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First imaging refractor - What would you buy?

astrophotography refractor beginner
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#1 DrFootleg

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Posted 12 September 2019 - 07:40 AM

I've reached the point where I am ready to buy a telescope specifically to image galaxies and nebula. So far my best image was taken with a DSLR and telephoto lens.

 

med_gallery_311004_11554_4148225.jpg

 

https://www.cloudyni...dromeda-galaxy/

 

I would like the replace the camera telephoto lens with a refractor. I see the ED and APO options in the Altair Wave series for example.

With all your collective experience, what would you have bought in hindsight as your first serious imaging scope?

What will I find making me want to upgrade again if I bought something like the Altair Starwave 102 ED Doublet Refractor or Altair Starwave v3 152mm F5.9 Achromat Refractor (both similar prices, I am guessing the smaller aperture with ED glass makes some difference? Or for double the price, the Altair Wave Series 115mm F7 ED Triplet APO Refractor. All the website shop listings say the same sort of thing 'an excellent scope for imaging'.

I'm a bit lost.


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#2 Jeff Struve

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Posted 12 September 2019 - 07:49 AM

Size is not really an upgrade... quality is...

 

I recommend an 80mm triplet to start AP... It is a great wide angle scope for both imaging and visual... it is realitively small, so makes a great grab n go scope... and it works great as a guide scope if you get a large scope later on.  

 

For wide FoV I use an 80mm triplet... for a medium wide I use my 152mm f4.8 Mak/Newt and/or 152mm f9 triplet... for medium narrow I use my 11" f10 SCT... for narrow I use a 14" f11 SCT... I dont consider one really being 'better' than the other... just different tools for different jobs.

 

My 2 cents!

 

Welcome to CN and Clear Skies!

Jeff


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#3 sg6

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Posted 12 September 2019 - 08:05 AM

For imaging specifically and still I suppose the only one I count as best for imaging was the William Optics GT 81 with the (at the time) dedicated field flattener.

 

Still guess it does all it needs to with the odd fact that the flattener makes it slower. Everyone expected either faster or the same and got slower lol.gif lol.gif . Me I wanted flat, slight change in speed didn't bother me. Either 2 or 3 more exposures or each are 5 seconds longer.

 

Western civilisation and the world order did not collapse because the result was a slightly slower scope, Although from the outcry and wailing you would have thought both had.

 

Have 3 others that have apo on them - all are ED doublets but the GT 81 is the more serious imaging scope.



#4 petert913

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Posted 12 September 2019 - 08:14 AM

80mm triplet



#5 25585

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Posted 12 September 2019 - 08:18 AM

Sky Watcher Esprit 80 triplet has a good reputation. Their slower doublet ED80 also.

 

What mount will you be using?



#6 Hesiod

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Posted 12 September 2019 - 08:20 AM

Galaxies are for the most small/very small (m31 and m33 being the most notable exception in the N hemisphere), while nebulae range from huges (several degrees) to diminutive (few arcsecs wide planetary nebulae), so probably should decide first the fov/sampling you want.
Most imaging refractors 4" or less have focals IMHO too close to your lens (300-500 mm); "visual-geared" 4" ones are usually in the 700-1000 range, but take note that could be unpleasantly surprised by their lack of speed.

Reflectors or CATs could give you both focal length and speed, but at the price of bulk* (and, depending on the chosen model, new and specific issues).

*not because are reflectors, but because are FAST and therefore need larger apertures.
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#7 Gary Z

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Posted 12 September 2019 - 08:58 AM

Very nice image of M31!!!  Well all this talk of which refractor you'd get, but what mount will you be putting this scope on?

 

As anyone will tell you, the scope/lens is important, but the mount should have the priority in terms of consideration. 

 

That out of the way, the suggestions for the 80mm triplet is most sound.  But add to that, your camera and imaging train, your guide scope and guide camera, maybe a filter wheel?  Depending on your other choices, you could have a total weight on your rig up to around 7k and counterweights don't count.  So for accurate tracking, you'll want to consider a fairly robust mount.  Many consider the Skywatcher EQ6 R Pro EQ mount a good investment as an astrophotography mount.

 

Forgive me if you have a mount your happy with.  I'm just trying to prevent skipping over this detail.

 

Gary


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#8 MrRoberts

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Posted 12 September 2019 - 09:17 AM

SW Esprit 80 or WO GT81

But as spoken of  don't cheat on the mount. Nothing less than an Ioptron CEM25P. The first pic is of my CEM25P with my now sold ES FCD102. I have yet to mount the 80 on my 25P as I have been using it as a G & G setup.

