ST80. Is it me?

[cwis]

Hi all,

I picked up one of these a while ago and keep setting it up on my AZGTI and then wandering off and observing through my 10" dob. I think I pointed it at Jupiter once when I first got it a few months ago and compared the views directly with the Bresser and saw a ball of mush instead of the GRS and barges and suchlike, but this was entirely my expectation and it was for star fields etc... Completely the wrong target.

So last night I decided to only take it out and look at more "ST80" type targets.  I was completely underwhelmed! 

Andromeda: Dim binocular type view. Couldn't make out M32 or M110.  M32 is clearly visible with the dob....

Polaris: Tried to make out the dimmer companion star that's obvious at 50X mag with the dob - nothing whatever I did.  I'm seeing nice concentric out of focus diffraction patterns so it's collimated (which I had to do when it arrived as it was banana shaped) but is contrast lacking? 

M103: Only a few of the brighter stars visible. Was small with 24mm eyepiece and got dimmer with any magnification so no colours were perceptible.  This is amazing with the dob - bright red and blue stars filling the field of view and more dimmer stars the longer you look...

Pleiades: OK - it fitted completely in the view which is something the dob cannot do. But the view is so much dimmer and all the stars are white, not blue because of this.

In fact this dimness was a constant theme of the session - I was continually turning my red light away or turning it off as it felt like it really intruded - not something I've ever experienced using the dob.

So, Is it me? The AZGTI came with a 130mm F5 newt that I personally think is better in almost every way (now I can collimate it) - it'll have a honest go at a planet (saw Mar's polar ice cap with it) it'll show all of the Pleiades but nice and bright and blue, I've split doubles with it (Polaris is easy at 50x!) etc etc.  It has coma but the ST80 does not have a flat focal plane so they on a par with stars in the corners of the view, really...

Also, it's far more comfortable to use - the tube is fairly short so the height of the eyepiece although obviously variable is easily accommodated by my drummer's throne (as is the dob). However the height variation required to use the ST80 appears to be far larger, even after turning the diagonal sideways.

So what am I missing with the ST80?   I was using a Baader contrast Booster and a Williams Optics erecting diagonal... Am I just a (don't giggle) confirmed dobber? Is it my rubbish eyeballs? Is my sky not dark enough (Bortle 5)? Anyone want a lightly used one?

[Peter Drew]

Pretty tough comparing an 80mm to a 250mm telescope hoping for some similarities in performance 🙂.  The aspects in favour of the ST80 are cheapness, wide field which displays many open clusters best even if the stars are fainter,  can easily be used for sunspot viewing and is a good grab & go telescope due to low weight and cool down time.  It can make a great finder for a 250 Newtonian.     🙂

[Tiny Clanger]

Area of the circular aperture of an 80mm diameter 'scope =   5027 mm sq.

Area of the circular aperture of a 250mm diameter 'scope = 49087 mm sq

The diameter of the 250mm aperture is only a little over three times that of the 80mm, but the area is nearly ten times greater. So the light gathering potential is increased nearly ten fold.

 

[Louis D]

I'll have to put a dovetail on my 2000-era ST80 and mount it opposite my 72ED on my DSV-2B mount and compare the views on various targets sometime.  The ST80 is limited to 1.25" eyepieces and thus can't accommodate a TSFLAT2 to flatten the field or provide extremely wide field views.  That aside, I'm curious how much purple fringing and spherical aberration intrudes into the view through the ST80 relative to the 72ED.

[Stu]

I guess you are dimming the view with the contrast booster, and erecting prisms aren’t the best for Astro observing. At similar exit pupils you should get similar brightness but at different magnifications. As they are very similar focal ratios, the same eyepiece will give roughly the same exit pupil in each scope, is this what you were comparing? Eg 32mm is each gives x12.5, a 4 degree field and a 6.4mm exit pupil in the ST80, but x37.5, a 1.3 degree field and a 6.6mm exit pupil in the 250.

Polaris is hardly a suitable target for the ST80 though, I would be looking at the larger open clusters like the DC, Stock 2 M45 and the Hyades, Kemble’s Cascade and Melotte 111 when it is better placed, or trawling along the MW with lowest power.

If you don’t ‘get’ widefield views there nothing wrong with that, but use the little scope for what it is best for, that way at least it has a chance 👍

[StarryEyed]

Once you understand the ST80 it never stops being useful. Try stopping it down a little to 70mm say. There is normally a plug in the lens cover you  can experiment with, removing this should sharpen up the view. Dont be to harsh on the little fella.

My favorite image if my ST80. 

