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Best way to piggyback 4SE on EdgeHD 8"?

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#1 Nitpick

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Posted 07 April 2013 - 07:06 PM

I have a Celestron 4SE on its mount. I have an EdgeHD 8" also on its mount (a CGEM).

I'd like to attach the 4SE to the EdgeHD tube rigidly so that I can use the 4SE as a guiding scope for the Edge and also so that I can have the 4SE attached to the CGEM for the CGEM's additional stability when using the 4SE for Lunar / Solar imaging.

The 4SE right now has the "small" dovetail. Ideally, rings or something that would attach to the EdgeHD tube and allow the 4SE to be mounted via the same dovetail that the 4SE uses to attach to its native mount.

Or...?

Thanks

#2 Geo.

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Posted 07 April 2013 - 08:23 PM

Yeah, I think you are going to have to go with a dovetail and rings - probably 160mm. In the day Celstron sold a two axis tangent arm mount for this type of thing. Bit of a collector's item now. I keep looking at the pile of old fork arms and their tangent arm Dec fine adjustment and think, Hmmmm.

#3 WarmWeatherGuy

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Posted 08 April 2013 - 02:04 AM

I have a CGEM 800 (not HD) and I found an old C5 to use as a guide scope. I considered mounting the C5 to the C8 but didn't like the idea of something that heavy attached to the C8. Also, that would cause the C5 to be further from the pivot point which would require more counterweight. My solution was a side-by-side bar from ADM:

http://admaccessorie..._Series_SBS.htm

I have one saddle that will accept either the CG5/Vixen/V or the CGE/Losmandy/D dovetails. Next comes the problem of pointing one OTA to a slightly different place than the other. ADM has a solution:

Max Guider
http://admaccessorie..._Max_Guider.htm

Before I found out about that though I saw this YouTube video by AstronomyShed:

Sky-Watcher Guide Scope Mount
http://www.youtube.c...h?v=EROhpDr_dXw

which convinced me to buy it from Europe:

http://www.modernast...ing_accessories

The problem is that the base doesn't have a dovetail. I bought a slab of aluminum from eBay and spent hours with a hacksaw to cut myself a piece that would allow me to attach the guide scope mount to my side-by-side bar. I suppose I could have bought a dove tail but then I would have needed an additional saddle. All this metal adds up to a lot of weight. I'm not sure if I saved myself any counterweights.

I have tried both the guide scope mount by Modern Astronomy and the one by ADM. I prefer the one by Modern Astronomy but it was a real PITA to make that fitting to attach it to the side-by-side bar.

Now my C8 + C5 + mounting hardware + camera + guide camera + dew stuff all add up to around 30 pounds. With the side-by-side solution you can balance the mount in DEC as well as RA.

Note that if you're going to go the ADM route that they sell the side-by-side bar with the MaxGuider attached. That way you save buying a saddle on that side. DSBS-MAX seems to have the D saddle on one side and the MaxGuider will take either the V or D dovetail provided it is long enough. It won't take a short stubby one.

This all gets expensive in both weight and dollars. I don't know an easier route. Most people just use a 50mm refractor lens and don't care where exactly it is pointing - they just hope their guide camera will see a star with its really wide field-of-view.

#4 Jon Isaacs

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Posted 08 April 2013 - 07:01 AM

I am not an imager but I wonder about the advisability of using a scope that focuses with a moving mirror as a guide scope.

:question:

Jon

#5 Raginar

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Posted 08 April 2013 - 08:06 AM

Jon,

It's not as big of a deal. As long as it can stay in relative focus all night. Many guider programs (such as PHD) actually like you to be out of focus slightly.

It'll work as well as any other telescope.

#6 Jon Isaacs

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Posted 08 April 2013 - 08:11 AM

Jon,

It's not as big of a deal. As long as it can stay in relative focus all night. Many guider programs (such as PHD) actually like you to be out of focus slightly.

It'll work as well as any other telescope.


The issue is not focus but mirror flop, if the mirror shifts during the exposure, things are not good...

Jon

#7 WarmWeatherGuy

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Posted 08 April 2013 - 11:37 AM

I am having a problem that could be due to mirror flop. I have mirrors that can "flop" in both the guide scope and the main one. I suspect it is something else and will be doing an experiment to determine which it is.

The problem is that the image drifts sometimes. The stars are slightly streaked and if I make a movie I can see that it drifts slowly the entire time, for well over a period of an hour. The motion is left/right (North is up).

I have a suspicion that it occurs only when imaging near the meridian. This is consistent with my memory and also consistent with mirror flop. Certainly the best explanation is one where the guide scope slowly and evenly moves relative to the main scope. The mirror would have to "flop" over a period of an hour or more, and it would have to "flop" at an even rate. The effect of gravity is changing at an even rate (relative "down" is changing due to the mount rotating). Could the mirror flop against the grease for that long of a period?

