First light with C8 Edge HD

[david_taurus83]

We had a few clear hours here in the midlands last Wednesday night I think it was. Just so happened the reducer and OAG turned up the same day so I was able to get some testing in. This is my first SCT so forgive the wonky stars as collimation isnt the best. I have orderd a tri bahtinov mask from ebay to try and help with this. I managed to get an hour of Lum data on M106 and 30 mins each in RGB. All 180s subs and binned 2x2 with the ASI533MM. Pretty pleased with the data considering the short integration. Its far from what I would normally post up but it was mainly a test image.

My first question is on collimation. How often do these need checking? It has Bobs Knobs at the moment but I may change. They are relatively tight so as they wont come loose but can they be too tight?

My second question is on flats. See below, the Lum flat has bright ring around the central bright spot. This has overcorrected the master Lum image. The flats were approx 2 seconds each and they were taken with the dew sheild on, same as the lights. They were not taken until last night so it could be slight shift of the mirrors but the dust donuts have been corrected so I'm not sure the time difference is an issue. Is there a particular way flats are taken on an SCT?

[Fegato]

I have an 8 Edge HD, but only use it with an OSC (ASI294MC Pro), and not at all recently as my RASA 11 tends to take preference. I'm not sure I can help much really, but thought I'd give you one response at least!

What I will say is that I'm surprised to see that much vignetting with a smallish sensor. What's your image train and what size filters?  I don't get anything like that with the 294 and 2" filters. And I'm afraid I don't know why you'd get such a bright central area with Lum. What method are you using for the flats?

As for collimation, I have the original screws not Bob's knobs. I find it holds reasonably well, and don't often bother to reset. But I think this is partly because I find the whole process a bit of a struggle - seeing always seems to be appalling when I attempt to work on collimation! Anyway - I wonder if your star shapes might relate to backspacing, as there's a bit of pointing into the middle going on? Maybe try pushing the sensor away a little and see if that helps?

 

[Fegato]

PS nice M106 despite your issues!

[Elp]

I think that's a very good result.

With my C6 I use the 6/8 inch flexible Celestron dew shield, it's not ideal because if you don't ensure its fully seated against the start of the dovetail it can shift slightly if you point it up and put a flat panel resting on top (haven't had an issue with it yet). A better solution would be the aluminium dew shield but it costs, there's also the storage issue (I pack mine away, the flex dew shield can simple wrap around the OTA and pack with it).

Regarding the flat, maybe you need to diffuse your light source even more. I used to have all sorts of issues until I diffused my panel with 4 pieces of acrylic starting from opal to almost black in colour, and put the panel on its dimmest setting. This ensures the auto exposed flats are a few seconds in duration (haven't done it at F6.3 for a while).

My collimation hardly changes, I would have thought it would considering the handling of the scope setting up and putting away (I'm also constantly removing the secondary for F2 imaging), the collimation is not as flimsy as a Newtonian which I was surprised by.

[david_taurus83]

On 21/04/2024 at 19:20, Fegato said:

I have an 8 Edge HD, but only use it with an OSC (ASI294MC Pro), and not at all recently as my RASA 11 tends to take preference. I'm not sure I can help much really, but thought I'd give you one response at least!

What I will say is that I'm surprised to see that much vignetting with a smallish sensor. What's your image train and what size filters?  I don't get anything like that with the 294 and 2" filters. And I'm afraid I don't know why you'd get such a bright central area with Lum. What method are you using for the flats?

As for collimation, I have the original screws not Bob's knobs. I find it holds reasonably well, and don't often bother to reset. But I think this is partly because I find the whole process a bit of a struggle - seeing always seems to be appalling when I attempt to work on collimation! Anyway - I wonder if your star shapes might relate to backspacing, as there's a bit of pointing into the middle going on? Maybe try pushing the sensor away a little and see if that helps?

 

Hi, the star shapes are probably a combination of poor collimation and imbalance in the mount. It is roughly balanced but just about on the OEM saddle. I know there are weight kits that you can use for the front of the dovetail but I really don't want to add weight. I have ordered an ADM saddle for the mount so should be able to slide the OTA a little further forward. Here's how it is currently.

 

On 21/04/2024 at 19:36, Elp said:

I think that's a very good result.

