M94 Croc's Eye Galaxy - LRGB stacks added to first post if anyone wants to try.

[Xplode]

Next time you are out imaging i suggest you take som shorter images, it would help find the frequency of the oscillations.
What you need is a satellite trail that starts and stops within your FOV, counting the oscillations would make it possible to calculate the frequency.

[wimvb]

Here's a quick combination of the pre-flip and post-flip images. The more vertical satellite trail is pre-flip, the more diagonal is post-flip. It seems to me that the wiggle is slower pre-flip but also a little stronger. The guide log will probably tell us more. Maybe also the frequency of the vibration. That's it for me for the night. I'm off to bed.

[wimvb]

Ok, a last quick one: I briefly inspected the R, G, and B masters and it looks like the red master has the tightest stars, followed by green and last blue, which has the fuzziest stars (small stars). Do you refocus between filters? With the ED80 you probably have to do that.

Now I'm really off to bed.

[tooth_dr]

1 minute ago, wimvb said:

Ok, a last quick one: I briefly inspected the R, G, and B masters and it looks like the red master has the tightest stars, followed by green and last blue, which has the fuzziest stars (small stars). Do you refocus between filters? With the ED80 you probably have to do that.

Now I'm really off to bed.

No I didn’t refocus, I don’t have an focuser capable of this.  I went for a compromise (please don’t shoot me)

[tooth_dr]

12 minutes ago, Xplode said:

Next time you are out imaging i suggest you take som shorter images, it would help find the frequency of the oscillations.
What you need is a satellite trail that starts and stops within your FOV, counting the oscillations would make it possible to calculate the frequency.

Makes sense. I have a lot of short exposures I took one night. I’ll trawl through them tomorrow and see if I can find one suitable. What do you think is happening here?

[Xplode]

2 minutes ago, tooth_dr said:

Makes sense. I have a lot of short exposures I took one night. I’ll trawl through them tomorrow and see if I can find one suitable. What do you think is happening here?

It's hard to say since it's so regular.
It's either something creating vibration or it's the mounts RA motor tracking with a varying speed.

Maybe post some images of your setup too

[tooth_dr]

10 minutes ago, Xplode said:

It's hard to say since it's so regular.
It's either something creating vibration or it's the mounts RA motor tracking with a varying speed.

Maybe post some images of your setup too

Its a mesu mount with a 10” reflector and an ED80.

 

[wimvb]

5 hours ago, tooth_dr said:

Its a mesu mount with a 10” reflector and an ED80.

 

I see you have motorfocus on your telescope, albeit a simple one. SGPro allows focuser offsets for various filters. If you don't switch filters too often during one session, you should be able to use that feature.

5 hours ago, Xplode said:

What you need is a satellite trail that starts and stops within your FOV, counting the oscillations would make it possible to calculate the frequency.

Those exposures may become very short, depending on the satellite. How fast does a (non geo-stationary) satellite travel across the sky? The fov of a 10" may be too small. Anyway, a guide log should also provide information.

[tooth_dr]

2 hours ago, wimvb said:

see you have motorfocus on your telescope, albeit a simple one. SGPro allows focuser offsets for various filters. If you don't switch filters too often during one session, you should be able to use that feature.

Thanks Wim. I also bought the hitec astro motor focuser controller but never set it up.  That would be a great idea, just to have offsets set up. 

[wimvb]

These simple, geared dc motors have lots of backlash, so you can't go back and forth between filters too much. And to be honest, if the hitec device also works with steppers, you might want to upgrade the motor at some point.

Edit: just found out that it's a dc motor controller

Edited April 30, 2020 by wimvb

[tooth_dr]

6 minutes ago, wimvb said:

These simple, geared dc motors have lots of backlash, so you can't go back and forth between filters too much. And to be honest, if the hitec device also works with steppers, you might want to upgrade the motor at some point. 

Thanks Wim, coming into the summer now I have time to improve my set up.

 

I've attached the guide and debug logs for each image.  I have included the object name in the file name, and I have also added what row within the log viewer that applies to that image.

 

I appreciate any help on this @wimvb @Xplode

 

 

 

M64_PHD2_DebugLog_2020-04-13_211832.txt M64_ROW8_PHD2_GuideLog_2020-04-13_211832.txt M94_PHD2_DebugLog_2020-04-14_192804.txt M94_ROW6+7+19_PHD2_GuideLog_2020-04-14_192804.txt M101_PHD2_DebugLog_2020-04-20_214745.txt M101_ROW4_PHD2_GuideLog_2020-04-20_214745.txt M106_PHD2_DebugLog_2020-04-19_220232.txt M106_ROW2_PHD2_GuideLog_2020-04-19_220232.txt NGC3344_PHD2_DebugLog_2020-04-21_224217.txt NGC3344_ROW4_PHD2_GuideLog_2020-04-21_224217.txt NGC4565_PHD2_DebugLog_2020-04-16_221746.txt NGC4565_ROW3_PHD2_GuideLog_2020-04-16_221746.txt

[Xplode]

Taking a peek at one of the guidelogs i can see some oscillation in there too.
Sometimes it seems to overcorrect so i would like you to set the RA aggressivenes to 75% of the current value.

