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FORUMS Photography Talk by Genre Astronomy & Celestial Talk 
Thread started 04 Feb 2018 (Sunday) 16:55
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Digital eyepiece cameras for telescopes

 
SkedAddled
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Feb 04, 2018 16:55 |  #1

Has anyone used these for casual observation or image recording?
If so, what are you using, and how well does it perform?

My thoughts for starting into astrophotography has me considering
using one of these(with prices ALL OVER the spectrum). My initial
thought is to obtain a telescope with a computerized tracking mount,
or just a motorized mount, while I can piggyback my camera onto
the scope tube/clamp, taking 20-second or so exposures and stacking.
Alternatively, I'd mount the camera directly to the eyepiece receiver.

It seems to me that a USB-connected camera in place of/on the viewing
eyepiece would allow me to monitor tracking accuracy on a laptop or phone,
making adjustments as needed, until satisfactory tracking is achieved.

Does this seem to be a sound reasoning, or am I likely just grasping
at straws with this?

Truly hoping for some sincere feedback about this, from you seasoned
& experienced folks, right down to the newbies such as myself.


CraigΣ 10-20|Tamron SP 28-80|Tamron SP 60-300|Soligor 75-260|Soligor 400|Soligor C/D 500|Zuiko 50 f/1.8|More Manual-Focus glass
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MalVeauX
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Feb 04, 2018 17:18 |  #2

Avoid it.

There's a reason no one who is outputting astrophotography that you know about or is commonly shared use them.

You're far better off using a small USB camera or a small little dSLR or mSLR or M43's mirrorless even.

You can get eyepieces that are threaded to allow an adapter that then attaches a camera (such as a dSLR or USB camera) to allow focus, which is useful on telescopes that cannot achieve focus with the camera directly attached instead of an eyepiece. Otherwise, it's ideal to just have the camera on the scope via the focuser at prime focus.

You're better off with a $50 Rebel XS.

Very best,


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nardes
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Feb 04, 2018 17:42 |  #3

Tracking, Computerised Mounts and Auto-Guiding are different capabilities.

TRACKING
Most tracking mounts use gears (usually worm gears) to track celestial objects at a rate called the Sidereal Rate which is a tad under one revolution in 24 hours. This is simple tracking with no feed back to the mount.

A simple motorised telescope mount will generally track at the Sidereal Rate, and just chug along all by itself. Depending on the quality of the mount and the accuracy of your set up, there will be tracking errors due to machining tolerances in the gear train, atmospheric refraction, set up errors, etc. These errors will produce elongated stars at longer focal lengths and/or longer exposure times.

COMPUTERISED
A computerised mount usually allows some alignment and positioning communication between the tracking mount and a computer so that once the mount is aligned to a known position in the skies, a computer “knows where it is pointing to” and can command the mount to slew to an object that you can chose on the computer screen for example. However, the mount is still only tracking at the Sidereal Rate so once again depending on the quality of the mount, the object will eventually drift within the field of view.

AUTO-GUIDING
To reduce the unwanted drifting of stars to a level where you can record pin point stars at longer focal lengths for minutes at a time, you need to add “Auto Guiding” to the simple tracking process. This adds a feed-back process to the mount to correct for any star drifting.

If we attach a smaller telescope to the mount with a camera in place of the eyepiece, that telescope/camera combination becomes an auto-guider (usually requires a computer) which you then calibrate by selecting a bright star (guide star) then commanding the auto-guider to move the mount for say, 5 to 15 secs Up-Down then Left-Right so the guide star moves to a different pixel location. Once the calibration routine has been completed successfully, the auto-guider “watches” the chosen guide star and keeps it centred on a fixed pixel location of the guide camera.

Cheers

Dennis




  
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SkedAddled
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Feb 04, 2018 17:45 |  #4

MalVeauX wrote in post #18556341 (external link)
Avoid it.

There's a reason no one who is outputting astrophotography that you know about or is commonly shared use them.

Thanks, Martin.
I sort of thought as much.

My plan also includes an adapter to mount the 50D directly, since I already have
a T-mount for my old Soligor 500/f.8 CAT lens, which seem to be the common
mount adaptation for such an application.

I was primarily interested in this approach as a way to monitor tracking
without having to keep an eye to the scope's eyepiece.


CraigΣ 10-20|Tamron SP 28-80|Tamron SP 60-300|Soligor 75-260|Soligor 400|Soligor C/D 500|Zuiko 50 f/1.8|More Manual-Focus glass
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SkedAddled
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Post edited 3 months ago by SkedAddled.
     
Feb 04, 2018 18:04 |  #5

nardes wrote in post #18556350 (external link)
Tracking, Computerised Mounts and Auto-Guiding are different capabilities.

Thanks, Dennis. I do understand the differences. Tracking and/or computerized are the only
options I'd even consider currently, due to income/budget constraints.
If I should see some promise and acceptable results in my attempts, I may consider
auto-guiding complexity, but certainly not before giving things a go with some more
rudimentary methods.

My initial inclinations are to try with my Soligor 500/f-8 CAT or Soligor 400/f-6.3,
but the use of my Sigma 10-20 wide open also appeals in some ways.
Both of the first two are surprisingly light-weight lenses, even though older
and made from aluminum with no plastic.


CraigΣ 10-20|Tamron SP 28-80|Tamron SP 60-300|Soligor 75-260|Soligor 400|Soligor C/D 500|Zuiko 50 f/1.8|More Manual-Focus glass
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Digital eyepiece cameras for telescopes
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