SCT focuser for imaging

[nmoushon]

I have recently purchased a 9.25" EdgeHD with the intent to eventually use it to image with. I have a lot of equipment upgrades planned but for this thread my question is regards to the focuser.

Ive only ever imaged with a refractor so not having the "traditional" focuser was new and something to get use to. My main targets will be DSOs with long exposures and CCD style camera (though I haven't picked a camera yet). I know you can image without getting a focuser but almost all the setups I've seen use one. Ive seen both Moonlight focusers used and Feathertouch focusers so i was wondering why people chose the focuser they did?

Was back focus a reason to pick one or the other? Is one able to hold a heavier imaging train? Better focus control? Or is it just a preference of one over the other? Thanks in advance.

PS: As far as imaging train i do plan on a mono with filter wheel and OAG for guiding. As well as imaging with a reducer though I haven't picked one yet...though I am leaning to the Lepus reducer as I've read good reviews on it.

[seo]

Hi nmoushon,

In my Edge 14" SCT I've replaced the main mirror focuser with a MIcroTouch and I've also installed a Feather Touch focuser in the visual back. As far as I know, for the Edge main mirror focuser there is only the MT focuser "upgrade" which will of course not eliminate mirror shifting and backlash but it will make focusing a lot more accurate and can also give you remote capabilities if and when you decide to also purchase its controller. On the other hand installing an extra focuser in your visual back/imaging train of your Edge, either is a FT, Baader, MoonLite,Optec,FLI, etc - in my opinion -  is a must,  especially if you doing long or remote Deep Sky imaging sessions - not necessary only for viewing. By manually - locally- focusing the primary mirror focuser (MicroTouch) in a suitable focus star just before your start your session, then locking the Mirror Lock Knobs you can then start your normal/remote session by only micro-adjust manually or remotely the visual back focuser (be it a FT, Baader,  MoonLite, Optec,FLI, etc) at your main target with no backlash anymore all night long and refocusing will be a snap.

Choosing between different firms/models, in my opinion, has to do with the 1) backfocus of each focuser so to leave the proper calculated space for the equipment you want to add in your imaging train, 2) lifting, moving properly and "holding" in place (in both imaging axes) even in near vertical positions your equipment,  3) Computer/software connection capabilities and usage, 4) overall quality and of course last but not least  money...!

When I did these upgrades to my system I personally found that the MT and FT where the most appropriate choice for all the 4 reasons . I still believe the same. 

Clear skies.

[nmoushon]

Thanks for your input Dimitris. Though I'm not sure if I agree with the need for both the MT and the FT. Especially if you plan on  getting a micro focuser. The MT might make it a bit quicker but not sure if it is really worth it....for my budget anyways. The MT alone would fund the micro focuser kit for the FT and for my budget I think that is what I would spend it on. 

[seo]

I'd just like to say that the main reason, at least for me, for upgrading the main focuser to MT (Micro Touch by Starizona) was and still is, not the ability to have a more accurate focuser, which of course is important but with the presence of the FT is not critical,  but the ability to control the main focuser through my computers, locally and remotely in certain scenarios where I don't use a mirror lock. For example, it's much easier and quicker to have different focus positions of planets, moon, stars, barlow, etc saved in the MT program plus the backlash steps needed to compensate and just make one click to go exactly there than doing it manually by hand.  

That been said, of course your needs, budget or simply your opinion is what will guide you to your final decisions on the matter.   

Clear skies and happy new year.

[nmoushon]

I thought you could control the micro focuser kit through the computer as well? And by micro focuser I meant the high res stepper motor kit. Just realized that could have been confusing sorry. 

[seo]

Ok, lets put things in some perspective and clarify things...

1. I was under the impression that our conversation was about the "need" or not to upgrade the stock main mirror focuser with a SCT Micro Touch (MT) autofocusing stepper motor and also install an extra focuser ( FT, Baader, MoonLite,Optec,FLI, etc) at your imaging train. If I got it right and this is the case then IMHO you "need" both focusers/upgrades - one at the main mirror and one at your imaging train - (I explained why).

