Pinwheel Galaxy with GPCAM, Anyone know what this streak is?

[cuivenion]

I was testing out the Vixen GP on Tuesday night and decided to try for the pinwheel. This is taken with the Altair GPCAM V1 colour with a Skywatcher 130p using AstroEQ for goto and tracking:

42 x 1 minute lights

100 x Bias frames

I used the bias as dark frames because my actual dark frames just seemed to add noise. The flats I took don't seem to work well either. I was hoping that the mounts periodic error would provide a kind of natural dither and used Kappa Sigma Clipping. It's worked better than the darks.

It was stacked in DSS and processed in gimp. If anyone know what the streak is let me know. It was in every light I took so I'm a bit baffled.

[UKJay1971]

Probably a satellite 

 

[UKJay1971]

Oh - didn't read it was in every shot. A smear on a lens then?

[cuivenion]

Could be, it didn't show up on the flats though, or some EAA shots I'd done earlier either.

[Cozzy]

Could it be internal light reflection? (if it's not on your flats)

 

Tim

[cuivenion]

6 minutes ago, Cozzy said:

Could it be internal light reflection? (if it's not on your flats)

 

Tim

Would that be in the same place in all the light frames? I wasn't using any filters and my dew shield is flocked. Could it be dew build up on the sensor?

[gonzostar]

Washing line. I have done that before  

[cuivenion]

1 minute ago, gonzostar said:

Washing line. I have done that before  

Nah, M101 was very high at the time and the scope was pointing straight up. There's no line in our garden at the moment. Nice try though.

[ecuador]

Interesting. What I am noticing is that it is parallel to the pattern noise that you have due to the drift caused by imperfect polar alignment. The "natural dither" you mention is not that good, as while it removes some issues it introduces this common pattern noise, so a suggestion is that every 2-3 shots you manually move the aim by a bit in a different direction every time to simulate a dither pattern, which will remove this noise. I wouldn't think it will remove the line you are asking about (so is it in every frame? same position?), but it will help with the noise

[cuivenion]

4 minutes ago, ecuador said:

Interesting. What I am noticing is that it is parallel to the pattern noise that you have due to the drift caused by imperfect polar alignment. The "natural dither" you mention is not that good, as while it removes some issues it introduces this common pattern noise, so a suggestion is that every 2-3 shots you manually move the aim by a bit in a different direction every time to simulate a dither pattern, which will remove this noise. I wouldn't think it will remove the line you are asking about (so is it in every frame? same position?), but it will help with the noise

Hi you don't have a link where I could read up on this common pattern noise do you? I still think it was periodic error as the image movement is side to side. Wouldn't PA drift be in one direction? It was definitely in every frame.

[cuivenion]

Here's a quick gif showing the movement.

[cuivenion]

Just had an idea, could it be a contrail?

[ollypenrice]

PE will not produce useful natural dither. Polar misalignment will do so though.

Like Ecuador I'm struck by the fact that the strong line is parallel with the general streaking. While this could be a concidence I'd be surprized if it were!

It is very important to know, when trouble shooting, the exact orientation of the camera relative to RA and Dec. I would strongly advise anyone to set their camera orthogonal to RA and Dec. It's quick and easy: take a short sub while slewing slowly. the angle of the star trails shows the angle of the camera.

Olly

[cuivenion]

57 minutes ago, ollypenrice said:

PE will not produce useful natural dither. Polar misalignment will do so though.

Like Ecuador I'm struck by the fact that the strong line is parallel with the general streaking. While this could be a concidence I'd be surprized if it were!

It is very important to know, when trouble shooting, the exact orientation of the camera relative to RA and Dec. I would strongly advise anyone to set their camera orthogonal to RA and Dec. It's quick and easy: take a short sub while slewing slowly. the angle of the star trails shows the angle of the camera.

Olly

Hi, the camera orientation was north = up, south = down, west = left and east = right. A quick question, from the gif does it look like an acceptable amount of PE for unguided Vixen GP? I'm still a layman on these things.

