First night guiding didn't go well.

[luke9857]

 

Hey,

I've been trying to photograph M31 in the last few days, all wasted nights so far but tonight being the first night using PHD2. Guide camera had no problem finding stars and calibrated fine and I thought all was going well until I looked closer on my subs which showed star trails.

As you can see from the attached graph it seems to be all over the place? Is there a way to figure out what would be causing this mess, balancing, PA, aggressiveness etc? My PA routine was to simply rotate RA until the diagram in the polar scope had the Polaris circle facing downwards and put polaris in that circle. I also balanced RA and DEC so they would stay level with the clutches loose. 

 

[Thalestris24]

Hi

Lots of things can cause guiding problems. All those you mentioned plus others such as poor guide star snr, poor seeing, clouds, wind, PA etc. I can't see what Y-axis scale you have for your guide graph? It's useful to run the guiding assistant tool. How was your calibration? There's a useful piece of software called PHDLab that will analyse your guide log. Also, there's a good phd2 tutorial video on youtube that's worth watching.

Louise

[wxsatuser]

Polaris may be in the circle but does it stay on the big circle as you rotate the mount.

Have you calibrated the polarscope reticule, best done in daylight on a distant object.

If your using EQMOD you can easily use it to polar align.

 

[Owmuchonomy]

Looking at the sub you posted I can't pick up any star trails?  There is an issue in the top right corner which suggests the camera spacing may be out or that you have a tilt in your imaging train. It is a good idea to align your chip with your RA/Dec axis then analysing star issues becomes much easier. I realise this is not an easy task with M31 though due to its size in your FOV but it would be worth doing this to see if it is a tracking/guiding issue or something more related to your imaging train.

[alacant]

Hi. Your photo looks fine so why not just go ahead and see what you get? I'm sure that a stack of 20 or so of those with a few flat and bias frames would get you a great snap. If you can't live with the spikes, then just switch to a lower vertical axis resolution or turn off the graph: look at the images rather than the graph. HTH.

[RayD]

Agree with all of the above.  The "trails" to me look more like alignment as they are in 2 directions on opposite corners.

If using the ES FF the spacing is 55mm so with your 1100D it should just need the T ring, so assuming you are, it's unlikely to be spacing.  I had some sagging issues with my original ES 80 focuser, which was particularly bad with a DSL attached, and had to swap if for a Moonlite one, but that was on the older type not the essentials which I don't believe has the same problem.

PA is very important, and from the looks of it you haven't quite nailed it.  Lots of good advice regarding that above.  I personally use Polemaster from QHY for initial alignment which is great and saves loads of time, but as you are using PhD already it's worth looking at the good videos on YouTube about drift alignment which will help hugely.  Those graphs and image to me, along with your description of how you've done your PA, look like a PA issue more than anything else, but I'm new to AP myself also, so too am in the middle of a steep learning curve.

Good luck and keep going as M31 is a great target when you nail it.

[Demonperformer]

< Is there a way to figure out what would be causing this mess, balancing, PA, aggressiveness etc? >

You may find this useful.

[RayD]

8 minutes ago, Demonperformer said:

You may find this useful.

Link shows dead for me.

[Demonperformer]

Don't know why it has done that. Anyway, copy of the document uploaded here:

Analyzing_PHD2_Guide_Logs.pdf

[RayD]

That's really useful, thanks 

[luke9857]

 

4 hours ago, wxsatuser said:

Polaris may be in the circle but does it stay on the big circle as you rotate the mount.

Have you calibrated the polarscope reticule, best done in daylight on a distant object.

If your using EQMOD you can easily use it to polar align.

 

Thanks everyone for the replies. 

 

Polaris does move around the circle and doesn't drift away.

 

 

[luke9857]

4 hours ago, wxsatuser said:

Polaris may be in the circle but does it stay on the big circle as you rotate the mount.

Have you calibrated the polarscope reticule, best done in daylight on a distant object.

If your using EQMOD you can easily use it to polar align.

 

 

3 hours ago, Owmuchonomy said:

Looking at the sub you posted I can't pick up any star trails?  There is an issue in the top right corner which suggests the camera spacing may be out or that you have a tilt in your imaging train. It is a good idea to align your chip with your RA/Dec axis then analysing star issues becomes much easier. I realise this is not an easy task with M31 though due to its size in your FOV but it would be worth doing this to see if it is a tracking/guiding issue or something more related to your imaging train.

If you open it in a new tab and zoom in, the stars towards the left trail slightly, but then the stars on the right trail but in a different direction which seems strange? Could it be imperfect focus?

When you say align the chip to the RA/Dec axis could you explain what  it is ttle bit more, as I'm not sure I understand? It may sound silly, but does the direction and tilt that the camera take when  in the telescope a big factor?

1 hour ago, RayD said:

Agree with all of the above.  The "trails" to me look more like alignment as they are in 2 directions on opposite corners.

