Advice on small refractor

[Richard136]

I need a small refractor for use as mega finder and portable second scope.

Thinking of 50-70ish mm. 80 probably too big.

Should be usable on a camera tripod and ble to piggyback on my bigger fractor. 2" decent focusser, and low focal length so that a 30mm eyepiece gives v wide fov.

The current WO61 looks good. Also I've seen a second hand Borg at ENS for similar money. No experience with Borg but would value to hear experiences.

Other suggestions also welcome.

[vlaiv]

https://www.firstlightoptics.com/pro-series/sky-watcher-evostar-72ed-ds-pro-ota.html

or if you want something mechanically better, then look at this one:

https://www.teleskop-express.de/shop/product_info.php/info/p8866_TS-Optics-Photoline-72mm-f-6-FPL53-und-Lanthanum-Apo---2-5--R-P-focuser.html

(retractable dew shield, better rings and very good 2.5" R&P focuser)

Again, in SW 72ED class, there is this scope:

https://www.teleskop-express.de/shop/product_info.php/info/p1151_TS-Optics-70-mm-F6-ED-Travel-Refractor-with-modern-2--RAP-Focuser.html

that should be mechanically better.

[IanL]

WO 61 definitely ticks all your boxes. Bought one for the Mrs recently and it is a delight to use; solidly build, focuser is super smooth, views are  very good - no appreciable colour fringing on the Moon for example. Works well on the cheapo photo tripod as it is so light and compact. With dewshield retracted it is very portable, not quite a pocket scope, but definitely fits a moderately sized handbag.

The only question would be mounting it for piggy-backing. It has a single tube ring with a vixen-style "foot" complete with a pair of tripod screw holes. Very handy for grab and go, but not so conventional for mounting on another scope.

[Richard136]

Thanks for both replies.

Noted about the WO61 and the mounting. Although cant you use female to female clamps for this sort of thing?

The TS scopes are of course an option. Is it worth the nearly 200 euro extra for the 72mm? Glass is stated as better and the mounting looks more substantial too. Though at that price I can have a WO ZS73.

[vlaiv]

24 minutes ago, Richard136 said:

The TS scopes are of course an option. Is it worth the nearly 200 euro extra for the 72mm? Glass is stated as better and the mounting looks more substantial too. Though at that price I can have a WO ZS73

TS Photoline 72mm is the same class instrument as WO ZS73 - both in aperture but also in optical quality (probably, I can't be 100% certain. I do own 80mm TS F/6 APO triplet and it is indeed very good optics). Same class focuser - 2.5" R&P.

There are few things that may sway you to TS side - like lower mass (2.2Kg vs 2.8Kg - probably due to carry handle, tube length and longer dovetail), shorter tube in TS model (315mm vs 390mm) and longer back focus.

I'm just guessing longer back focus - since tube is shorter in TS model and both are F/6 scopes with same focal length of ~430mm. TS website states 135mm focus position distance from end of 2" receptacle and 73mm focuser travel - that is going to be usable on both 2" and 1.25" diagonals "out of the box" - most 2" diagonals have around 110-115mm optical path while 1.25" have about 75-85 mm optical path (only prisms have significantly shorter path).

WO has couple of things going for it - local dealer which is much better in terms of transportation and any issues that you might have with scope, and stronger brand name which I suspect will be a plus in resale value.

Btw - both scopes I listed being TS models are available from Altair Astro:

Cheaper model - 70mm and 2" focuser:

https://www.altairastro.com/starwave-70ed-f6-travel-refractor-telescope-with-2-crayford-focuser-finder-diagonal-eyepiece.html

Better model - 72mm model with 2.5" focuser:

https://www.altairastro.com/Altair-72-EDF-Refractor-Deluxe-CNC.html

(you have "CNC - deluxe" model as well as a choice - £50 more but you get better focuser with rotator and optics test report).

If astro photography is not important for this scope and you are going to use it for grab&go, mega finder and travel scope - I would personally consider cheaper 70mm scope. Same aperture, could have some color on high magnifications - but I would not expect any serious observing on 70mm so that would not be too big of an issue. It will have edge over 61mm as travel scope - not much but I would not mind having 10mm more aperture in roughly the same "package" in terms of size and weight.