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#9 bridgman

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Posted 12 September 2019 - 09:20 AM

OK, Gary just covered everything I was going to say, including "very nice M31 pic" smile.gif

 

One attribute of "the right scope" is that it is small enough for your mount to carry it well. Looks like the M31 pic used an EQ5 mount - so I *think* you would want to stay with a 70mm or 80mm scope if you wanted to be safe. Unfortunately that won't necessarily give you much of a change from the lens you used (400mm f/5.6 corresponds roughly to a typical 70mm refractor). 

 

Have you thought much about future plans for mounts ? It's probably fair to say that if you buy a scope that will work well with the EQ5 then there's a good chance you'll find yourself wanting to upgrade in the future, but you'll probably need a bigger mount as well. 

 

Take all this with a grain of salt because I have no direct experience with an EQ5 myself, just going on what others have said.


Edited by bridgman, 12 September 2019 - 09:24 AM.

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#10 Jeff Lee

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Posted 12 September 2019 - 09:32 AM

I do mostly EAA, and can say that a 4" scope seems to be the sweet spot for me (as a companion to my C8). As long as you can find a good flattener and/or reducer for the scope you buy and if you mount is "good" enough you should be set for a long while with a 4". I like to buy for the long run, and as I said I do mostly EAA, but you done your learning and seem to know what your are doing, I just think in your case a 4" APO is a better investment over the long run as you are not really a "beginner".


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#11 Bomber Bob

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Posted 12 September 2019 - 10:32 AM

I recommend an 80mm triplet to start AP...

 

I agree.  I'm cheap, so I'd look for a used Meade Series 5000 80mm F6 triplet (or the ES equivalent -- same Chinese maker).  I didn't keep mine, but the color correction & resolution was outstanding for the price.  The hardware, fit, & finish is also very good.


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#12 bridgman

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Posted 12 September 2019 - 10:44 AM

I do mostly EAA, and can say that a 4" scope seems to be the sweet spot for me (as a companion to my C8). As long as you can find a good flattener and/or reducer for the scope you buy and if you mount is "good" enough you should be set for a long while with a 4". I like to buy for the long run, and as I said I do mostly EAA, but you done your learning and seem to know what your are doing, I just think in your case a 4" APO is a better investment over the long run as you are not really a "beginner".

Yep... given that you already have the ~70mm aperture covered with the Canon lens a relatively short 4" seems like the next step up.

 

I noticed that the SkyWatcher Esprit 102ED is pretty short and might be a good candidate. I'm guessing someone on CN has done the math to combine weight and scope length / polar moment into some kind of "mount challenge index" but if so I haven't found it yet.

 

https://astrobackyar...rit-100-review/


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#13 drd715

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Posted 12 September 2019 - 11:49 AM

First get the most substantial mount you are willing to transport around. The mount and tripod will do more for your sub arc second resolution than you might think. A very critical polar alignment is essential. Refractors as they get longer in dimensions need a super solid mount, they put a lot of torque on the axis due to a long lever arm. This can cause a bit of shakiness if there is any wind over 5mph. For example if you have a CGEM it would be far better to have a CGEM-DX just for the much more substantial tripod. This is a pretty heavy mount, but I believe for astrophotography you should limit the scope size on this mount to 700 or 800 mm fl for maximum tracking resolution. You could maybe push it to 1000 mm fl if there is no wind at all.

As for a telescope, for imaging i would favor a triplet of the highest quality up to the 115/120 mm size (on an oversized mount - on a lesser mount 102 mm). The 80mm scopes are decent, but if you can afford the dollars the 102 will gather a lot more light and have a little better ultimate resolution. The 115 mm you mentioned would be great properly mounted, but that is about as far a step up over what you have that would be reasonable in a next step learning curve.

Two more things to consider. You need to get a scope with a superior focuser especially if your scope is much under F-7. The focus zone will be narrower in a faster F# and the focuser has to be tight and smooth to find the perfect focus position. Larger focusers such as a 3.7 inch version can handle the load of a camera plus flattener and maybe a future filter wheel better than a simple 2 inch focuser. So don't skimp on the selection of a focuser. 2nd. Some flatteners such as the Ricardi need more than a 2 inch hole for fittment.

The route to getting the best image possible is a chain. Each link will be the limiting factor to the entire system. The mount, the telescope, the camera etc. As your system builds. You will probably get auto guiding. Maybe a "Polmaster", maybe a Starizona "Landing Pad" (if you are using a CGEM) or other convenience items. Just keep it fun.

