any one else had this from a DSLR

[Daniel-K]

this was the first time using my 450d from MPB photographic i was imaging as follows

canon 450d

120 secs

iso 400

quatrro 8s

SW coma corrector

SW 2" LP filter

moon 66%

there seems to be these rings in the image just wondering if i should send the camera back? i have used dslrs before and produced so nice images but never had this problem with one

picture is 1hr 12 min sacked in dss and strecthed in PS

Dan

[garethmob]

iv had them daniel, it was diagnosed to me as reflection from a bright star in the optical tube (or in my case lens) there was a photoshop routine which greatly reduced them but they were still there unfortunatly

[Daniel-K]

might be worth trying with no moon then as it was very very bright and the subs were on border line of blown out

[MartinMR2]

I've had it while keeping the shutter open on manual. If there is an object brighter than the rest, like a bright star or street lamp, the rings form around that. Tis a pain but mine is a budget dslr so can't really complain...

[Daniel-K]

but theres no bright star around m81 so it must have been the moon

[studdedsole]

I would try using the DSLR without the coma corrector and filter as the pattern looks similar to an interference pattern which may be a result of the spacing and/or interaction of the additional elements in the imaging chain.

Then try the same target with the coma corrector and filter in place individually and again as a pair using the same spacing you currently employ.

You might find the spacing is critical in your set up and requires some tweaking to achieve optimal.

[Daniel-K]

tried it without the coma corrector still there also the CC is meant for the use with DSLR's so i dont think spacing comes into it

[studdedsole]

tried it without the coma corrector still there

Any luck if you try without the filter also?

[studdedsole]

Just another thought as it's easy to assume, are you capturing in raw and processing in a lossless format, as image compression can cause this type of phenomenon particularly as you increase the degree of processing

[Daniel-K]

captured in RAW processed in PS6 16BIT and in NEB3 both show rings not tried it without the filter but my last DSLR i used the same filter and never had this, saying that though i did get something simlar when i was using the CCD with the filter

[studdedsole]

Maybe try some flats to see if it is actually part of the imaging train, if it is you could always use the flats to remove the problem.

[studdedsole]

Came across your other post regarding this issue and the single raw frame you posted doesn't appear to have the issue.

I found this link to someone having what seems an identical problem with DSS, they tried another stacking utility (Nebulosity) and this appears to have indicated the problem is with DSS.

http://www.astronomyforum.net/astro-imaging-forum/142628-gradient-issues-after-stacking-dss.html

You can download a free trial of nebulosity to try it out and see if this solves your problem

[Daniel-K]

i already have Neb3 and have tried it, still get the same issue, i wonder if it has anythin to do with offset and gain? i had the same effect when using my ccd when i changed the off set and gain in the settings, then when i changed them back to default it was ok. any thoughts on this? also in the settings i was shooting under neutral maybe i should have used standard?

[studdedsole]

Ah I wondered what the NEB3 was in your previous post, should have figured that one out, sorry.

I haven't used NEB for capture using a DSLR so my knowledge is very limited. I would think that the offset would be a function of the DSLR camera and NEB should recognise this automatically and apply the correct offset so I wouldn't play with this.

As far as I know you only need to establish the offset for CCD and it is trial and error to set but once you have it it is permanent for any imaging run with that CCD.

So using the default settings may be a good place to start.

I don't know anything about the neutral or standard settings so can't comment objectively. I capture DSLR images using canon utilities and then import them to NEB for alignment and stacking then PS for post processing.

I still puzzled as to why the single frame on your other post didn't show the effect (unless I can't see it on my pc), which would kind of suggest that processing may be the problem.

[Daniel-K]

i have checked the subs and its not present on any im going to stack it on a friends computer to see i get the same results

[Daniel-K]

i wonder if the usb hub has anything to do with it? the data is going through a hub then to the laptop all my other images i have never used a hub this is the first itme i have used a hub

[studdedsole]

I presume you mean the data from the camera is passing through the hub to the laptop, but the subs on the laptop are "clean" so the hub shouldn't be a factor.

It feels like you are on the right lines by trying a different computer and even a different stacking programme/routine

[Daniel-K]

now heres 11 subs which was taken towards the end of the session with the dew shield on with a different bayer matrix, there still there but not as clear just in the dark bits of the images, really going to have to wait for a moon less night, im also going to try the camera in a friends scope and then stack the data to see if its the same, theres a lot to go through. why is it never straight forward !

[studdedsole]

Do you use dropbox?

If not you could think about downloading it and sharing your subs.

You can drop the subs into a folder and provide a link which allows people with the link to download the data.

I and others who may be interested can have a go at processing the data and drop the finished versions back to you.

Here is a link to the app which is free.

https://www.dropbox.com/

[Rustysplit]

Hi Daniel,

I have had this whilst using my nikon D5000 occasionally. I have never got to the bottom of it but a set of flats usually get rid of it. Just make sure that your flats are not too dark, i.e. the histogram peak is just left of centre. Works for me anyhow.

I am also using a SW CC and SW 2" LPF

[studdedsole]

Hi Daniel,

I have had this whilst using my nikon D5000 occasionally. I have never got to the bottom of it but a set of flats usually get rid of it. Just make sure that your flats are not too dark, i.e. the histogram peak is just left of centre. Works for me anyhow.

I am also using a SW CC and SW 2" LPF

But the problem isn't present on any of the subs suggesting flats won't solve what is on the final processed image

[Tom OD]

While the pic is small and hard to see, it looks like image compression to me. Probably nothing wrong with your camera. Dropbox a TIFF file and we can play with it.

Tom.

[Daniel-K]

hi tom i thought that but why would it be in DSS if it was shot in RAW?

[studdedsole]

Hi Daniel, been thinking more about this, do you let NEB grade your subs in case there are any "poor" subs you are stacking which might corrupt the stack.

If not run them through the "Grade Image Quality" routine and see if there are any rogues in there.

As Tom says dropboxing some subs would be a great help so we could play with an aligning/combining routine.

[Daniel-K]

https://www.dropbox.com/home/m81qt8 heres the drop box with some subs in