Help needed choosing a new telescope for imaging

[vlaiv]

1 minute ago, Rallemikken said:

Once in a while people with problems posts flats here, pretty obvious which ones uses refractors..........

Usually people with newtonians having light leak

 

[ONIKKINEN]

2 hours ago, Lee_P said:

Ah, this is it, I don't like to tinker at all if I can help it! Hence being drawn to the 107PHQ.

I'm not fully clued up on binning... could you explain a bit more? If it only affects the length of my subexposures, then that's no problem. I currently shoot 2-minute subs, it would be easy to switch to 3-minutes. You're saying that if I boost those subframes then I could still aim for 20-hour integrations, rather than the 32-hours I calculated? I'm not sure what's meant by "working resolution". If I bin 2x2, that'll get me SNR faster, but will lower the final resolution?

Sounds like you would hate a newtonian, maybe pass that idea for now. Newtonians might be the furthest thing you can get from a petzval plug and play APO so probably not a good idea!

With the 107PHQ you could BINx2 to reach the (more or less) same resolution as your current setup gives you, so now you have the same working resolution but with more aperture = speed increases and you might find that you can get away with shorter total integrations (but with smaller FOV). But since you are using an OSC camera its not quite so simple, as using debayering methods other than superpixel debayering results in basically an upscaled image. So if you debayer the subframes using some method that does interpolation, you are basically artificially getting to the quoted 1.9'' per pixel resolution your current setup at a glance gives you. The camera samples the sky at half this rate in reality, so the real data is at best 3.8'' per pixel. If you then bin that already upscaled 1.9'' image to 3.8'', you dont get the full benefits of binning that a mono camera with the same sensor would. Its better than not binning at all but does not improve SNR by x2.

You can test this with your own data to see that it really is like this with OSC cameras. Resample one of your processed images to 50% using some quality preserving resampling method and then resample that back to 200%, so to the original resolution. There will be no change in the fine detail level as that level of detail was not captured in the first place.

[catburglar]

@vlaiv has probably hit the nail on the head in terms of what’s the ‘fastest’ option - an 8inch SCT or RC, with a suitable reducer and combined with pixel binning will be hard to beat if you can get by with the narrow FoV and lower effective pixel count…But if you’re going to do mosaic’s to make up the FoV then you’ll be negating the benefit… 
PS There’s an 8” Edge HD in the classifieds if you’re interested 😁 (no connection to the seller)

[Lee_P]

23 minutes ago, vlaiv said:

There is really little difference between the two - I mean cropping current setup and using longer focal length telescope.

Difference is in ability to actually achieve certain resolution - which depends on guide performance, seeing and aperture size (in non trivial way).

First thing you should do is to measure what you've been able to achieve in terms of resolution / star FWHM with your current setup.

My guess is that you'll find your stars to be in 3.5" to 4" FWHM range.

In order to say properly sample at something like 1.5"/px - you'll need about 2.4" - 2.5" FWHM stars. This requires decent seeing and at least 6" of aperture if not more.

Here's a FWHM analysis of the subframes that went into my latest image:

[vlaiv]

30 minutes ago, Lee_P said:

Here's a FWHM analysis of the subframes that went into my latest image:

What units are those?

Pixels or arc seconds?

Btw, your stars are rather elliptical with ~0.7 eccentricity.

Do you have big difference in RA and DEC guiding performance? Usually if you have elongation in X axis (RA aligned to X and worse guiding performance in RA due to backlash and good balance) it is hard to spot in image.

[tomato]

52 minutes ago, Rallemikken said:

Sooner or later all refractors fills up with god-knows-what, and you will have a hard time dismantling it and cleaning it up. Once in a while people with problems posts flats here, pretty obvious which ones uses refractors..........

How exactly do refractor cells fill up with stuff? Yes, you will get crud on the external surface of the lens, but that can be cleaned (when  necessary) just like a mirror, but aren’t all of the internal surfaces sealed in the lens cell?  With the number of refractors out there I would expect to see a steady stream of posts on this topic, but I haven’t seen any evidence of this.

[Rallemikken]

22 minutes ago, tomato said:

How exactly do refractor cells fill up with stuff?

