Guide Cam advice - Get mine working or get a dedicated guide cam?

[Brian Castro]

I have been trying to use the ASI 715 as a guide cam, but it's a color planetary camera with very small pixel size and field of view. It's been very finnicky with PHD2, having a hard time pick out stars, loosing them easily - calibration has been extremely difficult.

It might just be that I'm totally new to PHD2 and guiding, and all these kinks can be worked out pretty easily, but I'm wondeirng if I should just get a proper dedicated guide cam and leave the 715 for it's intended purpose - planetary imaging.

Ideally looking not to spent $200 (+ tarrifs) on it, so does anyone have an old guide camera they are looking to sell? Ideally a ASI 120 Mini.

If it matters, the guide scope I am using is an Svbony 240mm.

[Joel Lee]

Hi Brian, 

At that focal length on that guide scope small pixels and small sensors should be fine. It’s likely a PHD2 setting/focus thing. I’m happy to help you go over PHD2 settings if you want. I’d first recommend increasing gain, taking a dark library, and using bin 2. If your mount is a harmonic mount I’d recommend you don’t go over 2s exposure and instead increase gain till you are satisfied/have a good SNR. If these don’t work it will be worth changing around star detection settings in PHD2 to be more lenient. 

I’ve used a 678C, 678M, 585C, 220M(also called the 2210), and 249M before and haven’t had issues finding guide stars on any FL < 1150mm. I’ve also used the 678C and the 585C with that guide scope as well and haven’t had issues there. I wouldn’t recommend the 120 when there are options such as the above or the 462/662 nowadays. 

Clear Skies!

Joel

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[Brian Castro]

Thanks! I might take you up on that offer for some PHD2 help. For the record, my mount is an Orion Atlas Pro, and I've largely been using 2s exposures.

I think the focus is okay but I've had trouble telling when it is perfect - as it feels like there's a wide range where the star size barely changes, so perhaps I should get a tiny bahtinov mask for it?

I have a dark library, although I did not do the hot pixel map. Perhaps I need that too.

I'll try setting Binning to 2, but what does that actually do?

For increasing gain, how do I do that? I only see the slider which says it increases "screen gamma/brightness" Which I took to mean it was purely in how it displays the image, now how it captures it.

Sounds like you've used a lot of different cameras. Why do you recommend the 462/662 or others instead of the 120? I had heard good things about it, and have generally been happy with ZWO's stuff.

Also sorry for the weird black background in the text on my last message. Oops!

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[Joel Lee]

Hi Brian,

Sorry I forgot to respond earlier. Are your stars in the preview screen rather round and visible? A mask can help but I think if they are decently in focus without haloing they should be fine. 

I don’t think you need a hot pixel map if you have a dark library. 

Binning 2x2 should increase your SNR at the cost of pixel scale. If you aren’t getting too many stars this might be worth it. 

In order to increase gain, it should be a setting on the camera page in advanced PHD2 near where you set your camera to bin 2x2. 

The 662 and 462 are very similar to each other and use newer technologies than the 120MM. They are much more sensitive, especially in the NIR and IR wavelengths. The 662 also has a much larger full well depth which could enable 16 bit guiding for better SNR in PHD2. All of them are kinda small at 1/2.8 sized but that extra QE you get is significant.  As for the other sensors, they are larger and more sensitive with various pros and cons between each of them. But before buying, let’s check all the settings first. 

Hope this helps! Clear skies!

-Joel

P. S. If you are on discord you can hit me up @novixion  I’m in the CDSE server as well. If I’m currently imaging that night I can also try to get screenshots of my settings I use, though my rigs currently all use OAGs. 

To view this discussion visit https://groups.google.com/d/msgid/sf-bay-tac/CAGm%2BoZYovCPyvey2aUN_hoS244sts%3D6FMW1g5gf%2Bj_Br6eN4jQ%40mail.gmail.com.

[Brian Castro]

Update. I seems to work... at least for the most part!

I increased binning to 2, and it seem to be able to track stars better now :)

That said, I am still getting the following messages:

1. The darks library is not valid for the camera you have selected. (Not sure why, it's the same camera I used to create it, I ignore it)

2. Calibration should not be done in this part of the sky (I also ignore it and say calibrate here)

Do I need to calibrate every time I start guiding? I thought it was a more "now and then" procedure. I've been getting these messages every time. Perhaps I should still look into those, but at least guiding seems to work now. I have not yet processed the guided image so can't yet say if the resulting image is any improvement from before.

