Finderguider with lp filter?

[Thalestris24]

Hi all

I set up my 150pds last week with a SW 9 x 50 finder and a QHY5L-II to use as a guider. It works great most of the time but it sometimes seems to happen that S/N is poor and guiding is compromised and no brighter stars nearby (as happened last night, though seeing was poor). I suspect it's being exacerbated by the local lp which is pretty bad . I've tried changing the exposure and camera gain but that didn't seem to help (I'm generally using 1s exposure with gain set to 70%). I'm wondering if anyone has ever fitted a lp filter to a finderguider? I have a 1 1/4" filter which can screw in to the camera but there doesn't seem to be any way of fitting it with the camera connected via its finder adapter .  Any ideas or suggestions  anyone?

An alternative might be to use my ST-80 as the guidescope (with optional lp filter). Probably the better option! In that event, does anyone happen know the spec of the SW tube ring bolts/threads? They look like either M6 or 1/4" but the thread pitch is quite coarse so I'm not certain. I'd have to buy a drill too, lol.

Thanks in advance

Louise

[lensman57]

Hi Louise,

I used to have a Baader Neodymium filter attached to my AsI 120 MC and it worked very well for guiding,  since I got the 120 MM I only use an IR filter .

Regards,

A.G

[Thalestris24]

Hi Louise,

I used to have a Baader Neodymium filter attached to my AsI 120 MC and it worked very well for guiding,  since I got the 120 MM I only use an IR filter .

Regards,

A.G

Hiya - ok, tthanks. I intuitively feel a filter would be useful but there doesn't seem to be a way of attaching one with the finder - unless I'm missing something obvious!

Louise

[RikM]

I got better results with the finderguider than with an ST80. 200mm f/4 vs. 400mm f/5. More stars in the field to choose from and brighter due to the faster optics. Do you dark subtract your guiding frames? How high is the camera gain set? I had mine at 95% I have never had an issue with not finding a suitable guide star with the finderguider.

 Do you fit a dew shield extension or run heater bands? If the guider objective dews over, you won't see any stars in the image. I made a dew shield extension from mat black plastic sheet and a couple of layers of foam to widen it out so as not to vignette the field.

[Thalestris24]

I got better results with the finderguider than with an ST80. 200mm f/4 vs. 400mm f/5. More stars in the field to choose from and brighter due to the faster optics. Do you dark subtract your guiding frames? How high is the camera gain set? I had mine at 95% I have never had an issue with not finding a suitable guide star with the finderguider.

 Do you fit a dew shield extension or run heater bands? If the guider objective dews over, you won't see any stars in the image. I made a dew shield extension from mat black plastic sheet and a couple of layers of foam to widen it out so as not to vignette the field.

Hi Rik

"Do you dark subtract your guiding frames?" Hmm...  I think I'm  missing something there! Is that something you do in PHD? Do enlighten me!

Thanks

Louise

[RikM]

I can't remember the actual name but one of the control buttons is to take a dark frame with the scope covered (I just chuck my hat over the scope) PHD will then auto-subtract that dark frame from the subsequent guiding frames and it cleans the image up quite a bit. You need a new dark if you change the guide sub exposure but I normally use 3seconds. I'm still on version 1.13 because I just use PHD as an electronic finder these days rather than for guiding, so the newer versions may be different but the function will still be in there somewhere. 

Have a look into the dewing as well though because that used to give me a lot of grief before I made the shield for it.

[Thalestris24]

I can't remember the actual name but one of the control buttons is to take a dark frame with the scope covered (I just chuck my hat over the scope) PHD will then auto-subtract that dark frame from the subsequent guiding frames and it cleans the image up quite a bit. You need a new dark if you change the guide sub exposure but I normally use 3seconds. I'm still on version 1.13 because I just use PHD as an electronic finder these days rather than for guiding, so the newer versions may be different but the function will still be in there somewhere. 

Have a look into the dewing as well though because that used to give me a lot of grief before I made the shield for it.

Hi Rik

Ok, thanks.  I wasn't taking a dark frame, duh. I'll make sure I do that next time (whenever that will be with the current weather). I'll try changing the exposure  to  2 or 3 secs as well. It's def not a dew problem but I do generally have lp difficulties. I only got the guide camera on Tuesday so just getting to  know it. It was great the  first time I  used  it  but the sky transparency was poor last night  when I had the problems so  that didn't help.

