33 replies to this topic

[TopherTheME]

Well, its getting into galaxy season again, and frankly, I find it a bit boring. Galaxies, especially interacting galaxies, are some of my favorite objects but I don't really have a scope that works well for imaging them. I have an Orion ED80 which I've more or less retired for imaging duty and my DIY 140mm refractor that's 883mm in FL. The refractor is great for mid-field imaging, especially with the 0.65x reducer but it doesn't work all that great for galaxies with a pixel scale of 0.88"/pix with my IMX492 camera. I'm finding I really want more reach and more aperture for smaller objects. Here are some of my recent attempts: 

 

 

 

To remedy this I've recently fitted an AP Baradv barlow and will then bin the IMX492 to 2x2 for an image scale of ~0.5"/sec but this of course will be a very slow rate of acquisition with only 5in of aperture and will be a problem for my limited imaging time with Michigan skies. I haven't tried it out yet as I'm awaiting some clear skies but if I do end up disappointed, I'm strongly considering getting a second scope dedicated to galaxies and planetary nebula. 

 

Just a couple years ago, I would have built a 14in RC or newtonian but with having a young family now I just don't have the time or a big budget. So, I'm considering more of an off the shelf solution that's going to be relatively hassle-free and that I can just toss on the mount, hit go, and wake up to a hard drive full of lovely data. And something that works out of the box and doesn't need a lot of tinkering. Based on my experience with newtonians, the frequent collimation takes them off the list. RC's can be complicated to collimate but are also expensive and likely out of my budget for anything in the >=10in aperture range. I'm wondering if a 9.25 EdgeHD might be a good option?  Or if theres a not-outrageously-expensive newtonian out there that holds collimation well? Or is my refractor with a barlow likely going to be the best option and I just need to deal with very long integration times?

 

I'd like to keep the cost for the OTA under $1500 (will likely buy used), and a focal length of around 1800mm. 

 

 

[Tapio]

Instead of using a barlow you could just drizzle and crop your image.

As for larger scope, a C9.25 would make a good planetary scope.
A assume you have already a good mount for it. Longer fl scopes need good tracking/guiding.

[rgsalinger]

If you want the easiest route I'd recommend the Edge 11. Even with the reducer you're still at 2 meters of focal length and you've got F7 to keep the exposures reasonable. Of course, that scope (I own one), when reduced, doesn't have an image circle much bigger than the QHY533M that I use on it.  For small galaxies, it's hard to beat. It's also just portable enough that you can set it up by yourself and the image scale at .4" pixel is good enough for the seeing that most of us have.

 

If you can bust into the piggy bank, you cannot beat a CDK. I've owned a 12.5" and now a 14" and they have an image circle that supports a full frame small pixel camera easily. The 12.5, even though it's the same weight at the 14 is, IMHO, something that one person can handle the 14" is another matter but optically the spot diagrams are better with the 14". 

[Rasfahan]

For that budget you‘ll unfortunately buy a project, no matter what.

[Spaceman 56]

 RC's can be complicated to collimate but are also expensive and likely out of my budget for anything in the >=10in aperture range. 

I shoot galaxies with a 10 inch RC. focal length reduced is 1484mm and about F5.9.

 

this makes it pretty fast. not as fast as my Takahashi FSQ-106 but not too slow by comparison.

 

I think an 8 inch RC would be a good option. second hand might get you to the price point.  

[TopherTheME]

Instead of using a barlow you could just drizzle and crop your image.

As for larger scope, a C9.25 would make a good planetary scope.
A assume you have already a good mount for it. Longer fl scopes need good tracking/guiding.

 

Drizzling != greater focal length or aperture. Drizzling can certainly help with resolution but its not magic and cannot replace the benefits of a larger aperture with a longer focal length scope. And yes, I have a Fornax 51 mount which is good for ~45kg of payload. 

