Herzy

1 hour ago, Nigel G said:

I tried taking subs without the CLS filter,  the difference is massive,  now I wouldn't use the camera without it unless I was at a proper dark spot. 

Once modified, without a filter it will pick up far more red than wanted, sodium and most artificial light. This has to be blocked. 

A professionally modified camera should have a replacement infared filter installed to block the unwanted. 

That's a good point. I noticed that my pictures are very red. Not just the DSO's, the actual background is much more red then before. I think you're right. I'll be ordering an IDAS LPS filter to see how that helps.

The difference might be the CLS filter. I stretched my 3 min sub and I can just BARELY see the horse. Really it just looks like a dark patch because you can't see any features. All of my 3m subs are bright orange.

Nige, I'm very interested about your horse head nebula. Last night I couldn't see even the slightest trace of it in 3 min subs. I don't understand how you got that much detail with such short integrations. Would you mind posting a single picture for me to compare to?

Thanks, 

Hayden

22 hours ago, Nigel G said:

A quick adjustment to the shadows,  I don't know if I've over done it or not cos I can't find my reading glasses atm.? might be room for more. 

I will reprocess again soon, got the Crescent next. 

Nige.

edit, found glasses, don't like.

You seem to have a lot of patterned noise. Are you dithering? If you look closely it looks like there is a checkered pattern to the noise. That may be a result of drifting of the object in your FOV.

I have a modified T3i shipping to me right now!  can't wait to try it out at a dark site.

12 hours ago, alacant said:

Hi. Good suggestions but I think you're gonna have to wait until next week for the nebulae. HTH.

You're right. The moon was way to bright to do anything, so I packed up. 

Does anyone have any ideas of what I could image tonight? I want to image away from the horizons and I don't know of any bright nebula that I haven't already done. I've done the Eastern and Western veil, the Bubble nebula (although this could use 10x the integration that I have right now), the crescent nebula (this could use a lot more integration as well) and the Wizard nebula. Any ideas? Andromeda galaxy might be an option, although I'm not sure if 4 hours would do it justice. It might need far longer integrations.

You should try putting a blanket over the setup while taking flats. There is probably a lot of stray light getting in that will effect the accuracy of the flats.

This was 76 minutes from an AT72ED mounted on a SLT mount. It was 15 second exposures and my computer couldn't handle the amount of files I took in RAW form, so I had to use JPEG. This was just mainly a test with my alt/az while my EQ was packed away ready to move houses. I had to crop in really bad because my AT72ED is giving oblong stars in the corner. Speaking of the AT72ED, the CA is really easily corrected. I used a few methods to remove it on the bright star in the middle and it was gone in seconds. It did leave a few aberrations that I had to blur out, but that was still really easy to fix.

Overall, I've found imaging with an altaz MUCH easier. Other than hundreds of files that I have to work with, it works great for short exposures. I'm worried about imaging really faint objects, however, because the read noise will probably overwhelm the object signal. It isn't a beautiful image, but It's not too bad.CC is welcome!

16 minutes ago, parallaxerr said:

I DO already have an Alt/Az - the Nexstar SE. That's the point, I'm just having a go with what I've got!

That's what I suspected. Sorry, misread your post. Good luck! I'll go ahead and delete my post.

BTW, how has that mount been going for you? Is it stable? My old mount would always shake for some reason. That's not something inherent to alt/az, just something my specific mount suffered from.

*deleted* 

I misread the post and thought he hadn't bought anything yet. I can't figure out how to delete the post so just ignore this.

Both images are slightly out of focus. Other than that, it's a good image.

Light pollution is just awful. That picture of the light pollution is so ugly yet that is the case for most of the population.

Did you have gradients to deal with? I had trouble processing this target because I couldn't differentiate between noise and small gas structure. There are so many small gas clouds in the galaxy that look like noise. I would have gradients with heavy noise on one side and smooth on the other so I couldn't get anything out of it.

8 minutes ago, SteveNickolls said:

Hi Herzy,

Thanks for this post. I sometimes muse over getting a 'better' telescope to replace my achromat 102mm Startravel if just to remove the purple halo around brighter stars in my images. StarTools does a good job of altering the colour so my discontent has not been sufficient to make me move towards a replacement. I will be interested then to see how your 72mm ED doublet performs for you and good look with your future imaging. Alt-Az gear generally has the edge being lighter and more transportable.

