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Fork vs. German

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#1 nobbygon

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Posted 16 May 2009 - 05:07 AM

Hi,
I've been looking for a new scope for some time now and ive decided to go with a Meade LX200-ACF(either 8" or 10").

However, im not sure how to mount it. Should i go with the forks + wedge or go down the German equatorial path instead?

Has anyone made this decision before? What are you thoughts???? Please help.

P.s. The scope will be used for astrophotography.
Cheers, Angus

#2 Luigi

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Posted 16 May 2009 - 06:25 AM

>>>Has anyone made this decision before?<<<

Nope. You're the very first. :shocked:

Forks are great for viewing ergonomics when used in alt-az (they still track objects fine). If you want an equatorial mount for AP, the majority will recommend a suitably stout GEM.

#3 Chris Curran

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Posted 16 May 2009 - 06:48 AM

If you want an equatorial mount for AP, the majority will recommend a suitably stout GEM.


Yup. The 3 secrets to successful imaging are 1) the mount, 2) the mount and 3) the mount.

Just like space and money, you can never have too much mount.

#4 LLEEGE

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Posted 16 May 2009 - 11:57 AM

P.s. The scope will be used for astrophotography.
Cheers, Angus

Fork mounts have a few advantages over a GEM for imaging. The most important being you can image through the meridian without the need to do a meridian "flip". OK. So, that's the only real advantage I can think of. :grin: A GEM will be more versatile in that you can use several different OTA's. Easier polar alignment. Easier to balance without the cost of buying additional systems. No need to buy an expensive wedge. No worries that your imaging equipment will swing through the forks. No worries about the forks flexing at lower latitudes.

#5 Chris Curran

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Posted 16 May 2009 - 11:00 PM

The most important being you can image through the meridian without the need to do a meridian "flip".


Actually... Both my Tak EM-200 and AP 1200 image right though the meridian without any flipping. I almost always cross the meridian while imaging - that's where the good stuff is!

#6 jrcrilly

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Posted 16 May 2009 - 11:05 PM

The most important being you can image through the meridian without the need to do a meridian "flip".


Actually... Both my Tak EM-200 and AP 1200 image right though the meridian without any flipping. I almost always cross the meridian while imaging - that's where the good stuff is!


But you can't go horizon-to-horizon. It doesn't matter whether you flip an hour before or an hour after meridian - you still flip at some point.

#7 Chris Curran

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Posted 16 May 2009 - 11:27 PM

But you can't go horizon-to-horizon. It doesn't matter whether you flip an hour before or an hour after meridian - you still flip at some point.


??? Of course you can. I've done it - sometimes because I fell asleep "at the wheel". :)

I don't know why everyone seems think you have to flip in the middle of an imaging run. Just not so... at least not with Tak and AP GEM's. If my cables where long enough, those mounts would do 360's.

#8 Jimmy2K63

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Posted 16 May 2009 - 11:35 PM

Years ago I had this debate with our club when we talked about mounting our 16 inch cass/newtonian. I wanted it on a fork.

Go away from this hobby for 10 years and the first thing you hear is - if you want to do astrophotgraphy you need a GEM. That is NOT true. I had some punk at OPT tell me that NOTHING but a GEM would do for astrophotography. I hung up and vowed never to buy from these guys.

Tell that to Mt. Palomar. The 200 inch is on a horseshoe which is essentially a fork mount. Last I checked, their images are fine. The fork eliminates the big ugly knee rattling counterweights and shafts found on a large GEM in a public observatory. It puts the weight over the pier instead of turning the pier into some huge bending moment piece of I beam.

I have a GEM. I'd prefer to have a fork, especially when crossing the meridian, and especially with a newtonian. Your eyepiece is always where you can access it without doing contortions. For real astrophotography, reality is that you are doing it on the meridian for optimal results. I can cross the meridian with my GEM, but the eyepiece/camera gets in some hairy spots too.

You can keep your forks short with proper counterweights. You can build a simple polar alignment device with cradles for the polar shaft to aid in "rough" polar alignment. For accurate observatory quality polar alignment you can use the declination drift method.

And the first time you lock up the observatory and forget to turn off the drive with that GEM, guess what you find first thing in the morning?

I tolerate my GEM but I consider it inferior to a well designed fork mount. You asked for opinions.

