal said:

I've uploaded the Excel spreadsheet to my MediaFire Cloud Storage account. I've uploaded two versions. The .xlsx is for the latest versions of Excel which I used, while the .xls version should work with older versions of Excel that don't recognise the newer format. The free Open Office suite of programs should read the .xls file without problems if you don't have Microsoft Office. I don't know if it recognises the newer format.

ASI1600 Sky background ADU chart (.xlsx)

ASI1600 Sky background ADU chart (.xls)

If you want to enter your own values for gain and offset in columns one and two, you also need to enter the Read Noise in electrons (e-) in column three, and Gain in electrons/ADU (e-/ADU) in column four as read from the ASI1600 graphs in the manual which correspond to the column one gain. The values you've entered in columns three and four will be plotted on the graphs in the spreadsheet so you can see if the values are good as the curves should still retain their overall shape. I've posted the Zwo graphs below if you've misplaced the manual. 

I included a graph for the offset as originally I used the Zwo gain and offset values where the offset varied with the gain and the graph shape indicated if the values you entered followed the Zwo curve. If you use a fixed offset value then the offset graph doesn't tell you anything useful.

Hope Mark and Doug and anyone else finds this useful. 

Alan

Hi Alan,

Thank you very much for your advice and for uploading the charts.

Doug 

Great image.

I'm just setting my equipment up having bought a Zwo 1600MM for narrowband work and I hope at some point to be able to get an image like yours.

Doug

45 minutes ago, spillage said:

@Doug64 If you are imaging from only one location you could always upload the .fits and have one of us open it in sgp to get the median value for you.

Thanks for the reply.

Once I have everything set up, just getting APT to link to all my equipment, I'll take an image and see if I can get the background median value using APT, if not I may have to do as you suggest.

90% of my imaging will be done from my back garden, this is why I've just bought the mono camera as I'll need to use Narrowband most of the time due to light pollution (Bortle 7).  I do take my telescope etc with me twice a year to Kelling, and to other places such as the flooded SGL star party and Galloway.

I'm really looking forward to using this camera once I've learnt how to use it.

Doug

14 minutes ago, spillage said:

Its been a while but I am sure when you load the image you click the tools tab and choose pixel aid.

Thanks

8 hours ago, symmetal said:

Hi Doug,

Here's a CN post describing the read noise swamping by sky background calculations. Look for the Jon Rista entries.

I made an Excel chart calculating these values for various gain/offset values for the ASI1600. Initially I used the varying offset values recommended by Zwo but changed to a fixed offset for all gain settings (for simplicity) which avoided black clipping as the Zwo offsets were too low. The Read Noise and Gain graphs are plotted from the column entries and mimic the Zwo graphs from the ASI1600 manual.

During astro dark, take an image of a star field which doesn't contain large areas of bright nebulosity. The image sky background ADU can be read as the median value of the image statistics panel which your capture program should display. The mean value should be pretty much the same value as the median.

There are different opinions as to which calculation method (I've shown four) should be used for the 'swamping the read noise ADU value' and I use 10 x RN^2 which is the last column. The calculation for the 1386 ADU value in box J12 is shown in the equation at the top. If you use offset 50 just subtract 96 from these ADU values, ie. (56-50) * 16

Adjust your exposure duration until the sky background ADU is around the value in the table and that is the maximum exposure you need to use for that filter. The RG and B exposures should be fairly similar while the L should be about 1/3 that value. During astro dark, use these same exposures for your targets and you should be close to optimum. If you move to darker or lighter site you need to re-evaluate these exposure times. As currently there is no astro dark in the UK, exposures don't need to be as long to reach these ADU values. If you're in a light polluted site the exposure duration values will be a lot lower than than at a dark site.

Hope this helps Doug and hasn't left you more confused. 

Alan

Hi,

Thanks very much for your explanation and chart, it's really helped me understand, I think .

If I've understood everything for Gain 139 with 56 offset my background target ADU is 1386.  In order to find exposure times I set up my telescope etc and at astro dark I'll need to take some test exposures at varying exposure times until I get one where the background level is 1386 and I do this for each filter and record times etc.

Just a few questions if you don't mind:-

I'm going to be using Astrophotography Tools, if you know this software does this allow me to check background level. (I'm just starting to learn this and haven't taken an image using it).

If I image from my garden once I have these timings will they basically remain the same for each session and then I only need to check them again if I move to dark sight etc or in winter with astro dark.

Why do you choose offset 56 is it to stop the clipping.

Thanks again

Douh

Thanks for the replies,

Now I'm really confused  the more I read the more confused I get.

I think using unity gain will be a very good starting point for me for all filters as I then only have to work out exposure time.

I'm not use to all this ADU, well depth etc so I think I have a lot to learn, at least I can get imaging once I have clear skies using Unity gain.

Can anyone point me to the equation for working out exposure time and also where do you get the ADU level, is it from the histogram after taking the image.

Thanks

Doug

Hi Vlaiv,

Thanks for the comprehensive reply, some of it was a bit over my head but I'm starting to get the idea about gain and offset.

I understand little of the math, I knew this was going go be a massive learning curve and I'm not wrong.

