First Attempt at EEVA

[PeterC65]

This was my first attempt at EEVA with the new Altair GPCAM2 327C camera and not so new 72mm refractor (TS Optics Photoline 72).

I fitted the camera to the scope 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.

The SynScan software on the laptop would not connect to the mount so the only way to manually control scope pointing was via the handset. Stellarium was able to control the mount for GOTO and tracking but the mount seemed to have a slightly different, and more accurate, position for objects than did Stellarium.

I tried aligning the mount using the camera view on the laptop and using the handset alignment process. The field of view is much smaller with the camera than it is with an eyepiece and harder to change (by adding a Barlow / Reducer rather than just using the zoom eyepiece). In order to see even relatively bright stars the camera needs to be set to higher gain / longer exposure / image stacking and this makes it easy to miss objects. So aligning the mount proved frustrating with the camera and in the end I used the ES68 24mm eyepiece. This resulted in good alignment with Altair and Alpheratz using the Brightest Star method, but only after much frustration and wasted time.

I used the AltairCapture software for most of the session but also used SharpCap. SharpCap allows a greater range of exposure time adjustment (AltairCapture seems to be limited to 5 seconds maximum), the user interface seems easier and there seem to be more features. Next time I will use SharpCap as it can also be used with the Canon EOS 1100D camera and learning just one software tool would be easier. The images in both software tools looked similar.

At least half of the session was spend checking whether the mount was aligned and whether the camera image orientation was the same as the one shown by Stellarium. The image in AltairCapture in fact needed flipping vertically while the default in SharpCap was fine, but this could only be determined conclusively by looking at the Moon.

At the end of the session I removed the camera and looked at the same objects briefly with eyepieces to compare with what I was seeing via the camera. By this time the Moon was bright and with the sky not astronomically dark and still lots of heat in the atmosphere, conditions for seeing where not great.

Star Fields

During the first part of the session I was looking mainly at random stars and star fields.

With a 5 second exposure time the star fields started to appear, and sometimes a cluster, but this length of exposure meant that slewing the scope was no longer a real time activity. With live stacking the star fields came alive, with the individual stars very visible, and in particular their colour. This was much better that the view through an eyepiece, but far from real time.

I pointed the scope at what I thought might be a few nebulae but only managed to see the star fields with no sign of any nebulosity even after adjusting the gain, exposure and enabling image stacking. Increasing the gain made the image very noisy.

Moon

The camera view of the Moon was similar to the view with an eyepiece but it was much harder to change magnification (as I would normally do by changing the eyepiece) and to nudge the image around (as I would normally do with the handset slewing keys). Both things are important for observing the Moon and so overall the experience with the camera was not great.

With both the camera and an eyepiece the Moon was rippling because of atmospheric disturbance but this rippling seems a little more obvious in the camera image.

Jupiter

I observed Jupiter with the camera with no Barlow and with the Baader Hyperion x2.25 Barlow. Without a Barlow it was just a plain disc but the two main cloud bands could just be seen with the x2.25 Barlow. Anything more than minimum gain and a short exposure made the plant wash out to a bright disc with no detail, as did image stacking, but with the right settings and the x2.25 Barlow I could see more detail than with an eyepiece. Again there was much rippling.

Saturn

I observed Saturn with the Baader Hyperion x2.25 Barlow. I could see the rings but no detail. The image was better (bigger) with the camera than with an eyepiece, but only at minimum gain with a short exposure and no image stacking. Trying to zoom digitally just exposed the rippling, noise and pixilated the image.

So overall for Jupiter and Saturn, the camera image was better than with an eyepiece but not massively so.

M45

Towards the end of the session M45 was just above  the horizon and it is one of my favourite targets for the Photoline 72 (it being widefield). Even with an eyepiece (ES68 24mm and BCP 32mm) the view wasn’t good because of the excess light. With the camera I was able to see the bright stars but the field of view was insufficient to take in the whole group, even with the x0.5 Reducer, so it felt like it does looking at M45 with the Skymax 127 (like looking at it through a keyhole).

M31

I was feeling frustrated and disappointed by the end of the session but turned the scope towards M31. This never looks great with the Photoline 72 as despite the wide field of view the aperture is too small to see more than just the bright centre as a smudge of light and that was what I saw through the eyepiece (ES68 24mm).

The camera image was much better. With the gain set low and a 5 second exposure time, image stacking gradually revealed detail that I had never been able to see before. After a few minutes of stacking I could make out the extent of the galaxy (no spiral arm details though) and in particular I could clearly see the dark clouds on one side of the galaxies centre.

This bodes well for future sessions when I have sorted out the alignment process with a camera and mastered the software.

[Mike JW]

Hi Peter,

and so your journey begins and no doubt a few more frustrations lie ahead (I remember oh too well.....),

Aligning for me using the camera view - tried it but so much quicker using visual. I always do two star visual alignment, then GOTO a star in the region of interest (where I hope to observe various DSOs) and sync to this star visually, sometimes do a fourth star. Then using the synced star, I pop in the camera and sort out focus and that is me set up for the session.

For DSOs I would suggest go for Messiers and bright NGC objects at first as you sort out technique/software.

Good luck,

Mike

[Martin Meredith]

Hi Peter

Nice report, and good to hear about the visual comparison.