[ollypenrice]

10 hours ago, cuivenion said:

Hi, the camera orientation was north = up, south = down, west = left and east = right. A quick question, from the gif does it look like an acceptable amount of PE for unguided Vixen GP? I'm still a layman on these things.

I've never tried to image unguided so I don't know what's to be expected. However, the star movements are not all in one axis so perhaps you have some Dec backlash which it might be possible to tune out mechanically.

Olly

[cuivenion]

44 minutes ago, ollypenrice said:

I've never tried to image unguided so I don't know what's to be expected. However, the star movements are not all in one axis so perhaps you have some Dec backlash which it might be possible to tune out mechanically.

Olly

Hi, I thought the dec axis didn't move during RA only tracking, could it be wind or vibration?

[Shibby]

12 hours ago, cuivenion said:

 

I suspect some sort of internal reflection is going on - there appears to be a glow to the right-hand side of your raw frames. Was there a streetlight or security light nearby?

Quote

from the gif does it look like an acceptable amount of PE for unguided Vixen GP? I'm still a layman on these things.

Is it the new or old-style GP?

[cuivenion]

This is the one I'm using. There is plenty of light pollution, but I'm using a flocked dew shield and the scope was pointed straight up. I'm no expert though.

[Shibby]

I have the same mount. As long as you are well balanced in both axes, with a small weight bias on the rising RA side, and well aligned, the GP is one of the best there has ever been. I once spent a whole night imaging 10 min subs unguided! That was a one-off to be fair, but I regularly used to manage 5 min subs at 750mm focal length without too many rejects.

[cuivenion]

7 minutes ago, Shibby said:

I have the same mount. As long as you are well balanced in both axes, with a small weight bias on the rising RA side, and well aligned, the GP is one of the best there has ever been. I once spent a whole night imaging 10 min subs unguided! That was a one-off to be fair, but I regularly used to manage 5 min subs at 750mm focal length without too many rejects.

What focal length/resolution? I'm struggling to get one minute!

[Shibby]

FL 750mm, 5.2µm pixels.

Most of your subs look ok to me, the sudden movement between them looks like it may be backlash.

[cuivenion]

3 minutes ago, Shibby said:

FL 750mm, 5.2µm pixels.

Most of your subs look ok to me, the sudden movement between them looks like it may be backlash.

Maybe I'm being to picky, still though my subs are at 1 minute, not 5 or 10. I'll have to remember to bias the weight to the east next time I'm imaging.

[ecuador]

On 3/2/2017 at 15:01, cuivenion said:

Hi you don't have a link where I could read up on this common pattern noise do you? I still think it was periodic error as the image movement is side to side. Wouldn't PA drift be in one direction? It was definitely in every frame.

Hmm, I don't have a link, but anyone trying either unguided which has a little "natural" drift, or dithering in a single direction often comes across it. And my first unguided images were coming out exactly like that as well and, interestingly, worse PA would also fix it (but then the subframes were worse).

[cuivenion]

23 hours ago, ecuador said:

Hmm, I don't have a link, but anyone trying either unguided which has a little "natural" drift, or dithering in a single direction often comes across it. And my first unguided images were coming out exactly like that as well and, interestingly, worse PA would also fix it (but then the subframes were worse).

I think I understand a bit better now thanks for the link.

[ollypenrice]

On 03/03/2017 at 11:33, cuivenion said:

Hi, I thought the dec axis didn't move during RA only tracking, could it be wind or vibration?

People using very well polar aligned mounts still autoguide in Dec. Sure, theory says that the Dec axis doesn't do anything under perfect PA but ths is not borne out by experience! A bit of backlash is all it takes. Or wind, or vibration, yes.

You just need to work out the degree of precision needed to keep your tracking error to about half a pixel (where it needs to be) to see why we use autoguiders. This is not a 'norma'l degree of engineering precision. We want the impossible!

Olly