Re: large alignment error with polemaster & mach2


Andrea Lucchetti
 

Hi Peter,
sorry, I tend to write too quickly and my english doesn't really support me :-)
I will try to clarify:

Q:You don't have OTA ready but still get drift in your images? How can you get images if you don't have OTA ready?
A: yes, I friend borrowed me a C8, a Vixen R200, and I have a nikon  with a 300m f4. I always had trailed images in dec, field rotation if guiding.

The new OTA is under construction and I am documenting its building here: https://andrealucchetti.smugmug.com/Astrophotography
There is just a page on tube construction for now but I should publish the design page in a couple of days
It is "my project", it will be a 200mm f3,9 corrected newton, corrected over 52mm (carbon tube, zerodur mirrors, Big paracorr, ATLAS focuser)

Given the image scale and the typical sky condition here (over 2 arcsec FWHM),  I hope I will be able to avoid guiding without the model.
I know it depends on several factors, mount, ota, etc.
From what I see, in RA I can already get perfect stars in 8-10 min. I said 10 mins to be on the safe side, but probably I could decide for 300s subframes working at f.3.9.
10 minutes is what I used for the 16803 with TEC140, which is f7.

Modeling is something I could do during winter or when I go for two consecutive days, during summer the night is unfortunately too short.
Let's see what I can do, I am ready to guide (MAch2 guides very easily in my opinion)if needed.
In any case I need to eliminate field rotation due to polar misalignment.

Thank you,
Andrea


Il giorno sab 1 ago 2020 alle ore 22:24 Peter Nagy <topboxman@...> ha scritto:
On Sat, Aug 1, 2020 at 05:51 AM, Andrea Lucchetti wrote:
Hello,
I need to polar align my Mach 2 very quickly to save time on field.
I thought Polemaster would have been a good choice but I cant get a good alignment with it (I am ways off)
The procedure goes very well, till the end, including the precise alignment step, but I have drift in my images.
running the Polemaster twice results in a small change.


I am not using the refraction calculation , as I leave at 42 deg latitude: can this be one of the reason?

my aim is to shoot 10 min subs unguided (@790mm focal and 1,6 arcsec/pixel resolution).

I still don't have my OTA ready so it is difficult for me to check with the drift method for the time being ( I can borrow a dslr and C8)

Would the RAPAS be a better solution for my needs? 
I understand it can be mounted on the MACH2 using a dovetail, with repeatable accuracy.
Is the accuracy enough for imaging and how it compares to Polemaster?

Thank you,
Andrea
Andrea,

Your original post message is a little confusing.

First you said:

"The procedure goes very well, till the end, including the precise alignment step, but I have drift in my images."

then you said:

"my aim is to shoot 10 min subs unguided (@790mm focal and 1,6 arcsec/pixel resolution).

I still don't have my OTA ready so it is difficult for me to check with the drift method for the time being ( I can borrow a dslr and C8)"

You don't have OTA ready but still get drift in your images? How can you get images if you don't have OTA ready?

What scope were you using that's giving you drift and are you trying to image unguided? Also you said you are aiming for unguided imaging at 790mm focal length which can be very hard to do assuming you are not using pointing model with APCC-Pro. Are you using pointing model yet? If not, I would not expect absolute encoder alone to get pinpoint stars without the help of pointing model even with perfect polar alignment due to many external variables like refraction in the sky, flexure, etc.

So, if you polar align using PoleMaster and its software and use guiding, then I would expect excellent images. Like others said, I would prefer Sharp Cap Pro as well as it's not only accurate but super easy to use. If you already have PoleMaster, then you may not need RAPAS because PoleMaster with Sharp Cap Pro is really good and quick.

Can you clarify your original message a bit more?

Peter

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