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Help me choose a refractor

astrophotography equipment refractor imaging
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#1 radix655

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Posted 28 September 2020 - 01:32 AM

I have taken images of Orion nebulae, M31, M33 (very faint), and Pleiades with my Sony A7R II 85mm (127.5mm in crop mode) with no tracker. I feel slightly confident (like everyone) after this and want to dive deep into astrophotography.

 

1. Meade 6000 Series 70mm - f5 Quadruplet APO (350mm)

2. William Optics ZenithStar 73 - f/5.9 Doublet APO (430mm)

3. RedCat 51 - f4.9 APO (250mm)

4. Explore Scientific ED102 - f7 APO (714mm)

 

I am planning to use this mostly to shoot nebulae and some galaxies. I will be purchasing ASI533 once I am comfortable with using refractor with mount

 

I would like it to be fairly fast as I live in the outskirts of Chicago (bortle 7-8 skies).

 

My understanding:

1. William Optics as it is now far behind Meade but with field flattener it will probably come close to Meade ~5.3 and has longer reach (1.6x) than Redcat

2. Meade as it is the second fastest with reasonable focal length. I have nothing against it, but, price seems to be steeper than z73 however this is faster

3. RedCat 51 as it is the fastest however short focal length. My only concern is the shortest focal length out of all the 4

4. ED102 in the list because it has good reviews, I don't know if I am missing something with it, that's why it is in my list even though it is slower than the rest however longer focal length. I didn't choose ED80 version based on this review - https://www.amateura...ial-series-ed80

 

 

 

 

 

Please help me decide between these refractors or a better one with a 1200$ budget.


Edited by radix655, 28 September 2020 - 01:44 AM.


#2 bobzeq25

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Posted 28 September 2020 - 02:04 AM

The crucial information is missing.  What mount will you be using?

 

It's nit just a matter of weight capacity, focal length multiplies tracking errors.  The overall effect is large.  The 102 will require a mount that's maybe 2X the cost of what the Redcat would require.


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#3 Hesiod

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Posted 28 September 2020 - 02:27 AM

Indeed. You may use the RedCat with a star tracker or a "lowly" mount, but would do a big favor to yourself to pair the 102ED to a good mount (if are keen on galaxies, even an eq6/atlas, since will leave more room to handle longer focals).
As a personal preference I would pick the RedCat anyway, since will give you the widest field and there is an awful lot of huge nebulae.

#4 radix655

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Posted 28 September 2020 - 02:38 AM

@bobzeq25 My mistake, I am planning to use a eq6r to leave room if I were to get a newtonian in the distant future for longer focal lengths to shoot galaxies or planets up close.



#5 awong101

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Posted 28 September 2020 - 03:04 AM

Out of the 4, I am going to recommend the William Optics Redcat 51. If you are a beginner like I am (I'm ~ at most, 2 months into this), wide field/low focal length will give you some results quickly. From my short experience so far, there are a LOT that will down right demoralize you in this hobby. I personally have the Spacecat color, and it's been my gateway into this hobby along with a light, inexpensive, and portable mount Sky-Watcher Star Adventurer Pro

 

Pros for the Redcat

- It handles like a normal camera lens

- Fantastic images

- Quality build (just hold onto one and you'll see what I mean)

- Low focal length means you won't get lost in space.

- The wide field means you'll spend less time looking for stuff because you're not that zoomed in, and more time shooting

 

Con for the Redcat

- It's borderline luxury item

- William Optics nickle and dime the hell out of you for accessories/add-on

- People put them back onto the market as used items but with like-new pricing, because they're in such demand and everyone is out of stock

 

 

I too have the Explorer Scientific ED102, and recently got an upgrade to the HEQ5 Pro mount. But I am going to hold off on the ED102 and continue using my Spacecat because learning a computerized mount isn't easy as I would have thought. I already had trouble framing my targets due to the how zoomed in I was with the ED102 at 714mm. I'd like to spend at least a few weeks with a familiar equipment (Spacecat 51) while learning an entirely new rig (HEQ5 Pro)

 

As for the rest of your choices. Here are my thoughts because I am passively shopping still:

1) Meade 6000 series 70mm Quad - Sorry, that's $1,200 for 350mm. It is an luxury item. I can think of many alternatives since a beginner like me likely won't be able to appreciate how great this scope is. I think it would make more sense for a beginner to use a more affordable doublet like. I mean, there's not much of an upgrade room after this quad, right?

2) William Optics Zenithstar 73 - It sure is pretty, would love to get one if people aren't selling used William Optics stuff with like-new prices. I would cross shop with Astro Tech's offering in this focal length as well.

3) Explore Scientific ED102 - I have this scope sitting around. Personally, its focal length poses a big challenge for me. Finding and framing targets have been difficult with this focal length.

 

As for alternatives, for the 300/400mm range, have you considered Astro Tech AT60ED, and Astro Tech AT72EDII?


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#6 radix655

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Posted 28 September 2020 - 04:44 AM

@awong101 Astro Tech AT72EDII seems very good. It uses good glass and is reasonably fast and light.

 

I am also tempted by Redcat51, but, the focal length seems too wide. I have a 200mm lens and I can use it on my crop sensor Nikon d7200 to achieve an effective 300. Redcat51 seems to be only 50mm longer than it. I don't know if I will miss too much if I don't buy it.

 

Thanks for a very good recommendation. I will buy a Astro Tech AT72EDII if it has all the accessories like a field flattener, T mount adapter (Sony/Nikon). I don't know what else I would need if I were to buy a ASI 533. Did you ever use it?



#7 MrRoberts

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Posted 28 September 2020 - 09:22 AM

I really like my Esprit 80, but it is a little beyond you $.

