oymd

1 hour ago, alacant said:

Your 290 has a bin2 in firmware which combined with a bigger prism, should get you there. Failing that, the next step up would be a 174 which begins to get €silly, so gotta be worth trying the 290 first.

Good luck.

yes, im using bin2 and median3x3 in PHD2 to get ANY sort of guiding going!

35 minutes ago, alacant said:

Hi

Not sure where you are but you may not have the astronomical darkness necessary for faint stuff. Add to that light pollution and I think you've done extremely well, certainly a lot better than we were able to get.

Not sure either which is the 8se model, but we tried everything with an old orange tube Celestron 8-something; with and without reducer, with and without oag. 105mm, 85mm, Focus lock. No focus lock... It was great for looking at Saturn and drew frequent 'wows' when looking at craters on the moon, but for deep sky photography...? We gave up.

If we have the seeing to support this amount of focal length, we use a 6" f8 Newtonian. They're cheap, don't need a corrector and about the same focal length as your 6.3 Celestron but with clean-contrasty images. Our current favourite for galaxies is a GSO 203mm f5, which is not that much more expensive but only 1000mm focal length. TBH, if you have enough data, the focal length doesn't seem to make that much difference. 

Cheers and HTH

Thanks, I thought so.

I just wanted to hear: Don't worry too much, its the C8, and its not meant for AP, which is what you summarised.

I have an Edge 11HD, but I am first learning the SCT ropes with this C8. The Edge will definitely need a better OAG, and possibly a better guide camera. My current OAG is the OVL one, 8mm prism, 5mm opening in the OAG turret, which overall is a joke, and a PAIN to use. Its like threading a needle in total darkness!! I will also need a better mount!!

I am happy to keep experimenting, as long as I am doing something very wrong.

Since March there is hardly ANYTHING large to image, so the WO71 and Esprit100 are useless really, and its a good time to experiment with the1280mm FL of the C8 on the only thing out there to image these days, Galaxies.

BTW, what is the BACKFOCUS OF THE NON EDGE C8 WITHOUT the 0.63x reducer?

I'm contemplating trying 2030mm FL?

The galaxies are small anyways, so will always have to crop, and edges are not an issue?

5 minutes ago, beka said:

.I think this is a great image though of course each of us may have our own criteria - and I am no astrophotography expert. I imagine you might not get as much scale and resolution on your WOStar71. The corrected image size for the 6.3 reducer is specified as 24mm so in theory it should be okay for the 4/3" sensor of your camera to the edge of the field. The soft stars are also expected because of the 0.75 vs 2.7 arcsec/pixel image scale. Do you know the reason for the coarse noise patten of the background ?

Best!

 

Yes, I have been noticing a wishy washy ugly dirty background pattern

Its hard to give it a scientific name, or to describe it accurately, but it is like someone smudged the background.

I think my skies have been terrible recently, and might be haze? Not sure.

55 minutes ago, Droogie 2001 said:

Hi,

I have shared in a similar experience to you, in that I originally purchased a Celestron 8SE when I first became interested in Astronomy. However as I quickly became keen on Astrophotography I purchased a WO Star71 which made life a lot simpler, nice round stars with 25mins subs.

Moving back to the 8SE has been a challenge but if you accept that its not got a flat field and the focuser is not especially good then I think it can be worth while.

Is this an inherent property of the SCT, especially that its not an EDGE? - Yes

I get egg shaped stars on the corners which relates to coma. Cropping is basically the best way of dealing with that although its a shame to lose some resolution and image detail from doing this.
Within the centre you should get relatively round stars.

I have taken 20mins subs with the 8SE and could have gone longer. My main issue is that the OAG stars are quite distorted but PHD seems to cope with this.
Your guiding RMS looks good but don't be too taken with low RMS meaning good guiding. I have had RMS of 1.0 and have managed to get round stars within the centre of the image.

Have a look at my FlickR channel and you can see some of the results (Link within my signature) . They are not very special but I am fairly happy with them.
I do however find galaxies a lot tougher than nebula!

Good Luck.

Thank you for your reply.

That's exactly the same purchase route I went through!

