Horizon OSC...gradient or vignette?

[CraigG]

So my leaning curve with the Horizon is gradually flattening out as I get time to work with the camera! While waiting to hear from Atik on the horizontal banding question, I've noticed what I would call a vertical gradient (vignette?) effect in my images. I've attached an over processed stacked image to highlight what I'm seeing.

I was hoping that those of you that have worked with the Horizon and other cameras for way longer than I have could share your thoughts on this effect. Is this the camera's 4/3rds sensor merely telling me that there's a back focus issue or is it something else? I use a .8x ff/fr that's made for my 735mm refractor and I know that I'm about 2mm longer than the 55mm that manufacturer recommends for spacing. Before I order up an alternative spacer combo to address it, it would help to know if that will solve the issue or is the problem bigger than that? This is a simple imaging train with no diagonal, Barlow, etc. in the mix.

Thanks for your comments as always!
Craig

[theoatc]

Amp glow Maybe? Change the orientation, around 90 degrees. See if it change orientation as well. Then it is amp glow.
If it doesn't, shot with hydrogen alpha filter. Check if it shows up. If not, then it is stray light

[CraigG]

I forget to mention that I do have a Baader 2" UV/IR block filter mounted on the scope side of the FF/FR.
-Craig

[theoatc]

I forget to mention that I do have a Baader 2" UV/IR block filter mounted on the scope side of the FF/FR.
-Craig

only ha filter blocks out completely stray lights. UV/IR makes stars looks less bloated.

[bwa]

...
I was hoping that those of you that have worked with the Horizon and other cameras for way longer than I have could share your thoughts on this effect. Is this the camera's 4/3rds sensor merely telling me that there's a back focus issue or is it something else? I use a .8x ff/fr that's made for my 735mm refractor and I know that I'm about 2mm longer than the 55mm that manufacturer recommends for spacing. Before I order up an alternative spacer combo to address it, it would help to know if that will solve the issue or is the problem bigger than that? This is a simple imaging train with no diagonal, Barlow, etc. in the mix.

Thanks for your comments as always!
Craig

Wow, I've never seen a vertical gradient like your example!

I'm pretty sure it isn't a FF/FR problem.  In that case the gradient would be circular.  FF/FR backspace is pretty flexible and your stars appear nice and round all the way out to the edges, so don't worry about spacing.

It doesn't look like amp glow.  It normally shows up in a corner.  If I remember correctly, the lower right corner on the Horizon and Infinity.

Is there a chance you have lights off to the side(s) of your imaging setup?  Side light can sometimes cause a similar problem.

If this is the only time you've seen the problem, it might just have been a gradient in the sky from clouds?

Sorry I can't be of much help...

bwa

[CraigG]

Thanks bwa and theoatc-

Well I'm glad to know that it's not a spacing issue so I can concentrate my efforts elsewhere. Unfortunately, I don't think the cause is from stray light or seeing/transparency variations. I'm imaging from Bortle 3 rural skies with no lights anywhere around me. The image train components are tight and sealed. I have noticed the gradient in other images on different nights and noticed it again last night in some really good seeing and transparency conditions. Maybe it relates to the horizontal banding issue? The gradient does line up with the sensor's long axis.

Sigh, getting pretty frustrated with these issues that keep me from fully enjoying an imaging session but I am thankful for everyone's good council. Bwa, I'm appreciating your earlier comments about using this camera for EAA more and more each session.

Thanks guys!
Craig

[dpaul]

Hi Craig,

Maybe it is just light gradient in the sky, I get it all the time.

I did a very simple gradient extraction using Pixinsight (Dynamic Background Extraction) in Pixinsight. Then also a simple mask for the galaxies and reduced the background granulation. Finally a quick tweak with the Canon debanding tool. The attached result was only 5 mins work.

Just trying to be helpful showing that very simple post processing can make a difference.

One thing that is definately evident is 'undersampling' so the star looks quite pixelated. If you tried without the focal reducer you should see better detail (but less field of view of course). I have the opposite problem with an F3.5 mirror and a long focl length so my number of pixels per star is 'over-sampled'. I can't use a FR because it would create coma.

Hope this is helpful

David

[CraigG]

David-

You are ALWAYS helpful! Wow, your PI tweaks really made a difference. Just one more reason to take the plunge and go with PI.

