M31 - another step on the learning curve...

[Aramcheck]

1st light with our 130dps & my 4th attempt at getting an image with DLSR. Learnt a few lessons on this outing including the need to re-check focus if rotating camera to frame the target & to pay more attention to centering the object in the first place... Also, haven't yet sorted out taking Flats but wanted to take advantage of last Sunday's clear skies and the position of M31 whilst it's still visible from our back garden. Took 52 x 90 sec lights (ISO 800) + 50 darks + 50 bias, but stacking in DSS & Pixinsight proved fruitless. Using Pixinsight's manual Dynamic Alignment I could see that 1 x image was ruined by aircraft landing lights & another 20 by high mist (or dewing up of secondary?). Stars were also a little out of focus & I clipped M31 a bit... Took some time to process in Pixinsight, but fairly happy with result!
 

[rickwayne]

Both companions, dust lanes, yep you're getting there. Concur about the focus. What sort of mount were you using? Stars are a bit egg-shaped, axis about 20° from vertical in this image.

Which, now that I check, is about aligned with the RA axis, I think.

Heartily recommend a Bahtinov mask for focusing. MUCH more precise than doing it by eye for most folk.

Edited December 6, 2019 by rickwayne

[Aramcheck]

On 06/12/2019 at 02:10, rickwayne said:

What sort of mount were you using?

Thanks Rick. It's an AZ-EQ6 GT Pro mount, which I'm still getting used to. I did a 1-star align on Mirach but probably should have paid more attention to that. (There's an advanced polar alignment procedure in the Synscan manual that I've yet to attempt).

Focus was with a Bahtinov mask, but as Mirach was too faint for the camera live view, I had to take 10 sec shots at ISO 6400 & then make blind adjustments + repeat until it looked ok. The lesson here is that I would have been better off focusing on a brighter star so I could use the live camera view + also using using the camera zoom to get a larger image of the diffraction pattern. (Another mistake was deleting these image files, so I could have re-checked them later!)

I suspect that I probably disturbed the focus, when rotating the camera to re-orientate M31 in the frame, so should have rechecked focus afterwards.

Looking at the 1st & last picture I took (about 1hr 25min apart) the total drift was about 1% of the captured image size, which suggests to me that the tracking wasn't too bad? However looking at Pixinsight's Sub frame selector measurements on my subs on the other two images I've taken over the last couple of months, I've clearly got a way to go on getting better star shapes.

Thanks for your help!

Ivor

[wimvb]

3 hours ago, Aramcheck said:

It's an AZ-EQ6 GT Pro mount, which I'm still getting used to. I did a 1-star align on Mirach but probably should have paid more attention to that. (There's an advanced polar alignment procedure in the Synscan manual that I've yet to attempt).

Very nice catch! 

To get better polar alignment:

If you can see polaris, put it roughly correct in your polar scope. 

Do a 2-star goto alignment, preferably with a high power eyepiece (for my 150pds I used a 10 mm eyepiece with home made reticle). This will give you polar misalignment. 

Do a synscan polar alignment. When the scope slews away from the alignment star, follow it in the eyepiece, so you know in which direction to adjust. 

Then repeat goto and polar alignment.

With a bit of practice, this routine shouldn't take more than 15 - 20 minutes to complete. 

[rickwayne]

Since optical quality really isn't an issue -- at all -- a dirt-cheap reticle eyepiece like the SVBONY is well worth the whacking great $35 for a multi-star alignment. That also allows you to do a quick DEC drift check if you're so inclined (and don't want to do the camera-enabled version).

[Aramcheck]

I had another go at processing... having got a copy of the excellent "Inside Pixinsight" book... (Probably about the 6th iteration, but I guess that's what cloudy nights are for...)

On 09/12/2019 at 04:09, rickwayne said:

Since optical quality really isn't an issue -- at all -- a dirt-cheap reticle eyepiece like the SVBONY is well worth the whacking great $35 for a multi-star alignment. That also allows you to do a quick DEC drift check if you're so inclined (and don't want to do the camera-enabled version).

I'm finding that balancing the OTA is very fine-tuned, so opted to balance with the DLSR in req. position rather than align first with my reticle eyepiece. I should have just paid more attention to the focusing after rotating the camera.

A lot to learn still, just wish we had more clear nights to try...