Were you doing much in the way of histogram adjustments? You ought to be able to see plenty of stars in a 1s exposure but only if the black point is appropriately set, and the image stretched. Alternatively, it may be that your overall focal ratio is quite slow for EEVA. 

The selection of objects you've chosen is rather challenging for EEVA techniques. Planets (apart from Uranus outwards) require a different approach to DSOs, and M45 and M31 need a large FOV to make an impression, so it perhaps isn't surprising that the visual views equal or better the camera views. If you were to look at planetary nebulae, globular clusters or (especially) galaxies/galaxy groups, you'd immediately notice that the EEVA view goes many many magnitudes deeper.

cheers

Martin

 

[PeterC65]

2 hours ago, Mike JW said:

Hi Peter,

and so your journey begins and no doubt a few more frustrations lie ahead (I remember oh too well.....),

Aligning for me using the camera view - tried it but so much quicker using visual. I always do two star visual alignment, then GOTO a star in the region of interest (where I hope to observe various DSOs) and sync to this star visually, sometimes do a fourth star. Then using the synced star, I pop in the camera and sort out focus and that is me set up for the session.

For DSOs I would suggest go for Messiers and bright NGC objects at first as you sort out technique/software.

Good luck,

Mike

Good to know that others align visually before fitting the camera and its not just me!

Can you explain what you mean by "sync to this star visually"? I usually just do a two star align when I'm doing visual and sometimes do a Pointing Accuracy Enhancement if I GOTO an object of interest and find that the alignment is a bit out. I've noticed a Sync button in the scope control on Stellarium. Is it anything to do with this? I can't find any information about what this button does.

[PeterC65]

1 hour ago, Martin Meredith said:

Hi Peter

Nice report, and good to hear about the visual comparison.

Were you doing much in the way of histogram adjustments? You ought to be able to see plenty of stars in a 1s exposure but only if the black point is appropriately set, and the image stretched. Alternatively, it may be that your overall focal ratio is quite slow for EEVA. 

The selection of objects you've chosen is rather challenging for EEVA techniques. Planets (apart from Uranus outwards) require a different approach to DSOs, and M45 and M31 need a large FOV to make an impression, so it perhaps isn't surprising that the visual views equal or better the camera views. If you were to look at planetary nebulae, globular clusters or (especially) galaxies/galaxy groups, you'd immediately notice that the EEVA view goes many many magnitudes deeper.

cheers

Martin

 

I'm aware that there is a histogram but I didn't knowingly do anything with it! I set the Black Level in AltairCapture to zero as that seemed to make the background dark. Not sure what you mean by image stretching. Can you point me at something that describes the process for getting a basic EEVA image setup right?

The refractor is F6 which I thought was about right for EEVA.

Hopefully next time I won't spend half the session faffing about with setup problems and will try some of the targets you suggest.

I've managed to fix the issue that was preventing me from using the SynScan App. It needs the hand controller set to PC Direct Mode (Stellarium does not) and the USB driver needs to be restarted after I've made the cable connections (a faff, but OK now that I understand what's needed). The PC Direct Mode condition does mean that I cannot use Stellarium and the SynScan App to control the mount together which is a pity.

 

[Martin Meredith]

The role of the black (and white) points, and stretching, is to map an image with say 12-16 bits of intensity levels to a display that is only capable of showing 8 bits of intensity levels. If you don't do anything, then by default you are doing a linear stretch, which will show up just the cores of the brightest stars. It is typically better to dedicate more of the available range to the lower intensities in the image, and devote fewer bits to the higher intensities. This will make an enormous difference to what you will see even in a 1s capture.

This is done in two steps. First, since there is no point wasting any bits in displaying stuff that is far below the background level, the black point should be set to just below the background level (not to zero). The second step is to specify the mapping of image intensities to displayed intensities which is usually done with a 'curves' type of manipulation. My experience with EEVA software is limited (as I run on a Mac), but most software will provide a way to produce such a mapping. If you're using Sharpcap, google AstroJedi unofficial Sharpcap manual.

Indeed, F6 should be OK for EEVA

BTW I am one of those that aligns using the camera 🙂 

Martin

 

[Mike JW]

I am using the NEXUS handset/software with my scope. I have no knowledge of Stellarium.

After doing the two star alignment objects are likely to be in the fov for a wide field eyepiece.  My set up allows me to then refine the accuracy of the pointing by syncing on  further stars.  Often I will choose the second alignment star in a constellation of interest for the session and the objects will be in the fov in that area. However if go off to a very different part of the sky the object may be on the edge of the fov or even outside it so by choosing a third star in the area my set up becomes more accurate for that area - essential with the narrow fov of the camera. This sounds like your Pointing Accuracy Enhancement. 

Mike

[PeterC65]

Since this frustrating first attempt I've done some more investigation into SharpCap and how to use it. I used AltairCapture for most of the first attempt, and while it seems to be reasonable software, there is much less help available for it online. There is lots of online help available for SharpCap including a great manual which I'm wading through. I now understand better how to use the histogram and live stacking, and I've been able to analyse the camera sensor which enables some of the more interesting features of SharpCap. Just need a clear sky now to try it on the stars!