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Planning an upgrade...refractor or reflector?

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#1 jdk

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Posted 14 January 2020 - 08:28 PM

Ok, I’m seeking opinions on a new telescope upgrade for later this year (hopefully in the next few months).

The three most relevant background details are as follows:

1. My mount is a 10 micron 1000hps. 55lb weight capacity.

2. After giving mono a try, I’ve developed a preference for OSC. I’m about to place an order for a ZWO 6200. It requires a 43mm image circle. (I know that technically mono/LRGB is capable of faster data acquisition, but that is in a vacuum. So far I’ve found that seeing variation and clouds can level the playing field, even using an LRGB, LRGB, LRGB shooting approach)

3. I shoot exclusively from Bortle 1 sites.

So. I currently shoot with an 11” RASA. I like it, but I’m growing tired of routing cables over the corrector and the image scale with the 6200 will only be around 1.3”/px. Ideally, I’d like to be around .8”/px - or less...convince me 🙂 The speed of the RASA is hard to argue with but I know its going to come at the price of resolution.

Unfortunately, the large image circle drives me way into a brutal price bracket. I don’t think there’s any way out of putting up less than $5k for an upgrade. But that’s why I’m soliciting opinions; I want to make sure I’m not overlooking something that might work for me.

Right now, I’m looking at two options. One refractor, one reflector.

Option 1: TEC 140 with a focal reducer. I know this telescope is highly regarded and the available reducer options can get me to f/5 or f/6.3 while still maximizing the resolving power of the optics. I can’t find specs on the image circle but it seems to accommodate a 35mm sensor with no problems. The total cost with rings and a dovetail is around $8k. Ouch.

Option 2: Officina Stellare RH 200 AT mark II. There is less information about this one but it basically offers more speed with reduced resolution - 3.76u pixels @ 600mm is less than what I have now. But I’m still strongly considering it because the price is about the same as the TEC and the speed is palpably more. Total cost is also around $8k. Ouch.

What other options have I missed? Image scale and circle size is really driving my search here, with speed a very, very close second.

Also, important side note: diffraction spikes are a no go for me. No newts, rc’s, etc. I also do not want to bin.

What say ye?

Joe

#2 rockstarbill

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Posted 14 January 2020 - 08:36 PM

Well since diffraction spikes are a no go, you have Refractors, Honders, Mak Newts, and SCTs as your options. Refractors will cost a load per inch of aperture and SCTs are usually the best bang for the buck. They are slower however. Mak Newts are limited in options and may or may not provide the imaging circle you are looking for.

TEC140 is 706mm reduced with the AP Quad TCC, and will fill full frame. 620mm to 706 isn't that great of a difference either. I think it's around 1000mm with a flattener, but obviously slower.

Edited by rockstarbill, 14 January 2020 - 08:43 PM.

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#3 jdk

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Posted 14 January 2020 - 08:58 PM

TEC140 is 706mm reduced with the AP Quad TCC, and will fill full frame. 620mm to 706 isn't that great of a difference either. I think it's around 1000mm with a flattener, but obviously slower.

Yeah, it’s not a perfect solution. Is it worth a few thousand dollars to increase resolution by a modest amount and not have to deal with all of the issues that come with RASA imaging? hmmmmmm 



#4 John O'Grady

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Posted 14 January 2020 - 08:58 PM

In the case of option 2 - the difference between the RASA at 620mm vs the Officina at 600mm is negligible (20mm difference in focal length).  The resulting image scale (arcssec/pixel) would be 1.25 vs 1.29 respectively with an IMX455 sensor (ZWO6200).  If it was me, given the difference in image scale is marginal, I wouldn't trade up to the Officina from the RASA unless I was sigfnificantly unhappy with some aspect of how the RASA performs. 

 

I don't see what the Officina will get you given it's very close to the RASA.  Mind you, I haven't compared the spot diagrams between the two instruments.

Assuming there's not a practical difference between the two, I'd suggest you consider a longer focal length option, as I'm assuming you want to bring out more detail in DSOs.

I image with a C9 EDGE HD and I am very happy with the results and image scale (0.75"). (no diffraction spikes, 43mm image circle and less coin than other options)

 

As rockstarbill says, unless you go the flattener route (assuming 1x) to get the 0.8" degrees, you've not made that significant a change in focal length with the TEC either.

 

Setting aside the cabling issue with the RASA, what do you want to  image (or acheive) that's not working for you with the RASA?