Cheers,
Steve

 

I haven't been able to test out star tools yet because our family is moving houses and everything is packed up. Is it easy to remove halos? The AT72ED gives slight blue halos on bright stars (generally only 3-4 pixels wide) that might annoy me if I was shooting something like the Pleiades with lots of bright stars. Could you go into more detail on how you manage to tame the halos? 

I recently bought an AT72ED. It fits in my SLT mount holster and is pretty light so it should do well. I have an EQ mount, but the thing is so heavy and I get fed up with taking it out to a dark site (I have to separate it into many pieces and wrap them all in blankets), so being able to use the alt/az, which is much lighter, will be nice. 

As for CA on the scope, it's not that bad. It's an ED doublet refractor (not fully apochromatic). I would highly recommend this to anyone wanting to get into refractor astrophotography on an altaz mount.

---

Just a short review incase someone reading this thread was thinking about getting a refractor.

Is your camera modified? I'm really surprised you pulled out that much data from such short integrations. That's making me think I should give it a go too. 

Beautiful image, Ian. Love the detail in the edges of the Galaxy! Do you have the stack? Ide like to mess with it because this is something I want to go for soon and some processing practice would be great.

I always have trouble with color in Startools. I usually do color balancing in another software and do the rest in Startools.

1 hour ago, SteveNickolls said:

Wow, I could only dream of being able to spend so long on one target. They must have excellent conditions (lucky people).

Regards,
Steve

IKR! The craziest part is that all of that data was from a dark site. I'm not sure how close they live to the dark site, but for me that is an hour and a half drive... That would take many many months for me to get data like that.

I found a link to the thread.

It was 130 hours and the image is just beautiful. I'm not sure I can share it because it's on another site completely. Do you guys know if that's against the rules?

Nigel,

That object is really really faint. I can almost see the nebula coming out in only two hours. May I ask why you're going for such faint targets though? I saw a thread on a different forum where they had nearly 100 hours (a hardcore imager) on this target worth of 30m subs. That should tell you just how faint this is. Why not go for something like the veil or something else much brighter?

4 hours ago, Nigel G said:

Exposure times, now I've been told and read in books that ( example ) 120 x 30sec exposures is equal to say 6 x 10min exposures and that you need 2 hours of data for dso's. 

After 9 months of experimenting I have decided this is not strictly true. I believe longer exposures are much better than shorter for finding detail and light gathering but more frames is better for noise elimination .

I have taken images of Andromeda with as little as 15 minutes of data up to  2 hours of data with not much difference in the final images. The longer the exposure times the more detail captured regardless of total time.

My latest image, ngc 6543 , firstly I stacked about 45 minutes  of 30 to 45 second exposures,  second time around I stacked 2 hours 20 minutes of 30 to 45 second exposures,  both with darks and bias. Both lack the emissions of the cats eye, the second image has a touch more detail but was far better to work with in StarTools due to much less noise.  The cats eye is a difficult dso to capture and I'm not disappointed with the result although it lacks most of the nebula.

I think my test images of ngc 7000 showed the power of the longer exp times. Our greatest barrier is the exposure time limits of the Alt-Az mount.

Having said that there are plenty of dso's as we have seen in this thread where short exposures are all you need,  it's the fainter objects that require the long exp.

I have posted both images of ngc 6543 so they can be compared.   

First the 45 minute,  second the 2h 20 minutes. 

There are 2 other dso's within the image which are more apparent in the second image also there is a wiff more emissions  .  The second being far easier to process with far less noise reduction needed, I think due to there being 238 frames. Although noise is present in no 2 thats because I'm trying to extract emissions. 

I'm sure someone else with better processing skills could get more out of it if I knew how to upload a fits image. 

With 2 hours of 600s I believe the nebula would be greatly improved,  I might be wrong.

Cheers 

Nige.

 

 

I remember posting a thread concerning one of my pictures and the lack of detail even though I integrated 4 hours. The object was very faint, but I thought my integration should've showed more detail than it did. 

I was informed by wimvb that my exposures (60s) weren't long enough to do the object justice. He said that the reasoning for longer exposures making a difference is the amount of signal vs the amount of noise.

