phd2 help

[Calzune]

yesterday I tried to calibrate phd2 for the first time and I had some problems...

there is something wrong with my backlash, how do I fix that?

Can someone help me?

phd2 stats.fit

[kens]

Please post your guide log

[Thalestris24]

4 hours ago, Calzune said:

yesterday I tried to calibrate phd2 for the first time and I had some problems...

there is something wrong with my backlash, how do I fix that?

Can someone help me?

phd2 stats.fit 2.35 MB · 2 downloads

Make sure you're well-balanced and fairly close to being polar aligned  before calibrating with PHD2. Having the Rowan belt mod is the best way of dealing with backlash but, failing that, it's recommended to arrange your balance to be slightly East heavy.

Louise

[Skipper Billy]

I cant open a FIT file on this machine but of more help would be if you could post the log file.

Also there is a good document here - second item down on this page - https://www.davidbanksastro.com/how-to

[DKNicholson]

20 hours ago, Thalestris24 said:

Make sure you're well-balanced and fairly close to being polar aligned  before calibrating with PHD2. - . . .  it's recommended to arrange your balance to be slightly East heavy.

Louise

Louise Hi - With the telescope etc in the home position pointing very near to Polaris, I should be most grateful if you could explain to me what is meant by East Heavy.

Don't worry - I have just found an explanation elsewhere in the forum! 🤩

Edited November 7, 2019 by DKNicholson

[Thalestris24]

17 minutes ago, DKNicholson said:

Louise Hi - With the telescope etc in the home position pointing very near to Polaris, I should be most grateful if you could explain to me what is meant by East Heavy.

Don't worry - I have just found an explanation elsewhere in the forum! 🤩

Hi

Well, starting from having your eq mount pointed north, then the RA axis will track the stars from the East to West. By arranging for the balance to be biased slightly to the East, it will ensure that the weight of the scope will be pushing against the cogs of the RA motor and not able to 'flutter' around in between the cogs. Having a belt mod eliminates the motor cogs and hence the RA backlash. You can still have similar problems in DEC but you can reduce that via balance adjustments also or by being slightly out of PA, so that the scope drifts in one direction and is easier to manage. Similarly, a belt mod eliminates motor gear backlash in DEC also. There can still be issues with the worm gear meshing but you should be able to adjust that to minimise any problems with it. Pointing at the zenith can also be problematic and you have to think about readjusting balance as the scope moves down to the West. I should probably mention that it's a good idea to start of with correct balance in all 3 axes that the scope can move in. Then, if you don't have a belt mod, you can do your East heavy tweaks. This balancing malarkey can be slightly more trickier with a Newtonian than with a refractor, partly because of how a camera is mounted.

Hope that helps. If I've missed anything, I'm sure someone will chime in E&O.E.

Louise 

[DKNicholson]

56 minutes ago, Thalestris24 said:

Hi

Well, starting from having your eq mount pointed north, etc etc . . .

Hope that helps. If I've missed anything, I'm sure someone will chime in E&O.E.

Louise 

Louise - Thank you kindly for that. I have an EQ6-R Pro which comes belt driven, so it would seem that should have removed most of the issues. My concern is with guiding and I find the graph does jump around more than I expected. Whilst I know there can be various reasons for this, I have never applied any bias to balancing - except perhaps slightly camera heavy (refractor) and I had wondered therefore if balancing might be part of the problem.

David

[Thalestris24]

Just now, DKNicholson said:

Louise - Thank you kindly for that. I have an EQ6-R Pro which comes belt driven, so it would seem that should have removed most of the issues. My concern is with guiding and I find the graph does jump around more than I expected. Whilst I know there can be various reasons for this, I have never applied any bias to balancing - except perhaps slightly camera heavy (refractor) and I had wondered therefore if balancing might be part of the problem.

David

Yeah, as I said, with a belt mod, you don't want or need East heavy. You want perfect balance in all three axes. People often forget to position the scope vertically and check it's still balanced ok i.e. stays in the vertical position without falling to one side. Of course, you also have to make sure your guidescope is rigidly mounted without flex - more critical with longer focal lengths.

Louise

[DKNicholson]

22 hours ago, Thalestris24 said:

Yeah, as I said, with a belt mod, you don't want or need East heavy. You want perfect balance in all three axes. People often forget to position the scope vertically and check it's still balanced ok i.e. stays in the vertical position without falling to one side. Of course, you also have to make sure your guidescope is rigidly mounted without flex - more critical with longer focal lengths.

Louise

Louise hi - That is pretty much as it is balanced at the moment and everything is absolutely rigid. I have found a couple of settings in PHD2 that may help a little. Whilst the image of the main camera and the image of the guide camera are similar, it is plainly evident that it is better if they are carefully centred on the same object. Also the photosite size of the guide camera was not accurate whilst the focal length of the 'scope and Barlow X1.5 is! I should also calibrate again and see if that helps - otherwise it's a bit of a mystery!

David

Edited November 8, 2019 by DKNicholson

[Thalestris24]

10 minutes ago, DKNicholson said:

Louise hi - That is pretty much as it is balanced at the moment and everything is absolutely rigid. I have found a couple of settings in PHD2 that may help a little. Whilst the image of the main camera and the image of the guide camera are similar, it is plainly evident that it is better if they are carefully centred on the same object. Also the photosite size of the guide camera was not accurate whilst the focal length of the 'scope and Barlow X1.5 is! I should also calibrate again and see if that helps - otherwise it's a bit of a mystery!