 

[MalcolmM]

Hi, I think it's a little unfair to compare an 80mm with a 250mm! That being said, I'm a 'refractor man' but your descriptions of the views through your Dob sound fabulous! I could be sorely tempted!

[ollypenrice]

The ST80 is very cheap - I'm tempted to say disgustingly cheap 😁 - and gives a wide field of view. It makes a demon guidescope and finder for a large Dob, as Peter said. If you want something to do it's job rather better, try and find an elderly TeleVue Genesis, but it won't come at ST80 prices however old it is.

I don't know the contrast booster but no erecting prism I've ever tried was satisfactory for astronomy.

One thing to try with your ST80 would be to stand it vertically on a hard, solid surface with the lens down and tap the tube lightly with a wooden spoon or suchlike. Do this for a few minutes. On the ST range it can settle the two lens elements into better collimation.

Olly

[Stu]

12 minutes ago, ollypenrice said:

TeleVue Genesis

Yum 😀

[cwis]

Wow! Didn't expect so many responses - thank you all for your input!

Maybe I am being a little unfair comparing the st80's light pint glass to my dob's lightbucket but I thought that (apart from Polaris) I had chosen some targets that would allow it to shine.  My impression was that whereas wide open views showed lovely bright stars, once enough mag was added to frame a subject  (M103 in particular) the view had dimmed too much for me. I do like how stars "pop" into focus though!

The erecting prism gets pretty good reviews on FLO and I quite liked the idea of right way up stars  - I also used it on my holidays for terrestrial observing where the ST80 was really great actually. I can't see any of the artifacts associated with prisms with my particular example.

I'll remove the contrast booster in case it's dimming the view too much (hadn't thought of that, and it's yellow so maybe it's removing colour from blue stars? Dur!) and have another session.  Feel free to add to the targets below:

M45, Stock2, Hyades, Kemble’s Cascade and Melotte 111 (never heard of this one!)  and the next clear night I'll go out again with just the ST80. If I manage to "get" widefield views then I'll get a star diagonal.

Oh - and @MalcolmM - try a dob! Wherever I point mine I see stars. Hundreds of stars!

[Stu]

51 minutes ago, cwis said:

Wow! Didn't expect so many responses - thank you all for your input!

Maybe I am being a little unfair comparing the st80's light pint glass to my dob's lightbucket but I thought that (apart from Polaris) I had chosen some targets that would allow it to shine.  My impression was that whereas wide open views showed lovely bright stars, once enough mag was added to frame a subject  (M103 in particular) the view had dimmed too much for me. I do like how stars "pop" into focus though!

The erecting prism gets pretty good reviews on FLO and I quite liked the idea of right way up stars  - I also used it on my holidays for terrestrial observing where the ST80 was really great actually. I can't see any of the artifacts associated with prisms with my particular example.

I'll remove the contrast booster in case it's dimming the view too much (hadn't thought of that, and it's yellow so maybe it's removing colour from blue stars? Dur!) and have another session.  Feel free to add to the targets below:

M45, Stock2, Hyades, Kemble’s Cascade and Melotte 111 (never heard of this one!)  and the next clear night I'll go out again with just the ST80. If I manage to "get" widefield views then I'll get a star diagonal.

Oh - and @MalcolmM - try a dob! Wherever I point mine I see stars. Hundreds of stars!

Good stuff! Keep the mag low and enjoy the wide fields and maybe you will enjoy it. Certainly the contrast booster is not likely to help with the blue stars, so yes do remove that. I think they are more useful for removing CA at higher powers and on brighter objects like planets or the Moon. CA is generally not so much of an issue on the lower brightness stars in clusters, so it’s not needed.

I think the Stock and Collinder catalogues are worth checking out, and also Melotte. Pick the bigger ones such as Collinder 70 which is on Orion’s Belt. There is a lovely S shape of stars which runs through between Alnilam and Mintaka.

[Tiny Clanger]

My analogy : think  of  an ST80  as a pair of cheap nail scissors. You might find those ok for trimming a bonsai tree in a pot (altho' a specifically custom made for the job Japanese specialist tiny shear  would do it far better at a cost ... that'll be that Tak ...) but you'd be foolish to try the tiny cheap scissors to cut the grass on a football pitch . Yes, you could try, but they are not the tool to give a satisfactory result.

When my ST80 (or slightly bigger 102 'frac ) gets an outing in preference to my dob or mak  (neither of which are huge : 150mm and 127mm respectively) is when I see a short lived cloud gap appear, and am sure there is no point getting the other 'scopes out for what may well be just a quarter hour window of opportunity. The ST80 is eminently portable, mounted on a lightweight photo tripod and using the photo head. When the nova in Cass appeared I picked the whole ST80/tropod setup  up, and walked 'round the neighbourhood with it over my shoulder at 2 in the morning to find a place where I had a good line of sight out of most street light glare. The setup takes up hardly any of the car boot ,  and would fit in my 45L rucsac easily.

