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Fork mounts and AP

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#1 jerry32

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Posted 06 January 2013 - 12:57 PM

are fork mounts any good for AP?? just wondering.

#2 neotesla

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Posted 06 January 2013 - 01:03 PM

You will need a field derotator or a wedge to make it work...

#3 Cliff Hipsher

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Posted 06 January 2013 - 01:34 PM

Sure.

As long as you do a proper polar alignment and the mount tracks accurately.

I started out imaging the planets using a Meade 2080 LX5 on a wedge. Worked just fine.

#4 Startraffic

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Posted 07 January 2013 - 03:07 PM

Jerry,
Yes, they can be you'll need either a field de-rotator or a wedge to put the base at an angle equal to your latitude. I believe that the de-rotator is the more $$$ way to go, ut could be wrong.

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#5 David Pavlich

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Posted 07 January 2013 - 06:05 PM

Or you could give the ole' credit card a workout.

David

#6 neotesla

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Posted 07 January 2013 - 06:08 PM

Or you could give the ole' credit card a workout.

David


Makes these seem cheap...

http://trackthestars.com/

#7 MrJones

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Posted 07 January 2013 - 06:19 PM

Basically up to 30s exposures can be done without a wedge. Stacking programs like Deep Sky Stacker can compensate for the rotation between exposures.

#8 Starhawk

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Posted 08 January 2013 - 12:44 PM

The wedge really is the way to go. If you don't have one, the rotation solution for every single frame is different from every other frame.

So if your reference frame is 0, then the next one may need to be rotated .02 degrees, the one after that .04 degrees, the one after that got blurred so it was tossed out, the next one is .08, the one after that had to be tossed, the next is .12, and so on.

To say it is tedious is an understatement. And this has to be corrected before you can give them to an image stacker capable of auto-alignment.

The mounts behave quite well on a wedge, though they are quite heavy. For a C8 sized scope, the forks and base are 2/3 of the weight of what you have to move.

So, while they are usable, deforking is far more portable, and allows you to use the better mounts.

-Rich

#9 rmollise

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Posted 08 January 2013 - 01:13 PM

So if your reference frame is 0, then the next one may need to be rotated .02 degrees, the one after that .04 degrees, the one after that got blurred so it was tossed out, the next one is .08, the one after that had to be tossed, the next is .12, and so on.

To say it is tedious is an understatement. And this has to be corrected before you can give them to an image stacker capable of auto-alignment.


This is really not much of a problem with most software. The problem? You can stack as many subs as you want, but you are always limited to sub-frame exposures that show minimum trailing due to field rotation. You might get away with a minute in some areas of the sky, but a longer exposure than that is really much, much better. ;)

#10 Starhawk

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Posted 09 January 2013 - 09:15 AM

Well, yeah, but you can't take longer exposures in alt-az. That's why it's rotational heck. I have seen a lot of software claim it could do rotation automatically. I've never seen anything resembling a successfully rotated stack run in front of me. Auto-align, yes. Rotate- not even close.

-Rich

#11 rmollise

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Posted 09 January 2013 - 09:25 AM

Well, yeah, but you can't take longer exposures in alt-az. That's why it's rotational heck. I have seen a lot of software claim it could do rotation automatically. I've never seen anything resembling a successfully rotated stack run in front of me. Auto-align, yes. Rotate- not even close.

-Rich


Which is just what I said--or thought it was, anyhow. :lol:

As far as rotation, I have never, ever had a problem with Nebulosity correctly rotating frames. Granted, they weren't terribly rotated to begin with, but I am not a drift-aligner. ;)

#12 Starhawk

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Posted 09 January 2013 - 09:38 AM

I think that's the core issue, Rod. The amount of rotational error in even a lousy polar alignment is small. It varies across the sky for alt-az, and is worst in the sweet spot near the zenith, and pretty bad anywhere near the celestial equator.

So, I got into doing precision polar alignments and have enjoyed seeing frames stack like playing cards.

I've kept my deforked Nexstar GPS mounts and am nearly finished with an all-metal conversion of my Nexstar 8 forks into a small scope mount- which I expect to work quite well at focal lengths up to 1000mm, since it was pretty good at the C8's focal length. It is quite easy to move without a bulky and fragile OTA attached.

-Rich

#13 MrJones

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Posted 09 January 2013 - 10:19 AM

I don't disagree with the above, but for someone that just wants to try AP and have an easy to use visual scope that can see things at the azimuth :) driven alt-az mounts might be the better solution. Here's a quick Leo triplet from my LT6 with not that many 30s subs.

Attached Files



#14 rmollise

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Posted 09 January 2013 - 11:38 AM

Certainly I agree that if you want to start imaging and are set up for alt-az, give it a try. The results may surprise. That is a very nice picture, dude.






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