First images with 120mc

[don4l]

52 minutes ago, Thalestris24 said:

Hi

You may have some different options as you have a colour cam which is zwo, so different driver. You have to setup hardware such as mount in File -> SharpCap settings. I find it very useful to be able to control the mount (via eqmod in my case) and use blind plate solving (need to be within 15 deg) to get on target  You obviously have to download and configure the relevant plate solving tools - I use Astrotortilla..

Louise

 

I noticed the Mount options, but I don't think that I need to worry about these.  I have my CdC/EQMOD combination working beautifully, and I can platesolve the images from the 120 in Elbrus.  I don't normally take more than a couple of minutes to get my target centred.

[JamesF]

1 hour ago, don4l said:

Thank you!

I'll have a play to see if there is a fixed figure added on to each pixel.  This will be easy to test.  It would also mean that the dark frames that I have already taken can be corrected.

I did some quick tests with my 120MM-S.  I don't know if the other 120 models are the same, but it might be a helpful reference point.

I see the range of the brightness control returned by the camera driver as 0 to 20.  If I connect up the camera with a lens cap in place then I get a totally black image with the brightness setting at 0.  As I raise the value the entire frame gets slightly brighter, but even at 20 it's still quite dark grey in colour.

James

[don4l]

1 hour ago, JamesF said:

I did some quick tests with my 120MM-S.  I don't know if the other 120 models are the same, but it might be a helpful reference point.

I see the range of the brightness control returned by the camera driver as 0 to 20.  If I connect up the camera with a lens cap in place then I get a totally black image with the brightness setting at 0.  As I raise the value the entire frame gets slightly brighter, but even at 20 it's still quite dark grey in colour.

James

I've now done some tests.  I've taken two sets of 3 second darks with brightness values of 0, 5, 10 and 15.  The first set had Gain set to 10, and the second set had Gain set to 20.

The "Brightness" does seem to be adding a fixed value.  At gain of 20, this appears to be about 256 ADU per unit of brightness.  At a gain of 10, it appears to be about 240, but a bit less linear.

In future I'll leave it at 0.  I now need to take more darks, but at least I feel like I am getting somewhere.

 

There are a couple of reasons that I want to get to the bottom of this.  One is that the small pixel size gives greater resolution.  In the M42 image above I can just about make out 4 stars in the trapezium.  With the STL6303, you only get a blur that looks like it might have 3 stars.  So, I can definitely get some finer detail.

 

[don4l]

I've had another play with the 120mc.  I think that I am beginning to understand a bit about CMOS imaging.  I really do like some of the things that you can do. I also really dislike all the vague options that you get with these cameras.

The "Brightness" control appears to add a pedestal to the image.  I don't like ADU values of zero, so I have set it at 1.  This seems to add 128 to the image which doesn't give away much dynamic range.

 

I'm still at a loss about what gain to use.  As I don't have an autoguider when I am using the 120 for imaging, I am limited to 60s exposures.  I did notice that the Trapezium stars were better resolved with this camera than with my STL6303 (9um pixels), so I did a little experiment.  I set the gain very high and the exposure to 2s.  Bear in mind that I can barely tell that there are three stars with the 6303.  I am very pleased with the result.  I've attached it below.  I appear to have hints of the "e" and "f" stars!!!

I also took some shots of M82. I had to apply the darks in The Gimp because Sharpcap saved all the subs ing png format - so I couldn't use any of my stacking software.  (I will never, never buy software that even offers png as an option).  The image below is either 18 or 27 minutes integration.  The subs were 45 seconds, and the gain was 50.  The result is below.

I still have many questions, but I feel that I am getting somewhere.  I wish that ZWO provided some decent acquisition software. 

I'm toying with the idea of blending 120 data with data from my main camera.  This should give brilliant results on smaller objects.  If I had known this when I bought my autoguider, then I would have spent a few more pounds and got something with a bigger chip.

 

 

 

[Stub Mandrel]

9 hours ago, don4l said:

I also took some shots of M82. I had to apply the darks in The Gimp because Sharpcap saved all the subs ing png format - so I couldn't use any of my stacking software.  (I will never, never buy software that even offers png as an option).

Why? The web generally only accepts PNG, GIF and JPG files. JPG is compressed, GIF is only 8-bit so PNG is essential as a format for displaying images faithfully online.

DSS will accept PNG files, it seems.

Sharpcap will save as TIFF if you tell it, but as PNG is lossless you can convert to TIFF without any problems. Using RAW gives the best results.

[don4l]

2 minutes ago, Stub Mandrel said:

Why? The web generally only accepts PNG, GIF and JPG files. JPG is compressed, GIF is only 8-bit so PNG is essential as a format for displaying images faithfully online.

DSS will accept PNG files, it seems.

Sharpcap will save as TIFF if you tell it, but as PNG is lossless you can convert to TIFF without any problems. Using RAW gives the best results.

My problem is that when I tell Sharpcap to save in FITS,  it saves a few files in FITS and then reverts to PNG.  Several times this has happened and I haven't noticed for 30 minutes, or more. I've lost about half of my data becaus of this.  I took the M82 data on the night of the 11th.  It took me until yesterday to get it processed.

This "feature" really brings out the Victor Meldrew in me!

[Stub Mandrel]

3 hours ago, don4l said:

My problem is that when I tell Sharpcap to save in FITS,  it saves a few files in FITS and then reverts to PNG.  Several times this has happened and I haven't noticed for 30 minutes, or more. I've lost about half of my data becaus of this.  I took the M82 data on the night of the 11th.  It took me until yesterday to get it processed.

This "feature" really brings out the Victor Meldrew in me!

If you post the bug in the sharpcap thread witha log file Robin will look into it for you.