Advice on visual refractor ED/APO.

[pluton]

Hello,
I am currently looking for a good refractor for visual use, not photo, I imagine better with ED lens or APO triplet, no?
Also imagine that the size better about 4 ", more maybe for me is a little unmanageable, and less ... 2.4" or 3 "maybe a little small - no?
I would like you to give me your opinion on this, I would greatly appreciate it.
regards
Paul

[DRT]

Hi Paul,

Which type/style of mount do you have?

From the comments you have already made something like a SkyWatcher 100ED would probably fit the bill. It's not too heavy, gives superb views, and is a good all-rounder.

[ronin]

Really it comes down to budget - anything from say £500 to £5000 easily, the Astro Physics 140 Starfire is excellent easily £6000-£8000 and a 20 year waiting list.

Your location is important, Brussels is bad and a small island between Vancouver and Nanimo is good.

New ES 127 ED APO gets good reports, the FCD100 model.

[Moonshane]

I have never been content with views from scopes under 100mm especially as an only scope.

Based on what you say I agree with Derek.  I don't like triplets since I had a bad experience with one going out of collimation.

Key questions are what budget and what mount do you have?

 

[Timebandit]

Hello. If your budget can stretch to it then go for a Takahashi FC 100 DC or the DL model. A top draw refractor around the 4" mark and well respected on this site. A Top quality refractor which will last you a life time in the 4" bracket. I hope this helps.

[ollypenrice]

'Visual only' makes it easier because the very expensive part of making an astrographic refractor lies in getting first class colour correction in towards the UV, to which cameras are more sensitive than they eye, and also in obtaining a large flat field. On top of that a very fast F ratioo may not be what you're after unless you want an extremely wide field of view. Slower F ratios are cheaper to make.

The world is your oyster at 4 inches. You have the very fast TeleVues for ultra wide field, the premium Tak doublets with longer focal lengths, the Esprits, the Altair triplets and the very competent budget Skywatcher ED100. I'd be delighted by any of those.

Olly

[mikeDnight]

You don't need a triplet if you're purely a visual observer. Modern FPL53 ED doublets have excellent colour correction and can keep pace with the best refractors on most nights. The SW 100ED Pro is a very good refractor, and as its also among the cheapest apo's in its aperture class its a no brainer if funds are hard to come by. Prices rise sharply as you go up in aperture or if you choose to go for a higher brand, but the actual gain in performance is usually not immediately that noticeable.

Mike

[Alien_Photons]

There are a few considerations with APO,s they give better views with better eyepieces and diagonals. Matching eyepieces to your APO can be tricky or expensive or both. Bigger refractors at at high power need more rigid mounts or just better quailty mounts. These things will raise questions once you have the scope. Still it makes choosing birthday presents simple.

[Ben the Ignorant]

The Sky-Watcher 100mm f/9 is everywhere, and loved by everyone but a 100mm ED f/7 can produce wider fields at low power, a feature you need if it's your only scope. Without going too high in size and price, they also make 110mm ED f/7 scopes that are only semi-apo, but way better corrected than achromats.

A 115mm f/7 triplet is heavier but shorter than a 100mm f/9 tube, and a 120mm f/7.5 doublet is not longer than a 100 f/9, but quite stronger in brightness and resolution. All in all, the most compact and least heavy in large ED scopes is the 120 f/7.5, plus it sports the best kind of glass.

[Commanderfish]

Well for visual you're going to need aperture.  I'd go for a 5" Apo or a 6" Acrho.  Personally I use an ES ED127 Apo and an Altair Starwave 152 Achro side by side.  The Apo give beautiful, unparalleled super sharp views.  The Starwave has more aperture so it shows dimmer objects like DSOs a little better and brighter.  I can get a 3 degree field out of either with a Pantoptic 41mm.  I tend to have one set for a wide field and the other at about x100/1 degree.    You can take either of these scopes up as high as the seeing will allow, up to x200 on a good night.

