11 replies to this topic

[Stargazer3236]

After performing much logistic legerdemain, I have boiled down my choices for my next telescope: Either the Meade 8" F/10 ACF or the iOptron 8" F/8 RC. After posting topics to get the consensus of various users and experts, I came to the conclusion that the Edge has a few problems with imaging which is that the correcting elements are in the baffle tube and thus necessitate the need for a very expensive reducer vs the Meade F/6.3 or for that matter, any reducer corrector lens. The ACF has no problems using aftermarket reducer correctors like the Meade F/6.3 or the Starizona F/4.

 

On the other hand, the ioptron RC has no corrector plate and thusly has no CA, SA or Astigmatism. Also, I hardly think I would need a dew heater on dewy nights, although a dew shield may be in the offing. So the RC has a flatter field and no image shift due to the fact that the focuser is decoupled from the mirror mount and uses a 10:1 crayford focuser built in. The only drawback is that the RC , as I have heard, is a bear to collimate, should it need it. However, I happen to live about 15 miles from the iOptron corporate office and I am sure they can help me with collimation should I need it. And it can use after market reducer correctors or just reducers since the field is already self corrected.

 

So, I post this trying to get the forums take on either of these scope for my imaging purposes, which amounts to an ASI294MC camera, SharpCap 3.2 Pro and sub-exposures around 15-30 secs each.

[dhaval]

I have used an 8in RC, a C11 EdgeHD and a Meade 10in ACF F8 (note, not the F10 like you have, but the F8). I have seen a person here on CN do very good with his F10 version of Meade ACF.

 

Here's how I feel about it - the Meade (either the F8 or F10) will require ensuring you get a lot of things right in order for those scopes to be imaging scopes. If I have to choose between the F8 and F10 Meade scopes, I will choose the F8 scope - it has better imaging capabilities than the F10. At native F8, the mirrors will allow flat field for a 4/3 chip camera (KAF8300 or ZWO1600). The F10 will most definitely need a corrector (AP27TVPH or Optec version). Both those are also reducers as well, so if you are planning on using F10, then you obviously can't. I believe that Meade reducer that you have is useless when it comes to imaging - that is for visual (correct me if I am wrong, but that's what I've been told). 

 

A GSO manufactured (various brands) RC8 is not up to snuff mechanically. The focuser hangs off the primary mirror cell and it will invariably have issues with collimating the scope and will not hold focus when you are pointed towards zenith. What adds to the headache is that the focuser itself is not worth it and you will have to change it. This becomes an even bigger hassle because when you change the factory focuser and attach a heavier focuser, guess what happens because the focuser is attached to the primary mirror cell? Back in the day, Moonlite used to sell a tilt ring that would require dis-assembling the primary mirror from the cell, drilling holes in the primary mirror cell and then attaching the tilt ring to gain separation between the mirror cell and focuser. They don't anymore and GSO changed the design of just the truss tube RC scopes, they did not change the design on the steel or CF tube scopes. I would avoid those scopes at all costs.

 

That leaves the C11 EdgeHD. A friend of mine and I, we use a C11 EdgeHD in our remote observatory without any issues (we use it natively at F10). I know a few other people that use their C11/C14 EdgeHD scopes either natively or with a Celestron reducer. They have no issues as well. Now, if the worry is the cost of the reducer, then I'd say use the scope natively. Yes, it will be slow and pain to use it, but the resolution will be fantastic and at least IMHO, a more meaningful pain to bear rather than a GSO manufactured RC8. 

 

Really, your choice should be between the Meade F8 (not the F10) and a Celestron C11 EdgeHD. Both are better suited for imaging than either the Meade F10 (which can be made to work if you have lots of time and money to spend on getting the correct back focus with either the A-P or Optec reducers) or a GSO RC8 scope. 

 

CS! 

Edited by dhaval, 15 September 2019 - 12:42 PM.

