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Finally some insane focal length data!

Russell Croman Astrophotography NoiseXTerminator NGC1365 Galaxy Deep Sky NGC Objects
Insane focal lengths •20 replies•947 views
Daniel Petzen avatar
Daniel Petzen avatar
I've desperately been waiting for some clear skies to get another session with my C9.25 in.

I got a really mixed bag of four nights, but really made the most of it. Som nights had up to 80% cloud coverage, so, well, yes, not amazing results.

But, persistence is a virtue - I managed to get one of my best galaxy images ever once I've processed the data (a few times!): NGC 1365, The Great Barred Spiral Galaxy (Daniel Petzen) - AstroBin

I had some bad guiding but had 0.85" total RMS error on average. I even dipped down to 0.45" when it cleared up. That's not bad for an old SkyWatcher EQ6-Pro swinging 15kg (excluding counterweights) of equipment around!

I only had to throw away a handful of subs  (out of 200+) because of bad guiding. Most had to be discarded because of bad stats (high clouds etc).

I compared drizzle and Lanczos-3 integration (AstroPixel Processor) on the data (I was dithering (dither or die, right?)). Lanczos is much clearer with higher SNR, but the drizzled images most often comes out on top after some stretching and noise reduction.

I don't think NoiseXTerminator and Graxpert have been trained on Lanzcos-3 integrated images. I've been running Graxpert and NoiseXterminator and compared the results. Graxpert is a bit better at time. I also had better results using NX after stretching (normally with SetiAstro Statistical Stretch and some General Hyperbolic Stretch adjustments).

It would be intersting to hear what your experience with different types of integration is when using long focal lengths.
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Stephen Drapak avatar
Stephen Drapak avatar
That's a killer image, very cool!
Daniel Petzen avatar
Daniel Petzen avatar
Thanks, Stephen!
It came out amazingly well, as the conditions weren't ideal, but once the core features started coming out and the arms lit up, then it really turned into the best galaxy image I've taken.
…and even though I "cheated" by drizzling with 2x, having an image with 0.207"/pixel is pretty sweet!
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Salvatore Iovene avatar
Salvatore Iovene avatar

Congrats Daniel, this must've been so challenging, and yet the result is so good!

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Daniel Petzen avatar
Daniel Petzen avatar
Yes, thanks. That turned out really good, as the weather was a bit hopeless. I just bagged the tiny IC 4721 and the even smaller IC4720 (even though the latter is more of a blob!). It was really nice to get back to galaxies again.
MaksPower avatar
MaksPower avatar
Very nice !

Were you using the little Testar guide scope for this ? It seems insanely short. I have a 70mm/475mm  APO which I’ve used as a guidescope successfully …
Daniel Petzen avatar
Daniel Petzen avatar

MaksPower · Aug 18, 2025, 11:43 AM

Very nice !

Were you using the little Testar guide scope for this ? It seems insanely short. I have a 70mm/475mm  APO which I’ve used as a guidescope successfully …

Thanks!

Yes, I did :-)

I know it’s a terrible match, but I did get below 1” RMS guiding with it (0.85” according to my notes). It’s very fast and get razor sharp stars.

The ratio is 190mm/2,320mm - LOL!

I’m using a Celestron OAG now, but the Testar guide scope now sits on my Askar 103 APO, where 190mm/560mm is a slightly better ratio.

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Adam Cox avatar
Adam Cox avatar
Nice results Daniel,

I've always wanted to go to a longer (i.e. >1500mm) focal length and I'm keen to seen how you and others go with the EQ6-R Pro and SCT combos.

Cheers,
Adam
Tommy Mastro avatar
Tommy Mastro avatar
Adam Cox:
Nice results Daniel,

I've always wanted to go to a longer (i.e. >1500mm) focal length and I'm keen to seen how you and others go with the EQ6-R Pro and SCT combos.

Cheers,
Adam

I have a EQ6-R hyper-tuned and I still struggle with my C9.25 and C11, especially when I pair them with the Sony IMX585 sensor.  Nonetheless, I hover around 1.0 typically ranging from .75 to 1.2.   I cannot use this combination with any wind other than the slightest of breezes.