 

If you want the easiest route I'd recommend the Edge 11. Even with the reducer you're still at 2 meters of focal length and you've got F7 to keep the exposures reasonable. Of course, that scope (I own one), when reduced, doesn't have an image circle much bigger than the QHY533M that I use on it.  For small galaxies, it's hard to beat. It's also just portable enough that you can set it up by yourself and the image scale at .4" pixel is good enough for the seeing that most of us have.

 

If you can bust into the piggy bank, you cannot beat a CDK. I've owned a 12.5" and now a 14" and they have an image circle that supports a full frame small pixel camera easily. The 12.5, even though it's the same weight at the 14 is, IMHO, something that one person can handle the 14" is another matter but optically the spot diagrams are better with the 14". 

 

The 12.5 Planewave CDK is of course the correct answer, especially since they are made about an hour from home, but I'll get divorced if I buy one of those scopes. The Edge 11 is probably my best practical option but its way outside of my budget, even used. Even more so when you include the cost of a reducer. 

 

For that budget you‘ll unfortunately buy a project, no matter what.

I think you're probably right. I wanted to ask anyway in case someone more experienced than me could offer some wisdom. 

 

I shoot galaxies with a 10 inch RC. focal length reduced is 1484mm and about F5.9.

 

this makes it pretty fast. not as fast as my Takahashi FSQ-106 but not too slow by comparison.

 

I think an 8 inch RC would be a good option. second hand might get you to the price point.  

I could probably find a 10in RC within my price point but again, theres the issue of collimation with RCs. I know it can be done during the daytime but from what I've read the steel tube models are more or less hopeless when it comes to proper collimation and the truss tube models are way outside my price range. 

 

 

What about a C11? I know it doesn't have as good of optics as the Edge 11 but with the Starizona corrector it seems like it could be very comparable? 

[erictheastrojunkie]

Does your seeing even support that pixel scale? Why not something like a 8" f5 Newt? Not sure what's to be gained resolution wise by going longer for most locations, seeing is always the limiting factor. From what I've seen at our location there's really no point in imaging beyond ~0.8"/pixel resolution because the seeing limits it to that, going above 1000mm focal length with a camera like the ASI533 or ASI2600 just leads to oversampling. An 8" f5 Newt with a 533 sensor gives good framing for a lot of galaxies, the f5 aperture makes collimation a bit more forgiving as well, there's several scope options within your budget even with upgrades factored in. 

[rgsalinger]

Good point. My recommendation assumed that the OP has good enough seeing to support a sub arc second image scale. At the same time, I would also say that it's nice to know that you are getting the best resolution detail that you can. On the other hand a fast 1 meter Newt is a real light bucket. Nothing beats SNR when it comes to making striking pictures even if the details are a bit less than the best possible.

[TopherTheME]

According to meteoblue and some other sources the average seeing in my area is ~1.5" on average. If that truly is the case then I would want a pixel scale of about 0.5"/pix to achieve full resolution and of course optics to match.

[KGoodwin]

Meteoblue is generally…optimistic.

[rgsalinger]

Agree. At my site the best I ever get is around 1.5" seconds. I know that's the best because I use (but don't own) a 24" F8 RC with an image scale of around .3" un-binned. It's equipped with Renishaw Resolute absolute encoders so it's not wobbling. Yet Metroblue often shows slightly smaller numbers. I'll still stick with my recommendation of the Edge11 over anything else if the OP has 2" or better seeing on some nights, though.

[KGoodwin]

My site sometimes shows seeing down in the sub-1" range meteoblue.  The best I've ever done on a sub from my CDK (0.31"/pix) is 1.2".  I just checked to be sure.  I agree though that it would be hard to beat an SCT of some size/type for the OP's requirements.  For small field size targets I'd probably rather go a step larger in size rather than a smaller Edge, if the seeing supports it.  The reducer for the Edge is troublesome in my opinion, too.  It definitely seems less sharp than native, perhaps some spherical aberration or something.