Sent from my SM-N950U using Tapatalk
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#14 drd715

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Posted 15 September 2019 - 01:17 AM

Check this out it seems appealing to me..

 

APM Apo Astrograph 107 / 700 mm - f/6.5 - 3" Focuser

Price

2,149.00 €

- 20%

Offer

1,719.00 €

*

Shipping

12.50 €

in stock

Add to cart

 

Also look over all the refractors on the APM  website (english version).  It's a candy store. There is a 115 in the mix  And i am drooling over the 130mm triplet with the 3.7 inch focuser.  Sub $2k.


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#15 DrFootleg

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Posted 15 September 2019 - 03:29 PM

Thank you everyone for such a wealth of useful advice. I am already aware that my EQ5 mount is not adequate for my needs. I was looking at the EQ6-R Pro, or the iOptron CEM60. But a good friend has offered to lend me a Losmandy G11, so now I am looking at what to mount on it. I thought that my next priority should be a good refractor (hence the post at the top of this thread). I plan to add a deep sky cooled camera and filter wheel after that, but for now I can continue learning with my DSLR. It appears the right refractor choice depends on what I choose to image with it (or to put it another way, I need more than one). But I really appreciated the comment about taking the next step on the learning curve. So I need something that will take me further, and better inform me on what to spend money on beyond that.



#16 MalVeauX

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Posted 15 September 2019 - 03:49 PM

Your current lens, scope, is clearly producing tight color-free stars. You have what you need now.

 

It really depends on what you want to image. If you're after much smaller, fainter objects, when sure, there's room to grow. But imaging at 900mm focal length will require significant mounting requirements and a smaller sensor camera will exacerbate this.

I would not get an 80mm APO at this time. You clearly already have a good "refractor." Your camera lens is one and it's well corrected at this scale at least.

 

You probably need to take a moment and really look into what you're looking to gain or move into. If your goal is to stay with a dSLR and keep after DSO by getting a new scope, I would say... this is not the way to go. The way to go is to use this current lens/glass you already have, its clearly good, and look into a better sensor camera, like a cooled color camera or cooled monochrome camera with an HA filter at the least and start working with this. You do not need a big fancy aperture refractor to do this. You already have a good "refractor" in your lens. You will do far better having a better camera to handle noise and narrowband to handle light pollution. And a mount is more important anyways to even allow for long exposures in the first place regardless of what you do.

 

After you get a new camera, new mount, etc, and have it all under you belt and you're producing good long exposures and collecting hours of data to do integration time, then consider a Quad APO like this.

 

DSO imaging requires:

 

1 - Time first (doesn't matter what you're doing if you don't have time to devote to integration)

2 - Mount second (can't do long exposures for hours and hours if your mount can't do it)

3 - Cooled sensor (insert narrowband & HA filter minimum if in light pollution here) (because signal to noise and calibration makes the difference)

4 - OTA (the least of your worries)

5 - Lots of processing experience/time (this is really closer to #1 but cannot be unless you have data in the first place, so it by logic must be last, but it's critical)

 

Very best,


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#17 gnowellsct

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Posted 16 September 2019 - 10:31 PM

Size is not really an upgrade... quality is...

 

I recommend an 80mm triplet to start AP... It is a great wide angle scope for both imaging and visual... it is realitively small, so makes a great grab n go scope... and it works great as a guide scope if you get a large scope later on.  

 

For wide FoV I use an 80mm triplet... for a medium wide I use my 152mm f4.8 Mak/Newt and/or 152mm f9 triplet... for medium narrow I use my 11" f10 SCT... for narrow I use a 14" f11 SCT... I dont consider one really being 'better' than the other... just different tools for different jobs.

 

My 2 cents!

 

Welcome to CN and Clear Skies!

Jeff

I'm looking at that picture OP put up and I think he would--if he is willing to put out the money for a mount--have the skills to go for a larger fast refractor.   I think he can bypass the 80mm stage.   Which one is a question of finances and production schedules on the part of the OEMs and what kind of imaging equipment he wants to use.  

 

One of the F/6 ish TS telescopes, I think they have a 125mm (friend has one) might be good.  It would be available.  

 

And of course there's the Tak Epsilon!!  Not a refractor but a powerful instrument and as far as these things go reasonably priced.  There are two, big and small.  I think he would do very well with that.

 

I just think that the OP's pic is extremely impressive and he has the skills already to benefit from top tier.  For an F/6 ish refractor I don't know of anything by TEC and or TAK.  There's the Televue NP.  There's CFF.  I already mentioned TS.

