Best 60-90mm refractor for imaging?

[HunterHarling]

This summer I'm going to replace my hyperstar with a refractor, preferable more widefield than not. So what would be a good 60-90mm wide field refractor?

[swag72]

Do you have a budget in mind? What imaging will you use it for..... Narrowband predominantly or LRGB as well? And what camera will you be using? The sensor size could affect the imaging circle of the scope...... 

[Gina]

I have the SW Esprit 80ED Pro plus field flattener and found it excellent.

[alan potts]

I guess without putting exotic words like Lzos or Lomo in the description as well as another few other high quality marques the Espirit range seem to take a bit of beating from what I have read and have seen results from and even here SW's offering would be so close to these as to barely matter. I did have here for a while a 90mm APO triplet from Telescope Services that performed very nicely, I very nearly bought one 5 years back, I believe it was F6. That said owning a APM larger scope I would go for the 100mm Espirit, fast and wide enough, if I were to buy tomorrow.

[Craney]

The 100mm APO refractor niche seems very well populated with quality scopes.   There must be a point where local seeing conditions, mount guiding accuracy and a whole host of other factors just negate the extra  £4000  ($4000)  that you could spend.

eg.  I quite fancy some counterweights for my NEQ6  hewn out of Iridium based meteorites,  but......

[alan potts]

59 minutes ago, Craney said:

The 100mm APO refractor niche seems very well populated with quality scopes.   There must be a point where local seeing conditions, mount guiding accuracy and a whole host of other factors just negate the extra  £4000  ($4000)  that you could spend.

eg.  I quite fancy some counterweights for my NEQ6  hewn out of Iridium based meteorites,  but......

I feel there are some very nice 80mm and 70mm scopes out there and of course more affordable, Gina's suggestion is nice the Espirit 80mm . TS did a nice 80mm carbon fiber scope at a bit over 1000e think they still do, never seen one but I know someone that has one and he loves it.

[Craney]

... oops, sorry @alan potts,   didn't read the original post thoroughly enough.   Yes, the 80 Esprit gets very good reviews and again is on the right side of the price inflation /rarity value as the glass gets bigger.

Still If I was going for a quality refractor, I might weigh up a larger aperture for light grasp but slightly faster than F5 to get more galaxies and smaller DSO's..... but with a decent Focal reducer available as well, which ultimately makes the scope more flexible.   (if I dare to use such a word in the same context as imaging...😮)

[HunterHarling]

14 hours ago, swag72 said:

Do you have a budget in mind? What imaging will you use it for..... Narrowband predominantly or LRGB as well? And what camera will you be using? The sensor size could affect the imaging circle of the scope...... 

Not sure about the budget yet, but i would consider anything less than $3000. I will mostly do narrowband but I will use it for LRGB for about 30% of the time. The camera will be an ASI1600 with a 4/3 Panasonic sensor.

The Esprit looks great, although most of the excellent images I have seen from the Esprit scopes seem to be from the 100mm and 150mm, for example alan4908 's excellent images.

This may be because more people have the larger scopes, or they simple produce higher quality because of aperture.

I do like the price of the Esprit though...

What about William Optics telescopes? Or Stellarvue? Does anyone get good results from these?

 

Thanks!

[vlaiv]

I have 80mm TS F/6 triplet and that one is a peach (not to be confused with lemon! - ah those fruity metaphors). With x0.79 FF/FR it is brought down to ~384mm and that will give you about 2"/px with ASI1600 (I use the same camera on my scope).

Stellarvue might have same scope under their brand - there are quite a few that have been "shared" between brands recently (same Chinese manufacturer but different branding).

Yep, here it is:

https://www.stellarvue.com/stellarvue-svx080t-25sv-premier-apochromatic-triplet-refractor/

And I think that that one is pretty much the same as this one from TS (one that I have):

https://www.teleskop-express.de/shop/product_info.php/info/p3881_TS-Optics-PHOTOLINE-80mm-f-6-FPL53-Triplet-APO---2-5--RAP-Focuser.html

Anyways, SV says that "their" optics on this scope have above 0.98 strehl, to quote them:

" SVX series optics are rated at .98 - .996 Strehl with excellent optical correction for aberrations commonly seen in mass produced optics "

I can actually confirm this - I tested my scope (self test with use of win roddier test) and got strehl in 0.98 for red channel (green was a bit poorer at 0.94, and blue the worst - this is to be expected, I did analysis with OSC camera - channels are not quite well separated on it, at 0.8. For proper analysis I'll need to redo it with mono camera and narrow band filters).