God knows how, must be entrophy at it's best. But they are OK as guidescopes. Bought a ST80 for my newt, have even used it for imaging. This one is fairly easy to take apart, just two lenses. And don't forget, all big scopes in the world are newt's.

[vlaiv]

8 minutes ago, Rallemikken said:

And don't forget, all big scopes in the world are newt's.

I'd say RCs have the lead in that field.

[raadoo]

@Lee_P

I’m in the same boat as you - got an FRA400 paired with a 183 and am looking for an apo in the 700 - 900 focal length range to pair with a 2600. I’ve not yet reached a decision on what I’ll move to next but maybe my shortlist will help you narrow your search down or even prompt others to share their thoughts:

Refractors

• TS 115/800 - €1500 - affordable and gets a lot of praise from knowledgeable folk (e.g. @vlaiv).
• ES FCD-100 CF 102/714 - €2000 - Optics should be good and that carbon fiber means your mount has an easier time swinging the rig around.
• TS CF 102/714 - €2000 - Looks solid from a mechanical point of view, with all the right imaging accoutrements and each one gets tested before shipping.
• TS 106/700 - €2200 - FCD-100 should perform really well but it’s pretty new and untested.
• ES FCD-100 127/952 - €2700 - Bigger brother to the 102 is as light as a 4” aluminium scope but hey, bigger aperture. Do keep in mind that it’s pushing close to a meter in length for the scope alone (oversized dew shield extended).
• Vixen AX103/825 - €2900 - Vixen often get overlooked and no one knows what glass they are using but its pseudo-petzval design is quite appealing.
• Askar 107PHQ - €2900 - A thing to note about Askar’s Petzval scopes is that there will be some variability in quality. My FRA400 is no lemon but it does show chromatic aberrations across the field, whereas yours is a better corrected unit, from what I’ve seen in your images.
• APM LZOS 100/800 - €3900 - A lot of dosh but by all accounts should be an amazing optic even though it’s quite slow at f/8.

Reflectors

• Skywatcher 150PDS/750 - €410 - Cheap as chips and a large community of modders means you should find help for any issue. And f/5 is going to be more forgiving of collimation errors.
• Vixen R200SS/760 - €1400 - Despite the thick vanes and mediocre focuser, this one has a neat party trick in that it can become an 1120mm f/5.6 scope with the use of the Extender PH. And you can switch out the tube for a carbon one later down the line.
• Boren Simon 8”/568-800 - €2200 - This one’s interesting because it’s a carbon tube and can play double duty as an f/2.8 or f/4 scope with the use of a TSGPU Coma Corrector.
• TS 8” ONTC w/ FeatherTouch ~ €2900 - You do get a fine scope for the money, but be prepared to wait a while to get it and at this price you better love newts.

I’m intentionally leaving out RC’s from this list as you mentioned wanting to faff about as little as possible (a sentiment I echo), which kind of only leaves newtonians on the table for the focal lengths you’re after.

For what it’s worth, I’m personally leaning towards the ES102CF, as it seems to offer the most for one’s buck. I’d spring for the 127 even, but on my narrow balcony I’d probably end up crashing the scope against a wall. Alternatively, the R200SS and it’s party trick makes it appealing for next year’s galaxy season without moving to an SCT.

Did I miss any other potential candidates?

Slightly off-topic: Sharpstar just dropped news about their upcoming Z4, which is a 100mm f/5.5 refractor. Maybe they’ll follow up with a 120mm f/6? Strange naming though; not sure what the 4 means. Or why they needed another refractor in this focal length / f ratio to compete with their own 94EDPH, 100QII or FRA600?

[Rallemikken]

5 minutes ago, vlaiv said:

RC

I know, but "newt's" sounds better.   Considered to use "reflectors"....

And the refractor guy's don't know the difference anyway.

Edited July 20, 2022 by Rallemikken
To clearify comment.

[vlaiv]

2 minutes ago, raadoo said:

Did I miss any other potential candidates?

Do include SW MN190 and ES MN-152

There are few high end models from Intes Micro - but no longer produced and maybe only available second hand.

