Barlow ZEISS Abbe Barlow 2-3x, first light and comparisons

[H-Alpha]

Hi all,

Yesterday I received and tried for first time the ZEISS Abbe Barlow. According to Baader it can be used as 2x or 3x by changing the camera distance to it.

My main question is: Why the granulation disappears as we move from no Barlow to 2.2x and 3.3x?
Am I doing something wrong?

For the Lunt130MT F7 and my camera AS290MM, theoretically for H-alpha I should not go beyond F11, so 2x is already too much... Is this the reason?

The seeing conditions were not really different for the three captures, and actually worst for the best granulation with no Barlow.

SSM data.jpg (871.64 KiB) Viewed 443 times

2021-6-30, Barlow comparisons.jpg (1.5 MiB) Viewed 443 times

All comments are very welcome.

Best wishes,
Alexandros

[DeepSolar64]

Higher magnification not being supported by the seeing maybe? How about focus? 2.2x and 3.3x may require different focus positions. Just guessing...

James

[Montana]

These are magnificent however I would say that it was not supported by the seeing, the higher the mag the better the seeing you need.
What time of day are you imaging? over what are you imaging?
Try very early in the morning, when I was at Luca's in Italy the best seeing was around 7-8am. We also imaged over grass and away from buildings which the Sun can heat. Aiming over the sea was also a bonus.

Alexandra

[davidem27]

For the Lunt130MT F7 and my camera AS290MM, theoretically for H-alpha I should not go beyond F11, so 2x is already too much... Is this the reason?

Hi there, Alexandros!
I think this could be the best answer.

You reached and surpassed the refractor limit by sampling and after, that focal length, seeing kneads details

[MAURITS]

Nice comparation Alexandros.
Indeed the higher the magnification the better the seeing you need as you can see above ( most details in the first image).

[H-Alpha]

Thank you all very much!

Indeed, today with much better seeing the results were much, much better with the Barlow!
And also those images were 'false WL' i.e. blue wing of H-alpha. Today I tried pure WL and the granulation appeared much much better!
Alexandra's advice a couple of months ago was so helpful on this.

Hi there, Alexandros!
You reached and surpassed the refractor limit by sampling and after, that focal length, seeing kneads details

Davide your last post on how to achieve 1.7x (1.6x in your case) by removing the frontal part of the camera helped a lot! Many thanks!

Best wishes,
Alexandros

[davidem27]

That's great, Alexandros. That is the forum purpose

[george9]

Alexandros, I am not an imager, so this is likely very wrong. Consider it a question rather than a recommendation.

It seems to me that over sampling (Barlowed) is inefficient, but in the setting of having lots of light, it should not really lose granulation that is really there.

I assume those three images are image processed with sharpening of some sort.

All three have fine granulation if you look closely. It is just that in the second two, the granulation is so fine that you don't notice it and also it occurs at a scale that is unrealistic.

Therefore, I wonder if some of the granulation of the first (best) image is image sharpening artifact, not real granulation. And the second two images, because they are blown up, the sharpening artifact is at a scale that does not appear to be real granulation, so we skip right over it.

If those are unprocessed images, then that is a different story. Then I agree it must simply be oversampling.

If you take the raw images and bin the over-sampled ones down to the first image (without processing), do they then look similar?

George

[H-Alpha]

It seems to me that over sampling (Barlowed) is inefficient, but in the setting of having lots of light, it should not really lose granulation that is really there.

I assume those three images are image processed with sharpening of some sort.

All three have fine granulation if you look closely. It is just that in the second two, the granulation is so fine that you don't notice it and also it occurs at a scale that is unrealistic.

Therefore, I wonder if some of the granulation of the first (best) image is image sharpening artifact, not real granulation. And the second two images, because they are blown up, the sharpening artifact is at a scale that does not appear to be real granulation, so we skip right over it.
George

Dear George, excellent remark and observation! It is a processing artifact!
Those images are not 'true WL'. This is the blue wing of H-alpha. The granulation should not be really visible in this light, and only after your comment I realized that!
You can compare with my post and animated comparison of the next day, which is in 'true' WL:
viewtopic.php?f=4&t=32500&p=298765#p298765
There it becomes obvious that in the blue wing of H-alpha there is no granulation, that becomes visible only in WL!

For quite some time I was wondering if the 'granulation' I was getting was true or just processing artifact in the blue wing of H-alpha and at the end (don't know why) I ended up with the conclusion that this is granulation... Perhaps because this was my wish... ;-) I was wrong!

And many thanks for revealing the problem!

It is the convolution of ImPPG that creates these artificial 'granules' that I have seen also in pure H-alpha some times, especially at the limb around prominence.

Below I uploaded the 'non-Barlow' unprocessed image and the same image just slightly improved through the B&W levels in Photoshop, with no ImPPG process. I think as you noted, the absence of granules as we know them in WL is obvious.

Sun_17_15_22_unprocessed.jpg (151.15 KiB) Viewed 365 times

Sun_17_15_22_just level improvement.jpg (197.17 KiB) Viewed 365 times

Thanks once more for your remark!
Best wishes,
Alexandros