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Light weight APO refractor vs Telephoto

astrophotography refractor dslr imaging
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#1 Hyperion2

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Posted 10 July 2020 - 08:43 AM

Hi, I’ve been doing Astrophotography for about 3 years now and I want to start investing in a guide scope and telescope. I’m using the sky adventurer for tracking so I’m wondering if there are any good light weight (And inexpensive) refractors? Or should I consider buying fast telephoto lens?
Thank you!
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#2 Hyperion2

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Posted 10 July 2020 - 08:48 AM

I should also include some details the payload capacity is 11lbs and at some point I want to begin guiding.

#3 lee14

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Posted 10 July 2020 - 08:54 AM

Inexpensive is a pretty subjective term. There is a fairly wide price range for what people people would consider a 'good' apo. The main difference between a telephoto and even a fast apo is likely to be focal length. If your main objective is wide field, go with the camera lens. If you'd like to get a decent image scale for smaller objects, the scope will best serve you. Additionally, many folks here recommend not exceeding half the rated capacity of a mount for AP. Mounts vary significantly, but maxing out the capacity of a relatively inexpensive mount will not provide the best tracking results.

Lee


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#4 Jim R

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Posted 10 July 2020 - 09:04 AM

Try the space cat or one of the many variants of 60mm f6 doublet.

#5 Jim R

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Posted 10 July 2020 - 09:06 AM

Again, as Lee said, inexpensive is a relative term. Space cat about $800 but the doublet can occasionally be found used for about $300 including a flattener.
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#6 cst4

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Posted 10 July 2020 - 09:10 AM

I love my William Optics Z61 and think that would be a good scope for that mount.  It's the same as the Astro Tech 60mm ED scope I believe, and I think there are other rebrands too.  The next step up is a 72mm one and it would probably be light enough as well.  They are great scopes for the $.  You need the dedicated flatteners with them for quality AP.  



#7 sg6

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Posted 10 July 2020 - 09:14 AM

What is the guide scope for?

I understand the sky adventurer only has an RA drive so guiding in Dec is not possible.

Read the Skywatcher page on this and they have done their now standard bit of saying:

Built-in auto-guiding interface.

 

Doesn't actually say "Auto Guiding is possible". In effect all they have said is you can plug in to an ST4 port.

They did similar on their Newtonians when thay said you could attach a DSLR. You could attach one, what you couldn't do was get an image on one.

 

Maybe odd but what have you used up to now?

 

Small is essential on a Sky Adventurer, so you are going to need to consider the assorted 60ED's and a flattener.

The WO Redcat is another and that doesn't need a flattener.

 

After that is bigger as in the 72mm offerings and I expect that means WO 73 or an AT 72. Either may be on the too big side however. Will be close.

 

Don't think there is anything else, or at least not commonly available.

 

For a camera lens depends on the camera - assume you are attaching all this to a DSLR body. Good camera lens are expensive but can be used on the camera for normal things.

 

I would say the WO61/AT60ED is the best, would need a flattener so budget for one.

WO73 and AT72 are likely pushing your luck, especially if you add a guide scope.



#8 Hyperion2

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Posted 10 July 2020 - 09:19 AM

Thank you for everyone’s help especially so quick too! I have been considering a spacecat for sometime, but now AT60ED looks super promising.

#9 PhilA

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Posted 10 July 2020 - 09:23 AM

It is possible to guide in RA only and it works very well. The little ZWO 30mm guide and PHD2 work fine with the Star Adventurer or Sky Guider Pro and a DSLR. 

 

My take on small refractors vs camera lenses - the best solution is going to be the best glass and it probably isn't going to be inexpensive. A high quality camera lens beats a cheap refractor any day - and costs a lot more.

 

Even at this level this hobby can drain your bank account.