Yes, it has disadvantages : horrible CA at full aperture , sloppy focuser,  internal reflections . If you want to improve it a bit, have a search on here for ST80 and there are some threads about improving it , I posted to one of them with a link to a youtube vid which talks you through the simple easy diy upgrades and adjustments you can make. You are stuck with the CA though, the hole in the cap (If your model has one, or cardboard diy job if not) is calculated at the precise diameter to reduce the CA to a theoretically acceptable level , but obviously it loses some aperture and therefore light gathering, as would a filter.

I think of the ST80 as a slightly narrower field , somewhat better light gathering , more flexible magnification (with different eyepieces) and much steadier alternative to my 10x50 binoculars on a monopod. In fact , I've hardly used the binos since getting the ST80.

Heather

Edited October 5, 2021 by Tiny Clanger
clarity and grammar !

[Pixies]

The benefit of my ST80 over my 8" dob is its "grab-an-go-ness". There have been lots of late evenings recently where a surprise clear sky appeared and the ST80 meant I could be out in 5 minutes. I agree with Heather's analogy regarding binoculars. I've also taken it away on holiday a couple of times.

The Moon is good; planets not so. Big clusters are it's forte, as even the brighter but smaller open clusters, like the ones in Auriga, are still grey blotches. I can't wait until I get it to a dark sky for M33, though.

I had a similar experience with my old Mak 90 - "is that it?" The view was dark and unimpressive. Only the moon looked good and it lacked the resolution of the dob. The ST80 gets a lot more use.

Now - imagine if you had the ST80 when comet Neowise was about!

[Andrew_B]

From what you've described the ST80 is seriously underperforming even a decent 60mm scope which sounds odd to me. If your William Optics diagonal is the 45 degree one then I can say from experience that while it works well at low powers, going above 50x magnification will give you views that get very soft and there's a dramatic difference when using a decent non-erecting mirror or prism diagonal.

[cwis]

16 hours ago, Andrew_B said:

From what you've described the ST80 is seriously underperforming even a decent 60mm scope which sounds odd to me. If your William Optics diagonal is the 45 degree one then I can say from experience that while it works well at low powers, going above 50x magnification will give you views that get very soft and there's a dramatic difference when using a decent non-erecting mirror or prism diagonal.

Hi Andrew - the diagonal is the 90 degree one.  I was out again last night and noticed the prism was giving me me noticeable diffraction spikes on brighter stars, so perhaps I do need to look at a decent mirror diagonal. I found the reason I couldn't see Polaris B during the previous session was because it was hidden behind a diffraction spike!

[Pixies]

@cwis - Have you tried the trick of loosening off the objective cell and giving it a shake?

[cwis]

10 minutes ago, Pixies said:

@cwis - Have you tried the trick of loosening off the objective cell and giving it a shake?

Hello!

No - I see no need really? With a cheshire it all looks lined up now (Had to file a few screw holes and remove some paint though!) and I get lovely concentric diffraction patterns on stars?  What fault would I see with misaligned objectives? 

[Andrew_B]

2 hours ago, cwis said:

Hi Andrew - the diagonal is the 90 degree one.  I was out again last night and noticed the prism was giving me me noticeable diffraction spikes on brighter stars, so perhaps I do need to look at a decent mirror diagonal. I found the reason I couldn't see Polaris B during the previous session was because it was hidden behind a diffraction spike!

I've not had a chance to look through the 90 degree version, but I would be surprised if it didn't have similar issues and the tendency to show diffraction spikes is inherent to amici prism diagonals. Baader sell a couple of astro-spec erecting prisms but they're expensive - several times the cost of your entire scope!

A standard mirror or prism diagonal should be a lot better although the mirror diagonal will be the better choice for use with your scope due to its fast focal ratio.

[cwis]

Just as an addendum to this post - I finally got out last night for 40 minutes or so inbetween child and clouds to test out the budget mirror diagonal I got from Amazon. I flocked the inside of the diagonal before first use (the cloudy nights came in handy there....)

No cool down time needed (smugface!) but one thing I did notice was possible kidney beaning from my UFF24mm initially - perhaps because my pupils were still too small? Eye position was initially VERY important.

This  effect seemed to slowly subside during the session and was entirely absent from the 24-8mm zoom.

Impressions:

More contrast. No diffraction spikes. Slightly better colour perception?  At 50x with the zoom mini-Polaris was clearly visible, and the softness of the zoom off centre was more apparent for some reason. 