With my C6 I use the 6/8 inch flexible Celestron dew shield, it's not ideal because if you don't ensure its fully seated against the start of the dovetail it can shift slightly if you point it up and put a flat panel resting on top (haven't had an issue with it yet). A better solution would be the aluminium dew shield but it costs, there's also the storage issue (I pack mine away, the flex dew shield can simple wrap around the OTA and pack with it).

Regarding the flat, maybe you need to diffuse your light source even more. I used to have all sorts of issues until I diffused my panel with 4 pieces of acrylic starting from opal to almost black in colour, and put the panel on its dimmest setting. This ensures the auto exposed flats are a few seconds in duration (haven't done it at F6.3 for a while).

My collimation hardly changes, I would have thought it would considering the handling of the scope setting up and putting away (I'm also constantly removing the secondary for F2 imaging), the collimation is not as flimsy as a Newtonian which I was surprised by.

I got the scope with the Astrozap heated dew shield. I have to say it's a very nice piece of kit and the cut outs fit perfectly over the dovetail bar and the shield itself stays fairly rigid once it's on. It has no problem holding up my flats panel. You may have a point about the flats. I'm so used to refractor imaging and flats are just easy and always work. Mirror systems always give me flat foibles. I may try your suggestion and dim the flats panel for 5s exposures and take some flat darks, see if that helps. I have only used a master bias for calibrating the above.

Also have a 3D printed tri bahtinov mask coming from Ebay to see how it works with collimation. Will stick with the bobs knobs for now at least.

[Elp]

When I'm using my C6 F6.3 reduced the dovetail position is very similar to yours. I bought a vixen saddle clamp that has threaded holes in the underside, clamp that under the dovetail near the front and screw in stackable gimbal weights (they're 300g each) under the vixen saddle. Near enough good Dec balance.

[david_taurus83]

On 24/04/2024 at 12:35, Elp said:

When I'm using my C6 F6.3 reduced the dovetail position is very similar to yours. I bought a vixen saddle clamp that has threaded holes in the underside, clamp that under the dovetail near the front and screw in stackable gimbal weights (they're 300g each) under the vixen saddle. Near enough good Dec balance.

I got an ADM saddle for the mount. Can slide the OTA a bit further up now so all balanced without adding extra weight. Managed to collimate it with a tri bahtinov mask as well the other evening. Close enough I think! 

 

[dweller25]

That doughnut image does not really confirm good collimation as it is too far from focus.

Ideally you should perform final collimation at perfect focus, on a high star and at x300 plus power - you should be able to see a perfect airy disk if seeing allows…..

 

Edited April 26 by dweller25

[david_taurus83]

1 hour ago, dweller25 said:

That doughnut image does not really confirm good collimation as it is too far from focus.

Ideally you should perform final collimation at perfect focus, on a high star and at x300 plus power - you should be able to see a perfect airy disk if seeing allows…..

 

Yes, your right. That would be the correct method for perfect collimation, in an ideal situation high up in the Andes with plenty and more time to fiddle with Bobs Knobs!

 

Back here in Gulf Stream Alley, the donut method is as good as I'm ever likely to get it. I doubt I will ever look through the scope until the planets come back around again. A couple of test images from the other evening. Single Ha sub of 5 mins and Lum sub at 60s. The Lum has a bit of guiding error it seems but stars are reasonably round. The Ha looks pretty good to my eye.

 

 

[geeklee]

11 minutes ago, david_taurus83 said:

Single Ha sub of 5 mins and Lum sub at 60s.

That close up, FOV is crazy David, awesome   Is that still with the reducer?  Hope you get something before summer arrives.

Seeing it on the AZEQ6 has me reconsidering looking at one of these - it's (unsurprisingly) still a bit of a beast all in!  

[david_taurus83]

57 minutes ago, geeklee said:

That close up, FOV is crazy David, awesome   Is that still with the reducer?  Hope you get something before summer arrives.

Seeing it on the AZEQ6 has me reconsidering looking at one of these - it's (unsurprisingly) still a bit of a beast all in!  

Yes with reducer it's platesolving at 1480mm. I think native scale is around 0.5" with the ASI533MM or 1" binned 2x2. Guiding hovers around 0.6"/0.8". Hope we get better weather during summer as I will be imaging for the few darkish hours we get! My north view is pretty good apart from sky glow from Birmingham city so can keep popping at Cassiopeia and Cygnus in narrowband

[Elp]

2 hours ago, geeklee said:

has me reconsidering looking at one of these

Once you go SCT with its FL flexibility you start to wonder why keep the medium to long FL other scopes.