[raadoo]

5 minutes ago, vlaiv said:

Do include SW MN190 and ES MN-152

There are few high end models from Intes Micro - but no longer produced and maybe only available second hand.

Intentionally didn’t include those as:

• The ES 152 was discontinued last year
• The SW is 12kg, so too much for Lee’s mount

But, for sure, if one can find an ES or Intes on the used market, they’re worth considering.

[ONIKKINEN]

7 minutes ago, raadoo said:

Intentionally didn’t include those as:

• The ES 152 was discontinued last year
• The SW is 12kg, so too much for Lee’s mount

But, for sure, if one can find an ES or Intes on the used market, they’re worth considering.

TS and Astroshop.eu still sell the Explore scientific mak-newt. Long delivery times though.

https://www.astroshop.eu/telescopes/explore-scientific-maksutov-newton-telescope-mn-152-740-ota/p,22534

https://www.teleskop-express.de/shop/product_info.php/info/p12005_Explore-Scientific-MN-152-f-4-8-Maksutov-Newtonian-Telescope-with-Field-Correction.html

[900SL]

Having just gone through the same process and candidates, I've decided to get an ES 152 MN. Now waiting for them to arrive in stock. 

[Lee_P]

10 hours ago, vlaiv said:

What units are those?

Pixels or arc seconds?

Arc seconds, I think... Attached is a FITS file if you'd be so kind as to check!

NGC_3372_Light_600_secs_2022-03-24T21-00-32_001.fits

 

10 hours ago, vlaiv said:

Btw, your stars are rather elliptical with ~0.7 eccentricity.

Do you have big difference in RA and DEC guiding performance? Usually if you have elongation in X axis (RA aligned to X and worse guiding performance in RA due to backlash and good balance) it is hard to spot in image.

Thanks, I never noticed. Something for me to investigate further!

[Lee_P]

2 hours ago, 900SL said:

Having just gone through the same process and candidates, I've decided to get an ES 152 MN. Now waiting for them to arrive in stock. 

It is a tempting option. But annoying if they've just been discontinued though! Do you know if they fit a ZWO EAF? And does it come with a camera rotator?

[Lee_P]

11 hours ago, ONIKKINEN said:

Sounds like you would hate a newtonian, maybe pass that idea for now. Newtonians might be the furthest thing you can get from a petzval plug and play APO so probably not a good idea!

With the 107PHQ you could BINx2 to reach the (more or less) same resolution as your current setup gives you, so now you have the same working resolution but with more aperture = speed increases and you might find that you can get away with shorter total integrations (but with smaller FOV). But since you are using an OSC camera its not quite so simple, as using debayering methods other than superpixel debayering results in basically an upscaled image. So if you debayer the subframes using some method that does interpolation, you are basically artificially getting to the quoted 1.9'' per pixel resolution your current setup at a glance gives you. The camera samples the sky at half this rate in reality, so the real data is at best 3.8'' per pixel. If you then bin that already upscaled 1.9'' image to 3.8'', you dont get the full benefits of binning that a mono camera with the same sensor would. Its better than not binning at all but does not improve SNR by x2.

You can test this with your own data to see that it really is like this with OSC cameras. Resample one of your processed images to 50% using some quality preserving resampling method and then resample that back to 200%, so to the original resolution. There will be no change in the fine detail level as that level of detail was not captured in the first place.

Ok, thanks. So what if I didn't bin (i.e. BINx1) with the PHQ107? Better resolution but slower speed (0.6x my current?)

[Lee_P]

12 hours ago, GalaxyGael said:

Image scale as mentioned above is a good guide, and if your skies are bortle high then go down in scale from your 1.9 "/px  to roughly double your average guiding rms so that you get all the resolution your scope gives you for given skies.

With 2600mc, 650 mm is about 1.2 "/px and 760mm hits about 1" /px. If you look at your average star fwhm (maybe asi studio fits viewer has a star size button now), divide that value by 1.4-1.6 as a guide for your best seeing, and that might help decide the focal length and image scale. 

I'm guessing around 700mm will be your limit, any longer and you may not see the benefits compared to a crop ay 700mm. 