I bought a Nexstar C8SE off Amazon in Xmas 2019, and initially was enjoying it for just visual, and learning the skies. In Feb 2020 decided to get an EQ mount, and bought an AZ-EQ6 Pro, and since then, it has been downhill!! I am a much, much poorer individual now...

Hello everyone.

Have been in the hobby for 2 years, imaging with widefield refractors, mainly a WOStar71 and 294MC Pro, with good results. Image scale is 2.7"/pixel.

With galaxy seson starting a month or so ago, I decided to give it a go with my Celestron C8SE, which I had bough a couple of years ago as a full setup.

I used an OVL OAG and my 290MM Mini for guiding. I also used Celestron's 0.63x reducer.

I set back focus at 105mm

Collimation looks OK.

I platesolved and checked on Astrometry, and indeed my image scale was 0.75"/pixel, confirming my FL was 1280mm exactly.

I am well polar aligned, and PHD2 is showing RMS of 0.5-0.7, so overall good guiding. Looping on 2 seconds.

I am using a ZWO EAF for autofocus, and its been working well, except for the fact that it seems focus changes a little whenever I am slewing around. I guess that is Mirror flop? Anyways, durimg imaging, I set the focuser to AF every 10 images.

When imaging, and seeing the images come in on NINA, I can clearly see all around the periphery of the image that the stars look properly egg shaped, quite severe at the edges.

Is this an inherent property of the SCT, especially that its not an EDGE?

Since I have never imaged with an SCT before, I am not sure what to expect?

This is from yesterday, 60 L of 300s, 20 Fs, 20DFs and 20Ds. Dithering EVERY frame.

Compared to my refractor experience, images look very very soft.

I had to use a LP filter, the IDAS LPS D2, as my skies and LP is terrible.

Many thanks

5 hours ago, newbie alert said:

Which oag is this?

OVL OAG:

https://www.firstlightoptics.com/off-axis-guiders-oag/off-axis-guider.html

17 hours ago, Padraic M said:

It sounds strange that you can't reach focus with that setup. Can you double check your measurements?

Let's take this as the distance from the prism centre line to the imaging sensor:
OVL OAG (13mm/2 = 6.5)---> 10mm T2 extension---> 10mm T2 extension---> ZWO 11mm Spacer ---> 294MC Pro sensor recessed at 6.5mm = 44mm.

The distance from the prism centre line to the guide cam must be the same to achieve focus. I don't have schematics for the OVL OAG, but the ZWO OAG has a 35mm stalk. I also can't find the size of the OVL prism so I'm assuming 10x10mm. So the equivalent measurement is:
OAG stalk length 35mm - half the prism depth 5mm + ASI290mm Mini sensor inset distance 8.5mm = 38.5mm.

This should give you 5.5mm to spare. One obvious question - you don't happen to have the ASI290mm 1.25" extension fitted? Worth asking! You could unscrew the protective window, that would save a few millimeters but would be a risk to the sensor. I wouldn't chop anything off the stalk!!!

Reference pictures here:

15 hours ago, newbie alert said:

Sounds odd as Im using a SCT and 290 and my focus point is much further out, mind you my spacing is at 113.30 from the first of the threads and plate solved at 1280mm 

Here's a paragraph from the review of the OAG on FLO's website:

The Turret is 45mm long, which might be the problem?

The 90° prism was of high quality and no aberrations were visible when examining a daylight scene through it. The prism is held firmly in its socket at the end of the adjustable turret by a single tiny grub screw. There is no tilt adjustment for the prism but the 45mm long turret allows for plenty of adjustment in and out of the casing and this is secured in position by a single knurled bolt on its short side. I would have preferred to have had a second bolt working at right angles to the first to stop any chance of the turret ‘rocking’ in its channel but this is just in my personal wish-list as none of the commercially available OAGs have such a second bolt. I made up a tiny shim using kitchen foil to act as a buffer on one side of the turret and this ensured that there was no unwanted movement of the turret in any direction. The light port through the turret is 5.6mm in diameter which suited my 4.9mm x 3.7mm sized guide camera well but would cause vignetting with larger sensors – not a disaster but a shame as it could rob larger sensors of an increased guide star choice.