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#10 clemley

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Posted 20 July 2020 - 07:02 PM

PhilA is right on the money on several points - a great telephoto lens can be better than a cheap refractor, but it can also be many multiples of the price.  And I would add that telephoto lenses can be more finicky because of the range of focal ratios and so forth.  So for pure astrophotography use, I'd go with a nice, small refractor over trying to find the right telephoto lens at the right price.  I have had really good experiences using my William Optics Z61 and my Redcat 51 on my Star Adventurer, and you can get either one of them (including the necessary field flattener with the Z61) for the cost of a medium-quality telephoto lens.  One good alternative is to buy the Astro-Tech AT60ED - which is basically the same scope as the Z61 - from our friends at Astronomics, along with the field flattener, for less than the new Z61 costs alone.    

 

As for autoguiding, check out Peter Zelinka's article on autoguiding with a star tracker, along with the videos linked in the article, at this link: https://www.peterzel...e-skyguider-pro . Peter mostly uses the Skyguider Pro, but he always includes the Star Adventurer in his discussions, and he has tons of paid and free videos on both of them.  His paid courses are great from what I've seen, but I think you can find everything you'd want on this topic among the free videos linked in the article and on his youtube channel.  Good luck!   



#11 alwilder

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Posted 20 July 2020 - 07:49 PM

On the subject of using telephotos, has anyone tried the new 500/5.6 PF Nikkor for astrophotography such as deep sky applications or imaging nebula? While nowhere near the caliber of a top APO refractor like the Astro Physics 92mm F/6.65 Stowaway, I've had good luck getting lunar images with the new Nikkor. I expect shooting stars to be far more daunting task.


Edited by alwilder, 20 July 2020 - 08:08 PM.


#12 kel123

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Posted 20 July 2020 - 08:47 PM

What is the guide scope for?
I understand the sky adventurer only has an RA drive so guiding in Dec is not possible.
Read the Skywatcher page on this and they have done their now standard bit of saying:
Built-in auto-guiding interface.

Doesn't actually say "Auto Guiding is possible". In effect all they have said is you can plug in to an ST4 port.
They did similar on their Newtonians when thay said you could attach a DSLR. You could attach one, what you couldn't do was get an image on one.

Maybe odd but what have you used up to now?

Small is essential on a Sky Adventurer, so you are going to need to consider the assorted 60ED's and a flattener.
The WO Redcat is another and that doesn't need a flattener.

After that is bigger as in the 72mm offerings and I expect that means WO 73 or an AT 72. Either may be on the too big side however. Will be close.

Don't think there is anything else, or at least not commonly available.

For a camera lens depends on the camera - assume you are attaching all this to a DSLR body. Good camera lens are expensive but can be used on the camera for normal things.

I would say the WO61/AT60ED is the best, would need a flattener so budget for one.
WO73 and AT72 are likely pushing your luck, especially if you add a guide scope.


I am actually surprised that you are not familiar with the Star Adventurer. Yes, you can autoguide very well in RA. It is quite capable in what it does with telephoto lenses and small scopes of up to 400mm local length or even more, depending on weight. You need to try it one of these days, it is fun.

#13 kel123

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Posted 20 July 2020 - 08:58 PM

Thank you for everyone’s help especially so quick too! I have been considering a spacecat for sometime, but now AT60ED looks super promising.


You can also try the Sharpstar 61 EDPH II triplet. It is low weight and cost effective. Remember you are dealing with some limited capacity mount.

Also remember that you need the counterweight and declination bracket , that is the " astro kit" to use a telescope on a Star Adventurer mount. You may get a mini guide scope from ZWO or QHY of 130 mm focal length and 30 mm aperture.

#14 Traveler

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Posted 20 July 2020 - 10:14 PM

I use a Tak FS60-CB on my staradventurer with a Nikon D5500. The trick is: use a heavy duty tripod. I use a Gitzo series 5 for example.

And btw, when not doing AP, the little tak is a nice ultra G&G telescope as well. 


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#15 Hesiod

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Posted 21 July 2020 - 07:05 AM

I use a Vixen FL55ss with my Polarie tracker and it works extremely well.

Compared to telephotos has three advantages, that it is a very nice visual telescope as well (that may be, or may be not, of interest to you), it is more compact and way cheaper than a couple of primes (it could work at 320 or 230mm).

The greatest disadvantage is the lack of speed: being around f/6 at 320mm and around f/4 at 230mm it loses a lot against f/2.8 or faster teles (even if in some instances stars would be rather bad at full speed, that would make still a huge difference on large, diffuse objects where, likely, stars will be removed or reduced in PP).