Too wide field and you want image galaxies?

 

Good luck, I'm going to follow this thread as it's an interesting discussion.

 

Cheers - John


Edited by John O'Grady, 14 January 2020 - 09:00 PM.

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#5 rockstarbill

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Posted 14 January 2020 - 09:04 PM

Yeah, it’s not a perfect solution. Is it worth a few thousand dollars to increase resolution by a modest amount and not have to deal with all of the issues that come with RASA imaging? hmmmmmm


Honestly, no it isn't. If I had $8k and wanted to get a longer FL system I'd look at either getting over diffraction spikes, which opens up more options, or look at the Edge 9.25 with perhaps the reducer.
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#6 SilverLitz

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Posted 14 January 2020 - 10:35 PM

Why are you wanting to go all the way to full-frame sensor?  Is it FoV?

 

Your RASA 11 is not that long, so it will have a good size with an APS-C ASI2600 ($2K), you would have 130'x87' FoV, vs. 199'x133' with the ASI6200.  I guess it is to fit M31???  They both will be 1.25"/px, which is fine image scale for such large targets.

 

If it is detail you are after, pair the RASA with the ASI183MC-Pro ($800).  This will give you 0.8"/px and 73'x48' FoV, which will frame most small to medium targets.


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#7 jdk

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Posted 14 January 2020 - 10:46 PM

Honestly, no it isn't. If I had $8k and wanted to get a longer FL system I'd look at either getting over diffraction spikes, which opens up more options, or look at the Edge 9.25 with perhaps the reducer.

 

Why are you wanting to go all the way to full-frame sensor?  Is it FoV?

 

Your RASA 11 is not that long, so it will have a good size with an APS-C ASI2600 ($2K), you would have 130'x87' FoV, vs. 199'x133' with the ASI6200.  I guess it is to fit M31???  They both will be 1.25"/px, which is fine image scale for such large targets.

 

If it is detail you are after, pair the RASA with the ASI183MC-Pro ($800).  This will give you 0.8"/px and 73'x48' FoV, which will frame most small to medium targets.

 

I had the 183MM wink.gif 

 

It's the FOV I'm after. I would pair the 6200 with an Edge but the image scale is too extreme.

 

The RASA is a seriously powerful instrument but its a little like a Corvette...some of the creature comforts are missing. Routing cables, dealing with filters, collimation and focus @ f/2.2 is always an adventure...



#8 rockstarbill

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Posted 14 January 2020 - 10:52 PM

I had the 183MM wink.gif

It's the FOV I'm after. I would pair the 6200 with an Edge but the image scale is too extreme.

The RASA is a seriously powerful instrument but its a little like a Corvette...some of the creature comforts are missing. Routing cables, dealing with filters, collimation and focus @ f/2.2 is always an adventure...


Newt, RC, iDK/CDK are all things to explore in sizes and focal length and imaging circles. Just have to get past the spikes!

#9 jdk

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Posted 14 January 2020 - 10:54 PM

Newt, RC, iDK/CDK are all things to explore in sizes and focal length and imaging circles. Just have to get past the spikes!

I should probably try...the options in this area are really slim...



#10 rockstarbill

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Posted 14 January 2020 - 10:58 PM

Newts are pretty good and don't cost a fortune. Collimation is rather simple too. They tend to be fast, can be reduced to f2.8 in some cases and come in good sized apertures. You'll want to look at the Big Paracorr for large chip coma correction. The 10" f4 ONTC is nice.

#11 jdk

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Posted 14 January 2020 - 11:33 PM

Newts are pretty good and don't cost a fortune. Collimation is rather simple too. They tend to be fast, can be reduced to f2.8 in some cases and come in good sized apertures. You'll want to look at the Big Paracorr for large chip coma correction. The 10" f4 ONTC is nice.

I've never used a newt, so I guess other than diffraction spikes - lets say I can get over those - I'm worried that it would be a lateral move in complexity in terms of hassle. Sill requires collimation, especially at faster focal ratios, the balance issue is new with the imaging train hanging asymmetrically, it's not really any less of a wind sail than my RASA. I"m trying to keep an open mind, but those are troublesome issues.


Edited by jdk, 14 January 2020 - 11:34 PM.


