ST80 vs ST102

I recently wanted to purchase an ST80 or an ST102. I was undecided which to purchase and a wanted advert for an ST80 turned up 2 people wanting to sell me an ST80 AND an ST102. In such a pickle I decided to buy both so I could compare and then sell the one I liked least. I thought I’d share my findings here for those interested.

The ST80 is an 80mm f/5 (400mm) OTA and the ST102 is 102mm f/4.9 (500mm)

Both examples are made by Synta and are in Skywatcher blue. You can see the difference in size isn’t massive, with the ST102 being slightly larger. The weight of both tubes is comparable although when weighed “in the hand” I could tell the ST102 was slightly heavier.

Removing the dew shield revealed the lens cells. The ST80 seems to be made from plastic which perhaps isn’t a bad thing as it makes it lighter but it gives me concerns about the durability of the ‘scope. The ST102 lens cell seems to be a combination of metal and plastic, which is perhaps SLIGHTLY better than the ST80. Neither seem to be collimatable.

Viewing down the barrel the ST80 is well baffled and whilst the lens is coated it isn’t fantastic. That being said these are nice and cheap so I can’t really complain.

The ST102 is equally well baffled, but again the coatings leave something to be desired. I think the ST102 appeared a little better than the ST80 but thats subjective with both examples being second hand (although in good condition).

The ST80 has a cast aluminum 1.25” rack and pinion focuser whilst the ST102 has a 2” cast rack and pinion focuser. (Note the focus wheels on the ST102 have been replaced at some point, but this is a small modification). Both have been regreased but experience tells me that if brought new would be full of “syntaglue”. Easily fixed but god knows what the engineers were thinking when they used this “grease”.

All the following shots were taken with my Nikon D70 DSLR at prime focus. I’ve not had the opportunity to test both ‘scopes at night yet due to the weather (snowing here!).

The test chimney was fairly close, about 300 meters. You can see the difference in focal length immediately with the ST102 giving more magnification from the outset. You can also see that the ST80 image appears to be washed out a lot more than the ST102. I’m not sure if this was a function of the weather or if it’s due to the change in aperture. The ST102 definitely seems clearer though and despite it’s fast f/4.9 focal ratio in these daytime shots I can’t see much colour in either shot. I didn’t get a chance to barlow up to take a closer shot with both scopes but perhaps I need to test in that configuration too.



Taking a 100% crop of both these images from the 6 mega pixel originals gives more information. Again the ST102 seems MUCH clearer than the ST80 and I’m beginning to think that the added resolution of the 4” compared to the 3” lens makes a big difference to the contrast too, at least for these daytime shots. I was expecting the ST102 to show more colour as it’s f/4.9 not f/5 but to my eyes I can’t see much difference. Perhaps some moon limb shots will tell more.

ST80 Crop

ST102 Crop

All in all at the moment the ST102 is winning due to the larger aperture, however the ST80 is still the more portable OTA. Night time tests to follow as the weather allows!

Originally posted 24 January 2007