[rjkrejci]

According to meteoblue and some other sources the average seeing in my area is ~1.5" on average. If that truly is the case then I would want a pixel scale of about 0.5"/pix to achieve full resolution and of course optics to match.

a 10" f4 newtonian (I have the Quattro 250) (or 8" f5 if your mount isn't up to it) would be perfect match for your camera and what you're looking for then at 0.48"/pixel resolution and is in your budget.   I use it with 3.76u pixels camera at 0.78"/pixel and frankly my seeing seldom even supports that.    Mine worked well out of the box with a Zwo EAF and some gaffers tape around the focuser and a black shower cap at the rear to prevent light leaks...not exactly a project. Collimation is straightforward and I only do it every few months.    Yes, you can make more of a project out of it with replacing the spider and masking the primary and updating the focuser, but I've found it it great without them. 

 

I bought it with the Sky-Watcher Quattro Coma Corrector, which I've found to be excellent.  I also have the Starizona Nexus corrector/0.75x reducer which is also excellent.

 

And at f4, it's not so fast that you need special filters or making collimation a chore, but it's about 3x faster than the Edge at f7 and over 6x faster at f10.    So you can collect in 2 hours what the reduced Edge could in 6 hours.    The Edge would have a greater image scale, but beyond 0.5x/pixel, you are almost never gaining any real resolution.   And I've also used it at f3 with a Starizona Nexus, which makes it almost 5.x faster than the reduced Edge.   And with an Aperture of 10", it's right in between the 9.25 and 11 Edge for resolving power.

 

Here's on at f4 with an ASI2600 https://app.astrobin...=7tn9ml#gallery

Here's one at f3 with the Nexus https://app.astrobin...=wd3bxa#gallery

Edited by rjkrejci, 17 March 2025 - 04:53 PM.

[licho52]

There are no financial or manpower shortcuts to anything of value and galaxy imaging is one of these things.

[mayhem13]

With the 9.25, I can’t see a reason to go edge given the slower primary with less spherical abberation….unless you’re imaging in well above average seeing, your pixel scale will never notice.

 

Get the Starizona 2” reducer and replace the 925 visual back with a Baader click lock and done for galaxy season……1550mm at f6 will get it done with that budget.

[TopherTheME]

a 10" f4 newtonian (I have the Quattro 250) (or 8" f5 if your mount isn't up to it) would be perfect match for your camera and what you're looking for then at 0.48"/pixel resolution and is in your budget. I use it with 3.76u pixels camera at 0.78"/pixel...

Those are some nice images, but I'm surprised to see you say that you only collimate your scope every couple months. I've owned Synta newts before and I just can't see them being that mechanically stable over several sessions. Maybe things are different with the Quattro but I was under the impression they needed to be collimated every time they're pulled off the mount.

[TopherTheME]

With the 9.25, I can’t see a reason to go edge given the slower primary with less spherical abberation….unless you’re imaging in well above average seeing, your pixel scale will never notice.

Get the Starizona 2” reducer and replace the 925 visual back with a Baader click lock and done for galaxy season……1550mm at f6 will get it done with that budget.

Going with an SCT seems to be the popular opinion and I think you're right in that it's better to go with the XLT version if money is a concern. I still have concerns with mirror flop for the XLT version since it has no locks but maybe there's a fix for this?

[Tapio]

Going with an SCT seems to be the popular opinion and I think you're right in that it's better to go with the XLT version if money is a concern. I still have concerns with mirror flop for the XLT version since it has no locks but maybe there's a fix for this?

I have no problem with mirror flop and I only have Starbright version.

There can be better QC or just better individual scopes.

But external focuser is the common cure.

[rgsalinger]

If there are no mirror locks on the XLT an external focuser will not be able to eliminate mirror flop. I think that I'd rather just automate the actual focuser. That will let me finish my focusing run by pushing up against the mirror. If I do that, and remember to refocus after a flip, I don't see why there would be much of a problem. Maybe I'm just spoiled with my Edge. 