If I recall correctly, he gave this example:

Consider a REALLY faint object. It gives you roughly 1 photon (1 signal electron) per minute. At the same time, your cameras read noise will contribute 1 electron. It doesn't matter how many frames you take, your signal will remain 1 because stacking doesn't boost signal, it justs removes noise. SNR = 1.

Now consider you are imaging that same object with 10 minute exposures. Your capturing 10 signal electrons/photons and 1 read noise electron. SNR = 10.

Longer exposures give you more signal, and more of them give you less noise. The combination of long exposures and lots of them give you a really good SNR.

So in that regard, an alt/az mount user is limited. They can always remove more noise, but can never boost their signal much without field rotation. That doesn't mean they can't produce wonderful images - they certainly can. They are just limited to bright-ish targets. 

3 hours ago, Filroden said:

Another great effort. Thank you for taking the time to process it. I'm glad you had some fun with it.

I've had a second try, this time managing to use Deconvolution - probably the hardest module I've found in Pixinsight so far. I've also reduces the stars and toned back the red. I'm not sure this is better as I've completely killed the background but I can see more of the fainter nebula.

BTW, does anyone else think this nebula looks like a) a baby with its head at the lower end of the photo or Elvis, with his quiff to the top?

For interest, I've also included two pictures of my current set up position (one with and without flash). I'm having to use the fence to block the light right next to the garden. There is one at the end of the garden too. Pretty amazing that night seem to affect my images with little discernible pollution and a rough measure of SQM at 20.4. If I also stand by the fence I can just trace the Milky Way overhead.

You could probably get an old cardboard box and flatten it out and tape it with a small frame to the fence to keep the scope hidden from the streetlight. The light is most likely spilling into your frames and causing nasty gradients. 

This will be especially apparent if the seeing isn't great (i.e. A lot of dust and fog in the air) the light will start lighting up the surrounding air near it and you will be within that area. 

Last night the skies were incredible. The light pollution took the night off for some reason. I don't even know how it's possible...

My single 2m subs of the crescent were showing more detail then 2hrs of it I took a month ago. Unfortunately, some clouds rolled in and I couldn't get anything worthwhile. Tonight is looking good. Anyone else go out last night?

8 hours ago, The Admiral said:

Unlike a finely tuned EQ mount, there are two main problems with the Alt-Az mount: field rotation and tracking performance. In order to minimize the manifestation of field rotation on one's images one needs to use short exposures, only a few tens of seconds, so a total exposure of 4 hours or more will produce hundreds of subs. Star streaking will be evident in a percentage of these subs, the more as the exposure time is increased (even if that time is acceptable from a field rotation point of view), and DSS will reject them, so the integrated exposure will be less than one might hope for. I think it's also true that the overall tracking performance of Alt-Az mounts is somewhat below that of the correctly adjusted EQ mount, so if one did embark on a long exposure session it would have to be done in a number of shorter bites with mount realignment in between.

I'm not saying that all this couldn't be done, but the reason I'm using Alt-Az imaging is that I have to set up the gear each time I use it so it needs to be simple and quick to set up (and I can't see the Pole star from my observing position). As Steve alluded to, this is because here in the UK the weather seems so unpredictable that often the decision to image is a last minute one. Personally, I'm not striving for salon-quality images, but just to reveal the glory of what I can only see as a grey smudge when viewed by eye. That is not to say of course, that I don't want the best output that I can achieve within the constraints imposed by this style of imaging. But one has to be realistic about the law of diminishing returns.

Don't forget also that much of the UK is blighted by light pollution, so that is yet another issue we have to contend with.

Ian

I see. Even though I work with an EQ mount, I still use 30s subs for the most part because my mount isn't the most reliable. I usually end up with like 500 images, which causes trouble for my computer when I try to stack. 

I see what your talking about though. I dealt with the same problems not very long ago. 

Just keep in mind the potential of your setup if you were to go for "hardcore imaging" of several hours. Although it'll be difficult, the results are rewarding.

---------------

Btw, Steve, those images of Andromeda are pretty awesome. I've heard it's bright, but is it an easy target? I've never imaged it before and I'm thinking of giving it a go.