Thanks for your comments on undersampling of the stars. I do use the "Raw Pixel" setting when stacking in Infinity so maybe that's a factor. I wouldn't have guessed that undersampling would be an issue with this sensor in my setup but I'll try your suggestion!

Anyway, your post gave me encouragement just when I needed it. Hope I can return the favor some day!

Best wishes,
Craig

[dpaul]

Hi Craig,

No problem at all, just trying to help - be warned Pixinsight takes a lot of learning but even using 10% of its capabilities will get great results. I do the actual image stacking and post processing with Pixinsight.

Regarding undersampling vs oversampling, the following link should be useful:

https://www.atik-cameras.com/news/rules-1-2-arc-second-per-pixel-and-when-to-break-them/

I'm actually using about 0.6 arcseconds per pixel but the recommendation if 1-2. However as the link says you can break the rules sometimes. I think yours might be too much the other way, check the table on the link, you can calculate it.

Regards

David

[CraigG]

Well, after sending some additional image and bias frame files to the folks at Atik Support highlighting the banding and gradient issues, they suggested sending the camera in for repair under warranty. I did so and I'm happy to say that my initial tests show that the problems appear to have been resolved. I haven't had good enough weather and/or a decent moonless sky to fully test it but I'm pleased so far. Atik said that the fix involved a small modification on the circuit to smooth out one of the power supplies.

Although I was again pleased with my interactions with Support, what really impressed me was the turn around time for the repair. The camera was returned to me less than a month after I first shipped it to High Point Scientific for forwarding to Atik in the UK. The REALLY impressive part of the journey is that when Atik shipped the repaired camera back to me on a Wednesday from the UK, I had it in my hands here in Michigan before noon on the following Friday! You know that was not a cheap UPS bill that Atik covered with as much air time that the package would have needed to get here that fast. Pretty great service.

Thanks for everyone's input on this subject and I appreciate learning of some good tools and settings to deal with banding and gradients in the future!

Craig

[Noah4x4]

Hi Craig,

I live 60 miles from Atik's HQ and it was the primary reason I selected the Horizon. I have had too many problems getting warranty repairs promptly sorted with Asian manufactured items (not necessarily astro). I had a problem with my original Horizon USB3 connector which was promptly fixed (later models have the superior connector). Glad to hear that Atik is also offering great service in the USA too. I have had a fair bit if contact with their super helpful people. BTW, Robin at Sharpcap is now liasing with Atik Support over the driver issue in Sharpcap, so that too should be fixed soon.

[CraigG]

Hi Noah!

Lucky you for living within driving distance of Atik's HQ! Although I've been pleased with my online communications, it would great to meet with them face-to-face. It would be like the good old days when you could walk into your local camera shop for whatever you needed.

Great to hear that Robin is working with Atik on the driver issue. I'm guessing that you had a hand in making that happen with your communications with him. Maybe we'll see a true native Atik driver set for SharpCap as a result?! There's no good reason why Atik cameras shouldn't have the same support in SharpCap as ZWO cameras enjoy.

Craig

[CraigG]

Well, I finally had a couple of good imaging sessions before moonrise and I'm pleased to report that the banding and gradient issues are resolved. I was able to successfully stretch the images while stacking in Infinity and in post-processing. Now back to having fun!

M81 pic attached, 164 X 15" light subs, 2x2 binning, low gain stacked in Infinity. No FF/FR, filters, darks, flats, etc.

Craig

[dpaul]

Hi Craig
You are making BIG improvements!
If you zoom up the image it still looks under-sampled, note the obvious pixels in the zoomed up stars. Suggest you try 1x1 binning (although it will need longer exposure). Regarding image capture, I use Artemis to capture everything (with the sequencer), this seems more suited to imaging whereas Infinity is more suited to live video (in my opinion).

Regards

David

[CraigG]

Thanks so much David!

Well, I owe some of the improvements to getting the camera brought back up to spec and to your previous suggestion to try imaging without a reducer. Also, with Bode's being closer to the zenith I think the subs were less affected by my mounts tracking issues at lower altitudes. I'm been trying to get by with taking short subs and no guiding but my next session will include a PHD2 test. I'll also experiment with 1x1 binning again as you suggested.

I've never really warmed up to the Artemis software to this point so I was hoping that the new Dusk product would be the ticket but you've probably seen the forum posts on where that stands at the moment. Looks very promising though!

So, what have you been working on recently? I still can't get over how well your shots of M1 came out a few months ago!

Craig