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Options for fast Astrograph

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#1 ispybadguys

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Posted 26 July 2021 - 03:27 PM

I am wondering what might make a good choice for a fast astrograph as a alternative to a RASA. I started looking at Officina Stellare Veloce RH 200 but I am wondering if the 55% obstruction isn't such a great idea and that maybe a APO would be better.

 

Thanks 

 

Kurt



#2 Tapio

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Posted 26 July 2021 - 03:42 PM

It depends how fast you want, how wide image circle and how deep are your pockets.


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#3 rockstarbill

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Posted 26 July 2021 - 03:52 PM

Epsilon
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#4 photoracer18

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Posted 26 July 2021 - 05:41 PM

An older Tamron 60B 300mm F2.8 Adaptall 2 lens can be had in the $400 range. The last version 360B model cost some more then that. The Adaptall mount system includes ones for Canon EF, Nikon AI Pentax KA, and Minolta Alpha (Sony). Even AF 300/2.8 lenses can be had in common mounts like Nikon or Canon and used manually. I personally own a Tokina AF300/2.8 AT-X Pro SD II in Canon EF that is very good and cost me $700 on the used market. Pentax and Canon have made 400 F2.8 in the past ($$$). Then there is the SharpStar 150 F2.8 astrograph Newt. I think one is for sale on AM right now. That is about the size of a 400-450mm F2.8 camera lens but much lighter. Its almost prohibitive to make a lens at F2.8 any larger than around 400mm because the front element is the same size as a 6" APO and about the same cost. Smaller lenses can be made faster but not with the reach.



#5 ispybadguys

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Posted 26 July 2021 - 06:34 PM

Thanks. I’m glad you mentioned the lenses. I have a Sony A7R4 full frame camera and have considered the 400mm F2.8 and the 70-400 F4. I have the 200-600 F5.6.  The only complaint I have is how difficult it is to get perfect focus and the focus drift you get after a hour or so. I use the electronic remote control to focus which I can step the focus one step at a time with this. The problem is that the focus magnification isn’t enough to really to get the best focus. I say all this because I need a lens that can be remote focused. I have read that Minolta lenses fit the camera but I bet the electronic functionality isn’t there. These Sony lenses are 150mm and 95mm respectively. The 400 F2.8 I might buy if used but if I was going to drop $12k on a solution there would be probably some cheaper options.

 

The Sharpstar is a great option. I didn’t know this existed. I will take a look.

 

Kurt



#6 Todd N

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Posted 26 July 2021 - 07:38 PM

Thanks. I’m glad you mentioned the lenses. I have a Sony A7R4 full frame camera and have considered the 400mm F2.8 and the 70-400 F4. I have the 200-600 F5.6.  The only complaint I have is how difficult it is to get perfect focus and the focus drift you get after a hour or so. I use the electronic remote control to focus which I can step the focus one step at a time with this. The problem is that the focus magnification isn’t enough to really to get the best focus. I say all this because I need a lens that can be remote focused. I have read that Minolta lenses fit the camera but I bet the electronic functionality isn’t there. These Sony lenses are 150mm and 95mm respectively. The 400 F2.8 I might buy if used but if I was going to drop $12k on a solution there would be probably some cheaper options.

 

The Sharpstar is a great option. I didn’t know this existed. I will take a look.

 

Kurt

 

You might consider Borg(Hutech). They are modular systems so they can be configured in any number of ways. 

 

BORG 107FL F3.9ED

https://digiborg.wor...ercial-package/

 

Other Borg systems

https://hutech.com/Telescope.htm



#7 luxo II

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Posted 26 July 2021 - 08:14 PM

I am wondering what might make a good choice for a fast astrograph as a alternative to a RASA. 

A Celestron SCT of your choice + matching Hyperstar (from Stellarvue) + camera, resulting in about f/1.9 - f/2 depending on which exact ones you settle on, appears to be a pretty reasonable alternative price-wise.

 

The starting point is a C6 + HyperStar V4 for the C6 + ZWO ASI533, you can use a C8, C9.25 or C11... also note it is necessary to choose the Hyperstar to match the exact scope - aperture, an EdgeHD or standard SCT, and for the standard SCT's, how old; and then there is a spacer ring required to suit the camera used.


Edited by luxo II, 26 July 2021 - 08:17 PM.


#8 ChrisWhite

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Posted 27 July 2021 - 08:47 AM

I have no experience with epsilon but the new 160 is a rave from what I understand. You can use mono with filter wheel easily (unlike hyperstar) and correct for a full frame field with ridiculously good off axis performance.

If i wanted fast I'd look at this newish scope from tak.