Thanks for your help and advice

Louise

[wxsatuser]

Always take the dark, if you don't, you may end up trying to guide on a hot pixels.

[Thalestris24]

Always take the dark, if you don't, you may end up trying to guide on a hot pixels.

Hi there

I will!! Mind you I'm  still concerned about s/n and looking at examples of PHD displays my gguide camera images have been very light  in comparison. That suggests a lack of contrast which might be caused by overexposure, too high a gain setting else the dreaded light pollution  combined with low atmospheric transparency. As my exposure has only been at 1 sec and gain at 70% then the lp could still be a problem. If I attempt a long exposure of say 5min with the scope/dslr then the image tends to come out almost white even with the cls-ccd. I'll have to wait until a nice cold clear frosty night to really check things out properly. What happened to winter??!! No  frost here since November!

Cheers

Louise

[RikM]

Don't worry about how it looks on the PHD preview screen. That has a screen stretch applied, all the guiding calculation is done on the raw data before it hits the preview. The little display slider has no effect on the actual guide settings. I would be very surprised if (other than dark subtraction) it was a s/n effect. s/n is normally a problem for faint nebulosity, stars are bright enough to cut through. If you can't separate stars from background in an f/4 system in 1sec exposures you haven't a hope of getting an image anyway, never mind the guiding. 

Hope you get it sorted

[Thalestris24]

Don't worry about how it looks on the PHD preview screen. That has a screen stretch applied, all the guiding calculation is done on the raw data before it hits the preview. The little display slider has no effect on the actual guide settings. I would be very surprised if (other than dark subtraction) it was a s/n effect. s/n is normally a problem for faint nebulosity, stars are bright enough to cut through. If you can't separate stars from background in an f/4 system in 1sec exposures you haven't a hope of getting an image anyway, never mind the guiding. 

Hope you get it sorted

Hi Rik

Yeah I  realise that it's just the display but the fact that I couldn't adjust it to make it darker bothered me. The scope images I took were rubbish also. On reflection, I should have realised I was flogging a dead horse with the sky conditions. Live and learn.

Thanks

Louise

[Christopher Davenport]

If you want to add a filter to your QHY5L ii, it comes with a extension that has a 1.25' filter thread on it.

I personally don't think that you need a filter though, it could be to do with the driver you are using.

(There is a native driver, which passes through the raw data, and there is a WDM driver which passes through Debayer data)

I am having some problems myself where PHD crashes when I use the default QHY5L driver.

So the only way I can get it to work is with the WDM driver and running EZPlanetary as well.

(This is not a optimal solution, I am still trying to crack the right way to get this working.)

Anyway, if you work it out, lets us know

[wxsatuser]

Hi there

I will!! Mind you I'm  still concerned about s/n and looking at examples of PHD displays my gguide camera images have been very light  in comparison. That suggests a lack of contrast which might be caused by overexposure, too high a gain setting else the dreaded light pollution  combined with low atmospheric transparency. As my exposure has only been at 1 sec and gain at 70% then the lp could still be a problem. If I attempt a long exposure of say 5min with the scope/dslr then the image tends to come out almost white even with the cls-ccd. I'll have to wait until a nice cold clear frosty night to really check things out properly. What happened to winter??!! No  frost here since November!

Cheers

Louise

My LP may not be as bad as yours but imo get a really good LP filter.

I bought the Hutech P2 it's definately allows me to take a lot longer subs.

As for the guiding I have no filter on my guidescope and it seems ok.

Mine is Orion Starshoot mini guider.

[Thalestris24]

If you want to add a filter to your QHY5L ii, it comes with a extension that has a 1.25' filter thread on it.

I personally don't think that you need a filter though, it could be to do with the driver you are using.

(There is a native driver, which passes through the raw data, and there is a WDM driver which passes through Debayer data)

I am having some problems myself where PHD crashes when I use the default QHY5L driver.

So the only way I can get it to work is with the WDM driver and running EZPlanetary as well.

(This is not a optimal solution, I am still trying to crack the right way to get this working.)

