6 replies to this topic

[avodcap7]

Hello, 

 

So, since the weather forecasts are really good, and Christmas is coming up, I decided that I need to upgrade my gear.

Currently I have a:

• Celestron C8 with a 0.63 reducer
• Nikon D7200 camera
• Some random 60 mm finder scope with a touptek guide camera
• Skywatcher HEQ-5 Pro

My bortle class is about 5, but I still find it hard to do imaging with my C8, because of my narrow FOV.

But also, my camera doesn't pick up DSO's very well, it it not very sensitive, even in 600 second exposures.

 

So the question is - should I get a better telescope, or a better camera.

For the telescope, I'm thinking a William Optics ZenithStar 81

And for the camera - ZWO ASI294MC Pro

 

Tell me what you think is worth getting!

 

Cheers

 

[endless-sky]

A C8 on a HEQ-5 is really something hard to work with, for DSO imaging.

 

I know, because I tried with mine. On a NEQ6 Pro. I wasn't using guiding at the time (because I didn't have a guide-scope, nor a guide-camera), and was limited to 30-45s exposures top. Even with an astromodified D5300 I wasn't picking up much - the exposures were definitely too short.

 

So I have been using my kit 70-300mm zoom lens for quite a while, before I did my first major upgrade and bought the gear you see in my signature.

 

A nice 80mm short and fast refractor is a beauty to handle and produces amazing results. One of the most counterintuitive things in astrophotography is assuming that you need a large aperture to capture faint objects. This is true in visual, where you are limited to your own eyes sub-second exposures - therefore, the more light you feed them in that short time, the more you get to see.

 

A camera can take hours of exposures (conveniently divided in subframes) and even a 50mm aperture can give you beautiful views of the Cosmos.

 

That said, I don't really know what would give you the biggest bang for the buck. The small refractor would definitely be easier to handle for your mount, but I don't know if the camera would then be too much of a limiting factor on what you can acquire. On the other hand, the ASI 294MC has quite a small sensor and will tighten the field of view that you are now getting with the C8-DSLR combo even more (magnifying any guiding/tracking errors even more) - sensor is 19.1mm x 13.0mm, while the D7200 has a 23.5mm x 15.6mm sensor (the covered area is roughly 1.48x bigger).

 

Personally, I would get the telescope first, so that you can build a better foundation on your astro-gear. The camera can always be added later. I think it would be quite frustrating to keep working with the C8 and a small field of view.

 

Another option is buying a cheap, used DSLR and astromodifying it yourself (or having it done professionally by some store/company that offers the service) - if you do decide to change camera, in the future. I have done exactly that with a D5300 (that I modified myself) and couldn't be happier. Spent about 400 Euros between camera and UV/IR cut filter to replace the stock one with.

[Noah4x4]

The previous post accurately reflects the position with long exposures. But why limit yourself to long exposures?

 

I was in exactly your position about three years ago, except that I have an Evolution Mount and had a Nikon 5200. You have the advantage of already owning a decent quality GEM mount.

 

I messed about with wedge and an unmodified DSLR requiring longer exposures as it wasn't that sensitive. Whilst I got a few  decent modest length exposure images, many others were spoilt by aircraft trails, clouds. Buying a GEM would not assist me with that, whilst stacking short exposures is a darn sight easier than using long exposures. If you review Dr Robin Glover's YouTube presentations (n.b. he is the author of SharpCap) he eloquently demonstrates that there are few disadvantages of short stacked exposures over long exposures If using a modern low read noise astro camera CMOS sensor and instead many benefits, particularly if you are typical of most of us stuck hence under light polluted urban skies and with limited time.. See https://www.youtube....H93UvP358&t=6s 

 

I hence faced a decision, buy a GEM or do something else. I chose the latter and instead bought an Atik Horizon and HyperStar. Imaging DSOs at f/2 is incredibly easy as photons are captured 25x faster than at f/10. Today, I also image at f/6.3 with focal reducer and ASI294mc  on a 8" SCT. But you already have the GEM. Begs the question, is your current C8 Fastar compatible? If yes, I don't see much advantage in replacing it unless you go for a much larger aperture. That then begs questions about weight and portability. I think a 8" is manageable but anything larger then assembly and portability is a major consideration. With my 8" SCT, I  can image at f/10 (lunar/planets) or f/63 (smaller DSOs) or f/2 ((larger DSOs). That is very versatile. Frankly, I would not upgrade telescope at this stage. Don't unnecessarily  chase long exposures at this stage. You have tried that and recognise the challenges. 

