Nice patterns - shame about the image...

[fwm891]

My testing of my newly acquired William Optics ZenithStar 73 and it's Flat 73A flattener continue. Last night I wanted to try with a full frame sensor (Nikon 800E) to see how things were in the corners etc. I shot 15 x 3 minute sub frames at 400 iso, guided using the ST4 connection on the ASI120MM to the Star Adventurer and PHD2 on the laptop. All looked good when viewing the camera screen, but when trying to stack them in PI afterwards things didn't look right!

I've annotated images below as I think it would be easy to loose track.

Before attempting to stack all 15 frames I started with 5 at random from the set. No flats, darks or bias frames used: Star aligned and Integrated, followed with a Histogram stretch of each image component i.e. Low and High noise rejection and the final frame integration.

The first three images show my problem using just 5 frames. Images 4, 5 & 6 show the same but here I've reprocessed the original 5 frames and added drizzle frames. High and low rejection frames have changed and the overall pattern on the integrated frame is softer.

Frame seven is a single 3 min frame given a histogram stretch and SCNR applied to remove the green cast. Frame eight was grey-scaled in PI and then levels applied in Photoshop SC3.

My initial thought is that it is a moiré pattern possibly because I couldn't use any dither between sub frames as PHD2 had no idea when frames began or ended. Once I get my new mount I will try again with dithering between frames.

Interested if anyone else has had this or similar effects. The 800E has no anti-aliasing  filter.

 

[RT65CB-SWL]

I am no expert, but images 1, 2, & 4 make stunning computer wallpapers/backgrounds! 

...if you like that kind of thing! 

[tooth_dr]

I’m not sure if this is relevant but I’ve recently taken images with same camera (but lens not telescope) without dithering either and all stacked ok

[fwm891]

2 hours ago, tooth_dr said:

I’m not sure if this is relevant but I’ve recently taken images with same camera (but lens not telescope) without dithering either and all stacked ok

Can you tell me how you stacked them please: Program PI, DSS etc and what  modes were use: average, median etc etc.

I used Average and winsorised in PI and will try other modes later to see if it disappears.

Francis

[tooth_dr]

3 minutes ago, fwm891 said:

Can you tell me how you stacked them please: Program PI, DSS etc and what  modes were use: average, median etc etc.

I used Average and winsorised in PI and will try other modes later to see if it disappears.

Francis

Hi Francis

I loaded the images into Astro Pixel Processor, I tried with Bias and Flats, and without Bias and Flats, and no issues either way.  I average stacking, no clipping. I did have an issue when I used clipping but I think that was becuase it was mosaic I was stacking?  Now I'm thinking, the windsor clipping could actually have been the cause?  I can post that image later.  I would try without any clipping.  I only use clipping if I have dithered.

[fwm891]

Tried this again using Lightroom and Photoshop CS3-Extn.

There are background rings - they're due to me overcooking in LR...

Otherwise looking better