I sometimes run two rigs simultaneously - one at long FL and another at short FL (widefield).  During breezy days I can see the C9.25 guide >2.5 to 3, while my ASKAR SQA55 (264 FL) doesn't budge - solid .65 guiding.
Daniel Petzen avatar
Daniel Petzen avatar

Adam Cox · Aug 18, 2025, 10:00 PM

Nice results Daniel,

I've always wanted to go to a longer (i.e. >1500mm) focal length and I'm keen to seen how you and others go with the EQ6-R Pro and SCT combos.

Cheers,
Adam

Thanks!

I did take my EQ6 Pro (not even EQ6-R!) as far as I could with a belt conversion and zero backlash kit. I did get some 0.3” and 0.4” RMS guiding, but on average 0.75”, and sometimes over 1”. I found that an RMS exceeding 1” would blur the image and I would normally throw in the towel those nights.

Despite living in one of the windiest cities in the world (Wellington, NZ), I’ve very rarely had problems with wind, as I live in a sheltered valley (I have to put up with fog instead), but on the few occasions it has been windy, the results were pretty bad.

I’ve since built and observatory with a massive concrete pier and an upgraded EQ8-Rh, so I’m getting more consistent results now.

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Daniel Petzen avatar
Daniel Petzen avatar

Tommy Mastro · Aug 18, 2025, 10:28 PM

I have a EQ6-R hyper-tuned and I still struggle with my C9.25 and C11, especially when I pair them with the Sony IMX585 sensor.  Nonetheless, I hover around 1.0 typically ranging from .75 to 1.2.   I cannot use this combination with any wind other than the slightest of breezes.

That is interesting to hear!

I’ve been tempted to use my MiniCAM8M on my C9.25, but I thought that my seeing conditions (Bortle 5) wouldn’t be good enough to see a huge difference, and I was also concerned about the guiding.

I’m using my ASI294MC with my C9.25. It has 4.63µm pixel size, so it’s perfect for my C9.25.

As I mentioned in my reply to Adam, wind completely ruined it for me when I was using the EQ6 Pro / C9.25 (especially with the dew shield on).

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John Hawk avatar
John Hawk avatar
Great shot of NGC 1365! I came to deep sky from planetary imaging so I started using my C14 EdgeHD on galaxies and nebula at full focal length, no reducer. My mount is a Losmandy G11 and I use an Askar off axis guider for tracking in tandem with an ASIAIR. My RMS ranges from .40 to .80 depending on the night. Usual average is .65. I'm kind of surprised it tracks so well. Where I live in the California high dessert there is very little wind at night even if it is breezy during the day. We do have a condition called the Santa Ana winds that come from the Northeast and are very strong, but no one I know ever images then as the seeing is always terrible. Anyway check out my shots and let me know what you think. Thanks!
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Tommy Mastro avatar
Tommy Mastro avatar
John Hawk:
Great shot of NGC 1365! I came to deep sky from planetary imaging so I started using my C14 EdgeHD on galaxies and nebula at full focal length, no reducer. My mount is a Losmandy G11 and I use an Askar off axis guider for tracking in tandem with an ASIAIR. My RMS ranges from .40 to .80 depending on the night. Usual average is .65. I'm kind of surprised it tracks so well. Where I live in the California high dessert there is very little wind at night even if it is breezy during the day. We do have a condition called the Santa Ana winds that come from the Northeast and are very strong, but no one I know ever images then as the seeing is always terrible. Anyway check out my shots and let me know what you think. Thanks!

John - your images are stone cold breath-taking!  You have APOD level images there.  Most certainly IOTD.  I wanna be you when I grow up!
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Tommy Mastro avatar
Tommy Mastro avatar
Daniel Petzen:
Tommy Mastro · Aug 18, 2025, 10:28 PM

I have a EQ6-R hyper-tuned and I still struggle with my C9.25 and C11, especially when I pair them with the Sony IMX585 sensor.  Nonetheless, I hover around 1.0 typically ranging from .75 to 1.2.   I cannot use this combination with any wind other than the slightest of breezes.

That is interesting to hear!

