Visual Equipment Choices, well maybe some EAA

[glend (Glen)]

Since selling out of imaging gear, I am being tempted to acquire a good visual scope or two. I have a nice 8" f5 Newt, which is everybody's obvious choice as a visual allrounder, but there are some great bargains around in new scopes at the moment. I would like to get something suitable for planetary observation and maybe EAA imaging ( a la frame stacking), with long focal length. Of course practical limits to useful focal length need to be considered. I would rather not depend on Barlows but the alternatives seem to be big aperture and long focal length designs, like Cassegrain. GSO has a new 10" Cassegrain inbound to Andrews which looks very cost effective, but I do wonder how often I could use it.
There is a sale on Celestrons right now, so they could be an option, and I think I might not need HD type optics, so cheaper still.

Thoughts?

[mental4astro (Alexander)]

It mostly comes down to the chip size of the camera: small chip and you will need short focal length to capture DSO's.

But even with a cassegrain (of whatever flavour you care for), you will still need a barlow (again of whatever flavour you care for) for the planets. No getting around that.

AND it also comes down to the optical quality of the scope, doesn't it. Nothing changes there.

I have used both fast Newts and cassegrains for visual, EAA, and photo.

An 8" f/4 Newt is an excellent choice for EAA (aka video astronomy), and also very good for visual. It's short neat focal length (800mm) is coupled to a considerable aperture. And using a 5X barlow and you have a good planetary option. I have two 8" f/4 scopes, one a dedicated dob, and the other a solid tube scope that I can put onto a dob mount or an eq mount. As far as coma is concerned, of all the Newts I have, it is only these two f/4 Newts I use a coma corrector with when doing low mag widefield viewing. At medium to high magnification coma is not an issue. An 8" f/4 Newt is a terrific rich field scope. I can get a 3° TFOV with mine. And the coma corrector I use has no magnification factor to it so I get the full 3° with it, weighs very little and has bugger all focus shift.

An 8" f/5 scope is nearly just as good for EAA, but it's focal length being a little longer it starts becoming a question of chip size, and the larger the chip the greater the expense as well. f/4 or f/5, it comes down to one's personal preferences and bias.

A scope with a 2000mm focal length and a small chip will still do EAA, but it is very handicapped for FOV. You can use one of those ubiquitous 1.25" 0.5X reducers, but if tack sharp stars to the very edge are a significant must for you, then these modest reducers are not for you, and you will want to look at the right corrector/flattener for the scope or get an Edge or ACF SCT. But if the stars along the edge being a little bloated is not a big bug bear for you, then not only can these modest reducers work for you, but you can expand upon their reducing factor by using extension tubes between the reducer and the camera, as long as your focuser allows for it...

These same modest 0.5X reducers are not suitable with Newts at all. Only fracs & cassegrains, and the slower the f/ratio the better.

However, if your health is not too good, and you need to be setting up and taking down, CAREFULLY think about 8" or larger aperture. Any such large scope, Cassegrain or Newt, will present a significant carrying problem for you. Maybe consider a 6" aperture scope. And there is the mount to consider too. Or at the very least you will need to very seriously consider how you will move the gear about (trolley of some kind) and how you will assemble and take down the gear so you, and the gear, stays safe, or if someone can help you with it. And if things get very late and you are feeling too tired to safely take down the scope, a suitable tarp or scope cover over the gear will be sufficient to keep it safe until the morning - I've done this a few times myself here at home. No shame in that. And my gear and my person is intact.

Alex.

[glend (Glen)]

Thanks Alex, while my health/ strength is an issue, I should have mentioned I have a nice comfortable ROR observatory, with pier mounted CGX, which had no problems imaging with a 25kg load in my old imaging days. So i could leave a larger scope set up. And i have room to store a couple of other scopes in the Obs if needed. My current inventory consists of my: GSO 8" f5 Newt, and my 127mm iStar f12 R30 Anastigmatic (which I built about 5 years ago). The iStar has a 1524mm fl with minimal colour issues at f12 (, it's about equivalent to an f15 with the R30 objective).

Camera wise, I am leaning toward the ASI294MC, because of its reputation among EAA users on CN, and my past good experience with my old ASI1600MM-C (sold last year).. I know the ASI294 has issues when used in traditional long sub imaging but I would not use it for that.
It uses a 4/3s Sony IMX294 chip, diagonal of 23.2mm, pixel size 4.63.

Details are here:
https://www.bintel.com.au/product/zw...v=322b26af01d5

[mental4astro (Alexander)]

Glen, with the 8" f/5 Newt you don't need anything else! You are set!

The only thing for you then is the camera and if coma bugs you or not. But your camera is very capable with EAA. Maybe a good 3X or 5X barlow for planets if you want.

I have Newts from f/4 to f/5. I only use a coma corrector in the f/4 Newts at low power. The eyepieces I use handle the coma very well in the other Newts, and these eyepieces don't show astigmatism, which is the only other visual aberration that can be dealt with with suitable eyepiece selection.

With my EAA when using the f/4 Newt I also don't bother with the coma corrector. I could, but really it is not bothersome to me. But that's ME.

Alex.

[glend (Glen)]

Thanks Alex for that advice. I was paying attention to coma when I was looking at the Mars and Jupiter conjunction this week, and it was not an issue with the Newt in the EPs I was using (GSO Superviews I have had for years).
As to other possible scopes, I think that is off the agenda in the present Virus environment, I will choose to save my money.

[ChrisV (Chris)]

The asi294 would be Killer combo with your newt for eaa! And someone was selling a cheap comma corrector the other day