Djukka_

Thanks everyone, thats all for now. 

Clear skies!  

Also here is some Images of deep sky objects, personally this isn't that big of a zoom difference!

9 hours ago, vlaiv said:

Question of how "clearly" you can shoot the object is very complex.

There are a lot of variables that come into play, and quality of optics is not at the top of the list. In fact - it is probably one of the last ones if we consider importance.

When we are talking about clarity of deep sky objects / long exposure astrophotography - following things are more important than quality of the optics:

- how bad atmospheric seeing is

- what is the precision of the tracking / guiding of your mount

after those two come aprerture size and quality of the optics. Nowadays, most, if not all telescopes come with very decent quality optics. It's not premium, but most do have diffraction limited optics.

Without going into too much detail, with D3200, you should really keep your focal length at about 500mm to get the sharpest image at 100% zoom level.

This is why I said to use either refractor of about 400mm or reflector at about 600mm (650 + x0.9 coma corrector gives 585mm).

Here is handy tool to help you visualize what sort of image you'll get:

https://astronomy.tools/calculators/field_of_view/

For example, let's look what M51 would look like imaged with these two different scopes:

As you can see - yellow rectangle is field of view with refractor and red is field of view with reflector. In both images this galaxy looks small. This is because your camera has 6000x4000 pixels (give or take), and for astrophotography - it is not so much the FOV as something called sampling rate - how much sky is covered with single pixel.

For your conditions and skill level - this figure should be around 1.5 - 2"/px - which means that every pixel should roughly cover 1.5 arc seconds x 1.5 arc seconds of the sky. Depending on conditions - even this might not look sharp enough (poor seeing, or poor tracking).

Formula for calculating this value is pixel_size * 206.3 / focal_length so for D3200 with pixel size of 3.84um each scope will give:

3.84 * 206.3 / 420 = 1.89"/px for refractor

3.84 * 206.3 / 585 = 1.35"/px for reflector

Now, given that M51 has apparent size of some 12' x 7' and if you want to frame it right you can add another 10' around it so overall it will be something like 22' x 17' and that is 1320" x 1020" - that is apparent size in arc seconds.

When we map this to pixels, for refractor you get:

1320 / 1.89 = ~700px and 1020 / 1.89 = ~540px - so whole "interesting" image will be 700x540px

and for reflector it will be

1320 / 1.35 = ~980px by 1020 / 1.35 = ~755ox - or a bit larger at 980x755ox

I know that this looks small - but that is what you can realistically get to look sharp. In fact - most amateurs are going to be limited to about 1"/px. Sky simply does not allow for finer detail, so you'll be already very close to that limit with 130PDS and your camera with 1.35"/px

I think that it is a good scope - but I would not recommend that to you.

For imaging you want a stable platform. Larger scope is simply going to strain the mount more as it is heavier. It has larger cross section so wind will shake it more. It has almost the double the focal length - which translates into "empty' magnification with your camera (there are techniques to get around this, but are probably too advanced for beginner).

If you really want a bit bigger scope - then get this one:

https://teleskop.rs/reflektori-ota/117-150750-skywatcher-newton-tubus-sa-110-mikrofokuserom.html

Just make sure you get PDS version of Skywatcher 150 newtonian and not regular, because PDS comes with dual speed focuser and larger secondary mirror and is aimed at astrphotography rather than visual.

In any case - do keep in mind that you will likely want to start guiding at some point. Have a look at this:

That is a "video" that I made with EQ mount (not sure which one, could have been HEQ5) - but it shows two important aspects of the EQ mount.

First is polar alignment (PA for short) error and associated drift - in this video shown as drift from right to left, and second is periodic error (PE for short) of the mount - that is jumping up and down of the image.

First one is caused by less then perfect polar alignment of the mount and second is inherent to the mount because of the way reduction works - it uses machined gears and those gears are not perfect in shape - they are a bit "egg" shaped due to manufacturing errors (very small errors but at telescope magnifications - it shows). Both of these limit your exposure time and if you expose for longer - you get star trails.

