EAA setup with 8" newt?

[nickp87]

Hi all.

Looking to start building a EAA setup, I did plan to use my DSLR as the cam and possibly reuse my 8" 9kg newt, mostly for its light gathering ability.

I know i will need a sturdy mount, but I see that as a good investment anyway for AP etc. Portability isn't an issue as it will only be used at home. 

Do you think it would make a good scope for EAA or would I be better off with a lighter refractor? My main goal with this setup will be fast acquisition and display of the image more than anything else. 

Cheers

[PeterC65]

Can you tell us a little more about your scope (F ratio) and camera (pixel size, sensor size)?

You can check the suitability of the scope / camera combination for observing DSOs using this tool. For observing the Moon and Planets its a different criteria, and you need the scopes F ratio to be about x4-5 the camera pixel size in um.

Assuming you want to observe DSOs, that your scope is F5, then you will be about right with a camera having 4-7um pixels.

There are issues with using a DSLR for EAA I think ...

• Camera control from the most popular EAA software (SharpCap) is likely to be more limited (via ASCOM) than with a dedicated astro camera (direct control).
• If it has a physical shutter, this will be clicking away all of the time.
• It's likely to take power from its internal battery rather than from the mount supply (via USB) so you need to keep it charged up.
• It's quite a hefty lump to have hanging out of the focuser of an 8" Newt. You will need a VERY sturdy mount!
• Most DSLR's take up all of the 'standard' 55mm of back focus required to couple to a reducer / field flattener, so there is no room for manoeuvre for things like filter draws / wheels.

I have an Explorer 150 that I use for EAA, although I more often use the 72mm refractor. Additional light gathering does make a difference for EAA, but the improvement gained by using a camera is quite staggering and so most people worry less about aperture and more about the clarity of the image which tends to be better with refractors. Refractors, being smaller, are also less affected by wind buffeting (my Explorer 150 wobbles about in the wind).

I'd be happy using an 8" Newt for EAA, but I'd also want a smaller shorter focal length refractor, and I'd get a dedicated astro camera (IMX585 based would be my recommendation, unless you have £1000+ to spend).

 

[M40]

Going to echo what PeterC65 said in that the 8" newt will be very good for eeva enabling some very small galaxies but you will need a very good mount to go with it. People do use an heq5 with an 8" but its on its limits and as Peter said it becomes a windsock. I use an 85mm refractor on an heq5 and it enables most of the Messier objects, so it really comes down to which camera you match it with and what you want to see.

And as Peter said, use the calculator as a guide, stick in as many combo's as you can think of using both your telescope and dslr then swap things up. When playing with the calculator I tend to use M51 as a guide in the fov,  you have to start somewhere 😉 

All the best 

[nickp87]

Thank you both for the advice.

It's DSO's that I am looking to view.

Buying a dedicated astro cam is not a problem, I have a planetary cam so don't mind adding one for DSO's.

The scope is a 1200mm @f6. Maybe best just to get another scope, even another large aperture newt as the focal length on might to a bit long?

 

thanks again 

 

[PeterC65]

That is a big scope. Mine is just over half the length and it can be a little unmanageable. It's probably going to be best for observing smaller DSOs such as galaxies. That's what I mainly use my 6" Newt for.

 

[nickp87]

14 hours ago, PeterC65 said:

That is a big scope. Mine is just over half the length and it can be a little unmanageable. It's probably going to be best for observing smaller DSOs such as galaxies. That's what I mainly use my 6" Newt for.

 

It is indeed a large scope, and can only image it being more unwieldy on an eq mount lol.

As mentioned, the only reason for considering it is that it will allow faster acquisition, but a 8in with a shorter fl and faster f stop might be better, and lighter

[PeterC65]

As I understand it, the speed of acquisition is determined by the F ratio and not by the aperture. So your 8" F6 will take as long as my 72mm F6 refractor to acquire a sensible image. This has certainly been my experience in practice. My F11.8 Mak is pretty rubbish for EAA of anything other than the Moon and Planets, and if I add a x0.6 reducer to my refractor (making F6 into F3.6) then I get brighter objects faster than without.

I'm no expert, but my understanding is that you need more aperture when you want to get higher magnification with the same scope speed (acquisition time). So if I want to observe small galaxies for example then I need a higher magnification to make them occupy a sensible amount of my cameras sensor, and to get that I need a longer focal length, but I don't want to sacrifice the scope speed (acquisition time) so I also need more aperture. This is why I use my 6" Newt to observe small galaxies.

 

[nickp87]

4 hours ago, PeterC65 said:

As I understand it, the speed of acquisition is determined by the F ratio and not by the aperture. So your 8" F6 will take as long as my 72mm F6 refractor to acquire a sensible image. This has certainly been my experience in practice. My F11.8 Mak is pretty rubbish for EAA of anything other than the Moon and Planets, and if I add a x0.6 reducer to my refractor (making F6 into F3.6) then I get brighter objects faster than without.

I'm no expert, but my understanding is that you need more aperture when you want to get higher magnification with the same scope speed (acquisition time). So if I want to observe small galaxies for example then I need a higher magnification to make them occupy a sensible amount of my cameras sensor, and to get that I need a longer focal length, but I don't want to sacrifice the scope speed (acquisition time) so I also need more aperture. This is why I use my 6" Newt to observe small galaxies.

 

Thanks Peter, I didn't think about that, but should definitely look into it.

Regarding magnification, are you using eyepieces or Barlow's during EAA to get more reach?

[PeterC65]

43 minutes ago, nickp87 said:

Regarding magnification, are you using eyepieces or Barlow's during EAA to get more reach?

I sometimes use a x1.7 Barlow with my 6" Newt but you have to be very careful not to slow the scope too much. I can just about get away with x1.7.

I've tried using eyepiece projection but the image it produced had lots of distortion and the back focus requirement is very onerous.

If I had your 8" Newt I would use it natively for observing small faint DSOs. It's way too big for my mount though.

 

[AKB]

My first EAA results were from an 8" F4 Newtonian (Quattro) using a small, uncooled Ultrastar mono camera.

Some examples of results here:

Tony

 

[nickp87]

17 hours ago, PeterC65 said:

I sometimes use a x1.7 Barlow with my 6" Newt but you have to be very careful not to slow the scope too much. I can just about get away with x1.7.

I've tried using eyepiece projection but the image it produced had lots of distortion and the back focus requirement is very onerous.

If I had your 8" Newt I would use it natively for observing small faint DSOs. It's way too big for my mount though.

 

Yes if I were to use it for EAA it would be used at it's native FL. 

6 hours ago, AKB said:

My first EAA results were from an 8" F4 Newtonian (Quattro) using a small, uncooled Ultrastar mono camera.

Some examples of results here:

Tony

 

Amazing results Tony and exactly the kind of thing I would love to see. 

[Mike JW]

Hi Nick,

If you look through the EEVA section for posts by William Scutcher and Martin Meridith you will find many examples of what can be achieved with a 8" Newt. Operating at f6 will be fine but Bill (William) used a focal reducer and if I remember correctly Martin was using a Quattro at around the f4 region. Both used lodestar quide camers. When I was active at the same time as Bill and Martin there results frequently came close to my 15"/ultrastar set up.

Use what ever gear you have and enjoy yourself.

Cheers,

Mike

[nickp87]

Thanks Mike, I will look up there posts. And just so happens I was just looking at the skywatcher quattro and dps