I also think you should change to a longer guiding exposure, looking at the unguided graph during the guiding assistant i can see there is a lot of jumping up and down which is an effect from bad seeing either high up, but more likely local.
You might want to think a little about the thermals for your observatory and scope, it's incredibly important the both reach the same temp as ambient, an observatory should have some flow off air and the same would be great for the newtonian.

[tooth_dr]

5 minutes ago, Xplode said:

 

Taking a peek at one of the guidelogs i can see some oscillation in there too.
Sometimes it seems to overcorrect so i would like you to set the RA aggressivenes to 75% of the current value.

 

Thanks. I will try 75%. 
 

 

7 minutes ago, Xplode said:

I also think you should change to a longer guiding exposure, looking at the unguided graph during the guiding assistant i can see there is a lot of jumping up and down which is an effect from bad seeing either high up, but more likely local.

I used PHD2 GA and it nearly always recommends between 1.5 and 3.5s exposures.

 

8 minutes ago, Xplode said:

You might want to think a little about the thermals for your observatory and scope, it's incredibly important the both reach the same temp as ambient, an observatory should have some flow off air and the same would be great for the newtonian.

I’m not sure how much more flow I could achieve with an open roof? Could you offer suggestions?

With regards to the scope - I have a fan fitted.  Do you think at midnight with the scope being open, thermals are still relevant?

These are all things i have never considered in depth so I really appreciate the input.

 

 

[Laurin Dave]

Nice image Adam..  and good data..  maybe they are just spinning satellites ?  the guide RMS is c 0.5-0.8" your image scale is 0.9, the subs are 300 seconds and there are c 40 oscillations on a frame ie one every 7.5 seconds.. so every two guide exposures..  

Dave

[Xplode]

Even with an open roof there will most likely be stagnant air in the observatory, especially for smaller observatories
An open door in the observatory would help, but even better a fan, i suggest a fan sucking the air out of the observatory. A simple floor fan would be great for testing if you'd like to try.

Do you have heaters on any of your mirrors? I've seen heaters with too high wattage totally ruin guiding/imaging. I recently helped a guy that had a heater on his guider finder and he instantly got better guiding by turning it off.
The fan you have on the newtonian could in fact be the cause for the oscillations, might be a bad fan? Try turning it off.
I usually recommend very good quality fans like noctua, it's also best to mount them with some kind of rubber mounting

I believe the guiding assistant gives you exposure values based on the polar alignement/drift rate, i suggest you at least try longer exposure to see how it affects the guidegraph.

[wimvb]

54 minutes ago, Laurin Dave said:

maybe they are just spinning satellites

I thought of that, but that would only result in intensity variations. The wiggle you see, would be miles of amplitude for the satellite. 

[Xplode]

2 minutes ago, wimvb said:

I thought of that, but that would only result in intensity variations. The wiggle you see, would be miles of amplitude for the satellite. 

I agree, here's an example of a rotating satellite.

[tooth_dr]

1 hour ago, Xplode said:

Even with an open roof there will most likely be stagnant air in the observatory, especially for smaller observatories
An open door in the observatory would help, but even better a fan, i suggest a fan sucking the air out of the observatory. A simple floor fan would be great for testing if you'd like to try.

Do you have heaters on any of your mirrors? I've seen heaters with too high wattage totally ruin guiding/imaging. I recently helped a guy that had a heater on his guider finder and he instantly got better guiding by turning it off.
The fan you have on the newtonian could in fact be the cause for the oscillations, might be a bad fan? Try turning it off.
I usually recommend very good quality fans like noctua, it's also best to mount them with some kind of rubber mounting

I believe the guiding assistant gives you exposure values based on the polar alignement/drift rate, i suggest you at least try longer exposure to see how it affects the guidegraph.

I have a through-flow of air via open door, its open throughout the day when roof was open.  I dont have any heaters on the mirrors.  The fan isnt on when imaging, I've tested that, it does cause movement if on.  In fact I havent used it much.  It doesnt feel like this is a local issue with respect to thermals.  It's a good consideration, but it's not like I'm opening the roof after a baking hot day and imaging immediately.  I'm seeing these oscillations at 4am in the morning, in fact I'm seeing them all the time, so that to me points to a mechical issue.

GA I thought gave you information based on seeing, so it gives you the best guiding exposure time for that evening, as well as min movement values.

