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

Full frame DSLR imaging with 80mm APOs

DSLR Refractor Imaging Equipment DSO Astrophotography
  • Please log in to reply
9 replies to this topic

#1 ccormsby

ccormsby

    Lift Off

  • -----
  • topic starter
  • Posts: 5
  • Joined: 19 Nov 2019

Posted 05 December 2021 - 08:33 PM

I'm in the market for an 80mm APO refractor which I want to use with a full frame DSLR (Nikon D750). I've tentatively narrowed my choice to the William Optics ZenithStar 81mm f/6.9 Doublet with a 0.8 reducer/flattener OR the Astro Tech AT80EDT triplet with its 0.8 reducer/flattener. While the triplet seems inviting, I'm concerned the AT80EDT might not fully illuminate the full frame focal plane (only because the description doesn't say that it does). William Optics advertises that the ZenithStar 81mm is designed with full frame sensors in mind. Any commentary on this choice (costs are equal; ~$1000 with flatteners) would be welcome including any alternatives in roughly the same price range. BTW, the Williams scope uses an FPL53 element  in the primary while Astro Tech just says they use ED glass ... so probably not FPL53 or equivalent. Thanks for any advice provided.



#2 imtl

imtl

    Fly Me to the Moon

  • *****
  • Moderators
  • Posts: 5,023
  • Joined: 07 Jun 2016
  • Loc: Down in a hole

Posted 05 December 2021 - 08:49 PM

Giving you my own perspective here.

What these mass production companies (WO) advertise should be taken with a grain of salt, and also be fully understood.

Fully illuminate FF focal plane just means that vignetting is going to be negligeable from the optical tube perspective. This does not mean aberration free field. You need to look at the flatenner and reducer performance and what is the image circle that will give you.

 

There is a lot more in FF imaging the just fully illuminated.



#3 ccormsby

ccormsby

    Lift Off

  • -----
  • topic starter
  • Posts: 5
  • Joined: 19 Nov 2019

Posted 05 December 2021 - 09:04 PM

Thanks for that input. I guess I was focusing on making sure the focal plane was "fully"  illuminated first and then worrying about the quality of that illumination. I have a Meade LX600 SCT with a focal reducer which does not illuminate the corners of the focal plane (hardly at all). Don't want to bump into that problem with this 80mm!

 

Any info on image quality for these or other similar scopes (over a full frame) would be welcome.

 

BTW, I should have included the Explore Scientific ED80 (triplet) in my list ... also do not know how it matches up with a full frame sensor.



#4 imtl

imtl

    Fly Me to the Moon

  • *****
  • Moderators
  • Posts: 5,023
  • Joined: 07 Jun 2016
  • Loc: Down in a hole

Posted 05 December 2021 - 09:25 PM

What I can say is that very few manufacturers actually have optics that can fully illuminate and be fully corrected for FF. And they are not in the price range of what you are asking about here.

 

I think it is also dependent on what quality you are looking for and how much of a pixel peeper are you.

 

Searching here on these specific scopes would probably give you the answers you are looking for. (I don't own this scope myself sorry)



#5 andysea

andysea

    Fly Me to the Moon

  • *****
  • Posts: 5,253
  • Joined: 03 Sep 2010
  • Loc: Seattle, WA

Posted 05 December 2021 - 10:01 PM

I would do a search on here and also on Astrobin to see what kind of images people are getting with those scopes. Full frame is very demanding.

If possible I would ask people to send single unprocessed raw frames. That is the best way to assess vignetting and field correction. 


  • drd715 and imtl like this

#6 arbit

arbit

    Mariner 2

  • -----
  • Posts: 218
  • Joined: 19 Feb 2012

Posted 05 December 2021 - 11:23 PM

Thanks for that input. I guess I was focusing on making sure the focal plane was "fully" illuminated first and then worrying about the quality of that illumination. I have a Meade LX600 SCT with a focal reducer which does not illuminate the corners of the focal plane (hardly at all). Don't want to bump into that problem with this 80mm!

Any info on image quality for these or other similar scopes (over a full frame) would be welcome.

BTW, I should have included the Explore Scientific ED80 (triplet) in my list ... also do not know how it matches up with a full frame sensor.

The ES ED80 for sure will not work with FF as the image circle maxes out at 21-37mm for FCD100 version and 26-31 for the FCD1

https://explorescien...-specifications

I dont have the AT, but am sure the specs will be out there somewhere.

Sent from my SM-N960F using Tapatalk

Edited by arbit, 05 December 2021 - 11:31 PM.


#7 matt_astro_tx

matt_astro_tx

    Vanguard

  • -----
  • Posts: 2,392
  • Joined: 19 Jan 2021
  • Loc: Dallas, Texas

Posted 06 December 2021 - 08:53 AM

I can't recommend AT's products enough for their quality.  I would recommend you give Astronomics a call and ask them about the specs of the AT-80EDT and it's ability to fill FF.  Mike will answer the phone, and he's great to talk to.



#8 ccormsby

ccormsby

    Lift Off

  • -----
  • topic starter
  • Posts: 5
  • Joined: 19 Nov 2019

Posted 06 December 2021 - 11:19 AM

Thanks so much for taking the trouble to respond. The spec sheet on the Explore Scientific OTAs is great ... I wish all manufacturers provided that data (maybe they do and I just don't know where to look). I will call Astronomics and ask them about the AT scopes.

 

I'll give a summary of what I find out on this thread.



#9 ccormsby

ccormsby

    Lift Off

  • -----
  • topic starter
  • Posts: 5
  • Joined: 19 Nov 2019

Posted 06 December 2021 - 01:14 PM

Noite: Diagonal of full frame focal plane ~43 mm

 

Explore Scientific spec sheet for ED80 triplet reports image circle diameter = 21 to 37 mm depending on focus ( => huge vignetting)

Astronomics representative only quoted one size for AstroTech AT80EDT image circle: 41mm ( => moderate vignetting)

William Optics claims their ZenithStar 81APO doublet with 0.8 field flattener covers 97% of Full Frame focal plane with its 44mm image circle.(=> minor/mild vignetting)

 

All else being equal (it probably isn't) William Optics wins on this single issue ... but for me, it is a pretty big consideration.



#10 arbit

arbit

    Mariner 2

  • -----
  • Posts: 218
  • Joined: 19 Feb 2012

Posted 06 December 2021 - 10:14 PM

Note that a reducer will decrease the image circle. ES is the native specs, while WO is with reducer. I dont know about the AT.

A meaningful comparison is possible only after accounting for the reducer you are planning.

A very good article here (see Section 4)
https://agenaastro.c...recommendations

Sent from my SM-N960F using Tapatalk

Edited by arbit, 06 December 2021 - 10:23 PM.



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





Also tagged with one or more of these keywords: DSLR, Refractor, Imaging, Equipment, DSO, Astrophotography



Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics