Starting out in DSO astrophotography

[IDM]

Hi,

I currently have 2 scopes one  a Tal 100mm F10 Refractor and the second a Stella Lyra classical cassegrain (my new toy that I am still getting to grips with). I also have a Zwo ASI224MC camera. So clearly all these add up to planetary and lunar photography.  However, I have a bit of a yearning to start on the long and I suspect difficult road towards astrophotography of DSO's. From what I have read I would ideally need a fast F5 or 6 APO scope and a cooled camera maybe something like a Zwo ASI294MC pro (I don't think as a beginner I could go for a mono camera and filter wheel). My issue as I see it is that buying an APO scope and the Zwo camera is quite an outlay given I have little/no experience. I was therefore hoping someone could advise me on the best route in with potentially cheaper scope and camera. Though I don't want to buy something that becomes frustrating due to lack of its quality soon after purchase. I am very happy to buy secondhand. To me it feels wrong to spend a lot of money from the get-go without developing skills and competency along the journey. 

 

I should also add that I have an Ioptron IEQ30 go to mount, which I hope would/should be able to cope with a starter setup.

All thoughts recommendations and  experiences gratefully received.

Thanks,

Ian

[Clarkey]

If you want to keep you initial outlay low then a DSLR is a good start. A modified 600D can be picked up for a couple of hundred pounds second hand. If you get hooked you can always sell it on. As for scopes there are numerous options. A small ED doublet would probably be a good starting point, but a camera lens or small newtonian would also work. The obvious ones for the above are the SW ED72 / 80, Samyang 135mm and the 130 PDS. All of these have been shown to give good results on a budget. I am not an expert on the Ioptron mounts, but looking at the specifications yours would appear to fit the bill. As the mount is the most important part of AP, you are halfway there.

FWIW I started off 'just dabbling'. AP can be very addictive and very expensive - it is a slippery slope! I am now broke but happy😂

[MillHey Nebula]

Why not start your DSO journey by imaging galaxies?  Those such as M51 and M101 will fit quite nicely in your 100mm f10 / Zwo ASI224 field of view.  This will enable you to get up to speed with the image capture, stacking an processing techniques as these are quite differenet to lunar and planetary.  If from this, you do indeed get the DSO bug, then you could start the upgrade route with your camera.  Moving to something like a Hypercam 269 would give you a good increase in field of view.  It should be quite acceptable to go for a non-cooled version as modern CMOS cameras are pretty low noise and as long as you use a good set of calibration frames (darks, flats, dark flats) you should be able to start to move on to some of the smaller nebuale.  This camera would then still be very comaptible when you feel able to upgrade to a wider faster scope such as an 80mm f6.

 

Edited October 4, 2021 by MillHey Nebula

[vlaiv]

While purchasing suitable equipment is good way to go about it, why don't you start with what you have?

Get second hand DSLR and use your Classical Cassegrain. Is it 6" or 8" model? Maybe you already have DSLR?

These scopes have large corrected field and although they are "slow" at F/12 - they can be very nice imaging instruments if handled properly. Most people are worried about their "photographic speed", however - there is easy way to make them "faster".

Say you purchase 6000x4000px DSLR camera. If you bin x2 your data and accept 3000x2000 images - you'll get F/6 scope. If you bin x3 your data and accept 2000x1333 px images - you'll have effective F/4 scope.

[IDM]

22 minutes ago, MillHey Nebula said:

Why not start your DSO journey by imaging galaxies?  Those such as M51 and M101 will fit quite nicely in your 100mm f10 / Zwo ASI224 field of view. 

I really like the idea of trying with what I have. You can tell my lack of experience in that I didn't think this was possible!

 

16 minutes ago, vlaiv said:

While purchasing suitable equipment is good way to go about it, why don't you start with what you have?

Get second hand DSLR and use your Classical Cassegrain. Is it 6" or 8" model?

My Classical cassegrain is an 8 inch version though unfortunately I don't have a DSLR.

 

So it seems the best initial way is to try some galaxies so how I go. Then change the camera, either by finding a decent price second hand DSLR or potentially getting a dedicated astro-camera. 

[IDM]

22 minutes ago, vlaiv said:

Say you purchase 6000x4000px DSLR camera. If you bin x2 your data and accept 3000x2000 images - you'll get F/6 scope. If you bin x3 your data and accept 2000x1333 px images - you'll have effective F/4 scope.

I really need to get a good understanding of binning.

[Dazzyt66]

7 minutes ago, IDM said:

I really need to get a good understanding of binning.

I'm no photography expert and also new to AP but how I understand it is that binning reduces the size of your image (but improving noise levels) by 'combining' pixels. So basically is you start with an image (1x1 bin) and bin it by 50% (2x2 bin) you increase signal to noise ratio by 2 - I think! 🤣

I too don't like spending money if I don't need to (although it appears that AP can make you do this!) and have ditched imaging with scopes (for now) and am concentrating on DSLR/Lens AP. This can be REALLY cheap as you don't need a massive mount (although I have an HEQ5 already). In my case my kit is all used:

DSLR - Canon 1100d -£60 ebay. I paid for the astro mod which was £70ish

Lenses - I get these from ebay too. M42 lenses with adaptors are cheap. Dearest lens I have cost me £25. If you stick to prime lenses you can get some pretty decent images.