So, again, if this is the case, then for example you'll need the following =>

Case 1. Manually operated (Not by a computer/remotely)

-------------------------------------------------------------------------------------------------------------------

- A Feathertouch SCT MicroFocuser - Celestron Edge HD 9.25/CPC-925/CGEM-925 => http://starizona.com/acb/Feathertouch-SCT-MicroFocuser---Celestron-Edge-HD-925CPC-925CGEM-925-P2994C654.aspx

- Any brand focuser you like (plus an adapter) for your imaging train, suitable for your scope and needed bacfocus - (No need to buy a controller for computer control)

- In this case for both focusers you don't need a controller. You only need the focusers.

Case 2. Remotely and locally operated (controlled by a computer and by hand) =>

---------------------------------------------------------------------------------------------------------------------

Here, for the main focuser upgarde you have two options...

Upgrade the stock main mirror focuser either with  -> A SCT Micro Touch (MT) autofocusing stepper motor, EdgeHD edition - low profile => https://starizona.com/acb/MicroTouch-Low-Profile-Stepper-Motor-P3360C745.aspx - which I suggest or use the mix of the previous Feathertouch SCT MicroFocuser - Celestron Edge HD 9.25/CPC-925/CGEM-925 + a MicroTouch Small Stepper Motor - 2.0" Focusers and SCT MicroFocusers => https://starizona.com/acb/MicroTouch-Small-Stepper-Motor---20-Focusers-and-SCT-MicroFocusers-P2850C745.aspx if you want to install remote/computer capabilities at a later time - you need to pay attention in this case because this mix puts the whole focusing system way back and it may interfere with your imaging equipment.

- Any brand focuser you like (plus an adapter) for your imaging train, suitable for your scope and needed bacfocus + a stepper motor suitable for that focuser. Example of a stepper motor for a 2" Feather Touch focuser : HSM20 Handy Stepper Motor with manual focus over-ride => http://starlightinstruments.com/store/index.php?route=product/product&product_id=356 or a MSM20 Micro Touch Focusing System => http://starlightinstruments.com/store/index.php?route=product/product&product_id=88

- And finally you'll need controllers to connect both focusers with your PC. Here are also different choices depending on what features you like and what exactly you want to do and of course your budget. 

For example :

Focuser Boss FB-II-Kit 1 => http://starlightinstruments.com/store/index.php?route=product/product&path=96&product_id=305 if you like to have simultaneously control of both focusers (as I have) or

Focuser Boss FB-II-Kit 2 => http://starlightinstruments.com/store/index.php?route=product/product&path=96&product_id=304 , same kit but with extras, or

Micro Touch Digital Kits (from Starizona or Starlight Express) => http://starlightinstruments.com/store/index.php?route=product/category&path=41 or from Starizona => https://starizona.com/acb/MicroTouch-Autofocusers-C745.aspx

So, as you can see there are two different "discussions/questions" here :

1.  Do I need 2 different focusing systems/upgrades for my 9.25 EdgeHD ?

2. Do I need them both remotely/computer operated ?

In the first question, I've already answered : IMHO, if you doing long or remote or mostly imaging sessions, yes you need them - not necessary only/mostly for viewing.

As for the second question, in my opinion you are the only one you can answer it. Knowing what exactly you need for the first case and how much will cost you and depending on your budget you can decide which way fits you.

Clear skies.  

[nmoushon]

Ok, lets put things in some perspective and clarify things...

1. I was under the impression that our conversation was about the "need" or not to upgrade the stock main mirror focuser with a SCT Micro Touch (MT) autofocusing stepper motor and also install an extra focuser ( FT, Baader, MoonLite,Optec,FLI, etc) at your imaging train. If I got it right and this is the case then IMHO you "need" both focusers/upgrades - one at the main mirror and one at your imaging train - (I explained why).