#9 ispybadguys

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Posted 27 July 2021 - 08:56 AM

I must confess when I saw Bill’s most efficient post I didn’t know what he was talking about. Now after a quick Google both me and the Chinese know about this. I am thinking I will get the 130. It isn’t an manly aperture (am I allowed to say that) but I want something wide. I will need a electronic focuser that EKOS supports. Do I need something to adjust tilt?

 

Kurt


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#10 RajG

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Posted 27 July 2021 - 03:00 PM

There is a Sharpstar 130 f/2.8 listed for sale on CN classifieds for $1400 in case you are interested.

 

Since you mentioned that you have a Sony DSLR, you could also consider the Samyang (or Rokinon) 135mm f/2 for wide-field. For even wider options, there are the Voigtlander Apo-Lanthar f/2 lenses (35mm, 50mm and 65mm) which are designed for Sony e-mount (they also have a Leica mount version).



#11 Headshot

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Posted 27 July 2021 - 04:09 PM

The May 2014 issue of S&T has an excellent di Cicco review of TAK's (then) New Epsilon 130 D Astrograph. It is worth reading if you are looking for a decent astrograph.



#12 rockstarbill

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Posted 27 July 2021 - 08:28 PM

I must confess when I saw Bill’s most efficient post I didn’t know what he was talking about. Now after a quick Google both me and the Chinese know about this. I am thinking I will get the 130. It isn’t an manly aperture (am I allowed to say that) but I want something wide. I will need a electronic focuser that EKOS supports. Do I need something to adjust tilt?

Kurt

Sorry was on mobile so I tend to be brief. The 130 is a good price to performance scope. The mechanicals are a little dated but AndySea here on CN knows that scope inside and out. The e160ed is a refresh of the older design, has updated mechanicals and a very impressive corrector. Probably worth the premium pricing. The e180 is the speed demon of the bunch. Uses an older corrector but everything else is modern. For a fast newt with a big corrected field it's probably your best bet.

You don't have much room on the Epsilon (56.2mm) so a tilt corrector could be a big challenge.

Edited by rockstarbill, 27 July 2021 - 08:31 PM.


#13 ispybadguys

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Posted 28 July 2021 - 10:14 PM

No need to apologize. You made my brain work and I thought you reply was like a clue in a scavenger hunt. Everyone here has been very helpful. I found a used Epsilon 130 in mint condition  for $2675 with accessories ~$4K new but then started second guessing mostly because I am worried about having  to worry about collimation and tilt correction. Maybe this is unfounded and the egos of my 1968 Tasco 4.5 inch alignment pains should be forgotten after 50 years. The E130D is 430mm F3.3.

 

There is a mint Epsilon 180 complete system worth $7K new for $3980 F2.8 500mm.

 

I also found a used TAK FSQ85 with a .73 reducer which gives F3.8 unobscured 327mm for $4200. .  I also found an SVX80TR 480mm F6 for $1700 on CN I could add a 0.8 reducer and get F4.8 at 384mm. I think what I would love is the FSQ-106DX4 with 0.68 reduce for and F3 318mm. I heard that these are impossible to get.

 

So many choices 

 

Kurt



#14 luxo II

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Posted 28 July 2021 - 10:44 PM

C8 + hyperstar + ASI2600 would be half that cost - focal length 400mm at f/2.


Edited by luxo II, 28 July 2021 - 10:45 PM.

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#15 555aaa

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Posted 29 July 2021 - 12:05 AM

May I gently ask why? It should be because you want a very wide field at maximum physical aperture. Most fast telescopes like the RASA have a low Strehl (not diffraction limited) and if you have good enough seeing that’s actually detrimental.
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#16 luxo II

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Posted 29 July 2021 - 05:01 AM

Strehl  of the optics is almost irrelevant in this case - at this image scale envisaged the camera won't be anywhere near close to diffraction limited. 



#17 555aaa

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Posted 29 July 2021 - 08:36 AM

Strehl of the optics is almost irrelevant in this case - at this image scale envisaged the camera won't be anywhere near close to diffraction limited.

It’s relevant if you want to image faint objects because as the spot size increases the limiting magnitude gets worse. There’s no point in buying a fast astrograph and putting a little chip on it. It’s not really possible to answer the OPs question without knowing what camera will be used to cover what size field.

#18 ispybadguys

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Posted 29 July 2021 - 08:54 AM

Vender

 

I am not offended by any questions. I got started in February with a CEM70EC and a Sony 200-600 F5.6-6.3. Focusing and keeping focus has provide countless hours of frustration. I have gotten only a couple of good collections of Rho O and M8 and these seem to need more that the hour I got at F5.6. I have a CDK12.5 on order so I have the long focal length end covered.