My other hypothesis is that there is a force on the guide camera due to the wires hanging from my guide camera and that pulls on it in a different direction as time moves on. My experiment will be to tie up those wires so they apply the same force no matter the orientation. Due to the weather and the Moon and my schedule it could take me a year to figure this out.

This animation takes place over a 3 hour period. Each frame is a 10 minute exposure. It does seem to speed up in the middle. Everything happens in slow motion, otherwise it would have stopped guiding.

Animation of Horsehead and Flame nebulae

#8 bilgebay

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Posted 08 April 2013 - 02:27 PM

Jon is right!

I would go with an OAG. I am using this since 2011. It is very rigid and there is always a couple of star to guide with my Orion SSAG.

#9 Raginar

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Posted 08 April 2013 - 10:16 PM

Mirror flop *may* occur, but the guider won't care since you've already found your guide star by then. Mirror flop, as I experienced it, isn't a gradual process. It occurs when you're moving the scope or focusing it.

Personally, I use a finder-guider and love it. That's the route I'd go with this setup. I think you'll find an OAG to be very limiting in your selection of guide stars.

#10 bilgebay

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Posted 09 April 2013 - 01:15 AM

I think you'll find an OAG to be very limiting in your selection of guide stars.



I am talking based on my experience. Never ever was this the case with this OAG. There was always a guide star in the field.

Finder/guider was good upto 1000mm FL but for anything above I have used this OAG and always got very good results.

#11 Tom and Beth

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Posted 09 April 2013 - 03:01 AM

I think you'll find an OAG to be very limiting in your selection of guide stars.



I am talking based on my experience. Never ever was this the case with this OAG. There was always a guide star in the field.

Finder/guider was good upto 1000mm FL but for anything above I have used this OAG and always got very good results.


Interesting comment regarding 1 meter FL. Finding a decent OAG on this side without going into the $700 USD and up is hit and miss.

#12 EFT

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Posted 09 April 2013 - 09:29 AM

The issue is not focus but mirror flop, if the mirror shifts during the exposure, things are not good...

Jon


Because he has an Edge HD with mirror locks, mirror flop is not a problem. With relatively similar focal lengths, the SCT/MCT combination is probably a good match.

#13 Jon Isaacs

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Posted 09 April 2013 - 09:33 AM

The issue is not focus but mirror flop, if the mirror shifts during the exposure, things are not good...

Jon


Because he has an Edge HD with mirror locks, mirror flop is not a problem. With relatively similar focal lengths, the SCT/MCT combination is probably a good match.


I was more concerned with the possible mirror flop in the 4SE. If there is flop in either scope, it could be a problem.

Jon

#14 bilgebay

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Posted 09 April 2013 - 01:24 PM

Interesting comment regarding 1 meter FL. Finding a decent OAG on this side without going into the $700 USD and up is hit and miss.



This Lacerta OAG is a very robust one. It has a larger mirror than my Celestron OAG (which was a disaster on all departments), may be this helps finding a guide star easily. Another plus is it uses up only 11mm of back focus. It replaces your ordinary T-adaptor if you are shooting with a DSLR. For other type of connections the thickness is something like 15mm, again very good compared to many other OAGs.

And the price is Euros 159.-

What was it that you found interesting regarding 1 meter focal length ?

#15 Tom and Beth

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Posted 09 April 2013 - 05:28 PM

On the 1 meter "interest", I'm about to use a 1 meter FL scope to guide with. With a barlow in this scope and an AP .67 Reducer in the imaging one the two scopes are very close in FL. PRELIMINIARY tests shows that the two scopes hold alignment relative to each other very well, but haven't compared with both scopes being in the 2 Meter FL range. My Ap1200 is up to the task, just not sure of all the other "stuff"

I've been following a few discussions regarding OAG and which cameras are sensitive to use with them on several forums. CCD group was just one of them. Anyway. I lurk here and there trying to glean information.

Not sure if your reference to the Celestron OAG is the one sold in the 80s, and similar one recently was in the S&S area. I have that era of one and, it is indeed a disaster.

#16 Raginar

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Posted 09 April 2013 - 08:09 PM

I didn't ask if you were talking on your experience. In my experience, I found that an OAG wasn't the best. It works sometimes, and if I had a rotator it would work all the time.

Why are you two always hostile to me?

#17 bilgebay

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Posted 10 April 2013 - 01:29 PM

I didn't ask if you were talking on your experience. In my experience, I found that an OAG wasn't the best. It works sometimes, and if I had a rotator it would work all the time.

Why are you two always hostile to me?


Chris - I don't know how to answer this but I will try.

