Longer focal length Scope suggestions requested - Forums

Topic starter

Oct 1, 2021

Am looking to get a Scope with a longer focal length.

Have the following gear already:
Scope: WO Zenithstar 73 + WO FLAT73R Flattener/0.8x Reducer
Mount: iOptron CEM25P (CEM70 is already on its way to replace this)
Camera: ASI183MM pro
Control: NINA + ASTAP + PHD2
Guiding: WO Guidescope + ASI120 mini
Filters: Astronomik L3 + RGB + SII & OIII & Ha 6nm
Other: ZWO EFW 8*1.25" + ZWO EAF + Pegasus Ultimate Powerbox V2 + Pegasus Falcon Rotator

Now the issue is that the wallet can not stretch much further this year, so I am looking to only add a Scope + necessary reducer/corrector + dewshield (depending on FL OAG). As I see it now the Camera is the main limiting factor but after doing a lot of searching hopelessly lost in the dark on what is the best option. Budget is around €3k

Thanks in advance for sharing any experiences.

andrea tasselli

Frequent contributor

Oct 1, 2021

https://www.teleskop-express.de/shop/product_info.php/info/p2482_TS-Optics-10--Ritchey-Chr-tien-Pro-RC-Telescope-254-2000-mm-OTA.html

John

Oct 1, 2021

I would go for a F3 or F4 newton, you will have also much more resolution.

Or a C11 or C9 sct. but they are much slower.

Steve Solon

Oct 1, 2021

Hi Sean,
I have a Celestron 11" EdgeHD telescope that I've enjoyed for many years, and that has produced images that I'm astounded by. With the focal reducer, you're probably looking at closer to €3.5k, but, in my opinion, you're getting a wonderful instrument. I have the ZWO ASI183-MC-Pro, and have used it on the 11", binned 2x2 with terrific results.

Well Written Concise Supportive

Sean van Drogen

Topic starter

Oct 1, 2021

Hi Sean,
I have a Celestron 11" EdgeHD telescope that I've enjoyed for many years, and that has produced images that I'm astounded by. With the focal reducer, you're probably looking at closer to €3.5k, but, in my opinion, you're getting a wonderful instrument. I have the ZWO ASI183-MC-Pro, and have used it on the 11", binned 2x2 with terrific results.

Like the idea of this scope, would love to see where I can find one for that price. Lowest I see the OTA alone is like 4.5k

Steven

Oct 1, 2021 · Edited: Oct 2, 2021

There's probably a little more to consider except "focal length", Could you give a little more of an idea?

How big of a focal length? are we talking 800-900mm here? 1500? 2000? what are the targets? want to do planetary? small galaxies?
What kind of scope? want to stick to an APO refractor? SCT? Newtonian? Each come with their own workflows.

You are right that the 183 is probably the limiting factor, I have one too. Great for the 400-ish mm (and shorter) work, but you don't need much before you're oversampling the images. Of course, you could do binning, even a 2000mm could work then at about 0.50" arcseconds per pixel, which is still manageable.

If you want to stick to the refractor type of scope, you might not get a lot more than 800-900mm within the budget (turning into 600-700 depending on reducers), which makes it a small difference from the WO.

You could consider a "Celestron 925 EDGE HD", and consider a hyperstar add-on for it. Which also allows you to also use it as a 500mm, F2 light gathering monster, like a RASA. Getting both your scopes in 1, and you could perhaps consider selling the WO then. Granted, this is over budget.
The scope runs about 3.500 euro, hyperstar ads another 1000 quickly.
There are also the 11 and 14 inch version, bigger, but more expensive.

It is also possible I believe to do the same on a "non-EDGE HD" version. the C925. Which I believe runs at 2000, and then the 1000 for the hyperstar. But up to you if you consider the difference between the EDGE and the non Edge worth it.

Well within your budget are quite a few good Newtonians. They are probably the best bang for your buck.
Many good newtonians don't even touch half your budget and still give you good light gathering at 1200-1500mm.
But, they come with quite a different workflow and things to consider. Size is one thing.. collimation is another.

Also, you might want to consider your guiding, depending on the focal length. I believe the William optics guide scope is 200mm?
should be fine up to 1500mm, but maybe above that, you could start getting some trouble in the guiding.

Helpful

Sean van Drogen

Topic starter

Oct 1, 2021

There's probably a little more to consider except "focal length", Could you give a little more of an idea?

How big of a focal length? are we talking 800-900mm here? 1500? 2000? what are the targets? want to do planetary? small galaxies?
What kind of scope? want to stick to an APO refractor? SCT? Newtonian? Each come with their own workflows.