#12 rockstarbill

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Posted 14 January 2020 - 11:38 PM

I've never used a newt, so I guess other than diffraction spikes - lets say I can get over those - I'm worried that it would be a lateral move in complexity in terms of hassle. Sill requires collimation, especially at faster focal ratios, the balance issue is new with the imaging train hanging asymmetrically, it's not really any less of a wind sail than my RASA. I"m trying to keep an open mind, but those are troublesome issues.


Turn the camera facing down and buy a truss version of a GSO. Problem solved.

Collimation is required for everything but a refractor. If you want a large aperture long focal length refractor get ready to sell your house. Lol.
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#13 ezwheels

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Posted 14 January 2020 - 11:54 PM

Listen to Bill, he has tried a lot a stuff. A 10" iDK or a tricked out 10" ONTC would be where I was looking, especially considering my seeing is not going to support a super high resolution. If I win the lottery I'll order up a TEC 180FL and a 1600AE mount and a 24" PlaneWave CDK on a PW L600 and put them in Chile. 



#14 jdk

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Posted 14 January 2020 - 11:57 PM

Listen to Bill, he has tried a lot a stuff. A 10" iDK or a tricked out 10" ONTC would be where I was looking, especially considering my seeing is not going to support a super high resolution. If I win the lottery I'll order up a TEC 180FL and a 1600AE mount and a 24" PlaneWave CDK on a PW L600 and put them in Chile. 

Ok, considering that that's coming from someone who owns a TEC140...I'll pay attention. I'll have to do more research into the higher end newtonians...I've never considered them before. You would really look at a 10" ONTC over your 140?



#15 ezwheels

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Posted 15 January 2020 - 12:11 AM

Not over the TEC....but the 10" f4.7 ONTC is has about 1.5x the FL of the TEC140 with the .9x FF. To get that same FL in a refractor I would have to jump to the 180, and most possibly a bigger mount. I love my TEC 140 and probably would only replace it with a 160FL. I just bought an FSQ106EDXiii so I should have a wide field covered... especially with the imminent arrival of my 6200mm. For medium FL I would want something like 800-1000mm and the TEC160 would fit that nicely with the QTCC reducer and the TEC FF. For the long end, I think my seeing can support up to about 1500-2000mm max. I will be watching BIll's progress with his new 10"iDK, that looks like an awesome rig.


Edited by ezwheels, 15 January 2020 - 12:11 AM.

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#16 ezwheels

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Posted 15 January 2020 - 12:49 AM

Oh... and Bortle 1 skies? Super cool. I am definitely envious. 



#17 rockstarbill

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Posted 15 January 2020 - 01:26 AM

Not over the TEC....but the 10" f4.7 ONTC is has about 1.5x the FL of the TEC140 with the .9x FF. To get that same FL in a refractor I would have to jump to the 180, and most possibly a bigger mount. I love my TEC 140 and probably would only replace it with a 160FL. I just bought an FSQ106EDXiii so I should have a wide field covered... especially with the imminent arrival of my 6200mm. For medium FL I would want something like 800-1000mm and the TEC160 would fit that nicely with the QTCC reducer and the TEC FF. For the long end, I think my seeing can support up to about 1500-2000mm max. I will be watching BIll's progress with his new 10"iDK, that looks like an awesome rig.


Thanks, the iDK is sitting at UPS waiting out the winter storm that just blew through. Otherwise it would have been delivered Monday. For the OP, the 3.76um pixels of the 6200 might be a little small for what he's looking for. I do have the 2.7" AP Reducer I plan to try out at some point. F5 imaging ain't too shabby. Expensive scope though. For portability though I can't think of a better larger aperture rig.

The ONTC scopes are excellent though. Even the 8" would do. I think TS sells a special version with a full frame corrector included.

#18 rockstarbill

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Posted 15 January 2020 - 01:32 AM

Ok, considering that that's coming from someone who owns a TEC140...I'll pay attention. I'll have to do more research into the higher end newtonians...I've never considered them before. You would really look at a 10" ONTC over your 140?


I've also owned a TOA130 which IMO is a better imaging scope than the TEC140. Less issues with color correction, although there are solutions for the TEC scopes. I haven't directly owned the TEC but two friends of mine that are imagers have.