I’ve been tempted to use my MiniCAM8M on my C9.25, but I thought that my seeing conditions (Bortle 5) wouldn’t be good enough to see a huge difference, and I was also concerned about the guiding.

I’m using my ASI294MC with my C9.25. It has 4.63µm pixel size, so it’s perfect for my C9.25.

As I mentioned in my reply to Adam, wind completely ruined it for me when I was using the EQ6 Pro / C9.25 (especially with the dew shield on).

Oh yeah, the old Dew Shield in the wind trick. 

I love my dew shields because despite living in a Dark Sky community, I have some bad light pollution.  But you really do pay the price when the wind sets in.  That's why I really want a dome.  Right now, I have a ROR observatory, which is great on dark, windless nights.  But for long FL, I really need a dome.  I'm just a little intimated by the geometry and other issues I read about.  Plus, they're pricey!
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Adam Cox avatar
Adam Cox avatar
Daniel Petzen:
Adam Cox · Aug 18, 2025, 10:00 PM

Nice results Daniel,

I've always wanted to go to a longer (i.e. >1500mm) focal length and I'm keen to seen how you and others go with the EQ6-R Pro and SCT combos.

Cheers,
Adam

Thanks!

I did take my EQ6 Pro (not even EQ6-R!) as far as I could with a belt conversion and zero backlash kit. I did get some 0.3” and 0.4” RMS guiding, but on average 0.75”, and sometimes over 1”. I found that an RMS exceeding 1” would blur the image and I would normally throw in the towel those nights.

Despite living in one of the windiest cities in the world (Wellington, NZ), I’ve very rarely had problems with wind, as I live in a sheltered valley (I have to put up with fog instead), but on the few occasions it has been windy, the results were pretty bad.

I’ve since built and observatory with a massive concrete pier and an upgraded EQ8-Rh, so I’m getting more consistent results now.

Thanks Tommy and Daniel,

Your feedback on the EQ6 is what I suspected. I'll stick with my 0.4"-0.8" and 840mm FL for now until the bank account builds up for a heavier mount

Cheers,
Adam
Tony Gondola avatar
Tony Gondola avatar

Adam Cox · Aug 18, 2025, 06:00 PM

Nice results Daniel,

I've always wanted to go to a longer (i.e. >1500mm) focal length and I'm keen to seen how you and others go with the EQ6-R Pro and SCT combos.

Cheers,
Adam

From what I’ve seen in my own setup, the EQ6-R Pro has no issues handling up to 2000mm as long as there’s no wind. From what I see in guiding numbers I’d be confident probably out to 3600mm if everything is balanced right.

John Hawk avatar
John Hawk avatar

Tommy Mastro · Aug 19, 2025, 02:10 AM

John Hawk:
Great shot of NGC 1365! I came to deep sky from planetary imaging so I started using my C14 EdgeHD on galaxies and nebula at full focal length, no reducer. My mount is a Losmandy G11 and I use an Askar off axis guider for tracking in tandem with an ASIAIR. My RMS ranges from .40 to .80 depending on the night. Usual average is .65. I'm kind of surprised it tracks so well. Where I live in the California high dessert there is very little wind at night even if it is breezy during the day. We do have a condition called the Santa Ana winds that come from the Northeast and are very strong, but no one I know ever images then as the seeing is always terrible. Anyway check out my shots and let me know what you think. Thanks!


John - your images are stone cold breath-taking!  You have APOD level images there.  Most certainly IOTD.  I wanna be you when I grow up!

John Hawk avatar
John Hawk avatar

Tommy Mastro · Aug 19, 2025, 02:10 AM

John Hawk:
Great shot of NGC 1365! I came to deep sky from planetary imaging so I started using my C14 EdgeHD on galaxies and nebula at full focal length, no reducer. My mount is a Losmandy G11 and I use an Askar off axis guider for tracking in tandem with an ASIAIR. My RMS ranges from .40 to .80 depending on the night. Usual average is .65. I'm kind of surprised it tracks so well. Where I live in the California high dessert there is very little wind at night even if it is breezy during the day. We do have a condition called the Santa Ana winds that come from the Northeast and are very strong, but no one I know ever images then as the seeing is always terrible. Anyway check out my shots and let me know what you think. Thanks!