[Louis D]

Well, I wasn't able to photograph any significant SAEP in my 24mm APM UFF (see the fourth row, second column) in my 127 Mak.  Black or gray rings or shadows correspond to SAEP.  It's even less noticeable in my 72ED.

I also have never noticed any blackout issues under any visual conditions with it.  It does have a lot of eye relief; and if you don't wear eyeglasses, it may prove tricky to deal with it.  Since there is a thread under the eye cup, it may be possible to add an extension ring Morpheus style.  I believe both are M43 threaded.

[cwis]

7 hours ago, Louis D said:

Well, I wasn't able to photograph any significant SAEP in my 24mm APM UFF (see the fourth row, second column) in my 127 Mak.  Black or gray rings or shadows correspond to SAEP.  It's even less noticeable in my 72ED.

I also have never noticed any blackout issues under any visual conditions with it.  It does have a lot of eye relief; and if you don't wear eyeglasses, it may prove tricky to deal with it.  Since there is a thread under the eye cup, it may be possible to add an extension ring Morpheus style.  I believe both are M43 threaded.

 

Hi @Louis D, I'll certainly bow to your experience!  I'll try and describe the phenomena I noticed more carefully and see if you can identify it. I think you're right - it related to eye relief and eye positioning. 

I already had the ST80 set up on the AZGti and run that off an old motorbike battery - so I just carried the whole lot outside in one go, fired up the mount and did a rough alignment using the red dot finder. Then I turned off the shed lights (that illuminate the whole back garden when on) and straight away looked into the eyepiece.

If I had been using a newt I would have said I could see the shadow of the secondary.  There appeared to be something dimming the centre of the field that moved as I moved. Pulling back improved this, but then I lost the field stop. Moving off centre seemed to move the shadow in the the same direction.

Over the next 10 minutes or so this effect seemed to fade slowly but I was aware of being very careful with eye positioning for the whole session with this eyepiece. It was a short session - 40 minutes. I've not noticed this "issue" before but normally I take longer on setup and at least partially dark adapt in the process. I've even used the UFF24 barlowed and not noticed any issue with long eye relief (it seems to barlow very well, by the way!)

So is there a link between eye relief/eye positioning and pupil size?

 

[kev]

I use a Everbrite 90 degree with my St80. it beats any prism hands down.  Also use a fringe killer.  Makes my St80 a great throw it in the car with a tripod when im working away from home.  

 

[Louis D]

I dug out my ST80 from ~2000 and put my APM UFF 24mm in it during the daytime and looked for kidney-beaning.  I couldn't see any at all.  I did notice that if I took my eyeglasses off, it is quite easy to get inside the exit pupil and watch the field of view shrink.  However, it was very well behaved in that it shrunk from the field stop inward.

I then screwed the Baader M43 eye cup extender onto the top of the APM UFF after peeling off the eye cup.  It threaded all the way down and looked OEM.  However, I could not get the APM eye cup to fit onto the extender because it expects a threaded lip with undercut below it, not a complete threaded cylinder.  Thus, you'd have to get the Baader Morpheus threaded foldable eye cup to fit onto the Baader extender.  With both, you would definitely avoid blackouts when not wearing eyeglasses.

[Louis D]

I took images through the APM UFF and ST80 combination with two different phone cameras (Galaxy S7 and LG G5 UWA).  The second one is the ultra wide angle one that really exposed any SAEP if it exists.  I can't see any shadows or beaning in either, just edge blurriness due to severe field curvature in the ST80:

[davhei]

Having recently gotten my hands on an f6 80 mm refractor to complement my trusty 10" dob for visual work, I must say that when I first gave it a proper go at a dark site star party (SQM 21.5) I was blown away.

It offered wonderful views of all the brighter DSO's I looked at such as showing M31 close to three degrees in the EP, never seen it extended like that ever before. Core of M33 was distinct with lots of nebulosity visible. Veil nebula, both east and west in a single field of view and the best views of the double cluster that I ever had. Resolved masses of stars in M13 and a few on the outer edges of M15. Great views of Jupiter, GRS and detail in the belts. Was very surprised, certainly surpassed my expectations.

Here's the interesting thing though, back home at my normal dark site (SQM 21.0 or thereabout), granted with poorer transparency than the first session, the same objects were decidedly underwhelming. Closer to binocular views as you described it.

Conclusion, dark skies make a big difference and a small scope can really deliver under good conditions.

My main use for the small scope is doing brief sessions from my home, carrying it quickly in and out to observe variable stars, check out brighter open clusters, lunar and the planets. Very happy with it. But I am also very pleased that I found out its capacity under proper dark skies. Certainly validates its use as a light travel setup when the dob is too much to bring along.