[pluton]

Thanks for all response..

I have a Nexstar SE mount (for 6"/8" optical tube model), maybe the SW ED100 can be a good tube for this mount ? maybe best a 100mm F/7 ? this I understand that is ED with FPL-51 ? much difference between a FPL-53 and a 51 for visual ?

Thanks

Paul

[mikeDnight]

SW ED Pro Apos, though doublets, use high quality FPL53. Very much a Fluorite view! 

Mike

[Alfian]

On 05/06/2017 at 06:37, Ben the Ignorant said:

but a 100mm ED f/7 can produce wider fields at low power, a feature you need if it's your only scope

In the Ed100 F9,  a 40mm 68 degree EP in the 100ED will give 22.5 x ,a 3 degree fov and 4.4 mm exit pupil. How much lower power/wide field do you need?

[Ben the Ignorant]

23 hours ago, pluton said:

 much difference between a FPL-53 and a 51 for visual ?

Some FPL-53 doublets have less chromatic blur than some FPL-51 triplets, it depends on diameter and f/ratio. The advantage of 53 is even more visible when compared to a 51 doublet. But 51 makes the scope less expensive. The 4-inch f/7 "51" doublet is more compact and more panoramic than the 4-inch f/9 "53" doublet. Currently Teleskop Service has a f/7 FPL-51 doublet at a reduced price.

http://www.teleskop-express.de/shop/product_info.php/info/p9220_TS-Optics-ED-102mm-f-7-Refraktor-Teleskop-mit-2--Crayford-Auszug.html

If you accept a tiny bit of violet halo around a few very bright targets, that's a good compromise. The halo is invisible in all ordinary conditions.

[John]

On 05/06/2017 at 16:35, pluton said:

Thanks for all response..

I have a Nexstar SE mount (for 6"/8" optical tube model), maybe the SW ED100 can be a good tube for this mount ? ....

The problem with that mount will be that the long tube length of an F/9 refractor will severely limit how high an angle the scope can point to.

An F/7 4" scope might give you a little more but I suspect that the diagonal / eyepiece end of the scope is still going to hit the base of the mount when the scope is pointing above a certain angle

[Chris]

On 6/5/2017 at 16:35, pluton said:

Thanks for all response..

I have a Nexstar SE mount (for 6"/8" optical tube model), maybe the SW ED100 can be a good tube for this mount ? maybe best a 100mm F/7 ? this I understand that is ED with FPL-51 ? much difference between a FPL-53 and a 51 for visual ?

Thanks

Paul

Hi Paul, just to give you an idea, I had a 90mm f/5.5 achromat on the slightly smaller 4SE mount, and with the tube pushed forward I still needed to remove the diagonal before slewing to prevent a crash.

Apparently you can program altitude limits, but I tried this with the diagonal off and it didn't work...it would have crashed with it on! Maybe I programmed it incorrectly? but my point is it's not straightforward and I personally don't trust it. I've seen someone successfully use an ED80 with the 6/8SE mount, but did I hear this would be your only scope, paul? If so I echo previous comments about a 4" refractor being a better only scope choice. I have an 80mm but wouldn't have bought it if I didn't have other scopes.

Maybe a 100mm f/7 would just fit as suggested, but it could be an expensive gamble. I do remember liking the 4SE short achromat combo and I may have kept it longer if I didn't need to remove the diagonal and eyepiece for every slew. If you can find the right scope it could be a nice setup.

Otherwise rethink the mount and go with the ED100  

[pluton]

thanks for your message!!

Paul

[JG777]

What sort of objects are you aiming for? A 100 ED is a fine scope and packs a punch on planets and lunar but for deep sky the 100 mm will leave you wanting. I second the comment that the longer tube of an F9 100 will not operate well on your SE mount. I do occasionally use my ED 80 on an Evolution mount but that's about the limit for the length. 

[Alan White]

Owning an ED100 DS Pro, I would be amazed if the SE mount was viable in any way with my 100 scope!