 

What I would recommend is first buy the ZWO ASI294 or perhaps ASI533. Enjoy that at f/6.3 (and f/10) on your current telescope whilst you learn new skills as a decent cooled CMOS astronomy camera and live stacking  is somewhat different to a DSLR (which also might be CMOS), plus most astro-cam software has a learning curve. I think that will offer you greater immediate incremental benefit. You can later upgrade telescope, but what you already have is very usable, especially if the OTA is Fastar compatible permitting an upgrade to HyperStar as that then gives you something close to a RASA. 

 

This post will probably prompt two responses;

 

1. Arguments about DSLR versus astro camera.

 

2. Debates about vignetting and like aberrations. 

 

The fact is that unless you upgrade BOTH camera and OTA you will be accepting a compromise. But I think you will find a lot of joy from your 8" SCT on GEM (at f/6.3) just from adding the camera, whereas replacing your telescope (but not camera) won't. If this is a case of either/or on budgetary grounds, I would definitely go with a large sensor, high resolution OSC astro camera and pursue 2 second to 20 second stacked exposures. My DSLR has not been out of its case in three years. Do watch  Dr Glovers YouTube video for the science. 

Edited by Noah4x4, 03 December 2020 - 07:20 AM.

[avodcap7]

A C8 on a HEQ-5 is really something hard to work with, for DSO imaging.

 

I know, because I tried with mine. On a NEQ6 Pro. I wasn't using guiding at the time (because I didn't have a guide-scope, nor a guide-camera), and was limited to 30-45s exposures top. Even with an astromodified D5300 I wasn't picking up much - the exposures were definitely too short.

 

So I have been using my kit 70-300mm zoom lens for quite a while, before I did my first major upgrade and bought the gear you see in my signature.

 

A nice 80mm short and fast refractor is a beauty to handle and produces amazing results. One of the most counterintuitive things in astrophotography is assuming that you need a large aperture to capture faint objects. This is true in visual, where you are limited to your own eyes sub-second exposures - therefore, the more light you feed them in that short time, the more you get to see.

 

A camera can take hours of exposures (conveniently divided in subframes) and even a 50mm aperture can give you beautiful views of the Cosmos.

 

That said, I don't really know what would give you the biggest bang for the buck. The small refractor would definitely be easier to handle for your mount, but I don't know if the camera would then be too much of a limiting factor on what you can acquire. On the other hand, the ASI 294MC has quite a small sensor and will tighten the field of view that you are now getting with the C8-DSLR combo even more (magnifying any guiding/tracking errors even more) - sensor is 19.1mm x 13.0mm, while the D7200 has a 23.5mm x 15.6mm sensor (the covered area is roughly 1.48x bigger).

 

Personally, I would get the telescope first, so that you can build a better foundation on your astro-gear. The camera can always be added later. I think it would be quite frustrating to keep working with the C8 and a small field of view.

 

Another option is buying a cheap, used DSLR and astromodifying it yourself (or having it done professionally by some store/company that offers the service) - if you do decide to change camera, in the future. I have done exactly that with a D5300 (that I modified myself) and couldn't be happier. Spent about 400 Euros between camera and UV/IR cut filter to replace the stock one with.

Ok, so I think that you are right and I need a smaller telescope. It will give me a bigger FOV, better image quality (less chromatic aberration) and it is lighter, so better tracking.

 

I'm now looking through some APO's and I want to ask if this one: https://www.astrosho...ine-ota/p,52328

is a good option? It is only 600 euros, and it's a triplet with FPL-53 glass, which is really good in my opinion, as william optics GT81 costs twice as much. Is it just as good? I've heard it's from the same manufacturer but they're sold by different companies.