So how about the     ASTRO-TECH AT80EDT F/6 ED TRIPLET REFRACTOR OTA


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#8 drd715

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Posted 28 September 2020 - 09:58 AM

It's mo re e about what size is the object you wish to image. Take the various focal lengths between 250mm and 800mm then plug them into an imagining preview program with data on the physical size of the sensor you are using. This way you can "frame" the selected objects and see how they fit into a field of view. This may help you in choosing the telescope focal length and therefore the telescope itself.

If you are looking at the AT-102ED then you should instead look at the AT-102EDL as a better imaging scope.

Lots of choices out there - pick your focal length first. If you are going lower than F-6.5 in effective local length (with reducer flattener) then a triplet becomes more desirable. F-7 super ED doublets are quite good in their native focal length .


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#9 bobzeq25

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Posted 28 September 2020 - 10:52 AM

It's not only about what objects you want to image (experienced imager concern), it's about what scope will help you learn faster/better/cheaper.  There are targets for all scopes, you'll learn faster... if you start with bigger ones, makes it easier to diagnose issues.  There will be issues.  <smile>

 

The mount is great.  For right now I'd stick an inexpensive F6 AT72EDII on it, it will be a great learning tool.  The 533 is a fine choice. 

 

The other thing you'll need is an autoguiding system.  You could maybe "get away" without one right now, but autoguiding is a necessary skill to learn, and it's useful to take one source of problems out that could confuse issues.  The guidescope/guide camera can be cheap, I recommend the ZWO120MM mini and this guidescope (I have the 60mm version).

 

https://www.amazon.c.../dp/B0156ICXMI/

 

It's better, but not necessary at this focal length, to throw away the finder shoe, and mount the rings more solidly.  The important thing is to learn to autoguide.


Edited by bobzeq25, 28 September 2020 - 10:53 AM.

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#10 coblr

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Posted 30 September 2020 - 01:34 AM

The ASI533 comes with an M42 threaded adapter that will screw on to the AT2FF for a 2" focuser. It also comes with a M42 T-adapter that screws on to give the camera a 1.25" nose. You don't need the flattener now, but if you want it all at once you might as well get it too.

 

If you're using the ASI533 and a scope, you don't need anything extra.

If you're using the ASI533 with a flattener and a scope, you don't need anything extra, but the scope should have a 2" focuser for the field flattener. I recommend the AT2FF if you're going with an AT72EDii/AT80EDT.

Scope => 2" Flattener => M42 Adapter => ASI533

Scope => 1.25" Adapter => M42 Adapter => ASI533

 

You mentioned a Nikon adapter but I'm not sure how you meant.

If you're using a Nikon with the scope, you'll need a Nikon to M42 adapter. The Nikon won't screw onto the field flattener or any other nose piece that fits in a focuser.

If you're using a camera lens with the ASI, you'll need an M42 to Nikon lens adapter. The lenses won't screw on to the threads on the ASI.

 

Scope => 2" Flattener => M42-to-Nikon Adapter => Nikon (adapter plugs into camera, screws onto flattener)

Nikon lens => Nikon Lens-to-M42 Adapter => ASI533 (adapter plugs onto lens, screws onto camera)

 

BTW, I also recommend the AT72 or AT80EDT. I bought an AT90EDT more than 10 years ago and it's still a great scope. The optics are great.

 

Good luck!


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#11 radix655

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Posted 02 October 2020 - 05:08 PM

That's a very neat explanation of what I would need when buying a scope. Thank you @coblr.

 

I wanted to try this option so I can learn some stuff here and there before full foray into cooled camera.
Scope => 2" Flattener => M42-to-Nikon Adapter => Nikon (adapter plugs into camera, screws onto flattener)

 

As recommended by people who have been doing this for a while, I will go with AT72EDII.

 

Does any M42 to Nikon F Adapter fit the flattener like it needs to be certain width? I am wondering if it affects backfocus in any way. I searched in amazon and it gave me bunch of results



#12 coblr

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Posted 08 October 2020 - 01:06 AM

I believe most, if not all field flatteners will have male M42 threads on one end and a 2" barrel (like a 2" eyepiece) on the other. The M42 Nikon adapter should have female M42 threads on one side (so that it screws onto the flattener) and the other side locks into the camera body like a camera lens. "M42" stand for "(Metric) 42mm diameter" so all M42 is the same. Just make sure all the male and female directions match up. It seems that Nikon is just Nikon (i.e. NOT Canon, et al.) so unless Nikon F is somehow special from other Nikon connectors you should be ok.

 

20201007_224015.jpg

 

As far as focus from the primary, you should be able to reach it ok, but it will be further out than you would be with a diagonal. The bigger question is the back focus from the flattener to the sensor. Flatteners require a specific distance from the glass to the sensor or else it'll always be out of focus no matter what.

 

You can find out how much back focus your flattener will need by reading the description or tech specs for it.

Look up that number, then find how much your adapter will eat up plus how deep the sensor is inside the camera body. If the adapter and camera depth add up to to the flattener's back focus, then you're good. Otherwise, you'll need to look at spacers to reach that distance.

 

For example, I used the AT2FF and a Canon Rebel. The AT2FF requires 55mm (+/- 4mm) of back focus and while I didn't measure it exactly, it seemed to work out ok being screwed directly onto the adapter and plugged into the camera. The adapter probably adds like 10 or 15mm. I'm not sure. I just rolled with it as all the parts just fit together. When I moved to an ASI camera, I had to add a 30mm spacer because everything was just so much closer to the flattener.

 

20201007_225025.jpg

 

 



#13 alphatripleplus

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Posted 08 October 2020 - 09:58 AM

 

As recommended by people who have been doing this for a while, I will go with AT72EDII.

 

 

I also have an AT72EDii on order, intended primarily for EAA with small sensor cameras. I'll probably try it first without a flattener.




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