#9 jrcrilly

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Posted 16 May 2009 - 11:49 PM

But you can't go horizon-to-horizon. It doesn't matter whether you flip an hour before or an hour after meridian - you still flip at some point.


??? Of course you can. I've done it - sometimes because I fell asleep "at the wheel". :)

I don't know why everyone seems think you have to flip in the middle of an imaging run. Just not so... at least not with Tak and AP GEM's. If my cables where long enough, those mounts would do 360's.


OK. I take it back. What I should have said is that I can't go horizon to horizon. As you mention, my Tak NJP doesn't know any better, and would cheerfully try - but it wouldn't do any good. I don't set up outside, so if the OTA is below the mount I'll be shooting images of the West wall long before I reach the horizon. At least, I would if I had installed cables sufficiently long to permit that kind of rotation, which I haven't. Frankly, I'm accustomed to using mounts that know better than to permit something like that to happen. The lack of safety provisions on the Tak is hardly a selling point. I put up with this lack because I like the mount otherwise.

#10 nobbygon

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Posted 17 May 2009 - 12:07 AM

Thanks for all your input everyone. haha good arguments from both sides. Im still not 100% sure which way to go still.

Im probably swinging towards the fork mount for its ease of use.

A hypothetical question; If I were to buy a 10" SCT would a EQ6 PRO be able to take the weight or would I have to go someting bigger ans better??

Cheers, Angus

#11 nik hodges

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Posted 17 May 2009 - 03:53 AM

i think there is nothing wrong with forks as a design infact as stated above they have advantages and many big instruments use a fork design, the problem is i guess we are not talking about professional instruments but amateur telescopes with fork designs ie goto SCTs and these are a different kettle of fish typically been under engineered and not particularly rigid especially up on a wedge. It is possible to get very nice images with these as many people have shown especially with shorter focal lengths piggy backed to the main telescope or with other aids such as adaptive optics but overall i think for "amateur" imaging rigs GEMs seem to have numerous advantages as already stated in this thread and thus tend to dominate amongst "serious" amateur imagers (ie tak/AP/Paramount etc) althought there are some interesting new designs around e.g. Chronos mounts and i think RCOS supply a professional quality fork mount for use with large RC instruments

#12 Chris Curran

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Posted 17 May 2009 - 07:26 AM

John,

the lack of safety provisions on the Tak is hardly a selling point.

I don't consider it a "lack of safety provision" - I consider it a feature. Different strokes....

Please understand that my comments are in reference to the functionality of a GEM. They are NOT a comparison of Fork vs GEM. Quite frankly, I don't think the Fork vs GEM debate is a fair comparison. I don't know of anyone making fork mounts that are of the same quality as the top GEM vendors (Tak, AP, Paramount, etc).

You do not need a GEM for successful imaging - you need a very high quality mount of exceptional build. Right now, the only real offerings available to the amateur are GEM's. I'm quite certain that if someone started making/selling a fork mount that was of the same quality as a Tak, AP or Paramount there would be no "debate".

#13 Jimmy2K63

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Posted 17 May 2009 - 09:07 AM

Please understand that my comments are in reference to the functionality of a GEM. They are NOT a comparison of Fork vs GEM. Quite frankly, I don't think the Fork vs GEM debate is a fair comparison. I don't know of anyone making fork mounts that are of the same quality as the top GEM vendors (Tak, AP, Paramount, etc).

You do not need a GEM for successful imaging - you need a very high quality mount of exceptional build. Right now, the only real offerings available to the amateur are GEM's. I'm quite certain that if someone started making/selling a fork mount that was of the same quality as a Tak, AP or Paramount there would be no "debate".


Maybe I can shed some light on this a bit. Back in the 70's when I started into this hobby this was not even a debate. Most people were making their own mounts, in fact it was not unusual for a serious amateur to own a lathe at home. The equipment market wasn't this massive mess of Walmart style gadget-mania we see today. You generally could not even purchase a mount like you can today - you had to buy the whole unit with the OTA. The Orange tube Celestron's 14's all had fork mounts, but one complaint among owners was flexure in the forks - it was a heavy tube assembly.

Sometime in the 80's/90.s Celestron came out with their C8 on a GEM. It has evolved to the point today that the largest majority of mounts are GEM's. I was surprised to pick up a catalog and literally witness the demise of the fork and many other quality mount designs. The half-fork designs of today with GoTo Alt-Az mounts cannot be compared to these CGEM's, they are made to be CHEAP not useful. Even the move to GEM's was down purely for economic reasons.

