Mount with absolute encoders for exoplanet transits?

[PeterWar]

Hello everyone,
 
I need to place an order really soon for a remote controller observatory aimed to do diferential photometry for exoplanet transits and I'm undecided between these two mounts:
 
A ) Software Bisque Paramount ME II without the absolute encoders option
B ) 10Micron GM 3000 HPS
 
I can get them at almost the same price. I'll be mounting a Meade 16" ACF F8 OTA and use an Atik Infinity as an OAG.
 
I thought autoguiding was a must for the level of precission required on exoplanet transits, but I see people claim tracking accuracies below 1 arc second on the 10Micron without autoguiding and I have several questions: 
 
1- Would autoguiding with the 10 Micron GM 3000 HPS improve the accuracy of the guiding? 
2- Would I need to autoguide at all with the 10 Micron GM 3000 HPS for exoplanet diferential photometry?
3- How does the 10 Micron GM 3000 HPS + PEC compare to the Software Bisque Paramount MEII + PEC in terms of accuracy?
4- What would be your mount of choice for a remote controlled observatory?
 
Thank you in advance for your replies!

[Davey-T]

10Micron but then I'm biased  seriously though as it's built in Europe from a servicing point of view I'd go for the 10Micron, if I was doing it in the USA I'd say the Paramount.

1 Autoguiding won't improve the accuracy of the 10Micron as it's pretty damn accurate, if you're using a scope that won't model for some reason then you can guide it no problem.

2 No idea about photometry but don't see why it would be any different

3 Don't know how the PEC compares but both are pretty accurate

4 10Micron if setting up in Europe

Dave

 

[DaveS]

As Dave might expect I'll chuck in the ASA DDM 85 Std or Pro for 60 or 100 kg capacity. Direct Drive and absolute encoders. No periodic error or backlash. Guides on its encoders better than any OAG.

[Xplode]

Both mounts will probably do the job, but i would recommend a 10 Micron mount.

10 Micron is less software dependant than a Software Bisque mount, with a model uploaded into the controller you can run unguided all night long if you wanted, the SB mount needs a PC.

If anything happens with the mount it's much better to ship it within europe than overseas (there's also the thing with 10 micron having separate electronics box for the mount so you normally ship back just that box)

 

The scope you want to use will probably not model very well, but i don't think you need that long subs either for what you want to use it for? Shorter unguided subs should be doable even for a scope that doesn't model well.

 

 

[PeterWar]

11 hours ago, Xplode said:

Both mounts will probably do the job, but i would recommend a 10 Micron mount.

10 Micron is less software dependant than a Software Bisque mount, with a model uploaded into the controller you can run unguided all night long if you wanted, the SB mount needs a PC.

If anything happens with the mount it's much better to ship it within europe than overseas (there's also the thing with 10 micron having separate electronics box for the mount so you normally ship back just that box)

 

The scope you want to use will probably not model very well, but i don't think you need that long subs either for what you want to use it for? Shorter unguided subs should be doable even for a scope that doesn't model well.

 

 

Thank you for your comments.

Exoplanet transit involves sessions of 5 to 6 hours while taking images every minute or so. If I'm able to hold a star in the same pixels for the duration of the session then flat fielding becomes less critical.

How is cable management for the 10 Micron? I know software bisque mounts are very good on cable management.

Also I'm concerned about flexures and mirror movement on my Meade ACF F8 OTA with an Optec 3" temperature compensating focuser, I'm wondering how much of an improvement with a better mount can I get taking into consideration the OTA as well...

[Xplode]

Being able to hold the star in the exact same pixels comes down to your OTA, not one of these mounts as the flexure has a small amount of randomness to it.

What i believe you should be able to do untracked is to take short exposures and have a small deviation in the position of your star over many hours, if the small deviation isn't acceptable you would need an OAG as you have already planned for.

If the unguided way works within what you think is acceptable you might even be able to image several targets at the same time.

 

The GM3000 has internal cabling has well

[PeterWar]

1 hour ago, Xplode said:

Being able to hold the star in the exact same pixels comes down to your OTA, not one of these mounts as the flexure has a small amount of randomness to it.

What i believe you should be able to do untracked is to take short exposures and have a small deviation in the position of your star over many hours, if the small deviation isn't acceptable you would need an OAG as you have already planned for.

If the unguided way works within what you think is acceptable you might even be able to image several targets at the same time.

The GM3000 has internal cabling has well

Thanks a lot for your comments and the pic (very good catch!) I think the question that remains is what deviation is considered acceptable for exoplanet diferential photometry, I have no clue! Bruce Gary book on exoplanet observing for amateurs emphatises the importance of guiding on the LX200 mounts, but those mounts are not as accurate as the mounts I'm considering.

[Davey-T]

If Bruce can do it with the LX200 the 10Micron can do it standing on it's head 

Dave

[PeterWar]

Perhaps the GM3000 is a bit of an overkill, Maybe I could safe some money and buy the 10Micron GM2000 HPSII instead?

The weight of the Meade 16" F8 OTA is 70lbs (31,8kg) and the GM2000 HPS is rated for a max weight of 110lbs (50Kg).

Without an OAG, I would only need to add the weight of the dew shield, the spacers, the optec 3" temperature compensating focuser and focal reducer and the Moravian G2-3200 camera.

what do you guys think?

[Xplode]

The GM2000 should be fine for this too  One thing to note is that it doesn't have through mount cable management like the GM3000, but it's not a problem.

With the saved money maybe you could get a more stable OTA? My choice for this use without spending a ton would be a GSO truss tube RC upgraded with a 3" R&P focuser.

http://www.teleskop-express.de/shop/product_info.php/info/p7011_TS-Optics-14-inch-f-8-Ritchey-Chr-tien-Astrograph---carbon-truss-tube.html