21 replies to this topic

[astro_no0b]

Hello all.

 

I'm looking at small refactors for widefield imaging with a IMX571 and a IMX585 camera. I can't fit the bigger objects like M33, M42 or M45 into a single frame with a focal length longer than 400mm, so I'm not interest in anything with longer focal length than that. My budget is €1000 to 1500.

 

I can't decide if it's better to go with a smaller scope like the SQA55 and it's very good optical qualities, or size up a little to a TS-Optics 70mm FlatfieldAPO for 300 bucks more. Other options in that range would be the RedCat 51 and the FRA400. Or go even bigger with a 80mm ED triplet + flatfield reducer?

 

What are your opinions and experiences in that regard? Better optics or bigger scope?

[Jeff B]

Better optics.  Can never go wrong with better optics.

 

But pay attention to getting good, stable, mechanics too. 

[Digitaliz.se]

I would first decide what FoV you wish to have. Then decide on how much money you want to spend. 

 

/Stefan

[pyrasanth]

I have a good selection of optics ranging from 4.5 to 14 inches of mixed focal ratios. What I can tell you is that big optics don't necessarily mean better results. A bigger optic might capture more light but unless the seeing is good enough, and it rarely is, to trounce a smaller optic, then you just get a brighter image of bigger image scale but no more detail from a smaller optic but at a smaller image scale. It really is a mine field of deliberations as to what is best. Most keen imagers accept that there is no best- only luck that matches the target your trying to image with an optic most suited to object angular size and brightness.

 

I've had subjectively had better results from my little 115mm refractor than the 350mm C14 on a bad night! 

 

One last thing- the mount is everything- more so that the OTA as a brilliant optic will be let down by a poor mount but a mediocre optic will be seen at its best on a quality mount.

Edited by pyrasanth, 24 February 2025 - 03:14 PM.

[duck]

not clear to me why apochromatic lenses are needed if RGB filters are used.  Maybe for single shot color imagers.  Flat field and no coma are discriminators.

[astro_no0b]

Better optics.  Can never go wrong with better optics.

 

But pay attention to getting good, stable, mechanics too. 

 

I have a good selection of optics ranging from 4.5 to 14 inches of mixed focal ratios. What I can tell you is that big optics don't necessarily mean better results. A bigger optic might capture more light but unless the seeing is good enough, and it rarely is, to trounce a smaller optic, then you just get a brighter image of bigger image scale but no more detail from a smaller optic but at a smaller image scale. It really is a mine field of deliberations as to what is best. Most keen imagers accept that there is no best- only luck that matches the target your trying to image with an optic most suited to object angular size and brightness.

 

I've had subjectively had better results from my little 115mm refractor than the 350mm C14 on a bad night! 

 

One last thing- the mount is everything- more so that the OTA as a brilliant optic will be let down by a poor mount but a mediocre optic will be seen at its best on a quality mount.

That's my feeling too, but good optics can also be wasted if they don't match up with the camera. At 3.76µm the IMX571 is pretty much undersampled with any small scope, so the question is really, how good is good enough and at what point a bigger aperture is better, even if the optics are slightly worse. Seeing is usually between 1.5" and 2" in my Bortle 5 backyard.

 

My GEM28 can easily handle a 2-3" refractor and guide at under 1" without much problems. I also have a Wave150i on it's way which should do even better, but it'll mostly be used with a C8 EdgeHD.

 

I would first decide what FoV you wish to have. Then decide on how much money you want to spend. 

 

/Stefan

As I wrote... FoV is  M31, M42, M45, IC1805, etc... all the usual big DSOs. And money is at max €1500.

[amitshesh]

The first time I was able to photograph M31 and the Rosette nebula was after I purchased the Askar FMA 180. Those targets eluded me for a good 2 years as I upgraded my cameras and changed my telescopes.

 

The askar looks like a toy, but it isn't one. It doubles up as a (very premium) guidescope with a larger OTA. It weighs next to nothing. In its bare form you could fit in your coat pocket. I've heard from those who care more than me that it has some star distortion at the corners. And the lens-like focuser requires a more elaborate EAF kit. Its aperture is also very small. But all said and done, I cannot find a replacement that is around this size, this weight, an APO and this cost. It comes with a manual camera rotator, focuser length marks, finder shoe and finder mount.

Edited by amitshesh, 24 February 2025 - 03:56 PM.

[CHASLX200]

Smaller is better if sharper vs bigger with sloppy optics. Always takes me back to 1983 looking thru a 17" blue dob and seeing a sea of coma and mush.

[maniack]

The first time I was able to photograph M31 and the Rosette nebula was after I purchased the Askar FMA 180. Those targets eluded me for a good 2 years as I upgraded my cameras and changed my telescopes.

 

The askar looks like a toy, but it isn't one. It doubles up as a (very premium) guidescope with a larger OTA. It weighs next to nothing. In its bare form you could fit in your coat pocket. I've heard from those who care more than me that it has some star distortion at the corners. And the lens-like focuser requires a more elaborate EAF kit. Its aperture is also very small. But all said and done, I cannot find a replacement that is around this size, this weight, an APO and this cost. It comes with a manual camera rotator, focuser length marks, finder shoe and finder mount.

