PDA

View Full Version here: : thoughts on telescope now my 500mm canon is out


Bluknghtv
26-06-2018, 07:12 AM
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

bojan
26-06-2018, 07:18 AM
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 (http://www.iceinspace.com.au/63-201-0-0-1-0.html).

Benjamin
26-06-2018, 08:58 AM
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).

AstroBogan
26-06-2018, 09:13 AM
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?

xelasnave
26-06-2018, 09:48 AM
Can you get a 10 x barlow☺
Alex

leon
26-06-2018, 09:49 AM
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. :sadeyes:
However that is my two cents worth :shrug:

Leon :thumbsup:

Bluknghtv
17-07-2018, 11:14 AM
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

Merlin66
17-07-2018, 11:52 AM
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

JA
17-07-2018, 05:15 PM
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

skysurfer
17-07-2018, 08:28 PM
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.

Hemi
18-07-2018, 07:49 AM
How do you Barlow a dslr lens?

Hemi

JA
18-07-2018, 09:25 AM
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

bojan
18-07-2018, 10:04 AM
No need for stacking, tele-extender (as well as barlow) will have larger magnification if distance to camera is longer.

JA
18-07-2018, 12:52 PM
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

Hemi
19-07-2018, 06:56 PM
Thanks JA, just that he says, f4 x2 tele x3 Barlow to get to f24.

Cheers

H