The key to any mount is the proper intersection of the RA and DEC axis - it MUST be a precise 90 degrees. When you add flexure into this, that changes. My Astrola mount has some pretty decent machining in it, 1.5 inch shafts, roller bearings, good clutches, etc. They may make mounts like that today but even the Atlas made by Orion looks pathetic next to it and I wonder how stable it can really be when it is mounted on a tripod with legs and not a pier.

I love a well engineered hand made fork mount with a nice 12 inch Byer's drive on it. It keeps the shafts short to avoid flexure you can build the wedge from plate steel, and you can use heavy plate beams for the forks, properly support the OTA on 2 beams and couple that up with some rock solid bearings on pillow blocks. :-)

One thing that has not changed though is that anyone serious about wanting to love their instruments quickly realizes that the mount makes all the difference between a high power terrestrial telephoto and a serious astronomical instrument.

Someday, not in this forum, we can have a debate about this whole progression to "needing" an APO for "serious" imaging as well. Today it's all nothing but a money racket and the "serious" amateurs are the ones who know how to cash a check. :-)

#14 Luigi

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Posted 17 May 2009 - 09:36 AM

>>>The equipment market wasn't this massive mess of Walmart style gadget-mania we see today.<<<

I like that! Spoken like a true curmudgeonly luddite, just like me. :jump:

#15 Chris Curran

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Posted 17 May 2009 - 12:52 PM

Back in the 70's when I started into this hobby this was not even a debate.


Yes, but back in the 60's I.... I forget. Having been in this "hobby" for almost 40 years, there's not much I haven't seen. :)

#16 Jimmy2K63

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Posted 17 May 2009 - 02:41 PM

Hope I don't dig a hole here Chris, but.....

You have a $10,000 mount. That hardly qualifies on the same level as your typical amateur commercial grade equipment. Having said that, it's beautiful. I always thought that when white paint became the norm and equipment looked like it belonged in a medical lab instead of a farmers field it made it look nice on the outside. I'd be ashmaed if it wasn't perfect. I wish the links on your website weren't broken, I'd love to see the rest of your equipment.

Yet I would not be afraid to put it up against a well built homemade fork mount, similar desgned wedge low mounted with pillow block bearings, a Byers drive, and machined mating surfaces like we used to build. You could still build one for about a tenth of the cost that photographically would reveal the same results. You could have 2 inch shafts and where the mating surfaces of the fork met the shaft the collar would be precise. You could build a perfect fork (or even cast your own), use pillow blocks for the dec axis, and shim underneath with thin sheets to bring it to trueness. A Byers on that baby and it would track like a dream.

The mass of the mount is not always a good indicator of its build. The mass of a GEM is dictated by the mass of the OTA and the appropriate counterweight, or that dec shaft would "resonate" like an old plucked guitar string - thus heavy shafts. As far as damping vibration, that comes down to the clutches on the drive more than the mass of the mount. One good thing is when you hit it in the dark, it doesn't yield, just breaks a toe. :-)

Still I bow down to you oldtimer :-) Nice stuff.

#17 gavinm

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Posted 17 May 2009 - 05:23 PM

But you can't go horizon-to-horizon. It doesn't matter whether you flip an hour before or an hour after meridian - you still flip at some point.


??? Of course you can. I've done it - sometimes because I fell asleep "at the wheel". :)

I don't know why everyone seems think you have to flip in the middle of an imaging run. Just not so... at least not with Tak and AP GEM's. If my cables where long enough, those mounts would do 360's.


Seriously??? I am looking for a high spec robotic-ish mount that doesn't need flips. Ive basically ruled out the Paramount. MI-500 or 750 fork (with TCS) is coming close, but if the AP1200 can actually do this..... Ive never heard this extreme before.. crikey

BTW the flips stuff up my photometry

#18 LLEEGE

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Posted 17 May 2009 - 05:52 PM

It depends on what area of the sky you are imaging. The nice thing about the AP mounts is you can "back" the scope over the meridian (putting the OTA on the "wrong" side of the mount) using the meridian delay feature. Typically, if your object is in the east, your OTA is on the west side of the mount. You can tell the AP mounts (and now the CGEM and CGEPro) to put the OTA on the east side of the mount while aiming at an east target. This will extend your imaging session through the meridian. You need to be careful that your OTA will not run into the pier. The new AP Command Center will help prevent this with some of its new features. But, even if you have the OTA on the correct side of the mount, it will still image past the meridian as there are no hard stops. It will just keep on going until there is a collision. If your clutches are set properly, this will have little consequence as the clutches will just slip. So again, this must be done with caution. Depending on the length of the OTA and where you are aiming, this may or may not be an issue. This is true of the Tak mounts as well. Using these mounts will greatly lessen or eliminate the need to do a flip. One just needs to be cautious. ;)

