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Moonlite CHL w/ EdgeHD 925 + 0.7x FR + COAG

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#1 SilverLitz

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Posted 29 May 2020 - 04:47 PM

I am trying to get a handle on my focuser options with my new EdgeHD 925.

 

It seems that the Moonlite CHL is very popular with EdgeHDs.  The other option seems to be Celestron's Focus Motor (version 2, which is modified to work with the 925 + 0.7x FR).  The Celestron option is definitely less expensive at $200, vs. Moonlite ~$900, but the Moonlite minimizes mirror flop and image shift.  Build quality of the Moonlite is clearly better.  The Celestron option has the benefit of working with Hyperstar.

 

But I am coming to the conclusion that Moonlite CHL would NOT work w/ EdgeHD 925 + 0.7x FR + COAG, due to it taking too much of the 146mm backfocus.   Am I correct? 

 

I have not seen definite effective lengths for all of the parts of the path but here is my initial assessment, assuming the Moonlite at mid-range of its 0.7" range:

 

The most flexible arrangement, allowing both DSLRs and astrocams, needs 55mm between the sensor and OAG's exiting adapter.  The tightest I would consider would allow a 17.5mm deep camera + EFW, so ~38mm at the thinnest.

 

Moonlite CHL at minimum, 2.5"              ~64.0mm

Moonlite CHL mid-range, 0.35"                   9.0

OAG input adapter ???                               4.5             (assuming COAG Female M48 Telescope Adapter)

COAG body                                              29.0

Male M48 Camera Adapter                        12.5

                                                            =====

                                                             119.0mm

 

Give the EdgeHD 925's 146.05mm backfocus distance, this leaves only 27mm.  I could pick up a couple of mms by racking in the focuser from the mid-point, but I would still was some extra inward range.  The Moonlite could just barely work for my ASI183mm-Pro+EFW, but takes up 11mm too much length to be able to fit a deeper camera (such as ASI2600+EFW, still wishing for mono version), much less than allowing a DSLR.  The Moonlite could work for a ASI2600MC or ASI071MC, without the need for the EFW.

 

So it looks like for a EdgeHD 925 + 0.7x FR + COAG, Celestron's Focus Motor is the best option.

 

Am I missing something?

 

Thanks!

 



#2 kisstek

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Posted 29 May 2020 - 04:54 PM

Have you checked out the "Info All EdgeHD w Celestron Reducer & COAG Users Need to Know" thread? There are several people in there using some kind of Moonlight focuser with the EdgeHD, COAG, and ZWO.


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#3 ChrisWhite

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Posted 29 May 2020 - 08:27 PM

Take a look at the optec Leo. Its more expensive but if I remember correctly it takes up less backspacing than the moonlite and should work with the coag.

You are correct, its a bit tight for the moonlite and the coag. The shortest backfocus I could achieve was about 151mm. This didn't cause any problems at the native focal length of the scope with a small sensor (1") but might with the reducer.

I would not want an AF solution that didn't allow the mirror to be locked. Fortunately, I use qsi wsg cameras now and fw and large prism oag are integrated into the body and only takes up 50.2mm of backfocus.

Edit- looks like the Leo only takes up 1.25 to 1.6in backspacing

Edited by ChrisWhite, 29 May 2020 - 08:30 PM.

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#4 SilverLitz

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Posted 29 May 2020 - 09:52 PM

Have you checked out the "Info All EdgeHD w Celestron Reducer & COAG Users Need to Know" thread? There are several people in there using some kind of Moonlight focuser with the EdgeHD, COAG, and ZWO.

Yes, I have read the thread.  What is giving pause is being able to use a mono version of ASI2600 (does not exist yet???).  With current OSC APS-C the Moonlite should work, but ultimately what I want for my EdgeHD is a APS-C Mono, as I really like using flexibility/resolution/efficiency of mono.  I do not want to go down an expensive focuser path that will not work for my ultimate position.



#5 kisstek

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Posted 29 May 2020 - 11:11 PM

I would assume this hypothetical ASI2600mm will have the standard ZWO backspace. So the example in #58 (reducer, Moonlight, COAG, EFW, ASI) should hold for that new mono camera. It does look like a snug setup!

