Imaging with an AZ-GTI

[Ags]

....or get a big hard drive and do lots of short subs 😀

My best effort so far (945 mm focal length, sub 1-second subs). Still a lot to learn but I think the approach has promise.

Edited December 4, 2020 by Ags

[JeremyS]

Super image @Ags!

[gaz81]

4 hours ago, vlaiv said:

I did not actually measured PE error precisely from this mount, but we can do some very basic assessment of how it behaves.

Here is animated gif that displays effects of tracking errors over a course of one hour (60 subs of 1 minute):

Ra is roughly aligned with X axis and Y is DEC (there is very small drift in DEC due to rough polar alignment - I just used finder scope and pointed it to Polaris - not actual polar scope and did not account for offset).

I counted 6 "returns" of the star over the course of one hour - that corresponds with my calculation that worm period should be 10 minutes / 600 seconds.

According to this page:

http://eq-mod.sourceforge.net/prerequisites.html

It has 144 RA teeth - and hence each tooth in worm is 24 * 60 / 144 = 1440 / 144 = 10 minutes.

Stepper resolution is given as 0.0625" - which I believe is error and should be 0.625" according to other numbers. About x3-x4 should be guide RMS if I compare that to my HEQ5 that guides at 0.5" RMS and has ~0.143" step.

Although, I've heard a claim that AzGTI does not use stepper motors but plain DC motors instead, coupled with encoders? Not sure (I did open my mount to fix backlash, but did not pay attention. There are 4 wires to each motor if that means anything).

As for magnitude of the error - it goes like this, I measured 13px p2p on x4 zoomed in image, that makes 3.25px p2p on original image. Original image is roughly 4.8µm pixel at 85mm FL, so 11.65"/px.

This means that p2p is roughly around 40" - not unexpected given that entry level Synta mounts like Eq3 and Eq5 (even odd Heq5) have similar p2p values (30-40" p2p).

From what I'm seeing - it should be ok to guide this mount at about, well, maybe not 1-1.5" RMS (because of stepper resolution) but 1.5-2.0" RMS certainly.

Yeah, mine guides at about 1.5 -2. 

I do a SharpCap polar alignment with mine. 

 

[Snooze]

3 hours ago, Ags said:

....or get a big hard drive and do lots of short subs 😀

My best effort so far (945 mm focal length, sub 1-second subs). Still a lot to learn but I think the approach has promise.

Very nice image! I see you have a C6 in your signature and I have been tempted to buy one to put on my AZ GTi. Do you use it with the mount and how does it perform?

[david_taurus83]

Mine worked well at 350mm (Starwave 70EDQR) but with my 6D the pixel scale was around 3.9" and guiding was pretty good at around 1.5" RMS. The dec on mine had a lot of backlash so dithering isn't recommended as it couldn't recover on time before the next exposure started so I lost subs that way. I stripped mine down when I got it (second hand) as it had a tight spot on the RA axis that you could feel if you turned it in your hand. Added grease where needed and it was sound after. There's no way to tune out the backlash on the Dec side as the gearbox has 3 small nylon gears with an horrendous amount of play between them. But that's me being picky on a cheap little goto mount thats not at all designed for AP!

[vlaiv]

1 hour ago, david_taurus83 said:

There's no way to tune out the backlash on the Dec side as the gearbox has 3 small nylon gears with an horrendous amount of play between them.

I actually managed to tune out backlash on mine, but on my version, gears are made out of metal, same as in this video:

Btw, here is whole youtube video on how to tune out backlash in this mount: https://www.youtube.com/watch?v=hgEzeXrhhEg

Good to know that this mount will guide at 1.5" RMS - I guess that is about as good as can be expected from it.

[david_taurus83]

9 minutes ago, vlaiv said:

I actually managed to tune out backlash on mine, but on my version, gears are made out of metal, same as in this video:

Btw, here is whole youtube video on how to tune out backlash in this mount: https://www.youtube.com/watch?v=hgEzeXrhhEg

Good to know that this mount will guide at 1.5" RMS - I guess that is about as good as can be expected from it.

No, not those! The actual gearbox that's connected to the motors output shaft. Theres 3 nylon reduction gears in there with about 3 AU of space between them!

 

[Ags]

2 hours ago, Snooze said:

Very nice image! I see you have a C6 in your signature and I have been tempted to buy one to put on my AZ GTi. Do you use it with the mount and how does it perform?

That was taken with my C6 and 6.3 focal reducer on the AZ-GTi. THe combination works well!

[vlaiv]

14 minutes ago, david_taurus83 said:

No, not those! The actual gearbox that's connected to the motors output shaft. Theres 3 nylon reduction gears in there with about 3 AU of space between them!

I was not aware there is actual gear box in there!

Luckily, mine does not seem to suffer much backlash in those (but in reality, I'll need to see how it's guiding as final word on that).

[bomberbaz]

7 hours ago, Ags said:

....or get a big hard drive and do lots of short subs 😀

My best effort so far (945 mm focal length, sub 1-second subs). Still a lot to learn but I think the approach has promise.

Agnes, what are you doing, lots of short FITS and stacking?

TIA

Steve

[bomberbaz]

These are my favourite results to date. 

I think moon has slightly got a focus issue but all done with a Wifi GTi mouint, 130P-DS and a ZWO ASI 224MC.

I haven't got a lot of data for any of them but happy so far and i think I can go quite a bit better.

M82

M57

M31

Edited December 4, 2020 by bomberbaz

[Ags]

2 hours ago, bomberbaz said:

Agnes, what are you doing, lots of short FITS and stacking?

TIA

Steve

For this one I shot a series of 1 minute SER files, then processed each in Autostakkert and stacked the results in DSS. More recently I have had similar results with collecting short FITS and stacking in DSS.

Edited December 4, 2020 by Ags

[bomberbaz]

29 minutes ago, Ags said:

For this one I shot a series of 1 minute SER files, then processed each in Autostakkert and stacked the results in DSS. More recently I have had similar results with collecting short FITS and stacking in DSS.

How short please, the images I posted up were 10 seconds each.  However there ere only 40, far too few i know but it was just a trial at that length.

[Ags]

The M13 image is 100 ms frames.

[fireballxl5]

A couple of guided shots using a focal length of around 610mm, approx 1.9"/pixel with my FS60CB+extender/Canon 40D combo back in May 2020.

PHD on the ASIair Pro usually reporting guiding error in the range 0.8-2arcsec. Guided using a 50mm finder, f=150mm with ASI224MC.

NGC6888 Crescent Nebula / Tak FS60CB @ f10 / Canon 40Dmod / AZ GTi / 16x180s

M92 / Tak FS60CB @ f10 / Canon 40Dmod / AZ GTi / 26x60s

[Snooze]

The Horsehead Nebula - A work in progress

About 25 x 3 mins unguided subs because my ASI120MM works 1/10 times with PHD2.

Canon 1200Da + 72ED Pro + CLS Filter

Will try to add more time if/when my gude cam decides to cooperate. I also bought a SVbony Halpha filter that I have to try out properly and the combine the two to create an HaRGB image