Seems like all you need is a scope that has a short enough focal length for these objects to fit into the view. I can easily get pictures of these with a Seestar, nothing special is needed.

[weis14]

Better optics.  Can never go wrong with better optics.

 

But pay attention to getting good, stable, mechanics too. 

Absolutely the correct approach.  Get optics and mechanics right, then worry about aperture.  Just as true for visual as imaging in my opinion.

[Drothgeb]

not clear to me why apochromatic lenses are needed if RGB filters are used.  Maybe for single shot color imagers.  Flat field and no coma are discriminators.

Using mono and R,G,B filters doesn’t help that much with correcting CA, if that’s what you mean. Been there, done that with several scopes. The better the scope is corrected, the better.

 

OP, If you want sharp images, you need sharp optics. Things like guiding and seeing, have the effect of lowering your strehl. The higher it is before, the higher it will be after. Most scopes you list are good. The FRA400 doesn’t have the best spots though. The FRA300 is good.

 

Whether you want a tight crop, or wide with IFN showing, only you can decide on how you want to frame your target. And you listed 2 different cameras. Which do you want shoot what with? You list M33. I’ve shot that at 1075mm, definitely not a wide field target. Go to Astronomy Tools to figure out your preferred focal length. Personally, I shoot at 385mm with a SVX80T quite a bit. Seems to frame many targets well with an IMX571. If that’s not wide enough, I switch to my FMA180.

[astro_no0b]

OP, If you want sharp images, you need sharp optics. Things like guiding and seeing, have the effect of lowering your strehl. The higher it is before, the higher it will be after. Most scopes you list are good. The FRA400 doesn’t have the best spots though. The FRA300 is good.

 

Whether you want a tight crop, or wide with IFN showing, only you can decide on how you want to frame your target. And you listed 2 different cameras. Which do you want shoot what with? You list M33. I’ve shot that at 1075mm, definitely not a wide field target. Go to Astronomy Tools to figure out your preferred focal length. Personally, I shoot at 385mm with a SVX80T quite a bit. Seems to frame many targets well with an IMX571. If that’s not wide enough, I switch to my FMA180.

I list two cameras, because I want to use the scope with both of them, mostly the IMX585 though, as the IMX571 will be paired with my new C8 EdgeHD - funnily enough the C8 with the IMX571 will have the same FoV as my currently used combination of Quattro 150P + IMX585.

I have the EvoGuide 50 ED with flattener, but I don't think it'll work very well with the IMX571, that's the reason for me looking for an upgrade to that.

 

Ideally I would like to go for the SQA85, but that's a little out of my pricerange, now that I've just ordered a completely new setup for €9k.

Edited by astro_no0b, 25 February 2025 - 06:58 AM.

[Drothgeb]

I list two cameras, because I want to use the scope with both of them, mostly the IMX585 though, as the IMX571 will be paired with my new C8 EdgeHD - funnily enough the C8 with the IMX571 will have the same FoV as my currently used combination of Quattro 150P + IMX585.

I have the EvoGuide 50 ED with flattener, but I don't think it'll work very well with the IMX571, that's the reason for me looking for an upgrade to that.

 

Ideally I would like to go for the SQA85, but that's a little out of my pricerange, now that I've just ordered a completely new setup for €9k.

I actually have a 50ED and both the SW and Starizona flatteners. The SW works OK with APS, you’re just limited to 17.5mm backspacing. The Starizona has a full 55mm backspacing, but vignettes bad. With either, the focuser is a pain, but does work with an EAF. Since you already have it, I would give it a try. 

[astro_no0b]

I actually have a 50ED and both the SW and Starizona flatteners. The SW works OK with APS, you’re just limited to 17.5mm backspacing. The Starizona has a full 55mm backspacing, but vignettes bad. With either, the focuser is a pain, but does work with an EAF. Since you already have it, I would give it a try. 

I have the Sky-Watcher flattener and the 17.5mm backspacing isn't an issue in general, but the ability to use an OAG would make it much easier than strapping a 30mm guidescope ontop. The stars are undersampled and a little soft, even with the IMX585 and it's smaller pixels. Still a very good scope without much noticable CA in my case, especially at it's very low price at just under €400 incl flattener.

With an T2 to 1.25" filter-adapter screwed into the camera itself I'm also able to use filters with the smaller IMX585 sensor without conflicting with the backfocus limitation.

[amitshesh]

Seems like all you need is a scope that has a short enough focal length for these objects to fit into the view. I can easily get pictures of these with a Seestar, nothing special is needed.

Well ..yes. But seestar does not help if I want to use a better camera, take longer exposures, etc.