 

Or am I missing something obvious?



#6 ChrisWhite

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Posted 30 May 2020 - 05:11 AM

I would assume this hypothetical ASI2600mm will have the standard ZWO backspace. So the example in #58 (reducer, Moonlight, COAG, EFW, ASI) should hold for that new mono camera. It does look like a snug setup!

 

Or am I missing something obvious?

Problem is that ZWO is including tilt plates with their larger sensors which take up more backfocus than their standard 6.5mm... which is already too long for the COAG once you add in FW, etc...  The COAG takes up a whopping 39mm of backfocus!  


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#7 SilverLitz

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Posted 30 May 2020 - 07:41 AM

I would assume this hypothetical ASI2600mm will have the standard ZWO backspace. So the example in #58 (reducer, Moonlight, COAG, EFW, ASI) should hold for that new mono camera. It does look like a snug setup!

 

Or am I missing something obvious?

I am not looking at #58 specifically, but I am adding up the pieces, and with the Moonlite in middle of the range, I have only 27mm left for the camera and EFW.  Existing ASI2600 are OSC and would NOT have a EFW.  The ASI2600 takes 17.5mm and the EFW takes 20mm for 37.5mm > 27mm.



#8 kisstek

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Posted 30 May 2020 - 12:13 PM

Ah! I didn't know ZWO changed their seemingly standard back spacing on the newer cameras. It sounds like you've pretty much determined that there isn't enough back space for both the Moonlight and the COAG. Are there other alternatives to the Moonlight or the COAG that you'd be happy with? I know both are desirable but if they don't fit, it sounds like something has to give.

 

On my little C6, I have no real choice but the Celestron Focus Motor for SCT. And the COAG doesn't fit, width wise, so I have the ZWO thin OAG. The focus motor just fits between the guide camera sticking out from the OAG and the EFW. There's no room for changing the orientation for framing.

 

The back of SCTs can get crowded pretty quickly!

 

Good luck in finding a combo that will work for you.



#9 SilverLitz

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Posted 30 May 2020 - 01:00 PM

ZWO older APS-C and larger sensor camera also have the 17.5mm depth, even though larger sensors ideally need to be closer to the EFW to minimize vignetting.  But as others have said, larger sensors are more susceptible to tilt, and therefore could need a tilt plate.

 

At least Celestron's updated Focus Motor can fit with the EdgeHD 925 and FR; a year or two ago this would have been a significant problem.  I expect I will go the Focus Motor route, as the EdgeHD is NOT my main scope; it is only for small targets.  Medium targets will feed my Esprit 100 and large targets go to my camera lenses.  I do not want an expensive solution for a specialty scope.  If the Moonlite fit my expected expansion plans, it would have been the ticket.  



#10 RossW

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Posted 01 June 2020 - 07:00 PM

The Moonlight is a fine piece of workmanship but there are far less expensive alternatives that provide a similar level of performance. I have two EdgeHD 1100s that have the same backfocus as the 9.25. This is quite possible to have an external focuser, COAG, EFW and ZWO camera (6.5mm backfocus), with ample focuser travel for focusing throughout the year (summer and winter temperature variations covered).

 

I use two Diamond Steeltrack SCT focusers and they work superbly with my EdgeHDs. You can drive the Steeltrack via the microfocus shaft with something as simple as an Arduino driven 5 volt 28BYJ48 stepper (I have made several myFocuserPro focuser controllers and they work well with SGP/NINA etc.), or drive it on the main focuser shaft using a beefier NEMA stepper. For the COAG I use the thin M48 adapter on the scope side and the thin M42 adapter on the camera side. I note you want to go with M48 on the camera side of the COAG (but the ZWO EWF is M42?). The COAG set only comes with one M48 thin adapter, so if you can obtain another from Celestron or 2nd-hand you'll save yourself a lot of backfocus loss (or simply go with the M42 thin adapter directly to the EFW).

 

Here's my setup. Note there is also a 4mm spacer between the EFW and camera:

 

EdgeHD1100-imaging-train.jpg


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#11 SilverLitz

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Posted 02 June 2020 - 02:38 PM

The Moonlite would work with the COAG, EFW, and ZWO's 6.5mm offset cameras, BUT it would not work with deeper 17.5mm (w/ tilt plate) offset cameras.  I am planning for the possibility for a mono version of the ASI2600.  In this situation, neither the Moonlite or the Steeltrack would work.