If you are still keen on WO61 have a look at these two scopes:

https://www.teleskop-express.de/shop/product_info.php/info/p10095_TS-Optics-PhotoLine-60mm-f-6-FPL53-Apo---2--R-P-Focuser---RED-Line.html

and

https://www.altairastro.com/60EDF-ED-R-Refractor-Telescope.html

and keep in mind that most of these scopes are made in PRC or Taiwan and just branded differently

 

[celestron8g8]

I would agree on the Evo 72mm if funds are available .

[Richard136]

Excellent help, thanks.

[Richard136]

Leaning towards the Altair 70mm travel ED-R. Seems like best combination and value. 

[Paz]

I was looking for a travel scope for a long time and ended up going for a TS Photoline 72mm due to the light weight and small size it packs down to - there is significant variation in weight and size for scopes around 72mm.

I checked out a lot of options at the IAS and it fitted the bill for me.

I do agree that something around 60-70mm is a good idea as 80mm is a lot bigger.

I saw the 70mm Altair scope at the show and can say that looked good.

[Richard136]

Thanks, Paz.

Still juggling between the AA 70 and 72 (and the TS equivalents like you have), and the WO ZS61... 

Saw the ZS 61 and it's very slick and obviously ultra portable. The only question is it is too small for visual use as a grab-and-go?

Weight and length-wise, the AA and TS scopes seem very similar indeed; maybe 10% one way or the other

[vlaiv]

1 minute ago, Richard136 said:

Thanks, Paz.

Still juggling between the AA 70 and 72 (and the TS equivalents like you have), and the WO ZS61... 

Saw the ZS 61 and it's very slick and obviously ultra portable. The only question is it is too small for visual use as a grab-and-go?

Weight and length-wise, the AA and TS scopes seem very similar indeed; maybe 10% one way or the other

I used to have 60mm F/4 achromat scope. Well it was not quite scope - more guidescope / finder sort of thing, but it did show quite a few messier objects from my light polluted balcony (hand held even).

Having said that - I would not call it grab&go scope - it was more quick peak scope than anything else. I think you will need a bit more aperture than 60mm to keep you busy/interested longer than 5-10 minutes.

[timwetherell]

I use a WO66 and it's great - enough aperture to see most brighter Messiers and small enough to be able to achieve low magnification with normal EPs. It also has the advantage of accepting 2" EP,s  so with a 40mm ortho if gives almost 7 degree field which makes it an ideal finder. It's also a nice spotting scope in it's own right and a very capable wide angle astrophotography scope using the main scope as a guide. I actually use this scope as a visual instrument too, very large objects like M31 and the North America nebula look great - the latter especially with an OIII filter 

[Richard136]

33 minutes ago, vlaiv said:

I used to have 60mm F/4 achromat scope. Well it was not quite scope - more guidescope / finder sort of thing, but it did show quite a few messier objects from my light polluted balcony (hand held even).

Having said that - I would not call it grab&go scope - it was more quick peak scope than anything else. I think you will need a bit more aperture than 60mm to keep you busy/interested longer than 5-10 minutes.

This is what concerns me with the ZS61 for my purposes. Which pushes me to the 70 or 72.

[Richard136]

11 minutes ago, timwetherell said:

I use a WO66 and it's great - enough aperture to see most brighter Messiers and small enough to be able to achieve low magnification with normal EPs. It also has the advantage of accepting 2" EP,s  so with a 40mm ortho if gives almost 7 degree field which makes it an ideal finder. It's also a nice spotting scope in it's own right and a very capable wide angle astrophotography scope using the main scope as a guide. I actually use this scope as a visual instrument too, very large objects like M31 and the North America nebula look great - the latter especially with an OIII filter 

The 66 was  / is on the list; however I couldn't find one anywhere. Think the 70 or 72 may be preferred over the ZS61 on balance

[timwetherell]

9 hours ago, Richard136 said:

The 66 was  / is on the list; however I couldn't find one anywhere. Think the 70 or 72 may be preferred over the ZS61 on balance

Yes I'm probably a bit out of date, haven't bought a scope in some years  Was it the 71 triplet you were thinking of? Looks quite expensive from my brief research! but yes, I think 70ish would be slightly better than 61 especially if you can source one second hand. I'm using a TMB 40mm widefield ortho as an eyepiece - again another piece of astro-kit from the long, long ago. It has the advantage of the field stop being outside the optics so it's easy to install a crosshair.

 

[Richard136]

Could someone who owns the TS 72mm comment on the quality of the field.oc view?

 Is there any visible distortion toward the edges of the field? 

[Stu]

2 hours ago, Richard136 said:

Could someone who owns the TS 72mm comment on the quality of the field.oc view?

