Go Back   IceInSpace > Equipment > Astrophotography and Imaging Equipment and Discussions

Reply
 
Thread Tools Rate Thread
  #1  
Old 16-03-2019, 02:57 PM
LaughingBeagles's Avatar
LaughingBeagles (Peter)
Registered User

LaughingBeagles is offline
 
Join Date: Dec 2016
Location: Ocean Reef, Western Australia
Posts: 105
Lightbulb Innovation Frontier's ONAG-SC - Back Focus Question

Hi All,

I'm researching the idea of going for Innovation Frontier’s ONAG-SC (sensor size seems right for my Atik383L+ Mono). I emailed Gaston Bauda (the inventor / vendor) asking out of all the product options which would best suit my imaging train:

Atik 383L+ Mono > EFW2 (loaded with Astrodon 36mm 5nm Ha OIII and SII + LRGB) > Stellarvue 102 FF/FR > Moonlite focuser > Explore Scientific 102mm Carbon Fiber APO

My guide scope is the Orian MMAG.

Gaston responded by pointing me at his spreadsheet back focus calculator and suggesting I go with a guide scope with large sensor size.

I downloaded the spreadsheet and spent a fair bit of time reading Innovation Frontier’s website to understand what all the acronyms mean and how it all comes together and eventually worked out what figures to plug in where on the spreadsheet.

That said, according to my measurements I still don't have enough scope port back focus.

I tried googling what the back focus for my scope is but most folks when asking in forums get "try spacers until it comes into focus," which didn't really help (I was looking for something like “the back focus for an ES102CF is xxx or calculated by xxx”)

I measured the distance I wind the Moonlite focuser out to achieve focus in my current config and get 65mm, that's apparently 58.5 or so mm short:

http://postimg.cc/dkbTp1r4


Clearly, something is missing. Any thoughts?

Pete

Last edited by LaughingBeagles; 16-03-2019 at 06:06 PM.
Reply With Quote
  #2  
Old 16-03-2019, 03:38 PM
Merlin66's Avatar
Merlin66 (Ken)
Spectroscopy Wizard

Merlin66 is offline
 
Join Date: Oct 2005
Location: St Leonards, Vic
Posts: 7,074
Pete,
Are you sure the ATiK 383 needs 38mm back focus? I would have thought around 17mm.....
Reply With Quote
  #3  
Old 16-03-2019, 04:12 PM
LaughingBeagles's Avatar
LaughingBeagles (Peter)
Registered User

LaughingBeagles is offline
 
Join Date: Dec 2016
Location: Ocean Reef, Western Australia
Posts: 105
You're right, Ken.

It's 17 but you subtract that from the flattener / reducer (55mm) to arrive at 38mm (unless you're suggesting I should have added not subtracted?)
Reply With Quote
  #4  
Old 16-03-2019, 04:48 PM
Merlin66's Avatar
Merlin66 (Ken)
Spectroscopy Wizard

Merlin66 is offline
 
Join Date: Oct 2005
Location: St Leonards, Vic
Posts: 7,074
But you then have two constraints - the required flattened spacing 55mm and the camera back focus of 17mm may be the ONAG could fit between them?
What’s the width of the ONAG? 60mm????
Reply With Quote
  #5  
Old 16-03-2019, 06:30 PM
LaughingBeagles's Avatar
LaughingBeagles (Peter)
Registered User

LaughingBeagles is offline
 
Join Date: Dec 2016
Location: Ocean Reef, Western Australia
Posts: 105
Actually, it's more than that as it includes the Filter Wheel too.

Here's a link to IF's 'help' page (which took me a minute or two to unravel).

For some reason, the screenshot of the spreadsheet in my original post above is only displayed as a link rather than a picture. Suffice to say, you input:
  1. Scope Back Focus
  2. Camera Back Focus (Imager)
  3. Camera Back Focus (Guider)
  4. Focuser / Rotator Back Focus (fully retracted)
  5. Filter Wheel Back Focus

And then there's options to add back focus for any adaptors etc.

The Output data then provides details of what size spacer to add at the Scope Port, Imager Port and Guider Port. According to the data I've entered (based on specs for as many of the parts as I am able to gather), I have an 18.5mm spacer at the guider port, zero spacer at the imager port and -58.5 spacer at the scope port.

Not surprisingly, the last is in red with a warning that there is not enough back focus.

Hence my "does anyone know the scope side back focus of an ES102CF".

