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Choosing new refractor

Sky-Watcher Esprit 100ED ZWO ASI2600MM Pro Equipment Refractors Buying Advice
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Jimmazing1 avatar
Jimmazing1 avatar
I'm currently imaging with a William Optics ZenithStar 61II (360mm, f/5.9) paired with an ASI2600MM Pro. I think it's on the under-sampled side of things so I'm looking to find a better mate for the ASI2600MM.

I'm in a Bortle 7.5+ zone so I pretty much only do narrowband imaging of nebulae. Using a CEM70 mount, 7-position EFW, EAF, and OAG.

I'm trying to decide between:
Sky-Watcher Esprit 100ED (550mm, f/5.5) - Seems to be a lot of this pairing on Astrobin
William Optics FLT 91 (540mm, f/5.9)
Askar FRA600 (600mm, F5.6)
Askar 80PHQ (600mm, F7.5)

I've been tempted by the long focal lengths, but it seems like I've got tons of widefield targets to work through before reaching out further.

Given my imaging environment and equipment, does one from that list stand out? Any that I'm missing that I should consider?

Thanks all!
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Sean Mc avatar
Sean Mc avatar
It’s not easy to beat an esprit. With the phq, you gain virtually perfect stars, and remove the need for backspacing at the expense of speed. The FRA 600 is pretty damn good and reasonably fast. 

The FLT, well… I’d do some searches on the problems many users face, as well as taking a look at images from that scope. I gambled twice on an FLT 91 and lost both times so I’m jaded. Sure there are some that look good, but I’ve found MANY images where users proclaim virtual perfection, and it’s obvious that their scope has astigmatism. YMMV ¯\_(ツ)_/¯  

After saying all that, I did some FOV calculations and found that 500-550mm FL is just a smidge too small for my liking. I’d rather have 400ish to frame more targets without the need for mosaics. Either that or 900mm+

So yeah, I went with the 65phq. If you’re undersampled, dither and drizzle.
Joe Linington avatar
Joe Linington avatar
My choice without handling any of them would be the FRA 600, the optional 0.7x reducer offers some nice flexibility and speed.
Jan Erik Vallestad avatar
Jan Erik Vallestad avatar
I went through this decision last year and ended up with the Esprit 100ED and I couldn't be happier. I'm very glad i decided against some of the alternatives after seeing what issues acquaintances have had and others as well, to be fair that can be due to lack of QC but either way if I'm spending that amount of money on glass I want quality.
John Stone avatar
John Stone avatar
Also consider adding the Starizona Apex L to the Esprit 100 (rumor is that it was designed for this scope)

Link

357mm at F3.57 (reduced/30mm image circle)
550mm at F5.5 (native/43mm image circle)

Seems like a combo that can’t be beat:-)
Tim Ray avatar
Tim Ray avatar
I image with the 2600's at 400mm and 910mm with two different WO's. I like the GT81 better than the 132FLT. I'm not pushing a brand rather a Focal Length. If I had to keep one it would be the 910mm FL over the 386mm of the 81mm w reducer. The Esprit line is fantastic. @Jan Erik V and ​​​​@Sean Mc are correct on their recommendations about the Sky-Watcher. I own 3 of the ED's from Sky-Watcher and they are fantastic. Not to cause an up roar. I did do some experimenting with my Sky-Watcher 100ED at 910mm and the WO 132FLT on the same target. Slightly more sub's on the 100ED because it's a slower scope. The reason I did this was I wanted to see if BXT version 4 and Pix Insight could make the SW 100ED image as "good" as the WO 132FLT. Short answer was No. It took 3 more objects to really come to that decision... The results were very, very, very close and needed another PI guru to verify... So close that if I had to do it all over again and had BXT v4, I would have never upgraded from the Sky-Watcher ED's.  I have the 72, 80 and 100 ED's from Sky-Watcher... 

CS

Tim
Brian Puhl avatar
Brian Puhl avatar
I loved my Esprit 100 enough that I bought a second one.  Now I image with two Esprit 100s at the same time.     I'm still seeing limited but I've seen FWHM's in the low 2.0"s on occasion.    It's incredibly sharp and punches well above its weight.       My only ever so slightly negative comment about it is it leaves a little bit of purple fringing on stars.  I've seen it on alot of other folks data as well.   We've all agreed it's just an Esprit thing, it's not really that bad and very easy to process out. 

On the subject of the Apex reducer, I have yet to see an image produced by that corrector that I like.  Every one of them has extremely poor stars in the corner of the image.  I refuse to purchase it.  



Moving up from a doublet, everything will look good to you, but trust, the Esprit has a long line of satisfied customers.   You can't beat the bang for the buck.
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Jan Erik Vallestad avatar
Jan Erik Vallestad avatar
Brian Puhl:
On the subject of the Apex reducer, I have yet to see an image produced by that corrector that I like.  Every one of them has extremely poor stars in the corner of the image.  I refuse to purchase it.


