Advice for a couple of things.

[Rustang]

Hey, I know the info is probably out there in a round about way and you have probably gone over this with many others, time and time again but I promise Ive looked and I'm not intentionally trying to be lazy but I really struggle with understanding everything so I would like some clear, precise advice to spend my money wisely. I know where I would like to be but never and still dont fully undertand the fundamentals of whats going to get me there. So I live in the UK, Hertfordshire, my current set up: Sky-watcher EQ5 pro mount, Sky watcher 130pds scope (130mm f5 650mm focal length) Nikon D750 DSLR. I started imaging at the beginning of last year, in regards to the Orion nebula and Andromeda, I'm happy with my first results. I'm also fairly pleased with my first dumbbell nebula image. Ive been away from it for a while, busy with house move etc but I'm starting to look at over coming the issues Ive found so far and also where I want to go from here. Firstly like many, light pollution as I live in a town. I have tried using an IDAS LPS_P2 filter that has made a small difference. Even with a 130mm f5 scope, light/data gathering is limited with obviously the size of aperture although not that bad but also the exposure time allowed due to light pollution. I would say i sit comfortably around 1min to 1min 30 second exposure time before things get to bright. I struggle to get data for the Horsehead nebula and I thought the great American nebula was big and bright but all i get after a few i min exposures is a very faint, red hint of whats there. So at the moment I'm stuck with Orion and Andromeda in regards to their size and brightness for what my equipment can capture fairly well, beyond that it becomes a struggle. Secondly my focal length isant great for those objects further away, the Dumbbell nebula is stunning but very small, when my image is cropped it loses sharpness and detail to much. This brings me onto where do I want to go. Firstly I need to gather more data/ light, how can I do this? (with out finding a darker area) Change camera? Filter? scope? I'm stuck with where I live so i will have to deal with it, I know it can be done. Secondly I would like to bring those further away objects closer, I have come across so many stunning images that appear to be taken on small refractors say 70-80mm that are sharp, detailed cropped images of objects again such as the dumbbell nebula so how are people managing this with a small aperture and focal length? Is a long focal length really key for capturing objects further away or is it the quality of the scope etc. With my limited knowledge and thinking, if i ask myself the question what do i need to gather more light/data and capture far away objects I need to look at a really big refactor, wide aperture and long focal length. That will cost a fortune and I'm pretty sure that's not the really the case. Please help!? Again I'm not being lazy, i just easily get myself confused and frustrated trying to read whats on the web. I would like to keep my set up fairly simple aswell so if to solve my issues I need a ton of equipment then I'm going to struggle so with that said i would ideally like to keep my mount and camera set up so more looking at changing scope, filters etc but open to consider all options. Any advice will help work out if I need to work out if its my approached and combined lack of experience that i need to work on or change some equipment.

 

Regards

 

Russ

Edited June 17, 2020 by Rustang

[Dr Strange]

Russ-

You don't mention it so the question comes to mind... How many exposures are you taking and are you stacking them? If it is just one 1 minute 30 then you are not gathering enough data. You need to try taking several exposures then stack them together to build a "master" image. And you need to work with the completed stack image to bring out the details. PixInsight is a program to use to do that though there are others. There are also many tutorials on how to use it as well as a book by Keller teaching you step by step. Other people use Deep Sky Stacker to stack the exposures together then Photoshop. PixInsight is the less expensive option though. 

[rickwayne]

I second that -- total integration time is your friend for deep sky objects. In heavy light pollution, you may need to string together several nights' imaging on one object to get the results you desire.

More aperture per se will not help -- it is the focal ratio, not the width of the objective, that matters for light-gathering. That's not intuitively obvious but if you imagine two 130mm mirrors, one with a focal length of 500mm and one with a focal length of 2600mm, the former is curvier and is concentrating all its light on a small area, whilst the latter is flatter so the light is spread out more, hence dimmer. As an objective gets bigger, its curvature must be more and more extreme to achieve the same focal length, and it's harder and harder to avoid crippling levels of aberration. (In fact it's harder and harder to achieve the same focal ratio.) F/5 is already reasonably fast.

PixInsight is the "big gun" of astro image processing; personally I favor Astro Pixel Processor, which is a tad cheaper and a ton easier to use, so I recommend it to people early on their learning curve.