Why are you two always hostile to me?



1 - Who is the other person? I don't remember teaming up with somebody against you.
2 - I am not hostile to you at all, why would I be ? I may have different opinions or experiences but don't have anything against you. If I made you feel like that in any way, please accept my apologies.
3 - Always - Again, I am not aware of any consistency.

I didn't ask if you were talking on your experience



Well, I have posted the following first:

It is very rigid and there is always a couple of star to guide with my Orion SSAG.



to which you replied

I think you'll find an OAG to be very limiting in your selection of guide stars.



This sounded anecdotal to me and I replied

I am talking based on my experience. Never ever was this the case with this OAG. There was always a guide star in the field.


So, I leave it to you whether I was hostile to you or not.

Thanks

#18 bilgebay

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Posted 10 April 2013 - 01:41 PM

On the 1 meter "interest", I'm about to use a 1 meter FL scope to guide with



I see but I meant the imaging scope to be of max 1000mm FL. My finder/guider is a modified Celestron 9x50 finder, which should have a FL of Max 200mm.

Not sure if your reference to the Celestron OAG is the one sold in the 80s



Mine was purchased in 2005, a newer design but equally awkward to use. A friend of mine borrowed it from me and at the end of the night he was on the verge of demolishing all his astro equipment because of this OAG :lol:

#19 Geo.

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Posted 10 April 2013 - 04:02 PM

I am not an imager but I wonder about the advisability of using a scope that focuses with a moving mirror as a guide scope.:question:Jon


Image shift can be an issue on some, but I've never seen image shift on a C5. Guess the mass of mirror to baffle tube surface ratio is too low. Although I had a ETX125 that could shift the whole FOV out of the FOV :foreheadslap:

#20 Jon Isaacs

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Posted 10 April 2013 - 07:54 PM

Image shift can be an issue on some, but I've never seen image shift on a C5.



Were you using it to guide?

Jon

#21 Raginar

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Posted 11 April 2013 - 08:35 AM

Jon,

Argue much? I've used a C5 to guide and image through. I didn't experience any mirror flop or image shift.

Sedat,
Perhaps it's a cultural thing. The way you talk is antagonistic.


Chris

#22 Jason B

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Posted 11 April 2013 - 03:05 PM

I will never guide with a moving mirror telescope unless it is with an OAG. In my experience, if the mirror even moves a hair it messes up the frame. It will move slowly if you pass the meridian as well as the center of gravity shifts.

I was always having issues with my 90mm Mak when guiding and it had very little mirror flop, if any visually. As soon as I switched guidescopes (after several weeks of trying and trying to get it working), all my problems went away.

#23 WarmWeatherGuy

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Posted 11 April 2013 - 03:33 PM

I will never guide with a moving mirror telescope unless it is with an OAG. In my experience, if the mirror even moves a hair it messes up the frame. It will move slowly if you pass the meridian as well as the center of gravity shifts.

I was always having issues with my 90mm Mak when guiding and it had very little mirror flop, if any visually. As soon as I switched guidescopes (after several weeks of trying and trying to get it working), all my problems went away.


Earlier in this post I talked about my problem guiding with a C5 and I gave a link to this animation of the horsehead nebula that I made. Each frame is a 10 second exposure and the total elapsed time of the animation is over 3 hours.

Is it possible this is due to mirror "flop?" This "flop" would have to be incredibly slow, smooth, and even because I never lost track. Each image has about the same amount of star streaking, except for one image in the middle which has a little more. It would have to last for 3 hours and the total angle change from start to finish seems fairly large. Is this something similar to what you experienced?

#24 Jason B

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Posted 12 April 2013 - 01:20 PM

Is this guided? This looks like an unguided shot that did not have an exact polar alignment. You could experience drift such as that over the course of 3 hours without guiding. The drift amount would vary dependent on the preciseness of your polar alignment. Mirror shift would not be this slow IMHO.

I shoot much longer exposures than 10 seconds. Mine would show itself as streaked stars, double images or a lost guide star. There were all kinds of problems, especially when shooting through the meridian. Since switching to the much more stable refractor, no issues!

#25 WarmWeatherGuy

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Posted 13 April 2013 - 08:27 PM

Yes this is guided. North is up and the drift is left/right. I am thinking it could be because I left the wires to the guide camera dangle. As the rotation in RA occurs the pull of gravity on the wires changes and would "bend" my guide camera to point gradually to a different place than my camera scope. I'm not ruling out mirror flop though. I will experiment with wrapping the wires to keep them from changing any force on the guide camera during the process.

I used an AT72ED and a C5 on a side-by-side bar on a CGEM. The C5 is the guide scope and the AT72ED is what took the images. I estimate that the middle of the 3 hour period is when the scope went through the meridian.






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