I am on discord, although don't use it too much. Which discord server are you referring to? I'm currently on the NINA one and r/astrophotography one.

[Graham Smith]

1. I believe if you set binning to 2, you'll need to redo the darks library.

2. You can ask PHD2 to slew before calibration and it will move your mount to an area good for calibration. 

[Joel Lee]

Hey Brian!

Glad to hear it’s working now! 

Graham addressed all the questions well and I’d like to add to them. 

1) Agreed, you will have to redo darks whenever you change binning and gain just like darks for the main camera (if you take those). 

2) I also ignore them and typically calibrate on target. PHD2 seems to do well enough for most parts of the sky (0.2-0.5 most nights). My UMi20S has no problems calibrating anywhere, even very close to the NCP, but my AM5 doesn’t like it near the NCP so your mileage may vary. If it doesn’t work, Graham’s recommendation of using the calibration assistant to slew to near the equator works really well. 

But yeah, overall, as long as the stars are round in all sections of your image, that’s what matters. 

Ahh, I was referring to the Caldark one.  I’m not in the NINA or r/AP ones unfortunately but you can DM me if you want via username search.  

To view this discussion visit https://groups.google.com/d/msgid/sf-bay-tac/4b9945df-5927-4029-8fb6-ba320299fc4cn%40googlegroups.com.

[Brian Castro]

Thanks Joel, I'll send you a message there.

And thanks to both of you for the help. I think, at least for now - I can do without a separate guide cam. I'll put that money towards an autofocuser or something.

And I never got a clear answer - so just to be sure - am I supposed to do a new calibration every time I start up PHD2?  I knew that you can have PHD2 auto slew and recalibrate... I just dont want to do that if I can instead start imaging NOW haha

To view this discussion visit https://groups.google.com/d/msgid/sf-bay-tac/CAEawR1PHpbUa0vLUztPXtRSxhEagkDu3jtma_yvi4A0oa6GzWg%40mail.gmail.com.

[Brian Castro]

Also Joel, how do I find you or CalDark on Discord? Do I need a link? I dont see anything in search.

I swear using discord makes me understand what my grandparents must have felt learning to send an email the first time.

[Joel Lee]

Hi Brian,

I think you can use the old calibration for PHD2, there's a box in there that should be auto-restore calibration. I don't use it but it should do the trick. 

On Discord, you can use username search under the friends tab then enter my username novixion and it should be able to send me an invite or message. 

Clear skies! 

Joel 

To view this discussion visit https://groups.google.com/d/msgid/sf-bay-tac/CAGm%2BoZZ%2BRXw6OQj8NMmRFWCbnYGgw6h0YqMTa1Gu%2BVhrpeMmJg%40mail.gmail.com.

[Mark Wagner]

Quite a little imaging thread.

Joel, perhaps people interested in CalDark (CDSE) could join the google group first, so they can understand some of the guidelines?'

Thanks,

Mark

[Joel Lee]

Hi Mark,

I think my last message got bounced, I posted from the google groups page that time. Odd, since I was replying from Gmail before and had no issues.

That's a good recommendation, my bad. I was under the impression that there was a lot of overlap between the groups. I forgot how I joined that group haha.

Sincerely,

Joel

To view this discussion visit https://groups.google.com/d/msgid/sf-bay-tac/ffdcee37-6cf5-43bb-8eff-501f4efa233cn%40googlegroups.com.

[Bret McKee]

On Wed, Nov 5, 2025 at 1:06 AM Brian Castro <brian.g...@gmail.com> wrote:

And I never got a clear answer - so just to be sure - am I supposed to do a new calibration every time I start up PHD2?  I knew that you can have PHD2 auto slew and recalibrate... I just dont want to do that if I can instead start imaging NOW haha

If nothing has changed, you don't need to recalibrate, but "nothing" really means nothing -- if you have rotated the camera, physically moved the mount, etc. you should recalibrate. 

Bret

[Brian Castro]

Hey Mark, 

How do I join the CalDark Google Group then?

On Wed, Nov 5, 2025 at 1:37 PM Mark Wagner <itsmar...@gmail.com> wrote:

To view this discussion visit https://groups.google.com/d/msgid/sf-bay-tac/ffdcee37-6cf5-43bb-8eff-501f4efa233cn%40googlegroups.com.

[Mark Wagner]

Brian, I sent you an invite.

Thanks,

Mark