You can even see some star trailing in the video as each frame was about 1 minute exposure with the mount.

In order to avoid this and have round stars each exposure, and to be able to expose for longer - you really need to guide. Lack of guiding will really be the biggest source of blur in your images when you start in all but poorest seeing.

I'm telling you that so you can choose between scopes - in essence, go for smaller scope that has shorter focal length and is lighter on the mount and save the money for guide camera and guide scope as you will need them soon enough.

Yep

I'm also active on our local astronomy forum

Ohhh I see, thanks for the tips, I will use them  
I have one last question for you, since I now know something about this would you recommend me to buy  this one  https://teleskop.rs/reflektori-ota/117-150750-skywatcher-newton-tubus-sa-110-mikrofokuserom.html  (150/750 newtonian)

or this one  https://teleskop.rs/refraktori-ota/763-72420-skywatcher-evostar-ed-apo-tubus.html (72/420 SkyWatcher Evostar ED apo) , I want your opinion on what would you buy if you were in my situation.
And I also got a lot of recommendations for this 72ED apochromat  

(Also if you could put a link to our local astronomy forum, didn't even know such a thing existed!!!😮)

16 hours ago, vlaiv said:

Hi and welcome to SGL.

With that sort of budget - I think that most sensible option would be this one:

https://www.firstlightoptics.com/reflectors/skywatcher-explorer-130p-ds-ota.html

together with this

https://www.firstlightoptics.com/coma-correctors/skywatcher-coma-corrector.html

Alternative would be to get ~70mm ED doublet refractor with ~400mm of focal length with matching field flattener. Something like SkyWatcher 72ED for example.

There will be some differences between two setups:

- Newtonian will be more "all around" scope - meaning that it will give you better field of view on most targets, refractor is more a bit wider field instrument that will render most galaxies as very small

- Newtonian is a bit harder to setup as it requires maintenance - like collimation (sometimes - that really depends on how often you move the scope and how you handle it), and arguably it is a bit harder to get spacing for coma corrector right

- Newtonian will also produce diffraction spikes - so that is something you may or may not like. This model also sometimes shows issues from protruding focuser tube and mirror clips - but there are solutions for that - like 3d printing mirror mask and shortening focuser tube a bit.

- with added focal length - you will likely want to guide sooner with newtonian than with refractor - which is additional cost (guide camera, guide scope and computer).

 

 

So you are telling me that its just a bit harder to shoot with newtonian, but are images taken from it still good? Or are they "low in detail"
I would rather pick newtonian if refractor will have galaxies like very small objects (if i zoom in detail will be worse anyway)+ the price of 550$ is cheap for refractor but ok for reflector

PS: I saw you selling a telescope in like 2012 or smth, but i saw it on a site like a year ago and i remember your profile picture. What a coincidence. + we are both from Serbia

what do you think about this and a coma corrector
https://teleskop.rs/reflektori-ota/118-2001000-skywatcher-newton-tubus.html

can I put my DSLR on it with a T ring or smth?

I'm new to this hobby, All I want to do is to take pictures of the nebulae, galaxies and some star clusters. When it comes to buying a telescope I got a LOT of recommendation,

and all are different from each other...

Problem is I have a DSLR that I need to use (its old DSLR Nikon D3200) and my budget is very limited, after buying the mount and all the stuff I need, like the battery and Syn Scan Wi-Fi adapter and stuff... I'm left with like 500 Euros (550 American dollars)

And with that 550$ I need to buy one of this 3 things. Its either a lens for DSLR like 200~300mm or i can buy telescope (Reflector or Refractor) and so with that things in mind I hope some of you can recommend me what to spend my 550$ on.

Do I buy lens or Reflector or Refractor
(Also would like to mention 1 very important thing, what i need is good zoom and clear sharp image, i don't need a zoomed out image that is crystal clear and i don't need a very zoomed in image that has bad detail)
(And ofc I don't expect it to be like 10000$ monster telescope rigs, all I want is to take some stunning images of deep sky)

Thanks for reading, Clear Skies