Unless it means the focal length perhaps (physically 565 from the front lens to the back of the scope??)
Reply With Quote
  #6  
Old 16-03-2019, 08:11 PM
Merlin66's Avatar
Merlin66 (Ken)
Spectroscopy Wizard

Merlin66 is offline
 
Join Date: Oct 2005
Location: St Leonards, Vic
Posts: 7,074
Peter,
From the info:
The OIBF is 66mm....
If the filter wheel is placed on the camera (say 22 +17 =39mm) then you need a backfocus (from the focuser/OTA) of 66+39= 105mm
This is much more than the ff requirement of 55mm.
Let's assume you add the FF after the ONAG - then you'd need 55+66= 125mm backfocus behind the focuser/ OTA....
Reply With Quote
  #7  
Old 17-03-2019, 09:36 AM
LaughingBeagles's Avatar
LaughingBeagles (Peter)
Registered User

LaughingBeagles is offline
 
Join Date: Dec 2016
Location: Ocean Reef, Western Australia
Posts: 105
Ken,

Points noted with thanks. I think with the spreadsheet though the idea is to work out with the combination of the imager, guider and ONAG, what spacers (if any) do I need where to ensure the guider and imager camera are parfocal.

As you know, the moonlight focuser has a shed load of extension (and worse case, I have a series of extension tubes I can add, but I'm sure I wouldn't need to).

If anything with the additional 66mm that the ONAG gives, I would need less, not more extension from the Moonlite focuser. (Hope that makes sense!).

Oh, and by the way, the President of ASWA (Astronomy Society of WA) is trying to get me into spectroscopy. I figure one challenge at time; I want to master AP (DSO esp) more before taking a look.
Reply With Quote
  #8  
Old 17-03-2019, 10:27 AM
Merlin66's Avatar
Merlin66 (Ken)
Spectroscopy Wizard

Merlin66 is offline
 
Join Date: Oct 2005
Location: St Leonards, Vic
Posts: 7,074
Peter,
I believe in KISS...
The ONAG distances are:
backfocus for imaging=66mm
backfocus for guiding =90mm
A difference of 28mm.....
If the guider were in focus then the imaging camera CCD would be spaced 28mm behind the ONAG to also come to focus. Agreed?
If you can fit your filter wheel in this gap then it could work...
However if you need a fixed distance from the FF then the spacing from the front of the ONAG to the camera (=90mm) would be too much.
Placing the FF behind the ONAG would mean moving the final imaging focus to 66+55 = 121, and fitting spacers to the guide port to compensate..
I think if you sketch the components out using the dimensions you have will give a clearer picture.
Ken
Reply With Quote
  #9  
Old 17-03-2019, 10:52 AM
LaughingBeagles's Avatar
LaughingBeagles (Peter)
Registered User

LaughingBeagles is offline
 
Join Date: Dec 2016
Location: Ocean Reef, Western Australia
Posts: 105
Ken,

It would work as the Filterwheel is 22mm leaving 4mm.

I think you're right, I'll sketch and see what it comes up with. Section 8 / 9 of the ONAG Manual talks about Flatteners / Reducers and where place them and to be honest, it was way over complicated for me (I feel really dumb in this space sometimes).

I will go ahead and sketch as you suggest and see where that gets me.

Thanks for your patience with me Ken, much appreciated.

Pete
Reply With Quote
  #10  
Old 17-03-2019, 10:54 AM
Merlin66's Avatar
Merlin66 (Ken)
Spectroscopy Wizard

Merlin66 is offline
 
Join Date: Oct 2005
Location: St Leonards, Vic
Posts: 7,074
Peter,
I had a similar "learning curve" when I used a beamsplitter (as a slit guider) on the early Spectra-L200. Same issues as the ONAG.....
Ken
Reply With Quote
  #11  
Old 17-03-2019, 10:57 AM
LaughingBeagles's Avatar
LaughingBeagles (Peter)
Registered User

LaughingBeagles is offline
 
Join Date: Dec 2016
Location: Ocean Reef, Western Australia
Posts: 105
Thanks Ken,

Glad you get where I'm coming from!

Pete
Reply With Quote
Reply

Bookmarks

Thread Tools
Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +10. The time is now 12:11 AM.

Powered by vBulletin Version 3.8.7 | Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
Advertisement
Lunatico Astronomical
Advertisement
Meade Australia
Advertisement
OzScopes Authorised Dealer
Advertisement
Bintel
Advertisement
NexDome Observatories
Advertisement
SkyWatcher Australia
Advertisement
Celestron Australia
Advertisement
Astronomy and Electronics Centre
Advertisement