If using the ES FF the spacing is 55mm so with your 1100D it should just need the T ring, so assuming you are, it's unlikely to be spacing.  I had some sagging issues with my original ES 80 focuser, which was particularly bad with a DSL attached, and had to swap if for a Moonlite one, but that was on the older type not the essentials which I don't believe has the same problem.

PA is very important, and from the looks of it you haven't quite nailed it.  Lots of good advice regarding that above.  I personally use Polemaster from QHY for initial alignment which is great and saves loads of time, but as you are using PhD already it's worth looking at the good videos on YouTube about drift alignment which will help hugely.  Those graphs and image to me, along with your description of how you've done your PA, look like a PA issue more than anything else, but I'm new to AP myself also, so too am in the middle of a steep learning curve.

Good luck and keep going as M31 is a great target when you nail it.

What does the trailing in different directions mean? I've just noticed that now that you have mentioned it, and assumed that they would trail in the same direction if polar alignment was at fault?

I should also add that PHD2 never had any issue with the guide star, never lost it or threw up any errors which is why I thought all was going great, until I tried processing in DSS which told me only one frame would make the cut. That's when I took a further look into the subs and noticed the trailing.

 

It looks like it's going to be clear tonight again so I'll try and play around tonight for a few hours again, and have a go at drift alignment.

[Demonperformer]

11 minutes ago, luke9857 said:

What does the trailing in different directions mean?

I'm no expert, but it looks to me a lot like the field curvature photo in MEPC p181.

[RayD]

Unfortunately I too am no expert, in fact far from it.  However, my thought was poor alignment could lead to big movements in both RA and Dec, which would result in trailing in the 2 axes?

My understanding was that if it was coma, then the trailing would all be towards the centre from each corner?

I don't know, just throwing some ideas in the pot really, but I would have thought if you can get your PA spot on (or very near), which is the easiest bit if you following the drift alignment tutorials, then if the issue is still there, at least you can rule that out.

Be interesting to see the outcome anyway so good luck tonight.

[alexbb]

Hi,

How long was the exposure in the image you provided? How did you set up your guiding system? You might also have some flexing in your guiding setup and that would be visible in longer exposure.
For me, it looks like some field rotation with the guiding star being somewhere between center and top-right + some (maybe flattener) tilting + some coma.

Do you have a short exposure (<30s)?

Alex

[luke9857]

3 minutes ago, moise212 said:

Hi,

How long was the exposure in the image you provided? How did you set up your guiding system? You might also have some flexing in your guiding setup and that would be visible in longer exposure.
For me, it looks like some field rotation with the guiding star being somewhere between center and top-right + some (maybe flattener) tilting + some coma.

Do you have a short exposure (<30s)?

Alex

Hi Alex. 

The exposure was 240 seconds. As for my guiding system I'll start from scratch. 9x50 with a QHY5L II colour mounted to the finderscope bracket on the ED80, could I do with a more stable connection there? I then attach just the usb cable from the guide camera to my laptop and select my QHY5L II colour in PHD 2 equipment setup, and then I select 'EQmod Ascom HEQ5/6'. Everything seems to connect and talk to each other and I can find my stars. I also use 4 seconds exposures for the guide camera.

I have just come across this picture below on another thread about the ED80 and field curvature and it certainly seems to follow the pattern in the bottom image. The guiding star was top and very slightly to the right if that matters? It's a william optics FF/FR that I bought with the scope from the same seller.

 

I don't have a short exposure but tonight I'll take a few 30 second subs. 

[RayD]

The WO notes 56mm back focus, so if you are using a standard T-ring you may need to check and add a touch, perhaps a 1.0mm spacer, although I wouldn't think that would be the case looking at the manual and the fact that it says connects directly to a T-ring.

It it the newer essentials ES 80 you have, with the finder bracket on the focuser as opposed to the tube?

[alexbb]

What I do regarding the cable to the guiding camera is to tie it to the imaging scope. If there happens to be dragged or so, at least it doesn't move the guiding scope/camera by its own so the flexture rules out. I never used a finder scope for guiding, instead I used a scope or a camera lens, but with their position not adjustable. As long as they point in the same direction (as much as possible), the polar alignment is reasonably good and I don't image close to the pole, I didn't have any issue with exposures up to 5 minutes.

I can't figure out from your guiding image the scale and the min movement, but this looks like an usual graph if you set the min motion very small and you shoot from the city's lights where you have an average seeing that allows you usually no more than 2"/pixel resolution.

1 hour ago, luke9857 said:

When you say align the chip to the RA/Dec axis could you explain what  it is ttle bit more, as I'm not sure I understand? It may sound silly, but does the direction and tilt that the camera take when  in the telescope a big factor?

For this, put the camera to a right angle to the mount. This way, if the mount would rotate bad around one axis, the stars would trail vertically or horizontally in the image so it's easier to understand the direction that the mount rotates or adjusts unwanted.

