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Planning an upgrade...refractor or reflector?

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#26 jdk

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Posted 15 January 2020 - 12:04 PM

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.

That looks pretty nice, I have to admit. Any issues with rotating diffraction spikes over different nights?

 

It's clear I have more research to do. All recommendations welcome in the meantime.



#27 rockstarbill

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Posted 15 January 2020 - 12:16 PM

That looks pretty nice, I have to admit. Any issues with rotating diffraction spikes over different nights?

 

It's clear I have more research to do. All recommendations welcome in the meantime.

I have never seen an issue with diffraction spikes and rotation. Chris White has used a Newt much longer than I did, so maybe he will chime in with his experiences.


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#28 jdk

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Posted 15 January 2020 - 01:13 PM

I have never seen an issue with diffraction spikes and rotation. Chris White has used a Newt much longer than I did, so maybe he will chime in with his experiences.

Yeah, at this point I need to start surfing astrobin a little bit. It's hard to find full res samples shot with 35mm sensors though.



#29 rockstarbill

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Posted 15 January 2020 - 01:36 PM

Yeah, at this point I need to start surfing astrobin a little bit. It's hard to find full res samples shot with 35mm sensors though.

Yeah, and with that particular corrector. The Big Paracorr by TeleVue is pretty much the gold standard for large frame coma correction. The challenge is getting a large enough focuser to use it (3") in a well-priced design. The 10" f4 has the 3" FT as a standard option from TS. The 8" doesnt, but you may be able to ask them to make you one with the 3" FT and source the corrector yourself. 



#30 jdk

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Posted 15 January 2020 - 02:15 PM

Any thoughts on the CFF 140


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#31 bmhjr

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Posted 15 January 2020 - 02:21 PM

Any thoughts on the CFF 140

You could check with Joel (buckeyestargazer).  He has the 135mm version of this scope.


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#32 rockstarbill

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Posted 15 January 2020 - 02:21 PM

Any thoughts on the CFF 140

Expensive and slower than the other options with a smaller aperture. 



#33 jdk

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Posted 15 January 2020 - 02:23 PM

Expensive and slower than the other options with a smaller aperture. 

But hopefully very reliable with no fuss required. Comes with a focuser. Simplicity is worth money to me, I just have to figure out how much. 



#34 rockstarbill

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Posted 15 January 2020 - 02:33 PM

But hopefully very reliable with no fuss required. Comes with a focuser. Simplicity is worth money to me, I just have to figure out how much. 

It is hard to suggest options, since your interests are all over the place. I would buy the TEC140FL over this scope, personally. 

 

I owned a similar focal length refractor, the TOA130, and a shorter faster one the FSQ106. I sold both of them to get a used AP130 GTX (with a wanted ad on Astromart) and its been one of the best decisions I have made. Here is why:

  • With QuadTCC Reducer: 585mm @f4.5 - 50mm imaging circle
  • With GTX130 Flattener: 873mm @f6.7 - 65mm imaging circle

So it gets me fast, and can get me longer FL if I need it. I use both configurations and have been happy with the performance of both. Comes with a 3.5" focuser, which has a Feathertouch pinion on it, so you can use the Feathertouch motors for focusing. Again, you are not going to get one new, but a used one in excellent condition will perform incredibly well. 


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#35 jdk

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Posted 15 January 2020 - 03:41 PM

That AP130 would be a really good solution. I don't think my interests are all over the place, I'm just trying to be flexible and open to the optical configurations that might work for me in my price range. 



#36 rockstarbill

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Posted 15 January 2020 - 03:57 PM

That AP130 would be a really good solution. I don't think my interests are all over the place, I'm just trying to be flexible and open to the optical configurations that might work for me in my price range.


The TOA130 is good as well, but some folks have issues with their focusers. Esprit 150 isn't bad either, although at those prices the TEC140fl might be best.

#37 Der_Pit

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Posted 15 January 2020 - 04:23 PM

That AP130 would be a really good solution. I don't think my interests are all over the place, I'm just trying to be flexible and open to the optical configurations that might work for me in my price range. 

As I'm also musing about upgrades for this year I'm following the various threads with great interest.  From the specs, my top candidate is the Sharpstar AL-140PH/TSAPO140.  It's F/6.5, with a dedicated reducer to get F/4.8.  But like the other refractors, at 910mm FL the image scale with 3.8μ class sensors could be a bit better undecided.gif Then again, if you want large field, at F/4.8 (672mm) the 6200 would give you 3×2 degrees.