[cfosterstars]

I have a Meade 10" F/10 ACF and use it for AP. The main issue is not the need for a reducer or flattener. Backfocus is also not an issue that I know of or have experienced. It works fine at native with a flat field for a 4/3" chip. I have actually imaged with a Canon 6D full frame camera on the OTA without issue at native. I also have tried every focal reducer out there and I recommend the Optec Lepus or the A/P telecompressor. They are not hard to use at all and work fine for AP. The Meade or celestron F/6 reducers are not good and have serious reflection issues for A/P. The main issue with the Meade 10" F/10 ACF is the focuser mechanism on the F/10 Meade scopes. It is a main mirror focuser with really BAD and I mean really bad hysteresis and backlash. I have never been able, even trying everything I could think of, to fix it. For AP, I had to add a R/P focuser to the backplane and only use the main mirror focuser for course focus and then lock it. This issue was one of the main changes for the F/8 OTA and If you are buying new, I would recommend the F/8 for that reason alone, but you also get the faster optics. That being said, I have had a lot of success with my Meade 10" F/10 ACF for both LRGB or narrowband imaging. You can look at my astrobin page or posts made here on CN.  

 

You list as your mount the iOptron ZEQ25 GPS Mount. That would be undersized for either of these OTAs with all the peripherals that you need to hand on the OTA for AP. This is long focal length AP and the mount is critical.

[bobzeq25]

The inexpensive RCs are, to most people, a real pain to collimate.  I had a 6RC.  The optics were great, the mechanicals, not so much.  Many people replace inexpensive RC focusers with Moonlights or similar, so they're not that inexpensive.

 

I agree the choice is between a Meade ACF and a Celestron Edge.  I'd expect some people will be on either side of that one.

 

EDIT:  Missed the zeq25 bit.  Mine could not handle even the 6RC well, I bought a CEM60 to deal with that.

Edited by bobzeq25, 15 September 2019 - 01:04 PM.

[avarakin]

I had 6" ACF and I did not like the star shapes so I sold it. 

I also had 6" and still have 8" and 10" RCs and I really like them.

Here are some images taken with 8" RC:

http://www.colorsofc...es/gso-8-rc-cf/

Yes, collimating RC is not easy but can be done. I recommend to use instructions from Deep Sky Instruments. 

I am using pretty heavy CCD with filter wheel and not seeing much of a problem with focuser tilt. 

ASI294MC should be very easy for any of the RCs.

[Stargazer3236]

I have used an 8in RC, a C11 EdgeHD and a Meade 10in ACF F8 (note, not the F10 like you have, but the F8). I have seen a person here on CN do very good with his F10 version of Meade ACF.

 

Here's how I feel about it - the Meade (either the F8 or F10) will require ensuring you get a lot of things right in order for those scopes to be imaging scopes. If I have to choose between the F8 and F10 Meade scopes, I will choose the F8 scope - it has better imaging capabilities than the F10. At native F8, the mirrors will allow flat field for a 4/3 chip camera (KAF8300 or ZWO1600). The F10 will most definitely need a corrector (AP27TVPH or Optec version). Both those are also reducers as well, so if you are planning on using F10, then you obviously can't. I believe that Meade reducer that you have is useless when it comes to imaging - that is for visual (correct me if I am wrong, but that's what I've been told). 

 

A GSO manufactured (various brands) RC8 is not up to snuff mechanically. The focuser hangs off the primary mirror cell and it will invariably have issues with collimating the scope and will not hold focus when you are pointed towards zenith. What adds to the headache is that the focuser itself is not worth it and you will have to change it. This becomes an even bigger hassle because when you change the factory focuser and attach a heavier focuser, guess what happens because the focuser is attached to the primary mirror cell? Back in the day, Moonlite used to sell a tilt ring that would require dis-assembling the primary mirror from the cell, drilling holes in the primary mirror cell and then attaching the tilt ring to gain separation between the mirror cell and focuser. They don't anymore and GSO changed the design of just the truss tube RC scopes, they did not change the design on the steel or CF tube scopes. I would avoid those scopes at all costs.

