6 replies to this topic

[daveCC]

Hi,

 

I'm new at astronomy, and planning for photometry.  I have a 14 inch F8 on a fork mount from a promanent manufacturer.  This mounts performance is completely unacceptable.  The sky view from my pier is 110 degrees east to west.  I will replace this fork mount with a GEM, and keep the OTA.  The AP1100 GTO will track very, very far past the meridian such that meridian flips will never be needed.  Alternative mounts such as My-T and GM2000 only track for two hours past the meridian, but may be more easily obtained.  Performing a flip to access that last hour of sky view available to me seems unlikely to occur because I'm lazy and it's cold outside.

 

The question is:

If I choose to use one of these non-AP1100 mounts and...

If I were to fabricate a tilt-plate such that the north-south axis remained properly level, while the east west axis was tilted 30 degrees downward toward the west, it seems the mounts mechanical as-designed 'meridian position' would shift two hours eastward, the same, and the sky-referenced post-meridian maximum travel would now be two hours further west, four hours total past the local actual meridian.  The mount would now aim at the actual meridian with the as-designed gearing engaged 30 degrees eastward of the designer-anticipated 'meridian' position.

 

I've never owned a GEM.  I think this will work buy I am curious if I've overlooked some mechanical, geometric, polar alignment, or software/control feature that would cause this setup to fail, leaving me with just another stupid mistake.

 

Please share your comments with me.

 

Thanks,  Dave

[Tapio]

Some quick thoughts:

- autoguiding (to cure tracking performance) ?

- meridian flip "I'm lazy and it's cold outside" - it can be automatic and no need to suffer from cold

- track past meridian - not a question how long mount can track past meridian but if any part of scope/camera/etc hits the mount

- tilt-plate - don't understand why would you need one (I understand extension for mount to avoid scope collisions)

 

And finally, if you are just starting astronomy then starting with 14 inch scope and heavy mount and doing photometry is diving into deep end of the pool.

[WadeH237]

I've never owned a GEM.  I think this will work buy I am curious if I've overlooked some mechanical, geometric, polar alignment, or software/control feature that would cause this setup to fail, leaving me with just another stupid mistake.

This may or may not work.

 

If the only thing stopping the mount from tracking more than two hours past the meridian is a mechanical stop, then it might work.  Keep in mind, though, that the mount "knows" when your target really transits.  If the limit is implemented in software, it might stop tracking two hours after the target transits, regardless of the mechanical position of the mount.  In the software case, you might need to lie about your location and time as well, to convince the mount that you are physically located 30 degrees west of your actual location.

 

That said, I agree with Tapio on a number of points.  For the question at hand, I would be curious why you are trying to avoid a meridian flip.  I image with an Astro-Physics mount, but still let it flip around the time the object transits (I will allow it to finish up whatever exposure it's doing before flipping).  It is all coordinated by my automation software and I don't even think about it.

 

By far, the best thing to do - with whatever mount you get - is to use it as designed and intended.  There are far too many things that can potentially get in the way of successful results.  Why go looking for trouble?

[speedster]

Geometrically, it is very possible.  You can stick your mount on a wall as long as you can get your polar axis aligned.  PA would be a real adventure as movement in one axis would also move the other if the mount is not level as intended.  I suspect the downfall of this would be trying to tell the software what you've done.  NINA (and other software) does an excellent job of handling a flip and automatically plate solves, centers the target, and refocuses after the flip.  And, it's free.  That would be much easier than trying to fool the mount into thinking it is somewhere it is not designed to be.

[daveCC]

Thank you everyone for your thoughtful replies.

 

My thinking is:  I only gain hour of imaging with the flip, and I'm stacking images, so a plate solve will be needed and an adjustment slew (or two) and a re-focus.  From my bright sky, I need to stack a few  just to get a plate solve (although with a better mount giving longer than 20 second exposures, this would change), thus part of that hour is spent just on the flip- so why bother.

 

I had forgotten the tilt would hinder the polar alignment, and I had never considered the software would 'know' the true transit.  Because of your help, I have decided to be patient and wait for an AP1100.  Know anyone who teaches patience?

[Tom K]

Thank you everyone for your thoughtful replies.

 

My thinking is:  I only gain hour of imaging with the flip, and I'm stacking images, so a plate solve will be needed and an adjustment slew (or two) and a re-focus.  From my bright sky, I need to stack a few  just to get a plate solve (although with a better mount giving longer than 20 second exposures, this would change), thus part of that hour is spent just on the flip- so why bother.

 

I had forgotten the tilt would hinder the polar alignment, and I had never considered the software would 'know' the true transit.  Because of your help, I have decided to be patient and wait for an AP1100.  Know anyone who teaches patience?

Patience is certainly the #1 thing all astrophotographers need!  I agree with the others who have commented here - automated meridian flips, when configured correctly, are a non-issue and only take a short amount of time to flip over, recenter, refocus, and get back to data acquisition.

[TxStars]

Dave,

 I love the out of the box thinking.. 

Yes you could make a 30deg tilt plate to hold the mount and gain the two hours.

Polar alignment will just take a bit longer each time unless it is in an observatory. 

As long as the mount does not have absolute encoders you can lie to it and it will never know what you did.

The trick will be keeping the optical tube from hitting the pier/tripod..