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Last night I put the old Pentax 200mm F4.0 lens from around 1980 in front of the ASI1600mmp. Focusing was a bit tricky. I noticed a big difference between the focus points of the clear IR-cut filter that I normally use for focusing and the Baader Ha 7nm filter. They are described to be parfocal which they are not when you examine it in detail. I noticed that already last week with the 130/910 when I focused on Vega. I have to go deeper into that.

The image was made from 59 x 200s @ gain 139. Processing in APP and Photoshop. I wonder how the color data will look when I will hopefully shoot them the next days. I am afraid of heavy fringing because the old lens has no correction elements.




The old lens was able to reveal delicate. The starbursts maybe can be avoided with a stop-down ring but I do not own such a small one.

I invite you to take a walk in the full resolution version on Astrobin:

Fit to window:


Full size:


Have a nice weekend!

Pete

You da man, man. The tonal range and sharpness make this a really compelling image. I want to just keep looking and looking. I assume starnet went into to pot here?

Holy! That is impressive in full resolution! The M200/4 is quite terrible for CA, I guess the blue data will not be as sharp, but can you use Ha as luminance and treat CA in the other channels? If you want wide field with little CA the Samyang/Rokinon 135/2 does wonder. Extremely sharp and very little CA. Some people call it the Rokinon astrograph!

Keep posting your results, they are so impressive!

Great image, Pete. I don't mind the starbursts, even hubble gets them. I assume you used the lens wide open which should minimize them. Anyway, nice job!

Thank you three for the positive feedback!

The 200/4 is great, especially for narrowband images. If you like you can find another example from last night here Curly Veil Nebula Complex ( pete_xl ) - AstroBin

I shot at F5.6 and the starbursts are a bit bigger. But I like it :-)

I did not post it here because I am still uncertain if anybody feels disturbed because it is not full Pentax made.

The nights here are bright and short but we have a stable clear period. I want to grab OIII tonight and color tomorrow. Keep your fingers crossed....

Cheers and greetings,
Pete

Yeah Rick, starnet was in the pot again. In my workflow it is a game changer - another step up. It is simply not possible to get the very very very faint stuff up with the stars present. You get so many more degrees of freedom in processing when the stars are out of the way. I had felt I was already quite far with my Photoshop technique to take the stars to a separate layer but starnet is classes besser in every single image than I was with my best ones. If I knew how to donate money to the programmer I would spend him a beer abo for 2020. I can recommend it for everyone. In the moment you have elaborated a technique to get the stars onto a separate layer and a bit experience how to blend them in naturally so that you do not loose even the faintest star or background galaxy you have made 10 steps on the learning curve at once. The results will look classes better than what you knew before.

I use it on the well calibrated cautiously (pre-)stretched stacked image. In PS I put the stars layer above the starless one. Then I do a decent noise reduction on the starless and stretch it like hell. Then enhance the local contrast and sharpen the parts of the DSO that are worth it. The stars layer is blended in in "lighten" mode or "multiply negative" (I do not know if that is the correct name in the English PS version). The blending of the stars layer can be controlled nicely with a "levels" adjustment clipping mask above that layer.

None of my other workflows of the past years can beat that!

Keep posting Peter, it’s Pentax gear, I, for one, don’t mind seeing what my own M200 f4 is capable of.

David, I had the lens wide open in my first test and there were no starbursts visible. The lens was designed for full format. Now I have it an a small sensor. Maybe there is not a big difference under the night sky. I must test if there is really a degression in resolution between F5.6 and F4.0. But I loose myself in testing at the moment. How many of the rare clear nights can be spent for testing?!

Cheers
Pete

Ok, Keld, you said it! So sit down, lean back and enjoy what this old glass is capable to show (am totally "aus dem Häuschen", as we say here, which means something like going crazy from joy):



It is worth it to inspect the higher resolutions on Astrobin:

technical sheet:

fit window:

full resolution:

The image is made from 50 x 300s H-alpha and 38 x 300s OIII. I had planned to capture RGB for the stars tonight but clouds came up. So I let it be an HOO bicolor image. I could go quite deep and I'm happy that I managed to show the (upper) outer Ha shell in the image that is quite rare to see. For the stars I took the differences between the starless and the stary version of each filter as HOO layers and changed their weights until the stars looked a bit natural in color. Hope you like the result :-)

Under the balance: If the lens is focused separately for every channel it outperforms. I fear this is only possible with a mono cam or with RGB filters in front of the lense. I am glad I kept it in my cupboard where a (A) 135/3.5 and a (A) 28/2.8 are still waiting for a test.

All the best and greetings!

Pete

Hervorragend Peter!!!
Once I’ve finished my obsy on the garage, I’ll start putting money aside to a dedicated astrocamera - what you are doing is a huge inspiration, I simply have to go there as well
Actually, I’ll see if the money I save by not building an “on ground” observatory can cover the cost of an ASI1600MM Pro, just have to get i approved in the financial department

It's summertime here and that means darness falls much later and it is still quite hot well into the night. I won't be doing much now until late August or September. That gives me time to figure out the collimation on the RC telescope. I've done what i can do with a cheshire eyepiece and a straight laser but defucused disk is still a little offset. I would love the have a Howie Glatter focuser with the pattern projector but that has to wait awhile. I'm also trying to figure out the Stellarmate so that I can automate some of my tasks and hopefully get more accurate goto alignment. When it gets ust a little higher in the sky I want to image Albireo, a beautiful two-color binary pair, but other than that I'm mostly down until Autumn.

There certainly is in RGB but maybe not in narrowband. As for a RGB, apparently a Tiffen Haze 2 filter is effective at reducing the CA of this lens, which in my experience is excessive wide open (f/4) and just barely acceptable stopped down one stop (f/5.6). See here. I have yet to acquire such a filter and give it a try but I do intend to. They don't cost much.

As for stoppIng this lens down with an aperture, I use two step down rings that bring it from 52mm to 37mm final, which is f/5.4. You can buy sets of step-down and step-up rings quite inexpensively on Amazon. Note that the vignetting is somewhat worse when stopped down in this way.

What is starnet and how do I get it?

It is a neural-net program, written in Python, that processes 8-bit TIFFs to remove stars. It's pretty wild. I had a little trouble getting the prerequisites working on my Mac but basically you go here and follow the instructions. The trainings are a separate download, if you neglect those you'll get an obscure message about how it's unable to load its previous checkpoint or something like that.

It yields a version of your image with the nebulosity intact, but the stars missing. As Pete notes, you can then apply pretty vigorous modifications without worrying about bloated or blown-out stars.

If open the starless image in Photoshop as a layer above the original, you can temporarily set its blend mode (right-click on the layer) to "difference" and the stars will display all by themselves. Then you can use Photoshop's "stamp visible" command (on my Mac it's shift-option-command-E) to create a new layer with just the stars in it. Tuck that away at the bottom of the stack, set the starless layer back to "normal" blend mode, and go to town on the nebulosity. When you're done with that, do the same Stamp Visible trick to the enhanced starless image so you have an easily-portable capture of your manipulations. Put the star layer on top, perform any manipulations such as saturation enhancement or sharpening, Stamp Visible one more time. Put the starless Stamped Visible at the top of the stack, put the stars above that, set the blend mode on the stars to "Lighten". Pete's probably got the better technique for controller the starriness in the result; you could play with the star layer's opacity, or edit it with the Dust and Scratches filter if you prefer.

It occurs to me that we could probably do something clever with the "mask" image that starnet++ produces too.