12 hours ago, newbie alert said:

Sounds odd as Im using a SCT and 290 and my focus point is much further out, mind you my spacing is at 113.30 from the first of the threads and plate solved at 1280mm 

113mm!!

And you plate solved at 1280mm??

Guess those 0.63 reducers are not very consistent??

But, here's a question though....I think I read somewhere that the FL of SCTs changes with change of focus?

Maybe the variation is due to movement of the primary mirror?

14 hours ago, Padraic M said:

It sounds strange that you can't reach focus with that setup. Can you double check your measurements?

Let's take this as the distance from the prism centre line to the imaging sensor:
OVL OAG (13mm/2 = 6.5)---> 10mm T2 extension---> 10mm T2 extension---> ZWO 11mm Spacer ---> 294MC Pro sensor recessed at 6.5mm = 44mm.

The distance from the prism centre line to the guide cam must be the same to achieve focus. I don't have schematics for the OVL OAG, but the ZWO OAG has a 35mm stalk. I also can't find the size of the OVL prism so I'm assuming 10x10mm. So the equivalent measurement is:
OAG stalk length 35mm - half the prism depth 5mm + ASI290mm Mini sensor inset distance 8.5mm = 38.5mm.

This should give you 5.5mm to spare. One obvious question - you don't happen to have the ASI290mm 1.25" extension fitted? Worth asking! You could unscrew the protective window, that would save a few millimeters but would be a risk to the sensor. I wouldn't chop anything off the stalk!!!

Reference pictures here:

The OVL's OAG stalk is 45mm. That might be the problem?

Its this one:

https://www.firstlightoptics.com/off-axis-guiders-oag/off-axis-guider.html

Ok, so here's my problem:

I setup my imaging train as such:

C8--> reducer--> 50mm Celestron T2 extension--> OVL OAG (15mm width)---> 10mm T2 extension---> 10mm T2 extension---> ZWO 11mm Spacer ---> 294MC Pro sensor recessed at 6.5mm

My train is very very close to 105mm

I get good stars, and I platesolved and Astrometry shows that my pixel scale is 0.745 arcsec/pixel, so my focal length appears to be bang on 1280mm.

The problem is that I CANNOT push my 290MM mini far enough inside to get into focus.

I can see very unfocused stars in PHD2 looping, but the guide camera is bottomed out against the OAG's shaft that brings in light from the prism.

The only solutions I have are:

1- Moving the OAG farther away from the sensor: NOT POSSIBLE, AS THE CELESTRON T2 CONNECTION IS FIXED AT 50MM

2- Adding a 5mm T2 extension on the camera side, but this led to poor stars and my FL changed when I platesolved!

I ended up swapping one of the 10mm extensions with a 15mm extension, and I could finally focus my guide camera on the OAG.

Am I missing something?

Mu current setup puts the OAG at about 43mm from the sensor!! That is just too far for the OAG, but anything nearer, and I cannot focus the guide camera.#

Currently the guide camera is bottomed out completely against the OAG shaft in my helical focuser.

I am using the OVL OAG, and attached to it is the ZWO non rotating helical focuser.

P.S. Another crazy solution would be to chop off 5mm from the OAG's shaft that is holding the prism!!??

Or find a SCT T2 adaptor that fits to the reducer, but is smaller than 50mm??

Thanks

1 hour ago, Padraic M said:

Just to be clear with this - are you getting 1280mm focal length and good stars at 85mm back focus?

I platesolved my images that I took over the past 2 nights. I was using 105mm backfocus and indeed I calculated 1280mm focal length. 

18 hours ago, Fegato said:

I have the 8 Edge, Celestron OAG and use the 174mm mini as guide camera.

I can't really help with the backfocus. It's strange how little information on this there is. There are some threads on CN like this https://www.cloudynights.com/topic/612053-calculating-back-focus-for-celestron-063-reducercorrector/ . This one starts on C6, but covers other sizes. Anyway, sounds like it's a bit of a variable thing.  Certainly sounds harder than working with the Edge...  sorry, know that doesn't help!