I wouldn't expect field rotation that much at 240s at ~40 degrees DEC unless: you have a bad PA or the guiding scope is pointing far from the imaging scope. I don't get any trails with 120s exposures and 300mm FL and a PA error of 30'.

Hope that's useful,

Alex

[alexbb]

From the last image you provided, it looks like some tilt between the camera and the FF, but I think that's unusual. Could the optics be tilted inside the FF??

[Thalestris24]

Hi

Yeah, now I'm awake (!), and looking at your image, it does look like a field distortion (i.e. field not flat) problem and that's usually caused by ff spacing. Are you using a standard, as opposed to low-profile, t- ring?Which particular WO ff are you using? Spacing for some ff's can be critical i.e. needs to be within 1mm. If you have some digital calipers you could maybe try measuring the ff flange to camera sensor distance. As mentioned above, there might be some tilt there. Also. I'd say your focus was a tad out. I find using a Bahtinov Mask gets me the best focus.

Louise

[luke9857]

1 hour ago, RayD said:

The WO needs 56mm back focus, so if you are using a standard T-ring you made need to check and add a touch, perhaps a 1.0mm spacer?

Is that the length from dslr sensor to FF/FR lens?

Looks absolutely fine to me. As for spacing, I do remember something coming with the scope and FF/FR when I bought it, some small ring. It's at my parents house at the moment so I'll have a look later. I just hope that I kept it in the box...

 

1 hour ago, Thalestris24 said:

Hi

Yeah, now I'm awake (!), and looking at your image, it does look like a field distortion (i.e. field not flat) problem and that's usually caused by ff spacing. Are you using a standard, as opposed to low-profile, t- ring?Which particular WO ff are you using? Spacing for some ff's can be critical i.e. needs to be within 1mm. If you have some digital calipers you could maybe try measuring the ff flange to camera sensor distance. As mentioned above, there might be some tilt there. Also. I'd say your focus was a tad out. I find using a Bahtinov Mask gets me the best focus.

Louise

Hi Louise, it's just a standard T-ring from amazon. The FF/FR just says ' 0.8X REDUCER / FLATTENER APO' not Flattener III or IV. Is it usual or unusual for the need for spacers or does it just depend on what equipment is used?

Uhh, probably missing the obvious here but how exactly do you measure the distance as I do have some caliper? Do you need to go right up to the sensor or is there some sort of marking? It's not something I've done before and I'd never even held an SLR before a few weeks ago!

 

Edit - Just found some 30 and 15 second exposures of M33 (Or at least I thought it was!) and the same thing is happening. Is it safe to assume that it's the field rather than poor PA or guiding now? If I can separate the two then I can get to work on sorting the issue out without worrying about focusing on the wrong thing. 

[alexbb]

Looking at the first picture in the last post, I can see some moving during the exposure. It might be the focuser not locked or some sort of other movement.

In the second picture I can see the stars elongated in the top left, top right, bottom right corners with a radial pattern. Also there's a slight elongation at the bottom left corner, but much less and just at the corner.

Because other images look different, I think you have some moving at the focuser and/or the FF is not tightened enough to the camera, though I don't see how that could happen.

Alex

[Thalestris24]

Hi Luke

I dunno - there are lots of WO flatteners/reducers none of which I'm familiar with! Is it possible to contact the seller to check - especially about the ring you mention? Failing that, maybe a photo of it would be useful.  

All Canons have a mark to show where the sensor is. On the top of the camera, on the left, towards the rear there is a small circle with a line through it. The line marks the plane of the sensor. It's easy to see approximately what the sensor to field flattener distance is using digital calipers but it may be difficult to judge if it's slightly out. As mentioned by others, make sure your camera + ff is tight and square in the focusser.

Louise

[RayD]

47 minutes ago, luke9857 said:

Is that the length from dslr sensor to FF/FR lens?

Looks absolutely fine to me. As for spacing, I do remember something coming with the scope and FF/FR when I bought it, some small ring. It's at my parents house at the moment so I'll have a look later. I just hope that I kept it in the box...

That's the distance from the FF lens to the image sensor.  I believe on most Cannons the sensor is 44mm back, so typically you would need only add the T-ring, but if there was a small ring with the FF, then that could be a spacer.  Check the packaging if you have it to see.  As Louise noted, on some the spacing is pretty critical.

Also, just have a check with your T-ring security.  The reason I say this is that I once fell in to the buy cheap trap (that's not say you have, I did), and purchased a cheap T-ring.  This turned out to be flopping around in the DSLR like a pea in a bucket.  I subsequently bought a WO one and it was snug an perfect.  As Alex says you may have some movement, so that's an area to check.

Agree, the top image looks like general movement as the stars are trailed all over.

[Jokehoba]

I would reckon that it is to do with FF spacing. I have a WO FF. A 10mm spacer with a 71mm ZS/DSLR is perfect. Didn't  think about spacing when attaching an ASI1600 and got effects like yours. I've got sufficient spacers now to flattern everything nicely.