Anyway, if you work it out, lets us know

Hi Christopher

Unfortunately the nosepiece which would otherwise hold a filter has to be removed in order to attach the finder adapter. I could use it if I swapped to my ST-80 as guidescope. I have the current full version of PHD which doesn't support the QHY5L-II directly so I think I selected Ascom-compatible in the setup. There is a 'pre-release' version which does support the camera. However, I'm not sure about any bugs therein... I'm pretty sure it was the lp + atmospheric conditions which were ultimately responsible for the problems I had since earlier in the week it was ok and guiding reliably. Just waiting for some clear skies to try again...

Louise

[Thalestris24]

My LP may not be as bad as yours but imo get a really good LP filter.

I bought the Hutech P2 it's definately allows me to take a lot longer subs.

As for the guiding I have no filter on my guidescope and it seems ok.

Mine is Orion Starshoot mini guider.

Hi - yeah, I have the cls-ccd on my 1100d which is a great help

Louise

[Thalestris24]

Just for info, here is a single 3min sub (as jpg) that I took of M91 on the problematic night. I've just reduced the image size, no other processing.

[wxsatuser]

That is bright.

[Christopher Davenport]

That is bright.

Hi Christopher

Unfortunately the nosepiece which would otherwise hold a filter has to be removed in order to attach the finder adapter. I could use it if I swapped to my ST-80 as guidescope. I have the current full version of PHD which doesn't support the QHY5L-II directly so I think I selected Ascom-compatible in the setup. There is a 'pre-release' version which does support the camera. However, I'm not sure about any bugs therein... I'm pretty sure it was the lp + atmospheric conditions which were ultimately responsible for the problems I had since earlier in the week it was ok and guiding reliably. Just waiting for some clear skies to try again...

Louise

Thanks for this, I never thought of a ascom driver, then connect as a ascom camera. I will give it a go next time it clears.

Judging by your picture, your problem looks like it was definitely a LP problem.

[Alien 13]

Just a thought if the filter is for a guide scope only couldnt it just be a cheap green or blue one anything to remove the red component (light polution)

Alan

[Thalestris24]

Just a thought if the filter is for a guide scope only couldnt it just be a cheap green or blue one anything to remove the red component (light polution)

Alan

Hi Alan

Yes, probably, I think. Maybe... Probably one that blocks most of the yellow sodium light (depending on the source of lp) might be useful, but not so much a very cheap one. Maybe a blue filter from an RGB set? I'm not sure what their spectral characteristics are. I think it's something one would have to try out.  I happen to have a cheap 1 1/4" lp filter lying about but no way of easily attaching it to the finder to try it. I think the better solution (for me) will be to wait for clearer, darker skies. I'm sure the problems I had the other night were, at least, exacerbated by the atmospheric conditions. Sometimes, here in Glasgow, there are spells where there are no obvious clouds but it's still seems 'murky' high up. I assume it's something to do with moisture in the atmosphere. But whatever it is, it takes away the contrast and reflects lp. Not good. 

Louise

[Thalestris24]

Just thought I'd add - a cheap (very cheap!) blue filter appears to visually cut lp quite dramatically. It's a 58mm filter so also happens to just fit over the finder so shouldn't be too difficult to fix in place. Some double-sided tape might do it though I don't have any at the mo. I'll try it out properly - when the stars are visible! Will have to see if it has any unwanted side effects. It might require a gain boost or something. I'll post again once I have a result. Met forecast suggest there might be some clear sky tomorrow night But chilly east wind - not so good!

[Thalestris24]

Well in the end I superglued a  cheap 1.25" SW lp filter to the inside of the finder camera adapter. Only had brief opportunity to try it but s/n was much improved.

Go away clouds!

[Alien 13]

I am sure that will sort out your problem i am a bit suprised its not surfaced before.

Alan

[Thalestris24]

I am sure that will sort out your problem i am a bit suprised its not surfaced before.

Alan

Hi Alan

I hope so! I think a lot of the difficulties have arisen as a consequence of atmospheric conditions i.e. poor transparency reflecting back the local lp. It's always going to be an uphill battle trying to image from a city even with clear skies. The Jetstream hasn't been helping. Could really do with some cold, frosty nights like there was back in November. I'm contemplating going narrowband-ish. I might try out imaging with just a Baader blue ccd filter - on paper that should cut lp. Not sure if it would improve on a cls-ccd but I like experimenting :}

Louise

[Alien 13]

Hi Louise.

I am sure it the bad LP that i have that keeps me hooked, its more of a challenge and it provides endless experiments and DIY projects.

Alan