 

On the 290mm stars - I did find that in some parts of the sky I struggled with finding guide stars, even with the larger Celestron prism. So in the end I invested in the 174mm mini, which has a much larger chip obviously, and that problem has gone away. Perhaps try pointing at a fairly starry field (if you can find one at this time of year) at least to see if you can find stars and focus?

 

What I find confusing regarding using a guide camera with a LARGER sensor, or using an OAG with a larger prism, is the fact that the actual light beam coming through the OAG is barely 6 or 7mm wide?

What would be the point of getting a larger sensor, if the actual opening in the OAG that send the image to the guide camera is only 7mm in diameter? It barely even covers the 290mm mini's sensor?

5 hours ago, vlaiv said:

There is simple T2-1.25" filter adapter that just screws in the camera nose piece (even if you have that 11mm removable T2 extension).

After you put it in - you still have plenty of T2 thread to attach camera to rest of the system.

It saves you using filter drawer and optical path.

I get your point Vlaiv. But that will only work with 1.25" filters.

My problem is that ALL my filters are 2"!!

1 minute ago, vlaiv said:

It is better to guide on unfiltered light so OAG should come before filter.

Having said that - why are you using filter drawer with ASI294MC?

It is OSC sensor and I'm guessing you'll be using either LPS filter or some sort of UHC/Duo band filter. In any case - such filter won't need swapping mid session and it is sensible to just put it in T2 adapter right in front of the sensor rather than use filter drawer that facilitates easy filter change.

Sorry Vlad, I did not follow that?

I have the ZWO T2 filter drawer, which is 21mm. I plan to use the Optolong UV/IR filter in it as I have bad LP.

Yes, I plan to go: Camera ===> 21mm Filter drawer ===> OAG, so that the OAG gets unfiltered light, but that moves the OAG AWAY from the sensor?

4 minutes ago, ollypenrice said:

I suspect the 11 inch HD might actually be easier to use than the C8 which needs a flattener...

You have the OAG projecting into the middle of the long side of the chip, which is good. Did you also push it in as far as you could then back it out by the smallest possible amount? You can do this using a light source of the kind you'd use for flats. You just want to see the start of the OAG shadow then raise the prism very slightly so you don't. It's vital to get it as far in as you can.

Binning the guide cam will reduce its resolution but increase its sensitivity to light.  You have plenty of scope for reducing its resolution without its being inadequate for your guiding purposes.

You can measure your vignetting simply by comparing the ADU of a flatfield sub in the corners and then in the centre.  My Tak FSQ with full frame camera saw a 23% drop-off in light in the corners but flats eliminated it. It was absolutely not a problem.

Olly

I will certainly try the flats trick!!

I have a geoptic flat panel.

Will experiment tonight.

I am confused however regarding the back focus.

As Vlad pointed out, TS optics clearly states that back focus is 85mm.

FLO and several you tube videos advised that back focus is 105mm?

43 minutes ago, vlaiv said:

I see. I just checked specs at TS website and there it says:

This is bog-standard F/6.3 Celestron SCT reducer/corrector:

https://www.teleskop-express.de/shop/product_info.php/info/p2644_Celestron-Reducer---Corrector-f-6-3-for-Schmidt-Cassegrains-Telescopes--SCT-.html

Maybe you have EdgeHD version?

That one is 105mm back focus (according to TS website):

In the case you have standard one - then do pay attention that clear aperture is 41mm and with 0.63 reduction factor that translates into 25mm (at about 100mm away from focal plane), so even at 23mm you'll get vignetting.

Putting prism too far out will place OAG sensor in vignetted region - which will of course reduce amount of light it receives.

If you still have issues with your setup after shortening the distance and moving OAG closer to sensor - maybe consider sacrificing a bit of FOV (by cropping images) and pushing OAG prism closer to sensor (even if it starts casting shadow a bit).

 

Yes, I definitely am using the standard 0.63 reducer on my NON EDGE C8SE OTA.

I will try 85mm tonight.

FLO definitely recommended 105mm though.

I changed around my train, and now the OAG is IMMEDIATELY after the 11mm ring on the camera side. so around 11mm + 6.5mm from the sensor.

But that will cause a problem when I factor in a filter drawer down the line?

