Upgrading from the RedCat 51 - Forums

Topic starter

Apr 28, 2022

Hi all,

just after some advice on a scope upgrade, I’m looking for a suitable upgrade from the RedCat51. Pretty set on going deep sky! And or deep into a target to get crazy detail.

My current gear is~
533mc
EQ6-R pro
ZWO120 mini for guiding.

I’ve got a budget of 3-4K (don’t tell the misses) 😂

A few photos taken with my current set up to see where I’m at.

Cheers.

kuechlew

Apr 28, 2022

With the pixel scale of the 533 MC sensor you may choose to go for something in the 600 - 800mm range, leaving you above 1 arcsecond per pixel. With your budget and the existing mount you can go both for refractors or reflectors, whatever you prefer.

Clear skies
Wolfgang

Well written Concise

David Koslicki

Apr 28, 2022

My own progress was from the Red Cat 51 to a Stellarvue SVX 102T. I wanted to stick with a refractor and knew that my mount (a very well-used CGX) couldn't handle a longer focal length much longer than the 714mm 102T. On the advice of others though, I am likely to move to a Newt or other reflector in the near future given the significantly more affordable $/aperture.

Well written Concise

Robert Winslow

Apr 28, 2022

Wow, I was just here. I have the Redcat 71, it is fantastic, but I wanted a bit more magnification, and I wanted to stay with APO as I am only interested in imaging.

The APO's get expensive as you go up in size. I had about the same budget, so I settled on Sky-Watch ESpirt 100MM ED refractor.

Some might say that it is not that much larger, however when I went to the website to check FOV it will give me the perfect amount for more distant objects.

Vasile Unguru

Apr 28, 2022

Hi Codey,

If you want crazy detail then you need to go crazy with the aperture of the new telescope. So 8'' or even 10'' Newtonian will be brilliant. Of course you need to prepare to do the collimation and take care of other things.
Of course, if working with a newtonian will not be your taste and wish to stay with refractor then there are option with high quality of 4'' or 5'' ones like SW Esprit and similar others.

The decision will be yours and will not be easy but at least you are close to the established budget, 3-4 k is bare minimum for a high quality setup.

Cheers!

Concise

Steven

Apr 28, 2022 · Edited: Apr 28, 2022

Would agree with Wolfgang, that pixel size and sampling is probably a good factor to keep in mind.
Sure, you could go crazy with a Celestron C11. But that comes with such a heap of new issues and challenges, that it probably isn't the next step.
Maybe have a look in Stellarium or other software, where you can put in details of the camera and the scopes you are considering.
You might be able to pinpoint what focal length you want to get by looking at how targets will fit in the frame.

There are loads of options out there.
Also great newtonians and other design scopes, but they do often come with a new work flow. (collimation and such)
So you'd have to consider how "far" you want to step away from the redcat in your upgrade.

Either way; My suggestion in that budget would probably be a
Skywatcher Esprit 120/840.

this is the view you'd get on Orion.

Helpful

Codey

Topic starter

Apr 29, 2022

=16pxSure, you could go crazy with a Celestron C11. But that comes with such a heap of new issues and challenges, that it probably isn't the next step.

Either way; My suggestion in that budget would probably be a
Skywatcher Esprit 120/840.

So something like the Edge HD8 wouldn’t be the best choice for next upgrade?

kuechlew

Apr 29, 2022

Codey:
=16pxSure, you could go crazy with a Celestron C11. But that comes with such a heap of new issues and challenges, that it probably isn't the next step.

Either way; My suggestion in that budget would probably be a
Skywatcher Esprit 120/840.

So something like the Edge HD8 wouldn’t be the best choice for next upgrade?

It's a huge step from a RedCat 51. A factor of 8 in focal length will require much more accurate guiding. You will depend a lot on the seeing conditions. You will be oversampled - although you may consider 2x2 binning but then you will end up with less than 2 MP for your images. Only you can decide whether to take this leap or not.