Then, I would decide aperture for brightness and some resolution benefit, and then the size and weight and use all these criteria to narrow down. 

And the there are spikes. If you don't like them, the Mn190 is great if you have the mount payload capacity and the right pixel size, or a long, expensive heavy apo. The TS 130/910 is very good, and with 0.79x reducer is about 715mm or so at f/5.5. Perfect in my view. 

A 6 inch imaging newt, decent one is a good option, such as the ontc range from ts which are outstanding. 

Or an epsilon 130d with the 1.5x extender to give 650 mm at f/5 ( there is one available, hint hint, about to put mine on the block). The f ratio for objects that will now span across more pixels compared to the FRA5. 6 is partially moot once you are above the noise and plan do long longish integrations. Its longer, but does t scale with ratio of squares of f ratios unless the focal length and pixel scale are the same. So slower f ratios are no thin to be feared unless its f/12 or something! 

TS also have fcd 100 106mm apos with beefy focusers at f/ 6.something. 

Lastly, you are osc so binning in software is an option for ~1200mm mm at bin 2, giving you the same pixel scale as 600 mm with bin 1 on the same camera. 

 

Thanks, this is very helpful. It does sound like around 700mm is my limit; maybe a bit more on very steady nights. The MN190 and TS 130/910 are a bit heavy for my mount, I fear. An Epsilon 130d with 1.5 extender is an interesting proposition, and not something I'd considered. Do you know if it would fit a ZWO EAF? I'm not so keen on diffraction spikes, but could be persuaded if all my other boxes are ticked. Given that I image a single target over many weeks, would I need to consider the OTA's orientation to keep the diffraction spikes in the same positions? (If that question makes sense).

[900SL]

38 minutes ago, Lee_P said:

It is a tempting option. But annoying if they've just been discontinued though! Do you know if they fit a ZWO EAF? And does it come with a camera rotator?

https://www.cloudynights.com/topic/752071-focuser-on-explore-scientific-comet-hunter/

Google is your friend

Mak Newts are expensive to make. The 152MN is very well reviewed. 

I looked at an Intes Micro 56 initially but this is not ideal for imaging as it has a small illuminated circle. 

The 152MN is better suited for imaging

 

Edited July 21, 2022 by 900SL

[Lee_P]

10 hours ago, raadoo said:

@Lee_P

I’m in the same boat as you - got an FRA400 paired with a 183 and am looking for an apo in the 700 - 900 focal length range to pair with a 2600. I’ve not yet reached a decision on what I’ll move to next but maybe my shortlist will help you narrow your search down or even prompt others to share their thoughts:

Refractors

• TS 115/800 - €1500 - affordable and gets a lot of praise from knowledgeable folk (e.g. @vlaiv).
• ES FCD-100 CF 102/714 - €2000 - Optics should be good and that carbon fiber means your mount has an easier time swinging the rig around.
• TS CF 102/714 - €2000 - Looks solid from a mechanical point of view, with all the right imaging accoutrements and each one gets tested before shipping.
• TS 106/700 - €2200 - FCD-100 should perform really well but it’s pretty new and untested.
• ES FCD-100 127/952 - €2700 - Bigger brother to the 102 is as light as a 4” aluminium scope but hey, bigger aperture. Do keep in mind that it’s pushing close to a meter in length for the scope alone (oversized dew shield extended).
• Vixen AX103/825 - €2900 - Vixen often get overlooked and no one knows what glass they are using but its pseudo-petzval design is quite appealing.
• Askar 107PHQ - €2900 - A thing to note about Askar’s Petzval scopes is that there will be some variability in quality. My FRA400 is no lemon but it does show chromatic aberrations across the field, whereas yours is a better corrected unit, from what I’ve seen in your images.
• APM LZOS 100/800 - €3900 - A lot of dosh but by all accounts should be an amazing optic even though it’s quite slow at f/8.