7 minutes ago, vlaiv said:

I was able to find that back focus is 85mm for this reducer - why go with 104.5mm?

Further away you put sensor - more reduction you will get and hence more severe vignetting.

Make distance between SCT corrector camera side thread and sensor about 85mm.

If you don't want prism of your OAG to be effective aperture stop - put it close to sensor. Swap OAG and 21mm extension (or possibly loose 21 mm extension all together as that will take very close to right working distance).

Don't be afraid to:

1) bin your camera

(check out drop downs that I outlined in your version of PHD2)

2) use long exposure with OAG - like 4s guide exposure.

I prefer to use ASCOM driver for my camera rather than native drivers.

Thanks Vlad

The 105mm back focus was recommended by FLO when I emailed them?

I have also seen several YouTube videos where 105mm was the recommended back focus?

I will certainly give it a go with 85mm.

With regards to binning, the options on the 290mm mini are either x1 or x2. Should I choose x2? What does that change?

Many thanks Vlad.

Here we go again, after 2 years happily imaging with the 70mm apo, I am back to kindergarden with the SCT!!

I consider myself a beginner in AP, but I have gained some good experience over the past two years using a widefield Williams Optics 71 Star Apo and an EvoGuide 50mm for guiding.

I am fairly familiar with NINA, PHD2 and the quirks and problems with setup for AP.

Last week, with galaxy season arriving, I decided to give it a go with my Celestron C8 and an OAG.

Boy, this is a whole different level of DIFFICULT!!

I need some advice regarding my imaging train, and what am I doing wrong.

I setup the train for 105mm backfocus.

No matter what I do, I cannot get any sort of stars in the view of my 290mm mini on PHD2.

Just to check my imaging train is OK, I took 30 1 minute subs of M51 without any guiding.

Understandably the image is soft and stars are not that great.

Anyways, what am I doing wrong with regards to the OAG?

My imaging train is as follows:

C8 ===> Celestron 0.63 reducer ===> 50mm Celestron T2 extension ===> ZWO 42mm to 48mm adaptor ring ===> OVL OAG ===> 21mm ZWO extension ===> 11mm ZWO ring ===> ZWO 294MC Pro

Total imaging train amounts to about 104.5mm, but I added 2 thin spacers.

Issues I have:

1- There is obvious vignetting on the image window in NINA. Is this expected? Is it caused by the 0,63 reducer? Never saw that with any of my refractors?

Here is Arcturus. I used it for the autofocus routine in NINA

Why is there such obvious vignetting?

2- I imaged fine, but guiding was impossible. I CANNOT get the 290mm mini in to focus at night. During the day, I got it into focus on a very distant object, but for some reason, at night I just see GRAY NOISE? I tried Gain 0 and Gain 90. In PHD2 for the guiding focal length, I input 1280mm, which is what the 0.63 reducer amounts to. I realise that guiding is working at an incredibly small pixel scale of 0.5 pixels / arcsec!!

3- The OAG prism is correctly positioned, and I confirmed that by shining a light onto the scope. I placed the prism parallel to the long axis of the sensor, and is NOT covering the sensor.

4- Could it be that the OVL OAG i am using is not suitable for my imaging train?

5- I am aware of how small the 8x8mm prism is, and how borderline the 290mm mini is, and the 174mm mini is a better fit, but overall I am just trying to do a preliminary setup.

6- I am also aware that the Celestron C8SE OTA is not great for imaging, but as I mentioned, I am just dabbing into SCT astrophotography.

7- I have an EDGE 11HD, but I do not dare trying it yet. I want to familiarise myself with the C8 first.

Many thanks

I Thought I would update this thread I started.

I replaced the bearings on the RA worm shaft with SKF 608-2Z.

I fine tuned the backlash manually on both axis while the mount was stripped, and did some further tuning with Guiding assistant.

As of last week, the mount is behaving very well, with my guiding at 0.30 to 0.50 rms, constant, depending on the seeing.

Very happy here...

Especial thanks to @wimvb for all his help and patience in getting me over the line!!

Here is my first project after fixing the mount: IC 2177, the seagull nebula, taken during full moon over 6 nights, with loads of subs discarded...