I've also owned a ONTC 10" f4 Newt. Very well made scopes with excellent performance. They basically cherry pick GSO mirrors and supply their own mechanicals to build ONTCs. If you want fast, high quality optics, and don't want to break the bank the ONTC is hard to beat.
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#19 FredOS

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Posted 15 January 2020 - 05:18 AM

Having owned a OS 200 mark II, I would stay away from it. Dealing with tip tilt is very difficult. Support from manufacturer is non existent. The day I switched to the AP 130 GTX plus Quad made my imaging life so much better.
You may want to look at the Planewave cdk 12.5. If above budget, you can consider second hand.
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#20 jdk

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Posted 15 January 2020 - 10:23 AM

Thanks, the iDK is sitting at UPS waiting out the winter storm that just blew through. Otherwise it would have been delivered Monday. For the OP, the 3.76um pixels of the 6200 might be a little small for what he's looking for. I do have the 2.7" AP Reducer I plan to try out at some point. F5 imaging ain't too shabby. Expensive scope though. For portability though I can't think of a better larger aperture rig.

The ONTC scopes are excellent though. Even the 8" would do. I think TS sells a special version with a full frame corrector included.

 

Oooh. That iDK looks really nice. But at $10k with no focuser...a little out of reach this year considering I'm already into a new camera for $4k. 

 

I've also owned a ONTC 10" f4 Newt. Very well made scopes with excellent performance. They basically cherry pick GSO mirrors and supply their own mechanicals to build ONTCs. If you want fast, high quality optics, and don't want to break the bank the ONTC is hard to beat.

 

I guess I'm surprised at the glowing review because the price is so reasonable. I'm waiting for the "...but..."

 

Having owned a OS 200 mark II, I would stay away from it. Dealing with tip tilt is very difficult. Support from manufacturer is non existent. The day I switched to the AP 130 GTX plus Quad made my imaging life so much better.
You may want to look at the Planewave cdk 12.5. If above budget, you can consider second hand.

Man. I'm glad I asked around. My two top choices were apparently ill advised crazy.gif



#21 jdk

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Posted 15 January 2020 - 10:36 AM

A question about diffraction spikes: to what extent do they cause problems with integrating data over multiple nights? I'm strictly mobile, so I set up and tear down every time. The rotation of the tube and camera will not be exactly the same; or at least I don't think it will. Am I misunderstanding that? The only thing worse than diffraction spikes would be to have the rejection algorithm fail at attempting to take them out. 



#22 ezwheels

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Posted 15 January 2020 - 11:08 AM

Rotating diffraction spikes...I never thought of that before, but that seems like it could be an issue. I do not have a reflector yet so I would be curious about this as well.

 

Just to be clear, I am not un-recommending the TEC140, I was just saying that the FOV and image scale with the reducer would be relatively close to what you already have but it will be a lot slower. I prefer refractors in general, due to the ease of use, but you just can't beat reflectors for value. Outside of the spikes, I think the 'but' with the big Newts is they are sails and you have to trick them out to get a robust and reliable solution. ONTC+paracor+nice focuser+ collimation tools and patience seem to yield pretty great data. 

 

It sounds like with the 55lbs imaging capacity of your mount you might be looking at an 5-6" refractor (6" max if it was a light one. This will also max your budgetgrin.gif ) 8" ONTC or a 10"iDK as the larger OTA's. 



#23 jdk

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Posted 15 January 2020 - 11:13 AM

I think the 'but' with the big Newts is they are sails and you have to trick them out to get a robust and reliable solution. ONTC+paracor+nice focuser+ collimation tools and patience seem to yield pretty great data. 

Yeah I'm not looking to need more patience...that's one of the main purposes of the upgrade. This is tough...



#24 rockstarbill

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Posted 15 January 2020 - 11:20 AM

Oooh. That iDK looks really nice. But at $10k with no focuser...a little out of reach this year considering I'm already into a new camera for $4k.


I guess I'm surprised at the glowing review because the price is so reasonable. I'm waiting for the "...but..."

Man. I'm glad I asked around. My two top choices were apparently ill advised crazy.gif


Yeah the iDK is not cheap. I'm using a NiteCrawler Focuser I already have with it.

As for the ONTC, no real but, except for maybe tube length. Newts are longer than other mirror designs. The 8" I believe can be collimated easier than the 10" due to the length differences.

#25 rockstarbill

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Posted 15 January 2020 - 11:34 AM

Yeah I'm not looking to need more patience...that's one of the main purposes of the upgrade. This is tough...


They aren't really sails. If you're concerned about that the 8" is good.

https://www.teleskop...54mm-field.html

This is a fully ready to go version. Just add a Catseye system for collimation. I've never used their corrector though.
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