So that would be very good wide field option in those aperture ranges and budget. However, given budget, why constrain yourself to these apertures? Something in 100+ range with less than F/5 (with matching FF/FR) will give you moderate FOV range / resolution and will suck photons in faster.

 

 

[HunterHarling]

1 hour ago, vlaiv said:

I have 80mm TS F/6 triplet and that one is a peach (not to be confused with lemon! - ah those fruity metaphors). With x0.79 FF/FR it is brought down to ~384mm and that will give you about 2"/px with ASI1600 (I use the same camera on my scope).

Stellarvue might have same scope under their brand - there are quite a few that have been "shared" between brands recently (same Chinese manufacturer but different branding).

Yep, here it is:

https://www.stellarvue.com/stellarvue-svx080t-25sv-premier-apochromatic-triplet-refractor/

And I think that that one is pretty much the same as this one from TS (one that I have):

https://www.teleskop-express.de/shop/product_info.php/info/p3881_TS-Optics-PHOTOLINE-80mm-f-6-FPL53-Triplet-APO---2-5--RAP-Focuser.html

Anyways, SV says that "their" optics on this scope have above 0.98 strehl, to quote them:

" SVX series optics are rated at .98 - .996 Strehl with excellent optical correction for aberrations commonly seen in mass produced optics "

I can actually confirm this - I tested my scope (self test with use of win roddier test) and got strehl in 0.98 for red channel (green was a bit poorer at 0.94, and blue the worst - this is to be expected, I did analysis with OSC camera - channels are not quite well separated on it, at 0.8. For proper analysis I'll need to redo it with mono camera and narrow band filters).

So that would be very good wide field option in those aperture ranges and budget. However, given budget, why constrain yourself to these apertures? Something in 100+ range with less than F/5 (with matching FF/FR) will give you moderate FOV range / resolution and will suck photons in faster.

 

 

That looks interesting. Could you post some images you've take with it?

I would like a 100mm, but I would probably need to get it secondhand. 

[vlaiv]

I did not get much chance to use it, but here are couple of examples (all taken red/white border, mag 18.5 skies):

About two hours of exposure - lum only, testing out flattener - did not get spacing right, and had some trouble with tilt - edge stars suffer a bit. Check out full res of it for details.

Here is one full color version, maybe lacking in processing - this is about 18-19h total 7h lum and 3x4h per color or something like that:

 

[HunterHarling]

19 hours ago, vlaiv said:

I did not get much chance to use it, but here are couple of examples (all taken red/white border, mag 18.5 skies):

About two hours of exposure - lum only, testing out flattener - did not get spacing right, and had some trouble with tilt - edge stars suffer a bit. Check out full res of it for details.

Here is one full color version, maybe lacking in processing - this is about 18-19h total 7h lum and 3x4h per color or something like that:

 

That's great for red zone light pollution. It definitely has more detail than my hyperstat. How do you think this scope would compare with an Esprit 80?

[vlaiv]

16 minutes ago, HunterHarling said:

That's great for red zone light pollution. It definitely has more detail than my hyperstat. How do you think this scope would compare with an Esprit 80?

Honestly, I have no idea

I think that quality wise they are about the same - both are very good. I think that this scope can be faster than Esprit80 if you pair it with good FF/FR. Esprit is F/5. This one can be as fast as F/4.5 with fairly large flat/corrected field - but at a price. I think one of best FF/FRs can be paired with this scope - Riccardi FF/FR. It's not cheap though.

https://www.teleskop-express.de/shop/product_info.php/info/p11122_Riccardi-0-75x-APO-Reducer-and-Flattener-with-M63x1-Thread.html

 

[alan potts]

4 minutes ago, vlaiv said:

Honestly, I have no idea

I think that quality wise they are about the same - both are very good. I think that this scope can be faster than Esprit80 if you pair it with good FF/FR. Esprit is F/5. This one can be as fast as F/4.5 with fairly large flat/corrected field - but at a price. I think one of best FF/FRs can be paired with this scope - Riccardi FF/FR. It's not cheap though.

https://www.teleskop-express.de/shop/product_info.php/info/p11122_Riccardi-0-75x-APO-Reducer-and-Flattener-with-M63x1-Thread.html

 

At that reduction it's the time to buy it, I got a secondhand simialar TS Red 0.79 and that is expensive enough at 380e, normally Riccardi are 700e area.

Alan

[DaveS]

I've got a Ricardi reducer, and yes, it's damn good.

[HunterHarling]

Also I forgot to mention, the scope needs to have a full frame corrected field, as I will use a Nikon d810a with it. Is the reccardi reducer available in the USA?