Thanks again 

Doug

12 hours ago, vlaiv said:

Some good advice given on gain settings. I'll just expand a bit on how to choose it depending on your conditions, and I'll give advice on offset.

With gain you are balancing two things really - read noise and well depth.

Read noise bit is important in two ways. Firstly, it is of course source of noise, and should be kept as low as possible. It is however probably the smallest contributing noise in most cases. Only case when read noise is significant is if you have incredibly dark skies or you use narrow band filters (like really narrow 3nm) and imaging very faint target. In this case it will become dominant noise source and you might want to reduce it as much as possible.

Second way read noise impact things is single long vs multiple short exposures. Difference between the two is read noise. If read noise were 0, there would be absolutely no difference between two approaches, but as read noise becomes higher there will be more and more difference between many short subs and a few long ones (all of this depends on other factors/noise sources as well).

Depth of well is inverse of gain, so larger the gain you use - less pixel well depth you will have (and saturate in less time) - these two are fighting each other, because for narrow band, for example you want to raise gain (to have less of read noise) and you want longer exposures - but higher gain will lower full well capacity of pixels and longer exposure will saturate in some cases - you need to find a balance.

There are no exact settings that will work for everyone because all of the above depends on sky brightness but also on target brightness and scope used - how much aperture and what is working resolution (sampling rate - or arc seconds per pixel).

For most targets and LRGB, you can use unity gain and 1-4 minutes (if you use longer exposure, you star color will suffer on brighter stars, so you'll want to use a few short ones as filler for color - with luminance you don't need to worry about that - just make sure target is not clipping). For NB you'll want to use 4-5 minutes and higher gain - look at gain/read noise chart and select one that will not eat too much into full well capacity but will still provide you with low read noise.

Above is balancing act - so try with "recommended" settings, but tweak to your particular conditions.

Offset on the other hand is something that you want to do right, and there is right and wrong setting. With offset you aim to avoid clipping "to the left" - or trying to avoid 0 values in the image (in both darks and lights). Don't be afraid to go with high offset - it's impact on full well will be minimal, but it is safer bet that you won't get that clipping that will mess up your calibration. I personally use offset of 64, but anything higher than 50 is a good starting point.

There is a way to determine good offset for chosen exposure length (and it will probably be valid for range of exposure lengths) - take dozen or so darks, stack them with minimum method (not average, and no sigma clip and such, just straight minimum), do stats on resulting stack and if you find that you have pixels that are 16 in value (or 1 if you bit shift your images to 12 bits from 16bits) - or stats on that stack give you minimum of 16 (meaning there is at least one pixel with that value) - raise offset.

Thanks for all the replies.

I'll start off using unity gain and may try gain 200 with my narrowband filters, this way I can learn more about the software and filters etc.

Doug

Hi,

Thanks for the reply.

I have seen the charts you refer to and was initially going to work from them but the more reading I did the more I found people using different gain / offset settings.

This us why I got confused.

I live in a Bortle 7 area.  18.79 Magnitude.

Regards

Doug

Hi,

I've just bought the above camera to try some mono CMOS imaging having previously used a modified DSLR.

I've started reading about imaging / processing with this camera and it's going to be a big learning curve.

I'm already confused with regards to the gain settings.

I've read all sorts of settings people appear to use:- Unity Gain  - 139 offset 21, Gain 76 offset 21, Gain 76 offset 15, Gain 200 offset 30, Gain 200 offset 15, Gain 300 and also gain 0.

I will be using this camera with my ED80 with flatter/reducer and motorised filter wheel.  I live in a city with very bad light polution so was wondering if anyone could give me some advice about the gain and offset settings or is it just trial and error.

I have LRGB  and Ha OIII SII filters.

Thanks

Doug

Hi Mark,

Thanks for the reply.  The image I was initially using was the one you posted in your first post of the North American Nebula.  I copied that image onto my computer then processed it following your instructions and the image I have shown you is what I got.

I've now copied over your Photoshop PSD file and have viewed this in my version of Photoshop and it looks good, see below image so I don't know what is happening.

Thanks for your help anyway and I'll try your process which I've saved as a complete action on another image when the clouds clear.

Regards

Doug  

22 hours ago, sharkmelley said:

The effect you're seeing is posterisation, not pixelation.  It might simply be the way Photoshop is displaying the image.  Try displaying at 100% scale instead of 66%.

Otherwise - maybe the file you are processing has a bit depth of only 8bits.  You need 16bits in order to have sufficient levels of brightness to prevent posterisation when stretching the data.

Mark

Hi Mark,

Thanks for the reply,

I was using the image provided with the initial post and upon checking it is 16bit.  I've increased the view to 100% but still no change, the posterisation is still there as shown in the below image.

Regards

Doug

Hi Mark,

I'm just learning processing.  I've followed your instructions using the image you provided and below is what I'm getting, a very pixilated image.  It's obvious I'm doing something wrong but do you know what it is, I'm using Photoshop CC.

Regards

Doug

Thanks,

Will give it a go when we get some clear nights.

Doug.

Hi,

Will this work when using a side by side set up as I use a dual mount.

Regards

Doug