Second Attempt at EEVA (I think I'm missing something)

[PeterC65]

This was my second session with the Altair GPCAM2 327C camera. This time I used the SharpCap software, having read the manual up to and including the section about live stacking.

I fitted the camera to the Photoline 72 (72mm F6) without any Barlow / Reducer, with a 35mm extension tube and with a filter wheel, but in the end didn’t make use of the filter wheel. I made a point of noting the orientation of the sensor and kept this horizontal in the clamp so that the image was the same as in Stellarium. This was a big help.

This time I was able to control the mount with both the SynScan software and from Stellarium, although not at the same time. When under the control of the SynScan software the mount handset is disabled and the scope position cannot be seen in Stellarium. When under the control of Stellarium the mount handset can still be used but it is outside and I am inside.

I aligned the mount using the handset but this time using the camera view with cross hairs enabled instead of an eyepiece. Using the histogram stretch I could see the alignment stars clearly but needed to use the RDF to first get them into the field of view, even for the second alignment star. I aligned using the Brightest Star method with Altair and Deneb and this gave good alignment of the mount which was maintained throughout the session including after a later change of camera.

After aligning I focussed the scope on Altair using the Bahtinov focus mask which was straightforward to use and allowed very fine focus adjustment.

While the histogram stretch function did make it easier to see star fields it proved hard to see anything feint. The small field of view of the Altair GPCAM2 327C camera made me keep wishing I could just switch to another eyepiece when trying to find an object. This was a particular problem when the object was a DSO and therefore not immediately visible at all.

 

Saturn

I started with Saturn as I could clearly see it with the naked eye. The mount alignment didn’t bring it into the field of view so I had to use the SynScan software slew keys and the RDF. I could clearly see the planets disc but it was washed out with exposures longer that about 0.1 seconds (and 200 gain).

 

Jupiter

Same story as Saturn. It needed a short exposure time to see any detail and then I could see the two main cloud bands. Zooming in made these clearer but with pixilation. The short exposure made the moons very hard to see.

Overall the experience viewing plants was no better than with pure visual, and more frustrating because of the difficulty in changing magnification (without pixilation).

 

My aim for the session was to try to see DSOs so the planets were mainly to check things were working.

 

M71

This star cluster was in a good spot near to Altair, one of the alignment stars, and Stellarium indicated that it would fit easily within the field of view.

Adjusting the exposure I could just make out that there was a cluster and the histogram stretch made it more visible. Live stacking required longer exposure times to reveal more stars with which to align the frames. The live stacking histogram stretch just made the whole image white but I could adjust this. The histogram was mostly a peak at what I assume was the background black level with very little data elsewhere. I could widen this peak a little by increasing the exposure time but not by much. When the black level of the live stacking histogram was set to include the peak the whole image turned white and I had to carefully set the black level to exclude the peak. That just didn’t seem right.

I took this snapshot of the image after live stacking. You can see there is a star cluster but the image looks artificial and over exposed.

 

NGC6992

I’ve been wanting to see the Veil Nebula so gave it a try, but all I could make out was a star field with no sign of any nebulosity no matter what I did with the exposure, histogram stretch and live stacking.

 

M31

This is too big for the field of view but I thought I might be able to see the bright centre, and that this would appear easily. That was not the case.

Long exposure times (10 seconds) were still needed to see enough stars for alignment and live stacking only generated what looked like a noisy left hand side to the image. This may have been the galactic centre.

 

M33

I tried for M33 as it is smaller and should fit into the field of view but just saw a star field.

 

It was 2am in the morning by this point and I was thinking I might be needing to sell on the Altair GPCAM2 327C camera (!), so I decided to switch to the Canon EOS 1100D. This has a much wider field of view and the mount was able to put each target immediately and obviously within it.

 

M31

The smart histogram function told me to use a 25 second exposure time and a gain of 6400. With these setting I could make out the galaxy in the live view. Live stacking produced a really good image, but only after a couple of minutes of these relatively long exposures and only after carrying out histogram stretch multiple times in both the live a stacked histogram window. These are different histograms and I don’t yet understand the difference. I also had to adjust upwards the black level point in the histogram to get a sensible image.

M45

Feeling like I was finally getting somewhere, albeit with the DSLR, I tried for M45 which had now come up well above the horizon. It took more fiddling around with the histogram controls and also required 25 second exposure time and 6400 gain settings but produced an OK image.

These last two are nice images, showing much more detail than is possible with pure visual, particularly on M31, but they are far from live, taking minutes to appear. And the experience with the Altair GPCAM2 327C camera was pretty rubbish again!

What am I doing wrong?

 

 

[Steve in Boulder]

Your M31 and M45 with the Canon are pretty good!  It's going to take a few minutes for this type of view.  This isn't "video astronomy."

On M31 with the Altair cam.  The scope wasn't pointing at M31.  It did have M110 in the field.  I could tell this by submitting the image to astrometry.net:  https://nova.astrometry.net/user_images/6245893#annotated  That you can't see M110 (and some of the extended glow of M31) well is due to the black point being set too high.  The glow in the upper left might be amp glow, not a DSO.  

You might want to save your sub exposures so you can test different settings with them later. 

 

 

[PeterC65]

12 minutes ago, Steve in Boulder said:

Your M31 and M45 with the Canon are pretty good!  It's going to take a few minutes for this type of view.  This isn't "video astronomy."

On M31 with the Altair cam.  The scope wasn't pointing at M31.  It did have M110 in the field.  I could tell this by submitting the image to astrometry.net:  https://nova.astrometry.net/user_images/6245893#annotated  That you can't see M110 (and some of the extended glow of M31) well is due to the black point being set too high.  The glow in the upper left might be amp glow, not a DSO.  

