Which ccd ?

[ollypenrice]

39 minutes ago, Big Bang! said:

Well, Per

 

That is a seriously good colour photograph with great depth to it.  And I know I won't be satisfied until I can achieve close to that standard myself - which means lots of learning and hard work.  Which is the more important piece of kit, is it the camera or the optics?

Very inspiring indeed.

 

Gus 

In my view the priority order is mount-camera-optics. The mount doesn't need to out-perform the rest by a huge amount but if it won't track to meet your needs then it will stop the rest from performing. I put camera next because no great changes have been made in optics over the last twenty years but amateur astrophotos have improved out of recognition - because of the cameras.

How good do your optics need to be? For narrowband imaging they may not need to be all that great in terms of colour correction. But the moment you want to shoot in LRGB, broadband, then they suddenly do need to be good. Per's colour image (excellent) is a narrowband false colour image and has not tested his optics to the full. However, his telescope could also have taken a natural colour or HaOIII LRGB Eagle very successfully as well. If you really want to test the optics of a telescope then you need to see a broadband image taken with it. I use a TEC 140 like Per's (in fact they live about twenty metres apart from each other!) and the image I use to demonstrate the quality of the Tec's optics is this one: 

These are a from a stack of 10 minute luminance subs (so broadband) and the image on the right is a pure log stretch of the linear data on the left. Alnitak has remained cleanly split as a double star. A budget chinese telescope could probably achieve this in narrowband but certainly not in broadband. Alnitak in refractors soon looks like a huge saturated blob in lesser optics. The final image came out like this.

So beware when looking at images, particularly from refractors: only broadband will really show what the lens can or can't do. The other issue is the size of the flat field but, as Per said, nobody makes an amateur CCD chip big enough to trouble the TEC, or the Tak FSQ106 - or, indeed a few other scopes.

Olly

[perfrej]

And the LRGB one is full bandwidth with the same scope, same camera and same brand filters.

 

I agree that mount comes first, then camer then optics, but the latter two are much closer together.

 

/p

 

 

[Big Bang!]

OK,

Well, I have a 10 Micron mount, so that is an excellent start.  I have been using an RC250TT for the last year; I should be getting much better from it than I am.  There is an issue somewhere.  I have collimated the darn thing about 20 times over the last two months but I cannot get consistent results.  If something is moving I cannot find it.  The problem seems to show itself after changing filters (Luminance would come out perfect, Red would give me oval stars) and I originally thought that might be the problem - I am informed it won't be.  Anyhow, it has driven me to such frustration that I felt I deserved a second OTA and have just taken delivery of an Esprit 120ED Pro.  (I wanted a TEC 140 but just couldn't reach that far.)  The reviews of the 120ED are very good and I judged it to be the best compromise I could afford.  I haven't had first light yet - I am having one last go at the RC before I swap over the OTAs.  If the issue follows me then I will know it is not the OTA. Seriously, I would pay somebody to show me where I am going wrong - I must be getting something wrong that I don't understand.  After a total outlay of about £15k it is somewhat gut wrenching.  Having said that, the images you guys post here are an absolute inspiration.

 

Camera: I have an ATIK One 9 with an internal wheel, broadband only at the moment.  Don't see why that should be causing a problem but the results I see you guys getting with the QSI range has got my attention. Trouble is, £3000 is hard to find at the moment.

 

Gus

[ChrisLX200]

The Esprit120 is a good OTA, and will be stiffer than than the RC250TT (and shorter f/l of course which will make it more forgiving of small errors). Having said that I know you would want to resolve the issues with your RC. The way it models on the 10-Micron should offer some clue - what sort of RMS pointing error does it produce when creating a mount model with the RC loaded?

ChrisH

[ollypenrice]

I keep away from these 'difficult' optical systems because, as a provider, I see them come and go. When they work they are great. If your hobby is making things work, then great. If your job is offering an astrophotographic system which works - right now, tonight, all night - then not great!!

Refractors...

lly

[ChrisLX200]

I have to agree with Olly here, when I look at the raw output using my ODK12 compared to the 5" refractor well, there's little comparison. I get no reject subs with the refractor and neither do I get problems that result in wasted imaging time which I've certainly had with the ODK12. There are reasons for that and I hope most of my issues with the ODK12 are resolved, but some - like the time it takes to simply get it up and running - are just not going to go away. In hindsight a 180mm refractor would have been a better choice for the tasks I expected to do with the ODK12.

ChrisH