Double stack PST Mod

[bart1805]

A couple of weeks ago I thought about doublestacking the Bresser 127. I was advised not to start the journey because of the difficulties. But I am stubborn enough to boldly fail where others have failed before me.
Ken mailed me a drawing of an adaptor. On another forum Paul said that he wanted to try and 3D print the adaptor. An he did so last week. Yesterday I received the package.

The adaptor is very simple.

image_90603 by bart moors, on Flickr

And the etalon train looks like this:

20170826_143102_resized by bart moors, on Flickr

Yesterday first light, today second light. Images are taken with a Bresser 127 F9,5. 160mm D-Erff, 35 NM Baader H-Alpha, doublestacked, B1200, Powermate 2,5x. 2 degrees wedge prism and Grasshopper with IMX 174.

AR2671_inverted by bart moors, on Flickr

270817_Br127_Halpha_double_PM2,5_10.17_AR272 by bart moors, on Flickr

Is it a succes? Well, the 3D printed version of the adaptor certainly is. But I am not to sure about the results. It is much more difficult to handle, hard to get some focus, usable FOV is small etc. And have to compare double and singlestack images more carefully. To be continued.
ps The guy who printed the adaptor for me has also 3D printed a spectrograph: https://www.thingiverse.com/thing:2455390
Thanks for reading this, Bart.

[gabrieli]

Hi, Bart

To me, the images look competent and any unevenness can be fixed in processing.

One issue I've had with my large ERF setup is trying to find a focusser that I can mount at the end of all the extensions similar to what's shown in your first image. Focusers I've tried so far claim to handle additional weight but can't focus well when oriented vertically. I'm looking for a focuser that doesn't have to hold much weight.

Which focuser is shown in your image and what is it attached to?

Lou

[bart1805]

Hi Lou,
It is a JMI EV-1CM Event Horizon Motorized dual speed SCT focuser. And the 2 inch nosepiece of the etalon is arlttached to the standard focusser of the Bresser 127. Single stacked focussing is pretty easy. Did you try a motorized one? Maybe that is the solution to focus fairly easy even in near vertical position.
Bart.

[Merlin66]

Bart,
Looking very promising....
It will be interesting to hear about your future successes....

Lou,
I found the Borg helical focusers on my PST mod worked very well......

[Ronnie_Clayton]

Great mod.
I have tried to do one some years ago but I had no success. My main problem was the "disc ghost"...
Please keep us informed about your progress .

[Valery]

Focusers I've tried so far claim to handle additional weight but can't focus well when oriented vertically. I'm looking for a focuser that doesn't have to hold much weight.

Hi Lou,

To be honest, a good enough seeing never happens when the sun is high enough that a focuser need to be nearly vertically oriented!

Secondly, after a long time practice, I have found that a well adjusted manual two speed focuser allows MUCH easier and much faster
exact focusing than a motoarized one.


Valery

[gabrieli]

Hi, Valery

A 2 speed manual focuser is what I'm looking for except that I want it to slip into 2" draw tube (into a Powermate). A 2 speed focuser that I mounted directly onto the back of my 9.25 has trouble fine focusing when it carries a Powermate + etalon + camera. I tried all the tension adjustments I could with no luck. I want a small 2 speed manual focuser that just carries the etalon + camera that mounts into the Powermate. I know most focusers that I've seen don't mount this way.

Lou

[bart1805]

Thanks Ronnie, I hope to find a spot where it is possible to fill the complete FOV on band at 2500 mm with about 1.000x900 pixels. Then it would be allright for me.
@Lou: the JMI carries a 2 inch nosepiece, one or two etalons, a lunt BF1200, a 2,5x power mate (1,25 inch), a 2 degrees wedge prism and a Grasshopper. But focussing is still really smooth. I do it by hand and when I think I am there attach the gear of the motorfocusser.

[GUS]

Nice mod and images Bart.