You might want to save your sub exposures so you can test different settings with them later. 

Thanks for the feedback, very useful, especially the website link. I've just tried it on my captured image of the Veil and it confirms that I was pointing in almost the right place on that occasion.

Regarding your comment about video astronomy, what can I expect to see with objects like M31 on a close to live basis? Say one second or less exposures perhaps live stacked. Should I expect to see the galaxy extent, just the central glow, just a star field? My objective is EEVA and not astrophotography so while the M31 photo is very nice its not really what I'm aiming for.

I had been thinking I should have saved the exposures, after the event unfortunately. Now, in the daytime, I have nothing to play with other than the M42 test image that comes with SharpCap.

[Steve in Boulder]

That M31 is what one aims for with EEVA.  Live stacking doesn’t mean instantaneous or near-instantaneous real time views.  It just means you stack the images as they come in, instead of what the astrophotography people do (i.e. wake up the next morning and spend hours tweaking the hours of data they collected the night before).  I typically collect exposures for 5-10 minutes.  

[Steve in Boulder]

If you want a more instantaneous result, you might look into something like the Revolution Imager, though I have no experience with it. 
 

The Veil Nebula is pretty faint.  If you did a really aggressive histogram stretch, it might show up, but I find that a narrowband filter gives the best result. 

[PeterC65]

35 minutes ago, Steve in Boulder said:

The Veil Nebula is pretty faint.  If you did a really aggressive histogram stretch, it might show up, but I find that a narrowband filter gives the best result. 

I do have an OIII filter bought specifically to see the Veil but not yet tried. I want to get basic EEVA working before I go for anything faint. I'm thinking that good targets might be M33 (smaller than M31 so it will fit into the FoV) and M27 as its quite bright and not tiny.

The very narrow peak in the histogram I was seeing is, I think, because I wasn't pointing at a DSO as you mentioned earlier. I get the same result if I select an area of star field in the M42 reference image and histogram just that.

We are due some clear nights over the next few days so I will keep trying!

[Steve in Boulder]

M33 and M27 are excellent targets!  You might also try M57 (and M27) with your Altair.  Platesolving can help you locate targets with the smaller sensor.  

[PeterC65]

I tried again last night and had more success.

I turned up the gain to maximum and used a 1 second exposure with some auto stretch to try to frame the DSO. I could just make out the DSO in most cases and when I could not I took a snapshot and submitted it to Astrometry.net to find out where I was actually pointing. Sometimes that helped, sometimes it didn't. I made a point of only progressing to live stacking if I was sure I was on target, then I increased the exposure time to 10 seconds reduced the gain to 200 and started live stacking with some good results I think.

Here is M27 ...

I had no luck finding M33 or the centre of M31 but did manage to find the East Veil with some help from Astrometry.net ...

This was taken with the OII filter in place. The first time I've seen the Veil so I was very excited! I will try using the DSLR next time and try to capture the whole of the Veil in one shot.

Last night has shown me what is possible with EEVA I think. It's a different experience from straight visual and I'm not sure whether I prefer it, but given a few minutes to collect some data and live stack, the images are much better and you have the advantage of being inside and not having to worry about light pollution or dark eye adaption.

[Steve in Boulder]

Well done!  If you can get platesolving working, then centering DSOs is a piece of cake.  What software are you using for stacking? How long were your exposures for the Veil image?

[PeterC65]

21 minutes ago, Steve in Boulder said:

Well done!  If you can get platesolving working, then centering DSOs is a piece of cake.  What software are you using for stacking? How long were your exposures for the Veil image?

I'm using SharpCap software. It does seem to have plate solving but I think that requires the mount to be under the control of SharpCap and I haven't tried that yet.

The Veil photo I posted above was taken with an OIII filter with a 15s exposure and 200 gain, and there are about 10 frames in the stack. I took another one with a UHC filter and an 8s exposure but the image seemed noisy, although it did show more colour and perhaps more of the stronger detail. I didn't try to do much with filters last night as I was just pleased to get a reasonable image without! Thinking about it today I assume that filters will reduce the light being captured and so will need longer exposures to keep the noise down.

Still lots more to try but I'm suffering today from two late nights in a row!

 

[Steve in Boulder]

4 hours ago, PeterC65 said:

I'm using SharpCap software. It does seem to have plate solving but I think that requires the mount to be under the control of SharpCap and I haven't tried that yet.

The Veil photo I posted above was taken with an OIII filter with a 15s exposure and 200 gain, and there are about 10 frames in the stack. I took another one with a UHC filter and an 8s exposure but the image seemed noisy, although it did show more colour and perhaps more of the stronger detail. I didn't try to do much with filters last night as I was just pleased to get a reasonable image without! Thinking about it today I assume that filters will reduce the light being captured and so will need longer exposures to keep the noise down.

Still lots more to try but I'm suffering today from two late nights in a row!

 

I believe you're right about SharpCap, though I haven't used it.

The stars in the Veil image are a little elongated.  That could be your mount, or it could be that the Veil was near the zenith.  Images with an alt-az mount will start to have star trails due to field rotation, especially near the zenith.  I try to keep away from the zenith, and I typically do 20 second subs with a narrowband filter when I'm using my alt-az mount (AZ Mount Pro).

With the UHC filter, just try letting the stacking running longer, say 5 minutes total.  That'll reduce noise.  

[PeterC65]

2 minutes ago, Steve in Boulder said:

The stars in the Veil image are a little elongated.  That could be your mount, or it could be that the Veil was near the zenith.

The Veil was near to the zenith, but I also have a fairly basic Alt-Az mount so probably a bit of both.

I'm wrestling with ASCOM mount drivers just now. Having everything controlled by SharpCap would be nice ... if I can get the technology to work!