TheSkySearchers

Last night I bit the bullet and mounted my 50mm sighting scope on my 208mm reflector. After trying every conceivable selection of spacers and focal adjustments I finally ended up using EB green. "What is EB green?" you are probably asking. It is the worlds best duct tape. The EB stands for Electric Boat - one of two US shipyards that build submarines. Yes, I literally duct taped my ASI120MM to the sighting scope which is now a guiding scope. EB Green never seems to lose its grip.

So after dark, I went out and discovered that the first two Messier objects I wanted to photograph were already done. Which as it turns out was fortuitous. I set up on M-3 to re-take it using a 2x barlow. Unfortunately I had forgotten to align the main and guiding scope, and the plate solver could not solve for M-3 because of the barlow, but it did solve for the guiding scope. So I gave up using the barlow and shot M-3 anyway but it was close to the meridian so I only got 20 minutes before it hit the flip. It seemed like PHD was guiding fine. After the flip I went out and centered on my "third" object. I watched in horror as the DEC was given orders by PHD to correct the drift after about 30 seconds and instead of moving the red line UP the red line took an exponential downward curve, and within 3 seconds was off the chart. WTF? I used the "brain" two or three times (I'm a little fuzzy on how many times) but it kept sending the wrong signal. It finally dawned on me that the guiding scope is a refractor - not a reflector and the image was corrected. Oh, but how do I tell PHD that? I checked every option that I could find in PHD, and finally in exasperation I deleted the calibration. Somehow, I managed to accidentally start a new calibration and everything seemed to be going well... too well. I started this whole exercise at 2130.

It completed the calibration and I had it lock on a guide star... my gosh there are a lot more stars to choose from using a guide scope vs my TOAG (Orion's Thin Off Axis Guider). To my utter surprise, the history graph showed what I will refer to as a heartbeat sequence. That is tiny (ie less than 1/2 pixel) motions followed by a truly remarkable momentary large correction in a very repeatable sequence... like a heartbeat monitor. In using the TOAG I have never seen this behavior - usually PHD is doing corrections almost constantly. The first good image was started at 0015 - almost three hours later. <sigh> I have yet to process the images (I just got up from the all-nighter). But NGC4631 (a galaxy) and surrounding stars appeared in the images to be pretty crisply defined.

That is the story of last night. I do have one question though - for those that use a separate guiding scope and a barlow on the imaging scope - do you use the imaging scope or the guiding scope for plate solving? I could not get Astrotortilla to plate solve my imaging scopes images. But it worked fine on the guide scope images. If this is the case, I will have to perfectly align the guide scope with the imaging scope.

after attaching the barlow did you re edit the parameters including the focal length of the scope, pixel size, arc seconds per pixel ectt ? , you should always plate solve with the main scope and camera , unless you're running a very high magnification and can't get enough stars , typically deepsky and barlows don't belong, but there are exceptions, like eta carina (homunculus cloud) , a bright object that needs resolution to bring out detail .

I'm still not sure about how you connected your guide camera to the guide scope, but it seems to me that a duct tape connection would be particularly prone to flexure.

Cheers,
JT

Aside from the flexure issues JT mentioned, you should only guide in one direction for Dec.
My setup naturally drifts north just a touch, so I have pHD correct only for North. It fixed my spiking issues almost immediately.
As for flexure, @ f/4.9, you're probably ok. A tube of anything rigid to connect the two pieces, would be immensely helpful in stiffening the assembly up a bit.
You may get a small amount of "star marching" as I call it (when in each successive frame, the stars have moved a very small amount in a straight line.)
Good luck!

Amazingly my first processed image set of NGC4631 came out beautifully and the guiding was superb. It is arguably my best edge on image of a galaxy.

EB green is not your ordinary duct tape. I had the scope moving in all kinds of directions and the guide camera didn't move a pixel. I know that even as good as EB green is I need to find a more permanent solution.

I need to find me an adapter for the ZWO ASI120MM that has a 1/4" "nose" piece that can fit in the diagonal of the guide scope. I am loath to cut the one have have, because I'll need it if I ever go back to the TOAG. 1/4" would be just enough to get the guide scope in focus and tighten the retaining screws on the diagonal.

Alternatively, if I can find an adapter to replace the diagonal with a straight female thread to mate with the guide scope that would be ideal. Anyone have any ideas where I might such an extension tube?

Here's the scope I'm talking about: https://www.telescope.com/Orion/Orion-9 ... 101449.uts

I re-organized my spacers into seal-able containers. In the process I discovered that I have two of the ZWO adapters with a 1"? nose. Given that I now have a spare I will cut the majority of the nose off the spare one to fit into the prism of the scope to give a good tight fit using the in-place set screws.

For plate solving, use the image from the main imaging camera. If you reconfigure it with a barlow (or a reducer), you need to reconfigure the plate solver settings, so it know what the current image scale is. If you use SGP for session control, you can have that kind of information set up in different equipment profiles.

There is a setting in PHD to flip the configuration data after a meridian flip. If you don't use that setting, you will have to re-calibrate, since all the directions are backwards after a flip.

Roger that - I completely forgot to do that. But what do you enter for a 2x barlow - I mean that doesn't it depend on the distance between the barlow and camera for scaling?