Guiding options for C9.25

[SteveT]

Hi

Going to start imaging with my 9.25. I have a lodestar which I used a few times on a finder guider on a Equinox ED80 which I want to use with the 9.25.

Assuming the finder guider is a bit to short to use with the long FR of the 9.25 (even with 0.63 reducer), and difficult to mount as we'll, I was looking at the new Celestron OAG. Can I use the OAG with the FR with a DSLR for imaging or is it technically challenging?

Also, is a better alternative to mount a dovetail/bracket to the top of the OTA and use a guidescope (only have the Equinox ED80 which is a bit top heavy for this)?

I do have an ADM side by side dual bracket but that is even heavier.

What part would I need for screwing to the top of the 9.25 OTA to give me a platform to attach a guidescope?

Or should I just stick to the OAG, but would really like to know if the 0.63 FR can be accommodated on the imaging chain.

Any help or views appreciated.

Thanks.

Steve

Sent from my iPad

[swag72]

Having imaged with the C9.25 I would whole heartedly recommend an OAG.

The focal reducer you have is presumably a Celestron 0.63x (or similar) in which case it has a very generous spacing requirement of about 110mm and that's quite tolerant as well, so you should be able to fit an OAG in there no problem at all.

[Owmuchonomy]

If you are starting from scratch then I'd probably agree with the above. For me I already had an AA 80mm finder guider. I have just got a Lodestar so am trying guiding with that set up at the next chance on my 9.25SCT. I made a mount from 8 mm Alu flat bar which just attaches along the OTA diametrically opposite the dovetail using the existing bolt holes. It's very sturdy! Keen to try it out.

[SteveT]

I think I will try an make my own mounting bar, that sounds like a god idea! Did you have to use longer screws than toes already fitted to the OTA? I tried to find some longer screws once to fit a bigger finder but couldn't work out the thread needed as they were not metric.

The ED80 I'm sure would make a suitable guidescope and would also give me the option of reversing the 2 for imaging through the refractor and using the 9.25 as a guide scope (should be accurate!).

I think I will do some sums on the weight as it must be getting close to the limit of my CGEM. By the way, I cut my setup down to minutes now by using the new Starsense accessory which works great and was very accurate out of the box. Another reason to piggyback is it will allow me to use the Starsense to align the ED80, hmmmm..... So many options. I did read so where that there may be a future upgrade to allow the Starsense to become a guider too, anyone confirm that?

Sent from my iPad

[Owmuchonomy]

I think I will try an make my own mounting bar, that sounds like a god idea! Did you have to use longer screws than toes already fitted to the OTA? I tried to find some longer screws once to fit a bigger finder but couldn't work out the thread needed as they were not metric.

The ED80 I'm sure would make a suitable guidescope and would also give me the option of reversing the 2 for imaging through the refractor and using the 9.25 as a guide scope (should be accurate!).

I think I will do some sums on the weight as it must be getting close to the limit of my CGEM. By the way, I cut my setup down to minutes now by using the new Starsense accessory which works great and was very accurate out of the box. Another reason to piggyback is it will allow me to use the Starsense to align the ED80, hmmmm..... So many options. I did read so where that there may be a future upgrade to allow the Starsense to become a guider too, anyone confirm that?

Sent from my iPad

Yes, I used the longer bolts supplied with a camera piggyback accessory. The bar came from EBay for £8. They are not standard metric threads as you found out. I'm sure you are also aware but I'm expecting the guiding to be difficult at these focal lengths.

[ollypenrice]

For long FL imaging I would strongly advise an OAG. I love guidescopes for short FL but long FL is a different story and a glance at Sara's recent 9.25 images at native FL will give credibility to her advice. My own efforts, with Yves Van den Broek, also involved OAG guiding.

Olly

[PhotoGav]

I have a C8 EdgeHD, a bit different to the C9.25, but long FL and the 9.25 is only longer! I battled with trying to guide the C8 with a finder guider and it was a complete waste of time... I bought the Celestron OAG and immediately guiding worked brilliantly. The OAG itself seems very well made and is relatively easy to use. The only slight complication is initial focussing of the guide camera - go to a wide and rich cluster and you should have plenty of stars to focus on. Finding a guide star is not as simple as the finder guider on an ED80, but with a little methodical patience it's easy to get locked on. The results are spectacular - I can happily guide for 1200s subs.