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#12 ChrisWhite

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Posted 02 June 2020 - 02:51 PM

Yeah, I think the LEO is the only option for truly low profile.. and it ain't cheap!


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#13 Midnight Dan

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Posted 13 June 2020 - 11:35 AM

I would not want an AF solution that didn't allow the mirror to be locked. Fortunately, I use qsi wsg cameras now and fw and large prism oag are integrated into the body and only takes up 50.2mm of backfocus.

Chris:

 

You've clearly had a lot of experience with these configurations.  I'm trying to decide if I can eliminate my COAG now that I have an EdgeHD with the mirror locks.  In your opinion, would a piggybacked guide scope do just as well if the mirror locks are engaged and I use a crayford focuser?

 

-Dan



#14 ChrisWhite

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Posted 13 June 2020 - 09:14 PM

Chris:

You've clearly had a lot of experience with these configurations. I'm trying to decide if I can eliminate my COAG now that I have an EdgeHD with the mirror locks. In your opinion, would a piggybacked guide scope do just as well if the mirror locks are engaged and I use a crayford focuser?

-Dan


Dan,

I dont use a guidescope and honestly I wouldn't want to. The issue with guidescope vs oag isn't about the mirror locking or not... its about differential flexure. It won't take much between a guidescope and an oversampled imaging setup to show up in your stars.

Do you have the crayford yet? If not... take a look at the optec leo. Ive not used one but it appears to be made for this kind of situation. It might be short enough to allow you to keep the coag and maintain that 146mm of backfocus. Its pricey, so that might be a deal breaker.

Will you be using a reducer? If so, you might not need the large prism of the coag.

Also, if you are not using a reducer you can probably get away with using the coag at the additional backspace required to fit it in. I successfully had the moonlite+coag+filterwheel+zwo at 151mm. The field was still perfectly corrected for the asi183. Might be fine on a 4/3 size chip too.

I didn't test this configuration out with the reducer, and not sure if it would work.
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#15 lynnelkriver

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Posted 13 June 2020 - 10:00 PM

I put a Starlight Instruments crayford style focuser (FTF2008BCR "Shorty") on my C9.25 Edge and love it.  I'm not using a filter wheel or OAG as using a OSC with guide scope.  My give you another option to consider.  All the best, Scott



#16 cargostick

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Posted 13 June 2020 - 10:19 PM

I have a 9.25 but I have the ZWO OAG, I couldn't get the COAG to fit in any way with a moonlite.  I'm still at about 149mm back focus, but I cross the 146.5 to obtain focus with no problems.  I haven't had a single night that I couldn't focus.

unnamed


#17 Midnight Dan

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Posted 13 June 2020 - 10:35 PM

Dan,

I dont use a guidescope and honestly I wouldn't want to. The issue with guidescope vs oag isn't about the mirror locking or not... its about differential flexure. It won't take much between a guidescope and an oversampled imaging setup to show up in your stars.

Do you have the crayford yet? If not... take a look at the optec leo. Ive not used one but it appears to be made for this kind of situation. It might be short enough to allow you to keep the coag and maintain that 146mm of backfocus. Its pricey, so that might be a deal breaker.

Will you be using a reducer? If so, you might not need the large prism of the coag.

Also, if you are not using a reducer you can probably get away with using the coag at the additional backspace required to fit it in. I successfully had the moonlite+coag+filterwheel+zwo at 151mm. The field was still perfectly corrected for the asi183. Might be fine on a 4/3 size chip too.

I didn't test this configuration out with the reducer, and not sure if it would work.

Hi Chris:

 

I don't have the crayford yet, just considering my options.  That optec leo looks great but yeesh - $1300!

 

I'm at just 100 meters above sea level so looking though a lot of atmosphere.  At this elevation, it's hard to get sharp stars at 2000mm, so I'm trying to stick to using the 0.7x FR.  Seems way oversampled at full native focal length.