[Elp]

37 minutes ago, david_taurus83 said:

summer

I find there's around one week, maybe two of heatwave-ish weeks, this is summer nowadays. If you're lucky you can get three to four sessions in one week. I generally image all year round, but the summer early morning packaways can grate if you're a sleepy type.

[Fegato]

9 minutes ago, david_taurus83 said:

Back here in Gulf Stream Alley, the donut method is as good as I'm ever likely to get it.

yes indeed. I often find even the doughnut is so wobbly it's hard to make out the shape very well!

 

 

 

 

 

[Hals]

6 hours ago, david_taurus83 said:

Yes with reducer it's platesolving at 1480mm. I think native scale is around 0.5" with the ASI533MM or 1" binned 2x2. Guiding hovers around 0.6"/0.8". Hope we get better weather during summer as I will be imaging for the few darkish hours we get! My north view is pretty good apart from sky glow from Birmingham city so can keep popping at Cassiopeia and Cygnus in narrowband

My Edge8 with reducer platesolves at 1456mm. That's at the specified 105mm back focus and I could do to put a 1mm spacer in I reckon. Depends on the mirror position and no two are ever the same.  My guiding is anywhere from 0.6 -1.0 (CGEM DX). I've just updated the OAG guidecam to a 174MM Mini, a massive gamechanger for me as I could hardly use my QHY5L-II with it. Was lucky to get one decent guide star even then the SNR was poor despite binning and noise reduction, so I resorted to using a standard 50\200 guidescope. It guided ok with decent figures but I was throwing a lot of subs due to mirror flop\flexture\you name it. Now I'm able to multi-star guide through the OAG with a nice field of stars, although obviously some targets are OAG unfriendly. It's a challenge using an SCT but when everything clicks into place it makes it worthwhile.

Edited April 26 by Hals

[TiffsAndAstro]

9 hours ago, david_taurus83 said:

Yes, your right. That would be the correct method for perfect collimation, in an ideal situation high up in the Andes with plenty and more time to fiddle with Bobs Knobs!

 

Back here in Gulf Stream Alley, the donut method is as good as I'm ever likely to get it. I doubt I will ever look through the scope until the planets come back around again. A couple of test images from the other evening. Single Ha sub of 5 mins and Lum sub at 60s. The Lum has a bit of guiding error it seems but stars are reasonably round. The Ha looks pretty good to my eye.

 

 

This last pic in particular is really making me want to try this. At some point in distant future. Really nice image

[Vic L S]

16 hours ago, Hals said:

My Edge8 with reducer platesolves at 1456mm. That's at the specified 105mm back focus and I could do to put a 1mm spacer in I reckon. Depends on the mirror position and no two are ever the same.  My guiding is anywhere from 0.6 -1.0 (CGEM DX). I've just updated the OAG guidecam to a 174MM Mini, a massive gamechanger for me as I could hardly use my QHY5L-II with it. Was lucky to get one decent guide star even then the SNR was poor despite binning and noise reduction, so I resorted to using a standard 50\200 guidescope. It guided ok with decent figures but I was throwing a lot of subs due to mirror flop\flexture\you name it. Now I'm able to multi-star guide through the OAG with a nice field of stars, although obviously some targets are OAG unfriendly. It's a challenge using an SCT but when everything clicks into place it makes it worthwhile.

 

Sorry for jumping in, but may I ask what OAG you are using? This is something I was looking into a few months ago when I was getting my C8, but decided to go with a guidescope as that was easier to use with my refractor as well, but I might well get an OAG + 174mm just to go on the C8 in the future. 

Edited April 27 by Vic L S

[Hals]

1 hour ago, Vic L S said:

 

Sorry for jumping in, but may I ask what OAG you are using? This is something I was looking into a few months ago when I was getting my C8, but decided to go with a guidescope as that was easier to use with my refractor as well, but I might well get an OAG + 174mm just to go on the C8 in the future. 

