ICEINSPACE
Moon Phase
CURRENT MOON
Waning Gibbous 90.6%
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26-06-2018, 07:12 AM
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Registered User
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Join Date: May 2018
Location: Burrill Lake nsw Australia
Posts: 55
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thoughts on telescope now my 500mm canon is out
Okay I'm now thinking of using a telescope for deep sky and planets instead of my 500mm L I f4 Canon prime lens. What options would be a good choice of scope. I've been looking at the skywatchers or orions
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26-06-2018, 07:18 AM
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amateur
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Join Date: Jul 2006
Location: Mt Waverley, VIC
Posts: 6,932
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Canon 500mm L f/4 is excellent lens for DS.... (I have 400mm Lf/2.8, stepped down to f/4 by external aperture mask).
However, planets (and Moon) are different - for that you will need telescope and good barlow.. and camera capable of taking video (which can be stacked with help of Registax, for example).
Fantastic work on planets was done by some members of this forum, using 8~12" Nextonians, see here.
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26-06-2018, 08:58 AM
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Registered User
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Join Date: Jun 2013
Location: Moorooka, Brisbane
Posts: 906
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Depends a bit on what mount you plan on using? I found that an ED80 on an HEQ5 works beautifully for deep sky stuff (nebulae, larger galaxies). If you plan on guiding a simple Finderguider also works well with this setup. Nice wide field. Planets and smaller galaxies (which most of them are) benefit from a longer focal telescope, which are generally heavier and benefit from a slightly bigger mount (EQ6 and the like).
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26-06-2018, 09:13 AM
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Jacob
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Join Date: Mar 2018
Location: Sydney
Posts: 175
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Agreed with the below post, HEQ5 and an ED80 are perfect for deep sky. it's what i've started with and have been using for the past 6 months (only recently purchased a GSO RC6).
Never used the ED80 for planetary but i'm assuming with a barlow it could be ok?
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26-06-2018, 09:48 AM
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Gravity does not Suck
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Join Date: Mar 2005
Location: Tabulam
Posts: 16,866
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Quote:
Originally Posted by Jsmitt94
Agreed with the below post, HEQ5 and an ED80 are perfect for deep sky. it's what i've started with and have been using for the past 6 months (only recently purchased a GSO RC6).
Never used the ED80 for planetary but i'm assuming with a barlow it could be ok?
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Can you get a 10 x barlow☺
Alex
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26-06-2018, 09:49 AM
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Registered User
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Join Date: Apr 2006
Location: Warrnambool
Posts: 12,430
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For deep space imaging Daniel I would stick with the Canon 500mm F4.00 Prime mate, they are such a beautiful lens for that sort of stuff.
I have owned one some time ago and still to this day I regret the minute it left the house.
However that is my two cents worth
Leon
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17-07-2018, 11:14 AM
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Registered User
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Join Date: May 2018
Location: Burrill Lake nsw Australia
Posts: 55
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thanks for the replys, thinking that I will use both the 500 and 100-400 canons and also purchase a sct probably a celestron 925 and eq6 or cgem. I'm liking the iptron cem60 but bit exy for my price point
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17-07-2018, 11:52 AM
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Registered User
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Join Date: Oct 2005
Location: Junortoun Vic
Posts: 8,904
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The optimum focal ratio for planetary imaging is 5 times the pixel size in micron. For a 5micron pixel this means around f30.
For typical scopes this infers using Barlow’s from x2 to x4
Just my 2c
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17-07-2018, 05:15 PM
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.....
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Join Date: Oct 2016
Location: Melbourne, Australia
Posts: 2,945
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Add a 2x teleconverter and a Canon APS body to your Canon 500mm f/4 and you will get a 1600mm equivalent field of view, with a light gathering equivalent aperture of f/12.8. That might be enough to experiment with for low or no investment, depending on what else you have.
Best
JA
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17-07-2018, 08:28 PM
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Dark sky rules !
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Join Date: Dec 2011
Location: 52N 6E (EU)
Posts: 1,152
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Stick to the 500mm f/4L, you can use it as a telescope. For planetary imaging, use a teleconverter (e.g. Canon extender 2x) and a 3x Barlow, which makes it f/24.
If you should purchase it new, then an APO refractor is cheaper, but you already have it.
It has an excellent quality and is even lighter than a 125mm APO refractor.
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18-07-2018, 07:49 AM
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Registered User
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Join Date: Dec 2010
Location: Darwin
Posts: 608
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How do you Barlow a dslr lens?
Hemi
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18-07-2018, 09:25 AM
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.....
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Join Date: Oct 2016
Location: Melbourne, Australia
Posts: 2,945
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Quote:
Originally Posted by Hemi
How do you Barlow a dslr lens?
Hemi
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It's not a Barlow, but you can use a teleconverter (a telecentric amplifier ) which is like a powermate to increase the focal length, typically 1.4, 1.7 or 2 times, and even stack them if you REALLY must.
Best
JA
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18-07-2018, 10:04 AM
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amateur
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Join Date: Jul 2006
Location: Mt Waverley, VIC
Posts: 6,932
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Quote:
Originally Posted by JA
It's not a Barlow, but you can use a teleconverter (a telecentric amplifier ) which is like a powermate to increase the focal length, typically 1.4, 1.7 or 2 times, and even stack them if you REALLY must.
Best
JA
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No need for stacking, tele-extender (as well as barlow) will have larger magnification if distance to camera is longer.
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18-07-2018, 12:52 PM
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.....
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Join Date: Oct 2016
Location: Melbourne, Australia
Posts: 2,945
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Quote:
Originally Posted by bojan
No need for stacking, tele-extender (as well as barlow) will have larger magnification if distance to camera is longer.
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Hi Bojan,
That's true for a Barlow (typically using a negative doublet lens) but, not true for a telecentric amplifier (teleconverter, telextender or powermate) which typically use a negative doublet and positive doublet in concert. With a true Barlow (negative doublet) the light rays diverge coming out and hence the possibility of adjusting magnification with position. With a telecentric amplifier device( teleconverter, power mate, etc..) the light rays are parallel out and the magnification is fixed by the focal length ratio of the negative and positive doublets it contains.
I can't imagine one would want to use a Barlow with a camera lens (and camera) when it so easy and back registration distances are easily controlled by design of the normal teleconverter device. Just click them together. But, like anything, there's no free lunch and image quality and light will be reduced compared with a prime focus optic of equivalent focal length,( depending on the quality of that optic of course)
Best
JA
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19-07-2018, 06:56 PM
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Registered User
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Join Date: Dec 2010
Location: Darwin
Posts: 608
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Quote:
Originally Posted by JA
It's not a Barlow, but you can use a teleconverter (a telecentric amplifier ) which is like a powermate to increase the focal length, typically 1.4, 1.7 or 2 times, and even stack them if you REALLY must.
Best
JA
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Thanks JA, just that he says, f4 x2 tele x3 Barlow to get to f24.
Cheers
H
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