Re: IEXOS-100 with prototype polar scope unguided images #iEXOS-100

jrichard333 <>



Probably the previously owned lens was defective when you bought it?  You could always send it back to Sigma and have them inspect it.  They have a firmware update as well.


I have four setups for planet-imaging using an APSC-body camera:

1.       Sigma 150-600mm lens/ a combination of two teleconverters 2.8X (The Moon will fill your frame)

Focal length 1680mm/ Focal Ratio 18


2.       Celestron C90/ a combination of two teleconverters 2.8X/ (A Frugal-based Planet Killer J)

Focal length 3500mm/ Focal Ratio 42


3.       Celestron C90/ a combination of multiple teleconverters 5.6X to 11.2 X (Super-Duper Frugal Planet Killer J)

Focal length 7000mm-14000mm/ Focal Ratio 77.8 - 155.7; manually variable J


Super Duper Frugal Planet Killer (backend):


Things to note:

1.       I can’t see Polaris

2.       Red dot finder is a must for planetary and bright star imaging

3.       Current Canon/ Sigma teleconverters do not mate.  You might consider using all Vivitar or generic teleconverters.

4.       If mounting to a scope, you will have to cover the contacts of the teleconverter closet to the camera body

5.       I will only use Maksutov scopes….less headaches J.

6.       I am currently looking at picking up either the Explorer Scientific 152mm Maksutov (I love the rings) or  the Sky-Watcher 150mm Maksutov (I love the price). 


If you are interested in DSOs, I would go with a 150-600mm lens and pick up used teleconverters on eBAY to do planetary imaging.  Upgrade equipment as needed. 


I will not fulfill item 6 on my list until I have imaged Mars.  If it goes South, then I will invest in one of the scopes in item 6.



From: [] On Behalf Of Wes Mcdonald
Sent: Wednesday, July 10, 2019 4:09 PM
Subject: Re: [ESPMC-Eight] IEXOS-100 with prototype polar scope unguided images #iexos-100


Right Jerry, good advice.  The ST-80, and most other 80mm f5 scopes of course have a 400mm fl.  But the danged camera sensor can make things longer if it is a cropped sensor like a DX in Nikons.  In that case a .8 flattener/focal reducer can help.  


I suppose the idea of just using a good 400 mm camera prime lens is maybe the best.  I don't know.  Same as for the telescope, one would ideally want the ES 80mm APO.  All gets down to cost and where on the learning curve you are and how much you want to spend to climb up it in case you decide to bail on it.  I bought a 400mm Sigma lens for a song at a star party.  Turns out it does not focus worth beans.  Focus wheel is so soft you cannot let go of it without turning it.  Also the glass just seems poor.  Now it sits and clogs up my camera bag.  So if you go with a prime, buy a good one.



sooo, YMMV.




Wes, Southport NC
PMC-8, ES ED 127, 10" LX200GPS, Astro-Tech 8" Newt, ETX-90
Polemaster, Orion ST-80 and SAG
Electrical Engineer, Retired

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