First images in Ha

[Ric]

Hi all, here are my first images from tonight in Ha using the Astronomiks 13nm filter and the DSI II Pro with a f/3.3 focal reducer.

The Eagle Nebula was a combination of 75 images @ 21.2 seconds each and the Eta Carina Nebula was a combination of 100 images @ 8 seconds each.

Minimal processing was done in Maxim and darks have been subtracted. I am quite happy with the first results allthough there is still a lot more to do.


Cheers :)

[ballaratdragons]

Ric,

The nebula has come up beautiful in both images :thumbsup:
There is an enormous amount of detail!!!!!

Do you have an IR/UV Filter to kill the blobby stars? Would be nice to see the result using both the HA and IR/UV filters.

Good stuff though :)

[monoxide]

very nice!
lots of detail in both

[iceman]

Nice work Ric, I love h-a shots. Will you combine some RGB data with them?

[Ric]

Hi all and thanks for the comments.

Ken, I didn't use the IR/UV filter with these images, I was reading some info on the net that suggested it was not needed but on reflection I will give it a try to reduce the blobbiness.

Tj, thanks for the comments.

Mike, last night was a quick test to get familiar with the filter and how the image looked through the DSI II. I will definitely be re-imaging in RGB as well.

Cheers all

[Garyh]

good going Ric!! :thumbsup:
lots of detail showing in the Ha!
I notice some aberrations in one corner of your images?
Would that be from the focal reducer?
shall be great when you put it all together as a HaRGB.
cheers

[Ric]

Hi Gary, thanks for the comments. I'm not sure about the aberrations, they could be from my processing which is still a bit limited in knowledge at the moment.

Cheers

[leon]

Ric, i love those images, i'm a bit partial to greyscale images as well, great work

Leon

[jase]

Good start Ric. Well done. I came across some DSI tips on the net once. It was recommended setting the gain to 0%. Apparently this significantly reduces star bloat. It wasn't related to IR leak at all. You may also need to consider your sampling to ensure your getting a suitable arcsec/pixel coverage for DSOs with this camera.

[jase]

Also note your focus. A 12" SCT operating at F/3.3 has a extremely short critical focus zone of 23.9 microns. So you need to get within this zone for the field to look sharp. We are talking a distance of 0.0239 mm here! This is not impossible but may take some time to get right. Obviously, the further out of this zone, the larger your stars will look.

When you put this in perspective, your first results are a pretty fine effort.

[Ric]

Thanks Leon and Jase.

Jase, the gain is usually around 46 to 50 so I shall experiment with that and see what happens, also the focal reducer has extenders which allow to image at f/3.3, f/5.0 or f/6.3 so I'll investigate that area as well. I assume imaging at a higher f value would increase the critical focus zone.

Thanks for the advice, and now I have a little project to work on, I see the clouds are rolling in on cue.
:cloudy:

Cheers

[jase]

12" SCT @ F/5 has a CFZ of 55microns.
12" SCT @ F/6.3 has a CFZ of 87microns.

Of course as you change your F ratio, your focal length and in turn your FOV also changes.

This is the DSI gain reference I mentioned - I found it again! http://www.hamiltonastronomy.com/ARTICLES/High_Gain_vs_Zero_Gain_DSI.pdf

[Ric]

Many thanks Jase, I've downloaded the article for printing tomorrow. I've had a good read of it and found it to be very interesting and I am keen to test it out.

Cheers

[ballaratdragons]

A little 'Bird' sat next to me at camp and showed me how to use 'Gain'.

The tip: 0%

Since then I always use 0% gain. I have tested it a few times since, and the results are terrible when I turn gain up. The images get very grainy and noisy, and Stars supernova!