Yes of course. It's the Celestron OAG with the 12x12mm prism. The ZWO OAG-L would be a good match too but if you get the 174 I'd stay clear of the thin ZWO standard OAG as the sensor size of the 174 is too big for that one really.

[Elp]

I had the standard ZWO OAG, it was a fiddly thing to setup and I didn't like it much. For the C6 I bought the old (Japan?) Celestron Radial Guider, so simple to setup and use and adjust. You can adjust the angle of the prism and also rotate it around the central axis within a limit to align it square with your sensor or find other stars without rotating anything else.

Edited April 27 by Elp

[Vic L S]

12 hours ago, Hals said:

Yes of course. It's the Celestron OAG with the 12x12mm prism. The ZWO OAG-L would be a good match too but if you get the 174 I'd stay clear of the thin ZWO standard OAG as the sensor size of the 174 is too big for that one really.

Thanks. I did come across some people saying the Celestron OAG taking quite abit of backfocus? But it's got a bigger prism. 

I might have to look at the OAG-L. Seems like a good compromise of prism size and having more backfocus allowance. 

Edited Sunday at 03:00 by Vic L S

[Hals]

3 minutes ago, Vic L S said:

Thanks. I did come across some people saying the Celestron OAG taking quite abit of backfocus? But it's got a bigger sensor. 

I might have to look at the OAG-L. Seems like a good compromise of sensor size and having more backfocus allowance. 

Take a look here...https://www.google.com/url?sa=t&source=web&rct=j&opi=89978449&url=https://www.ancientphotonsastro.com/post/back-focus-for-the-edge-hd-8-at-f-7-and-f-10-using-a-celestron-oag&ved=2ahUKEwixgb_t1OKFAxXJSkEAHU7LD7MQFnoECBUQAQ&usg=AOvVaw0_W8pERpcnbX-nDLc-Snex

[david_taurus83]

On 27/04/2024 at 15:59, Vic L S said:

Thanks. I did come across some people saying the Celestron OAG taking quite abit of backfocus? But it's got a bigger prism. 

I might have to look at the OAG-L. Seems like a good compromise of prism size and having more backfocus allowance. 

The Celestron OAG does take up a good bit of backspace but if using the dedicated 0.7 reducer on the C8 you get 105mm to play with. I've had a few OAG units and this one is one of the best made I've come across. You can rotate the OAG prism independently of the OTA and imaging gear. The same with the imaging gear. It uses a dovetail like clamping system similar to what you get with Baader items. What I don't like about it is the camera helical focuser only uses 2 thumbscrews to hold the camera, not even a brass compression ring so you are likely to mark the barrel of the camera. Also, the prism only lowers down so far so with the C8 Edge 0.7 reducer, it is just about in the light path. It's OK if you have a big sensor like the 174MM but might be an issue with smaller sensors.

 

[Vic L S]

53 minutes ago, david_taurus83 said:

The Celestron OAG does take up a good bit of backspace but if using the dedicated 0.7 reducer on the C8 you get 105mm to play with. I've had a few OAG units and this one is one of the best made I've come across. You can rotate the OAG prism independently of the OTA and imaging gear. The same with the imaging gear. It uses a dovetail like clamping system similar to what you get with Baader items. What I don't like about it is the camera helical focuser only uses 2 thumbscrews to hold the camera, not even a brass compression ring so you are likely to mark the barrel of the camera. Also, the prism only lowers down so far so with the C8 Edge 0.7 reducer, it is just about in the light path. It's OK if you have a big sensor like the 174MM but might be an issue with smaller sensors.

 

Thank you. This is good to know. 

Do you know if the Celestron OAG will take the ASI462MC as a guide camera, as I am already using this as a guide camera on my current guidescope, trying to see where I can save some money! 

Edited Sunday at 16:22 by Vic L S

[david_taurus83]

13 hours ago, Vic L S said:

Thank you. This is good to know. 

Do you know if the Celestron OAG will take the ASI462MC as a guide camera, as I am already using this as a guide camera on my current guidescope, trying to see where I can save some money! 

As long as you have the 1.25" nose piece for it I should think so. I will try and measure mine later and work out where the sensor is at focus.

[Vic L S]

8 hours ago, david_taurus83 said:

As long as you have the 1.25" nose piece for it I should think so. I will try and measure mine later and work out where the sensor is at focus.

That would be so helpful, thank you!