 Is there any visible distortion toward the edges of the field? 

I've been pretty pleased with mine, but confess I've just enjoyed the views rather than critically assessed it.

Is there anything in particular you are interested in? I would imagine most of these 72mm clones would be similar, it's the mechanics and build which differentiate them.

I generally use mine with 1.25" eyepieces, the lowest being a 24mm Panoptic, although I have used a 30mm 82 degree ES in it. I'll have a closer look next time out. In theory it will show field curvature due to the short focal length but I've not found that objectionable to date.

[Richard136]

Thanks - would like to know.

I've got the 70ED from Altair Astro and the build etc is very good. It does show a small loss of quality on star fields towards the edges of the field at low power - eg with a 2" 28mm eyepiece. 

[Louis D]

14 hours ago, Richard136 said:

Thanks - would like to know.

I've got the 70ED from Altair Astro and the build etc is very good. It does show a small loss of quality on star fields towards the edges of the field at low power - eg with a 2" 28mm eyepiece. 

Well, have you field flattened it?  All of the 70mm class ED scopes have very short focal lengths and thus very curved fields.  If you refocus the edges, are the stars sharp?  If so, invest in a TSFLAT2 field flattener.  I use one with my AT72ED.  I swapped out the nosepiece on my GSO 2" diagonal with a 15mm SCT threaded extension that has 48mm threads on the opposite end.  I then screw the TSFLAT2 into those 48mm threads.  Now I have pinpoint stars across the field.

[Richard136]

I'm just doing visual not photography, so no flattener. The slight distortions maybe an artefact of short focal length.

[Stu]

1 minute ago, Richard136 said:

I'm just doing visual not photography, so no flattener. The slight distortions maybe an artefact of short focal length.

Do the edge stars come to focus at all if you refocus slightly? If so then it will be caused by field curvature and as Louis says a field flattener can be used visually to get rid if it, I've done it myself in the past.

If they don't come to pinpoint focus the it will be some other effect, likely astigmatism, possibly in the eyepiece.

[Richard136]

I'll check. Good point about the eyepiece possibly introducing an effect.

 

Main question was how does it compare to others of similar FL. Is the curvature an effect of the FL or the design of my specific scope.

[vlaiv]

1 minute ago, Richard136 said:

I'll check. Good point about the eyepiece possibly introducing an effect.

 

Main question was how does it compare to others of similar FL. Is the curvature an effect of the FL or the design of my specific scope.

It is feature of all simple scope designs and in general it is a function of focal length of telescope - shorter FL stronger curvature.

With most scopes for visual and most eyepieces - you will not see it. Only when you have short focal length scope and wide field long focal length eyepiece (large fields stop that covers large area of focal plane) - you will see it at the edges.

Amount of field curvature that one sees - depends on observer. It is much more visible when imaging because sensor can't adapt to small changes in focus position - while eyes can and we do that instinctively - as soon as you shift your central vision to a new object it adjusts focus without you doing anything. You only see out of focus when you have two objects near each other that are large distance away - like holding finger in front of a distant object - one of them is going to be blurry - either finger or distant object - but then you can switch your focus at will.

If you observe center of the field and then shift your attention to edge - eyes will try to adjust automatically. Only if you observe both at the same time or difference in focus is large enough for eye to fail to adjust - you will see field curvature.

Above two images explain what happens - imagine line going from center of the lens to focal plane - as you move from center and keep same focal length - you are starting to draw a circle instead of straight line. Longer focal length will draw larger circle (bottom image), which will be less curved - less deviate from straight surface.

[Louis D]

1 hour ago, vlaiv said:

Amount of field curvature that one sees - depends on observer. It is much more visible when imaging because sensor can't adapt to small changes in focus position - while eyes can and we do that instinctively - as soon as you shift your central vision to a new object it adjusts focus without you doing anything.

Unless you're old like me and have presbyopia that leaves you with fixed focus eyes.

6 hours ago, Richard136 said:

I'm just doing visual not photography, so no flattener. The slight distortions maybe an artefact of short focal length.

I do visual only and couldn't stand the defocused stars at the edge at low powers.  I mainly use the AT72ED for low powers, so this wasn't an occasional thing, it was all the time.

[vlaiv]

9 minutes ago, Louis D said:

Unless you're old like me and have presbyopia that leaves you with fixed focus eyes.

I did mean to mention that - with age ability of eyes to do that goes down.

One of the reasons people report different levels of field curvature when testing eyepieces / scopes.