Thanks for the input, and it is useful to explore all possibilities.

Edited April 30, 2020 by tooth_dr

[tooth_dr]

1 hour ago, Laurin Dave said:

Nice image Adam..  and good data..  maybe they are just spinning satellites ?  the guide RMS is c 0.5-0.8" your image scale is 0.9, the subs are 300 seconds and there are c 40 oscillations on a frame ie one every 7.5 seconds.. so every two guide exposures..  

Dave

Thanks Dave, that was well worked out!  What does this frequency tell me?

[tooth_dr]

Does this help any?

Two frames taken on dual rig of M101.

10" 300s 1200mm

ED80 600s 522mm

I can see a larger oscillation that is visible in both, and a smaller oscillation within that larger oscillation in the 10" scope.  This implies mechanical rather than thermal as its affecting both scopes equally?  The 10" and ED80 cameras are not lined up, the angle is close to 90 degrees difference.  I can see the elongation of stars in the two mages is at 90 degrees to each other.  I do get drift in my ED80 (not guided), which I assume is differential flexure (to be dealt with another time).

 

*EDIT I'm not sure these were taken at an identical time, as I cant see two of the trails in Lum that are present in the blue channel.  But the main bright trail lines up pretty well.

 

 

 

 

 

Edited April 30, 2020 by tooth_dr

[Laurin Dave]

41 minutes ago, tooth_dr said:

Thanks Dave, that was well worked out!  What does this frequency tell me?

After reading Xplode and Wims  views on a spinning satellite (which I accept) I have no idea!! …..  strange how such a good guide trace can result in a line that wobbles by couple of pixels..  although two other thoughts have just occurred to me..  (happy to be debunked)  1.  it is simply an artefact caused by the fact that the satellite is moving diagonally through the frame and therefore progressing along the pixels in a staircase fashion.    2.. the imaging camera fan is vibrating,  although as it appears on both imaging cameras this is perhaps unlikely

Also I saw this the other night on a particularly bright trail on one of my subs.. other subs taken within an hour or so with "dim" satellites didn't show the effect...  close inspection make me favour idea 1. above..     I think that  I'd expect the frequency to be a function of the satellites angle through the frame being at a max at 45deg... which having just looked back at your image I think you can see … you could test this by looking at contemporaneous images from both cameras if they aren't orthogonal (which for M94 I don't think they were)..  inspection would show the same satellite trail but with it wobbling at different frequencies

Edited April 30, 2020 by Laurin Dave

[tooth_dr]

5 minutes ago, Laurin Dave said:

After reading Xplode and Wims  views on a spinning satellite (which I accept)  …..  strange how such a good guide trace can result in a line that wobbles by couple of pixels..  although two other thoughts have just occurred to me..  (happy to be debunked)  1.  it is simply an artefact caused by the fact that the satellite is moving diagonally through the frame and therefore progressing along the pixels in a staircase fashion.    2.. the imaging camera fan is vibrating, the fan?  although as it appears on both imaging cameras this is perhaps unlikely

Also I saw this the other night on a particularly bright trail on one of my subs.. other subs taken within an hour or so with "dim" satellites didn't show the effect...  close inspection make me favour idea 1. above..     I think that  I'd expect the frequency to be a function of the satellites angle though the frame being at a max at 45deg... which having just looked back at your image I think you can see 

Thanks Dave.  It could be the imaging camera fan.  The QHY9 camera is particularly smooth, but the Atik is noisier.  The Atik is on the ED80, and the QHY9 on the 10".  It was clear I could try turning off the Atik, and image only with the QHY9, and then just hope I capture a satellite

[wimvb]

4 hours ago, Laurin Dave said:

Nice image Adam..  and good data..  maybe they are just spinning satellites ?  the guide RMS is c 0.5-0.8" your image scale is 0.9, the subs are 300 seconds and there are c 40 oscillations on a frame ie one every 7.5 seconds.. so every two guide exposures..  

Dave

Unfortunately, we can't see that from the image. The satellite could have shot through that frame in a fraction of a second. That's why you'd need a short exposure, where, for example, when you start the exposure, the satellite is inside the frame already, and it still is when you end the exposure.

[Laurin Dave]

2 hours ago, wimvb said:

Unfortunately, we can't see that from the image. The satellite could have shot through that frame in a fraction of a second. That's why you'd need a short exposure, where, for example, when you start the exposure, the satellite is inside the frame already, and it still is when you end the exposure.

Of course!    edit.. but doesn't it put a lower bound on the oscillation frequency?

Edited April 30, 2020 by Laurin Dave

[wimvb]

6 hours ago, Laurin Dave said:

Of course!    edit.. but doesn't it put a lower bound on the oscillation frequency?

Yes it does.