As for using the reducer, OAG & a DSLR, I am hoping to do this, but it is not currently possible with my setup - there is a smaller adapter that will be available in this country soon from FLO that will make it work (http://www.firstlightoptics.com/off-axis-guiders-oag/celestron_sct_oag_adaptor_93652.html). Consider 55mm for the DSLR & mount ring and you can work out your total chain size - the OAG spec document is very detailed, you will find the link to it here at the end of the item description: http://www.firstlightoptics.com/off-axis-guiders-oag/celestron-off-axis-guider-sct.html

Good luck and whatever you end up doing, I look forward to seeing your images soon!

[Tinker1947]

The celestron OAG while being very sturdy and well made is designed to be used with the "Edge" type SCT where the Flattener is built into the scope , the manual on the Celestron site has the measurements, using it on a non edge scope leave very little movement for the correct spacing while a CCD  will allow the 105mm to be obtained a DSLR won't it comes out around 120mm...

this is a link to the manual....  http://www.celestron.com/support/manuals-software 

what it looks like attached to a DSLR

[Owmuchonomy]

The celestron OAG while being very sturdy and well made is designed to be used with the "Edge" type SCT where the Flattener is built into the scope , the manual on the Celestron site has the measurements, using it on a non edge scope leave very little movement for the correct spacing while a CCD  will allow the 105mm to be obtained a DSLR won't it comes out around 120mm...

this is a link to the manual....  http://www.celestron.com/support/manuals-software 

what it looks like attached to a DSLR

Can I ask about your image train. Looks like you've got a Baader click stop between the reducer and the scope? I can also attach my reducer directly to the scope visual back. Would that help with the back focus? Thanks Chris

[Tinker1947]

The Visual back is the Baader Click Lock type, next is the FR, OAG then DSLR the distance from the FR to the DSLR Sensor is 15mm over the required distance, i did have the 48mm female adapter altered to a SCT thread this got the distance down to 105mm but put the prism right next to the rear lens on the FR, so unless your in a star crowded part of the sky there will be next to no guide stars, i have consigned the OAG back to its box and settled for a Finder Scope with a Lodestar screwed in the end, loads of stars and some nice round ones on a 15 minute test sub.....

[SteveT]

Olly and others, thanks for the feedback and experience. The manual for the OAG does not mention the FR in the imaging chain so I guess it is not intended to be used for imaging on a standard C9.25 with this OAG which seems odd ? As mentioned above, it seems designed for the HD version OTA's with built in correction. Olly, have you used this arrangement or in your opinion, would it work, before I go off and spend £219......

Also, has anyone got one of those finder brackets as shown in the above image attached to Tinker's OTA that they are able to sell, I have been looking out for one for ages and can't find one anywhere for sale (except as a bundle with a 9x50 finder which I already have).

[Tinker1947]

My Bracket came in the box with the scope....its quite sturdy......There is this option at a price...

http://www.firstlightoptics.com/adm-mini-dovetail-series/adm-mini-dovetail-guidescope-rings.html

[RobertI]

I was advised to use an OAG for imaging with my C8 using a 0.63 FR. It seemed like the best option and I do want to try it, but I decided to try guiding using my existing William Optics ZS66 refractor + lodestar mounted to the side of the C8 opposite the mount. I've tried this on only short exposures so far of around 60 seconds and the images are fine but I need to do a lot more testing. However a big downside is that it created a surprising amount of extra leverage and I have had to add a large additional counterweight to balance - the total weight is now more than I am happy with for the modest mount so I don't think this is a good solution long term. My Altair Astro 60mm guider is VERY light so the longer focal length AA 80mm version is probably a good bet. Having read the posts above I'm not sure the OAG will be plain sailing either. Not much help to you Steve but just my experience so far.

[Earl]

in my limited experience with scts i found adding a guide scope (ST80) just made it all to heavy and hard to balance.