The open question is, is it as good as they claim it is?


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#38 jdk

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Posted 15 January 2020 - 04:44 PM

As I'm also musing about upgrades for this year I'm following the various threads with great interest.  From the specs, my top candidate is the Sharpstar AL-140PH/TSAPO140.  It's F/6.5, with a dedicated reducer to get F/4.8.  But like the other refractors, at 910mm FL the image scale with 3.8μ class sensors could be a bit better undecided.gif Then again, if you want large field, at F/4.8 (672mm) the 6200 would give you 3×2 degrees.

The open question is, is it as good as they claim it is?

I'm not sure how I missed that one. Is there a 1x flattener available for it? It's so hard to keep track of all the compatibility confused1.gif  



#39 rockstarbill

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Posted 15 January 2020 - 05:30 PM

I'm not sure how I missed that one. Is there a 1x flattener available for it? It's so hard to keep track of all the compatibility confused1.gif

Tread carefully on those scopes. Lots of good ones but some lemons as well.

There's also the Takahashi Epsilon. Very fast, flat field, full frame. I'd buy new if it were my money though. Focuser may need a pinion upgrade for stability.

Note that's a wide field scope...

Edited by rockstarbill, 15 January 2020 - 06:16 PM.

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#40 Der_Pit

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Posted 15 January 2020 - 05:31 PM

I'm not sure how I missed that one. Is there a 1x flattener available for it? It's so hard to keep track of all the compatibility confused1.gif  

I don't really know.  I also tried to find out.  But Sharpstar doesn't have one to offer (so far?).  The connect thread on the focuser is a bit uncommon, M88×1.  So it might be difficult to get generic ones (like the TSFlat3) connected.


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#41 jdk

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Posted 15 January 2020 - 09:43 PM

Ugh. I'm all over the place...now I'm looking at the Esprit 120. Nice bump in resolution from the RASA, 43mm field looks great; just have to deal with f/7. I know I could put that thing on my mount and it would churn out great data night after night. And the price is really tough to argue with. 



#42 rockstarbill

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Posted 15 January 2020 - 10:02 PM

TSA120 is nice too.

#43 ezwheels

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Posted 15 January 2020 - 10:48 PM

I have an Esprit 100 and it is a fantastic scope with a few limitations. Relatively short back focus distance, no dedicated reducer and only a 40mm claimed flat imaging circle (which did not use to be a liability). If those do not become an issue for you then they are kind of the deal of the century for refractors. Many users out there with them and very very few, if any, negative reviews or reports and I can 100% vouch for the customer service I have received from SW. The 120 has longer back focus than the 100 and a larger imaging circle (claimed). There are some good reports of using the riccardi reducer or the TS version with the 100, but I did not have too much luck with the Riccardi reducer on my 100. If you are looking at the OSC version of the 6200 then you will have plenty of back focus distance to play with as you would not be using a FW. 

 

But to the point of you jumping all over the place; I think you might find calming limitations to all the choices and circular paralysis by analysis if you settle on a FOV or FL or imaging scale (sometimes these overlap) and just stick to it. And remember that no matter what scope you choose, you can probably rest assure that it won't be your last and more than likely you will have a few different imaging rigs for various targets and or for whether you travel or build a home observatory or use a remote observatory. 



#44 RogeZ

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Posted 16 January 2020 - 12:22 AM

I would suggest you do some soul search on your main goals.

The scopes mentioned are slow compared to the RASA and for an imager that travels to every location thats a very important metric imo. Also the newts have horrific spot diagrams compared to RASA when you factor in full frame. The spot diagram in the TS website is 100 microns at the full circle; with 3.8 micron pixels your stars wont be pinpoints.

From a 11” RASA the only way up is a 14” RASA. Everything else I think would be too slow to compete.

#45 Kevin Ross

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Posted 16 January 2020 - 04:19 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. 

It won't be a problem as long as the tube stays rotated the same in the rings. You can rotate the camera all you want, that won't change the diffraction spikes. So just don't take the scope out of the rings when you tear down. You can, of course, take the scope (with rings attached) off the mount, and when you remount it, the diffraction spikes should line up.


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#46 ChrisWhite

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Posted 16 January 2020 - 04:33 AM

That looks pretty nice, I have to admit. Any issues with rotating diffraction spikes over different nights?

It's clear I have more research to do. All recommendations welcome in the meantime.


