What are these odd spots on my image?

[Jay6879]

First shots from my new 533mc. 300s preview exposure (beyond the star elongation at the bottom suggesting wrong backspacing?) what could these dark spots be? The weird thing is they weren't visible with a 5s exposure?

 

They don't look quite like dust motes? And what is happening on the bottom half of the image? The stars are radiating away from the center of the image. Its happening at the top as well but not quite as bad. Is this a spacing issue? This was taken on a Zenithstar 61 with the 1.0x adjustable field flattener.

 

Any help would be appreciated, this was my first night out in MONTHS. It took me awhile to aquire this camera and when the first test images came in I got pretty dejected with the results!

Edited June 15, 2022 by Jay6879

[newbie alert]

Look like you need more spacing

[VectorQuantity]

22 minutes ago, Jay6879 said:

First shots from my new 533mc. 300s preview exposure (beyond the star elongation at the bottom suggesting wrong backspacing?) what could these dark spots be? The weird thing is they weren't visible with a 5s exposure?

 

They don't look quite like dust motes? And what is happening on the bottom half of the image? The stars are radiating away from the center of the image. Its happening at the top as well but not quite as bad. Is this a spacing issue? This was taken on a Zenithstar 61 with the 1.0x adjustable field flattener.

 

Any help would be appreciated, this was my first night out in MONTHS. It took me awhile to aquire this camera and when the first test images came in I got pretty dejected with the results!

This may possibly give some indication

https://astronomy.tools/calculators/dust_reflection_calculator

 

[Ibbo!]

They look like dust bunnies close to sensor, do you have flats ? If so they should confirm.

 

Sorry I got it the wrong way round corrected by Vlaiv see below.

[vlaiv]

Yes, it is dust - but rather far away from sensor.

Closer dust is to sensor "more concentrated" shadow is, and opposite happens when dust is further away - fainter and larger shadow becomes.

[Jay6879]

30 minutes ago, newbie alert said:

Look like you need more spacing

Ayy, the top image looks quite similar to mine. Ok, this is encouraging! I only used one of the spacers that came with the camera (16.5mm), I'll try attaching the other one that came with it (21mm iirc).

 

 

25 minutes ago, VectorQuantity said:

This may possibly give some indication

https://astronomy.tools/calculators/dust_reflection_calculator

 

I use astronomy tools all the time and never knew of this tool, I'm on mobile right now so it won't let me click and drag around the circles but I'm going to give this a go first chance I get.

 

 

17 minutes ago, Ibbo! said:

They look like dust bunnies close to sensor, do you have flats ? If so they should confirm.

Geez, I literally took the camera out of the box, threaded in a 1.25" ircut filter and put it on the telescope! Though I guess it wouldn't take much for dust to hit the protective window on the sensor, even in that small amount of time. And no I don't have flats, by the time I got everything set up clouds rolled in. These were just some 5 minutes exposures taken on the preview screen of the asiair plus, then I just took a screenshot of them with my phone.

The point of that test exposure was to see how far I could push my new belt modded heq5-pro, and the jury is still out on that until I can fix these spacing issues!

 

Thanks for the quick replies, all is not lost! I dropped a decent chunk of change on the camera and got pretty freaked out by these issues, I never had anything with my t3i. Just pop it on and go.

[vlaiv]

Just now, Jay6879 said:

Geez, I literally took the camera out of the box, threaded in a 1.25" ircut filter and put it on the telescope!

Given that you have spacing issues - dust is most likely on field flattener rather than on sensor or IR cut filter.

[Jay6879]

5 minutes ago, vlaiv said:

Yes, it is dust - but rather far away from sensor.

Closer dust is to sensor "more concentrated" shadow is, and opposite happens when dust is further away - fainter and larger shadow becomes.

Ok, so the dust is more likely to be on the flattener optics or further down at the end of the refractor then? Any tips on getting rid of stubborn dust? I've got one of those lens bulb things but it doesn't do much.

[vlaiv]

1 minute ago, Jay6879 said:

Any tips on getting rid of stubborn dust?

Blow bulb, but really you want to take flats as flats sort out issues with dust (and other things like uneven sensor response if there is any).

 

[newbie alert]

11 minutes ago, Jay6879 said:

Ayy, the top image looks quite similar to mine. Ok, this is encouraging! I only used one of the spacers that came with the camera (16.5mm), I'll try attaching the other one that came with it (21mm iirc).

What scope are you using?

[Jay6879]

14 minutes ago, vlaiv said:

Blow bulb, but really you want to take flats as flats sort out issues with dust (and other things like uneven sensor response if there is any).

 

Oh yeah for sure, flats are always used. I'll look into a more heavy duty bulb, like a Rocket Blower.

 

5 minutes ago, newbie alert said:

What scope are you using?

 

Zenithstar 61

Edited June 15, 2022 by Jay6879

[newbie alert]

Just now, Jay6879 said:

Oh yeah for sure, flats are always used. I'll look into a more heavy duty bulb, like a Rocket Blower.

 

 

Zenithstar 61

Check the specs but usually 55mm

[newbie alert]

18 minutes ago, newbie alert said:

Check the specs but usually 55mm

Zenithstar_61_Owner_Manual (1).pdf

Edited June 15, 2022 by newbie alert
Added info

[Jay6879]

1 hour ago, newbie alert said:

Zenithstar_61_Owner_Manual (1).pdf 3.21 MB · 2 downloads

 

Ah ok this is good info.  The asi533 comes with a 16.5mm and 21mm spacer, and a few really thin spacers. I'll have to figure out the math to see if I need more spacers or not. Or maybe the adjustment on the flattener will provide enough that those two spacers will be good enough.

[newbie alert]

9 minutes ago, Jay6879 said:

 

Ah ok this is good info.  The asi533 comes with a 16.5mm and 21mm spacer, and a few really thin spacers. I'll have to figure out the math to see if I need more spacers or not. Or maybe the adjustment on the flattener will provide enough that those two spacers will be good enough.

Don't forget to include the 6.5mm backspace ( camera body to sensor) within the spacing distance 

[Jay6879]

1 hour ago, newbie alert said:

Don't forget to include the 6.5mm backspace ( camera body to sensor) within the spacing distance 

21mm spacer+16.5mm spacer+6.5mm camera body to sensor gets me to 44mm.

67.9mm-44mm=23.9mm

So my flattener should be set to 23.9mm? Am I doing this math correctly?

[Jay6879]

1 hour ago, newbie alert said:

Don't forget to include the 6.5mm backspace ( camera body to sensor) within the spacing distance 

Wait...no hold on. The camera already comes with an 11mm spacer threaded on. So the math would be..

21mm+16.5mm+11mm+6.5mm(camera body to sensor)=55mm

ZWO says to set the flattener at 12.9mm for dslr's, a dslr also requires 55mm of backfocus. So essentially I just need to add that other 21mm spacer (which I wasn't using before, only the 16.5mm and 11mm spacers) and I should be fine....right?

[newbie alert]

Depends if you're using the flat61A

The spec says 67.9mm if you are

 

[Jay6879]

12 hours ago, newbie alert said:

Depends if you're using the flat61A

The spec says 67.9mm if you are

 

Yes it's a flat61A. He is a screenshot from tonight after adding the other 21mm spacer..

 

And a link to the raw sub..

https://drive.google.com/file/d/1aztjkp9c_haXMsfYKMmv5UZW8yqVm2xV/view?usp=drivesdk

 

Stars look way better! 

 

 

Edited June 16, 2022 by Jay6879