Problems changing optical train during observing planets

[Alastro]

Hi Everyone,  I wonder if there is any advise for my problem described below or if it is just a problem that can not easily be solved but I thought I ask anyway:

I'm trying to make images of the planets with a ZWO ASI120MC webcam. The telescope is not perfectly aligned and I just point the scope with a laser pointer towards Mars or Saturn and fine tune with the finderscope until the planet is perfectly in the crosshairs.  I use an 19 mm eyepiece (2" Eyepiece mounted into visual back with only a 2" adapter in between) and to confirm visual alignment to the planet.  Than I replace the eye piece with the ZWO webcam (web cam is mounted into ZWO ADC, which is going into a small adapter to fit in the 2" visual back). At this point the alignment to the planet is still good and the planet appears on the computer screen. I have to change the focus since this optical train is longer than the the one with eyepiece.  Also it is very apparent that the ZWO webcam has a native magnification that is quite a bit more than what can be seen when looking through the eyepiece. Which is fine because it gets me closer to the planet.

Now here comes my problem when I want to zoom even further in with a 2.5 barlow lens.    In order to add the 2" barlow lens I have to remove the entire webcam optical train (described above) so that he barlow can be put into the optical back before the webcam optical train can be put into the barlow.  This procedure throws of my alignment to the plant so far that it can't be seen anymore on the computer screen. Now the barlow fits pretty tight in the visual back which probably moves the entire scope slightly. So I than look through the finderscope to bring the plant back into the crosshairs. At this point I would think  that the planet should be visible again on the computer screen once I adjust the focus again, accounting for the 3" longer optical train now because of the length of the barlow.    But the planet is now so far out of alignment and the magnification so high that I can't find the planet anymore. It is by pure luck if I find the planet again on the computer screen by panning the scope up and down, left and right along the crosshairs of the finderscope.   

As far as I can see I could have two problems.  1. the optical train is mechanically unstable and adding the barlow points the lightpath inside the optical train of the center of the webcam chip.  2. the change in magnification because of the barlow is so high so that the planet is not visible anymore without major adjustment in zoom length, compounding any means to find the planet again.  

Now it is on the other hand easy for me to visually find the planet even if I use 90 degree prism, the 2,5 barlow lens and 19 mm eyepiece. This optical train (light path) is even longer and yet it is fairly easy to find the planet.  The only difference is the native magnification of the ZWO webcam is not there. 

How is it that I "fly practically blind" when using the webcam in combination with the barlow yet it's easy to find and focus the plant visually?

Is this a common problem? Is there any procedure to avoid this problem?

 

[Steve Ward]

Start by turning up the Gain and Brightness settings in the capture software , a Barlowed image is considerably less bright than un- Barlowed and the planet may well be on-chip but hard to see without adjustments.

[CraigT82]

You could get yourself a flip mirror diagonal? 

[Owmuchonomy]

Have you chosen the maximum chip setting rather than an ROI when using the Barlow? If not, try that and then once centred go back to your desired ROI setting for the capture. That's what I have to do.

[Stargazer33]

Hi Alastro, I think it is highly unlikely that you will be able to remove your ZWO and adapter and then insert a 2" barlow; then replace the camera and adapter and get everything lined up again. 

1. If the planet isn't dead centre of your eyepiece and your alignment/tracking accurate then increasing the magnification by 2.5x will increase the misalignment by 2.5x also. Which could mean your target is not hitting the sensor.

2. The extra weight of adding a 2" barlow will deflect the imaging train a lot more than just the camera and adapter.

Get your finderscope really zeroed in. If you can't do this during the day on a distant object (about 2km away) then when you have a target in the centre of your eyepiece, dial in your finder. You can't beat a 12mm ep with illuminated crosshairs for this. Also find out which way you have to turn your focuser when changing from ep to camera. This at least gives you half a chance. And of course nothing beats good basic alignment. The DARV method is really simple; if you have clear views of the meridian/ce junction and either East or West.

[neil phillips]

Steve is right, it may be on screen but now will be out of focus because of the barlow. As such unless you light blast the camera settings you will not see the out of focus planet ring.

Right here is the best procedure I think, get the planet in the finder scope. then get the planet dead centre of a high power eyepiece higher the better. light blast your camera settings, full gain, gamma way up,  exposure set around 33 mili secs  should be bright enough with the other settings that high.

  put your resolution of the camera on full, if it doesn't fit your laptop screen and is too big, which it will be, just drop zoom down so it fits your laptop screen probably around zoom 50 or 60% because you want to see all the chip. Now put the camera in, and centre the planet. now carefully put the barlow in and insert. At this point the planet may well be there, start moving the focuser slowly until you see the out of focus ring. You may see it already. if not move the focuser slowly in and out until you do see it. This procedure should work, I got it to work with Neptune with a w25 filer and that is quite faint. ive never needed a flip mirror in 9 years of doing this. if this procedure fails, start again until you get it basically. From centering the planet in a high power eyepiece onwards hope this works for you it should

[kirkster501]

+1 regardign the focus.  Maybe it's so far out you cannot see anything in the FoV, stars included.  I always found this a challenge with long focal length scope like CPC and a barlow, getting the darn object in the FoV.

[Alastro]

Thanks for your comment guys.  It appears that that a flip mirror diagonal maybe the best way to solve my problem.