Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Small triplet or quadruplet for full-frame DSLR

  • Please log in to reply
14 replies to this topic

#1 CrossoverManiac

CrossoverManiac

    Explorer 1

  • -----
  • topic starter
  • Posts: 98
  • Joined: 10 Apr 2018

Posted 23 September 2018 - 08:30 PM

This is for a full-frame camera in the 300-500mm focal length range, specifically for DSOs that are larger than 60 arc-minutes across but not so large that the object only takes up a small portion of the picture as it would with a wide-angle camera lens ( ≤ 300 mm).



#2 PirateMike

PirateMike

    Surveyor 1

  • -----
  • Posts: 1928
  • Joined: 27 Sep 2013
  • Loc: A Green Dot On A Blue Sea

Posted 23 September 2018 - 10:57 PM

Are you asking for a suggestion?



#3 t-ara-fan

t-ara-fan

    Vostok 1

  • -----
  • Posts: 165
  • Joined: 20 Sep 2017

Posted 23 September 2018 - 11:32 PM

Budget?



#4 Jerry Lodriguss

Jerry Lodriguss

    Vendor

  • *****
  • Vendors
  • Posts: 6575
  • Joined: 19 Jul 2008
  • Loc: Voorhees, NJ

Posted 24 September 2018 - 12:18 AM

AT65EDQ quadruplet apochromat is 420mm of focal length at f/6.5.

 

You will get a some vignetting with a full frame camera, but it can be corrected with flats.

 

To do better than this, you would need something like a Tak with a larger focuser and large focal reducer, and that can get pretty expensive.

 

Jerry


Edited by Jerry Lodriguss, 24 September 2018 - 12:23 AM.


#5 CrossoverManiac

CrossoverManiac

    Explorer 1

  • -----
  • topic starter
  • Posts: 98
  • Joined: 10 Apr 2018

Posted 24 September 2018 - 01:15 AM

Are you asking for a suggestion?

Yes.  Also, I'm trying to keep the OTA down to 2.5 kg or less.


Edited by CrossoverManiac, 24 September 2018 - 01:16 AM.


#6 PirateMike

PirateMike

    Surveyor 1

  • -----
  • Posts: 1928
  • Joined: 27 Sep 2013
  • Loc: A Green Dot On A Blue Sea

Posted 24 September 2018 - 01:45 AM

The 65EDQ is no longer sold by Astro-Tech but you can find the same scope (I presume) here... https://www.teleskop...d-flatener.html

 

It does weight 2.8kg which includes the weight of the rings.



#7 Samir Kharusi

Samir Kharusi

    Vanguard

  • *****
  • Posts: 2480
  • Joined: 14 Jun 2005
  • Loc: Oman

Posted 24 September 2018 - 01:51 AM

If you are willing to go to twice the price but end up with dual daytime/astro use, consider the Canon EF 400mm f5.6; a great birding lens and great for astro, though one f-stop slower than I would have preferred for use unguided. At a dark site using a Canon APS-C camera ideally you need 4 minute subs as minimal (though you might get away with 3 minute subs or even two minute subs if there is any light pollution). With the later model 5D's you may happily use 2-minute subs even at the darkest sites. The later 5D versions have lower Read Noise than the more common Canon APS-C. That should be short enough for most mid-price mounts, unguided. On the other hand if you are already using autoguiding you may well prefer to save yourself some hundreds of $ and go for the APO at f6.5 (minimal length subs on an APS-C 5+ minutes, hence autoguiding necessary on most mounts). So, basically, to get a more focused recommendation, I think you should state what camera you wish to use it with, and whether you autoguide or not. Personally I place great preference for non guided use, but others are already set up for autoguiding...



#8 einarin

einarin

    Apollo

  • -----
  • Posts: 1224
  • Joined: 23 Dec 2016

Posted 24 September 2018 - 01:54 AM

Or this.



#9 CrossoverManiac

CrossoverManiac

    Explorer 1

  • -----
  • topic starter
  • Posts: 98
  • Joined: 10 Apr 2018

Posted 24 September 2018 - 02:24 AM

Or this.

According to the site, field correction is 32 mm.  For a full-frame camera, it would have to be 43 mm.



#10 CrossoverManiac

CrossoverManiac

    Explorer 1

  • -----
  • topic starter
  • Posts: 98
  • Joined: 10 Apr 2018

Posted 24 September 2018 - 02:26 AM

What about the Meade 70mm quadruplet?  How would that compare with a 80mm cf triplet ?