Reflectors

• Skywatcher 150PDS/750 - €410 - Cheap as chips and a large community of modders means you should find help for any issue. And f/5 is going to be more forgiving of collimation errors.
• Vixen R200SS/760 - €1400 - Despite the thick vanes and mediocre focuser, this one has a neat party trick in that it can become an 1120mm f/5.6 scope with the use of the Extender PH. And you can switch out the tube for a carbon one later down the line.
• Boren Simon 8”/568-800 - €2200 - This one’s interesting because it’s a carbon tube and can play double duty as an f/2.8 or f/4 scope with the use of a TSGPU Coma Corrector.
• TS 8” ONTC w/ FeatherTouch ~ €2900 - You do get a fine scope for the money, but be prepared to wait a while to get it and at this price you better love newts.

I’m intentionally leaving out RC’s from this list as you mentioned wanting to faff about as little as possible (a sentiment I echo), which kind of only leaves newtonians on the table for the focal lengths you’re after.

For what it’s worth, I’m personally leaning towards the ES102CF, as it seems to offer the most for one’s buck. I’d spring for the 127 even, but on my narrow balcony I’d probably end up crashing the scope against a wall. Alternatively, the R200SS and it’s party trick makes it appealing for next year’s galaxy season without moving to an SCT.

Did I miss any other potential candidates?

Slightly off-topic: Sharpstar just dropped news about their upcoming Z4, which is a 100mm f/5.5 refractor. Maybe they’ll follow up with a 120mm f/6? Strange naming though; not sure what the 4 means. Or why they needed another refractor in this focal length / f ratio to compete with their own 94EDPH, 100QII or FRA600?

This is a brilliant list, thanks! I've spent some time this morning looking through them all. I think the two that appeal to me most are:

• ES102CF. This has a good specification, and a like how light it is. Would it need a flattener though? It sounds like it can take a ZWO EAF but longer bolts are needed.
• Askar 107PHQ. This was my original thought for an upgrade and it's hard to shift it out of my head. I hear you about the quality control issues, but FLO bench test all their Askars, which means they should pick up on any lemons.
   
• And the ES MN152 is an interesting proposition that may be the best of all worlds. Maybe hard to get hold of though!

Have you been following the other posts in this thread? It's interesting to hear about the limits of sky conditions and the like, and vlaiv's comments around how there may not be much gained by having a new telescope rather than just cropping in on the images we're taking already. (Although you and I are using different cameras).

Edited July 21, 2022 by Lee_P

[GalaxyGael]

27 minutes ago, Lee_P said:

Thanks, this is very helpful. It does sound like around 700mm is my limit; maybe a bit more on very steady nights. The MN190 and TS 130/910 are a bit heavy for my mount, I fear. An Epsilon 130d with 1.5 extender is an interesting proposition, and not something I'd considered. Do you know if it would fit a ZWO EAF? I'm not so keen on diffraction spikes, but could be persuaded if all my other boxes are ticked. Given that I image a single target over many weeks, would I need to consider the OTA's orientation to keep the diffraction spikes in the same positions? (If that question makes sense).

The epsilon takes a ZWO EAF. There is an adapter that can be 3D printed from a freely available file on the web (I have a bunch of these) and it slots on, attached the EAF as normal. The OTA orientation will always remain the same really to maintain overlaid spikes, so nothing should change unless you are taking the scope out of its rings, which you probably don't do anyway with your other scopes. the epsilon is easier to balance when then camera et al. are point straight up, rather than pointing down parallel to the counterweight bar like most imaging newts do. You can do it either way, but pointing up for the short length of the epsilon works very well.

The 107PHQ intruiged me too, but I wonder did sharpstar just lengthen the focal length to deal with the documented color issues on the FRA series, notably the FRA600. It looks to be a nice scope, although quite heavy as there is a trend for big CNC parts that give a good fit and finish, but are (I think) a little heavier than needs to be.

the TS 115/800 option is another and I had that. It is light, easily carrier on your mount and you get 800 mm at f.6.9 or 632 mm at f/5.5 with the 0.79x TSRED379 reducer. That could be a good option too.

[The Admiral]

Just to muddy the waters further, have you looked at the Altair triplet scopes? I had a Wave 102ED triplet and that gave some nice results. I see that there is a new 130mm triplet, which with the reducer gives about 700mm effective FL at f/5.6. Might be a bit heavy though. These scopes might exist as other brands of course (i.e. TS APO range for example). They all come with an optical bench test results sheet.