#19 gavinm

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Posted 17 May 2009 - 07:25 PM

Im not worried about the pier.. there are ways around that.. I just assumed the bearings might not be up to being inverted etc.. interesting

#20 LLEEGE

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Posted 17 May 2009 - 08:16 PM

Nope. They could care less.

#21 Chris Curran

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Posted 18 May 2009 - 07:12 AM

Jimmy,

Actually, it's closer to $12k once you buy all the junk you need to go with it. :) Also, I never claimed it was "typical" in any way, shape or form. However, I think it is fair to use it as a standard for what's available to amateurs at the high-end. Please let me state that I am not ashamed of paying that much for a mount. This is my "thing". I've been doing it almost 40 years and I traded my way up to where I'm at now. It took a long time - I didn't just write a check. Moreover, I have many friends who spend far more on their toys - cars, boats, golf lessons (OK, that's 1 buddy), etc... I suspect the same is true for all of us.

Perfect? That's not me. I carry my cw's in the back of my truck, don't own a case for the mount (and wouldn't spend a dime to buy one), and I clean the dust off once a year - whether it needs it or not. :) It's a mount - I'm not goping to have sex with it! BTW, did you know that the 18lb AP cw's are really good for holding 2x4 concrete forms in place?!?!?

I don't know how a 1200 would do against a homebuilt anything. A DIY mount is a whole different bucket of worms that you're not going to get me to comment on... but as I stated above - my comments are NOT about a GEM being a "better" mount than a Fork. What I'm saying is that this Fork vs GEM is a pointless debate. You can't go out and choose between three or four high-end fork mount vendors - they don't exist. Comparing a Meade fork to an AP 1200 just isn't fair. They operate under very different constraints. If you want a high-end mount you pretty much have to buy a GEM. It's really that simple.

Dampening is more a function of the pier/tripod/etc the mount is sitting on so I guess we're on different pages there.

Thanks for the heads-up on the broken links. I guess TNR has changed links yet again... I go fix now.

#22 Chris Curran

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Posted 18 May 2009 - 07:16 AM

Yup. Ditto...

It depends on what area of the sky you are imaging. The nice thing about the AP mounts is you can "back" the scope over the meridian (putting the OTA on the "wrong" side of the mount) using the meridian delay feature. Typically, if your object is in the east, your OTA is on the west side of the mount. You can tell the AP mounts (and now the CGEM and CGEPro) to put the OTA on the east side of the mount while aiming at an east target. This will extend your imaging session through the meridian. You need to be careful that your OTA will not run into the pier. The new AP Command Center will help prevent this with some of its new features. But, even if you have the OTA on the correct side of the mount, it will still image past the meridian as there are no hard stops. It will just keep on going until there is a collision. If your clutches are set properly, this will have little consequence as the clutches will just slip. So again, this must be done with caution. Depending on the length of the OTA and where you are aiming, this may or may not be an issue. This is true of the Tak mounts as well. Using these mounts will greatly lessen or eliminate the need to do a flip. One just needs to be cautious. ;)



#23 Chris Curran

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Posted 18 May 2009 - 07:18 AM

The new AP Command Center will help prevent this with some of its new features.

I've been hearing about that for what, two years now? I'm starting to think it's vaporware... I know - it was at NEAF. It was a video... (kidding).

#24 LLEEGE

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Posted 18 May 2009 - 08:24 AM

NO, Howard gave me a step by step demo at NEAF. He said they are working out a few bugs with ASCOM before they release it. There are two versions. Free with limited features similar to what is available with PulseGuide and a full version. No price was mentioned. What was cool with the mount limits was you can draw your limits on a graph. The same for horizon limits. It's going to be nice. I'd rather wait for a working version then get a "Windows" release.

#25 Chris Curran

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Posted 18 May 2009 - 08:34 AM

He said they are working out a few bugs with ASCOM before they release it.

We've been hearing that for a long time... I'm not holding my breath.






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