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What's the maximum exposure recommended for a mount with overweight?

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8 replies to this topic

#1 caballerodiez91

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Posted 21 October 2019 - 06:44 AM

Hi,

 

In astrophotography, what's the maximum exposure time recommended for an AZ mount with a bit of overweight?

 

I don't plan to take exposures longer than 30 sec (I know I can't with an AZ mount)

 

Thanks!


Edited by caballerodiez91, 21 October 2019 - 07:05 AM.


#2 freddie

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Posted 21 October 2019 - 07:20 AM

Impossible to say, it depends on so many variables. You will have to determine the answer with a few trials.


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#3 pyrasanth

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Posted 21 October 2019 - 07:45 AM

If you plan to image on a mount that has equipment that is overweight for its capabilities then you need to pay attention to balance- this becomes critical- perhaps more so on the DEC axis if your only doing AZ.

 

You will also do better with shorter focal lengths as this will be more forgiving with respect to guiding errors. It will be important to slow down your slew rates because the motors will be under pressure as they will require increased torque to move a heavy load.

 

One last thing you need to be aware of. There is a reason why mounts are rated for the loads they can carry. If you get it wrong you may cause serious damage to the mount and equipment and will not be covered by any warranties- manufacturers are not in the business of covering risk taking.


Edited by pyrasanth, 21 October 2019 - 08:06 AM.


#4 TOMDEY

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Posted 21 October 2019 - 08:02 AM

By far... by far... the greatest causes of mount damage and failure are --- overloading and imbalance. And those are also the two things that amateurs tend to blithely violate. Throw in abuse in storage and transport... and even the best mounts will give up the ghost. Then they either get returned to the dealer as faulty or offered for sale used, with no disclaimer. Just invest in a good mount with double the capacity, pamper it, align it, balance it... and take subs as long as you please!    Tom


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#5 Stelios

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Posted 21 October 2019 - 12:48 PM

Hi,

 

In astrophotography, what's the maximum exposure time recommended for an AZ mount with a bit of overweight?

 

I don't plan to take exposures longer than 30 sec (I know I can't with an AZ mount)

 

Thanks!

You are talking about an alt-az mount, correct? The most common rule used is the rule of 500--expose for 500/focal_length_of_lens. 

 

So if you are using a 50mm lens, expose for 10 seconds (500/50) to avoid star trails. 

 

It doesn't matter (except to your mount) whether it's overloaded or not, since the mount doesn't move. 



#6 caballerodiez91

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Posted 21 October 2019 - 01:05 PM

You are talking about an alt-az mount, correct? The most common rule used is the rule of 500--expose for 500/focal_length_of_lens. 

 

So if you are using a 50mm lens, expose for 10 seconds (500/50) to avoid star trails. 

 

It doesn't matter (except to your mount) whether it's overloaded or not, since the mount doesn't move. 

thanks. my mount is an AZ goto though.



#7 kel123

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Posted 27 October 2019 - 09:40 AM

You are talking about an alt-az mount, correct? The most common rule used is the rule of 500--expose for 500/focal_length_of_lens.

So if you are using a 50mm lens, expose for 10 seconds (500/50) to avoid star trails.

It doesn't matter (except to your mount) whether it's overloaded or not, since the mount doesn't move.

Totally out of point answer.

Please do not overload your mount. I repeat, do not. Hence, the question shouldn't arise. You already have the issue of field rotation to deal with. Leave it at that and be patient until you get a more capable mount, preferably equatorial.

One thing I can assure you is that the Orion nebula and Andromeda galaxy will still be there waiting.

Edited by kel123, 27 October 2019 - 05:45 PM.

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#8 bobzeq25

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Posted 27 October 2019 - 09:43 AM

Hi,

 

In astrophotography, what's the maximum exposure time recommended for an AZ mount with a bit of overweight?

 

I don't plan to take exposures longer than 30 sec (I know I can't with an AZ mount)

 

Thanks!

With an inexpensive AZ mount (GOTO or not), and a telescope (like your 150mm) you won't be able to take 30 second exposures, overweight or not.  The telescope magnifies motion.

 

The TTS-160 AZ mount you've mentioned before uses complicated electronics to act like an equatorial mount.  It's over $4000 with those, more expensive than a comparable equatorial mount.

 

You could use a wide angle camera lens, see post #5 for details.  That solves the weight problem, also.  It's the only way to go with an inexpensive AZ mount.


Edited by bobzeq25, 27 October 2019 - 09:56 AM.


#9 Greg Campbell

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Posted 01 November 2019 - 06:51 PM

Keep in mind that the 'load capacity' reported by the manufacturers is not based on ANY sort of standard. It is largely a number dreamed up by the resident marketing-monkey, perhaps tempered by an engineer's contribution of, "You can't tell them THAT much!"   I suspect that most mounts will work fairly well with a lot more weight than they are 'rated' for, IF that weight is well balanced and centralized.  I've seen folks hang all manner of nonsense off a mid-range star tracker, with no sign of destroyed bearings or an overloaded drive motor. (That said, I quite doubt that these folks will enjoy any level of stability.)  Like everyone else says, "It all depends!"  grin.gif




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