78 replies to this topic

[csauer52]

 

If the TDM had actually worked well, wouldn't we all have them? At least all of us without premium mounts. The reason it failed is that if the mount itself isn't precise, it can't react precisely to the encoders. It was an idea years ago, but it has been throughly tested now, and it is history.

I thought I would revive this thread with an image of M27 The Dumbbell Nebula. This was taken with the 6-inch ES 152 ED APO CF scope with the 3-inch ES 0.7x FR/FF and SBIG ST2000XM camera. The mount is a Losmandy G11 with PMC-Eight and Telescope Drive Master (TDM) drive correction system. The FOV is 48x36 arc-min and the FL is 851.2 mm (as measured with a plate solve). This provides and effective f/5.6 focal ratio. This image is 6 x 5-min frames calibrated and stacked for a total exposure of 30 minutes.

 

To be clear, this is an UNGUIDED image only relying on the accurate polar alignment and TDM.

 

M27 DD 30min calibrated 1a.jpg

 

Thats pretty good Jerry. Compare that to my 10 minute, uncalibrated single exposure with tracking enabled. It looks pretty similar and I'm not using one of those premium mounts, just an off the shelf Meade at 2881mm as measured by platesolve. This FOV is 33'x22'.

Attached Thumbnails

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Edited by csauer52, 09 August 2017 - 07:30 PM.

[gunny01]

Saturated guide star is never a problem. There is always a dimmer star. With my mount permanently mounted I sometimes do 30 40 second guide exposures. I discovered this works when I tried to use an older SBIG camera with the guide chip behind filters. I said why not, and it works as good. The only draw back was dithering. It took too long to settle. 

  With the IF ONAG, I routinely guide at 15 sec exposures for 2127 mm f/l.  Saturated stars are not a problem with even 30 min subs.  Where the saturation will probably affect things with the IF is the software for automated focusing that can be purchased.  I never used it as I figure it just adds another layer of complication to what I want to be KISS.

 

  Argue all the theory you want, but the ends justify the means in the final result.  What works for me won't necessarily guarantee the same results for others

[Jerry Hubbell]

 

 

If the TDM had actually worked well, wouldn't we all have them? At least all of us without premium mounts. The reason it failed is that if the mount itself isn't precise, it can't react precisely to the encoders. It was an idea years ago, but it has been throughly tested now, and it is history.

I thought I would revive this thread with an image of M27 The Dumbbell Nebula. This was taken with the 6-inch ES 152 ED APO CF scope with the 3-inch ES 0.7x FR/FF and SBIG ST2000XM camera. The mount is a Losmandy G11 with PMC-Eight and Telescope Drive Master (TDM) drive correction system. The FOV is 48x36 arc-min and the FL is 851.2 mm (as measured with a plate solve). This provides and effective f/5.6 focal ratio. This image is 6 x 5-min frames calibrated and stacked for a total exposure of 30 minutes.

 

To be clear, this is an UNGUIDED image only relying on the accurate polar alignment and TDM.

 

M27 DD 30min calibrated 1a.jpg

 

Thats pretty good Jerry. Compare that to my 10 minute, uncalibrated single exposure with tracking enabled. It looks pretty similar and I'm not using one of those premium mounts, just an off the shelf Meade at 2881mm as measured by platesolve. This FOV is 33'x22'.

 

I assume you mean by "...with tracking enabled" that you are auto-guiding. I calculated the plate scale for your image at approximately 0.644 arc-seconds/pixel. I was curious, with the 10 minute exposure, what do you estimate the limiting magnitude in that image is?

​Thanks

[csauer52]

 

 

 

If the TDM had actually worked well, wouldn't we all have them? At least all of us without premium mounts. The reason it failed is that if the mount itself isn't precise, it can't react precisely to the encoders. It was an idea years ago, but it has been throughly tested now, and it is history.

I thought I would revive this thread with an image of M27 The Dumbbell Nebula. This was taken with the 6-inch ES 152 ED APO CF scope with the 3-inch ES 0.7x FR/FF and SBIG ST2000XM camera. The mount is a Losmandy G11 with PMC-Eight and Telescope Drive Master (TDM) drive correction system. The FOV is 48x36 arc-min and the FL is 851.2 mm (as measured with a plate solve). This provides and effective f/5.6 focal ratio. This image is 6 x 5-min frames calibrated and stacked for a total exposure of 30 minutes.

 

To be clear, this is an UNGUIDED image only relying on the accurate polar alignment and TDM.

 

M27 DD 30min calibrated 1a.jpg

 

Thats pretty good Jerry. Compare that to my 10 minute, uncalibrated single exposure with tracking enabled. It looks pretty similar and I'm not using one of those premium mounts, just an off the shelf Meade at 2881mm as measured by platesolve. This FOV is 33'x22'.

 

I assume you mean by "...with tracking enabled" that you are auto-guiding. I calculated the plate scale for your image at approximately 0.644 arc-seconds/pixel. I was curious, with the 10 minute exposure, what do you estimate the limiting magnitude in that image is?

​Thanks

 

Yep, with tracking enabled is correct.

 

Pure speculation on the limiting magnitude but I'm guessing somewhere ~17 or so?