Clear skies
Wolfgang

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Steven

Apr 29, 2022 · Edited: Apr 29, 2022

Codey:
So something like the Edge HD8 wouldn’t be the best choice for next upgrade?

Well, I'm not saying no. It's up to you to decide. As the Celestron are interesting scopes!
It's also great for galaxies, great for planetary imaging. And you can always, at some point, look into putting a "hyperstar" on it. And turn it into a 400mm/F2 scope. It certainly is a scope I'm considering for an upgrade at some point in the future.

I don't have any experience with them, so perhaps others can provide better information on them.
but I can tell that it is quite a step up from the redcat.. not impossible.. but less forgiving than a wide field setup.

Edge8 + 533

here you go, that's a few of the images that people have made with that combination.
So it is certainly something that could work

Things to keep in mind:

- You're going from 250mm to 2032mm (or 1422mm with the reducer)
Meaning polar alignment needs to be spot on, it means guiding needs to be spot on.

- Speaking of the guiding, I don't know what guide scope you're using?
but at those focal lengths, you might want to consider an off-axis-guider.
And speaking of the off-axis-guider but the 120mini might not be sufficient for off axis guiding.
Most recommend a 174MM mini for an off axis guider at that focal length. (But a 290mm might be fine)

- You will be slightly oversampling your images. This occurs when the camera’s pixels are too small for a given scope’s focal length. The incoming light is being spread over too many pixels resulting in a soft and bloated image. + you might need to do longer exposures to get enough light into those pixels and get a good signal to noise ratio.
This also means your seeing conditions (the state of the atmosphere) becomes more important for your imaging.
(you're only slightly oversampling though, so the issues might be manageable)

It certainly is an impossible upgrade. Just keep in mind that might just be a bit of learning curve, and there are more things to consider, it's not always as simple as slapping a camera onto a new scope and start imaging. Others with more experience with those kinds of focal lengths might be able to help you better though.

Helpful

Codey

Topic starter

Apr 29, 2022

Codey:
So something like the Edge HD8 wouldn’t be the best choice for next upgrade?

Well, I'm not saying no. It's up to you to decide. As the Celestron are interesting scopes!
It's also great for galaxies, great for planetary imaging. And you can always, at some point, look into putting a "hyperstar" on it. And turn it into a 400mm/F2 scope. It certainly is a scope I'm considering for an upgrade at some point in the future.

I don't have any experience with them, so perhaps others can provide better information on them.
but I can tell that it is quite a step up from the redcat.. not impossible.. but less forgiving than a wide field setup.

Edge8 + 533

here you go, that's a few of the images that people have made with that combination.
So it is certainly something that could work

Things to keep in mind:

- You're going from 250mm to 2032mm (or 1422mm with the reducer)
Meaning polar alignment needs to be spot on, it means guiding needs to be spot on.

- Speaking of the guiding, I don't know what guide scope you're using?
but at those focal lengths, you might want to consider an off-axis-guider.
And speaking of the off-axis-guider but the 120mini might not be sufficient for off axis guiding.
Most recommend a 174MM mini for an off axis guider at that focal length. (But a 290mm might be fine)

- You will be slightly oversampling your images. This occurs when the camera’s pixels are too small for a given scope’s focal length. The incoming light is being spread over too many pixels resulting in a soft and bloated image. + you might need to do longer exposures to get enough light into those pixels and get a good signal to noise ratio.
This also means your seeing conditions (the state of the atmosphere) becomes more important for your imaging.
(you're only slightly oversampling though, so the issues might be manageable)

It certainly is an impossible upgrade. Just keep in mind that might just be a bit of learning curve, and there are more things to consider, it's not always as simple as slapping a camera onto a new scope and start imaging. Others with more experience with those kinds of focal lengths might be able to help you better though.

Yeah this makes a lot of sense! Thank you for this reply!

Björn Arnold

Perfect post

Apr 29, 2022

First I want to clean up with a myth:
„The longer the focal length, the more accurate guiding needs to be“.
That‘s not generally true. What matters is image scale (arcsec/pixel). If you keep image scale constant, the guiding requirements remain exactly the same. For long focal lengths, you can always bin. Of course, if you believe you need to image at 0.2“/pixel while the guide scope has 3“/pixel, then you’ll have issues but I guess you’re scope is not in Chile or space.

