First light RC8 - Horsehead & problems

[cybereye]

Hello!!

Friday night was the first time that I could get my new scope, the GSO RC8 aka "Machiavelli", out for its first light.

I purposely chose a target that I knew would test my imaging train and that target was the Horsehead Nebula and Alnitak. This has a wide dynamic range and would certainly tell me how the system was working, or so the theory goes! I've attached the first light image which was taken using a QHY8L with a Baader UHC-S filter. It consists of 27 x 5 minute subs with darks, flats and dark flats applied. The processing isn't optimum as I wanted to highlight some problems I've encountered.

There are two problems that I can see besides some secondary mirror collimation which needs to be done. Firstly there is a line that goes across the image that correlates with the position of Alnitak. I can only assume that the star is overpowering the sensor and this is manifesting itself along the line of pixels. Secondly there are some fairly strong airy disks evident around/near Alnitak. Does anybody have any idea what might be causing those? :help:

All in all I'm happy with my first light - I just need to sort out these teething problems!!

Any help/hints/advice greatly appreciated!!

Cheers,
Mario

PS I've also attached a picture of my setup in case it has a bearing on my image. Please note that the diagonal visible is NOT in my imaging train. It goes straight through...

[cybereye]

Good evening.

If the Horsehead was a bowler and I was a batsman, I would be its bunny!! This is the third year that I've tried to image it and I'm still having issues!! I've tried processing what I collected on Friday but I think I'll give up. I've attached my latest attempt at dragging some detail out of the data but the line that I mentioned previously is really bugging me and the data is quite noisy. As you can see I have managed to remove the airy disks - by cropping the image!!

In regards to the airy disks, are they likely to be caused by light bouncing/reflecting off my filter? Does anybody have any ideas to help?

Mario

[alpal]

I have idea as to what has caused that line.
Could it be processing artifacts from over shapening?
This picture is no where near as good as the other pics on your web page.
The horsehead is a terrible target to try & image except from a dark site.

A one shot colour camera will make it even harder as the
best pics of this always include Ha filter sub-frames taken with a mono.

better luck next time.

cheers
Allan

[Tandum]

Mario, the black line is most likely the A/D converter in the camera being overloaded. I'm not familiar with qhy8L drivers, but if there is a clamping function in there, flick it the other way to what it is now and try again.

[cybereye]

Allan, the line isn't caused by the processing however the processing I've done on this image to try and drag something out certainly hasn't helped! As I said in the first post I felt this would be a good target to test out my new setup. In hidsight however I think I should of gone for something easier and something I've imaged before so I could get a feel for the new scope. I guess there's always M42!!



Robin, thanks for the tip. I figured that the sensor was being overloaded but the A/D converter is a good place to look for a culprit. I'm not sure if EZCap has options to adjust the clamping as it's fairly basic software but I'll look in some of the menus.

Cheers,
Mario

[swannies1983]

Mario, this is rather perfect timing as I posted something a few days ago asking about reflections with my new RC8. I also imaged the Horse Head. See here (http://www.iceinspace.com.au/forum/showthread.php?t=100445). I was imaging with a dslr and also got the airy disks around/near Alnitak. They aren't as strong as yours because your contrast is much more than my image. It was suggested that it might have been from the LPS filter.

I have collected more data from when I took that image and am now up to 30x5mins. I started processing the image last night.

[cybereye]

Dan,

I knew I'd seen some mention of something like the problem I was having but for the life of me I couldn't remember where! And guess what, I attach my UHC-S filter to my camera using the same adapter that you use!!

In the business I'm in - seismic processing - we get secondary bounces of sound called multiples - these are sound signals that are either bouncing of the water bottom or within coal horizons. It makes sense that if the light is bouncing between the filter and the glass of the camera that the focal length will have changed and would then look like an out of focus star. However I'm not sure why it is offset from Alnitak rather than centred around it? :question:

Now if there was some way to tame these light multiples....

Cheers,
Mario

Edit: What about a light bounce off the front of the filter up to the secondary and then back down to the camera?

[swannies1983]

As suggested in my thread, maybe try imaging without the filter?



That all sounds reasonable with me.



Yeah, that is what I wondered too. You can also see heaps of little ones that go around Alnitak (~2cm away).




Simple...don't use the filters :rofl:

[cybereye]

Dan,

I've done some quick searching on the web and have found this website which talks about imaging the moon (http://www.nightsky.co/knowhow/photography.html). However the part that really interested me was point 7 which states:

7. When photographing a full, or near full (gibbous) Moon, the problem is one of abundance of light. Using filters to reduce light and enhance contrast can dramatically improve pictures. However, cheap filters (and sometimes expensive ones) can cause a double-image from Moon-light bouncing off the front of the lens, onto the inner side of the filter and back down the lens, so some experimentation is necessary. (Photographing the Moon off-centre will more easily show up these reflections.)

I'm going to retry (when I get some time!) imaging the Horsehead but try and keep Alnitak well and truly out of the frame, although I feel it pumps out so much light it probably will still have an influence.

Cheers,
Mario

[swannies1983]

Thanks for the link Mario. I came across something similar the other day but can't find it.

In my case, I'm wondering if a clip in LPS filter will reduce/eliminate the reflection?

[allan gould]

The more glass you have in your imaging train the more likely you are to get internal reflections. Especially if you use an LPS filter with a DSLR.
Light pollution shows up quickly with a DSLR but not a cooled CCD which is my recommendation.
Alnitak will show up every reflection in your system in spades.
Ive attached a recent image taken with a refractor, cooled CCD + FR, 5KM from BrisVegas and with heavy light pollution using 10 min subs. So it can be done its a matter of learning how each piece of your system works under certain conditions.

[Poita]

Sometimes tilting the problem filter can help too.

[allan gould]

I had a problem with reflections in my QHY8 camera but solved it by moving the IR filter which was causing the problem another 40mm away from the CCD chip. You could try this.

[LewisM]

I have had some very intriguing issues using a UHC /LP filter.

When I used it with my ED refractors, the only issue is blueish stars, but NICE high contrast. When I tried it with my fluorite refractor, I get WOEFUL, globular, pixelated messes of images - yet without, they are FINE. I have NO IDEA why, unless just the difference between ED and Fluorite glass????

Anyway, here's B33 I did with my beloved fluorite Vixen 102 refractor from light pollution central a little while ago - only 5 x 5 subs.

http://imageshack.us/f/441/horseheadnebula2.png/

Minimal processing - mainly to remove the dust mote "blobs" (they were on the DSLR sensor platen)

[Ross G]

Hi Mario.

Good luck with the RC8. The solution of your problems might also be mine.
Although I have not properly used my RC8 yet I have noticed that the guy I bought it off has stuck flocking inside the large extension tubes between the telescope and the focuser.
Maybe this was a source of reflections.

Ross.