NGC7023 - Iris Nebula

Wow Anne @annehouw,

That is a superb Iris Nebula 😉

Can you share more about the optics? A F/D 3.0 R.C. telescope ?

Thanks for sharing the processing details.

Cheers,

Mabula

Hi Mabula,

Thanks for the wow 😀 

The telescope is a so-called "Hypergraph", made by Philipp Keller in Germany.  It is a corrected RC, meaning that it has correctors in the prime and cassegrain focus to provide for a flat surface over medium format. Using the secondary mirror it is a F/9 system, but replacing the secondary mirror with a lens corrector gives F/3 (camera in the front like with e.g. a Schmidt telescope). Actually it is a F/2.9 system, but I put a 3D printed diafragma in front of the primary mirror as I get cleaner stars that way (turned edge effect).  A mirror scope this fast is very finicky to tune. Tolerances are small. I am still in the process of re-tuning it. I had to crop the image because there is still astigmatism due to the fact that I changed the distance between the primary and secondary. Tolerance is 0,5mm.... I can spend a lot of time doing this without ever taking a pretty picture, but with no moon I also want get something nice to look at and that is  how the image of the Iris Nebula came to be. The stars could be better because the resulting image is a combination of various collimation and primary-secondary distance images. 

15 hours at F/3 is a brute force attack to overcome light pollution. The milky way is only visible with averted vision over here. So, two months to make one image  🤣 

Regards,

Anne

Posted by: Annehouw

Hi Mabula,

Thanks for the wow 😀 

The telescope is a so-called "Hypergraph", made by Philipp Keller in Germany.  It is a corrected RC, meaning that it has correctors in the prime and cassegrain focus to provide for a flat surface over medium format. Using the secondary mirror it is a F/9 system, but replacing the secondary mirror with a lens corrector gives F/3 (camera in the front like with e.g. a Schmidt telescope). Actually it is a F/2.9 system, but I put a 3D printed diafragma in front of the primary mirror as I get cleaner stars that way (turned edge effect).  A mirror scope this fast is very finicky to tune. Tolerances are small. I am still in the process of re-tuning it. I had to crop the image because there is still astigmatism due to the fact that I changed the distance between the primary and secondary. Tolerance is 0,5mm.... I can spend a lot of time doing this without ever taking a pretty picture, but with no moon I also want get something nice to look at and that is  how the image of the Iris Nebula came to be. The stars could be better because the resulting image is a combination of various collimation and primary-secondary distance images. 

15 hours at F/3 is a brute force attack to overcome light pollution. The milky way is only visible with averted vision over here. So, two months to make one image  🤣 

 

Regards,

Anne

 

Hi Anne @annehouw,

Thank you for sharing the details about the optics, that's impressive 😉

Mabula

Beautiful picture!  I could use some coaching if you get some free time to answer some questions.

I have been working on this target the last few weeks.  I am really curious what the image looked like coming out of APP before you tweaked it in PS.  I am not attaining the same quality as other images I have seen despite having good acquisition time.  I am trying a reprocessing APP with your cited adjustments.  I guess I am just curious if I need more practice in processing or if I am having optical/camera issues.  Linked my image below. I took another 5 hours last night without the Nebula filter and did 3 minute subs instead of 5 minute as I did in the linked image.

https://telescopius.com/pictures/view/39099/deep_sky/by-logan_m

Hello strandon,

Happy to shed some light on this. This subject has some challenges: A reflection nebula brightly lit in a very dark cocoon of dust.

As per your request, here the image out of APP (with a DPP of 20% background setting). You can see that all elements are already there.

The first issue is to make sure the core does not burn out. Make sure that your sub exposures are short enough so that only the central star is saturated, not the reflection nebula. 

Second: to get good data on the dust envelope, you need a lot of integration time and preferably dark skies. I do not have very good dark skies (orange zone), but compensated a bit for that by exposing for 15 hours at F/3! That is a lot of light gathered.

In processing out of APP you can do a number of things: Develop for the core and the dust (by using the highlight sliders) or develop for the core and the dust separately. A low DDP level for the core and a high DDP level for th dust. Combine in Photoshop or some other program. 

I did not use any nebula filter, because it takes away part of the light. Color pollution can be handled quite well with the "remove light pollution tool" in APP.

I hope this helps?

Looking at your picture, I can see that you start to capture the dust, but you just need more hours of exposure.