 

By the way, I have the EdgeHD 8, and using the 0.7xFR cuts down the back focus to 105mm.  Don't see how I can make a crayford fit along with the FR, COAG, and a small filter drawer (about 15mm thick).

 

Unfortunately, using an autofocus motor on the focus knob (with a FeatherTouch Micro focuser) means I can't use the mirror locks, so I end up with a lot of mirror shift during the night.  That affects collimation and effective sensor tilt and I can see it in the stars.  

 

Looks like I have a choice between using the COAG, focus knob, and no mirror locks, or using a guide scope, crayford focuser, and mirror locks.  :-(

 

-Dan


Edited by Midnight Dan, 13 June 2020 - 10:39 PM.


#18 RossW

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Posted 13 June 2020 - 10:38 PM

I am planning for the possibility for a mono version of the ASI2600. 

 

Yes please!

 

BUT it would not work with deeper 17.5mm (w/ tilt plate) offset cameras

 

Can the tilt plate be removed? I doubt it will be needed at f/10 and f/7.



#19 RossW

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Posted 13 June 2020 - 11:11 PM

I have a 9.25 but I have the ZWO OAG, I couldn't get the COAG to fit in any way with a moonlite.  I'm still at about 149mm back focus, but I cross the 146.5 to obtain focus with no problems.  I haven't had a single night that I couldn't focus.

Cargostick, did you see my image above? I think the Moonlight you have is even shorter than the Baader Steeltrack I use, and I have enough room for a COAG + EFW. I have no spacers between the COAG and the EFW. With your ZWO OAG there should be even more free space available. If your OAG focuser is hitting the EFW body, just rotate the OAG until it doesn't hit, then reduce the length of the large spacer you have between the OAG and EFW.

 

On the other hand, the Celestron Edge white paper shows (from memory) that you can get good focus at the centre of the FOV using a BF anywhere from 100 to 200mm; it is only the outer stars that suffer degradation when the 146.5mm BF is not used. Perhaps 151mm BF is good enough on a small'sh sensor?



#20 cargostick

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Posted 13 June 2020 - 11:58 PM

With the ZWO OAG that adapter is part of the OAG, it can't be changed unfortunately. I don't really like that part of the design, the way they went with the new M68 OAG is much better, and I think they should adjust that design down to the smaller M48 version.  With the ZWO the guide cam receiver sits almost all the way down on the body of the OAG so you can spin it in 360 degrees and it will still touch the EFW without a spacer.  Remember your backfocus will travel back and forth the length of your focuser drawtube, so if you set it right you should cross 146mm and be in focus.


Edited by cargostick, 14 June 2020 - 12:00 AM.


#21 ChrisWhite

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Posted 14 June 2020 - 06:15 AM

Dan,

Thanks for clarifying which scope you have.

With the 925 the moonlite threads onto the reducer. With the edge 8 I believe that the reducer inserts into the moonlite to preserve backfocus.

Never hurts to try. Buy the moonlite, and see if you can fit the coag in and still get good stars with your camera despite have a little too much backspacing.

If you can't, sell the coag and buy a slimmer oag and use a smaller prism. At f7 and 1400mm focal length you probably would be ok.

#22 SilverLitz

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Posted 14 June 2020 - 09:11 AM

I am planning for the possibility for a mono version of the ASI2600. 

 

Yes please!

 

BUT it would not work with deeper 17.5mm (w/ tilt plate) offset cameras

 

Can the tilt plate be removed? I doubt it will be needed at f/10 and f/7.

Yes, the tilt plate could be removed and a mono ASI2600 (vapor cam) could fit, but would it be needed for the larger APS-C?

 

I did not want to get an expensive solution that might not work for my expected camera, so last week I got a Celestron Focus Motor.   The new version A of this fits with the EdgeHD 925 with the 0.7x FR.  It installed very easy and it works.  I have not yet tried AF, so I have been using Baht mask, and it works great.  I lock the mirror after focusing.  So far I have not seen the need for auto focusing, as a single focus with Lum seems to work fine for LRGB.  For NB, I only shoot a single filter at a time, as I find NB filters need separate focus per filter.   

 

If the lack of AF becomes an issue, I will reconsider my options, but at least the Celestron Focus Motor is an inexpensive ($200) solution.




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