Hey guys,
On the weekend, I took a stack of pictures at the IISAC using my Nikon D7000, through my B250 astro imager, which was mounted on my NEQ6.
One of my targets/goals was to grab the horsehead.. so, I did around 20 images@ iso 650 for 5m 30sec.
Unfortunately, to my disappointment, I have got home to find they are pretty well all useless. At the time I couldnt see the movement on the screen (and perhaps in my excitement didnt look hard enough for it anyway), but then I had another look, and I dont understand what Im looking at.
If you look at the top left of the image, it looks like there is a fair bit of movement there, same on the top right... but the movement is in a different direction.. again, same with each bottom corner.
I was wondering if anyone could advise what this could be... Im using a baader coma correcter (which I am still not sure is set to the right position), could this be coma? Flexure (is that even a word?) or does it look like movement or something else?
Hey Andrew
I wouldn't call that useless! You got NGC2024 and 2023, Alnitak looks lovely, you can see the horsey, and a bit of processing magic will bring out some detail. Certainly a lot better than some attempts I have seen so well done. I cannot offer any advice as to the elongated stars except to say they are only really noticeable in the top left and a little bottom left. Do a bit of processing and a judicious crop and you will have a not bad image there IMHO.
Hopefully an more expert imager will help you out but I would be happy with that result for starters.
Maybe "useless" is a strong word lol... I am impressed with what I got... but really disappointed in a "time spent getting to this point / end result" way.
Yes, there is some usable stuff... but before I spend this amount of time photographing anything else, Id really like to sort out that issue.
You need to stretch the data to see anything, this will bring out the horse-head . Ivo on here created Startools so he might post up a quick jpg that he processed, which are generally very good.
I'm not an expert imager, but am curious to understand the elongation.
looks like flexure, but could you post some details?
was each sub 5m30, did you use autoguiding, if so what guidescope/camera, did you use phd?
doesn't look like coma as that would be radial.
did you balance the scope, how was your polar alignment?
maybe someone else can ask you specifics more closely related to your elongation, but its good to cover everything else.
can you also post one sub which shows the most movement?
Some of the stars - especially the bottom right - look not too bad.
There will be others who know more about this than I do - but some ideas are:
1. I think that the most likely cause of this is that you camera is not sqaure to the image plane. If you are using an MPCC, these can be tricky to seat squarely in the focuser.
2. If it was flexure, I think all of your stars would be similar shapes
3. coma is elongated stars that all have their long axis pointing towards the middle of the image.
4. It may also be some field rotation if your polar alignment was off.
Looking at the image, I'm thinking Adam may be spot on with point #1 (camera is not square to the image plane). But I could be wrong...
Quote:
Originally Posted by A23649
You need to stretch the data to see anything, this will bring out the horse-head . Ivo on here created Startools so he might post up a quick jpg that he processed, which are generally very good.
Hehehe Always happy to do a repro or give tips to anyone who needs help - and it doesn't have to involve ST if you're using other software.
However in this case it sounds like an easily fixable hardware problem. It's always better to fix any problem at the acquisition stage, rather than post-processing. For those with limited hardware or imaging under less-than-ideal conditions there is a lot that can be fixed during post-processing though.
thanks for the replies people, it's great to get other peoples interpretation of a fault.
when you say "not square with the scope" I'm not sure if it was or not. I always push the camera as hard In as it will go (it's an slr not a ccd) so that all the adapters are flush with one another, but with the weight of the slr. it is possible that it moved. if it were that, each photo would have the same effect... to the same degree yes?
In regards to other questions asked in this thread, yes I'm guiding with phd, my polar alignment was excellent, and The scope was balanced with the weight ever so slightly on the west side of the scope.
hey andrew, the MPCC has a little ring around it, if its still there GET RID OF IT as it is the biggest useless piece of snot. I have come to realise that the MPCC is actually poorly designed. Works perfectly but the over all design isn't really for photography. I have actually contemplated putting the whole thing into the lathe and milling down the barrel of it so that it might sit in the focuser properly. But then again I will most likely move to a wynne 3" corrector to solve my issues and kill two birds with one stone in preperation for my next steps in astrophotography.
Thats my take on the situation and i echo what has been said that your camera isn't sitting flush with the focuser draw tube because the stars are focusing at a inclined plane. Are you also able to take some close up photos of your focusing unit?
I am not expert, but a simple way to test if it is not square would be take an image, then rotate the camera 180 degrees, take another shot. Then repeat with just rotating the MPCC? That would tell you which part of the train is causing the prob and also confirm the nature of the prob.
I'm probably wrong but that's my take on this!
visual inspection will tell you if its out as it is quite a lot in that image. just look at the gaps between the MPCC, camera and focuser shine a light things become apparent
Yeah, Im suspecting thats it, Ive never been happy about the way the MPCC fits into the focuser, Ill have a good look at t this week and check what youve suggested. It would also explain why as the night went on, and the angle got higher, the images got worse.
Ill check and report back.
Always happy to do a repro or give tips to anyone who needs help - and it doesn't have to involve ST if you're using other software.