So, again, if this is the case, then for example you'll need the following =>

Case 1. Manually operated (Not by a computer/remotely)

-------------------------------------------------------------------------------------------------------------------

- A Feathertouch SCT MicroFocuser - Celestron Edge HD 9.25/CPC-925/CGEM-925 => http://starizona.com/acb/Feathertouch-SCT-MicroFocuser---Celestron-Edge-HD-925CPC-925CGEM-925-P2994C654.aspx

- Any brand focuser you like (plus an adapter) for your imaging train, suitable for your scope and needed bacfocus - (No need to buy a controller for computer control)

- In this case for both focusers you don't need a controller. You only need the focusers.

Case 2. Remotely and locally operated (controlled by a computer and by hand) =>

---------------------------------------------------------------------------------------------------------------------

Here, for the main focuser upgarde you have two options...

Upgrade the stock main mirror focuser either with  -> A SCT Micro Touch (MT) autofocusing stepper motor, EdgeHD edition - low profile => https://starizona.com/acb/MicroTouch-Low-Profile-Stepper-Motor-P3360C745.aspx - which I suggest or use the mix of the previous Feathertouch SCT MicroFocuser - Celestron Edge HD 9.25/CPC-925/CGEM-925 + a MicroTouch Small Stepper Motor - 2.0" Focusers and SCT MicroFocusers => https://starizona.com/acb/MicroTouch-Small-Stepper-Motor---20-Focusers-and-SCT-MicroFocusers-P2850C745.aspx if you want to install remote/computer capabilities at a later time - you need to pay attention in this case because this mix puts the whole focusing system way back and it may interfere with your imaging equipment.

- Any brand focuser you like (plus an adapter) for your imaging train, suitable for your scope and needed bacfocus + a stepper motor suitable for that focuser. Example of a stepper motor for a 2" Feather Touch focuser : HSM20 Handy Stepper Motor with manual focus over-ride => http://starlightinstruments.com/store/index.php?route=product/product&product_id=356 or a MSM20 Micro Touch Focusing System => http://starlightinstruments.com/store/index.php?route=product/product&product_id=88

- And finally you'll need controllers to connect both focusers with your PC. Here are also different choices depending on what features you like and what exactly you want to do and of course your budget. 

For example :

Focuser Boss FB-II-Kit 1 => http://starlightinstruments.com/store/index.php?route=product/product&path=96&product_id=305 if you like to have simultaneously control of both focusers (as I have) or

Focuser Boss FB-II-Kit 2 => http://starlightinstruments.com/store/index.php?route=product/product&path=96&product_id=304 , same kit but with extras, or

Micro Touch Digital Kits (from Starizona or Starlight Express) => http://starlightinstruments.com/store/index.php?route=product/category&path=41 or from Starizona => https://starizona.com/acb/MicroTouch-Autofocusers-C745.aspx

So, as you can see there are two different "discussions/questions" here :

1.  Do I need 2 different focusing systems/upgrades for my 9.25 EdgeHD ?

2. Do I need them both remotely/computer operated ?

In the first question, I've already answered : IMHO, if you doing long or remote or mostly imaging sessions, yes you need them - not necessary only/mostly for viewing.

As for the second question, in my opinion you are the only one you can answer it. Knowing what exactly you need for the first case and how much will cost you and depending on your budget you can decide which way fits you.

Clear skies.  

Very detailed explanation. Thank you.

I actually was originally just trying to figure out what brand to pick for the 2" focuser i.e. moonlite or feathertouch. I wasnt even considering using the MT for imaging. You explained why so I wont go back to that. 

But that still leaves the brand question. I'm assuming you are using a 2" feathtouch focuser to match the feathertouch MT focuser. Is there a reason other than to match why you went with feathertouch? 

Though you have made a very convincing argument for using both the 2" and MT focusers for imaging my budget will only allow for 1 for now so which would you chose if you had to pick 1? And this is for imaging.

I don't have any plans on going completely remote but I do want some automation that will help me out so that is where the computer controlled focusing comes in. Would eventually like to have it run from my house like your obsy is setup but thats far down the road. 

Thanks again for taking time to explain all this. 

[seo]

You're welcome.