I agree, I've been wanting to add an option at that FL but the reducer is more expensive than a good used 300mm lens that could probably work just as well. I spoke to TS in Germany as well about their reducers, specifically  the 0.6x one. They said that technically reducers like these would match, but no APO's they knew about would be able to correct stars and color across the frame at F/3.3 with APS-C format. 

I would be tempted to try, but too much risk.
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Jimmazing1 avatar
Jimmazing1 avatar
Sean Mc:
It’s not easy to beat an esprit. With the phq, you gain virtually perfect stars, and remove the need for backspacing at the expense of speed. The FRA 600 is pretty damn good and reasonably fast. 

The FLT, well… I’d do some searches on the problems many users face, as well as taking a look at images from that scope. I gambled twice on an FLT 91 and lost both times so I’m jaded. Sure there are some that look good, but I’ve found MANY images where users proclaim virtual perfection, and it’s obvious that their scope has astigmatism. YMMV ¯\_(ツ)_/¯  

After saying all that, I did some FOV calculations and found that 500-550mm FL is just a smidge too small for my liking. I’d rather have 400ish to frame more targets without the need for mosaics. Either that or 900mm+

So yeah, I went with the 65phq. If you’re undersampled, dither and drizzle.

Thanks everybody for all the feedback. I recently published my first image on Astrobin and I'm pretty happy with it for the rig I'm using. and my current skillset.

I am dithering and drizzling to help with the undersampling. Maybe I just stick with this for a few more years until I'm ready to move out to the country and decide to build an observatory and set up two rigs.

If I was going to buy today, I think I'd end up going with the Esprit 100ED, but your comment that something in the 400mm range would probably ideal has me thinking.

Maybe the Esprit 80D or going to a GT81, but then are the images going to be significantly improved enough to justify that cost? Or should I just stick with what I have for widefield until I'm ready to go into that 900mm+ range?
Tim Ray avatar
Tim Ray avatar
I have a GT81 and a Sky-Watcher 80ED, also a 132FLT…  With that said… I hate to tell someone how to spend money… I would stay with what you have and add FL with an additional OTA in the 900 to 1000mm telescope…

CS Tim
Deepan Vishal avatar
Deepan Vishal avatar
If I had to pick between the 4 choices,I’d narrow down to Esprit 100 and FRA600.
If you require the flexibility of reducer, pick FRA600. Else, l’d go with Esprit 100. 

Outside of these four OTAs, I’d recommend the FSQ-85EDX. One of the best OTAs I have ever used.
John Stone avatar
John Stone avatar
Brian Puhl:
On the subject of the Apex reducer, I have yet to see an image produced by that corrector that I like.  Every one of them has extremely poor stars in the corner of the image.  I refuse to purchase it.


https://www.astrobin.com/search/?q=apex+l+&d=i&subject=&telescope=esprit+100&sort=-likes

There are quite a few "liked" pictures with this combo.
tazdevil71 avatar
tazdevil71 avatar
Hi,
In the same situation as you, i Have just ordered an esprit 100ed with a 0,75x riccardi Reducer. Unfortunately, bad Sky and no Fierst light yet. I cannot tell you if it’s a good combination
Jimmazing1 avatar
Jimmazing1 avatar
Hi,
In the same situation as you, i Have just ordered an esprit 100ed with a 0,75x riccardi Reducer. Unfortunately, bad Sky and no Fierst light yet. I cannot tell you if it’s a good combination

It's been an extra cloudy year with the weather patterns. Hopefully it clears up for you soon!
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Brian Puhl avatar
Brian Puhl avatar
John Stone:
Brian Puhl:
On the subject of the Apex reducer, I have yet to see an image produced by that corrector that I like.  Every one of them has extremely poor stars in the corner of the image.  I refuse to purchase it.


https://www.astrobin.com/search/?q=apex+l+&d=i&subject=&telescope=esprit+100&sort=-likes

There are quite a few "liked" pictures with this combo.




I'm not sure what 'liking' a photo has anything to do with it.    All you did is reinforce my statement.   90% of those images are all from the same person, and they all have poorly corrected frames.     Here is an example from one of the images you referenced from Mr. Balasi.   Significant abberation in the corners, and this was likely much worse prior to editing.   I'd like to take this moment to apologize to Mr. Balasi for using his work as an example, but there are PLENTY others further down that list that you linked who suffer from the same issue.  It's not just him.   There may be some backfocus issue, but I'd expect after the amount of images he's produced with the gear, he would have tried to fix it by now.    The Apex cannot correct for APS-C.     There are some reasonable images from this combo with a 533 sensor, but it has a much smaller image circle, so it really holds little value in this disusssion.    The Esprit 100 is already plenty fast at F/5.5 and does not need to be reduced further.