David

It shouldn't matter whether target and guide images are centered. Have you entered the focal length of your guide scope into PHD2? Are you displaying the basic PHD2 tools that you need - guide star profile, bullseye target etc. What PHD2 settings are you using? If you're imaging with the Evo 72, that's a short focal length so guiding requirements are fairly minimal and should work beautifully on your mount (If your  seeing is good you should get guiding accurate to with an arc sec or 2, run the PHD2 guiding assistant to see how your mount behaves without guiding). Balancing out the dslr might be tricky. I take it you are pulse guiding with Ascom/Eqmod? I've no idea what you mean by "the photosite size of the guide camera was not accurate", and why are you using a Barlow - not a good idea! Maybe you can get a log file and/or a screen clip showing it all in action?

Louise

[DKNicholson]

I'm using an Altair Wave Series 115 refractor with a Starlight Xpress Trius-694 camera. The guide camera is a Lodestar x2 through a TS-50 and Barlow x1.5. The image from the guide camera is very good and the ratio of guiding to imaging is 1:1.6 which I understand to be quite good for this set-up. I do have an SW ST80 where the ratio is 1: 2.2 which is OK, but the clarity of the stars is not particularly good. Using the TS-50 on its own pushes the ratio a bit far and the image through the Barlow and TS-50 is better than that using the ST80, so I've settled on that for the time being. The photosites (pixels) are the active cells on the chip and PHD2 seems to presume they are square as there is only one box available to enter the size. The Lodestar x2 has rectangular photosites (pixels) that are 8.4um x 9.8um. For some odd reason I had this set to 8.0um, but have now set it to 9.1um as the mean. I'm currently waiting for some clear sky to recalibrate PHD2 and run the guiding assistant. If I can get the RMS total error below 0.8 then I should be a happy bunny.

David

Edited November 8, 2019 by DKNicholson

[Thalestris24]

30 minutes ago, DKNicholson said:

I'm using an Altair Wave Series 115 refractor with a Starlight Xpress Trius-694 camera. The guide camera is a Lodestar x2 through a TS-50 and Barlow x1.5. The image from the guide camera is very good and the ratio of guiding to imaging is 1:1.6 which I understand to be quite good for this set-up. I do have an SW ST80 where the ratio is 1: 2.2 which is OK, but the clarity of the stars is not particularly good. Using the TS-50 on its own pushes the ratio a bit far and the image through the Barlow and TS-50 is better than that using the ST80, so I've settled on that for the time being. The photosites (pixels) are the active cells on the chip and PHD2 seems to presume they are square as there is only one box available to enter the size. The Lodestar x2 has rectangular photosites (pixels) that are 8.4um x 9.8um. For some odd reason I had this set to 8.0um, but have now set it to 9.1um as the mean. I'm currently waiting for some clear sky to recalibrate PHD2 and run the guiding assistant. If I can get the total error below 1.0 then I should be a happy bunny.

David

Sorry, I was confusing you with Calzune's OP. My bad, though same principles apply The 50mm finder will be fine. You really don't want a barlow on your guide scope - better off having the wide field of view to select guide stars. PHD2 is very good at sub-pixel guiding because it calculates the star's centroid. As regards calibration and guiding, make sure you manually select a star with good snr and not clipped. Adjust guide exposure to be around 2-2.5s. The small pixel size difference between 8.4 and 9.8um won't make any difference, I don't think - lots of people use Lodestars.  When calibrating find a star at about 30 deg and in the region of the sky in which you are imaging. When guiding monitor the bullseye - if there's an offset to one side it's likely you are out of balance. If you can't get a decent calibration you'll have to investigate why that is. The Guiding Assistant can give you a lot of info.

Louise

ps make sure none of your cables are dragging on the scope!

Edited November 8, 2019 by Thalestris24

[DKNicholson]

2 hours ago, Thalestris24 said:

Sorry, I was confusing you with Calzune's OP. Not a problem. The 50mm finder will be fine. You really don't want a barlow on your guide scope - better off having the wide field of view to select guide stars. PHD2 is very good at sub-pixel guiding because it calculates the star's centroid. Currently running with Barlow in place as I was more interested in seeing how my new SX camera would perform and I spent a while calibrating PHD. At the moment the RMS Total error is between 1.0 -> 0.6 which is a significant improvement over previously. I shall certainly try taking the Barlow out and seeing how it goes. Because of the reduction in 'brightness', as a consequence of the Barlow, the stars are quite faint this evening and the Moon isn't helping much! As regards calibration and guiding, make sure you manually select a star with good snr and not clipped. Adjust guide exposure to be around 2-2.5s. All done already. The small pixel size difference between 8.4 and 9.8um won't make any difference, I don't think - lots of people use Lodestars.  When calibrating find a star at about 30 deg and in the region of the sky in which you are imaging. I calibrated just above the equator (in the South) as that was the instruction following an error message when I tried calibrating in the North (I'm imaging the Iris Nebula) - so I'll see how it goes, at the moment it's working well.   When guiding monitor the bullseye - if there's an offset to one side it's likely you are out of balance. I did check the balance again and adjusted it very slightly, so hopefully that will also help. If you can't get a decent calibration you'll have to investigate why that is. It calibrated surprisingly quickly with no error messages - so it is looking good. The Guiding Assistant can give you a lot of info.

Louise - thank you for your time and help - David

ps make sure none of your cables are dragging on the scope! That has always been an important consideration and I just slewed all over the place without any issue.

 

Edited November 8, 2019 by DKNicholson