Where focal length plays another major role is field of fiew, which brings me to my question:
what do you want to image?

Your RedCat is a wide-field setup. If you‘re looking for something for galaxies, planetary nebulae or planets then you should get a „longer“ FL scope (1000mm++) as you wouldn’t need a large FOV and for the image scale, you can bin (for planets, you wouldn’t).

Regarding image size (mega pixels): I don’t see a reason for a mega pixel arm race in most cases.
Most of the times, I am sitting in front of a screen which has about 2MP (1920x1080).

Björn

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Codey

Topic starter

Apr 29, 2022

what do you want to image?

I think I’ll mainly do nebula, with galaxies every so often.

Björn Arnold

Perfect post

Apr 29, 2022

Codey:
I think I’ll mainly do nebula, with galaxies every so often.

If nebula means all kinds of nebula and not „just“ planetary nebulae, then I would suggest either a Newton telescope (8“ f/4) or an APO (4 to 5“), both at about 800mm FL.

The Newton of course will have the larger aperture and the better price (of course everything is available for different quality levels spanning whole price ranges).

kuechlew

Apr 29, 2022

Björn Arnold:
First I want to clean up with a myth:
„The longer the focal length, the more accurate guiding needs to be“.
That‘s not generally true. What matters is image scale (arcsec/pixel). If you keep image scale constant, the guiding requirements remain exactly the same. For long focal lengths, you can always bin. Of course, if you believe you need to image at 0.2“/pixel while the guide scope has 3“/pixel, then you’ll have issues but I guess you’re scope is not in Chile or space.

Where focal length plays another major role is field of fiew, which brings me to my question:
what do you want to image?

Your RedCat is a wide-field setup. If you‘re looking for something for galaxies, planetary nebulae or planets then you should get a „longer“ FL scope (1000mm++) as you wouldn’t need a large FOV and for the image scale, you can bin (for planets, you wouldn’t).

Regarding image size (mega pixels): I don’t see a reason for a mega pixel arm race in most cases.
Most of the times, I am sitting in front of a screen which has about 2MP (1920x1080).

Björn

Good point Björn. One of the reasons why I recommended 600-800mm FL as next step was that currently with the RedCat 51 Codey can cover 250 - 500mm by cropping down to about 2MP. As an old fashioned guy I still like to print some of my stuff and 2 MP files are borderline printable but for screens they are perfectly fine. So binning is indeed an option.

Clear skies
Wolfgang

Helpful Concise

David Nozadze

Apr 29, 2022

Hi Codey,

I had the same question a year ago, with the same budget and the same mount (just a different camera - ASI294 MM Pro). I chose Takahashi Epsilon 160ED. Never regreted. That is an amazing telescope.

Clear skies.

D

Steven

Apr 29, 2022 · Edited: Apr 29, 2022

Björn Arnold:
First I want to clean up with a myth:
„The longer the focal length, the more accurate guiding needs to be“.
That‘s not generally true. What matters is image scale (arcsec/pixel). If you keep image scale constant, the guiding requirements remain exactly the same.

Not sure I 100% agree on that one. Sure. Guiding has to do with image scale, and accurate guiding comes partly from having a good image scale in your guiding that is matched well with the image scale of your imaging rig.. Keeping that scale constant, helps.

But by moving from a Redcat, with an image scale of 3-ish arc seconds/pixel to a Celestron edge HD8 at 0.55-ish arc seconds per pixel, your image scale isn't remaining constant when switching to a different focal length if you keep the same camera. And a ZWO120mm has about 8 arc seconds/pixel in a 130mm guide scope.. So clearly something needs to be done to the guiding.

Wether you want to call that "making your guiding more accurate" or "adjusting your image scale of your guiding setup to match better with the image scale your imaging rig".. potato.. tomato.. sure, one might be better worded than the other, but in the end it's the same thing.