As long as you dont rotate the ota in the rings, spikes will line up from night to night.
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#47 bigjy989

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Posted 18 January 2020 - 12:31 PM

From bortel 1 skies imaging speed isn't going to be a big issue for something like the TEC140 at 0.9" or 1.1".  One thing to remember is the effective QE is reduced for OSC.  I would go mono on the 6200 with the new TEC flatterner at 0.9" and not look back.   If you stay with the OSC then maybe the Quad-TCC is better.

 

I use the Quad-TCC for nebula and tried the FF for galaxies (old FF at 0.8) from bortel 5, I struggle with eccentricity of stars at 0.8" but I use an Atlas... not a 10micron which will have no issue.   Speed at 1.1" is perfectly adequate and most of my images an astrobin are 4-6 hours.   Galaxies need more like 12 hours at 0.8" but sky fog is my limit so generally still use the Quad.  I do not consider myself an expert at processing... still very much learning but the scope is not the limitation.


Edited by bigjy989, 18 January 2020 - 12:33 PM.

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#48 jdk

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Posted 18 January 2020 - 12:49 PM

From bortel 1 skies imaging speed isn't going to be a big issue for something like the TEC140 at 0.9" or 1.1".  One thing to remember is the effective QE is reduced for OSC.  I would go mono on the 6200 with the new TEC flatterner at 0.9" and not look back.   If you stay with the OSC then maybe the Quad-TCC is better.

 

I use the Quad-TCC for nebula and tried the FF for galaxies (old FF at 0.8) from bortel 5, I struggle with eccentricity of stars at 0.8" but I use an Atlas... not a 10micron which will have no issue.   Speed at 1.1" is perfectly adequate and most of my images an astrobin are 4-6 hours.   Galaxies need more like 12 hours at 0.8" but sky fog is my limit so generally still use the Quad.  I do not consider myself an expert at processing... still very much learning but the scope is not the limitation.

Hm...what makes you say imaging speed won't be a big issue? At f/7 or even f/5 the optimal subexposure times are at least 10 minutes I would think (based on the read noise of the 6200). 



#49 bigjy989

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Posted 18 January 2020 - 03:26 PM

Rough numbers from memory:
From my experience I have and SQM of about 20.3 mag. A bortel 1 will be about 21.8 mag. Or 4x dimmer.

With an ASI1600 (same pixels size) and QE 60% at Bortle 5 my lum generate about 2.5e- per second; at Bortel1 maybe 0.6e- per second (no moon). 10*RN^2 = 40e (unity 1600) so I would need a 60-70 second exposure (L) in bortel1 and 3 minute in RGB. But RN is improved for the ASI 6200 (1.5e At gain 100) with increased QE80% (OSC effective 80x50+80x25+80x25/300=25%) is either 40x80/60x25/30 = 30s (mono) or 90s (OSC). No problem for either.

The author stated that OSC is the focus.

For kicks -
Narrowband is about 0.08e-/s (5nm) in bortel 5 vs 0.02e-s in bortel1. 25% better QE, RN 40% less This would imply 10xRN^2 (23e) swamping for narrowband in 1200s for ASI6200 mono. This is excellent and almost never seen with any CCD camera (maybe 2-3RN^2 best case in 20 min).

The native ADC is 16bit so a large number of subs is not needed (main drawback with other CMOS). When put on a 10micron (as the author suggests) then no issue for bortel1 narrowband (20min) or LRGB (1.5min mono or 5 min OSC).

Example: compared to a QSI690 (similar pixel size) RN>4 we have a healthy full well 11000 (gain 100) vs 18000 (qsi) and require 6-7 times less exposure with the ASI. I never see exposures greater than 1800s with theQSI so a similar image (RN swamp) could be obtained using subs of 300s or so with the ASI but you would still retain 3x-4x more effective full well (shorter subs) to avoid blow out stars.

Edited by bigjy989, 18 January 2020 - 07:59 PM.

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#50 jdk

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Posted 18 January 2020 - 04:06 PM

Ok, so hold on...maybe I've misunderstood something then. 

 

I've been working with the formula 10*( RN/ LPR), where LPR is the light pollution rate in e/px/second. 

 

Assume the RN is 1.5e- for the 6200, and the light pollution rate is .09e- for a OSC camera @ f/7:

 

lpr.jpg

 

Using those values, I would be aiming for subexposures that are minimally 250 seconds, or just over 4 minutes. By contrast, the RASA @ f/2.2 would be about 28 seconds - about 9 times faster data acquisition at the expense of a roughly 30-35% loss in resolution depending on what refractor we'd be talking about.

 

Is my math right? Are my assumptions right?


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