 

At the same time, you will want the wider image circle that the Edge version will give you. Yes, most individual galaxies are small, but you'll want to take, in many cases, groups of galaxies which will span an considerable amount of sky. 

 

The SCT's are compact and easy to handle. A 10" F4 Newtonian is a beast and is no fun to use. You may enjoy the challenge and you may have a mount that can cope. That fact is never demonstrated by just publishing finished images. Instead links to raw data make or break the case. 

 

So, I'm still liking an Edge 9.25 or 11 as the best bang for the money. 

[mayhem13]

 I still have concerns with mirror flop for the XLT version since it has no locks but maybe there's a fix for this?

Most SCT users that rely on the OE focuser have learned that your final focus adjustment needs to be clockwise or IN which keeps the mirror pre loaded avoiding flop……it’s really not that big of a deal. I’m not a remote imager but some what automated. I check and manually refocus every hour and I perform my own meridian flip and refocus after. 
 

There are auto focus routines used here together with NINA that assure the final focus motion is always an IN motion. These guys have worked out the amount of steps to HFR and all. Some awesome YouTube tutorials on AF from James Lamb too.

[Dan_I]

Those are some nice images, but I'm surprised to see you say that you only collimate your scope every couple months. I've owned Synta newts before and I just can't see them being that mechanically stable over several sessions. Maybe things are different with the Quattro but I was under the impression they needed to be collimated every time they're pulled off the mount.

The main weakness is not the mirror cell (if adjusted properly) but the spider. There are several aftermarket choices to replace the spider with a more rigid one.

Edited by Dan_I, 19 March 2025 - 05:18 AM.

[Mert]

I'd go for a carbon RC8 plus the decoupler plate from nateman_doo ( here on this forum )
and a nice focusser. ( I use a Baader RT with focusmotor ).
With the decoupler it is easy to collimate.
Works fantastic IMHO.

Edited by Mert, 19 March 2025 - 07:15 AM.

[Drothgeb]

I’m getting ready to pull out my 10” F4 for galaxy season. With the Paracorr II it’s a 1150mm F4.65. Works well on good seeing nights, but my Esprit 150 usually outperforms it. I typically use the 10” with a OSC camera on it, while using the Esprit and a mono camera to shoot L or Ha. 
 

I collimate the 10” every time I take it out. But with a barlowed laser, it only takes a few minutes to get it done.

[f430]

An 11" Edge HD with one of these focusers is a great way to go. https://optecinc.us/...=35708466725013

 

Lock the mirror down, and auto focus with the secondary focuser. Simple, reliable and accurate, with no mirror flop. 

 

Arch the wires like in the picture, for no image spikes.

 

 

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[rjkrejci]

 A 10" F4 Newtonian is a beast and is no fun to use. You may enjoy the challenge and you may have a mount that can cope. That fact is never demonstrated by just publishing finished images. Instead links to raw data make or break the case. 

 

 

Here's a link to the raw stack consisting of 3:42 worth of 60 second calibrated luminance images.   I only ran Graxpert to remove the Denver light gradient since I'm south of the city.    No other processing at all.

 

Seeing was well below average (2-3") and the wind was blowing about 15mph, and being a wind sail is a disadvantage of the 10" Newt for sure.   But you can get the idea.   Corner stars are not significantly different than center.  Definitely has the known mirror edge/bracket refraction issues around the bright stars.   May get or print a mirror mask some day as a simple fix.   But this is stock everything (focuser, spider, mirror).

 

http://www.ricksastr...ocrop_grax.xisf
 

And here the raw stack 1:36 worth of 2 minute Lums for the M33 I posted

http://www.ricksastr...o_autocrop.xisf

Edited by rjkrejci, 19 March 2025 - 01:08 PM.