It's not a trivial concern. I cannot get even 20s exposures in my seestar without trailing. So 10s it is. Then add the significant rejection rate of the seestar. Clear nights are like gold where I live. I don't want to discover in the morning that I spent 8 hours at a single target but got only 4 hours worth of subs. And the biggest limitation according to me: there is almost nothing you can do about this than live with it (or use software that is not officially supported). Seestar is great, but once the initial thrill wore off, I could see it had significant limitations over any other custom rig if one wanted to do anything other than live stacking.

My point is that at least I did not consider that 180mm is a "telescope" worth buying. So I did not consider such a small focal length a worthwhile expense given that I have camera lenses and a mirrorless camera. But once I got over that after reading rave reviews, I was happy with just how small and light this is.

Edited by amitshesh, 25 February 2025 - 09:08 AM.

[maniack]

Well ..yes. But seestar does not help if I want to use a better camera, take longer exposures, etc.

It's not a trivial concern. I cannot get even 20s exposures in my seestar without trailing. So 10s it is. Then add the significant rejection rate of the seestar. Clear nights are like gold where I live. I don't want to discover in the morning that I spent 8 hours at a single target but got only 4 hours worth of subs. And the biggest limitation according to me: there is almost nothing you can do about this than live with it (or use software that is not officially supported). Seestar is great, but once the initial thrill wore off, I could see it had significant limitations over any other custom rig if one wanted to do anything other than live stacking.

My point is that at least I did not consider that 180mm is a "telescope" worth buying. So I did not consider such a small focal length a worthwhile expense given that I have camera lenses and a mirrorless camera. But once I got over that after reading rave reviews, I was happy with just how small and light this is.

The point isn't that you should be using the Seestar instead, it's that the Seestar makes it obvious to a casual user that relatively inexpensive optics of a small aperture can be highly capable. The S50 is only a 50mm run-of-the-mill triplet. You should be able to do even better with a nice 40mm-50mm triplet on a setup more appropriate for astrophotography.

[mdanese]

Don't forget that you can use mosaics to stitch together frames and get the whole image.  More work, more time, and more potential things to go wrong, of course.  But if it lets you get a scope you like better, it is something to consider.

Edited by mdanese, 26 February 2025 - 01:57 PM.

[Wildetelescope]

All the scopes you list are likely comparable with respect to optical QUALITY, meaning the likelihood that you get a good sample for a given design.  Looks like these are all Petzvals for the most part.   Your real question is what aperture are you going for. If you want to up the quality, you would be looking at Televue or Tak FSQ line of Petzval scopes. 

 

That said, I have seen happy reviews of most of the scopes in your list, so if you get a good sample you are good to rock and roll, at a greatly reduced cost.    As others have suggested, what is probably more important is identifying the proper scope, camera combination and purchase based on the total cost of your system.

 

JMD

[astro_no0b]

To be honest, I probably would've allready made up my mind, if it were'nt for the recently released SQA line from Askar which rivals the optical quality of Televue or Takahashi scopes at a much lower pricetag.

[Wildetelescope]

To be honest, I probably would've allready made up my mind, if it were'nt for the recently released SQA line from Askar which rivals the optical quality of Televue or Takahashi scopes at a much lower pricetag.

by what measure?   to be honest, if you look at the Pinned DPAC thread, you can see many examples of overseas optics that approach the quality of Tak and Televue.  The venerable  F9 100mm ED and the 120 mm F7 ED scopes come to mind.  The AT 92 and the Esprit line of scopes also have very excellent reputations.  I have also seen a lot of impressive images coming from the AT 60 mm Petzvel scope as well.   

 

Where Tak/AP/TEC really hit is that their quality is generally much more consistent from scope to scope,  compared to the mass produced scopes.  This is not so much a question of where they are made, but more about compromises made to accommodate much higher volumes at lower price points.   As I said, for the scopes in the mid tier price range you are considering, chances are that you will get a good to excellent scope. Stepping up to the big guys means you are likely to get an excellent scope to a superlative scope.  In your range I think it is more important is matching the camera to whichever optics you ultimately choose.   I would go with larger aperture, with that round of scopes.

 

JMD

[astro_no0b]

I finally made a decision and went with a Sharpstar 15028HNT-AL fast newtonian instead. Fast scopes are the optimal solution for my situation, as I only get some 15, maybe 20 if I'm lucky, clear nights per year. So in the future I'll be using my trusty Quattro 150P with the IMX585C and the new one with a larger IMX571C sensor, as the Quattro 150P simply can't illuminate the bigger sensors.

[PKDfan]

I finally made a decision and went with a Sharpstar 5028HNT-AL fast newtonian instead. Fast scopes are the optimal solution for my situation, as I only get some 15, maybe 20 if I'm lucky, clear nights per year. So in the future I'll be using my trusty Quattro 150P with the IMX585C and the new one with a larger IMX571C sensor, as the Quattro 150P simply can't illuminate the bigger sensors.

Good Hunting with the new gear astro_noOb !!

I feel for you and your lack of clear skies so i hope that your new data gathering process goes...swimmingly.

Looking forward to see the results !



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