[ollypenrice]

1 hour ago, HunterHarling said:

Also I forgot to mention, the scope needs to have a full frame corrected field, as I will use a Nikon d810a with it. Is the reccardi reducer available in the USA?

Ah, now this is a game changer because very few smaller scopes cover full frame. And beware of the fact that there are one or two manufacturers who claim that their scopes cover full frame when, in reality, they either don't do so at all or only do so if the QC has resulted in a good example. If you are willing to buy second hand you could do a lot worse than an older fluorite Tak FSQ106N. These should come in on budget and are easy to like. We use two of them here with full frame cameras. The later ED versions of the FSQ106 are prone to focus drift during cooldown (which can mean all night) and are very expensive. Here's an example of a full frame image from our FSQ106N:

https://www.astrobin.com/full/383965/0/

Olly

 

[vlaiv]

According to spot diagram of Riccardi reducer it is almost likely that it will cover full frame. Field correction and illumination is quoted at 42mm.

Here is spot diagram when paired with 80/500 APO

At 21mm off-axis distance star shape is still round. This is with F/6.25 scope. With F/6 - things are probably going to be somewhat worse, just tiny bit?

 

[ollypenrice]

4 minutes ago, vlaiv said:

According to spot diagram of Riccardi reducer it is almost likely that it will cover full frame. Field correction and illumination is quoted at 42mm.

Here is spot diagram when paired with 80/500 APO

At 21mm off-axis distance star shape is still round. This is with F/6.25 scope. With F/6 - things are probably going to be somewhat worse, just tiny bit?

 

Tak claim 44mm for the FSQ85 and that certainly won't cover full frame as I know from two examples of the scope. I wouldn't buy anything from which I hadn't seen full frame images. You cannot trust the published claims.

Olly

[HunterHarling]

12 minutes ago, ollypenrice said:

Ah, now this is a game changer because very few smaller scopes cover full frame. And beware of the fact that there are one or two manufacturers who claim that their scopes cover full frame when, in reality, they either don't do so at all or only do so if the QC has resulted in a good example. If you are willing to buy second hand you could do a lot worse than an older fluorite Tak FSQ106N. These should come in on budget and are easy to like. We use two of them here with full frame cameras. The later ED versions of the FSQ106 are prone to focus drift during cooldown (which can mean all night) and are very expensive. Here's an example of a full frame image from our FSQ106N:

https://www.astrobin.com/full/383965/0/

Olly

 

Yes, the Tak is definitely excellent. However a new version would be too expensive and an older one might be hard to come by. I'll look for one though. 

Would an Esprit 100 be able to handle full frame? Has anyone here had experience with one?

[vlaiv]

Btw, for US retailer, quick google search returned this:

https://skygazeoptics.com/products/apm-riccardi-apo-reducer-0-75-x-m63-small

[vlaiv]

1 minute ago, HunterHarling said:

Yes, the Tak is definitely excellent. However a new version would be too expensive and an older one might be hard to come by. I'll look for one though. 

Would an Esprit 100 be able to handle full frame? Has anyone here had experience with one?

Have a look here, recent thread:

There is a link to a blog post by someone using Esprit 100 and Riccardi reducer. They claim that stars look better with Riccardi FF/FR compared to SW flattener for Esprit. However, sensor is rather small being Atik383.

[HunterHarling]

7 hours ago, vlaiv said:

Have a look here, recent thread:

There is a link to a blog post by someone using Esprit 100 and Riccardi reducer. They claim that stars look better with Riccardi FF/FR compared to SW flattener for Esprit. However, sensor is rather small being Atik383.

Interesting. My only concern would be if the field covers full frame with the reducer. What focal ratio would this bring it to?

[swag72]

Good points made about trying to get an imaging circle that will cover your full frame camera. I think I'd be going to a very friendly retailer and telling them exactly what you want and making it clear that you will be returning the scope if it doesn't entirely cover your full frame sensor. Don't let anyone say that it's OK if the edges aren't great, its only a small amount and you can crop it out...... No you want to cover the whole frame and that's that.

The Tak FSQ106 is the obvious answer when knowing the imaging circle needed - The rest I think will be a little suck it and see (hence the friendly retailer!) 

Aren't there some WO scopes claiming that their imaging circle is sufficient to cover a full frame sensor?

[fwm891]

Picking up on Sara's point about WO's I have just got a ZS 73 with the Flat 73A 1x field flattener. It's a 430mm fl at f5.9 and I've just been 'playing' with it on a star adventurer with my Nikon 800E

I've attached a 180s sub, 1250 iso with a 300% inset from the top left corner. I know it's on a star Adventurer mount so not the best. This is at it's standard back focus position and I'm just playing with the adjusted to see what difference small changes make...