So ever since I was shown, I always image with Zero gain :thumbsup:

[Ric]

I shall not forget this tip that for sure. I've always let the auto exposure set it for me. It is written into my hardbound Astro notebook and highlighted, I always keep it with my gear so I cant miss it :)

Now it looks clouded for the weekend so I cant test it out. Don't you just hate that :lol:

Cheers

[strongmanmike]

Well Ric, you too have found the power of the Ha filter :thumbsup:

Nice images mate, I have a Starlightxpress MX716 which is similar to the DSI ProII I think (?) and it was a great camera to use with my 12" SCT and an F3.3 reducer when I first started imaging.

Nice work

Mike

[Bassnut]

The Nebulae come out very nicely Ric, stars need work.

Cheers

[Ric]

Thanks Mike & Fred.

Fred, I totally agree with you regarding the stars I have received a few good tips and read up on some info on focussing techniques so hopefully I will solve that problem.

Cheers

[Dr Nick]

Wonderfull images ! ;)

I have to thank everyone else as well, i have had trounble with star-bloat and you may have answered my prayers!

Reading more about gain now...


Ken, that "Bird" is a very smart man, I would have no chance of getting images of the quality I do without him, he has been a great help to me.

[dcalleja]

Ric
Great images. I just got the same Ha filter so I'll have to try it out. Some really good advice in this thread for us DSI users too. Its terrific to get this level of help - I'd spend hours experimenting otherwise.

[Ric]

Thanks Nick & Dan, I'm glad that this has helped out the both of you as well. It is a testament to the great spirit of this forum.

I managed another imaging run on M16 again last night. This is a combination of 50 images @ 21.2 seconds with the DSI II Pro and the f/3.3 focal reducer. The gain was set to 0 this time and darks were subtracted.

The stars have now sharpened considerably which is very pleasing however I now have noticed that there are what looks like record player grooves appearing, especially to the right of the nebula.

I'm not sure what has caused it as it was not present in the preview when taking the subs only after combining. I have not encountered this before so I'm a bit clueless as to what it is. A few ideas that have sprung to mind is that the image was taken very close to a 98% Moon so that might have had an effect or now that the gain is at 0 should I have adjusted the offset as well which was set to 50.

All thoughts and comments appreciated.

Cheers all :)

[jase]

Hi Ric,
I’ve seen the “record groove” effect before when using MaximDL’s flatten background function. I’m not sure if you used this at all, but its caused by insufficient map points to measure the background.

Are you saying this effect is not in your subs (or at least a few of them). I can’t imagine the problem being related to the moon considering it emits strongly in the blue wavelengths which is being blocked by the Ha filter.

Perhaps try a different combine method. It also looks like you need to stretch your data more as its black clipped.

Just a tip: in MaximDL, open up all your subs in Maxim. Select one of the images and perform a screen stretch to the desired levels (that most details reasonably easily). Then from the menu View | Equalise screen stretch. This will stretch all you images to the same screen stretch value as the reference image. Then select View | Animate. Select all images for animation and play them (blink them). Have a close look at each sub as they pass. The animation will loop. You may find a few offending images that you dont want to include in the combine function. Simply take note of the offending filename and drop it when you do the combine.

[Ric]

Hi Jase, thanks for the tips I shall give that a go. It certainly looks a lot darker on the desktop CRT monitor, this morning it was processed and posted on the laptop with a LCD display which fools me into thinking the images are a lot brighter.

Cheers

[jase]

Hi Ric,
This has just “clicked”. If you’re indicating the effect does not occur in any of your subs, it will be the drizzle (field derotation function) causing the problem. The subs may not be successfully derotated as they are stacked or they are successfully being derotated, but there are differences between you subs (other than rotation). I suspect the latter considering the stars are derotated. I would check your subs. I don’t believe there is any correlation between the gain setting and drizzle process.

[Ric]

Hi Jase I did use the "Drizzle" function rather than the "Deep Sky". I find that the Deep Sky mode gives a lot more star trailing that is almost impossible to remove in the Alt/Az mode.

Cheers

[skeltz]

Nice images ric pretty good for such short exposures to!!
good job mate...

[Ric]

Thanks Skelty

Cheers