#11 Coconuts

Coconuts

    Vostok 1

  • *****
  • Posts: 115
  • Joined: 23 Sep 2012

Posted 24 September 2018 - 08:00 PM

I would suggest that you consider the Hutech/Borg 360 mm f/4.0 astrograph family.  Here are four "standard" configurations:

 

https://www.sciencec...rgPackage/9.htm

https://www.sciencec...gPackage/10.htm

https://www.sciencec...gPackage/11.htm

https://www.sciencec...gPackage/12.htm

 

All configurations are equally fast (f/4.0), and a hallmark of Hutech/Borg systems is very light, thin-walled but stiff components that keep the overall mass down.  The last in the list above has a mass of 1.9 kg, well below your 2.5 kg goal, but a lot faster than many other candidates.  All of their astrographs started off designed for medium format film, and so are even better corrected for full-frame sensors.

 

The Hutech/Borg "system" can be a bit intimidating at first; any specific configuration consists of a number of compatible components selected from a long list, which you can peruse here:

 

https://www.sciencec...parts/index.htm

 

The pre-configured astrographs listed above parse that long component part list for you, though.  Their optical quality is excellent, and the price when compared to peers (Takahashi, etc) is very reasonable.  This last comment may seem a stretch, but these are certainly great astrographs at a reasonable price.

 

All the best,

 

Kevin


Edited by Coconuts, 24 September 2018 - 08:20 PM.

  • GlenM likes this

#12 Samir Kharusi

Samir Kharusi

    Vanguard

  • *****
  • Posts: 2480
  • Joined: 14 Jun 2005
  • Loc: Oman

Posted 25 September 2018 - 03:42 AM

Dang! You do get what you pay for undecided.gif  f-ratio costs.

 

$750 f6.5 TSAPO65Q

$1250 f5.6 Canon EF 400mm

$2000+ f4 Borg



#13 CrossoverManiac

CrossoverManiac

    Explorer 1

  • -----
  • topic starter
  • Posts: 98
  • Joined: 10 Apr 2018

Posted 25 September 2018 - 02:30 PM

Dang! You do get what you pay for undecided.gif  f-ratio costs.

 

$750 f6.5 TSAPO65Q

$1250 f5.6 Canon EF 400mm

$2000+ f4 Borg

That seems to true...except with Newtonian astrographs...sort of.  TPO does offer some pretty cheap imaging Newtonians starting at $300 for a 6-inch f/4, which would put the focal length around 600 mm, which would encompass the entire Andromeda Galaxy in the FOV using a full-frame DSLR.  However, the problem is now dropping at least $1500 minimum for a mount big enough to handle it.  Also spending a few hundred on a coma corrector for correcting distortions of the stars that are common among fast Newtonian telescopes and making sure it is one that will correct for a field large enough for a full-frame camera otherwise it defeats the entire purpose of getting a scope with a 600-mm focal length, which has the user going back to looking for the right telephoto lens or short refractor.  I only have a Star Adventurer that maxes out at 11 lbs since it was made primarily for wide angle astrophotography (though I *originally* bought my Star Adventurer for this: https://www.youtube....?v=Bz0sBkp2kso)

 

One way or another, you will pay $$$ for that shot.

 

It's only now I see why some many people in AP putting more emphasis on getting the right tracking mount than the right telescope.


Edited by CrossoverManiac, 25 September 2018 - 02:43 PM.


#14 17.5Dob

17.5Dob

    Soyuz

  • ****-
  • Posts: 3935
  • Joined: 21 Mar 2013
  • Loc: Colorado,USA

Posted 25 September 2018 - 11:22 PM

What objects are you planning on photographing that are larger than 60' ? There are only 8 M-Objects larger than that, and a few more NGC/IC objects, but most of them are much fainter and require a modded camera or narrowband imaging. There are targets like the nebula complex around Sadr and the entire Horsehead area, but for all intents, in AP, 300mm is still a very wide angle lens.

Andromeda is the largest target in the N Hemisphere, (not counting Barnards Loop), but it's still only 3.5 sq deq. A 300mm lens has an FOV of 31.7 sq deq. on a FF camera, so Andromeda will only take up 11% of the field. The Pleiades, the second largest M-Object is half the size of Andromeda.

 

Full frames excel for wide angle, but to get any sort of reach at the long end is going to require some expensive long glass, be it a lens or an APO.

 

Andromeda frames nicely at 500-600mm on a FF. For most other DSO's, you'll need even more fl, a lot more,(or you could just crop down to an APS-c sensor FOV, and sacrifice your wasted pixels.)

 

BTW, good luck getting the Star Adventurer to work at those focal lengths, even with autoguiding.

 



#15 Kendahl

Kendahl

    Apollo

  • *****
  • Posts: 1114
  • Joined: 02 Feb 2013
  • Loc: Omaha, Nebraska

Posted 26 September 2018 - 12:25 AM

KEH has a well used Canon 400mm F/5.6 L USM EF lens for $648. Adorama has three of them from $729 to $879. B&H has one for $916.50.

 

For similar money, there are several wide field, triplet ED refractors with focal length reducers / field flatteners that get you near 400 mm focal length.




CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics