A question about a AP155 EDFS with the 2.7" focuser


Dean Jacobsen
 

One of my observatory partners has an AP155 EDFS with the 2.7" focuser and are going to put it on the Mach2 and try some unguided imaging with it with my small pixel ASI1600MM CMOS camera.

His recollection is that at the native f/7 focal length we will need to put the imaging chip 86.5mm back from the back of the focuser barrel to be able to get the camera into focus.  Is this correct?

Thanks in advance to anyone who can confirm this.
--
Dean Jacobsen
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Dean Jacobsen
 

OK, now I am hearing from the scope's owner that the 86.5 number is the spacing for the flatener - which I do not anticipate that we will need with a 4/3" sized detector (the same size as a 8300 CCD).  

How far back should I set the camera detector from the back of the focuser barrel to be able to have some reasonable in and out travel of the focuser?
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Dean Jacobsen
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Stuart <stuart.j.heggie@...>
 

Dean, without a rear element in the imaging train, I think you can put the darn thing wherever you want and just bring it to focus. If you have a FF or Reducer/Flattener in play, they only deliver their promise at the precise distance to the chip. No flattener, no issue. Pretty sure.

Stuart Heggie (who has an AP155EDF w FF and 155TCC)


On Sat, 20 Jun 2020 at 19:58, Dean Jacobsen <deanjacobsen@...> wrote:
OK, now I am hearing from the scope's owner that the 86.5 number is the spacing for the flatener - which I do not anticipate that we will need with a 4/3" sized detector (the same size as a 8300 CCD).  

How far back should I set the camera detector from the back of the focuser barrel to be able to have some reasonable in and out travel of the focuser?
--
Dean Jacobsen
http://astrophoto.net/wp/ 
Image Gallery - http://astrophoto.net/wp/image-gallery/
Astrobin - https://www.astrobin.com/users/deanjacobsen/ 


--

Stuart
http://www.astrofoto.ca/stuartheggie/


Dean Jacobsen
 

Thanks Stuart.  Sounds good.  

I figure that having the camera in focus with the focuser barrel about 1” extended would be a good place to be.  So I was hoping to avoid that situation I am sure we have all been in where I am scrounging around for adapters in the dark trying to get a good spacing.
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Dean Jacobsen
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Dean Jacobsen
 

I guess I could guesstimate the focal point by measuring 43” back from the front of the objective and then measuring how far it is from that point to the focuser barrel.
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Dean Jacobsen
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Roland Christen
 

Aim it at the sun, then place a piece of white paper at the focus point and measure where it comes to focus. Should be somewhere around 8" from the fully racked in focuser back.

Rolando



-----Original Message-----
From: Dean Jacobsen <deanjacobsen@...>
To: main@ap-gto.groups.io
Sent: Sat, Jun 20, 2020 9:32 pm
Subject: Re: [ap-gto] A question about a AP155 EDFS with the 2.7" focuser

I guess I could guesstimate the focal point by measuring 43” back from the front of the objective and then measuring how far it is from that point to the focuser barrel.
--
Dean Jacobsen
http://astrophoto.net/wp/ 
Image Gallery - http://astrophoto.net/wp/image-gallery/
Astrobin - https://www.astrobin.com/users/deanjacobsen/ 


Geert
 

I would prefer using the Moon to find the focal point, unless you want to set fire on a piece of paper :-)

Geert

Op zo 21 jun. 2020 om 18:42 schreef uncarollo2 <chris1011@...> via groups.io <chris1011=aol.com@groups.io>:

Aim it at the sun, then place a piece of white paper at the focus point and measure where it comes to focus. Should be somewhere around 8" from the fully racked in focuser back.

Rolando



-----Original Message-----
From: Dean Jacobsen <deanjacobsen@...>
To: main@ap-gto.groups.io
Sent: Sat, Jun 20, 2020 9:32 pm
Subject: Re: [ap-gto] A question about a AP155 EDFS with the 2.7" focuser

I guess I could guesstimate the focal point by measuring 43” back from the front of the objective and then measuring how far it is from that point to the focuser barrel.
--
Dean Jacobsen
http://astrophoto.net/wp/ 
Image Gallery - http://astrophoto.net/wp/image-gallery/
Astrobin - https://www.astrobin.com/users/deanjacobsen/ 


Dean Jacobsen
 

On Sun, Jun 21, 2020 at 09:49 AM, Geert wrote:
I would prefer using the Moon to find the focal point, unless you want to set fire on a piece of paper :-)
 
Geert
Hey Geert, sometimes ya' just gotta live dangerously.  ;-)

Thanks Roland, I can work with that. 

--
Dean Jacobsen
http://astrophoto.net/wp/ 
Image Gallery - http://astrophoto.net/wp/image-gallery/
Astrobin - https://www.astrobin.com/users/deanjacobsen/ 


Andrew Arai
 

Dean,

I have been looking into the spacing of some of the older AP field flatteners. Many were configured for the Pentax 6x7 system. IN that case 86.5 mm is close to the 86.4 +/- 2.5 mm I thought was the correct spacing. I found this on an old thread that was forward from the Yahoo group into the AP User group).

Andrew


Dean Jacobsen
 

Thanks Andrew.  I am keeping my fingers crossed that we don’t need the flattener but that is good to know if we do.
--
Dean Jacobsen
http://astrophoto.net/wp/ 
Image Gallery - http://astrophoto.net/wp/image-gallery/
Astrobin - https://www.astrobin.com/users/deanjacobsen/