 

I looked at the RASA and I would need a camera for the 8 inch and maybe the 11 would work with my Sony but the configuration and F2 suggests more frustration to me. So like $6000 for the RASA and camera and electronic focus and I get one focal length.

 

Kurt



#19 rgsalinger

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Posted 29 July 2021 - 09:07 AM

I've watched too many people struggle with the RASA and the Hyperstars to feel comfortable with them as slam dunk recommendations. I would strongly urge anyone buying one to get with someone who uses one if possible to see the challenges. For some people, getting the tilt/collimation/focus just right is, if not easy, straighforward. For others, it will be an exercise in futility. My own recommendations would be a fast refractor or one of the Tak Epsilons. Again, any fast reflector is going to require more care and tending than a roughly equivalent fast refractor. My two observatory partners use Taks and produce wonderful data with them. 

 

I'm pretty happy at F5.2 with my Tv127is. I recommend the Taks over it but it's a close race. My scope is no 11 years old and still in fine fettle. The build quality is excellent and you can get a reducer to take it down to F4 is you like. 

 

I don't want to hijack the thread but I really can't see a PW 12.5 CDK working well on a CEM70EC. While the tube is shown as weighing only 46 pounds, once you add the focuser and the extra dovetail (really needed if you plan to carry the scope) you're over 50 pounds. Add in an imaging system and it's not hard to reach 60. The other big problem is that all of the weight is at the back of the system. That gives the mount a real workout because of the 31" moment arm. I can provide a lot more discussion in a different thread, but I would get something like a Mach2 or a CEM120 (budget choice) or the MX+ that mine is mounted on. 

 

So, my recommendation is to just get a fast refractor. Perfect the problems of tilt and focus and then consider if a fast reflector really makes sense or is necessary. Just another opinion. 

 

Rgrds-Ross 


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#20 555aaa

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Posted 29 July 2021 - 09:20 AM

Dslrs don’t work well with the RASA 11 for two reasons: first, the lens attachment opening is far too small so you lose all the corners and secondly, you still need to add tilt adjustment which is a consequence of how you have to collimate the RASA lens group. So I am with Ross there and a medium fast refractor is the most pain free option. I like the little Tak Newts and for your dollar an 8” f/4 Newtonian with a coma corrector is very versatile when you start adding guiders and filter wheels.

#21 RichA

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Posted 29 July 2021 - 09:35 PM

An older Tamron 60B 300mm F2.8 Adaptall 2 lens can be had in the $400 range. The last version 360B model cost some more then that. The Adaptall mount system includes ones for Canon EF, Nikon AI Pentax KA, and Minolta Alpha (Sony). Even AF 300/2.8 lenses can be had in common mounts like Nikon or Canon and used manually. I personally own a Tokina AF300/2.8 AT-X Pro SD II in Canon EF that is very good and cost me $700 on the used market. Pentax and Canon have made 400 F2.8 in the past ($$$). Then there is the SharpStar 150 F2.8 astrograph Newt. I think one is for sale on AM right now. That is about the size of a 400-450mm F2.8 camera lens but much lighter. Its almost prohibitive to make a lens at F2.8 any larger than around 400mm because the front element is the same size as a 6" APO and about the same cost. Smaller lenses can be made faster but not with the reach.

Those Tamrons are terrible lenses for deep-sky work as they are only corrected to about 1 wave.  Besides, if he's talking a Veloce or a larger apo, he's really not in the market for old (70-80's) in the $400 bracket.  Even a modern $5000-$9000 300mm f/2.8 from one of the "big two" camera companies probably won't be as good as a dedicated imaging telescope. 


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#22 ispybadguys

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Posted 29 July 2021 - 11:53 PM

Thanks to all. I guess all the comments on the RASA and fast astrographs resonate with me. I think I am going to get the TAK FSQ85-EDX. It comes with the 0.73 reducer which gets me F3 and is about $400 less that new without the wait. I need to figure out how to add electronic focus compatible with EKOS.

 

I do have the same concerns with the CEM70. I am getting an OAG and night crawler and with the camera I am guessing something like 52-54 lbs. The 70EC is kind of heavy already so I can' imagine a 120. Maybe I will be putting my 4 month old  CEM70EC on CN the week after I get the CDK. I do like the Epsilons.



#23 OldManSky

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Posted 30 July 2021 - 12:34 PM

I decided to try one of these:

 

https://agenaastro.c...ca_s_color=6321

 

It just arrived.  First light with an ASI183mm and ASI2600MC should be in a week or so.

Initial impression is of outstanding fit & finish.  It was close to collimated when it arrived.  Very nice case it comes in.

smile.gif

 

 

 

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Edited by OldManSky, 30 July 2021 - 12:34 PM.

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