John - your images are stone cold breath-taking!  You have APOD level images there.  Most certainly IOTD.  I wanna be you when I grow up!

Thank you ever so much Tommy, you’re too kind!

MaksPower avatar
MaksPower avatar
Agreed. I suffer here from appalling weather, so on the rare clear nights I try to get what I can in 1 - 2 hours max per target.
I know it's nowhere near long enough, but that's what we have to play with.

On one hand I have scope that is optically superb and works reliably, like an appliance.
But my processing skills are crap, and I just rely on what the scope delivers. OTOH having been a visual observer for 50 years I'm quite happy if an image comes out resembling its visual appearance with a tad of colour; IMHO a lot of images are very over-cooked.

The best part IMHO is it brings targets within reach in suburbia that I would have had no chance of seeing visually. But the scope delivers, and it can go deep if/when I have the time.
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Cyg avatar
Cyg avatar
Hello,

Way too soft for me (too much denoising/bluring/extrapolations), I can't detect individual pixels with galactic clusters or sharp dust around the heart for instance, but flat group of pixel areas, I don't know if everyone opened it fullscreen/fullsize on a screen instead of the homepage preview on a smartphone ;-)

I prefer to be honest as we are in the long focal length forum and the idea is to get the best from this, not to do a classic focal length photo that is "zoomed and blurred" as final result (the size doesn't make the resoluton/sampling).

Regaring the theorical 0.2arc/pix scale (or 0.4 before drizzle), your guiding should have been half of that to be "Shannon" sampling theorem compliant and as you mentionned the guiding was hard and you got a 0.85arc/pix, 4 times more than the theorical need although the drizzle may have helped a little…

Maybe the raw individual photos were already too blury: a not optimal focus, the guiding not at its best, the wind, the seeing, etc. many factors can affect from the start, and then many other can happen during the processing…
Also 4min is quiet long to capture galaxies with a clear filter and guiding issues/limits, and it can affect the FWHM depending on the guiding conditions during this time. It could be interesting to compare the 120s vs the 240s subs to see if the FWHM is the same and if it really brings more details / a better SNR.

Best regards,
Cyg / Fabrice
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Daniel Petzen avatar
Daniel Petzen avatar

Cyg · Aug 20, 2025, 11:23 AM

Hello,

Way too soft for me (too much denoising/bluring/extrapolations), I can't detect individual pixels with galactic clusters or sharp dust around the heart for instance, but flat group of pixel areas, I don't know if everyone opened it fullscreen/fullsize on a screen instead of the homepage preview on a smartphone ;-)

I prefer to be honest as we are in the long focal length forum and the idea is to get the best from this, not to do a classic focal length photo that is "zoomed and blurred" as final result (the size doesn't make the resoluton/sampling).

Regaring the theorical 0.2arc/pix scale (or 0.4 before drizzle), your guiding should have been half of that to be "Shannon" sampling theorem compliant and as you mentionned the guiding was hard and you got a 0.85arc/pix, 4 times more than the theorical need although the drizzle may have helped a little…

Maybe the raw individual photos were already too blury: a not optimal focus, the guiding not at its best, the wind, the seeing, etc. many factors can affect from the start, and then many other can happen during the processing…
Also 4min is quiet long to capture galaxies with a clear filter and guiding issues/limits, and it can affect the FWHM depending on the guiding conditions during this time. It could be interesting to compare the 120s vs the 240s subs to see if the FWHM is the same and if it really brings more details / a better SNR.

Best regards,
Cyg / Fabrice

Hey Fabrice

Yes, you’re right about the level of detail when zooming in, but please keep in mind that the guiding was quite bad as was the seeing. Please also note that the image was Lanczos-3 interpolated and not drizzled, which means that Bx and Nx have very limited impact as they appear to have been trained on drizzle data (Nx v3 seems better, though). It also sacrifices detail for brightness.

You may want to have a peek at NGC 5128, Centaurus A, the very peculiar galaxy, where I had better guiding and drizzled.

I’ve started experimenting with 5 minute exposures. FWHM increased, but a lot of dim structures are teased out, so I’ll see what I can get out of my old C9.25 XLT when the clouds part again.

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