Gradual bloat/halo

[david_taurus83]

What'ds going on with the bright star below M51 in my Luminance subs? There appears to be a gradual bloat or halo creeping in? The earlier subs from 10pm don't have it but as M51 gets near the zenith after 1am that star seems to start glowing a bright halo? It doesn't appear to affect the brighter stars on the left? I've looked at my binned RGB data and it's not as bright but it does start to creep in later in the night again on the blue. Is it dew on the scope though I run a dew heater 100% all the time? Atmospheric conditions? (Star shapes are poor as I've incorrectly set up my tilt adapter a few weeks ago)

[michael8554]

Could you post jpeg of first and last sub ?

Michael

[david_taurus83]

Yes, here's a timeline.

10pm

 

11pm

 

12am

 

1am

 

And the last sub at 1.45am

 

[michael8554]

Beats me David.

All I can say is that the "eyedropper" reading of the star is 188 on the first image and 202 on the last.

But the core of the galaxy shows a similar increase in brightness without any obvious flare.

Michael

[david_taurus83]

I'm stumped as well! The other filters were shot on different nights and the blue shows a similar increase but not as obvious unless you look for it. I've looked at some early shots on the Pleiades when I first got the camera and filters and they don't show any obvious halos. I just don't get why that one star shows it so obviously buy the ones on the left don't as they are equally as bright at mag 7. Could it be the horrendous tilt I've got? 🤔

[ollypenrice]

Thoughts:

- Are you refocusing regularly?

- As you approach the zenith the full weight of the camera/FW is hanging on whatever is locking your drawtube at its present extension. If it's going to slip, the zenith is the place where it will do so.

- As you approach the zenith the atmosphere's tendency to induce blue bloat is at its lowest so your problem is contrary to that.

- In thinking about this, don't forget that luminance passes blue, so bloat in L and bloat in B can have precisely the same origin.

- I'd check for dew on the lens, the filters and, above all, on the chip window. That's where it gets me on the rare occasions when it does get me.

Olly

 

[gorann]

It could also be just a small cloud that happens to drift across that star.

[JeremyS]

Gradual bloat sounds like me during lockdown 🤔

[david_taurus83]

On 11/04/2021 at 15:21, ollypenrice said:

Thoughts:

- Are you refocusing regularly?

- As you approach the zenith the full weight of the camera/FW is hanging on whatever is locking your drawtube at its present extension. If it's going to slip, the zenith is the place where it will do so.

- As you approach the zenith the atmosphere's tendency to induce blue bloat is at its lowest so your problem is contrary to that.

- In thinking about this, don't forget that luminance passes blue, so bloat in L and bloat in B can have precisely the same origin.

- I'd check for dew on the lens, the filters and, above all, on the chip window. That's where it gets me on the rare occasions when it does get me.

Olly

 

Hi Olly

Yes, have an autofocuser set to focus if temp changes by 1°C or star HFR changes by 10%!

The focuser is R&P and the AF holds it solid.

I added another dew strap the other night, cleaned the objective and checked the sensor window on the Atik after a while of running the cooler. Couldn't see anything obvious..

[david_taurus83]

I done some testing the other evening on M44. I removed the LP filter from the flattener for this. Took half an hour on each filter, 60s subs on L and 90s subs on RGB. Each filter showed some halo on the brighter star on the right.

 

M44 LRGB

 

L filter

 

Red filter

 

Green filter

 

Blue filter

There's a strange artifact on the brightest culprits on all filters. It's on the centre star and right one with halo in LRG and on B its more so on the right one, despite the star to the left looking brighter with no issues! Checking on Sky Safari they are both practically the same magnitude, around 6.5. (39 Cancri - halo, 40 Cancri - no halo)

I just don't understand why it's not on all the brighter stars? Perplexed!

 

 

[david_taurus83]

This is a 300s sub I took of M45 last November. If anything is going to show halos, it'd going to be this, right?

 

 

Looks good to me. That's with the IDAS D2 on front of the flattener and through the Lum filter in the wheel. No visible issues.

 

So last night I done some sanity checks. Took another series of subs on the Beehive, this time with no filter at all. No IDAS D2 and Lum filter removed from the wheel. Here's the calibrated stack.

 

Halos still present and a new one left of sensor. So I can safely rule out the IDAS D2 and Astronomik filters.

Also took a couple of shots of Arcturus. These show another strange artifact. Reflection? It moves when I set Arcturus off centre.

 

 

 

Reflections in the camera? The sensor needs a good clean. I spoke to Atik a while ago as it has these small dots which I thought was dust but Atik say it looks like the sensor had frost on it the once and left some marks behind. See typical master flat.

 

Or could it be electronic? Here's a cropped gif of last night's subs showing a close up of the new halo in M44. There's no halo in the first few subs but it suddenly blinks on the same time as that little chevron type artifact appears. The same artifact appears in the bright star above right at the same time! Anyone ever seen anything like this?

[david_taurus83]

Its the reducer. The last piece of glass to check. I just stuck a nosepiece on the camera tonight and into the back of the scope. No glass or filters between objective and camera. No halos or reflections. Oddly enough, apart from 2 corners I appear to have better stars across the field at the scopes native F7.