Accuracy can also comes from other things than image scale and you can do a lot to make the job easier for your guiding:
Better polar alignment for example,
fine tuning the mount,
removing backlash,
proper balance in RA and DEC of the scope,
correct calibration of the guiding,
RA and DEC step size and aggression,
OAG to reduce flex,
+ a ZWO120MM might struggle in an OAG, so camera sensitivity affects accuracy too
etc.

Any error in those will be amplified with a high magnification and you will probably notice that a lot earlier compared to a wide field setup, even with a great image scale. And you're making the job a lot easier for your guiding by being accurate in those elements. You can't just have perfect image scale, call it "job done", and then not do an accurate polar alignment or put an unbalanced scope on your mount.

Helpful

Torben van Hees

May 1, 2022

May I make another suggestion? I've just "tested" a rather cheap 8" f/6 Newtonian, with an ASI183 (so about the FOV of your 533) and a GPU coma corrector on a whim and was delighted. Here's why I suggest it:

Collimation at f/6 is a breeze (compared to my f/4 Dobson and my RC)
You can get a f/6 quartz mirror "on the cheap"
You will not be as oversampled as with an SCT
If you have good seeing, the image scale will be good for the small targets (0.7"/px)
You have almost twice the FOV as with the SCT
While a bit more bulky than an f/5 or f/4, the EQ6-R should handle it (but I'ld suggest an OAG instead of guide scope)
With your budget, you could get a premium imaging Newtonian
And there'll still be money left to get a better guider (the ASI120MM will be workable but marginal at 8" f/6)

If you're in for more of a challenge, get an f/5 mirror, and when everything works add a 0.75x reducer/corrector.
Or for maximum "fun" start at f/4 with the 0.75x reducer (<- this is not meant seriously).

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Codey

Topic starter

May 2, 2022

Torben van Hees:
May I make another suggestion? I've just "tested" a rather cheap 8" f/6 Newtonian, with an ASI183 (so about the FOV of your 533) and a GPU coma corrector on a whim and was delighted. Here's why I suggest it:
Collimation at f/6 is a breeze (compared to my f/4 Dobson and my RC)
You can get a f/6 quartz mirror "on the cheap"
You will not be as oversampled as with an SCT
If you have good seeing, the image scale will be good for the small targets (0.7"/px)
You have almost twice the FOV as with the SCT
While a bit more bulky than an f/5 or f/4, the EQ6-R should handle it (but I'ld suggest an OAG instead of guide scope)
With your budget, you could get a premium imaging Newtonian
And there'll still be money left to get a better guider (the ASI120MM will be workable but marginal at 8" f/6)

If you're in for more of a challenge, get an f/5 mirror, and when everything works add a 0.75x reducer/corrector.
Or for maximum "fun" start at f/4 with the 0.75x reducer (<- this is not meant seriously).

Great suggestion! I will look into this thank you

Jure

May 2, 2022

Some great images you have there, Codey, well done!

I am also in the same spot. Having done some imaging last winter with a 60mm FL: 360mm refractor, AsiAir Pro and an ASI2600MM, I am close to the point where I want to upgrade to something bigger. My images are here. I have an old EQ-6 which is prone to spiking anywhere from 3 - 7 arc secs in R.A every now and then. Very annoying. So my plan is :

- upgrade the EQ-6 to Rowan belt drive
- almost decided on this APO. 106mm F/6.6 and with the included flattener/reducer I will be at F/4.95. I'll also get a x1 flattener/reducer
- my existing 60mm refractor for guiding with the ASI120MM Mini

I know I am undersampling but seeing at my location is not worth mentioning, so with that and dithering/drizzling I'm perfectly happy. I set up this limit in my head for a refractor to be around 100-110mm max.

I do have a 250mm F/6.3 Orion Optics UK SPX reflector but never even thought about using it for astrophotography (except planets, that is). Too much hassle and at my age I am not prepared to wrestle with my equipment too much.

My two eurocents...

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