Edited by avodcap7, 03 December 2020 - 07:57 AM.

[Topographic]

I used https://www.astrosho...pro-ota/p,56994 to learn on, add the OVL flattener (not the Skywatcher), look at the ASI533 pro which seems a good introduction to CMOS cooled camera imaging.

 

The whole lot would cost £1300-£1400. Mind you availability for christmas is a whole different thing. First Light Optics in UK is a good place to order from.

[endless-sky]

Some good points are raised by Noah, as well. However, the length of the exposure is also quite dependant on your sky conditions (light pollution). It's very easy to swamp read noise with short exposures under a very light polluted sky.

 

In your case, you are right in the middle of the scale (Bortle 5). I shoot from a 5/6 location. 30-45s with a low read noise DSLR (D5300) were not enough to give me a correctly exposed image. Granted, I wasn't guiding - and I haven't tried acquiring images with the C8 even now that I do have an autoguiding setup. Mainly for fear of differential flexure and mirror flop. Also, because I would have to find a way of attaching the guide scope to the C8.

 

I am more interested in large nebulae, rather than tiny galaxies. So, for now, the 384mm focal length of the refractor is plenty good enough.

 

That's another thing to take into consideration when thinking about a telescope and the camera to match it. How wide (or narrow) will the field of view be and will the objects you are interested in fit, be cropped too much, or so small that you would be wasting the majority of the sensor?

 

Telescopius.com is a wonderful resourse. And its Telescope Simulator a tool that does exactly that. Add your choice(s) of camera(s) sensor dimensions, the focal length(s) of the telescope(s) you intend on using, search for some objects and see how big or small they will appear in your final image.

 

As far as the TS Optics telescope, when I went out looking for an apo triplet, at the end I narrowed down my choice between the TS Optics 80mm f/6 and the Tecnosky SLD 80mm f/6. Both FPL-53, both triplets. The salesperson adviced me on the latter (the store sells both brand and it's not particularly affiliated to a single brand). He said the optics have better quality/treatments and the mechanics are better. I ended up buying the OWL (the upgraded and improved version of the SLD), since the SLD was sold out and discontinued a few days before I placed my order.

 

I am also based in Italy, so other brands (like William Optics, Stellarvue, etc.) are a lot harder to come by, so the choices are quite limited.

 

That said, the TS Optics you linked is actually an f/7, so a little "slower" than what I would pick. I actually tried to make my scope as fast as possible, since I bought a 0.8x flattener/reducer (this is another thing you'll need to consider: for a refractor, you need at least a flattener) to bring it to f/4.8. Field of view on most of the objects I am interested in is still quite large, but I gather light faster than f/6.

 

I guess the price of the telescope increases also due to how fast the system is. The TS Optics f/6 is 2-300 Euros more expensive than the f/7 you cited, despite optics and machanics being almost the same.

[Stelios]

Ok, so I think that you are right and I need a smaller telescope. It will give me a bigger FOV, better image quality (less chromatic aberration) and it is lighter, so better tracking.

 

I'm now looking through some APO's and I want to ask if this one: https://www.astrosho...ine-ota/p,52328

is a good option? It is only 600 euros, and it's a triplet with FPL-53 glass, which is really good in my opinion, as william optics GT81 costs twice as much. Is it just as good? I've heard it's from the same manufacturer but they're sold by different companies.

Where do you see that it's a triplet? It's almost certainly an F/7 doublet (when they don't say it's a triplet, it isn't). The triplet by TS-Optics (an F/6) is $1,070. And yes, these are excellent scopes, with good focusers and nice mounting rings. 

 

I don't view the F/7 vs F/6 to be a significant issue, but triplets will have less bloat in the blue channel than doublets. It's something that will not be a bottleneck for years, as there are many more important things to optimize in AP (PA, tracking, focus, framing & platesolving, calibration, post-processing). 

 

And yes, upgrading your scope is more important than getting a camera. As for Hyperstar, even if available it costs as much as an APO, and doesn't provide *nearly* the same quality IMO (though it does provide very high acquisition speed which matters if you have very limited imaging time).