Another go at 47 Tuc

[sharptrack2 (Kevin)]

Hi Guys,

Tried again the next night after another mount alignment. Drift alignment has me baffled just a little, so there's still a bit of star trailing.

Would appreciate some post processing suggestions, using just DSS. This image is done in PhotoDirector (I can't justify the subscription to PS just yet ). Please ignore the chromatic fringing, I'm just looking to get the basics down pat then I'll be looking for a better scope.

40 60 sec subs
20 dark subs
ISO 800
Nikon D7200
90 x 500mm refractor (F5.5)
HEQ5 Pro

All comments welcome.

[raymo]

Kev, I suggest that you get the basics right first, and then fix problems one by one. Your focus is a mile out, what method are you using? If you blow up your image 400% you will see that the bright stars are two parallel streaks which
is strange!!!!!!! alignment problem in DSS maybe. Don't bother with stacking lots of images, or darks, flats, etc until you have the basic image acquisition process working reliably.No good looking at processing until you have images worth the time processing them.
For focusing, focus on a bright object using whatever method you like,
lock the focuser, recheck the focus, and slew to your target.
For alignment, google the DARV method, by far the easiest to learn, and after a couple of times will get you aligned in 10-20 mins, depending upon how far out you were at the beginning. When you achieve your first really
accurate alignment, mark the positions of the tripod feet, to make it quicker in the future.
raymo

[sharptrack2 (Kevin)]

Thanks Raymo,

I am starting to think the cheap telescope is really a detriment instead of a tool to learn. I noted the doubled stars as well and cannot find a reason for them. I don't think it is focus related. That artefact didn't show up in the first set of images, but it was a different camera. The double star affect hasn't shown up in images I took last night of M42 but again a different camera (could be a trend developing).

Getting all of this worked out is my objective, hence the posting of mistakes. I certainly can look at it and say it's not right, but I don't know what or why... yet!

Focus is still very manual, live view, zoomed in as far as the camera can go and focusing as tight of a spot as possible. Has been a bit tricky with the only visible stars fading in and out a fair bit. Working on a Bahtinov mask to improve accuracy. I've not invested anything yet into laptop monitoring and such, so knowing some yoga positions has been a definite advantage (Backyard EOS and Backyard NIKON are both on the wishlist).

Not to hijack my own thread, but the one obstacle I'm encountering with polar aligning with DARV (Peter Kennett's version), is the precise alignment of the reticle for each adjustment. What isn't specified is what the viewer's orientation to the scope is. I do have a rudimentary understanding what is being done and can sort of rationalise what should happen, but I find that setting the reticle to be something I just cannot get past. Fortunately tonight should be clear again so I will be out fussing with it. Based on my images of M42 (that I haven't processed yet) I'm very close.

I do have my mount position standardised and quite accurate as far as pointing South and latitude setting. The 2 star alignment error is never reported more than 1 arc minute out in either plane. I usually go through a couple of adjustment rounds to get it down to less than 10 arc seconds. Is this still not close enough?

Back to slicing and dicing my mask(s)...

[raymo]

If the artefact doesn't show up again, forget it, might be a one off.
I suggest Robert Vice's version of DARV; it is usually the first version on
the list when you google it. You don't need reticle eyepieces or anything
else, just your scope and your DSLR with Live View. I don't use my computer,
just a shutter release cable, and time the exposures with my watch. When doing the exposures you can save time by starting out on each axis with shorter ones than the recommended, because if your alignment is well out even a short [30 secs] exposure will show it. Make the exposures longer as
you get nearer to your goal to improve accuracy, as obviously if the alignment is almost good enough, the error will need longer to reveal itself.
There are a couple of people here on IIS who will make you a Bahtinov
mask with their 3D printers, definitely better than Live View.
raymo

[sharptrack2 (Kevin)]

Thanks Raymo,

Realising that I had confused the more elaborate method of drift alignment, I dug out Robert's version from my notes (I think i have every version ever put out there in my notebook). Now that I have the mechanics to use a camera I'll give this a go... if I can find a suitable star to track according to the procedure.

I've managed to fabricate something that will get me through for a little while, but I was thinking the same thing, getting a mask printed up from someone here on IIS.

Time to get moving if I'm to be ready for M42 and M45 later tonight.