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Flip Mirror

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#1 JGray

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Posted 12 July 2018 - 03:02 PM

I plan to try planetary imaging for a change and am in the process of setting up an imaging train.  The components are an Edge8 HD, 2.5x PowerMate, Williams 20mm centering eyepiece, ZWO ASI 120 MC-S or ZWO ASI 120 MM-S, and an Agena flip mirror.  My question involves the location of the PowerMate.  It seems to me that the PowerMate should go behind the flip mirror so that initial finding and centering through the eyepiece  without the PowerMate will be easier at the lower magnification and larger FOV; then flip the mirror out of the path and knowing that the target is centered, go to work on focusing the camera.  Am I OK in my assumption or will I significantly alter the extension of the PowerMate with the longer focal length?  Should I instead place the PowerMate prior to the flip mirror so that both the centering and the camera focus take place with the PowerMate in the train?  Thank you for your help.

 

Jim



#2 Achernar

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Posted 12 July 2018 - 04:21 PM

I put the flip mirror between the camera and the Barlow, because to do otherwise would make the eyepiece and camera come to very different focal planes. Just get your finder scope reasonably well aligned then center your subject in that. Then use the flip mirror to find the subjects in the eyepiece. After flipping the mirror out of the way, you should see it on the laptop screen and then you can focus the telescope to suit your camera. I use the same flip mirror you have, and it works very well out of the box. You may need a short extension tube for the eyepiece, which are available widely. I set up my imaging train as follows. Focal reducer if needed, then the visual back, then the Barlow lens if needed, atmospheric dispersion corrector if needed, the flip mirror and viewing eyepiece, then the camera. As you can imagine, if all of those devices are used at the same time, that is quite a load on the rear of the tube. I place a 1 lb. counterweight on the EdgeHD OTA I use near the front of the tube to balance the declination axis, and two 11 lb. counterweights to balance in right ascension. I got the counterweight from ADM, which offers a host of useful accessories that enable successful imaging with SCT's. The flip mirror is something I use almost all the time with my Celestron, because I also enjoy looking at the moon and planets while imaging them too.

 

Taras


Edited by Achernar, 12 July 2018 - 06:34 PM.

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#3 JGray

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Posted 12 July 2018 - 08:14 PM

Thank you, Taras for your answer to my question.  I just finished assembling and installing the imaging train as you suggested.  I had to really dig to come up with a finder scope.  I haven't used one it quite some time.  Its just after sunset here and I tried it out on a distant tree line.  I had no trouble hitting the rather small sensor in the ASI 120 after using the centering eyepiece.  It worked well.  I think I can get the hang of it with a bit of practice.  



#4 RedLionNJ

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Posted 13 July 2018 - 11:05 AM

This is one topic which rarely ceases to amaze me - comes up with startling regularity.

 

Unless you wish to also observe visually (as Taras says) while not imaging, but without breaking down your imaging train, a flip mirror is not necessary.

 

A well-aligned, quality finder is sufficient to put a target onto even a chip the size of an ASI120MM at 6 meters focal length.



#5 ToxMan

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Posted 13 July 2018 - 01:41 PM

I'm with Grant.

 

An image train needs to be sleek, light, sweet...few components as possible. Threaded versus pinch clamped as much as possible. Weight and a lot of pinch clamping makes for "sag" and difficult collimation.

 

I rely on an accurately aligned Telrad although a guidescope works too. I do all that visually with a 9mm eyepiece. Smallest field of view as possible. Use a bright alignment star. Vega is what I use currently. 

 

Yes, the "finders" only get you near the object, and the monitor is black...turn up the gain, higher than you would image at...open the histogram...any light from the planet or its moons will start to fill the histogram...Sometimes rarely, you nail the subject without doing the "sweeping grid search." (Sorry, it's from my Search and Rescue days.) Your camera will need to be in focus or nearly focused. Use the Moon if it is up.

 

My scope is EQ mounted...So, with a "sweeping grid search,"  I manually turn the DEC knob back and forth (sweeping motion) as I hold down the RA button and let the RA motor advance 2 to 4 x tracking speed...and, reverse the motor if I miss it...the histogram blips, and screen shows bright circle flash as sensor catches some light...final centering...then, adjust camera to start video captures.

 

About things that amaze me that always come up...Powermate 2.5x...probably the most popular device to get your focal length up for high resolution imaging. And, probably the most incorrectly used. You want the Powermate top surface as close to the camera sensor to maximize magnification. They make an adapter for that. When you get beyond 100mm, it effectively becomes a 2x barlow. So, one has to consider where it is placed in the sequence of components. Otherwise, use a 2x barlow and place it anywhere you want.

 

Filter wheel, ADC, Powermate, camera is my current configuration. I'm using an 8 inch SCT. If you go monochrome, this will work...if you go color, you won't have the filter wheel, and an even sleeker design.



#6 Achernar

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Posted 13 July 2018 - 07:17 PM

This is one topic which rarely ceases to amaze me - comes up with startling regularity.

 

Unless you wish to also observe visually (as Taras says) while not imaging, but without breaking down your imaging train, a flip mirror is not necessary.

 

A well-aligned, quality finder is sufficient to put a target onto even a chip the size of an ASI120MM at 6 meters focal length.

I have imaged without the flip mirror, but I find it much easier to use one than go without it. Moreover, I find the finder to be enough to get on the paper, but not precise. It is really convenient to be able to switch from one mode to the other, without having to rebalance the telescope.

 

Taras




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