 I'm assuming you are using a 2" feathtouch focuser to match the feathertouch MT focuser. Is there a reason other than to match why you went with feathertouch?

You're right. I'm using the 2" FTF2015BCR => http://starlightinstruments.com/store/index.php?route=product/product&path=37_49&product_id=51 though I could also use the FTF2008BCR => http://starlightinstruments.com/store/index.php?route=product/product&path=37_49&product_id=58 which offers more backfocus, if I needed more. 

The reasons I went with FT are the following, in significance order : 

1. Because I have 2 more telescopes in my obsy except my Edge14", which all have FT focusers - so 3 telescopes in total, installing an FT focuser on the Edge14" imaging train permits the use of Focuser Boss FB-II-Kit 1. So with one controller I can simultaneously control 2 different focusers from my computers, so less money spend, less cable clutter + installations and less driver clutter in my copmuters.

2. Besides that FT focusers are widely known as one of the best focusers (used by almost all well known telescopes companies for their telescopes), I personally like very much their built quality, continuous hardware and software upgrades, aesthetics, and many options to choose from Starlight Instruments as of course their customers support. No "hard feelings" for any other brands, just a personal like. That been said, If I had a bigger budget, especially for my Edge14", I'd certainly go with the PDF focuser from FLI.

Though you have made a very convincing argument for using both the 2" and MT focusers for imaging my budget will only allow for 1 for now so which would you chose if you had to pick 1? And this is for imaging.

MoonLite focusers are very nice ones and I think are cheaper (focuser + controller + adapter?) than FT - not sure about pricing though. From the other hand, besides my telescope setup inside my main obsy (I also have a second smaller type of obsy - permanent setup and 2 more portable setups => that is 6 telescopes + all other equipment which goes with them, in total, and on all of them I use FT focusers and never ever had the slightest problem with them. Precision and endurance for years. So I'd go for an FT focuser. Of course that's my personal preference and in NO circumstances I don't want this to imply that other brands are worst / inferior.

That been said, I strongly suggest to firstly accurately measure the backfocus needed for your specific imaging train setup + any other upgrades you think you''l do to that in the near future, before you start comparing focusers. It'll be a good thing also to write down each candidate focuser's + controller's weight and install position and then add all the weights (of your imaging system setup) to find out how much you'll have to balance your scope (forwards or backwards) and what will take to do that (check out balance and rotation in all ra/dec positions...), before you come to your final purchase decision. 

Clear skies.

[seo]

Well sorry, I've answered half of your question... I speed up when I'm writing...

Here is the other half...

If I had to choose one of the two I certainly choose first to install a 2" or 2.5" focuser on my imaging train. especially if full remote control wasn't in my plans for the short future. That been said, if you decide, for your reasons, to buy a focuser that leaves you a small backfocus space (after you install all your imaging equipment)  then I suggest that the use of a Feathertouch SCT MicroFocuser - Celestron Edge HD 9.25/CPC-925/CGEM-925 => http://starizona.com...-P2994C654.aspx for your main mirror is a must even for manual/not-remote operation. In any case and in my opinion it's safer, budget wise, that you first buy and install the 2" or 2.5" focuser (don't know your setup needs...) then do focusing accuracy tests and then decide if you need the main mirror focuser upgarde.

One last advice : 

When calculating the backfocus needed for your specific setup, make sure to accurately measure the focus distance from your visual back for at least : 1) a star of a Magnitude between 4 and 4.6  2) a planet - Saturn will be nice if its up when you'll do this but any other will also do the job and 3) the Moon. Then calculate the total backfocus needed including the inner and the outer focus point between all three plus at least 6 mm.    

Clear skies

[nmoushon]

I really appreciate all the time you've spent walking me through all this. You're knowledge is greatly appreciated. I will try and figure out what kind of back focus I will need with a couple different setup options I'm looking at and see how they all fit. 

[seo]

It's my pleasure. Happy that I can offer my help to a fellow astronomer. 

If and when you need anything else, I'll be happy to offer any of my personal knowledge and experience.