#1  
Old 08-11-2012, 08:27 PM
rcheshire's Avatar
rcheshire (Rowland)
Registered User

rcheshire is offline
 
Join Date: Apr 2010
Location: Geelong
Posts: 2,617
Borg Canon Takahashi glass.

Hi. Delving into equipment decisions again???

Are there any Borg users out there willing to share their experience.

In mind is widefield, 71FL f3.9 Astrograph, 5 elements including triplet focal reducer - Cost around 2k. Will atttach an SBIG ST-8300C.

The Tak 4 element Petzval's are superb and in another thread I understand that there was disappointment with the FSQ-85ED @ 3.8k. I'm not sure that the 106 (5.6k), as beautiful as it is, suits my needs - essentially wide field.

Perhaps I should stick with my Canon 200mm for now, which is stopped down with an aperture disk - aka inverted reducer rings - stack thereof.

I would consider a Ritchey Cretien for narrow field if I ever got around to it - happy with wide field right now.

Second question - I understand that the SBIG crop factor is 1.95; that is, 18 x 13.5mm, relating it to full frame - because I am using a camera lens with it - effective focal length is 390mm which is close to the Borg in any case.

For wide field, am I gaining anything by purchasing what is essentially an achromat Fluorite doublet, in the Borg. I don't know if the triplet focal reducer is also a field flattener.

Questions, questions

Last edited by rcheshire; 09-11-2012 at 04:52 AM.
Reply With Quote
  #2  
Old 08-11-2012, 09:12 PM
DavidTrap's Avatar
DavidTrap (David)
Really just a beginner

DavidTrap is offline
 
Join Date: Jun 2009
Location: Brisbane
Posts: 3,032
Effective focal length has little to do with it when it comes to astronomy. The Borg at 390mm will have roughly double the magnification compared to your Canon 200mm.

For a given scope, "magnification" will be the same whether you use a small or large chip camera, but you'll see a wider field of view with a larger chip. The resulting image from a smaller chip camera might appear more zoomed in, but that's only because you've blown the image up larger to fill your screen/print vs the image from a larger chip.

If the math were correct, a longer focal length scope with a larger chip will give the same image as a shorter focal length scope with a small chip, but there will be less detail with the latter combination - eg. and FSQ-106 and ST-11000 might give a similar field of view to an FS-60 and a ST-8300, but the former will give a more detailed image through greater magnification.

Hope this helps!

DT
Reply With Quote
  #3  
Old 09-11-2012, 05:05 AM
rcheshire's Avatar
rcheshire (Rowland)
Registered User

rcheshire is offline
 
Join Date: Apr 2010
Location: Geelong
Posts: 2,617
Thank you David. You are correct , effective focal length is not a consideration. I am more concerned with FOV and resolution and think the 200mm is just about right with a DSLR 1.6 crop factor. This will change with the increased crop factor of the KAF8300 chip. Perhaps I am looking at this from the wrong perspective.

My first consideration consistent with FOV and resolution is the quality of the optics. Finding a small aperture scope that fits the bill is more challenging than I thought. I'm getting to the stage where I'm not satisfied to settle for less than excellence and if buying another scope is merely a compromise then I'll stick with the apprentices tool in the 200mm Canon.

Thinking this through and elucidating a bit more, I'm looking for a small instrument with excellent optics to replace my 200mm in the hope that I can improve on it too.
Reply With Quote
  #4  
Old 09-11-2012, 06:27 AM
astroboy's Avatar
astroboy
Registered User

astroboy is offline
 
Join Date: Dec 2005
Location: Lake Bathurst NSW
Posts: 696
Hi Rowland
I think the Borg works out to be 280mm
Its worth remebering the FSQED can take a reducer giving you a 380 mm FL @ F3.64 and will cover FF chips if you ever upgrade there is also a 1.6x that works well too .
So the FSQED can work at F3.6 , F5 and F8 , you will need a solid mount though , they are heavy.

Zane
Reply With Quote
  #5  
Old 10-11-2012, 04:13 PM
rcheshire's Avatar
rcheshire (Rowland)
Registered User

rcheshire is offline
 
Join Date: Apr 2010
Location: Geelong
Posts: 2,617
You are right Zane. Not only am I confused, but I'm managing to confuse everyone else.

I was hoping Borg owners might chip in with their experiences using the equipment.

Is the Borg a good instrument? Let's leave it at that...
Reply With Quote
  #6  
Old 11-11-2012, 05:36 AM
astroboy's Avatar
astroboy
Registered User

astroboy is offline
 
Join Date: Dec 2005
Location: Lake Bathurst NSW
Posts: 696
Hi Rowland
The only Borg scope I've owned in one of there 5" APOs with the DG-L .85x reducer , nice scope but the Helical focuser was not up to the task and I replaced it with a Feather Touch .
The coulout correction could have been better to but this scope had ED optics not FL ones in the 71mm .
There very vercatile scopes and very light wieght , I would look at a focuser upgrade ( which Borg can do ) to a FT focuser for CCD work.

Zane
Reply With Quote
  #7  
Old 12-11-2012, 06:23 AM
rcheshire's Avatar
rcheshire (Rowland)
Registered User

rcheshire is offline
 
Join Date: Apr 2010
Location: Geelong
Posts: 2,617
Thanks Zane. I took a few shots over the weekend, to tune up my system for the SVAA camp this weekend. The 8300 - 200mm combination produces a nice image. Stars look great, but a flatter field would be nice. It would be nice to take in more sky which is a little restricted in my view. This setup in square mode would frame eta C well.

The idea of interchangable objectives, reducers and so on makes the Borg very attractive. And the .7 focal reducer is also a flattener, as it turns out. Borg don't go into a lot of detail at times. The user group is the best resource.

Rowland.
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 09:06 AM.

Powered by vBulletin Version 3.8.7 | Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Advertisement
Testar
Advertisement
Bintel
Advertisement