A fact which may interest you is that telephoto lenses tend to be lighter than a "telescope" with the same focal length and ratio.



#16 sg6

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Posted 21 July 2020 - 07:22 AM

I am actually surprised that you are not familiar with the Star Adventurer. Yes, you can autoguide very well in RA. It is quite capable in what it does with telephoto lenses and small scopes of up to 400mm local length or even more, depending on weight. You need to try it one of these days, it is fun.

Didn't say you could not guide in RA, well or otherwise, said it has no Dec motor so you cannot guide in Dec.

Second line of my post.

Said it because I am familiar with the mount.

Hence I know the features available to it and guiding in the Dec axis is not one of them.

RA guide may be very good, what happens if the Dec drifts?

 

Said as people see ST4 port for guiding and the immediate presumption is you can go guide in full.



#17 kel123

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Posted 21 July 2020 - 07:40 AM

Didn't say you could not guide in RA, well or otherwise, said it has no Dec motor so you cannot guide in Dec.
Second line of my post.
Said it because I am familiar with the mount.
Hence I know the features available to it and guiding in the Dec axis is not one of them.
RA guide may be very good, what happens if the Dec drifts?

Said as people see ST4 port for guiding and the immediate presumption is you can go guide in full.


I think that is why it is a little, low capacity mount. It is primarily a star tracker. So, as far as you are reasonably under the payload capacity, you are fine with only RA guiding.
It is also about keeping expectations at the right place as it is just widefield star tracker.

#18 Hesiod

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Posted 21 July 2020 - 08:09 AM

DEC drift should be addressed primarily through a better polar alignment; indeed, at least in theory, the guide should intervene only to adjust the uneven tracking speed caused by the drive/gears.

Of course reality is different, but at the focals allowed to such diminutive devices the "theory" works well (the accuracy ensured by the polarscope is more than adequate to manage the sub-exposures allowed, unless are trying to take very long ones with a mono sensor; but mind that the trackers have been basically designed to be used with DSLRs, therefore it is not so strange to find issues if try to use them with very different setups).

The lack of DEC drive has however a more serious consequence as it hampers the possibility to dither automatically between frames



#19 Jarno

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Posted 22 July 2020 - 03:44 PM

My personal preference would be a small refractor. While it has its benefits, a telephoto lens will never be as good for astrophotography as a refractor. The refractor is designed solely for sharp focus at infinity and doesn't require additional optical elements for focusing or image stabilization. No matter how good the coatings and optical elements inside the telephoto are, they'll still add light scatter, reflection and absorption. They'll also never be as well collimated as those of a refractor since some of the elements have to be able to move. And finally, a telephoto lens doesn't have the fine focus control a refractor offers. The refractor will therefore always be sharper, brighter and lighter than the telephoto. But like I said there are benefits to the telephoto. The first is of course ease of use since you don't have to fiddle with adapters, just connect it to the camera and go. The second large benefit is that the telephoto will very have a large, well-corrected image circle while the refractor probably needs a flattener and you need to get the spacing just right. Plus of course you can also use the telephoto lens for normal photography.

 

TL;DR: the telephoto offers convenience and flexibility and the refractor has the best performance. Having said that, a telephoto can produce nice results as well:

 

M42%2003-S.jpg

Taken with a D3s and Nikon 500mm f/4.

 

Jarno


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#20 Bowlerhat

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Posted 22 July 2020 - 06:42 PM

I use a Tak FS60-CB on my staradventurer with a Nikon D5500. The trick is: use a heavy duty tripod. I use a Gitzo series 5 for example.

And btw, when not doing AP, the little tak is a nice ultra G&G telescope as well. 

Didn't know it's even possible. Tak is small but still rather bulky. That's impressive.

 

Refractor is where it's at, camera lens can be sharp but telescopes are solely just manufactured for that sharpness alone. Or why not both, there's redcat/spacecat/whatcat if you'd like, and it's pretty good. I wouldn't really get a  lens unless you use it on daylight to maximize it's use.




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