ZWO 174MM as guide cam?

[codemonkey]

So, after being out of action for exactly four months due to a never-ending stream of hardware issues, I finally got the Avalon Linear out tonight for a couple of hours before the clouds rolled in.

Only problem is, my QHY5L-IIM now appears to be bricked. Worked fine the last time I used it, but now the computer doesn't find it and the red LED doesn't light up. Tried on multiple computers, tried the same USB cable with other devices and they were all fine, so it looks like it's the camera that is busted.

I was thinking to get a ZWO 174MM as a guide cam eventually, but now it looks like it'll be happening sooner rather than later. Is anyone aware of a reason that I should not buy this?

I intend to use it on an OAG with a 12.5mm prism. The sensor looks highly efficient, large chip for a guide cam, fast download rates, seems like a winner...

[h0ughy]

why waste it as a guide cam - get a lodestar or the cheaper zwo 120mm

[codemonkey]

It's cheaper than a lodestar x2, has a much bigger FOV and technically is a hair ahead in QE as well. Why buy a lodestar?

Lodestar sensor is 6.45 x 4.75mm, 174MM is ~11.34 x ~7.12mm. ASI120mm is only 4.8mm x 3.6mm.

I'm wanting a high QE sensor that has the biggest chip I can get, to increase the odds of finding a guide star without rotating my OAG.

[h0ughy]

well you have just answered your own post ;)

imaging is such a bad habit:lol:

[codemonkey]

Cheers mate :-)

I guess I just wasn't sure if there was some reason that I wasn't aware of that would make this camera ill suited to guiding. It's not marketed as a guide camera and I figured maybe there's a reason for that.

QHY does have a guide camera with the same sensor, but that doesn't mean the camera is suited to guiding. Why might it not be? NFI, but I didn't want to fork out money and find out otherwise.

And yeah, imaging is nasty on the bank account.

[codemonkey]

One minor issue is the form factor. My EFW is connected directly to my OAG, and due to the wide body of the ZWO (62mm), it'll collide with the EFW at some positions. Not insurmountable, a minor inconvenience. Of course, if everything works out I'll never even have to rotate it, so that won't be a problem.

[codemonkey]

Annnd I just bought one. I'll report back if I have any issues.

[Atmos]

I use a ZWO ASI120 but that is in a guide scope and gets the same FOV as my main camera so never an issue with guide stars :)

[codemonkey]

Good to know; thanks Colin! As handy as a guide scope is in some ways, I can't go back to one... there's always some flex. Failing that I'm going for a sensitive cam with a big FOV and hoping that does the trick.

[ZeroID]

I use a 120mc as a guider on an 80F5 with PHD2. Brilliant !
Sensitive enough that I haven't even had to move the scope to find a star and I guide through the camera to the mount.
I'm looking at the 174 cooled for DSO imaging eventually though.

[Camelopardalis]

I use 224mc, it's very sensitive and low noise, more so than the others. Doubles up as a planetary cam :D

[codemonkey]

Thanks guys. Looks like lots of happy ZWO owners. Hopefully soon I'll be one of them.

Now if only I knew what magnitude star I could successfully guide on. I never even know what star I'm on, let along its magnitude, it's either bright enough or not.

[ZeroID]

Interestingly I find it's the smaller stars that work better. Big stars have wide peaks and sometimes hollows in the peak which PHD can occasionally misread. I normally select a star that is a bit isolated from the rest to prevent any loss of visibility and reacquiring the star and a smaller one that gives a good sharp peak.
Judging by my results with the ZWO you won't have too many problems and PHD2 just about makes it all automatic anyway. It will also do a good drift align as well.

[codemonkey]

Cheers mate.

I didn't explain at all why I was interested in the magnitude of stars that I could guide on, which was remiss of me.

As I use an OAG, I have a fairly limited FOV. This camera will have a significantly larger FOV than my QHY5L-IIM, actually bigger than my imaging camera, amusingly enough, but it's still much smaller than you would have with a typical guide scope.

I was thinking that if I knew that the minimum magnitude I could guide on was X, then I could use something like Cartes Du Ciel to plot out the FOV, and by sampling "randomly" I could get an idea of whether I'll be able to find a star to guide on at any point in the sky without rotating my OAG.

The last few times I was guiding I was using a NIR filter on my guide camera, which obviously will limit the stars that I can find. It did give much better star profiles, but the open question is whether that results in improved guiding or not. If it limits the stars I can guide on and doesn't actually result in better guiding then I would obviously be better off removing it. I'll need to test that out.

I've been using PHD's drift alignment routine for some time now; it's pretty good. PA will be much simpler now without the terrible EQ6 alt adjustment bolts as well. But then hopefully I won't have to do it very often or at all now that my mount is better fastened to the pier with the Avalon's plate.

[Camelopardalis]

Which is why I suggested the 224...the read noise is so low that you can dial up the gain almost without consequence. It's a small chip though - 4.8x3.6mm

[codemonkey]

That's an interesting point. I didn't think of it like that. Ah well, nothing to be done for it now.

The 174MM is here now and does show vignetting with my OAG. Haven't done a proper flat on it, I was looking at it through PHD where it had been auto stretched so I'm not sure of the extent, but it doesn't look significant.

[bismark]

i Have the ZWO 120 mono and running it as guige cam on PHD2 2.6 anfortunately the weather in SE QLD is bad most of the time and to set the camera up takes some time to find the right setup between exposure and camera Gain, depending on the Guide Star exposure between 1-2 sec and Camera Gain between20-40