Chances are really good that the images you see of smaller objects with short-focal-length optics are captured using a dedicated astro camera. Those tend -- tend -- to have smaller sensors with finer pixel pitches, so when you blow up the image obtained with one you are magnifying a smaller swathe of the sky. The attached image isn't the best comparison I've seen, but it was easy to find :-).

For example, my 16 megapixel APS-C Pentax DSLR would frame the moon in the example below with plenty of room around it. My 20-megapixel 1" ASI 183MM would crop it much more tightly, and when you blew the two images up to the same pixels-per-inch level, the features on the moon would be much, much larger with the 183.

If you haven't already picked up a copy of Making Every Photon Count or The Deep-Sky Imaging Primer, I highly recommend that you do so. The latter was really transformational for me.

Edited June 17, 2020 by rickwayne

[rickwayne]

Oh, I forgot to mention that the North America Nebula emits light primarily at the hydrogen-alpha wavelength, unlike Orion or Andromeda. H-alpha is a deep red, and the IR cut filters necessary for general-purpose cameras usually are broad enough to significantly affect H-alpha light. When you read that someone had their DSLR "astro modded", that's what they mean -- removing the IR cut filter. So the NA Neb is going to be dimmer to start with for you. Orion has a lot of other wavelengths going on, and shines by reflected starlight as well as by emission. Andromeda, of course, is a broadband source.

To be clearer, when folks post stunning images of small objects with small scopes, they are usually done with hours and hours of total integration time -- hundreds of sub-exposures stacked. They use high-end mounts with autoguiding to enable long exposures, if their light-pollution levels permit.

Edited June 17, 2020 by rickwayne

[Rustang]

Thanks for your time in replying guys and for the info. I forgot to say I do come at this with some knowledge, and I do take as many exposures and subs as I can ( normally 1min to 1min 30) but not as many as I should. For my best Orion and Andromeda images from what I remember was around 2hrs worth with the flats, bias dark's etc. I definitely need to improve on what I'm doing and I know I can improve its just now gaining the etc info to do so. All the info on what certain objects give off and how to capture this has been a slow sinking in process but I'm getting there. I already know that I should look to get a crop sensor camera which will get me in closer, I may look to get something that has been astro modified as you say when the time comes to get a crop sensor and this will also improve somethings. I know you need to spend well in this hobby so I just dont want to keep buying lots, I want to buy well and little even if it costs more. I like my set up, and i guess i need to keep going with it a little longer before changing scope etc but I'm certainly happy to look at a crop sensor camera right now because as mentioned that will get me in a little closer. I was using deep sky stacker which again I need to learn better but when ready I will look at PixInsight. I've been having a nose around the internet as I didn't want all of you to do the hard work and looking at some of the nicer 80mm 480mm refractors, its surprising to see from looking at astronomy tools field of view calculator, that with a crop sensor camera, it will get me the same field of view I have with my current setup! Something to think about.

[rickwayne]

One reason I chose the 183 when I had Christmas money to spend was that its sensor is so much smaller than my Pentax. So now I have the option of widefield with the DSLR, or somewhat closer-up with the 1"-sensor camera. That said, I don't think I've hung the Pentax on the scope since I got the 183 two years ago!

[Chefgage]

You do not mention what you are using to process the stacked images. Are you using Photoshop, gimp etc??

[Rustang]

Photoshop, maybe a little bit of light room for colour which I know is not correct in my images but I'm not to worried about that for now. I think there is just to much to learn for my poor little brain and I struggle to pick out whats more important to start with and try and over come issues in baby steps! This forum is awesome but alot goes straight over my head because the lingo isn't written in dumb dumb language, to many  abbreviations etc I just cant keep up! There's mods, tips, equipment ideas that go on and on and on that to try and work out whats best, makes it all really difficult which is why I guess for someone like me you just keep asking the same questions others have asked because trying to pick out information from some threads and the internet can, hand on heart, be really difficult! This hobby for someone with my very slow understanding is not the best to tackle but I'm not giving up! I thought just normal photography when I first started was hard to get my head around but this, this is on a very different level of complexity! Its very easy to try and take on everything at once but also can be difficult to find the most important but simple steps to start with that make the biggest difference and go from there.

Edited June 18, 2020 by Rustang