M31...and a black hole?

[Maxrayne]

As the title suggests, it appears I've discovered a black hole

Okay, I obviously haven't, but does anyone have any ideas?

Taken with an unmodded 700D, Canon 55-250mm f/4-f/5.6 lens. About 90 minutes worth of 1 minute subs at ISO 800 plus darks and flats

[Thalestris24]

Hi

Probably a flats/calibration problem. What are individual subs like? Likewise individual darks and flats.

Louise

[Maxrayne]

10 minutes ago, Thalestris24 said:

Hi

Probably a flats/calibration problem. What are individual subs like? Likewise individual darks and flats.

Louise

Just finished going thru the subs now, pulled a couple at random and it's there on those too. I'm guessing its a lens issue or perhaps body/sensor. I'm inclined to go with the latter as I never had a problem with the lens on my old 550D

In fact I've just finished stacking another image at 55mm and its there as well, same dimensions etc

[Thalestris24]

1 minute ago, Maxrayne said:

Just finished going thru the subs now, pulled a couple at random and it's there on those too. I'm guessing its a lens issue or perhaps body/sensor. I'm inclined to go witht he latter as I never had a problem with the lens on my old 550D

Maybe dew on the lens? Did you take flats at the same time? It might be possible to process out - maybe via 'artificial flats' but I'm not sure. I'm sure someone here with more processing expertise than me will be able to help.

Good luck

Louise

[Maxrayne]

8 minutes ago, Thalestris24 said:

Maybe dew on the lens? Did you take flats at the same time? It might be possible to process out - maybe via 'artificial flats' but I'm not sure. I'm sure someone here with more processing expertise than me will be able to help.

Good luck

Louise

Definitely not dew I don't think, had the warmer on the whole time, up to temp before I started capturing anything. 

The flats on the M31 image I took on my last session, the one's for the 55mm image I took tonight.

Thanks Louise, think it rules those out at least

[Thalestris24]

Does the lens have an led on it and do you cover the viewfinder?

Just a couple of thoughts.

[Maxrayne]

No LED on the lens no, and taped off the viewfinder after the red glow issues previously

[Thalestris24]

Nothing on darks or flats? What does it look like inverted i.e. in negative - might give a clue.

[Maxrayne]

Good question, I've not inverted anything. Not actually sure I even know how ?

[Thalestris24]

This is what I was thinking but it doesn't help much

 

The only thing I can think of that might produce a dark spot surrounded by a light area is a water drop or something similar.

 

[wimvb]

23 hours ago, Maxrayne said:

perhaps body/sensor

There are stars visible inside the dark area. Is this the same on the single subs? That would indicate it's not directly on the sensor. But imo, you should definitely check the sensor anyway.

[Maxrayne]

1 hour ago, wimvb said:

There are stars visible inside the dark area. Is this the same on the single subs? That would indicate it's not directly on the sensor. But imo, you should definitely check the sensor anyway.

Hi Wim

Definitely on the single subs as well. I've given it a blow clean so I'll be using it again the next opportunity. I'll also try it with another lens, just to make sure. If it turns out to be body related then I'll pop it back into my local LCE for them to sort, as it's less than a month old (albeit second hand)

[Thalestris24]

1 hour ago, Maxrayne said:

Hi Wim

Definitely on the single subs as well. I've given it a blow clean so I'll be using it again the next opportunity. I'll also try it with another lens, just to make sure. If it turns out to be body related then I'll pop it back into my local LCE for them to sort, as it's less than a month old (albeit second hand)

What it could be is a bubble of something that has burst and dried on the sensor. If that's the case you'd need to clean the sensor. However, if it was on the sensor or in the optical path, it would also be on the flats and they would cancel out the original. The thing is, has it occurred again?

Louise

[cresskh]

I had this issue when my scope mirror is full of dust and water stains.

Somehow the flats are not doing a good job in getting rid of that, thus producing negative-like effect like yours.
I ended up stacking my subs without the flats. The dusts are there but not as visible as the ones calibrated with flats.

Maybe you can give it a try too.

[Thalestris24]

1 hour ago, cresskh said:

I had this issue when my scope mirror is full of dust and water stains.

Somehow the flats are not doing a good job in getting rid of that, thus producing negative-like effect like yours.
I ended up stacking my subs without the flats. The dusts are there but not as visible as the ones calibrated with flats.

Maybe you can give it a try too.

Good idea - except the op image was taken with a lens but I think it must have been something along those lines

Louise

[coatesg]

Usually something that distinct isn't related to the objective, as something over the front of the lens affects light across virtually the whole field (but it may induce some kind of diffractive effect). 

Can you post stretched versions of a light, darks and flats? What's very strange is that it is a clear edge to the dark surrounded by light (not out of focus like a dust bunny) - I'm inclined to think this might be sensor related. Taking photos of a flat field with different lenses should rule this out.