 

Greg N


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#18 DrFootleg

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Posted 17 September 2019 - 12:22 PM

Thank you for the kind words about my image Greg. Those fast refractors are a little beyond my budget at this stage (I've only been out imaging 5 different nights so far!). But maybe something like the Altair Wave Series 115mm F7 ED Triplet might be a good next step?

 

Marty, your suggestions also give me a lot to think about. I was seriously considering a cooled mono camera and filter wheel to take me further. The problem with the lens I used on the Canon is that to use it with an astro camera I'd need an adaptor (costing around £300+ I think). Now that would cover all my wide field needs given that I could use the lens (100-400mm zoom) or my wider lenses with that. the Canon DSLR has high background noise so unless a target is very bright I need multi-minute exposures to capture enough signal to rise above the noise. And it is not very sensitive at the red end so emission nebulae hardly register. If I go for the camera and filter wheel then I'd have to stick with the Canon lens for now, or use it on my 200mm f5 Newtonian (but that doesn't have a great focuser so I think I'll be making things difficult for myself there). With a refactor giving me around 600mm focal length I could continue shooting with the Canon DSLR for now, trying longer exposures if I get the loan of the G11 mount a friend has offered at some point.

 

Lots to think about, and lots of great suggestions of kit for me to read up about.



#19 Hesiod

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Posted 17 September 2019 - 12:44 PM

If want to increase the reach up to 600mm could think to the Canon extender. You'd reach roughly the same specs of the "basic" 80mm refractor (560 @ f/8): not really exciting in term of raw speed, but still somewhat manageable.

But, if are aiming at small galaxies, and feel up to the challenge, the loaned G11 could manage some very interesting options among reflectors or Schmidt-Cassegrain telescopes



#20 bridgman

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Posted 17 September 2019 - 06:06 PM

Marty, your suggestions also give me a lot to think about. I was seriously considering a cooled mono camera and filter wheel to take me further. The problem with the lens I used on the Canon is that to use it with an astro camera I'd need an adaptor (costing around £300+ I think). 

The adapter should be a lot cheaper than that... closer to £30 than £300. 

 

I use the following adapter (plus a Pentax M42->EOS adapter) to image with my old Pentax screw mount lenses on a ZWO ASI290MC. 

 

https://astronomy-im...-eos-t2-adapter

 

If I remember correctly the Canon zoom has an 'L' bracket - maybe bolt that to a dovetail and use a ring or similar to stabilize the camera, then chuck the dovetail into the mount. 


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#21 SilverLitz

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Posted 19 September 2019 - 09:49 PM

If want to increase the reach up to 600mm could think to the Canon extender. You'd reach roughly the same specs of the "basic" 80mm refractor (560 @ f/8): not really exciting in term of raw speed, but still somewhat manageable.

But, if are aiming at small galaxies, and feel up to the challenge, the loaned G11 could manage some very interesting options among reflectors or Schmidt-Cassegrain telescopes

In my limited experience, a camera lens + extender is almost a full-stop slower than the equivalent f/ telescope.  This is the difference between t/stop (light transmission) and f/stop (geometric, FL/aperture).  The camera lens + extender has many times more lenses which decrease its light transmission efficiency.  Telescopes are MUCH nicer to focus and have focal locks, as well.

 

I came to this conclusion by comparing my Canon 70-200 f/2.8L + 2x extender iii (400mm at f/8) compared to my ES ED102CF (714 at f/7) while imaging full moons on clear nights.  The proper exposure for the camera lens + extender was ~1/160, while it was ~1/400 for the telescope.



#22 DrFootleg

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Posted 20 September 2019 - 10:29 AM

The adapter should be a lot cheaper than that... closer to £30 than £300. 

 

I use the following adapter (plus a Pentax M42->EOS adapter) to image with my old Pentax screw mount lenses on a ZWO ASI290MC. 

 

https://astronomy-im...-eos-t2-adapter

 

If I remember correctly the Canon zoom has an 'L' bracket - maybe bolt that to a dovetail and use a ring or similar to stabilize the camera, then chuck the dovetail into the mount. 

Thanks for that tip. I have had the ZWO ASI290MC in my sights for some time, initially as a planetary imaging camera but realised it could double as a guide camera when I have a guideable mount. I found a supplier in the EU for the Canon lens adaptor and I already have both the 1.4x and 2x extenders for my Canon lens. So for a relatively small outlay I can try some imaging with an Astro camera and my Canon lens with and without the extenders. A much lighter weight setup than I have been using on my mount, so maybe it will allow be some longer exposures too.

The camera, Canon lens adaptor and a dovetail bar arrived in the post today, so I'll report back after my next clear night (once the moon stops being in the night sky).




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