103L, about 8 hours.

13 minutes ago, ONIKKINEN said:

To me it looks like the dithers do happen on schedule and like they should. The log says your settling has failed, but i dont think that has to do with dithering success but is just the result of your settings.

You have here the dither spike as it should in the directions ordered. The "settling failed" notification is there i think because you have a high settling time of 120 and strict settling limits. Not sure why your settling limits in the log appear to be less than 1'' but they are set as 1.5 pixels in NINA which would obviously be a lot more than that 🧐. I dont think this has anything to do with your issue, but this does waste 55 seconds after a dither. Im pretty sure NINA starts the next exposure only after PHD2 informs NINA that settling has completed, and since it fails for you every time it has to wait the 55s you have set it to in the settle timeout setting.

Many thanks

Can you please advise me how to populate my Dither settings to fix this issue?

3 hours ago, ONIKKINEN said:

.html file format? Something went wrong, its supposed to be a .txt file

Apologies..

here's the guide log and my Dither settings in NINA

PHD2_GuideLog_2022-02-15_204257.txt

2 hours ago, ONIKKINEN said:

.html file format? Something went wrong, its supposed to be a .txt file

Yes. Sorry. I tried to upload it from my phone. 
will upload it from the PC once I get home. 

52 minutes ago, ONIKKINEN said:

I cant see the problem in the raw subs. Also cant open the .xisf files so cant check the masters, but from the looks of your screenshot it does look like walking noise. It could also be the result of some funny sigma clipping issue where a bad sub is chosen as the reference by the stacker and so a lot of good data that deviates from the bad sub gets rejected in the end. I had this happen with deep sky stacker once, but not sure if its all that common of a problem.

Your dithering schedule looks good, i dont think i would bother dithering more often. I dither every 10 subs when i shoot 30s ones, so every 5 minutes as well. I also dither in RA only and it still works well like this so not sure whats the problem. Can you check your PHD2 logs and see if the dithering actually took place? And if it did, how many pixels was the dithering set to. If your dithers are very small, like maybe 1 or 2 pixels i think they might not work that well with OSC cameras.

I’m also attaching the PHD2 guide log. 

44 minutes ago, ONIKKINEN said:

I cant see the problem in the raw subs. Also cant open the .xisf files so cant check the masters, but from the looks of your screenshot it does look like walking noise. It could also be the result of some funny sigma clipping issue where a bad sub is chosen as the reference by the stacker and so a lot of good data that deviates from the bad sub gets rejected in the end. I had this happen with deep sky stacker once, but not sure if its all that common of a problem.

Your dithering schedule looks good, i dont think i would bother dithering more often. I dither every 10 subs when i shoot 30s ones, so every 5 minutes as well. I also dither in RA only and it still works well like this so not sure whats the problem. Can you check your PHD2 logs and see if the dithering actually took place? And if it did, how many pixels was the dithering set to. If your dithers are very small, like maybe 1 or 2 pixels i think they might not work that well with OSC cameras.

Dithering is set to 5 pixels. 

14 minutes ago, geordie85 said:

I'm assuming that you didn't dither?

13 minutes ago, malc-c said:

I downloaded the three subs and stacked them in deep sky stacker and even stretching the result I personally couldn't see the artefacts.  Not sure what would happen if the darks and flats were added.  Here's the resulting FTS file, and a screen shot.  Can't answer your question as to what is causing the issue, but my guess is that is "generated" as part of the stacking process as, as far as I can tell,  it doesn't seem to be part of the data captured.

 

 

test.FTS 133.84 MB · 0 downloads

 

Thank you for your replies.

Yes, the artefacts do not show up in the individual subs.

I have been advised to generally Dither every 5 minute sub. When I use the L-eXtreme, I usually take 300s subs of Nebulae. I dither EVERY SUB.

I used the same calculation when I was imaging M42.

For the 2 minute subs, I dithered every THREE subs. for the 30 second subs I dithered every 10 frames etc, so basically dithering every 5 minutes or so. With the 10s subs, I dithered every 25 subs.

Could be the effect of UNDER DITHERING? If so, how often should one dither with 10s subs?