Strange circles after stacking

[Dan13]

Hi,

I received my guiding set up in the week and had a clear sky for an hour or two to test last night, everything seems great guiding wise but ive just gone to stack 20 x 4min subs with 10 darks and 10 bias (no flats) and the below has happened. Ive not seen this before so can anyone shed some light at all?

many thanks

Dan

[MarkAR]

Dust spots, flats should remove them.

[Dan13]

4 minutes ago, MarkAR said:

Dust spots, flats should remove them.

Thanks mark, you think because I havent imaged at that exposure length before I havent seen this? 

 

I'll take some flats now

[MarkAR]

3 minutes ago, Dan13 said:

Thanks mark, you think because I havent imaged at that exposure length before I havent seen this? 

 

I'll take some flats now

Possibly.

[Craney]

If you have time before the next clear night (!!)  and can easily separate the components of the optical path (after the focuser), have a look at each optical surface and decide if a clean is needed.

I convinced myself a similar problem were reflections off of a light pollution filter... there was lots of documented evidence on-line supporting this.... it must be true.....

NOPE !!..... good ol'dust in the system. Took about 5 mins to rectify, but my "certainty" it was something else lost 3 nights imaging....

 

[Dan13]

2 minutes ago, Craney said:

If you have time before the next clear night (!!)  and can easily separate the components of the optical path (after the focuser), have a look at each optical surface and decide if a clean is needed.

I convinced myself a similar problem were reflections off of a light pollution filter... there was lots of documented evidence on-line supporting this.... it must be true.....

NOPE !!..... good ol'dust in the system. Took about 5 mins to rectify, but my "certainty" it was something else lost 3 nights imaging....

 

Ok thank you I'll take you up on this, maybe my scope could do with a clean.

Just strange I havent seen this in all my other exposures prior to this but again I'm guessing but I reoon that's due to the length of my new exposure time is showing up more in post

[Craney]

There is a formula somewhere .....I'll dig it out ......  that works out how far off the sensor the dusties actually are. 

It surprised me when I calculated it through to learn that mine were on the optical glass of the camera itself, thankfully on the outside.  Although this surface had been sealed up with a field flattener for a good 6 weeks.... Where had this 'dust' come from??... well it was there....magic ??!!!!  Anyway, I sorted it.

Word of caution.  Read some advice on cleaning surfaces before attacking the glass.  There are some major  'don'ts'  in terms of air-propellents and lint strewn tissues.  Certain coatings may not like a solvent (!!) being applied...etc...etc... there is a lot of good wisdom on these pages about this kinda of stuff.

Here's the formula...

https://www.ccdware.com/resources/dust.cfm

Good luck.

Sean.

[Dan13]

2 minutes ago, Craney said:

There is a formula somewhere .....I'll dig it out ......  that works out how far off the sensor the dusties actually are. 

It surprised me when I calculated it through to learn that mine were on the optical glass of the camera itself, thankfully on the outside.  Although this surface had been sealed up with a field flattener for a good 6 weeks.... Where had this 'dust' come from??... well it was there....magic ??!!!!  Anyway, I sorted it.

Word of caution.  Read some advice on cleaning surfaces before attacking the glass.  There are some major  'don'ts'  in terms of air-propellents and lint strewn tissues.  Certain coatings may not like a solvent (!!) being applied...etc...etc... there is a lot of good wisdom on these pages about this kinda of stuff.

Here's the formula...

https://www.ccdware.com/resources/dust.cfm

Good luck.

Sean.

Thank you Sean appriciate it. 

[spillage]

If you take your camera off the scope after every session then you will need to take flats before you remove the camera. If it all stays together then just run off some flats and keep using the same ones until they appear to stop working.

I have has worse and flats have removed it all.

 

[MarkAR]

Thanks as well Sean, the calculator will come in very handy.

[Dan13]

Flats did the job @MarkAR thank you