I did this one last night with a 200mm prime lens (£20). There are some used Canon 350D's on ebay at the moment for around £20 and 600d around £100

 

 

[vlaiv]

10 minutes ago, IDM said:

So it seems the best initial way is to try some galaxies so how I go. Then change the camera, either by finding a decent price second hand DSLR or potentially getting a dedicated astro-camera. 

I'm all for dedicated astro camera, and I think you should get that, but DSLR is really good way to get started and learn basics.

I started out with web camera, then moved onto planetary camera with which I did some DSO imaging. I was hooked fairly quickly so I moved onto cooled cameras.

9 minutes ago, IDM said:

I really need to get a good understanding of binning.

There is not much to it really. Speed of telescope is determined by two factors - one being aperture and another being pixel size - or more precisely - how much sky is covered by single pixel.

We say that 4" F/4 scope is faster than 4" F/5 scope simply because later has longer focal length and "more zoom" (although zoom is not correct term in this case) - meaning each pixel covers less sky than in case of F/4 scope with shorter FL.

Binning of pixels is just joining group of them to act as single pixel. You can think of it as being buckets left out in the rain. Single bucket will gather some rain water, but if you put 4 buckets next to each other (2x2) and measure amount of rain they collect - it will be x4 as much.

In the same way binned pixels gather x4 more photons (in case of 2x2 bin) than single pixel, making them more sensitive to light.

Downside of binning is that you loose resolution. In astro imaging, especially with DSO - resolution is in fact determined by other factors - like seeing, mount performance and so on. It is for this reason that you can safely afford to bin even 4x4 with your scope (being very long focal length scope).

As beginner, you want to be somewhere in range of 1.5-2"/px (each pixel covering 1.5 to 2 arc seconds of the sky). There is simple formula that determines how much sky is covered by each pixel - 206.3 * pixel_size / focal_length (pixel size in µm and focal length in mm).

If you take modern DSLR with 6000x4000 px resolution - its pixels are usually 3.8µm in size. With above formula for your scope, you'll get 206.3 * 3.8 / 2436 = ~0.32"/px. This is extremely high sampling rate (low number means small part of sky covered by single pixel) and you need to bin that considerably to get to above. With bin 4x4 you'll be at 0.32 x 4  = ~1.28. Still lower than I would like, but it will provide you with ok images.

This will give you image size of roughly 1500x1000 (a bit larger than ASI224 with ~1300x900).

If you add some sort of reducer - you'll get better working resolution, however these tend to be expensive. Maybe this one:

https://www.teleskop-express.de/shop/product_info.php/info/p8932_TS-Optics-Optics-2--CCD-Reducer-0-67x-for-RC---flatfield-telescopes-ab-F-8.html

[Jp114]

I have to say, although a DSLR is a good choice, if you're planning to use a laptop (perhaps for autoguiding) I'd be inclined to pick up a dedicated camera if possible - there are bargains available on used cameras.  

I moved from a Canon 7D to a used Atik 314L+ and the difference is night and day.  On the 7D, any stretching brought out loads of ugly green noise but the Atik 314L+ subs are really clean. 

[AstroMuni]

20 hours ago, IDM said:

I currently have 2 scopes one  a Tal 100mm F10 Refractor and the second a Stella Lyra classical cassegrain (my new toy that I am still getting to grips with). I also have a Zwo ASI224MC camera.

Hi Ian,

You already have the ASI224Mc and 2 decent scopes. My suggestion is have a go with that. I am new to AP as well and have a 130mm Celestron & ASI224mc and I have managed to capture a few DSOs (see my signature). Good luck

Depending on how accurate your mount is in tracking, you may need a better one. But try your existing mount before you buy.

[vlaiv]

11 minutes ago, AstroMuni said:

Hi Ian,

You already have the ASI224Mc and 2 decent scopes. My suggestion is have a go with that. I am new to AP as well and have a 130mm Celestron & ASI224mc and I have managed to capture a few DSOs (see my signature). Good luck

Depending on how accurate your mount is in tracking, you may need a better one. But try your existing mount before you buy.

That won't work well. ASI224 is very small sensor with small pixels and both scopes are long FL scopes.

Just to get an idea of what the FOV will look like - use astronomy.tools FOV calculator:

Yes - that is the heart of Orion's nebula M42 - only trapezium can be seen. FOV is tiny.

Even adding something like x0.5 reducer will not make things better:

However, look at that scope with DSLR on that target:

Now we are getting somewhere ...

Not to mention that 1000mm FL with 3.75µm pixel size of ASI224 will give 0.77"/px - so that needs to be binned x2 which will result in image size being 650x450px

[AstroMuni]

37 minutes ago, vlaiv said:

That won't work well. ASI224 is very small sensor with small pixels and both scopes are long FL scopes.

I agree it wont suffice for larger targets and in the longer run, but just to make a start without any major investment; I think its suitable. Plenty of smaller DSOs around to play with like Dumbell nebula, Ring nebula etc.

EDIT: Had I done all this research I would never have started off in AP It took the 'see what I can get with my existing equipment' approach and I have and learning a lot in the bargain.

Edited October 4, 2021 by AstroMuni