Ian

Edited July 21, 2022 by The Admiral

[vlaiv]

1 hour ago, Lee_P said:

Arc seconds, I think... Attached is a FITS file if you'd be so kind as to check!

AstroImageJ gives quite different results. Something else seems to be off

Average FWHM seems to be around 3.5-3.6px.

FITS header of that file is also very strange - it gives:

Pixel size seems to be reported correctly, but focal length is set to 749mm and hence pixel scale is 1.0356"/px?

Do you plate solve or did you manually enter 750mm FL for some reason? Is this image from that 400mm scope?

If image is from 400mm and all else is correct apart from wrong FL reported - then your FWHM values are about ~6.75", which means that you should be sampling at about ~4.2"/px or image should be about 2.2 times smaller (it is over sampled by factor of x2).

Indeed - if we reduce it to 50% (a bit less than it should be - but easy to do in order to remove bayer matrix), and crop it to 100% "zoom level":

It still looks good and sharp (above is just linear stretch - white/black point to show what is there).

[raadoo]

1 hour ago, Lee_P said:

This is a brilliant list, thanks! I've spent some time this morning looking through them all. I think the two that appeal to me most are:

• ES102CF. This has a good specification, and a like how light it is. Would it need a flattener though? It sounds like it can take a ZWO EAF but longer bolts are needed.
• Askar 107PHQ. This was my original thought for an upgrade and it's hard to shift it out of my head. I hear you about the quality control issues, but FLO bench test all their Askars, which means they should pick up on any lemons.
   
• And the ES MN152 is an interesting proposition that may be the best of all worlds. Maybe hard to get hold of though!

Have you been following the other posts in this thread? It's interesting to hear about the limits of sky conditions and the like, and vlaiv's comments around how there may not be much gained by having a new telescope rather than just cropping in on the images we're taking already. (Although you and I are using different cameras).

In my case (FRA400 + 183 sensor), sampling should already be realistic in terms of my local seeing (~3"). Pairing a larger scope (4" - 5") with a 571 sensor like yours means I would end up with similar sampling rates (but significantly better S/N). The 571 sensor I'm eyeing is a mono one, to pair up with my current colour camera. So it's more about doubling up and giving myself more imaging flexibility while reducing time spent on a single target, but - and this is coming back to sampling and bad skies of course - for those occasions when I go to a dark site (B2), I should, theoretically, be able to stick the 183 sensor on the big scope and get decently sampled results.

Apologies for a bit of introspection:

At the end of the day, though, we're not professional astronomers, we're just passionate about the crazy stuff that's up there in the sky. So, if you under or oversample your images, is that the end of the world? Did any of us that started out by pointing a DSLR attached to a modest camera lens up at the sky - with or without a tracker - even know what sampling was? Did that lessen the fun or awe or just child-like giddiness when you see that first image of Orion or Andromeda or the Moon and you feel like you trapped lightning in a bottle? And sure, we into imaging are often gear-heads of the highest caliber and can't help but dive deep into all the fun technical details of this hobby, but I for one won't let technical limitations, theoretical or practical, get in the way of having plain old fun. And if I'm lucky, I might also learn a few things along the way.

[Lee_P]

16 minutes ago, raadoo said:

At the end of the day, though, we're not professional astronomers, we're just passionate about the crazy stuff that's up there in the sky. So, if you under or oversample your images, is that the end of the world? Did any of us that started out by pointing a DSLR attached to a modest camera lens up at the sky - with or without a tracker - even know what sampling was? Did that lessen the fun or awe or just child-like giddiness when you see that first image of Orion or Andromeda or the Moon and you feel like you trapped lightning in a bottle? And sure, we into imaging are often gear-heads of the highest caliber and can't help but dive deep into all the fun technical details of this hobby, but I for one won't let technical limitations, theoretical or practical, get in the way of having plain old fun. And if I'm lucky, I might also learn a few things along the way.

Totally agree, 100%! (Although I'm very grateful to the experts here on SGL who assist with my understanding of the technical aspects!)