 

That leaves the C11 EdgeHD. A friend of mine and I, we use a C11 EdgeHD in our remote observatory without any issues (we use it natively at F10). I know a few other people that use their C11/C14 EdgeHD scopes either natively or with a Celestron reducer. They have no issues as well. Now, if the worry is the cost of the reducer, then I'd say use the scope natively. Yes, it will be slow and pain to use it, but the resolution will be fantastic and at least IMHO, a more meaningful pain to bear rather than a GSO manufactured RC8. 

 

Really, your choice should be between the Meade F8 (not the F10) and a Celestron C11 EdgeHD. Both are better suited for imaging than either the Meade F10 (which can be made to work if you have lots of time and money to spend on getting the correct back focus with either the A-P or Optec reducers) or a GSO RC8 scope. 

 

CS! 

The Newer GSO manufactured RC 8's have the focuser de-coupled from the mirror mount. That is, there are no issues with the mirror flopping around when moving to and from zenith. Also, I always use my ASI294MC camera, which by all accounts is very light weight and thus will not incur any issues with the mirror or optical train.

 

I do very simple astro-imaging: scope, mount, ZWO camera, no filter wheel, no focusing motor, no SGP, no PHD; only SharpCap 3.2 Pro on my laptop. I get very accurate goto's with my ZEQ25 mount, no plate solving required. My alignments are nearly always dead nuts. The object I want to image always appears in the FOV and may need a little tweaking to get into the center of the FOV, but that's it.

 

I use my Meade F/6.3 Reducer with or without any spacers. My FOV are usually sharp stars edge to edge, but I usually crop my images to just get the object in the center of the FOV.

 

My subs are always 15-30 secs, up to 10 minutes per image. I use a narrowband Optolong L-eNhance filter and get very good results from object to object. I am not a huge fan of super wide field pics of expansive emission nebula, I am always going after planetary nebula and other objects between 10" and up to 300"-400" in diameter (think Ring nebula, Dumbbell, NGC 6781, Abell 39, etc).

 

I do not and probably never will image anything more than  20 minutes. I don't have the patience for that. I want to get my images and move on to the next object, usually getting between 10-20 objects per night.

[bobzeq25]

Ok, your concerns will be different from people who do long subs, and many of them.   I'm not sure how much we can help.  I will say, if you do such short exposures/total imaging time, the speed of the optics may dominate everything.

 

You'd get better advice on the EAA forum, they do what you do.

 

Minor point.  RCs do have a fair amount of field curvature.

Edited by bobzeq25, 16 September 2019 - 01:54 AM.

[dhaval]

The Newer GSO manufactured RC 8's have the focuser de-coupled from the mirror mount. That is, there are no issues with the mirror flopping around when moving to and from zenith. Also, I always use my ASI294MC camera, which by all accounts is very light weight and thus will not incur any issues with the mirror or optical train.

 

 

I would like to see images of the back of those RC8's. I spoke with Agena Astro very recently, they carry all GSO RCs, and they confirmed to me that none of the RC8s (regardless of tube type, also RC8s don't come in truss tube version) have the focuser decoupled from the primary mirror cell. If they have, that is awesome news, because those scopes do have wonderful mirrors, just that the mechanics are crap (but it is also what you pay for). 

 

CS!

[Eric Benson]

Minor point.  RCs do have a fair amount of field curvature.

Agreed, and they suffer from off-axis astigmatism, which coupled to the stars being 'out-of-focus' makes things look even worse in the corners.

 

For spot diagrams see here:

http://www.dreamscop...04/ccvrc-07.htm

http://planewave.com/technology/

and page 19 of:

https://www.deepskyi...ure_Ver_1.0.pdf

 

Of course this is not an issue for small sensors, but then almost any well executed telescope design works for small sensors

 

Regards,

EB

[avarakin]

A simple filed flattener, like AT2FF, which can also be used for refractors, fixes all issues even for APS-C size sensor.

[John Miele]

"The Newer GSO manufactured RC 8's have the focuser de-coupled from the mirror mount."

 

 

Last time I checked none of the RC8s had decoupled focusers...are you sure about that being the case? Great news if it is...John

[avarakin]

I know that Moonlite was making the decouplers for 10". Are they still making them? Anyone attempted DIY route for decoupling?