You are right that the 183 is probably the limiting factor, I have one too. Great for the 400-ish mm (and shorter) work, but you don't need much before you're oversampling the images. Of course, you could do binning, even a 2000mm could work then at about 0.50" arcseconds per pixel, which is still manageable.

If you want to stick to the refractor type of scope, you might not get a lot more than 800-900mm within the budget (turning into 600-700 depending on reducers)

You could consider a "Celestron 925 EDGE HD", and consider a hyperstar add-on for it. Which also allows you to also use it as a 500mm, F2 light gathering monster, like a RASA. Getting both your scopes in 1, and you could perhaps consider selling the WO then. Granted, this is over budget.
The scope runs about 3.500 euro, hyperstar ads another 1000 quickly.
There are also the 11 and 14 inch version, bigger, but more expensive.

It is also possible I believe to do the same on a "non-EDGE HD" version. the C925. Which I believe runs at 2000, and then the 1000 for the hyperstar. But up to you if you consider the difference between the EDGE and the non Edge worth it.

Well within your budget are quite a few good Newtonians. They are probably the best bang for your buck.
Many good newtonians don't even touch half your budget and still give you good light gathering at 1200-1500mm.
But, they come with quite a different workflow and things to consider. Size is one thing.. collimation is another.

Also, you might want to consider your guiding, depending on the focal length. I believe the William optics guide scope is 200mm?
should be fine up to 1500mm, but maybe above that, you could start getting some trouble in the guiding.

Yeah will probably have to add in the cost for an OAG which will probably require a better guidecam as well. Been looking around the edge HD options and a C8 with reducer seems to be where I end up and stay within budget

dkamen

Oct 1, 2021

Hi Sean,

Do you want to do planetary and similarly sized bright compact objects? If not, I don't think there is much point going above the equivalent of 700mm with your camera (or maybe 1000 with another camera that has larger pixels) in an urban/suburban location. Because seeing is the limiting factor and you find yourself having to reduce the larger instrument one way or another. It is true you can adjust a Schmidt-Cassegrain to do pretty much anything and with extremely good results, but it seems like an overkill getting a 3 meter FL instrument just to reduce-larger-pixel-and-bin your way down to the workable effective FL which the smaller instrument would deliver in the first place

I think with this limitation in mind, you can't really beat a 6" to 8" f/5 Newt in terms of value for money. This has been my experience, six months after the upgrade from a ZS73II to a 8" F/5 TS Photon. I also own a 1050mm VMC110L. The Newt beats it hands down and so does the ZS73II for the most part. Admittedly the VMC110L is not exactly the queen of cats, but what really makes it lose are aspects inherent to its large FL and catadioptric design: Stars look like fuzzy hairballs in less than perfect atmospheric conditions, the reducer introduces CA and coma (in addition to the CA and coma inherent to the scope) and there is mirror flop which is a very nasty thing since you have to refocus every time you cross the meridian and the focuser is a true torture to work with compared to a crayford.

Cheers,
Dimitris

Helpful

Sean van Drogen

Topic starter

Oct 1, 2021

Hi Sean,

Do you want to do planetary and similarly sized bright compact objects? If not, I don't think there is much point going above the equivalent of 700mm with your camera (or maybe 1000 with another camera that has larger pixels) in an urban/suburban location. Because seeing is the limiting factor and you find yourself having to reduce the larger instrument one way or another. It is true you can adjust a Schmidt-Cassegrain to do pretty much anything and with extremely good results, but it seems like an overkill getting a 3 meter FL instrument just to reduce-larger-pixel-and-bin your way down to the workable effective FL which the smaller instrument would deliver in the first place

I think with this limitation in mind, you can't really beat a 6" to 8" f/5 Newt in terms of value for money. This has been my experience, six months after the upgrade from a ZS73II to a 8" F/5 TS Photon. I also own a 1050mm VMC110L. The Newt beats it hands down and so does the ZS73II for the most part. Admittedly the VMC110L is not exactly the queen of cats, but what really makes it lose are aspects inherent to its large FL and catadioptric design: Stars look like fuzzy hairballs in less than perfect atmospheric conditions, the reducer introduces CA and coma (in addition to the CA and coma inherent to the scope) and there is mirror flop which is a very nasty thing since you have to refocus every time you cross the meridian and the focuser is a true torture to work with compared to a crayford.

Cheers,
Dimitris

Hi Dimitris,
Thanks for the insights. Would still want to Focus on DSO mainly but would like to image some smaller and more obscure objects. In the alternative I have to keep saving until I can also add a new Camera + Filters + Filterwheel which will probably need to double the budget

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