Author Topic: AltAzimuth Astrophotography - Current Status -  (Read 246 times)

plurcontitear

  • Active Astronomer
  • ***
  • Posts: 127
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
AltAzimuth Astrophotography - Current Status -
« on: December 29, 2017, 12:42:43 AM »
Hi all,
I'm finishing a mid-size Newton telescope project (20" f3,5) dedicated to astrophotography.
The mount is essentially alt-azimuth but can be converted to equatorial (if needed!).
Mechanically speaking, in alt-az it will work way better but I still have many doubts about de-rotation and tracking accuracy.
Surfing the web it seems that it's not well managed by amateur equipment nor well proven by field application.
Some tracking system can do it but a big question mark remains.

With this thread I'd like to make the point on this, gathering as much field experience as possible.

Any kind of help, suggestion, thought is really welcome.

Marco



handthedemo

  • Active Astronomer
  • ***
  • Posts: 123
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Re: AltAzimuth Astrophotography - Current Status -
« Reply #1 on: January 10, 2018, 08:56:11 AM »
Have you seen Danish TTSĀ“s solution?

https://trackthestar...trophotography/

buckfeedssapfai

  • Active Astronomer
  • ***
  • Posts: 122
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Re: AltAzimuth Astrophotography - Current Status -
« Reply #2 on: January 11, 2018, 09:15:29 AM »
Unfortunately the system can't fit my big Newton and honestly I think it is useless for small scopes. An eq mount does it just right...
Marco

steviselath

  • Active Astronomer
  • ***
  • Posts: 122
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Re: AltAzimuth Astrophotography - Current Status -
« Reply #3 on: January 11, 2018, 11:38:31 AM »
If you'd like to see some excellent images obtained with a de-rotator, look up images by Jason Ware. He had a Meade LX200 16" that he used a de-rotator on and got great results. So it is possible to get good results from de-rotation. I would guess that with the proliferation of highly sensitive cameras allowing shorter integration times that it would work more easily now than when using film (which Jason did on many shots) and taking hours long exposures. But I don't think field rotation will be your biggest obstacle. You will still have the same issues (tracking, periodic error) whether alt/az or eq mounted, so taking exposures longer than a few seconds will probably need guiding. Does your mount have the ability to be auto guided? At close to 1800mm FL, unguided imaging will be tough for long exposures. If the mount can't be auto guided, you could go old school and do it manually.

Good luck with the project.

exjeraca

  • Active Astronomer
  • ***
  • Posts: 127
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Re: AltAzimuth Astrophotography - Current Status -
« Reply #4 on: January 13, 2018, 03:12:02 PM »
I agree that de-rotation isn't the biggest problem.
I'm at the point of choosing the right motorization system and, although they all accept autoguiding, I'm still uncertain if it will work. I think the only way to go is to put an OAG after derotation.

ithoclirans

  • Active Astronomer
  • ***
  • Posts: 123
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Re: AltAzimuth Astrophotography - Current Status -
« Reply #5 on: January 15, 2018, 03:56:10 PM »
Quote
Unfortunately the system can't fit my big Newton and honestly I think it is useless for small scopes. An eq mount does it just right...
Marco

I can understand it (the TTS mount) is too small for your 20" Newtonian, butcan you explain why it is"useless for small scopes"?

Kyle Johnson

  • Active Astronomer
  • ***
  • Posts: 128
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Re: AltAzimuth Astrophotography - Current Status -
« Reply #6 on: January 18, 2018, 12:08:02 AM »
I think that for OTAs up to 20kg circa there are plenty of good eq mounts that work very well and provide a lot of flexibility, there is no need to try something different.
For bigger OTAs eq mount are much more expensive and only a few exist, plus their counterweight shaft is really intrusive.
In this case, AltAz is a real opportunity, much more compact and mechanically stable.
The only point it's that for amateur market only minor experiences exist, it's still a blue ocean where only few dared to swim and not a lot tell the true story.

Marco

David Williams

  • Active Astronomer
  • ***
  • Posts: 121
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Re: AltAzimuth Astrophotography - Current Status -
« Reply #7 on: January 21, 2018, 05:26:37 AM »
Quote
Unfortunately the system can't fit my big Newton and honestly I think it is useless for small scopes. An eq mount does it just right...
Marco

I thought you asked for "Any kind of help, suggestion, thought"

Lasaro Tourabi

  • Active Astronomer
  • ***
  • Posts: 130
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Re: AltAzimuth Astrophotography - Current Status -
« Reply #8 on: January 22, 2018, 07:59:47 PM »
I would think with that size OTA and fast speed, you shouldn't have too much problem with short integration times.
Keep your stills within 30 seconds and just stack them and process.
Keep us posted.

Dave Hawkins

  • Active Astronomer
  • ***
  • Posts: 126
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Re: AltAzimuth Astrophotography - Current Status -
« Reply #9 on: January 22, 2018, 08:40:59 PM »
Quote
Unfortunately the system can't fit my big Newton and honestly I think it is useless for small scopes. An eq mount does it just right...
Marco


Hi Marco,

I don't have the first hand experience with TTS-300. Judging from TTS-160 experience,
TTS-300 may work for you. I think it is worth emailing Niels Haagh to get his opinion.

Tammy

Theodore Inlaw

  • Active Astronomer
  • ***
  • Posts: 130
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Re: AltAzimuth Astrophotography - Current Status -
« Reply #10 on: January 23, 2018, 10:58:46 AM »
Marco, I am interested in your project. I am building a new servo control system for large amateur telescopes. How heavy do you anticipate your telescope will be? What sort of bearings and mounting? What sort of budget (money) are you planning to spend?

faubloginac

  • Active Astronomer
  • ***
  • Posts: 127
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Re: AltAzimuth Astrophotography - Current Status -
« Reply #11 on: January 23, 2018, 12:14:47 PM »
Thank you all for the suggestions.
My scope will be 150kg (everything included), on bearings (both axis), friction drive on azimuth and worm/wheel on altitude. Very smooth and balanced. Provision for secondary encoders.
Budget for motors/drives: 1500e max
Marco

esrescioripp

  • Active Astronomer
  • ***
  • Posts: 124
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Re: AltAzimuth Astrophotography - Current Status -
« Reply #12 on: January 30, 2018, 08:46:33 AM »
20" at f 3.5 is less than 2m focal length, so the imaging scale is reasonable. The servo-cat (stellar Cat) system is around your budget for 2 axes of control. For a system comprising a servomotor, controller, gearbox, and motor encoder it's difficult to go less than $500 in parts, per axis. So it may be challenging to add the image rotator within your budget. A simpler stepper-motor based derotator should work and the load is low, so the drive is unlikely to miss steps.